diff --git a/clang-tools-extra/clang-tidy/ClangTidyCheck.cpp b/clang-tools-extra/clang-tidy/ClangTidyCheck.cpp
--- a/clang-tools-extra/clang-tidy/ClangTidyCheck.cpp
+++ b/clang-tools-extra/clang-tidy/ClangTidyCheck.cpp
@@ -150,11 +150,11 @@
   unsigned EditDistance = 3;
   for (const auto &NameAndEnum : Mapping) {
     if (IgnoreCase) {
-      if (Value.equals_lower(NameAndEnum.second))
+      if (Value.equals_insensitive(NameAndEnum.second))
         return NameAndEnum.first;
     } else if (Value.equals(NameAndEnum.second)) {
       return NameAndEnum.first;
-    } else if (Value.equals_lower(NameAndEnum.second)) {
+    } else if (Value.equals_insensitive(NameAndEnum.second)) {
       Closest = NameAndEnum.second;
       EditDistance = 0;
       continue;
diff --git a/clang-tools-extra/clang-tidy/altera/KernelNameRestrictionCheck.cpp b/clang-tools-extra/clang-tidy/altera/KernelNameRestrictionCheck.cpp
--- a/clang-tools-extra/clang-tidy/altera/KernelNameRestrictionCheck.cpp
+++ b/clang-tools-extra/clang-tidy/altera/KernelNameRestrictionCheck.cpp
@@ -70,9 +70,9 @@
 
 bool KernelNameRestrictionPPCallbacks::fileNameIsRestricted(
     StringRef FileName) {
-  return FileName.equals_lower("kernel.cl") ||
-         FileName.equals_lower("verilog.cl") ||
-         FileName.equals_lower("vhdl.cl");
+  return FileName.equals_insensitive("kernel.cl") ||
+         FileName.equals_insensitive("verilog.cl") ||
+         FileName.equals_insensitive("vhdl.cl");
 }
 
 void KernelNameRestrictionPPCallbacks::EndOfMainFile() {
diff --git a/clang-tools-extra/clang-tidy/bugprone/ArgumentCommentCheck.cpp b/clang-tools-extra/clang-tidy/bugprone/ArgumentCommentCheck.cpp
--- a/clang-tools-extra/clang-tidy/bugprone/ArgumentCommentCheck.cpp
+++ b/clang-tools-extra/clang-tidy/bugprone/ArgumentCommentCheck.cpp
@@ -176,8 +176,8 @@
     return InComment == InDecl;
   InComment = InComment.trim('_');
   InDecl = InDecl.trim('_');
-  // FIXME: compare_lower only works for ASCII.
-  return InComment.compare_lower(InDecl) == 0;
+  // FIXME: compare_insensitive only works for ASCII.
+  return InComment.compare_insensitive(InDecl) == 0;
 }
 
 static bool looksLikeExpectMethod(const CXXMethodDecl *Expect) {
diff --git a/clang-tools-extra/clang-tidy/cppcoreguidelines/PreferMemberInitializerCheck.cpp b/clang-tools-extra/clang-tidy/cppcoreguidelines/PreferMemberInitializerCheck.cpp
--- a/clang-tools-extra/clang-tidy/cppcoreguidelines/PreferMemberInitializerCheck.cpp
+++ b/clang-tools-extra/clang-tidy/cppcoreguidelines/PreferMemberInitializerCheck.cpp
@@ -159,7 +159,7 @@
     if (S->getBeginLoc().isMacroID()) {
       StringRef MacroName = Lexer::getImmediateMacroName(
           S->getBeginLoc(), *Result.SourceManager, getLangOpts());
-      if (MacroName.contains_lower("assert"))
+      if (MacroName.contains_insensitive("assert"))
         return;
     }
     if (isControlStatement(S))
diff --git a/clang-tools-extra/clang-tidy/misc/StaticAssertCheck.cpp b/clang-tools-extra/clang-tidy/misc/StaticAssertCheck.cpp
--- a/clang-tools-extra/clang-tidy/misc/StaticAssertCheck.cpp
+++ b/clang-tools-extra/clang-tidy/misc/StaticAssertCheck.cpp
@@ -104,8 +104,8 @@
 
     StringRef FalseMacroName =
         Lexer::getImmediateMacroName(FalseLiteralLoc, SM, Opts);
-    if (FalseMacroName.compare_lower("false") == 0 ||
-        FalseMacroName.compare_lower("null") == 0)
+    if (FalseMacroName.compare_insensitive("false") == 0 ||
+        FalseMacroName.compare_insensitive("null") == 0)
       return;
   }
 
diff --git a/clang-tools-extra/clang-tidy/readability/InconsistentDeclarationParameterNameCheck.cpp b/clang-tools-extra/clang-tidy/readability/InconsistentDeclarationParameterNameCheck.cpp
--- a/clang-tools-extra/clang-tidy/readability/InconsistentDeclarationParameterNameCheck.cpp
+++ b/clang-tools-extra/clang-tidy/readability/InconsistentDeclarationParameterNameCheck.cpp
@@ -93,8 +93,8 @@
     return L.empty() || R.empty() || L == R;
   // We allow two names if one is a prefix/suffix of the other, ignoring case.
   // Important special case: this is true if either parameter has no name!
-  return L.startswith_lower(R) || R.startswith_lower(L) ||
-         L.endswith_lower(R) || R.endswith_lower(L);
+  return L.startswith_insensitive(R) || R.startswith_insensitive(L) ||
+         L.endswith_insensitive(R) || R.endswith_insensitive(L);
 }
 
 DifferingParamsContainer
diff --git a/clang-tools-extra/clang-tidy/readability/UppercaseLiteralSuffixCheck.cpp b/clang-tools-extra/clang-tidy/readability/UppercaseLiteralSuffixCheck.cpp
--- a/clang-tools-extra/clang-tidy/readability/UppercaseLiteralSuffixCheck.cpp
+++ b/clang-tools-extra/clang-tidy/readability/UppercaseLiteralSuffixCheck.cpp
@@ -93,7 +93,7 @@
   // Else, find matching suffix, case-*insensitive*ly.
   auto NewSuffix = llvm::find_if(
       NewSuffixes, [OldSuffix](const std::string &PotentialNewSuffix) {
-        return OldSuffix.equals_lower(PotentialNewSuffix);
+        return OldSuffix.equals_insensitive(PotentialNewSuffix);
       });
   // Have a match, return it.
   if (NewSuffix != NewSuffixes.end())
diff --git a/clang-tools-extra/clangd/CodeComplete.cpp b/clang-tools-extra/clangd/CodeComplete.cpp
--- a/clang-tools-extra/clangd/CodeComplete.cpp
+++ b/clang-tools-extra/clangd/CodeComplete.cpp
@@ -1680,7 +1680,7 @@
           C.SemaResult->Kind == CodeCompletionResult::RK_Macro) ||
          (C.IndexResult &&
           C.IndexResult->SymInfo.Kind == index::SymbolKind::Macro)) &&
-        !C.Name.startswith_lower(Filter->pattern()))
+        !C.Name.startswith_insensitive(Filter->pattern()))
       return None;
     return Filter->match(C.Name);
   }
diff --git a/clang-tools-extra/clangd/CompileCommands.cpp b/clang-tools-extra/clangd/CompileCommands.cpp
--- a/clang-tools-extra/clangd/CompileCommands.cpp
+++ b/clang-tools-extra/clangd/CompileCommands.cpp
@@ -296,9 +296,9 @@
 DriverMode getDriverMode(const std::vector<std::string> &Args) {
   DriverMode Mode = DM_GCC;
   llvm::StringRef Argv0 = Args.front();
-  if (Argv0.endswith_lower(".exe"))
+  if (Argv0.endswith_insensitive(".exe"))
     Argv0 = Argv0.drop_back(strlen(".exe"));
-  if (Argv0.endswith_lower("cl"))
+  if (Argv0.endswith_insensitive("cl"))
     Mode = DM_CL;
   for (const llvm::StringRef Arg : Args) {
     if (Arg == "--driver-mode=cl") {
diff --git a/clang-tools-extra/clangd/ConfigYAML.cpp b/clang-tools-extra/clangd/ConfigYAML.cpp
--- a/clang-tools-extra/clangd/ConfigYAML.cpp
+++ b/clang-tools-extra/clangd/ConfigYAML.cpp
@@ -169,7 +169,7 @@
 
   void parse(Fragment::IndexBlock::ExternalBlock &F,
              Located<std::string> ExternalVal) {
-    if (!llvm::StringRef(*ExternalVal).equals_lower("none")) {
+    if (!llvm::StringRef(*ExternalVal).equals_insensitive("none")) {
       error("Only scalar value supported for External is 'None'",
             ExternalVal.Range);
       return;
diff --git a/clang-tools-extra/clangd/HeaderSourceSwitch.cpp b/clang-tools-extra/clangd/HeaderSourceSwitch.cpp
--- a/clang-tools-extra/clangd/HeaderSourceSwitch.cpp
+++ b/clang-tools-extra/clangd/HeaderSourceSwitch.cpp
@@ -27,13 +27,13 @@
   // Lookup in a list of known extensions.
   auto SourceIter =
       llvm::find_if(SourceExtensions, [&PathExt](PathRef SourceExt) {
-        return SourceExt.equals_lower(PathExt);
+        return SourceExt.equals_insensitive(PathExt);
       });
   bool IsSource = SourceIter != std::end(SourceExtensions);
 
   auto HeaderIter =
       llvm::find_if(HeaderExtensions, [&PathExt](PathRef HeaderExt) {
-        return HeaderExt.equals_lower(PathExt);
+        return HeaderExt.equals_insensitive(PathExt);
       });
   bool IsHeader = HeaderIter != std::end(HeaderExtensions);
 
diff --git a/clang-tools-extra/clangd/InlayHints.cpp b/clang-tools-extra/clangd/InlayHints.cpp
--- a/clang-tools-extra/clangd/InlayHints.cpp
+++ b/clang-tools-extra/clangd/InlayHints.cpp
@@ -156,7 +156,7 @@
       return false;
 
     StringRef Name = getSimpleName(*Callee);
-    if (!Name.startswith_lower("set"))
+    if (!Name.startswith_insensitive("set"))
       return false;
 
     // In addition to checking that the function has one parameter and its
@@ -168,10 +168,10 @@
     // This currently doesn't handle cases where params use snake_case
     // and functions don't, e.g.
     //   void setExceptionHandler(EHFunc exception_handler);
-    // We could improve this by replacing `equals_lower` with some
+    // We could improve this by replacing `equals_insensitive` with some
     // `sloppy_equals` which ignores case and also skips underscores.
     StringRef WhatItIsSetting = Name.substr(3).ltrim("_");
-    return WhatItIsSetting.equals_lower(ParamNames[0]);
+    return WhatItIsSetting.equals_insensitive(ParamNames[0]);
   }
 
   bool shouldHint(const Expr *Arg, StringRef ParamName) {
diff --git a/clang-tools-extra/clangd/Quality.cpp b/clang-tools-extra/clangd/Quality.cpp
--- a/clang-tools-extra/clangd/Quality.cpp
+++ b/clang-tools-extra/clangd/Quality.cpp
@@ -378,7 +378,7 @@
 wordMatching(llvm::StringRef Name, const llvm::StringSet<> *ContextWords) {
   if (ContextWords)
     for (const auto &Word : ContextWords->keys())
-      if (Name.contains_lower(Word))
+      if (Name.contains_insensitive(Word))
         return Word;
   return llvm::None;
 }
@@ -552,7 +552,7 @@
   int NumMatch = 0;
   if (Relevance.ContextWords) {
     for (const auto &Word : Relevance.ContextWords->keys()) {
-      if (Relevance.Name.contains_lower(Word)) {
+      if (Relevance.Name.contains_insensitive(Word)) {
         ++NumMatch;
       }
     }
diff --git a/clang-tools-extra/clangd/index/SymbolCollector.cpp b/clang-tools-extra/clangd/index/SymbolCollector.cpp
--- a/clang-tools-extra/clangd/index/SymbolCollector.cpp
+++ b/clang-tools-extra/clangd/index/SymbolCollector.cpp
@@ -285,7 +285,7 @@
     Line = Line.ltrim();
     if (!Line.startswith("error"))
       return false;
-    return Line.contains_lower("includ"); // Matches "include" or "including".
+    return Line.contains_insensitive("includ"); // Matches "include" or "including".
   }
 
   // Heuristically headers that only want to be included via an umbrella.
diff --git a/clang-tools-extra/clangd/support/Path.cpp b/clang-tools-extra/clangd/support/Path.cpp
--- a/clang-tools-extra/clangd/support/Path.cpp
+++ b/clang-tools-extra/clangd/support/Path.cpp
@@ -13,7 +13,7 @@
 
 #ifdef CLANGD_PATH_CASE_INSENSITIVE
 std::string maybeCaseFoldPath(PathRef Path) { return Path.lower(); }
-bool pathEqual(PathRef A, PathRef B) { return A.equals_lower(B); }
+bool pathEqual(PathRef A, PathRef B) { return A.equals_insensitive(B); }
 #else  // NOT CLANGD_PATH_CASE_INSENSITIVE
 std::string maybeCaseFoldPath(PathRef Path) { return Path.str(); }
 bool pathEqual(PathRef A, PathRef B) { return A == B; }
diff --git a/clang-tools-extra/modularize/ModularizeUtilities.cpp b/clang-tools-extra/modularize/ModularizeUtilities.cpp
--- a/clang-tools-extra/modularize/ModularizeUtilities.cpp
+++ b/clang-tools-extra/modularize/ModularizeUtilities.cpp
@@ -470,9 +470,9 @@
   StringRef Extension = llvm::sys::path::extension(FileName);
   if (Extension.size() == 0)
     return true;
-  if (Extension.equals_lower(".h"))
+  if (Extension.equals_insensitive(".h"))
     return true;
-  if (Extension.equals_lower(".inc"))
+  if (Extension.equals_insensitive(".inc"))
     return true;
   return false;
 }
diff --git a/clang/lib/ASTMatchers/Dynamic/Marshallers.cpp b/clang/lib/ASTMatchers/Dynamic/Marshallers.cpp
--- a/clang/lib/ASTMatchers/Dynamic/Marshallers.cpp
+++ b/clang/lib/ASTMatchers/Dynamic/Marshallers.cpp
@@ -20,7 +20,7 @@
     ++MaxEditDistance;
   llvm::StringRef Res;
   for (const llvm::StringRef &Item : Allowed) {
-    if (Item.equals_lower(Search)) {
+    if (Item.equals_insensitive(Search)) {
       assert(!Item.equals(Search) && "This should be handled earlier on.");
       MaxEditDistance = 1;
       Res = Item;
@@ -40,7 +40,7 @@
       auto NoPrefix = Item;
       if (!NoPrefix.consume_front(DropPrefix))
         continue;
-      if (NoPrefix.equals_lower(Search)) {
+      if (NoPrefix.equals_insensitive(Search)) {
         if (NoPrefix.equals(Search))
           return Item.str();
         MaxEditDistance = 1;
diff --git a/clang/lib/Analysis/CalledOnceCheck.cpp b/clang/lib/Analysis/CalledOnceCheck.cpp
--- a/clang/lib/Analysis/CalledOnceCheck.cpp
+++ b/clang/lib/Analysis/CalledOnceCheck.cpp
@@ -478,7 +478,7 @@
     return llvm::any_of(
         CONVENTIONAL_CONDITIONS,
         [ConditionName](const llvm::StringLiteral &Conventional) {
-          return ConditionName.contains_lower(Conventional);
+          return ConditionName.contains_insensitive(Conventional);
         });
   });
 }
diff --git a/clang/lib/Analysis/RetainSummaryManager.cpp b/clang/lib/Analysis/RetainSummaryManager.cpp
--- a/clang/lib/Analysis/RetainSummaryManager.cpp
+++ b/clang/lib/Analysis/RetainSummaryManager.cpp
@@ -189,20 +189,20 @@
 }
 
 static bool isRetain(const FunctionDecl *FD, StringRef FName) {
-  return FName.startswith_lower("retain") || FName.endswith_lower("retain");
+  return FName.startswith_insensitive("retain") || FName.endswith_insensitive("retain");
 }
 
 static bool isRelease(const FunctionDecl *FD, StringRef FName) {
-  return FName.startswith_lower("release") || FName.endswith_lower("release");
+  return FName.startswith_insensitive("release") || FName.endswith_insensitive("release");
 }
 
 static bool isAutorelease(const FunctionDecl *FD, StringRef FName) {
-  return FName.startswith_lower("autorelease") ||
-         FName.endswith_lower("autorelease");
+  return FName.startswith_insensitive("autorelease") ||
+         FName.endswith_insensitive("autorelease");
 }
 
 static bool isMakeCollectable(StringRef FName) {
-  return FName.contains_lower("MakeCollectable");
+  return FName.contains_insensitive("MakeCollectable");
 }
 
 /// A function is OSObject related if it is declared on a subclass
@@ -1100,7 +1100,7 @@
   if (S.isKeywordSelector()) {
     for (unsigned i = 0, e = S.getNumArgs(); i != e; ++i) {
       StringRef Slot = S.getNameForSlot(i);
-      if (Slot.substr(Slot.size() - 8).equals_lower("delegate")) {
+      if (Slot.substr(Slot.size() - 8).equals_insensitive("delegate")) {
         if (ResultEff == ObjCInitRetE)
           ResultEff = RetEffect::MakeNoRetHard();
         else
diff --git a/clang/lib/Basic/FileManager.cpp b/clang/lib/Basic/FileManager.cpp
--- a/clang/lib/Basic/FileManager.cpp
+++ b/clang/lib/Basic/FileManager.cpp
@@ -128,7 +128,7 @@
   // Stat("C:") does not recognize "C:" as a valid directory
   std::string DirNameStr;
   if (DirName.size() > 1 && DirName.back() == ':' &&
-      DirName.equals_lower(llvm::sys::path::root_name(DirName))) {
+      DirName.equals_insensitive(llvm::sys::path::root_name(DirName))) {
     DirNameStr = DirName.str() + '.';
     DirName = DirNameStr;
   }
diff --git a/clang/lib/CodeGen/TargetInfo.cpp b/clang/lib/CodeGen/TargetInfo.cpp
--- a/clang/lib/CodeGen/TargetInfo.cpp
+++ b/clang/lib/CodeGen/TargetInfo.cpp
@@ -2610,7 +2610,7 @@
   bool Quote = (Lib.find(' ') != StringRef::npos);
   std::string ArgStr = Quote ? "\"" : "";
   ArgStr += Lib;
-  if (!Lib.endswith_lower(".lib") && !Lib.endswith_lower(".a"))
+  if (!Lib.endswith_insensitive(".lib") && !Lib.endswith_insensitive(".a"))
     ArgStr += ".lib";
   ArgStr += Quote ? "\"" : "";
   return ArgStr;
diff --git a/clang/lib/Driver/Driver.cpp b/clang/lib/Driver/Driver.cpp
--- a/clang/lib/Driver/Driver.cpp
+++ b/clang/lib/Driver/Driver.cpp
@@ -591,9 +591,9 @@
   A = Args.getLastArg(options::OPT_march_EQ);
   if (A && Target.isRISCV()) {
     StringRef ArchName = A->getValue();
-    if (ArchName.startswith_lower("rv32"))
+    if (ArchName.startswith_insensitive("rv32"))
       Target.setArch(llvm::Triple::riscv32);
-    else if (ArchName.startswith_lower("rv64"))
+    else if (ArchName.startswith_insensitive("rv64"))
       Target.setArch(llvm::Triple::riscv64);
   }
 
@@ -1755,7 +1755,7 @@
   // case-insensitive sorting for consistency with the -help option
   // which prints out options in the case-insensitive alphabetical order.
   llvm::sort(SuggestedCompletions, [](StringRef A, StringRef B) {
-    if (int X = A.compare_lower(B))
+    if (int X = A.compare_insensitive(B))
       return X < 0;
     return A.compare(B) > 0;
   });
@@ -3585,7 +3585,7 @@
     if (Args.hasArg(options::OPT_emit_llvm))
       Diag(clang::diag::err_drv_emit_llvm_link);
     if (IsCLMode() && LTOMode != LTOK_None &&
-        !Args.getLastArgValue(options::OPT_fuse_ld_EQ).equals_lower("lld"))
+        !Args.getLastArgValue(options::OPT_fuse_ld_EQ).equals_insensitive("lld"))
       Diag(clang::diag::err_drv_lto_without_lld);
   }
 
@@ -5346,7 +5346,7 @@
       case llvm::Triple::MSVC:
       case llvm::Triple::UnknownEnvironment:
         if (Args.getLastArgValue(options::OPT_fuse_ld_EQ)
-                .startswith_lower("bfd"))
+                .startswith_insensitive("bfd"))
           TC = std::make_unique<toolchains::CrossWindowsToolChain>(
               *this, Target, Args);
         else
diff --git a/clang/lib/Driver/ToolChains/Arch/RISCV.cpp b/clang/lib/Driver/ToolChains/Arch/RISCV.cpp
--- a/clang/lib/Driver/ToolChains/Arch/RISCV.cpp
+++ b/clang/lib/Driver/ToolChains/Arch/RISCV.cpp
@@ -610,17 +610,17 @@
   // rv64* -> lp64
   StringRef MArch = getRISCVArch(Args, Triple);
 
-  if (MArch.startswith_lower("rv32")) {
+  if (MArch.startswith_insensitive("rv32")) {
     // FIXME: parse `March` to find `D` extension properly
-    if (MArch.substr(4).contains_lower("d") || MArch.startswith_lower("rv32g"))
+    if (MArch.substr(4).contains_insensitive("d") || MArch.startswith_insensitive("rv32g"))
       return "ilp32d";
-    else if (MArch.startswith_lower("rv32e"))
+    else if (MArch.startswith_insensitive("rv32e"))
       return "ilp32e";
     else
       return "ilp32";
-  } else if (MArch.startswith_lower("rv64")) {
+  } else if (MArch.startswith_insensitive("rv64")) {
     // FIXME: parse `March` to find `D` extension properly
-    if (MArch.substr(4).contains_lower("d") || MArch.startswith_lower("rv64g"))
+    if (MArch.substr(4).contains_insensitive("d") || MArch.startswith_insensitive("rv64g"))
       return "lp64d";
     else
       return "lp64";
@@ -696,11 +696,11 @@
   if (const Arg *A = Args.getLastArg(options::OPT_mabi_EQ)) {
     StringRef MABI = A->getValue();
 
-    if (MABI.equals_lower("ilp32e"))
+    if (MABI.equals_insensitive("ilp32e"))
       return "rv32e";
-    else if (MABI.startswith_lower("ilp32"))
+    else if (MABI.startswith_insensitive("ilp32"))
       return "rv32imafdc";
-    else if (MABI.startswith_lower("lp64"))
+    else if (MABI.startswith_insensitive("lp64"))
       return "rv64imafdc";
   }
 
diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -2049,7 +2049,7 @@
       D.Diag(diag::warn_drv_unsupported_sdata);
     }
   } else if (Args.getLastArgValue(options::OPT_mcmodel_EQ)
-                 .equals_lower("large") &&
+                 .equals_insensitive("large") &&
              (Triple.getArch() == llvm::Triple::riscv64)) {
     // Not support linker relaxation for RV64 with large code model.
     SmallDataLimit = "0";
@@ -6317,7 +6317,7 @@
   // -finput_charset=UTF-8 is default. Reject others
   if (Arg *inputCharset = Args.getLastArg(options::OPT_finput_charset_EQ)) {
     StringRef value = inputCharset->getValue();
-    if (!value.equals_lower("utf-8"))
+    if (!value.equals_insensitive("utf-8"))
       D.Diag(diag::err_drv_invalid_value) << inputCharset->getAsString(Args)
                                           << value;
   }
@@ -6325,7 +6325,7 @@
   // -fexec_charset=UTF-8 is default. Reject others
   if (Arg *execCharset = Args.getLastArg(options::OPT_fexec_charset_EQ)) {
     StringRef value = execCharset->getValue();
-    if (!value.equals_lower("utf-8"))
+    if (!value.equals_insensitive("utf-8"))
       D.Diag(diag::err_drv_invalid_value) << execCharset->getAsString(Args)
                                           << value;
   }
@@ -7252,17 +7252,17 @@
     StringRef GuardArgs = A->getValue();
     // The only valid options are "cf", "cf,nochecks", "cf-", "ehcont" and
     // "ehcont-".
-    if (GuardArgs.equals_lower("cf")) {
+    if (GuardArgs.equals_insensitive("cf")) {
       // Emit CFG instrumentation and the table of address-taken functions.
       CmdArgs.push_back("-cfguard");
-    } else if (GuardArgs.equals_lower("cf,nochecks")) {
+    } else if (GuardArgs.equals_insensitive("cf,nochecks")) {
       // Emit only the table of address-taken functions.
       CmdArgs.push_back("-cfguard-no-checks");
-    } else if (GuardArgs.equals_lower("ehcont")) {
+    } else if (GuardArgs.equals_insensitive("ehcont")) {
       // Emit EH continuation table.
       CmdArgs.push_back("-ehcontguard");
-    } else if (GuardArgs.equals_lower("cf-") ||
-               GuardArgs.equals_lower("ehcont-")) {
+    } else if (GuardArgs.equals_insensitive("cf-") ||
+               GuardArgs.equals_insensitive("ehcont-")) {
       // Do nothing, but we might want to emit a security warning in future.
     } else {
       D.Diag(diag::err_drv_invalid_value) << A->getSpelling() << GuardArgs;
diff --git a/clang/lib/Driver/ToolChains/Fuchsia.cpp b/clang/lib/Driver/ToolChains/Fuchsia.cpp
--- a/clang/lib/Driver/ToolChains/Fuchsia.cpp
+++ b/clang/lib/Driver/ToolChains/Fuchsia.cpp
@@ -54,8 +54,8 @@
   CmdArgs.push_back("now");
 
   const char *Exec = Args.MakeArgString(ToolChain.GetLinkerPath());
-  if (llvm::sys::path::filename(Exec).equals_lower("ld.lld") ||
-      llvm::sys::path::stem(Exec).equals_lower("ld.lld")) {
+  if (llvm::sys::path::filename(Exec).equals_insensitive("ld.lld") ||
+      llvm::sys::path::stem(Exec).equals_insensitive("ld.lld")) {
     CmdArgs.push_back("-z");
     CmdArgs.push_back("rodynamic");
     CmdArgs.push_back("-z");
diff --git a/clang/lib/Driver/ToolChains/Gnu.cpp b/clang/lib/Driver/ToolChains/Gnu.cpp
--- a/clang/lib/Driver/ToolChains/Gnu.cpp
+++ b/clang/lib/Driver/ToolChains/Gnu.cpp
@@ -51,9 +51,9 @@
                                           ArgStringList &CmdArgs) {
   if (Arg *A = Args.getLastArg(options::OPT_mcpu_EQ)) {
     StringRef CPUArg(A->getValue());
-    if (CPUArg.equals_lower("krait"))
+    if (CPUArg.equals_insensitive("krait"))
       CmdArgs.push_back("-mcpu=cortex-a15");
-    else if(CPUArg.equals_lower("kryo"))
+    else if(CPUArg.equals_insensitive("kryo"))
       CmdArgs.push_back("-mcpu=cortex-a57");
     else
       Args.AddLastArg(CmdArgs, options::OPT_mcpu_EQ);
diff --git a/clang/lib/Driver/ToolChains/Hexagon.cpp b/clang/lib/Driver/ToolChains/Hexagon.cpp
--- a/clang/lib/Driver/ToolChains/Hexagon.cpp
+++ b/clang/lib/Driver/ToolChains/Hexagon.cpp
@@ -38,7 +38,7 @@
   // Handle the unsupported values passed to mhvx-length.
   if (Arg *A = Args.getLastArg(options::OPT_mhexagon_hvx_length_EQ)) {
     StringRef Val = A->getValue();
-    if (!Val.equals_lower("64b") && !Val.equals_lower("128b"))
+    if (!Val.equals_insensitive("64b") && !Val.equals_insensitive("128b"))
       D.Diag(diag::err_drv_unsupported_option_argument)
           << A->getOption().getName() << Val;
   }
@@ -218,8 +218,8 @@
   bool IncDefLibs = !Args.hasArg(options::OPT_nodefaultlibs);
   bool UseG0 = false;
   const char *Exec = Args.MakeArgString(HTC.GetLinkerPath());
-  bool UseLLD = (llvm::sys::path::filename(Exec).equals_lower("ld.lld") ||
-                 llvm::sys::path::stem(Exec).equals_lower("ld.lld"));
+  bool UseLLD = (llvm::sys::path::filename(Exec).equals_insensitive("ld.lld") ||
+                 llvm::sys::path::stem(Exec).equals_insensitive("ld.lld"));
   bool UseShared = IsShared && !IsStatic;
   StringRef CpuVer = toolchains::HexagonToolChain::GetTargetCPUVersion(Args);
 
diff --git a/clang/lib/Driver/ToolChains/MSVC.cpp b/clang/lib/Driver/ToolChains/MSVC.cpp
--- a/clang/lib/Driver/ToolChains/MSVC.cpp
+++ b/clang/lib/Driver/ToolChains/MSVC.cpp
@@ -181,24 +181,24 @@
 
       // whatever/VC/bin --> old toolchain, VC dir is toolchain dir.
       llvm::StringRef TestPath = PathEntry;
-      bool IsBin = llvm::sys::path::filename(TestPath).equals_lower("bin");
+      bool IsBin = llvm::sys::path::filename(TestPath).equals_insensitive("bin");
       if (!IsBin) {
         // Strip any architecture subdir like "amd64".
         TestPath = llvm::sys::path::parent_path(TestPath);
-        IsBin = llvm::sys::path::filename(TestPath).equals_lower("bin");
+        IsBin = llvm::sys::path::filename(TestPath).equals_insensitive("bin");
       }
       if (IsBin) {
         llvm::StringRef ParentPath = llvm::sys::path::parent_path(TestPath);
         llvm::StringRef ParentFilename = llvm::sys::path::filename(ParentPath);
-        if (ParentFilename.equals_lower("VC")) {
+        if (ParentFilename.equals_insensitive("VC")) {
           Path = std::string(ParentPath);
           VSLayout = MSVCToolChain::ToolsetLayout::OlderVS;
           return true;
         }
-        if (ParentFilename.equals_lower("x86ret") ||
-            ParentFilename.equals_lower("x86chk") ||
-            ParentFilename.equals_lower("amd64ret") ||
-            ParentFilename.equals_lower("amd64chk")) {
+        if (ParentFilename.equals_insensitive("x86ret") ||
+            ParentFilename.equals_insensitive("x86chk") ||
+            ParentFilename.equals_insensitive("amd64ret") ||
+            ParentFilename.equals_insensitive("amd64chk")) {
           Path = std::string(ParentPath);
           VSLayout = MSVCToolChain::ToolsetLayout::DevDivInternal;
           return true;
@@ -217,7 +217,7 @@
         for (llvm::StringRef Prefix : ExpectedPrefixes) {
           if (It == End)
             goto NotAToolChain;
-          if (!It->startswith_lower(Prefix))
+          if (!It->startswith_insensitive(Prefix))
             goto NotAToolChain;
           ++It;
         }
@@ -507,14 +507,14 @@
   // Control Flow Guard checks
   if (Arg *A = Args.getLastArg(options::OPT__SLASH_guard)) {
     StringRef GuardArgs = A->getValue();
-    if (GuardArgs.equals_lower("cf") || GuardArgs.equals_lower("cf,nochecks")) {
+    if (GuardArgs.equals_insensitive("cf") || GuardArgs.equals_insensitive("cf,nochecks")) {
       // MSVC doesn't yet support the "nochecks" modifier.
       CmdArgs.push_back("-guard:cf");
-    } else if (GuardArgs.equals_lower("cf-")) {
+    } else if (GuardArgs.equals_insensitive("cf-")) {
       CmdArgs.push_back("-guard:cf-");
-    } else if (GuardArgs.equals_lower("ehcont")) {
+    } else if (GuardArgs.equals_insensitive("ehcont")) {
       CmdArgs.push_back("-guard:ehcont");
-    } else if (GuardArgs.equals_lower("ehcont-")) {
+    } else if (GuardArgs.equals_insensitive("ehcont-")) {
       CmdArgs.push_back("-guard:ehcont-");
     }
   }
@@ -584,10 +584,10 @@
     = Args.getLastArgValue(options::OPT_fuse_ld_EQ, CLANG_DEFAULT_LINKER);
   if (Linker.empty())
     Linker = "link";
-  if (Linker.equals_lower("lld"))
+  if (Linker.equals_insensitive("lld"))
     Linker = "lld-link";
 
-  if (Linker.equals_lower("link")) {
+  if (Linker.equals_insensitive("link")) {
     // If we're using the MSVC linker, it's not sufficient to just use link
     // from the program PATH, because other environments like GnuWin32 install
     // their own link.exe which may come first.
@@ -646,7 +646,7 @@
       // find it.
       for (const char *Cursor = EnvBlock.data(); *Cursor != '\0';) {
         llvm::StringRef EnvVar(Cursor);
-        if (EnvVar.startswith_lower("path=")) {
+        if (EnvVar.startswith_insensitive("path=")) {
           using SubDirectoryType = toolchains::MSVCToolChain::SubDirectoryType;
           constexpr size_t PrefixLen = 5; // strlen("path=")
           Environment.push_back(Args.MakeArgString(
diff --git a/clang/lib/Driver/ToolChains/MinGW.cpp b/clang/lib/Driver/ToolChains/MinGW.cpp
--- a/clang/lib/Driver/ToolChains/MinGW.cpp
+++ b/clang/lib/Driver/ToolChains/MinGW.cpp
@@ -427,7 +427,7 @@
 
   NativeLLVMSupport =
       Args.getLastArgValue(options::OPT_fuse_ld_EQ, CLANG_DEFAULT_LINKER)
-          .equals_lower("lld");
+          .equals_insensitive("lld");
 }
 
 bool toolchains::MinGW::IsIntegratedAssemblerDefault() const { return true; }
diff --git a/clang/lib/Format/Format.cpp b/clang/lib/Format/Format.cpp
--- a/clang/lib/Format/Format.cpp
+++ b/clang/lib/Format/Format.cpp
@@ -1429,23 +1429,23 @@
 
 bool getPredefinedStyle(StringRef Name, FormatStyle::LanguageKind Language,
                         FormatStyle *Style) {
-  if (Name.equals_lower("llvm")) {
+  if (Name.equals_insensitive("llvm")) {
     *Style = getLLVMStyle(Language);
-  } else if (Name.equals_lower("chromium")) {
+  } else if (Name.equals_insensitive("chromium")) {
     *Style = getChromiumStyle(Language);
-  } else if (Name.equals_lower("mozilla")) {
+  } else if (Name.equals_insensitive("mozilla")) {
     *Style = getMozillaStyle();
-  } else if (Name.equals_lower("google")) {
+  } else if (Name.equals_insensitive("google")) {
     *Style = getGoogleStyle(Language);
-  } else if (Name.equals_lower("webkit")) {
+  } else if (Name.equals_insensitive("webkit")) {
     *Style = getWebKitStyle();
-  } else if (Name.equals_lower("gnu")) {
+  } else if (Name.equals_insensitive("gnu")) {
     *Style = getGNUStyle();
-  } else if (Name.equals_lower("microsoft")) {
+  } else if (Name.equals_insensitive("microsoft")) {
     *Style = getMicrosoftStyle(Language);
-  } else if (Name.equals_lower("none")) {
+  } else if (Name.equals_insensitive("none")) {
     *Style = getNoStyle();
-  } else if (Name.equals_lower("inheritparentconfig")) {
+  } else if (Name.equals_insensitive("inheritparentconfig")) {
     Style->InheritsParentConfig = true;
   } else {
     return false;
@@ -2959,22 +2959,22 @@
 static FormatStyle::LanguageKind getLanguageByFileName(StringRef FileName) {
   if (FileName.endswith(".java"))
     return FormatStyle::LK_Java;
-  if (FileName.endswith_lower(".js") || FileName.endswith_lower(".mjs") ||
-      FileName.endswith_lower(".ts"))
+  if (FileName.endswith_insensitive(".js") || FileName.endswith_insensitive(".mjs") ||
+      FileName.endswith_insensitive(".ts"))
     return FormatStyle::LK_JavaScript; // (module) JavaScript or TypeScript.
   if (FileName.endswith(".m") || FileName.endswith(".mm"))
     return FormatStyle::LK_ObjC;
-  if (FileName.endswith_lower(".proto") ||
-      FileName.endswith_lower(".protodevel"))
+  if (FileName.endswith_insensitive(".proto") ||
+      FileName.endswith_insensitive(".protodevel"))
     return FormatStyle::LK_Proto;
-  if (FileName.endswith_lower(".textpb") ||
-      FileName.endswith_lower(".pb.txt") ||
-      FileName.endswith_lower(".textproto") ||
-      FileName.endswith_lower(".asciipb"))
+  if (FileName.endswith_insensitive(".textpb") ||
+      FileName.endswith_insensitive(".pb.txt") ||
+      FileName.endswith_insensitive(".textproto") ||
+      FileName.endswith_insensitive(".asciipb"))
     return FormatStyle::LK_TextProto;
-  if (FileName.endswith_lower(".td"))
+  if (FileName.endswith_insensitive(".td"))
     return FormatStyle::LK_TableGen;
-  if (FileName.endswith_lower(".cs"))
+  if (FileName.endswith_insensitive(".cs"))
     return FormatStyle::LK_CSharp;
   return FormatStyle::LK_Cpp;
 }
@@ -3034,7 +3034,7 @@
   // If the style inherits the parent configuration it is a command line
   // configuration, which wants to inherit, so we have to skip the check of the
   // StyleName.
-  if (!Style.InheritsParentConfig && !StyleName.equals_lower("file")) {
+  if (!Style.InheritsParentConfig && !StyleName.equals_insensitive("file")) {
     if (!getPredefinedStyle(StyleName, Style.Language, &Style))
       return make_string_error("Invalid value for -style");
     if (!Style.InheritsParentConfig)
diff --git a/clang/lib/Format/SortJavaScriptImports.cpp b/clang/lib/Format/SortJavaScriptImports.cpp
--- a/clang/lib/Format/SortJavaScriptImports.cpp
+++ b/clang/lib/Format/SortJavaScriptImports.cpp
@@ -113,7 +113,7 @@
   // Empty URLs sort *last* (for export {...};).
   if (LHS.URL.empty() != RHS.URL.empty())
     return LHS.URL.empty() < RHS.URL.empty();
-  if (int Res = LHS.URL.compare_lower(RHS.URL))
+  if (int Res = LHS.URL.compare_insensitive(RHS.URL))
     return Res < 0;
   // '*' imports (with prefix) sort before {a, b, ...} imports.
   if (LHS.Prefix.empty() != RHS.Prefix.empty())
@@ -327,7 +327,7 @@
     SmallVector<JsImportedSymbol, 1> Symbols = Reference.Symbols;
     llvm::stable_sort(
         Symbols, [&](const JsImportedSymbol &LHS, const JsImportedSymbol &RHS) {
-          return LHS.Symbol.compare_lower(RHS.Symbol) < 0;
+          return LHS.Symbol.compare_insensitive(RHS.Symbol) < 0;
         });
     if (!Reference.SymbolsMerged && Symbols == Reference.Symbols) {
       // Symbols didn't change, just emit the entire module reference.
diff --git a/clang/lib/Format/UsingDeclarationsSorter.cpp b/clang/lib/Format/UsingDeclarationsSorter.cpp
--- a/clang/lib/Format/UsingDeclarationsSorter.cpp
+++ b/clang/lib/Format/UsingDeclarationsSorter.cpp
@@ -48,7 +48,7 @@
         return -1;
 
       // Two names within a group compare case-insensitively.
-      return NamesA[I].compare_lower(NamesB[I]);
+      return NamesA[I].compare_insensitive(NamesB[I]);
     }
 
     // I is the last index of NamesB and NamesB[I] is a non-namespace name.
@@ -57,7 +57,7 @@
       return 1;
 
     // Two namespaces names within a group compare case-insensitively.
-    int C = NamesA[I].compare_lower(NamesB[I]);
+    int C = NamesA[I].compare_insensitive(NamesB[I]);
     if (C != 0)
       return C;
   }
diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
--- a/clang/lib/Frontend/CompilerInvocation.cpp
+++ b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -3986,13 +3986,13 @@
   if (Arg *A = Args.getLastArg(OPT_msign_return_address_EQ)) {
     StringRef SignScope = A->getValue();
 
-    if (SignScope.equals_lower("none"))
+    if (SignScope.equals_insensitive("none"))
       Opts.setSignReturnAddressScope(
           LangOptions::SignReturnAddressScopeKind::None);
-    else if (SignScope.equals_lower("all"))
+    else if (SignScope.equals_insensitive("all"))
       Opts.setSignReturnAddressScope(
           LangOptions::SignReturnAddressScopeKind::All);
-    else if (SignScope.equals_lower("non-leaf"))
+    else if (SignScope.equals_insensitive("non-leaf"))
       Opts.setSignReturnAddressScope(
           LangOptions::SignReturnAddressScopeKind::NonLeaf);
     else
@@ -4002,10 +4002,10 @@
     if (Arg *A = Args.getLastArg(OPT_msign_return_address_key_EQ)) {
       StringRef SignKey = A->getValue();
       if (!SignScope.empty() && !SignKey.empty()) {
-        if (SignKey.equals_lower("a_key"))
+        if (SignKey.equals_insensitive("a_key"))
           Opts.setSignReturnAddressKey(
               LangOptions::SignReturnAddressKeyKind::AKey);
-        else if (SignKey.equals_lower("b_key"))
+        else if (SignKey.equals_insensitive("b_key"))
           Opts.setSignReturnAddressKey(
               LangOptions::SignReturnAddressKeyKind::BKey);
         else
diff --git a/clang/lib/Lex/HeaderMap.cpp b/clang/lib/Lex/HeaderMap.cpp
--- a/clang/lib/Lex/HeaderMap.cpp
+++ b/clang/lib/Lex/HeaderMap.cpp
@@ -224,7 +224,7 @@
     Optional<StringRef> Key = getString(B.Key);
     if (LLVM_UNLIKELY(!Key))
       continue;
-    if (!Filename.equals_lower(*Key))
+    if (!Filename.equals_insensitive(*Key))
       continue;
 
     // If so, we have a match in the hash table.  Construct the destination
diff --git a/clang/lib/Lex/PPDirectives.cpp b/clang/lib/Lex/PPDirectives.cpp
--- a/clang/lib/Lex/PPDirectives.cpp
+++ b/clang/lib/Lex/PPDirectives.cpp
@@ -196,7 +196,7 @@
 static bool warnByDefaultOnWrongCase(StringRef Include) {
   // If the first component of the path is "boost", treat this like a standard header
   // for the purposes of diagnostics.
-  if (::llvm::sys::path::begin(Include)->equals_lower("boost"))
+  if (::llvm::sys::path::begin(Include)->equals_insensitive("boost"))
     return true;
 
   // "condition_variable" is the longest standard header name at 18 characters.
@@ -1723,7 +1723,7 @@
         // If these path components differ by more than just case, then we
         // may be looking at symlinked paths. Bail on this diagnostic to avoid
         // noisy false positives.
-        SuggestReplacement = RealPathComponentIter->equals_lower(Component);
+        SuggestReplacement = RealPathComponentIter->equals_insensitive(Component);
         if (!SuggestReplacement)
           break;
         Component = *RealPathComponentIter;
diff --git a/clang/lib/Lex/PPMacroExpansion.cpp b/clang/lib/Lex/PPMacroExpansion.cpp
--- a/clang/lib/Lex/PPMacroExpansion.cpp
+++ b/clang/lib/Lex/PPMacroExpansion.cpp
@@ -1430,7 +1430,7 @@
   StringRef VendorName = TI.getTriple().getVendorName();
   if (VendorName.empty())
     VendorName = "unknown";
-  return VendorName.equals_lower(II->getName());
+  return VendorName.equals_insensitive(II->getName());
 }
 
 /// Implements the __is_target_os builtin macro.
diff --git a/clang/lib/Sema/CodeCompleteConsumer.cpp b/clang/lib/Sema/CodeCompleteConsumer.cpp
--- a/clang/lib/Sema/CodeCompleteConsumer.cpp
+++ b/clang/lib/Sema/CodeCompleteConsumer.cpp
@@ -755,7 +755,7 @@
   std::string XSaved, YSaved;
   StringRef XStr = X.getOrderedName(XSaved);
   StringRef YStr = Y.getOrderedName(YSaved);
-  int cmp = XStr.compare_lower(YStr);
+  int cmp = XStr.compare_insensitive(YStr);
   if (cmp)
     return cmp < 0;
 
diff --git a/clang/lib/Sema/SemaChecking.cpp b/clang/lib/Sema/SemaChecking.cpp
--- a/clang/lib/Sema/SemaChecking.cpp
+++ b/clang/lib/Sema/SemaChecking.cpp
@@ -6971,18 +6971,18 @@
 
     bool ValidString = true;
     if (IsARMBuiltin) {
-      ValidString &= Fields[0].startswith_lower("cp") ||
-                     Fields[0].startswith_lower("p");
+      ValidString &= Fields[0].startswith_insensitive("cp") ||
+                     Fields[0].startswith_insensitive("p");
       if (ValidString)
         Fields[0] =
-          Fields[0].drop_front(Fields[0].startswith_lower("cp") ? 2 : 1);
+          Fields[0].drop_front(Fields[0].startswith_insensitive("cp") ? 2 : 1);
 
-      ValidString &= Fields[2].startswith_lower("c");
+      ValidString &= Fields[2].startswith_insensitive("c");
       if (ValidString)
         Fields[2] = Fields[2].drop_front(1);
 
       if (FiveFields) {
-        ValidString &= Fields[3].startswith_lower("c");
+        ValidString &= Fields[3].startswith_insensitive("c");
         if (ValidString)
           Fields[3] = Fields[3].drop_front(1);
       }
diff --git a/clang/lib/Sema/SemaCodeComplete.cpp b/clang/lib/Sema/SemaCodeComplete.cpp
--- a/clang/lib/Sema/SemaCodeComplete.cpp
+++ b/clang/lib/Sema/SemaCodeComplete.cpp
@@ -9491,10 +9491,10 @@
         // Only files that really look like headers. (Except in system dirs).
         if (!IsSystem) {
           // Header extensions from Types.def, which we can't depend on here.
-          if (!(Filename.endswith_lower(".h") ||
-                Filename.endswith_lower(".hh") ||
-                Filename.endswith_lower(".hpp") ||
-                Filename.endswith_lower(".inc")))
+          if (!(Filename.endswith_insensitive(".h") ||
+                Filename.endswith_insensitive(".hh") ||
+                Filename.endswith_insensitive(".hpp") ||
+                Filename.endswith_insensitive(".inc")))
             break;
         }
         AddCompletion(Filename, /*IsDirectory=*/false);
diff --git a/clang/lib/StaticAnalyzer/Checkers/CStringChecker.cpp b/clang/lib/StaticAnalyzer/Checkers/CStringChecker.cpp
--- a/clang/lib/StaticAnalyzer/Checkers/CStringChecker.cpp
+++ b/clang/lib/StaticAnalyzer/Checkers/CStringChecker.cpp
@@ -2039,7 +2039,7 @@
         RightStrRef = RightStrRef.substr(0, s2Term);
 
       // Use StringRef's comparison methods to compute the actual result.
-      int compareRes = IgnoreCase ? LeftStrRef.compare_lower(RightStrRef)
+      int compareRes = IgnoreCase ? LeftStrRef.compare_insensitive(RightStrRef)
                                   : LeftStrRef.compare(RightStrRef);
 
       // The strcmp function returns an integer greater than, equal to, or less
diff --git a/clang/lib/StaticAnalyzer/Checkers/ContainerModeling.cpp b/clang/lib/StaticAnalyzer/Checkers/ContainerModeling.cpp
--- a/clang/lib/StaticAnalyzer/Checkers/ContainerModeling.cpp
+++ b/clang/lib/StaticAnalyzer/Checkers/ContainerModeling.cpp
@@ -763,14 +763,14 @@
   const auto *IdInfo = Func->getIdentifier();
   if (!IdInfo)
     return false;
-  return IdInfo->getName().endswith_lower("begin");
+  return IdInfo->getName().endswith_insensitive("begin");
 }
 
 bool isEndCall(const FunctionDecl *Func) {
   const auto *IdInfo = Func->getIdentifier();
   if (!IdInfo)
     return false;
-  return IdInfo->getName().endswith_lower("end");
+  return IdInfo->getName().endswith_insensitive("end");
 }
 
 const CXXRecordDecl *getCXXRecordDecl(ProgramStateRef State,
diff --git a/clang/lib/StaticAnalyzer/Checkers/GCDAntipatternChecker.cpp b/clang/lib/StaticAnalyzer/Checkers/GCDAntipatternChecker.cpp
--- a/clang/lib/StaticAnalyzer/Checkers/GCDAntipatternChecker.cpp
+++ b/clang/lib/StaticAnalyzer/Checkers/GCDAntipatternChecker.cpp
@@ -80,7 +80,7 @@
     if (const auto *CD = dyn_cast<ObjCContainerDecl>(OD->getParent())) {
       std::string ContainerName = CD->getNameAsString();
       StringRef CN(ContainerName);
-      if (CN.contains_lower("test") || CN.contains_lower("mock"))
+      if (CN.contains_insensitive("test") || CN.contains_insensitive("mock"))
         return true;
     }
   }
diff --git a/clang/lib/StaticAnalyzer/Checkers/Iterator.cpp b/clang/lib/StaticAnalyzer/Checkers/Iterator.cpp
--- a/clang/lib/StaticAnalyzer/Checkers/Iterator.cpp
+++ b/clang/lib/StaticAnalyzer/Checkers/Iterator.cpp
@@ -29,8 +29,8 @@
     return false;
 
   const auto Name = CRD->getName();
-  if (!(Name.endswith_lower("iterator") || Name.endswith_lower("iter") ||
-        Name.endswith_lower("it")))
+  if (!(Name.endswith_insensitive("iterator") || Name.endswith_insensitive("iter") ||
+        Name.endswith_insensitive("it")))
     return false;
 
   bool HasCopyCtor = false, HasCopyAssign = true, HasDtor = false,
diff --git a/clang/lib/StaticAnalyzer/Checkers/MallocChecker.cpp b/clang/lib/StaticAnalyzer/Checkers/MallocChecker.cpp
--- a/clang/lib/StaticAnalyzer/Checkers/MallocChecker.cpp
+++ b/clang/lib/StaticAnalyzer/Checkers/MallocChecker.cpp
@@ -3145,9 +3145,9 @@
 static bool isReferenceCountingPointerDestructor(const CXXDestructorDecl *DD) {
   if (const IdentifierInfo *II = DD->getParent()->getIdentifier()) {
     StringRef N = II->getName();
-    if (N.contains_lower("ptr") || N.contains_lower("pointer")) {
-      if (N.contains_lower("ref") || N.contains_lower("cnt") ||
-          N.contains_lower("intrusive") || N.contains_lower("shared")) {
+    if (N.contains_insensitive("ptr") || N.contains_insensitive("pointer")) {
+      if (N.contains_insensitive("ref") || N.contains_insensitive("cnt") ||
+          N.contains_insensitive("intrusive") || N.contains_insensitive("shared")) {
         return true;
       }
     }
diff --git a/clang/lib/Tooling/Inclusions/HeaderIncludes.cpp b/clang/lib/Tooling/Inclusions/HeaderIncludes.cpp
--- a/clang/lib/Tooling/Inclusions/HeaderIncludes.cpp
+++ b/clang/lib/Tooling/Inclusions/HeaderIncludes.cpp
@@ -252,9 +252,9 @@
   //  1) foo.h => bar.cc
   //  2) foo.proto.h => foo.cc
   StringRef Matching;
-  if (MatchingFileStem.startswith_lower(HeaderStem))
+  if (MatchingFileStem.startswith_insensitive(HeaderStem))
     Matching = MatchingFileStem; // example 1), 2)
-  else if (FileStem.equals_lower(HeaderStem))
+  else if (FileStem.equals_insensitive(HeaderStem))
     Matching = FileStem; // example 3)
   if (!Matching.empty()) {
     llvm::Regex MainIncludeRegex(HeaderStem.str() + Style.IncludeIsMainRegex,
diff --git a/clang/lib/Tooling/InterpolatingCompilationDatabase.cpp b/clang/lib/Tooling/InterpolatingCompilationDatabase.cpp
--- a/clang/lib/Tooling/InterpolatingCompilationDatabase.cpp
+++ b/clang/lib/Tooling/InterpolatingCompilationDatabase.cpp
@@ -256,7 +256,7 @@
 
     // Otherwise just check the clang executable file name.
     return !CmdLine.empty() &&
-           llvm::sys::path::stem(CmdLine.front()).endswith_lower("cl");
+           llvm::sys::path::stem(CmdLine.front()).endswith_insensitive("cl");
   }
 
   // Map the language from the --std flag to that of the -x flag.
diff --git a/clang/tools/clang-refactor/TestSupport.cpp b/clang/tools/clang-refactor/TestSupport.cpp
--- a/clang/tools/clang-refactor/TestSupport.cpp
+++ b/clang/tools/clang-refactor/TestSupport.cpp
@@ -328,8 +328,8 @@
     // Try to detect mistyped 'range:' comments to ensure tests don't miss
     // anything.
     auto DetectMistypedCommand = [&]() -> bool {
-      if (Comment.contains_lower("range") && Comment.contains("=") &&
-          !Comment.contains_lower("run") && !Comment.contains("CHECK")) {
+      if (Comment.contains_insensitive("range") && Comment.contains("=") &&
+          !Comment.contains_insensitive("run") && !Comment.contains("CHECK")) {
         llvm::errs() << "error: suspicious comment '" << Comment
                      << "' that "
                         "resembles the range command found\n";
diff --git a/clang/tools/clang-scan-deps/ClangScanDeps.cpp b/clang/tools/clang-scan-deps/ClangScanDeps.cpp
--- a/clang/tools/clang-scan-deps/ClangScanDeps.cpp
+++ b/clang/tools/clang-scan-deps/ClangScanDeps.cpp
@@ -465,7 +465,7 @@
         auto FlagsEnd = llvm::find(Args, "--");
         if (FlagsEnd != Args.begin()) {
           ClangCLMode =
-              llvm::sys::path::stem(Args[0]).contains_lower("clang-cl") ||
+              llvm::sys::path::stem(Args[0]).contains_insensitive("clang-cl") ||
               llvm::is_contained(Args, "--driver-mode=cl");
 
           // Reverse scan, starting at the end or at the element before "--".
diff --git a/clang/tools/driver/driver.cpp b/clang/tools/driver/driver.cpp
--- a/clang/tools/driver/driver.cpp
+++ b/clang/tools/driver/driver.cpp
@@ -273,7 +273,7 @@
   // If the clang binary happens to be named cl.exe for compatibility reasons,
   // use clang-cl.exe as the prefix to avoid confusion between clang and MSVC.
   StringRef ExeBasename(llvm::sys::path::stem(Path));
-  if (ExeBasename.equals_lower("cl"))
+  if (ExeBasename.equals_insensitive("cl"))
     ExeBasename = "clang-cl";
   DiagClient->setPrefix(std::string(ExeBasename));
 }
diff --git a/clang/tools/libclang/CIndexCodeCompletion.cpp b/clang/tools/libclang/CIndexCodeCompletion.cpp
--- a/clang/tools/libclang/CIndexCodeCompletion.cpp
+++ b/clang/tools/libclang/CIndexCodeCompletion.cpp
@@ -1026,7 +1026,7 @@
       if (XText.empty() || YText.empty())
         return !XText.empty();
             
-      int result = XText.compare_lower(YText);
+      int result = XText.compare_insensitive(YText);
       if (result < 0)
         return true;
       if (result > 0)
diff --git a/clang/unittests/Tooling/CompilationDatabaseTest.cpp b/clang/unittests/Tooling/CompilationDatabaseTest.cpp
--- a/clang/unittests/Tooling/CompilationDatabaseTest.cpp
+++ b/clang/unittests/Tooling/CompilationDatabaseTest.cpp
@@ -210,7 +210,7 @@
 struct FakeComparator : public PathComparator {
   ~FakeComparator() override {}
   bool equivalent(StringRef FileA, StringRef FileB) const override {
-    return FileA.equals_lower(FileB);
+    return FileA.equals_insensitive(FileB);
   }
 };
 
diff --git a/lld/COFF/DebugTypes.cpp b/lld/COFF/DebugTypes.cpp
--- a/lld/COFF/DebugTypes.cpp
+++ b/lld/COFF/DebugTypes.cpp
@@ -464,7 +464,7 @@
 
 static bool equalsPath(StringRef path1, StringRef path2) {
 #if defined(_WIN32)
-  return path1.equals_lower(path2);
+  return path1.equals_insensitive(path2);
 #else
   return path1.equals(path2);
 #endif
diff --git a/lld/COFF/Driver.cpp b/lld/COFF/Driver.cpp
--- a/lld/COFF/Driver.cpp
+++ b/lld/COFF/Driver.cpp
@@ -234,7 +234,7 @@
     error(filename + ": is not a native COFF file. Recompile without /GL");
     break;
   case file_magic::pecoff_executable:
-    if (filename.endswith_lower(".dll")) {
+    if (filename.endswith_insensitive(".dll")) {
       error(filename + ": bad file type. Did you specify a DLL instead of an "
                        "import library?");
       break;
@@ -474,7 +474,7 @@
       return None;
   }
 
-  if (path.endswith_lower(".lib"))
+  if (path.endswith_insensitive(".lib"))
     visitedLibs.insert(std::string(sys::path::filename(path)));
   return path;
 }
@@ -1142,9 +1142,9 @@
     // text between first and second % as variable name.
     buf.append(altPath.substr(cursor, firstMark - cursor));
     StringRef var = altPath.substr(firstMark, secondMark - firstMark + 1);
-    if (var.equals_lower("%_pdb%"))
+    if (var.equals_insensitive("%_pdb%"))
       buf.append(pdbBasename);
-    else if (var.equals_lower("%_ext%"))
+    else if (var.equals_insensitive("%_ext%"))
       buf.append(binaryExtension);
     else {
       warn("only %_PDB% and %_EXT% supported in /pdbaltpath:, keeping " +
@@ -1272,8 +1272,8 @@
 
   // If the first command line argument is "/lib", link.exe acts like lib.exe.
   // We call our own implementation of lib.exe that understands bitcode files.
-  if (argsArr.size() > 1 && (StringRef(argsArr[1]).equals_lower("/lib") ||
-                             StringRef(argsArr[1]).equals_lower("-lib"))) {
+  if (argsArr.size() > 1 && (StringRef(argsArr[1]).equals_insensitive("/lib") ||
+                             StringRef(argsArr[1]).equals_insensitive("-lib"))) {
     if (llvm::libDriverMain(argsArr.slice(1)) != 0)
       fatal("lib failed");
     return;
diff --git a/lld/COFF/DriverUtils.cpp b/lld/COFF/DriverUtils.cpp
--- a/lld/COFF/DriverUtils.cpp
+++ b/lld/COFF/DriverUtils.cpp
@@ -99,17 +99,17 @@
   SmallVector<StringRef, 1> splitArgs;
   fullArg.split(splitArgs, ",");
   for (StringRef arg : splitArgs) {
-    if (arg.equals_lower("no"))
+    if (arg.equals_insensitive("no"))
       config->guardCF = GuardCFLevel::Off;
-    else if (arg.equals_lower("nolongjmp"))
+    else if (arg.equals_insensitive("nolongjmp"))
       config->guardCF &= ~GuardCFLevel::LongJmp;
-    else if (arg.equals_lower("noehcont"))
+    else if (arg.equals_insensitive("noehcont"))
       config->guardCF &= ~GuardCFLevel::EHCont;
-    else if (arg.equals_lower("cf"))
+    else if (arg.equals_insensitive("cf"))
       config->guardCF = GuardCFLevel::CF;
-    else if (arg.equals_lower("longjmp"))
+    else if (arg.equals_insensitive("longjmp"))
       config->guardCF |= GuardCFLevel::CF | GuardCFLevel::LongJmp;
-    else if (arg.equals_lower("ehcont"))
+    else if (arg.equals_insensitive("ehcont"))
       config->guardCF |= GuardCFLevel::CF | GuardCFLevel::EHCont;
     else
       fatal("invalid argument to /guard: " + arg);
@@ -257,17 +257,17 @@
 // Parses a string in the form of "EMBED[,=<integer>]|NO".
 // Results are directly written to Config.
 void parseManifest(StringRef arg) {
-  if (arg.equals_lower("no")) {
+  if (arg.equals_insensitive("no")) {
     config->manifest = Configuration::No;
     return;
   }
-  if (!arg.startswith_lower("embed"))
+  if (!arg.startswith_insensitive("embed"))
     fatal("invalid option " + arg);
   config->manifest = Configuration::Embed;
   arg = arg.substr(strlen("embed"));
   if (arg.empty())
     return;
-  if (!arg.startswith_lower(",id="))
+  if (!arg.startswith_insensitive(",id="))
     fatal("invalid option " + arg);
   arg = arg.substr(strlen(",id="));
   if (arg.getAsInteger(0, config->manifestID))
@@ -277,7 +277,7 @@
 // Parses a string in the form of "level=<string>|uiAccess=<string>|NO".
 // Results are directly written to Config.
 void parseManifestUAC(StringRef arg) {
-  if (arg.equals_lower("no")) {
+  if (arg.equals_insensitive("no")) {
     config->manifestUAC = false;
     return;
   }
@@ -285,12 +285,12 @@
     arg = arg.ltrim();
     if (arg.empty())
       return;
-    if (arg.startswith_lower("level=")) {
+    if (arg.startswith_insensitive("level=")) {
       arg = arg.substr(strlen("level="));
       std::tie(config->manifestLevel, arg) = arg.split(" ");
       continue;
     }
-    if (arg.startswith_lower("uiaccess=")) {
+    if (arg.startswith_insensitive("uiaccess=")) {
       arg = arg.substr(strlen("uiaccess="));
       std::tie(config->manifestUIAccess, arg) = arg.split(" ");
       continue;
@@ -305,9 +305,9 @@
   do {
     StringRef swaprun, newArg;
     std::tie(swaprun, newArg) = arg.split(',');
-    if (swaprun.equals_lower("cd"))
+    if (swaprun.equals_insensitive("cd"))
       config->swaprunCD = true;
-    else if (swaprun.equals_lower("net"))
+    else if (swaprun.equals_insensitive("net"))
       config->swaprunNet = true;
     else if (swaprun.empty())
       error("/swaprun: missing argument");
@@ -560,21 +560,21 @@
   while (!rest.empty()) {
     StringRef tok;
     std::tie(tok, rest) = rest.split(",");
-    if (tok.equals_lower("noname")) {
+    if (tok.equals_insensitive("noname")) {
       if (e.ordinal == 0)
         goto err;
       e.noname = true;
       continue;
     }
-    if (tok.equals_lower("data")) {
+    if (tok.equals_insensitive("data")) {
       e.data = true;
       continue;
     }
-    if (tok.equals_lower("constant")) {
+    if (tok.equals_insensitive("constant")) {
       e.constant = true;
       continue;
     }
-    if (tok.equals_lower("private")) {
+    if (tok.equals_insensitive("private")) {
       e.isPrivate = true;
       continue;
     }
@@ -883,10 +883,10 @@
   SmallVector<StringRef, 16> tokens;
   cl::TokenizeWindowsCommandLineNoCopy(s, saver, tokens);
   for (StringRef tok : tokens) {
-    if (tok.startswith_lower("/export:") || tok.startswith_lower("-export:"))
+    if (tok.startswith_insensitive("/export:") || tok.startswith_insensitive("-export:"))
       result.exports.push_back(tok.substr(strlen("/export:")));
-    else if (tok.startswith_lower("/include:") ||
-             tok.startswith_lower("-include:"))
+    else if (tok.startswith_insensitive("/include:") ||
+             tok.startswith_insensitive("-include:"))
       result.includes.push_back(tok.substr(strlen("/include:")));
     else {
       // Copy substrings that are not valid C strings. The tokenizer may have
diff --git a/lld/Common/Args.cpp b/lld/Common/Args.cpp
--- a/lld/Common/Args.cpp
+++ b/lld/Common/Args.cpp
@@ -89,7 +89,7 @@
 }
 
 StringRef lld::args::getFilenameWithoutExe(StringRef path) {
-  if (path.endswith_lower(".exe"))
+  if (path.endswith_insensitive(".exe"))
     return sys::path::stem(path);
   return sys::path::filename(path);
 }
diff --git a/lld/ELF/Relocations.cpp b/lld/ELF/Relocations.cpp
--- a/lld/ELF/Relocations.cpp
+++ b/lld/ELF/Relocations.cpp
@@ -820,10 +820,10 @@
 
   // Case mismatch, e.g. Foo vs FOO.
   for (auto &it : map)
-    if (name.equals_lower(it.first))
+    if (name.equals_insensitive(it.first))
       return it.second;
   for (Symbol *sym : symtab->symbols())
-    if (!sym->isUndefined() && name.equals_lower(sym->getName()))
+    if (!sym->isUndefined() && name.equals_insensitive(sym->getName()))
       return sym;
 
   // The reference may be a mangled name while the definition is not. Suggest a
diff --git a/lld/ELF/ScriptParser.cpp b/lld/ELF/ScriptParser.cpp
--- a/lld/ELF/ScriptParser.cpp
+++ b/lld/ELF/ScriptParser.cpp
@@ -1126,24 +1126,24 @@
 static Optional<uint64_t> parseInt(StringRef tok) {
   // Hexadecimal
   uint64_t val;
-  if (tok.startswith_lower("0x")) {
+  if (tok.startswith_insensitive("0x")) {
     if (!to_integer(tok.substr(2), val, 16))
       return None;
     return val;
   }
-  if (tok.endswith_lower("H")) {
+  if (tok.endswith_insensitive("H")) {
     if (!to_integer(tok.drop_back(), val, 16))
       return None;
     return val;
   }
 
   // Decimal
-  if (tok.endswith_lower("K")) {
+  if (tok.endswith_insensitive("K")) {
     if (!to_integer(tok.drop_back(), val, 10))
       return None;
     return val * 1024;
   }
-  if (tok.endswith_lower("M")) {
+  if (tok.endswith_insensitive("M")) {
     if (!to_integer(tok.drop_back(), val, 10))
       return None;
     return val * 1024 * 1024;
diff --git a/lld/MinGW/Driver.cpp b/lld/MinGW/Driver.cpp
--- a/lld/MinGW/Driver.cpp
+++ b/lld/MinGW/Driver.cpp
@@ -401,7 +401,7 @@
   for (auto *a : args) {
     switch (a->getOption().getID()) {
     case OPT_INPUT:
-      if (StringRef(a->getValue()).endswith_lower(".def"))
+      if (StringRef(a->getValue()).endswith_insensitive(".def"))
         add("-def:" + StringRef(a->getValue()));
       else
         add(prefix + StringRef(a->getValue()));
diff --git a/lld/lib/Driver/DarwinLdDriver.cpp b/lld/lib/Driver/DarwinLdDriver.cpp
--- a/lld/lib/Driver/DarwinLdDriver.cpp
+++ b/lld/lib/Driver/DarwinLdDriver.cpp
@@ -293,7 +293,7 @@
 
 /// Parse number assuming it is base 16, but allow 0x prefix.
 static bool parseNumberBase16(StringRef numStr, uint64_t &baseAddress) {
-  if (numStr.startswith_lower("0x"))
+  if (numStr.startswith_insensitive("0x"))
     numStr = numStr.drop_front(2);
   return numStr.getAsInteger(16, baseAddress);
 }
diff --git a/lld/tools/lld/lld.cpp b/lld/tools/lld/lld.cpp
--- a/lld/tools/lld/lld.cpp
+++ b/lld/tools/lld/lld.cpp
@@ -131,7 +131,7 @@
 
   // Deduct the flavor from argv[0].
   StringRef arg0 = path::filename(v[0]);
-  if (arg0.endswith_lower(".exe"))
+  if (arg0.endswith_insensitive(".exe"))
     arg0 = arg0.drop_back(4);
   return parseProgname(arg0);
 }
diff --git a/lldb/source/Commands/CommandObjectMultiword.cpp b/lldb/source/Commands/CommandObjectMultiword.cpp
--- a/lldb/source/Commands/CommandObjectMultiword.cpp
+++ b/lldb/source/Commands/CommandObjectMultiword.cpp
@@ -98,7 +98,7 @@
     return result.Succeeded();
   }
 
-  if (sub_command.equals_lower("help")) {
+  if (sub_command.equals_insensitive("help")) {
     this->CommandObject::GenerateHelpText(result);
     return result.Succeeded();
   }
diff --git a/lldb/source/Host/common/NativeRegisterContext.cpp b/lldb/source/Host/common/NativeRegisterContext.cpp
--- a/lldb/source/Host/common/NativeRegisterContext.cpp
+++ b/lldb/source/Host/common/NativeRegisterContext.cpp
@@ -60,8 +60,8 @@
   for (uint32_t reg = start_idx; reg < num_registers; ++reg) {
     const RegisterInfo *reg_info = GetRegisterInfoAtIndex(reg);
 
-    if (reg_name.equals_lower(reg_info->name) ||
-        reg_name.equals_lower(reg_info->alt_name))
+    if (reg_name.equals_insensitive(reg_info->name) ||
+        reg_name.equals_insensitive(reg_info->alt_name))
       return reg_info;
   }
   return nullptr;
diff --git a/lldb/source/Host/windows/ProcessLauncherWindows.cpp b/lldb/source/Host/windows/ProcessLauncherWindows.cpp
--- a/lldb/source/Host/windows/ProcessLauncherWindows.cpp
+++ b/lldb/source/Host/windows/ProcessLauncherWindows.cpp
@@ -86,7 +86,7 @@
   const char *hide_console_var =
       getenv("LLDB_LAUNCH_INFERIORS_WITHOUT_CONSOLE");
   if (hide_console_var &&
-      llvm::StringRef(hide_console_var).equals_lower("true")) {
+      llvm::StringRef(hide_console_var).equals_insensitive("true")) {
     startupinfo.dwFlags |= STARTF_USESHOWWINDOW;
     startupinfo.wShowWindow = SW_HIDE;
   }
diff --git a/lldb/source/Initialization/SystemInitializerCommon.cpp b/lldb/source/Initialization/SystemInitializerCommon.cpp
--- a/lldb/source/Initialization/SystemInitializerCommon.cpp
+++ b/lldb/source/Initialization/SystemInitializerCommon.cpp
@@ -96,7 +96,7 @@
 #if defined(_WIN32)
   const char *disable_crash_dialog_var = getenv("LLDB_DISABLE_CRASH_DIALOG");
   if (disable_crash_dialog_var &&
-      llvm::StringRef(disable_crash_dialog_var).equals_lower("true")) {
+      llvm::StringRef(disable_crash_dialog_var).equals_insensitive("true")) {
     // This will prevent Windows from displaying a dialog box requiring user
     // interaction when
     // LLDB crashes.  This is mostly useful when automating LLDB, for example
diff --git a/lldb/source/Interpreter/CommandInterpreter.cpp b/lldb/source/Interpreter/CommandInterpreter.cpp
--- a/lldb/source/Interpreter/CommandInterpreter.cpp
+++ b/lldb/source/Interpreter/CommandInterpreter.cpp
@@ -2675,7 +2675,7 @@
     const bool search_long_help = false;
     const bool search_syntax = false;
     const bool search_options = false;
-    if (command_name.contains_lower(search_word) ||
+    if (command_name.contains_insensitive(search_word) ||
         cmd_obj->HelpTextContainsWord(search_word, search_short_help,
                                       search_long_help, search_syntax,
                                       search_options)) {
diff --git a/lldb/source/Interpreter/CommandObject.cpp b/lldb/source/Interpreter/CommandObject.cpp
--- a/lldb/source/Interpreter/CommandObject.cpp
+++ b/lldb/source/Interpreter/CommandObject.cpp
@@ -316,11 +316,11 @@
   llvm::StringRef long_help = GetHelpLong();
   llvm::StringRef syntax_help = GetSyntax();
 
-  if (search_short_help && short_help.contains_lower(search_word))
+  if (search_short_help && short_help.contains_insensitive(search_word))
     found_word = true;
-  else if (search_long_help && long_help.contains_lower(search_word))
+  else if (search_long_help && long_help.contains_insensitive(search_word))
     found_word = true;
-  else if (search_syntax && syntax_help.contains_lower(search_word))
+  else if (search_syntax && syntax_help.contains_insensitive(search_word))
     found_word = true;
 
   if (!found_word && search_options && GetOptions() != nullptr) {
@@ -330,7 +330,7 @@
         GetCommandInterpreter().GetDebugger().GetTerminalWidth());
     if (!usage_help.Empty()) {
       llvm::StringRef usage_text = usage_help.GetString();
-      if (usage_text.contains_lower(search_word))
+      if (usage_text.contains_insensitive(search_word))
         found_word = true;
     }
   }
diff --git a/lldb/source/Interpreter/OptionArgParser.cpp b/lldb/source/Interpreter/OptionArgParser.cpp
--- a/lldb/source/Interpreter/OptionArgParser.cpp
+++ b/lldb/source/Interpreter/OptionArgParser.cpp
@@ -20,11 +20,11 @@
   if (success_ptr)
     *success_ptr = true;
   ref = ref.trim();
-  if (ref.equals_lower("false") || ref.equals_lower("off") ||
-      ref.equals_lower("no") || ref.equals_lower("0")) {
+  if (ref.equals_insensitive("false") || ref.equals_insensitive("off") ||
+      ref.equals_insensitive("no") || ref.equals_insensitive("0")) {
     return false;
-  } else if (ref.equals_lower("true") || ref.equals_lower("on") ||
-             ref.equals_lower("yes") || ref.equals_lower("1")) {
+  } else if (ref.equals_insensitive("true") || ref.equals_insensitive("on") ||
+             ref.equals_insensitive("yes") || ref.equals_insensitive("1")) {
     return true;
   }
   if (success_ptr)
@@ -125,13 +125,13 @@
   if (success_ptr)
     *success_ptr = true;
 
-  if (s.equals_lower("python"))
+  if (s.equals_insensitive("python"))
     return eScriptLanguagePython;
-  if (s.equals_lower("lua"))
+  if (s.equals_insensitive("lua"))
     return eScriptLanguageLua;
-  if (s.equals_lower("default"))
+  if (s.equals_insensitive("default"))
     return eScriptLanguageDefault;
-  if (s.equals_lower("none"))
+  if (s.equals_insensitive("none"))
     return eScriptLanguageNone;
 
   if (success_ptr)
diff --git a/lldb/source/Interpreter/OptionValueProperties.cpp b/lldb/source/Interpreter/OptionValueProperties.cpp
--- a/lldb/source/Interpreter/OptionValueProperties.cpp
+++ b/lldb/source/Interpreter/OptionValueProperties.cpp
@@ -630,11 +630,11 @@
       } else {
         bool match = false;
         llvm::StringRef name = property->GetName();
-        if (name.contains_lower(keyword))
+        if (name.contains_insensitive(keyword))
           match = true;
         else {
           llvm::StringRef desc = property->GetDescription();
-          if (desc.contains_lower(keyword))
+          if (desc.contains_insensitive(keyword))
             match = true;
         }
         if (match) {
diff --git a/lldb/source/Interpreter/ScriptInterpreter.cpp b/lldb/source/Interpreter/ScriptInterpreter.cpp
--- a/lldb/source/Interpreter/ScriptInterpreter.cpp
+++ b/lldb/source/Interpreter/ScriptInterpreter.cpp
@@ -85,11 +85,11 @@
 
 lldb::ScriptLanguage
 ScriptInterpreter::StringToLanguage(const llvm::StringRef &language) {
-  if (language.equals_lower(LanguageToString(eScriptLanguageNone)))
+  if (language.equals_insensitive(LanguageToString(eScriptLanguageNone)))
     return eScriptLanguageNone;
-  if (language.equals_lower(LanguageToString(eScriptLanguagePython)))
+  if (language.equals_insensitive(LanguageToString(eScriptLanguagePython)))
     return eScriptLanguagePython;
-  if (language.equals_lower(LanguageToString(eScriptLanguageLua)))
+  if (language.equals_insensitive(LanguageToString(eScriptLanguageLua)))
     return eScriptLanguageLua;
   return eScriptLanguageUnknown;
 }
diff --git a/lldb/source/Plugins/Language/CPlusPlus/CPlusPlusLanguage.cpp b/lldb/source/Plugins/Language/CPlusPlus/CPlusPlusLanguage.cpp
--- a/lldb/source/Plugins/Language/CPlusPlus/CPlusPlusLanguage.cpp
+++ b/lldb/source/Plugins/Language/CPlusPlus/CPlusPlusLanguage.cpp
@@ -1152,7 +1152,7 @@
   const auto suffixes = {".cpp", ".cxx", ".c++", ".cc",  ".c",
                          ".h",   ".hh",  ".hpp", ".hxx", ".h++"};
   for (auto suffix : suffixes) {
-    if (file_path.endswith_lower(suffix))
+    if (file_path.endswith_insensitive(suffix))
       return true;
   }
 
diff --git a/lldb/source/Plugins/Language/ObjC/ObjCLanguage.cpp b/lldb/source/Plugins/Language/ObjC/ObjCLanguage.cpp
--- a/lldb/source/Plugins/Language/ObjC/ObjCLanguage.cpp
+++ b/lldb/source/Plugins/Language/ObjC/ObjCLanguage.cpp
@@ -1126,7 +1126,7 @@
 bool ObjCLanguage::IsSourceFile(llvm::StringRef file_path) const {
   const auto suffixes = {".h", ".m", ".M"};
   for (auto suffix : suffixes) {
-    if (file_path.endswith_lower(suffix))
+    if (file_path.endswith_insensitive(suffix))
       return true;
   }
   return false;
diff --git a/lldb/source/Plugins/Language/ObjCPlusPlus/ObjCPlusPlusLanguage.cpp b/lldb/source/Plugins/Language/ObjCPlusPlus/ObjCPlusPlusLanguage.cpp
--- a/lldb/source/Plugins/Language/ObjCPlusPlus/ObjCPlusPlusLanguage.cpp
+++ b/lldb/source/Plugins/Language/ObjCPlusPlus/ObjCPlusPlusLanguage.cpp
@@ -19,7 +19,7 @@
 bool ObjCPlusPlusLanguage::IsSourceFile(llvm::StringRef file_path) const {
   const auto suffixes = {".h", ".mm"};
   for (auto suffix : suffixes) {
-    if (file_path.endswith_lower(suffix))
+    if (file_path.endswith_insensitive(suffix))
       return true;
   }
   return false;
diff --git a/lldb/source/Plugins/Process/Windows/Common/ProcessWindows.cpp b/lldb/source/Plugins/Process/Windows/Common/ProcessWindows.cpp
--- a/lldb/source/Plugins/Process/Windows/Common/ProcessWindows.cpp
+++ b/lldb/source/Plugins/Process/Windows/Common/ProcessWindows.cpp
@@ -86,10 +86,10 @@
 
 static bool ShouldUseLLDBServer() {
   llvm::StringRef use_lldb_server = ::getenv("LLDB_USE_LLDB_SERVER");
-  return use_lldb_server.equals_lower("on") ||
-         use_lldb_server.equals_lower("yes") ||
-         use_lldb_server.equals_lower("1") ||
-         use_lldb_server.equals_lower("true");
+  return use_lldb_server.equals_insensitive("on") ||
+         use_lldb_server.equals_insensitive("yes") ||
+         use_lldb_server.equals_insensitive("1") ||
+         use_lldb_server.equals_insensitive("true");
 }
 
 void ProcessWindows::Initialize() {
diff --git a/lldb/source/Plugins/Process/minidump/ProcessMinidump.cpp b/lldb/source/Plugins/Process/minidump/ProcessMinidump.cpp
--- a/lldb/source/Plugins/Process/minidump/ProcessMinidump.cpp
+++ b/lldb/source/Plugins/Process/minidump/ProcessMinidump.cpp
@@ -548,7 +548,7 @@
 
     // check if the process is wow64 - a 32 bit windows process running on a
     // 64 bit windows
-    if (llvm::StringRef(name).endswith_lower("wow64.dll")) {
+    if (llvm::StringRef(name).endswith_insensitive("wow64.dll")) {
       m_is_wow64 = true;
     }
 
diff --git a/lldb/source/Plugins/SymbolFile/NativePDB/CompileUnitIndex.cpp b/lldb/source/Plugins/SymbolFile/NativePDB/CompileUnitIndex.cpp
--- a/lldb/source/Plugins/SymbolFile/NativePDB/CompileUnitIndex.cpp
+++ b/lldb/source/Plugins/SymbolFile/NativePDB/CompileUnitIndex.cpp
@@ -43,7 +43,7 @@
 
   llvm::SmallString<64> normalized(other);
   llvm::sys::path::native(normalized);
-  return main.equals_lower(normalized);
+  return main.equals_insensitive(normalized);
 }
 
 static void ParseCompile3(const CVSymbol &sym, CompilandIndexItem &cci) {
diff --git a/lldb/source/Plugins/SymbolFile/NativePDB/PdbFPOProgramToDWARFExpression.cpp b/lldb/source/Plugins/SymbolFile/NativePDB/PdbFPOProgramToDWARFExpression.cpp
--- a/lldb/source/Plugins/SymbolFile/NativePDB/PdbFPOProgramToDWARFExpression.cpp
+++ b/lldb/source/Plugins/SymbolFile/NativePDB/PdbFPOProgramToDWARFExpression.cpp
@@ -41,7 +41,7 @@
   auto it = llvm::find_if(
       register_names,
       [&reg_name](const llvm::EnumEntry<uint16_t> &register_entry) {
-        return reg_name.compare_lower(register_entry.Name) == 0;
+        return reg_name.compare_insensitive(register_entry.Name) == 0;
       });
 
   if (it == register_names.end())
diff --git a/lldb/source/Plugins/SymbolFile/PDB/SymbolFilePDB.cpp b/lldb/source/Plugins/SymbolFile/PDB/SymbolFilePDB.cpp
--- a/lldb/source/Plugins/SymbolFile/PDB/SymbolFilePDB.cpp
+++ b/lldb/source/Plugins/SymbolFile/PDB/SymbolFilePDB.cpp
@@ -84,8 +84,8 @@
 static bool ShouldUseNativeReader() {
 #if defined(_WIN32)
   llvm::StringRef use_native = ::getenv("LLDB_USE_NATIVE_PDB_READER");
-  return use_native.equals_lower("on") || use_native.equals_lower("yes") ||
-         use_native.equals_lower("1") || use_native.equals_lower("true");
+  return use_native.equals_insensitive("on") || use_native.equals_insensitive("yes") ||
+         use_native.equals_insensitive("1") || use_native.equals_insensitive("true");
 #else
   return true;
 #endif
diff --git a/lldb/source/Target/Language.cpp b/lldb/source/Target/Language.cpp
--- a/lldb/source/Target/Language.cpp
+++ b/lldb/source/Target/Language.cpp
@@ -196,7 +196,7 @@
 
 LanguageType Language::GetLanguageTypeFromString(llvm::StringRef string) {
   for (const auto &L : language_names) {
-    if (string.equals_lower(L.name))
+    if (string.equals_insensitive(L.name))
       return static_cast<LanguageType>(L.type);
   }
 
diff --git a/lldb/source/Target/RegisterContext.cpp b/lldb/source/Target/RegisterContext.cpp
--- a/lldb/source/Target/RegisterContext.cpp
+++ b/lldb/source/Target/RegisterContext.cpp
@@ -58,8 +58,8 @@
   for (uint32_t reg = start_idx; reg < num_registers; ++reg) {
     const RegisterInfo *reg_info = GetRegisterInfoAtIndex(reg);
 
-    if (reg_name.equals_lower(reg_info->name) ||
-        reg_name.equals_lower(reg_info->alt_name))
+    if (reg_name.equals_insensitive(reg_info->name) ||
+        reg_name.equals_insensitive(reg_info->alt_name))
       return reg_info;
   }
   return nullptr;
diff --git a/lldb/source/Utility/ArchSpec.cpp b/lldb/source/Utility/ArchSpec.cpp
--- a/lldb/source/Utility/ArchSpec.cpp
+++ b/lldb/source/Utility/ArchSpec.cpp
@@ -464,7 +464,7 @@
 // Get an architecture definition by name.
 static const CoreDefinition *FindCoreDefinition(llvm::StringRef name) {
   for (unsigned int i = 0; i < llvm::array_lengthof(g_core_definitions); ++i) {
-    if (name.equals_lower(g_core_definitions[i].name))
+    if (name.equals_insensitive(g_core_definitions[i].name))
       return &g_core_definitions[i];
   }
   return nullptr;
diff --git a/lldb/source/Utility/ConstString.cpp b/lldb/source/Utility/ConstString.cpp
--- a/lldb/source/Utility/ConstString.cpp
+++ b/lldb/source/Utility/ConstString.cpp
@@ -253,7 +253,7 @@
   // perform case insensitive equality test
   llvm::StringRef lhs_string_ref(lhs.GetStringRef());
   llvm::StringRef rhs_string_ref(rhs.GetStringRef());
-  return lhs_string_ref.equals_lower(rhs_string_ref);
+  return lhs_string_ref.equals_insensitive(rhs_string_ref);
 }
 
 int ConstString::Compare(ConstString lhs, ConstString rhs,
@@ -270,7 +270,7 @@
     if (case_sensitive) {
       return lhs_string_ref.compare(rhs_string_ref);
     } else {
-      return lhs_string_ref.compare_lower(rhs_string_ref);
+      return lhs_string_ref.compare_insensitive(rhs_string_ref);
     }
   }
 
diff --git a/lldb/source/Utility/FileSpec.cpp b/lldb/source/Utility/FileSpec.cpp
--- a/lldb/source/Utility/FileSpec.cpp
+++ b/lldb/source/Utility/FileSpec.cpp
@@ -500,7 +500,7 @@
                                              raw_ostream &Stream,
                                              StringRef Style) {
   assert(
-      (Style.empty() || Style.equals_lower("F") || Style.equals_lower("D")) &&
+      (Style.empty() || Style.equals_insensitive("F") || Style.equals_insensitive("D")) &&
       "Invalid FileSpec style!");
 
   StringRef dir = F.GetDirectory().GetStringRef();
@@ -511,7 +511,7 @@
     return;
   }
 
-  if (Style.equals_lower("F")) {
+  if (Style.equals_insensitive("F")) {
     Stream << (file.empty() ? "(empty)" : file);
     return;
   }
@@ -527,7 +527,7 @@
     Stream << GetPreferredPathSeparator(F.GetPathStyle());
   }
 
-  if (Style.equals_lower("D")) {
+  if (Style.equals_insensitive("D")) {
     // We only want to print the directory, so now just exit.
     if (dir.empty())
       Stream << "(empty)";
diff --git a/lldb/source/Utility/Log.cpp b/lldb/source/Utility/Log.cpp
--- a/lldb/source/Utility/Log.cpp
+++ b/lldb/source/Utility/Log.cpp
@@ -60,17 +60,17 @@
   bool list_categories = false;
   uint32_t flags = 0;
   for (const char *category : categories) {
-    if (llvm::StringRef("all").equals_lower(category)) {
+    if (llvm::StringRef("all").equals_insensitive(category)) {
       flags |= UINT32_MAX;
       continue;
     }
-    if (llvm::StringRef("default").equals_lower(category)) {
+    if (llvm::StringRef("default").equals_insensitive(category)) {
       flags |= entry.second.m_channel.default_flags;
       continue;
     }
     auto cat = llvm::find_if(
         entry.second.m_channel.categories,
-        [&](const Log::Category &c) { return c.name.equals_lower(category); });
+        [&](const Log::Category &c) { return c.name.equals_insensitive(category); });
     if (cat != entry.second.m_channel.categories.end()) {
       flags |= cat->flag;
       continue;
diff --git a/llvm/include/llvm/ADT/SmallString.h b/llvm/include/llvm/ADT/SmallString.h
--- a/llvm/include/llvm/ADT/SmallString.h
+++ b/llvm/include/llvm/ADT/SmallString.h
@@ -93,8 +93,8 @@
   }
 
   /// Check for string equality, ignoring case.
-  bool equals_lower(StringRef RHS) const {
-    return str().equals_lower(RHS);
+  bool equals_insensitive(StringRef RHS) const {
+    return str().equals_insensitive(RHS);
   }
 
   /// Compare two strings; the result is -1, 0, or 1 if this string is
@@ -103,9 +103,9 @@
     return str().compare(RHS);
   }
 
-  /// compare_lower - Compare two strings, ignoring case.
-  int compare_lower(StringRef RHS) const {
-    return str().compare_lower(RHS);
+  /// compare_insensitive - Compare two strings, ignoring case.
+  int compare_insensitive(StringRef RHS) const {
+    return str().compare_insensitive(RHS);
   }
 
   /// compare_numeric - Compare two strings, treating sequences of digits as
diff --git a/llvm/include/llvm/ADT/StringRef.h b/llvm/include/llvm/ADT/StringRef.h
--- a/llvm/include/llvm/ADT/StringRef.h
+++ b/llvm/include/llvm/ADT/StringRef.h
@@ -189,12 +189,15 @@
               compareMemory(Data, RHS.Data, RHS.Length) == 0);
     }
 
-    /// equals_lower - Check for string equality, ignoring case.
+    /// equals_insensitive - Check for string equality, ignoring case.
     LLVM_NODISCARD
-    bool equals_lower(StringRef RHS) const {
-      return Length == RHS.Length && compare_lower(RHS) == 0;
+    bool equals_insensitive(StringRef RHS) const {
+      return Length == RHS.Length && compare_insensitive(RHS) == 0;
     }
 
+    LLVM_NODISCARD
+    bool equals_lower(StringRef RHS) const { return equals_insensitive(RHS); }
+
     /// compare - Compare two strings; the result is -1, 0, or 1 if this string
     /// is lexicographically less than, equal to, or greater than the \p RHS.
     LLVM_NODISCARD
@@ -209,9 +212,12 @@
       return Length < RHS.Length ? -1 : 1;
     }
 
-    /// compare_lower - Compare two strings, ignoring case.
+    /// compare_insensitive - Compare two strings, ignoring case.
     LLVM_NODISCARD
-    int compare_lower(StringRef RHS) const;
+    int compare_insensitive(StringRef RHS) const;
+
+    LLVM_NODISCARD
+    int compare_lower(StringRef RHS) const { return compare_insensitive(RHS); }
 
     /// compare_numeric - Compare two strings, treating sequences of digits as
     /// numbers.
@@ -290,7 +296,12 @@
 
     /// Check if this string starts with the given \p Prefix, ignoring case.
     LLVM_NODISCARD
-    bool startswith_lower(StringRef Prefix) const;
+    bool startswith_insensitive(StringRef Prefix) const;
+
+    LLVM_NODISCARD
+    bool startswith_lower(StringRef Prefix) const {
+      return startswith_insensitive(Prefix);
+    }
 
     /// Check if this string ends with the given \p Suffix.
     LLVM_NODISCARD
@@ -301,7 +312,12 @@
 
     /// Check if this string ends with the given \p Suffix, ignoring case.
     LLVM_NODISCARD
-    bool endswith_lower(StringRef Suffix) const;
+    bool endswith_insensitive(StringRef Suffix) const;
+
+    LLVM_NODISCARD
+    bool endswith_lower(StringRef Prefix) const {
+      return endswith_insensitive(Prefix);
+    }
 
     /// @}
     /// @name String Searching
@@ -327,7 +343,12 @@
     /// \returns The index of the first occurrence of \p C, or npos if not
     /// found.
     LLVM_NODISCARD
-    size_t find_lower(char C, size_t From = 0) const;
+    size_t find_insensitive(char C, size_t From = 0) const;
+
+    LLVM_NODISCARD
+    size_t find_lower(char C, size_t From = 0) const {
+      return find_insensitive(C, From);
+    }
 
     /// Search for the first character satisfying the predicate \p F
     ///
@@ -365,7 +386,12 @@
     /// \returns The index of the first occurrence of \p Str, or npos if not
     /// found.
     LLVM_NODISCARD
-    size_t find_lower(StringRef Str, size_t From = 0) const;
+    size_t find_insensitive(StringRef Str, size_t From = 0) const;
+
+    LLVM_NODISCARD
+    size_t find_lower(StringRef Str, size_t From = 0) const {
+      return find_insensitive(Str, From);
+    }
 
     /// Search for the last character \p C in the string.
     ///
@@ -388,7 +414,12 @@
     /// \returns The index of the last occurrence of \p C, or npos if not
     /// found.
     LLVM_NODISCARD
-    size_t rfind_lower(char C, size_t From = npos) const;
+    size_t rfind_insensitive(char C, size_t From = npos) const;
+
+    LLVM_NODISCARD
+    size_t rfind_lower(char C, size_t From = npos) const {
+      return rfind_insensitive(C, From);
+    }
 
     /// Search for the last string \p Str in the string.
     ///
@@ -402,7 +433,10 @@
     /// \returns The index of the last occurrence of \p Str, or npos if not
     /// found.
     LLVM_NODISCARD
-    size_t rfind_lower(StringRef Str) const;
+    size_t rfind_insensitive(StringRef Str) const;
+
+    LLVM_NODISCARD
+    size_t rfind_lower(StringRef Str) const { return rfind_insensitive(Str); }
 
     /// Find the first character in the string that is \p C, or npos if not
     /// found. Same as find.
@@ -468,15 +502,25 @@
 
     /// Return true if the given string is a substring of *this, and false
     /// otherwise.
+    LLVM_NODISCARD
+    bool contains_insensitive(StringRef Other) const {
+      return find_insensitive(Other) != npos;
+    }
+
     LLVM_NODISCARD
     bool contains_lower(StringRef Other) const {
-      return find_lower(Other) != npos;
+      return contains_insensitive(Other);
     }
 
     /// Return true if the given character is contained in *this, and false
     /// otherwise.
     LLVM_NODISCARD
-    bool contains_lower(char C) const { return find_lower(C) != npos; }
+    bool contains_insensitive(char C) const {
+      return find_insensitive(C) != npos;
+    }
+
+    LLVM_NODISCARD
+    bool contains_lower(char C) const { return contains_insensitive(C); }
 
     /// @}
     /// @name Helpful Algorithms
@@ -687,14 +731,18 @@
 
     /// Returns true if this StringRef has the given prefix, ignoring case,
     /// and removes that prefix.
-    bool consume_front_lower(StringRef Prefix) {
-      if (!startswith_lower(Prefix))
+    bool consume_front_insensitive(StringRef Prefix) {
+      if (!startswith_insensitive(Prefix))
         return false;
 
       *this = drop_front(Prefix.size());
       return true;
     }
 
+    bool consume_front_lower(StringRef Prefix) {
+      return consume_front_insensitive(Prefix);
+    }
+
     /// Returns true if this StringRef has the given suffix and removes that
     /// suffix.
     bool consume_back(StringRef Suffix) {
@@ -707,14 +755,18 @@
 
     /// Returns true if this StringRef has the given suffix, ignoring case,
     /// and removes that suffix.
-    bool consume_back_lower(StringRef Suffix) {
-      if (!endswith_lower(Suffix))
+    bool consume_back_insensitive(StringRef Suffix) {
+      if (!endswith_insensitive(Suffix))
         return false;
 
       *this = drop_back(Suffix.size());
       return true;
     }
 
+    bool consume_back_lower(StringRef Suffix) {
+      return consume_back_insensitive(Suffix);
+    }
+
     /// Return a reference to the substring from [Start, End).
     ///
     /// \param Start The index of the starting character in the substring; if
diff --git a/llvm/include/llvm/ADT/StringSwitch.h b/llvm/include/llvm/ADT/StringSwitch.h
--- a/llvm/include/llvm/ADT/StringSwitch.h
+++ b/llvm/include/llvm/ADT/StringSwitch.h
@@ -138,21 +138,21 @@
 
   // Case-insensitive case matchers.
   StringSwitch &CaseLower(StringLiteral S, T Value) {
-    if (!Result && Str.equals_lower(S))
+    if (!Result && Str.equals_insensitive(S))
       Result = std::move(Value);
 
     return *this;
   }
 
   StringSwitch &EndsWithLower(StringLiteral S, T Value) {
-    if (!Result && Str.endswith_lower(S))
+    if (!Result && Str.endswith_insensitive(S))
       Result = Value;
 
     return *this;
   }
 
   StringSwitch &StartsWithLower(StringLiteral S, T Value) {
-    if (!Result && Str.startswith_lower(S))
+    if (!Result && Str.startswith_insensitive(S))
       Result = std::move(Value);
 
     return *this;
diff --git a/llvm/include/llvm/Support/FormatProviders.h b/llvm/include/llvm/Support/FormatProviders.h
--- a/llvm/include/llvm/Support/FormatProviders.h
+++ b/llvm/include/llvm/Support/FormatProviders.h
@@ -75,7 +75,7 @@
   }
 
   static bool consumeHexStyle(StringRef &Str, HexPrintStyle &Style) {
-    if (!Str.startswith_lower("x"))
+    if (!Str.startswith_insensitive("x"))
       return false;
 
     if (Str.consume_front("x-"))
diff --git a/llvm/include/llvm/Support/VirtualFileSystem.h b/llvm/include/llvm/Support/VirtualFileSystem.h
--- a/llvm/include/llvm/Support/VirtualFileSystem.h
+++ b/llvm/include/llvm/Support/VirtualFileSystem.h
@@ -752,7 +752,7 @@
   // that, other than the root, path components should not contain slashes or
   // backslashes.
   bool pathComponentMatches(llvm::StringRef lhs, llvm::StringRef rhs) const {
-    if ((CaseSensitive ? lhs.equals(rhs) : lhs.equals_lower(rhs)))
+    if ((CaseSensitive ? lhs.equals(rhs) : lhs.equals_insensitive(rhs)))
       return true;
     return (lhs == "/" && rhs == "\\") || (lhs == "\\" && rhs == "/");
   }
diff --git a/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp b/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
--- a/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
@@ -4590,7 +4590,7 @@
       continue;
 
     for (const MCPhysReg &PR : *RC) {
-      if (RegName.equals_lower(RI->getRegAsmName(PR))) {
+      if (RegName.equals_insensitive(RI->getRegAsmName(PR))) {
         std::pair<unsigned, const TargetRegisterClass *> S =
             std::make_pair(PR, RC);
 
diff --git a/llvm/lib/DebugInfo/PDB/Native/GSIStreamBuilder.cpp b/llvm/lib/DebugInfo/PDB/Native/GSIStreamBuilder.cpp
--- a/llvm/lib/DebugInfo/PDB/Native/GSIStreamBuilder.cpp
+++ b/llvm/lib/DebugInfo/PDB/Native/GSIStreamBuilder.cpp
@@ -163,7 +163,7 @@
     return memcmp(S1.data(), S2.data(), LS);
 
   // Both strings are ascii, perform a case-insensitive comparison.
-  return S1.compare_lower(S2.data());
+  return S1.compare_insensitive(S2.data());
 }
 
 void GSIStreamBuilder::finalizePublicBuckets() {
diff --git a/llvm/lib/FileCheck/FileCheck.cpp b/llvm/lib/FileCheck/FileCheck.cpp
--- a/llvm/lib/FileCheck/FileCheck.cpp
+++ b/llvm/lib/FileCheck/FileCheck.cpp
@@ -1229,7 +1229,7 @@
   // If this is a fixed string pattern, just match it now.
   if (!FixedStr.empty()) {
     size_t Pos =
-        IgnoreCase ? Buffer.find_lower(FixedStr) : Buffer.find(FixedStr);
+        IgnoreCase ? Buffer.find_insensitive(FixedStr) : Buffer.find(FixedStr);
     if (Pos == StringRef::npos)
       return make_error<NotFoundError>();
     return MatchResult(Pos, /*MatchLen=*/FixedStr.size(), Error::success());
diff --git a/llvm/lib/MC/MCParser/AsmParser.cpp b/llvm/lib/MC/MCParser/AsmParser.cpp
--- a/llvm/lib/MC/MCParser/AsmParser.cpp
+++ b/llvm/lib/MC/MCParser/AsmParser.cpp
@@ -3238,9 +3238,9 @@
   APFloat Value(Semantics);
   StringRef IDVal = getTok().getString();
   if (getLexer().is(AsmToken::Identifier)) {
-    if (!IDVal.compare_lower("infinity") || !IDVal.compare_lower("inf"))
+    if (!IDVal.compare_insensitive("infinity") || !IDVal.compare_insensitive("inf"))
       Value = APFloat::getInf(Semantics);
-    else if (!IDVal.compare_lower("nan"))
+    else if (!IDVal.compare_insensitive("nan"))
       Value = APFloat::getNaN(Semantics, false, ~0);
     else
       return TokError("invalid floating point literal");
diff --git a/llvm/lib/MC/MCParser/COFFMasmParser.cpp b/llvm/lib/MC/MCParser/COFFMasmParser.cpp
--- a/llvm/lib/MC/MCParser/COFFMasmParser.cpp
+++ b/llvm/lib/MC/MCParser/COFFMasmParser.cpp
@@ -322,11 +322,11 @@
   if (getLexer().is(AsmToken::Identifier)) {
     StringRef nextVal = getTok().getString();
     SMLoc nextLoc = getTok().getLoc();
-    if (nextVal.equals_lower("far")) {
+    if (nextVal.equals_insensitive("far")) {
       // TODO(epastor): Handle far procedure definitions.
       Lex();
       return Error(nextLoc, "far procedure definitions not yet supported");
-    } else if (nextVal.equals_lower("near")) {
+    } else if (nextVal.equals_insensitive("near")) {
       Lex();
       nextVal = getTok().getString();
       nextLoc = getTok().getLoc();
@@ -340,7 +340,7 @@
 
   bool Framed = false;
   if (getLexer().is(AsmToken::Identifier) &&
-      getTok().getString().equals_lower("frame")) {
+      getTok().getString().equals_insensitive("frame")) {
     Lex();
     Framed = true;
     getStreamer().EmitWinCFIStartProc(Sym, Loc);
diff --git a/llvm/lib/MC/MCParser/MasmParser.cpp b/llvm/lib/MC/MCParser/MasmParser.cpp
--- a/llvm/lib/MC/MCParser/MasmParser.cpp
+++ b/llvm/lib/MC/MCParser/MasmParser.cpp
@@ -1133,8 +1133,8 @@
       MutableArrayRef<AsmToken> Buf(NextTok);
       size_t ReadCount = Lexer.peekTokens(Buf);
       if (ReadCount && NextTok.is(AsmToken::Identifier) &&
-          (NextTok.getString().equals_lower("equ") ||
-           NextTok.getString().equals_lower("textequ"))) {
+          (NextTok.getString().equals_insensitive("equ") ||
+           NextTok.getString().equals_insensitive("textequ"))) {
         // This looks like an EQU or TEXTEQU directive; don't expand the
         // identifier, allowing for redefinitions.
         break;
@@ -1515,7 +1515,7 @@
       }
     }
     // Parse named bitwise negation.
-    if (Identifier.equals_lower("not")) {
+    if (Identifier.equals_insensitive("not")) {
       if (parsePrimaryExpr(Res, EndLoc, nullptr))
         return true;
       Res = MCUnaryExpr::createNot(Res, getContext(), FirstTokenLoc);
@@ -2082,7 +2082,7 @@
     if (!IDVal.startswith("."))
       return Error(IDLoc, "unexpected token at start of statement");
   } else if (Lexer.is(AsmToken::Identifier) &&
-             getTok().getString().equals_lower("echo")) {
+             getTok().getString().equals_insensitive("echo")) {
     // Intercept echo early to avoid lexical substitution in its message, and
     // delegate all handling to the appropriate function.
     return parseDirectiveEcho();
@@ -2260,7 +2260,7 @@
 
     // Special-case handling of structure-end directives at higher priority,
     // since ENDS is overloaded as a segment-end directive.
-    if (IDVal.equals_lower("ends") && StructInProgress.size() > 1 &&
+    if (IDVal.equals_insensitive("ends") && StructInProgress.size() > 1 &&
         getTok().is(AsmToken::EndOfStatement)) {
       return parseDirectiveNestedEnds();
     }
@@ -2496,7 +2496,7 @@
 
   // Special-case handling of structure-end directives at higher priority, since
   // ENDS is overloaded as a segment-end directive.
-  if (nextVal.equals_lower("ends") && StructInProgress.size() == 1) {
+  if (nextVal.equals_insensitive("ends") && StructInProgress.size() == 1) {
     Lex();
     return parseDirectiveEnds(IDVal, IDLoc);
   }
@@ -2527,7 +2527,7 @@
     return parseDirectiveEquate(nextVal, IDVal, DirKind, IDLoc);
   case DK_BYTE:
     if (afterNextTok.is(AsmToken::Identifier) &&
-        afterNextTok.getString().equals_lower("ptr")) {
+        afterNextTok.getString().equals_insensitive("ptr")) {
       // Size directive; part of an instruction.
       break;
     }
@@ -2538,7 +2538,7 @@
     return parseDirectiveNamedValue(nextVal, 1, IDVal, IDLoc);
   case DK_WORD:
     if (afterNextTok.is(AsmToken::Identifier) &&
-        afterNextTok.getString().equals_lower("ptr")) {
+        afterNextTok.getString().equals_insensitive("ptr")) {
       // Size directive; part of an instruction.
       break;
     }
@@ -2549,7 +2549,7 @@
     return parseDirectiveNamedValue(nextVal, 2, IDVal, IDLoc);
   case DK_DWORD:
     if (afterNextTok.is(AsmToken::Identifier) &&
-        afterNextTok.getString().equals_lower("ptr")) {
+        afterNextTok.getString().equals_insensitive("ptr")) {
       // Size directive; part of an instruction.
       break;
     }
@@ -2560,7 +2560,7 @@
     return parseDirectiveNamedValue(nextVal, 4, IDVal, IDLoc);
   case DK_FWORD:
     if (afterNextTok.is(AsmToken::Identifier) &&
-        afterNextTok.getString().equals_lower("ptr")) {
+        afterNextTok.getString().equals_insensitive("ptr")) {
       // Size directive; part of an instruction.
       break;
     }
@@ -2570,7 +2570,7 @@
     return parseDirectiveNamedValue(nextVal, 6, IDVal, IDLoc);
   case DK_QWORD:
     if (afterNextTok.is(AsmToken::Identifier) &&
-        afterNextTok.getString().equals_lower("ptr")) {
+        afterNextTok.getString().equals_insensitive("ptr")) {
       // Size directive; part of an instruction.
       break;
     }
@@ -3594,7 +3594,7 @@
     if (parseExpression(Value))
       return true;
     if (getTok().is(AsmToken::Identifier) &&
-        getTok().getString().equals_lower("dup")) {
+        getTok().getString().equals_insensitive("dup")) {
       Lex(); // Eat 'dup'.
       const MCConstantExpr *MCE = dyn_cast<MCConstantExpr>(Value);
       if (!MCE)
@@ -3752,11 +3752,11 @@
   APFloat Value(Semantics);
   StringRef IDVal = getTok().getString();
   if (getLexer().is(AsmToken::Identifier)) {
-    if (IDVal.equals_lower("infinity") || IDVal.equals_lower("inf"))
+    if (IDVal.equals_insensitive("infinity") || IDVal.equals_insensitive("inf"))
       Value = APFloat::getInf(Semantics);
-    else if (IDVal.equals_lower("nan"))
+    else if (IDVal.equals_insensitive("nan"))
       Value = APFloat::getNaN(Semantics, false, ~0);
-    else if (IDVal.equals_lower("?"))
+    else if (IDVal.equals_insensitive("?"))
       Value = APFloat::getZero(Semantics);
     else
       return TokError("invalid floating point literal");
@@ -3798,7 +3798,7 @@
           getTok().isNot(AsmToken::GreaterGreater))) {
     const AsmToken NextTok = peekTok();
     if (NextTok.is(AsmToken::Identifier) &&
-        NextTok.getString().equals_lower("dup")) {
+        NextTok.getString().equals_insensitive("dup")) {
       const MCExpr *Value;
       if (parseExpression(Value) || parseToken(AsmToken::Identifier))
         return true;
@@ -4162,7 +4162,7 @@
           getTok().isNot(AsmToken::GreaterGreater))) {
     const AsmToken NextTok = peekTok();
     if (NextTok.is(AsmToken::Identifier) &&
-        NextTok.getString().equals_lower("dup")) {
+        NextTok.getString().equals_insensitive("dup")) {
       const MCExpr *Value;
       if (parseExpression(Value) || parseToken(AsmToken::Identifier))
         return true;
@@ -4445,7 +4445,7 @@
     QualifierLoc = getTok().getLoc();
     if (parseIdentifier(Qualifier))
       return addErrorSuffix(" in '" + Twine(Directive) + "' directive");
-    if (!Qualifier.equals_lower("nonunique"))
+    if (!Qualifier.equals_insensitive("nonunique"))
       return Error(QualifierLoc, "Unrecognized qualifier for '" +
                                      Twine(Directive) +
                                      "' directive; expected none or NONUNIQUE");
@@ -4489,7 +4489,7 @@
     return Error(NameLoc, "ENDS directive without matching STRUC/STRUCT/UNION");
   if (StructInProgress.size() > 1)
     return Error(NameLoc, "unexpected name in nested ENDS directive");
-  if (StructInProgress.back().Name.compare_lower(Name))
+  if (StructInProgress.back().Name.compare_insensitive(Name))
     return Error(NameLoc, "mismatched name in ENDS directive; expected '" +
                               StructInProgress.back().Name + "'");
   StructInfo Structure = StructInProgress.pop_back_val();
@@ -5635,7 +5635,7 @@
 
     // Emit an error if two (or more) named parameters share the same name.
     for (const MCAsmMacroParameter& CurrParam : Parameters)
-      if (CurrParam.Name.equals_lower(Parameter.Name))
+      if (CurrParam.Name.equals_insensitive(Parameter.Name))
         return TokError("macro '" + Name + "' has multiple parameters"
                         " named '" + Parameter.Name + "'");
 
@@ -5660,9 +5660,9 @@
                                     Parameter.Name + "' in macro '" + Name +
                                     "'");
 
-        if (Qualifier.equals_lower("req"))
+        if (Qualifier.equals_insensitive("req"))
           Parameter.Required = true;
-        else if (Qualifier.equals_lower("vararg"))
+        else if (Qualifier.equals_insensitive("vararg"))
           Parameter.Vararg = true;
         else
           return Error(QualLoc,
@@ -5682,7 +5682,7 @@
 
   std::vector<std::string> Locals;
   if (getTok().is(AsmToken::Identifier) &&
-      getTok().getIdentifier().equals_lower("local")) {
+      getTok().getIdentifier().equals_insensitive("local")) {
     Lex(); // Eat the LOCAL directive.
 
     StringRef ID;
@@ -5716,7 +5716,7 @@
     // Otherwise, check whether we have reached the 'endm'... and determine if
     // this is a macro function.
     if (getLexer().is(AsmToken::Identifier)) {
-      if (getTok().getIdentifier().equals_lower("endm")) {
+      if (getTok().getIdentifier().equals_insensitive("endm")) {
         if (MacroDepth == 0) { // Outermost macro.
           EndToken = getTok();
           Lexer.Lex();
@@ -5728,7 +5728,7 @@
           // Otherwise we just found the end of an inner macro.
           --MacroDepth;
         }
-      } else if (getTok().getIdentifier().equals_lower("exitm")) {
+      } else if (getTok().getIdentifier().equals_insensitive("exitm")) {
         if (MacroDepth == 0 && peekTok().isNot(AsmToken::EndOfStatement)) {
           IsMacroFunction = true;
         }
@@ -6053,7 +6053,7 @@
   TheCondState.TheCond = AsmCond::IfCond;
   if (CaseInsensitive)
     TheCondState.CondMet =
-        ExpectEqual == (StringRef(String1).equals_lower(String2));
+        ExpectEqual == (StringRef(String1).equals_insensitive(String2));
   else
     TheCondState.CondMet = ExpectEqual == (String1 == String2);
   TheCondState.Ignore = !TheCondState.CondMet;
@@ -6263,7 +6263,7 @@
 
     if (CaseInsensitive)
       TheCondState.CondMet =
-          ExpectEqual == (StringRef(String1).equals_lower(String2));
+          ExpectEqual == (StringRef(String1).equals_insensitive(String2));
     else
       TheCondState.CondMet = ExpectEqual == (String1 == String2);
     TheCondState.Ignore = !TheCondState.CondMet;
@@ -6443,13 +6443,13 @@
 
   if (CaseInsensitive)
     TheCondState.CondMet =
-        ExpectEqual == (StringRef(String1).equals_lower(String2));
+        ExpectEqual == (StringRef(String1).equals_insensitive(String2));
   else
     TheCondState.CondMet = ExpectEqual == (String1 == String2);
   TheCondState.Ignore = !TheCondState.CondMet;
 
   if ((CaseInsensitive &&
-       ExpectEqual == StringRef(String1).equals_lower(String2)) ||
+       ExpectEqual == StringRef(String1).equals_insensitive(String2)) ||
       (ExpectEqual == (String1 == String2)))
     return Error(DirectiveLoc, Message);
   return false;
@@ -6634,7 +6634,7 @@
       return true;
   }
   if (peekTok().is(AsmToken::Identifier) &&
-      peekTok().getIdentifier().equals_lower("macro"))
+      peekTok().getIdentifier().equals_insensitive("macro"))
     return true;
 
   return false;
@@ -6656,7 +6656,7 @@
 
     // Otherwise, check whether we have reached the endm.
     if (Lexer.is(AsmToken::Identifier) &&
-        getTok().getIdentifier().equals_lower("endm")) {
+        getTok().getIdentifier().equals_insensitive("endm")) {
       if (NestLevel == 0) {
         EndToken = getTok();
         Lex();
@@ -6846,7 +6846,7 @@
                                   Parameter.Name + "' in '" + Dir +
                                   "' directive");
 
-      if (Qualifier.equals_lower("req"))
+      if (Qualifier.equals_insensitive("req"))
         Parameter.Required = true;
       else
         return Error(QualLoc,
@@ -7010,7 +7010,7 @@
   // substitutions in the message. Assert that the next token is the directive,
   // then eat it without using the Parser's Lex method.
   assert(getTok().is(AsmToken::Identifier) &&
-         getTok().getString().equals_lower("echo"));
+         getTok().getString().equals_insensitive("echo"));
   Lexer.Lex();
 
   std::string Message = parseStringTo(AsmToken::EndOfStatement);
diff --git a/llvm/lib/Option/OptTable.cpp b/llvm/lib/Option/OptTable.cpp
--- a/llvm/lib/Option/OptTable.cpp
+++ b/llvm/lib/Option/OptTable.cpp
@@ -185,7 +185,7 @@
     if (Str.startswith(Prefix)) {
       StringRef Rest = Str.substr(Prefix.size());
       bool Matched = IgnoreCase
-          ? Rest.startswith_lower(I->Name)
+          ? Rest.startswith_insensitive(I->Name)
           : Rest.startswith(I->Name);
       if (Matched)
         return Prefix.size() + StringRef(I->Name).size();
diff --git a/llvm/lib/ProfileData/InstrProfReader.cpp b/llvm/lib/ProfileData/InstrProfReader.cpp
--- a/llvm/lib/ProfileData/InstrProfReader.cpp
+++ b/llvm/lib/ProfileData/InstrProfReader.cpp
@@ -159,16 +159,16 @@
 
   while (Line->startswith(":")) {
     StringRef Str = Line->substr(1);
-    if (Str.equals_lower("ir"))
+    if (Str.equals_insensitive("ir"))
       IsIRInstr = true;
-    else if (Str.equals_lower("fe"))
+    else if (Str.equals_insensitive("fe"))
       IsIRInstr = false;
-    else if (Str.equals_lower("csir")) {
+    else if (Str.equals_insensitive("csir")) {
       IsIRInstr = true;
       IsCS = true;
-    } else if (Str.equals_lower("entry_first"))
+    } else if (Str.equals_insensitive("entry_first"))
       IsEntryFirst = true;
-    else if (Str.equals_lower("not_entry_first"))
+    else if (Str.equals_insensitive("not_entry_first"))
       IsEntryFirst = false;
     else
       return error(instrprof_error::bad_header);
diff --git a/llvm/lib/Support/StringExtras.cpp b/llvm/lib/Support/StringExtras.cpp
--- a/llvm/lib/Support/StringExtras.cpp
+++ b/llvm/lib/Support/StringExtras.cpp
@@ -25,7 +25,7 @@
   if (N > M)
     return StringRef::npos;
   for (size_t i = 0, e = M - N + 1; i != e; ++i)
-    if (s1.substr(i, N).equals_lower(s2))
+    if (s1.substr(i, N).equals_insensitive(s2))
       return i;
   return StringRef::npos;
 }
diff --git a/llvm/lib/Support/StringRef.cpp b/llvm/lib/Support/StringRef.cpp
--- a/llvm/lib/Support/StringRef.cpp
+++ b/llvm/lib/Support/StringRef.cpp
@@ -34,8 +34,8 @@
   return 0;
 }
 
-/// compare_lower - Compare strings, ignoring case.
-int StringRef::compare_lower(StringRef RHS) const {
+/// compare_insensitive - Compare strings, ignoring case.
+int StringRef::compare_insensitive(StringRef RHS) const {
   if (int Res = ascii_strncasecmp(Data, RHS.Data, std::min(Length, RHS.Length)))
     return Res;
   if (Length == RHS.Length)
@@ -44,18 +44,18 @@
 }
 
 /// Check if this string starts with the given \p Prefix, ignoring case.
-bool StringRef::startswith_lower(StringRef Prefix) const {
+bool StringRef::startswith_insensitive(StringRef Prefix) const {
   return Length >= Prefix.Length &&
       ascii_strncasecmp(Data, Prefix.Data, Prefix.Length) == 0;
 }
 
 /// Check if this string ends with the given \p Suffix, ignoring case.
-bool StringRef::endswith_lower(StringRef Suffix) const {
+bool StringRef::endswith_insensitive(StringRef Suffix) const {
   return Length >= Suffix.Length &&
       ascii_strncasecmp(end() - Suffix.Length, Suffix.Data, Suffix.Length) == 0;
 }
 
-size_t StringRef::find_lower(char C, size_t From) const {
+size_t StringRef::find_insensitive(char C, size_t From) const {
   char L = toLower(C);
   return find_if([L](char D) { return toLower(D) == L; }, From);
 }
@@ -173,10 +173,10 @@
   return npos;
 }
 
-size_t StringRef::find_lower(StringRef Str, size_t From) const {
+size_t StringRef::find_insensitive(StringRef Str, size_t From) const {
   StringRef This = substr(From);
   while (This.size() >= Str.size()) {
-    if (This.startswith_lower(Str))
+    if (This.startswith_insensitive(Str))
       return From;
     This = This.drop_front();
     ++From;
@@ -184,7 +184,7 @@
   return npos;
 }
 
-size_t StringRef::rfind_lower(char C, size_t From) const {
+size_t StringRef::rfind_insensitive(char C, size_t From) const {
   From = std::min(From, Length);
   size_t i = From;
   while (i != 0) {
@@ -211,13 +211,13 @@
   return npos;
 }
 
-size_t StringRef::rfind_lower(StringRef Str) const {
+size_t StringRef::rfind_insensitive(StringRef Str) const {
   size_t N = Str.size();
   if (N > Length)
     return npos;
   for (size_t i = Length - N + 1, e = 0; i != e;) {
     --i;
-    if (substr(i, N).equals_lower(Str))
+    if (substr(i, N).equals_insensitive(Str))
       return i;
   }
   return npos;
diff --git a/llvm/lib/Support/VirtualFileSystem.cpp b/llvm/lib/Support/VirtualFileSystem.cpp
--- a/llvm/lib/Support/VirtualFileSystem.cpp
+++ b/llvm/lib/Support/VirtualFileSystem.cpp
@@ -1318,12 +1318,12 @@
     if (!parseScalarString(N, Value, Storage))
       return false;
 
-    if (Value.equals_lower("true") || Value.equals_lower("on") ||
-        Value.equals_lower("yes") || Value == "1") {
+    if (Value.equals_insensitive("true") || Value.equals_insensitive("on") ||
+        Value.equals_insensitive("yes") || Value == "1") {
       Result = true;
       return true;
-    } else if (Value.equals_lower("false") || Value.equals_lower("off") ||
-               Value.equals_lower("no") || Value == "0") {
+    } else if (Value.equals_insensitive("false") || Value.equals_insensitive("off") ||
+               Value.equals_insensitive("no") || Value == "0") {
       Result = false;
       return true;
     }
diff --git a/llvm/lib/Support/Windows/Path.inc b/llvm/lib/Support/Windows/Path.inc
--- a/llvm/lib/Support/Windows/Path.inc
+++ b/llvm/lib/Support/Windows/Path.inc
@@ -669,7 +669,7 @@
 
   // Then compare against the list of ancient reserved names.
   for (size_t i = 0; i < array_lengthof(sReservedNames); ++i) {
-    if (path.equals_lower(sReservedNames[i]))
+    if (path.equals_insensitive(sReservedNames[i]))
       return true;
   }
 
diff --git a/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp b/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
--- a/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
+++ b/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
@@ -8038,7 +8038,7 @@
                         : std::make_pair(0U, &AArch64::PPRRegClass);
     }
   }
-  if (StringRef("{cc}").equals_lower(Constraint))
+  if (StringRef("{cc}").equals_insensitive(Constraint))
     return std::make_pair(unsigned(AArch64::NZCV), &AArch64::CCRRegClass);
 
   // Use the default implementation in TargetLowering to convert the register
diff --git a/llvm/lib/Target/AArch64/AArch64MachineFunctionInfo.cpp b/llvm/lib/Target/AArch64/AArch64MachineFunctionInfo.cpp
--- a/llvm/lib/Target/AArch64/AArch64MachineFunctionInfo.cpp
+++ b/llvm/lib/Target/AArch64/AArch64MachineFunctionInfo.cpp
@@ -73,8 +73,8 @@
 
   const StringRef Key =
       F.getFnAttribute("sign-return-address-key").getValueAsString();
-  assert(Key.equals_lower("a_key") || Key.equals_lower("b_key"));
-  return Key.equals_lower("b_key");
+  assert(Key.equals_insensitive("a_key") || Key.equals_insensitive("b_key"));
+  return Key.equals_insensitive("b_key");
 }
 
 AArch64FunctionInfo::AArch64FunctionInfo(MachineFunction &MF) : MF(MF) {
@@ -95,8 +95,8 @@
   }
 
   const StringRef BTIEnable = F.getFnAttribute("branch-target-enforcement").getValueAsString();
-  assert(BTIEnable.equals_lower("true") || BTIEnable.equals_lower("false"));
-  BranchTargetEnforcement = BTIEnable.equals_lower("true");
+  assert(BTIEnable.equals_insensitive("true") || BTIEnable.equals_insensitive("false"));
+  BranchTargetEnforcement = BTIEnable.equals_insensitive("true");
 }
 
 bool AArch64FunctionInfo::shouldSignReturnAddress(bool SpillsLR) const {
diff --git a/llvm/lib/Target/AArch64/AsmParser/AArch64AsmParser.cpp b/llvm/lib/Target/AArch64/AsmParser/AArch64AsmParser.cpp
--- a/llvm/lib/Target/AArch64/AsmParser/AArch64AsmParser.cpp
+++ b/llvm/lib/Target/AArch64/AsmParser/AArch64AsmParser.cpp
@@ -2707,7 +2707,7 @@
 
   // The optional operand must be "lsl #N" where N is non-negative.
   if (!Parser.getTok().is(AsmToken::Identifier) ||
-      !Parser.getTok().getIdentifier().equals_lower("lsl")) {
+      !Parser.getTok().getIdentifier().equals_insensitive("lsl")) {
     Error(Parser.getTok().getLoc(), "only 'lsl #+N' valid after immediate");
     return MatchOperand_ParseFail;
   }
@@ -3669,9 +3669,9 @@
   // Some SVE instructions have a decoration after the immediate, i.e.
   // "mul vl". We parse them here and add tokens, which must be present in the
   // asm string in the tablegen instruction.
-  bool NextIsVL = Parser.getLexer().peekTok().getString().equals_lower("vl");
+  bool NextIsVL = Parser.getLexer().peekTok().getString().equals_insensitive("vl");
   bool NextIsHash = Parser.getLexer().peekTok().is(AsmToken::Hash);
-  if (!Parser.getTok().getString().equals_lower("mul") ||
+  if (!Parser.getTok().getString().equals_insensitive("mul") ||
       !(NextIsVL || NextIsHash))
     return true;
 
@@ -5442,7 +5442,7 @@
   for (auto Name : RequestedExtensions) {
     bool EnableFeature = true;
 
-    if (Name.startswith_lower("no")) {
+    if (Name.startswith_insensitive("no")) {
       EnableFeature = false;
       Name = Name.substr(2);
     }
@@ -5478,7 +5478,7 @@
     return true;
 
   bool EnableFeature = true;
-  if (Name.startswith_lower("no")) {
+  if (Name.startswith_insensitive("no")) {
     EnableFeature = false;
     Name = Name.substr(2);
   }
@@ -5544,7 +5544,7 @@
 
     bool EnableFeature = true;
 
-    if (Name.startswith_lower("no")) {
+    if (Name.startswith_insensitive("no")) {
       EnableFeature = false;
       Name = Name.substr(2);
     }
diff --git a/llvm/lib/Target/AMDGPU/AMDGPULibCalls.cpp b/llvm/lib/Target/AMDGPU/AMDGPULibCalls.cpp
--- a/llvm/lib/Target/AMDGPU/AMDGPULibCalls.cpp
+++ b/llvm/lib/Target/AMDGPU/AMDGPULibCalls.cpp
@@ -1370,9 +1370,9 @@
 
   StringRef CPU = TM->getTargetCPU();
   StringRef Features = TM->getTargetFeatureString();
-  if ((CPU.empty() || CPU.equals_lower("generic")) &&
+  if ((CPU.empty() || CPU.equals_insensitive("generic")) &&
       (Features.empty() ||
-       Features.find_lower("wavefrontsize") == StringRef::npos))
+       Features.find_insensitive("wavefrontsize") == StringRef::npos))
     return false;
 
   Function *F = CI->getParent()->getParent();
diff --git a/llvm/lib/Target/AMDGPU/AMDGPUSubtarget.cpp b/llvm/lib/Target/AMDGPU/AMDGPUSubtarget.cpp
--- a/llvm/lib/Target/AMDGPU/AMDGPUSubtarget.cpp
+++ b/llvm/lib/Target/AMDGPU/AMDGPUSubtarget.cpp
@@ -98,12 +98,12 @@
   FullFS += "+enable-prt-strict-null,"; // This is overridden by a disable in FS
 
   // Disable mutually exclusive bits.
-  if (FS.find_lower("+wavefrontsize") != StringRef::npos) {
-    if (FS.find_lower("wavefrontsize16") == StringRef::npos)
+  if (FS.find_insensitive("+wavefrontsize") != StringRef::npos) {
+    if (FS.find_insensitive("wavefrontsize16") == StringRef::npos)
       FullFS += "-wavefrontsize16,";
-    if (FS.find_lower("wavefrontsize32") == StringRef::npos)
+    if (FS.find_insensitive("wavefrontsize32") == StringRef::npos)
       FullFS += "-wavefrontsize32,";
-    if (FS.find_lower("wavefrontsize64") == StringRef::npos)
+    if (FS.find_insensitive("wavefrontsize64") == StringRef::npos)
       FullFS += "-wavefrontsize64,";
   }
 
diff --git a/llvm/lib/Target/ARM/ARMISelLowering.cpp b/llvm/lib/Target/ARM/ARMISelLowering.cpp
--- a/llvm/lib/Target/ARM/ARMISelLowering.cpp
+++ b/llvm/lib/Target/ARM/ARMISelLowering.cpp
@@ -18632,7 +18632,7 @@
     break;
   }
 
-  if (StringRef("{cc}").equals_lower(Constraint))
+  if (StringRef("{cc}").equals_insensitive(Constraint))
     return std::make_pair(unsigned(ARM::CPSR), &ARM::CCRRegClass);
 
   return TargetLowering::getRegForInlineAsmConstraint(TRI, Constraint, VT);
diff --git a/llvm/lib/Target/ARM/AsmParser/ARMAsmParser.cpp b/llvm/lib/Target/ARM/AsmParser/ARMAsmParser.cpp
--- a/llvm/lib/Target/ARM/AsmParser/ARMAsmParser.cpp
+++ b/llvm/lib/Target/ARM/AsmParser/ARMAsmParser.cpp
@@ -5012,7 +5012,7 @@
   if (Tok.isNot(AsmToken::Identifier))
      return MatchOperand_NoMatch;
 
-  if (!Tok.getString().equals_lower("csync"))
+  if (!Tok.getString().equals_insensitive("csync"))
     return MatchOperand_NoMatch;
 
   Parser.Lex(); // Eat identifier token.
@@ -5032,7 +5032,7 @@
   if (Tok.is(AsmToken::Identifier)) {
     StringRef OptStr = Tok.getString();
 
-    if (OptStr.equals_lower("sy"))
+    if (OptStr.equals_insensitive("sy"))
       Opt = ARM_ISB::SY;
     else
       return MatchOperand_NoMatch;
@@ -6194,7 +6194,7 @@
         return true;
       // If this is VMRS, check for the apsr_nzcv operand.
       if (Mnemonic == "vmrs" &&
-          Parser.getTok().getString().equals_lower("apsr_nzcv")) {
+          Parser.getTok().getString().equals_insensitive("apsr_nzcv")) {
         S = Parser.getTok().getLoc();
         Parser.Lex();
         Operands.push_back(ARMOperand::CreateToken("APSR_nzcv", S));
@@ -12278,7 +12278,7 @@
       {ARM::AEK_XSCALE, {}, {}},
   };
   bool EnableFeature = true;
-  if (Name.startswith_lower("no")) {
+  if (Name.startswith_insensitive("no")) {
     EnableFeature = false;
     Name = Name.substr(2);
   }
diff --git a/llvm/lib/Target/Hexagon/AsmParser/HexagonAsmParser.cpp b/llvm/lib/Target/Hexagon/AsmParser/HexagonAsmParser.cpp
--- a/llvm/lib/Target/Hexagon/AsmParser/HexagonAsmParser.cpp
+++ b/llvm/lib/Target/Hexagon/AsmParser/HexagonAsmParser.cpp
@@ -510,19 +510,19 @@
         "supported with this architecture";
     StringRef Option = Parser.getTok().getString();
     auto IDLoc = Parser.getTok().getLoc();
-    if (Option.compare_lower("endloop01") == 0) {
+    if (Option.compare_insensitive("endloop01") == 0) {
       HexagonMCInstrInfo::setInnerLoop(MCB);
       HexagonMCInstrInfo::setOuterLoop(MCB);
-    } else if (Option.compare_lower("endloop0") == 0) {
+    } else if (Option.compare_insensitive("endloop0") == 0) {
       HexagonMCInstrInfo::setInnerLoop(MCB);
-    } else if (Option.compare_lower("endloop1") == 0) {
+    } else if (Option.compare_insensitive("endloop1") == 0) {
       HexagonMCInstrInfo::setOuterLoop(MCB);
-    } else if (Option.compare_lower("mem_noshuf") == 0) {
+    } else if (Option.compare_insensitive("mem_noshuf") == 0) {
       if (getSTI().getFeatureBits()[Hexagon::FeatureMemNoShuf])
         HexagonMCInstrInfo::setMemReorderDisabled(MCB);
       else
         return getParser().Error(IDLoc, MemNoShuffMsg);
-    } else if (Option.compare_lower("mem_no_order") == 0) {
+    } else if (Option.compare_insensitive("mem_no_order") == 0) {
       // Nothing.
     } else
       return getParser().Error(IDLoc, llvm::Twine("'") + Option +
@@ -838,7 +838,7 @@
   MCParsedAsmOperand &Operand = *Operands[Operands.size() - Index - 1];
   if (!Operand.isToken())
     return false;
-  return static_cast<HexagonOperand &>(Operand).getToken().equals_lower(String);
+  return static_cast<HexagonOperand &>(Operand).getToken().equals_insensitive(String);
 }
 
 static bool previousIsLoop(OperandVector &Operands, size_t Index) {
@@ -892,7 +892,7 @@
               HexagonOperand::CreateReg(getContext(), Register, Begin, End));
           const AsmToken &MaybeDotNew = Lexer.getTok();
           if (MaybeDotNew.is(AsmToken::TokenKind::Identifier) &&
-              MaybeDotNew.getString().equals_lower(".new"))
+              MaybeDotNew.getString().equals_insensitive(".new"))
             splitIdentifier(Operands);
           Operands.push_back(
               HexagonOperand::CreateToken(getContext(), RParen, Begin));
@@ -910,7 +910,7 @@
               HexagonOperand::CreateReg(getContext(), Register, Begin, End));
           const AsmToken &MaybeDotNew = Lexer.getTok();
           if (MaybeDotNew.is(AsmToken::TokenKind::Identifier) &&
-              MaybeDotNew.getString().equals_lower(".new"))
+              MaybeDotNew.getString().equals_insensitive(".new"))
             splitIdentifier(Operands);
           Operands.push_back(
               HexagonOperand::CreateToken(getContext(), RParen, Begin));
diff --git a/llvm/lib/Target/Hexagon/MCTargetDesc/HexagonMCDuplexInfo.cpp b/llvm/lib/Target/Hexagon/MCTargetDesc/HexagonMCDuplexInfo.cpp
--- a/llvm/lib/Target/Hexagon/MCTargetDesc/HexagonMCDuplexInfo.cpp
+++ b/llvm/lib/Target/Hexagon/MCTargetDesc/HexagonMCDuplexInfo.cpp
@@ -637,9 +637,9 @@
       return false;
   }
 
-  if (STI.getCPU().equals_lower("hexagonv5") ||
-      STI.getCPU().equals_lower("hexagonv55") ||
-      STI.getCPU().equals_lower("hexagonv60")) {
+  if (STI.getCPU().equals_insensitive("hexagonv5") ||
+      STI.getCPU().equals_insensitive("hexagonv55") ||
+      STI.getCPU().equals_insensitive("hexagonv60")) {
     // If a store appears, it must be in slot 0 (MIa) 1st, and then slot 1 (MIb);
     //   therefore, not duplexable if slot 1 is a store, and slot 0 is not.
     if ((MIbG == HexagonII::HSIG_S1) || (MIbG == HexagonII::HSIG_S2)) {
diff --git a/llvm/lib/Target/Lanai/AsmParser/LanaiAsmParser.cpp b/llvm/lib/Target/Lanai/AsmParser/LanaiAsmParser.cpp
--- a/llvm/lib/Target/Lanai/AsmParser/LanaiAsmParser.cpp
+++ b/llvm/lib/Target/Lanai/AsmParser/LanaiAsmParser.cpp
@@ -754,9 +754,9 @@
     return nullptr;
 
   // Check if identifier has a modifier
-  if (Identifier.equals_lower("hi"))
+  if (Identifier.equals_insensitive("hi"))
     Kind = LanaiMCExpr::VK_Lanai_ABS_HI;
-  else if (Identifier.equals_lower("lo"))
+  else if (Identifier.equals_insensitive("lo"))
     Kind = LanaiMCExpr::VK_Lanai_ABS_LO;
 
   // If the identifier corresponds to a variant then extract the real
diff --git a/llvm/lib/Target/MSP430/AsmParser/MSP430AsmParser.cpp b/llvm/lib/Target/MSP430/AsmParser/MSP430AsmParser.cpp
--- a/llvm/lib/Target/MSP430/AsmParser/MSP430AsmParser.cpp
+++ b/llvm/lib/Target/MSP430/AsmParser/MSP430AsmParser.cpp
@@ -327,7 +327,7 @@
 bool MSP430AsmParser::parseJccInstruction(ParseInstructionInfo &Info,
                                           StringRef Name, SMLoc NameLoc,
                                           OperandVector &Operands) {
-  if (!Name.startswith_lower("j"))
+  if (!Name.startswith_insensitive("j"))
     return true;
 
   auto CC = Name.drop_front().lower();
@@ -390,7 +390,7 @@
                                        StringRef Name, SMLoc NameLoc,
                                        OperandVector &Operands) {
   // Drop .w suffix
-  if (Name.endswith_lower(".w"))
+  if (Name.endswith_insensitive(".w"))
     Name = Name.drop_back(2);
 
   if (!parseJccInstruction(Info, Name, NameLoc, Operands))
diff --git a/llvm/lib/Target/PowerPC/AsmParser/PPCAsmParser.cpp b/llvm/lib/Target/PowerPC/AsmParser/PPCAsmParser.cpp
--- a/llvm/lib/Target/PowerPC/AsmParser/PPCAsmParser.cpp
+++ b/llvm/lib/Target/PowerPC/AsmParser/PPCAsmParser.cpp
@@ -1207,28 +1207,28 @@
     return true;
 
   StringRef Name = getParser().getTok().getString();
-  if (Name.equals_lower("lr")) {
+  if (Name.equals_insensitive("lr")) {
     RegNo = isPPC64() ? PPC::LR8 : PPC::LR;
     IntVal = 8;
-  } else if (Name.equals_lower("ctr")) {
+  } else if (Name.equals_insensitive("ctr")) {
     RegNo = isPPC64() ? PPC::CTR8 : PPC::CTR;
     IntVal = 9;
-  } else if (Name.equals_lower("vrsave")) {
+  } else if (Name.equals_insensitive("vrsave")) {
     RegNo = PPC::VRSAVE;
     IntVal = 256;
-  } else if (Name.startswith_lower("r") &&
+  } else if (Name.startswith_insensitive("r") &&
              !Name.substr(1).getAsInteger(10, IntVal) && IntVal < 32) {
     RegNo = isPPC64() ? XRegs[IntVal] : RRegs[IntVal];
-  } else if (Name.startswith_lower("f") &&
+  } else if (Name.startswith_insensitive("f") &&
              !Name.substr(1).getAsInteger(10, IntVal) && IntVal < 32) {
     RegNo = FRegs[IntVal];
-  } else if (Name.startswith_lower("vs") &&
+  } else if (Name.startswith_insensitive("vs") &&
              !Name.substr(2).getAsInteger(10, IntVal) && IntVal < 64) {
     RegNo = VSRegs[IntVal];
-  } else if (Name.startswith_lower("v") &&
+  } else if (Name.startswith_insensitive("v") &&
              !Name.substr(1).getAsInteger(10, IntVal) && IntVal < 32) {
     RegNo = VRegs[IntVal];
-  } else if (Name.startswith_lower("cr") &&
+  } else if (Name.startswith_insensitive("cr") &&
              !Name.substr(2).getAsInteger(10, IntVal) && IntVal < 8) {
     RegNo = CRRegs[IntVal];
   } else
diff --git a/llvm/lib/Target/PowerPC/PPCISelLowering.cpp b/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
--- a/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
+++ b/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
@@ -15743,7 +15743,7 @@
                           &PPC::G8RCRegClass);
 
   // GCC accepts 'cc' as an alias for 'cr0', and we need to do the same.
-  if (!R.second && StringRef("{cc}").equals_lower(Constraint)) {
+  if (!R.second && StringRef("{cc}").equals_insensitive(Constraint)) {
     R.first = PPC::CR0;
     R.second = &PPC::CRRCRegClass;
   }
diff --git a/llvm/lib/Target/PowerPC/PPCTargetTransformInfo.cpp b/llvm/lib/Target/PowerPC/PPCTargetTransformInfo.cpp
--- a/llvm/lib/Target/PowerPC/PPCTargetTransformInfo.cpp
+++ b/llvm/lib/Target/PowerPC/PPCTargetTransformInfo.cpp
@@ -371,7 +371,7 @@
       InlineAsm::ConstraintInfo &C = CIV[i];
       if (C.Type != InlineAsm::isInput)
         for (unsigned j = 0, je = C.Codes.size(); j < je; ++j)
-          if (StringRef(C.Codes[j]).equals_lower("{ctr}"))
+          if (StringRef(C.Codes[j]).equals_insensitive("{ctr}"))
             return true;
     }
     return false;
diff --git a/llvm/lib/Target/Sparc/AsmParser/SparcAsmParser.cpp b/llvm/lib/Target/Sparc/AsmParser/SparcAsmParser.cpp
--- a/llvm/lib/Target/Sparc/AsmParser/SparcAsmParser.cpp
+++ b/llvm/lib/Target/Sparc/AsmParser/SparcAsmParser.cpp
@@ -1125,7 +1125,7 @@
       return true;
     }
 
-    if (name.substr(0, 3).equals_lower("asr")
+    if (name.substr(0, 3).equals_insensitive("asr")
         && !name.substr(3).getAsInteger(10, intVal)
         && intVal > 0 && intVal < 32) {
       RegNo = ASRRegs[intVal];
@@ -1196,7 +1196,7 @@
     }
 
     // %fcc0 - %fcc3
-    if (name.substr(0, 3).equals_lower("fcc")
+    if (name.substr(0, 3).equals_insensitive("fcc")
         && !name.substr(3).getAsInteger(10, intVal)
         && intVal < 4) {
       // FIXME: check 64bit and  handle %fcc1 - %fcc3
@@ -1206,7 +1206,7 @@
     }
 
     // %g0 - %g7
-    if (name.substr(0, 1).equals_lower("g")
+    if (name.substr(0, 1).equals_insensitive("g")
         && !name.substr(1).getAsInteger(10, intVal)
         && intVal < 8) {
       RegNo = IntRegs[intVal];
@@ -1214,21 +1214,21 @@
       return true;
     }
     // %o0 - %o7
-    if (name.substr(0, 1).equals_lower("o")
+    if (name.substr(0, 1).equals_insensitive("o")
         && !name.substr(1).getAsInteger(10, intVal)
         && intVal < 8) {
       RegNo = IntRegs[8 + intVal];
       RegKind = SparcOperand::rk_IntReg;
       return true;
     }
-    if (name.substr(0, 1).equals_lower("l")
+    if (name.substr(0, 1).equals_insensitive("l")
         && !name.substr(1).getAsInteger(10, intVal)
         && intVal < 8) {
       RegNo = IntRegs[16 + intVal];
       RegKind = SparcOperand::rk_IntReg;
       return true;
     }
-    if (name.substr(0, 1).equals_lower("i")
+    if (name.substr(0, 1).equals_insensitive("i")
         && !name.substr(1).getAsInteger(10, intVal)
         && intVal < 8) {
       RegNo = IntRegs[24 + intVal];
@@ -1236,14 +1236,14 @@
       return true;
     }
     // %f0 - %f31
-    if (name.substr(0, 1).equals_lower("f")
+    if (name.substr(0, 1).equals_insensitive("f")
         && !name.substr(1, 2).getAsInteger(10, intVal) && intVal < 32) {
       RegNo = FloatRegs[intVal];
       RegKind = SparcOperand::rk_FloatReg;
       return true;
     }
     // %f32 - %f62
-    if (name.substr(0, 1).equals_lower("f")
+    if (name.substr(0, 1).equals_insensitive("f")
         && !name.substr(1, 2).getAsInteger(10, intVal)
         && intVal >= 32 && intVal <= 62 && (intVal % 2 == 0)) {
       // FIXME: Check V9
@@ -1253,7 +1253,7 @@
     }
 
     // %r0 - %r31
-    if (name.substr(0, 1).equals_lower("r")
+    if (name.substr(0, 1).equals_insensitive("r")
         && !name.substr(1, 2).getAsInteger(10, intVal) && intVal < 31) {
       RegNo = IntRegs[intVal];
       RegKind = SparcOperand::rk_IntReg;
@@ -1261,7 +1261,7 @@
     }
 
     // %c0 - %c31
-    if (name.substr(0, 1).equals_lower("c")
+    if (name.substr(0, 1).equals_insensitive("c")
         && !name.substr(1).getAsInteger(10, intVal)
         && intVal < 32) {
       RegNo = CoprocRegs[intVal];
diff --git a/llvm/lib/Target/Sparc/LeonPasses.cpp b/llvm/lib/Target/Sparc/LeonPasses.cpp
--- a/llvm/lib/Target/Sparc/LeonPasses.cpp
+++ b/llvm/lib/Target/Sparc/LeonPasses.cpp
@@ -87,7 +87,7 @@
 
         if (MO.isGlobal()) {
           StringRef FuncName = MO.getGlobal()->getName();
-          if (FuncName.compare_lower("fesetround") == 0) {
+          if (FuncName.compare_insensitive("fesetround") == 0) {
             errs() << "Error: You are using the detectroundchange "
                       "option to detect rounding changes that will "
                       "cause LEON errata. The only way to fix this "
diff --git a/llvm/lib/Target/WebAssembly/AsmParser/WebAssemblyAsmParser.cpp b/llvm/lib/Target/WebAssembly/AsmParser/WebAssemblyAsmParser.cpp
--- a/llvm/lib/Target/WebAssembly/AsmParser/WebAssemblyAsmParser.cpp
+++ b/llvm/lib/Target/WebAssembly/AsmParser/WebAssemblyAsmParser.cpp
@@ -391,9 +391,9 @@
     auto &Flt = Lexer.getTok();
     auto S = Flt.getString();
     double Val;
-    if (S.compare_lower("infinity") == 0) {
+    if (S.compare_insensitive("infinity") == 0) {
       Val = std::numeric_limits<double>::infinity();
-    } else if (S.compare_lower("nan") == 0) {
+    } else if (S.compare_insensitive("nan") == 0) {
       Val = std::numeric_limits<double>::quiet_NaN();
     } else {
       return true;
diff --git a/llvm/lib/Target/X86/AsmParser/X86AsmParser.cpp b/llvm/lib/Target/X86/AsmParser/X86AsmParser.cpp
--- a/llvm/lib/Target/X86/AsmParser/X86AsmParser.cpp
+++ b/llvm/lib/Target/X86/AsmParser/X86AsmParser.cpp
@@ -1784,21 +1784,21 @@
   if (Name.compare(Name.lower()) && Name.compare(Name.upper()) &&
       !getParser().isParsingMasm())
     return false;
-  if (Name.equals_lower("not")) {
+  if (Name.equals_insensitive("not")) {
     SM.onNot();
-  } else if (Name.equals_lower("or")) {
+  } else if (Name.equals_insensitive("or")) {
     SM.onOr();
-  } else if (Name.equals_lower("shl")) {
+  } else if (Name.equals_insensitive("shl")) {
     SM.onLShift();
-  } else if (Name.equals_lower("shr")) {
+  } else if (Name.equals_insensitive("shr")) {
     SM.onRShift();
-  } else if (Name.equals_lower("xor")) {
+  } else if (Name.equals_insensitive("xor")) {
     SM.onXor();
-  } else if (Name.equals_lower("and")) {
+  } else if (Name.equals_insensitive("and")) {
     SM.onAnd();
-  } else if (Name.equals_lower("mod")) {
+  } else if (Name.equals_insensitive("mod")) {
     SM.onMod();
-  } else if (Name.equals_lower("offset")) {
+  } else if (Name.equals_insensitive("offset")) {
     SMLoc OffsetLoc = getTok().getLoc();
     const MCExpr *Val = nullptr;
     StringRef ID;
@@ -1814,24 +1814,24 @@
   } else {
     return false;
   }
-  if (!Name.equals_lower("offset"))
+  if (!Name.equals_insensitive("offset"))
     End = consumeToken();
   return true;
 }
 bool X86AsmParser::ParseMasmNamedOperator(StringRef Name,
                                           IntelExprStateMachine &SM,
                                           bool &ParseError, SMLoc &End) {
-  if (Name.equals_lower("eq")) {
+  if (Name.equals_insensitive("eq")) {
     SM.onEq();
-  } else if (Name.equals_lower("ne")) {
+  } else if (Name.equals_insensitive("ne")) {
     SM.onNE();
-  } else if (Name.equals_lower("lt")) {
+  } else if (Name.equals_insensitive("lt")) {
     SM.onLT();
-  } else if (Name.equals_lower("le")) {
+  } else if (Name.equals_insensitive("le")) {
     SM.onLE();
-  } else if (Name.equals_lower("gt")) {
+  } else if (Name.equals_insensitive("gt")) {
     SM.onGT();
-  } else if (Name.equals_lower("ge")) {
+  } else if (Name.equals_insensitive("ge")) {
     SM.onGE();
   } else {
     return false;
@@ -1933,7 +1933,7 @@
       if (Parser.isParsingMasm()) {
         const AsmToken &NextTok = getLexer().peekTok();
         if (NextTok.is(AsmToken::Identifier) &&
-            NextTok.getIdentifier().equals_lower("ptr")) {
+            NextTok.getIdentifier().equals_insensitive("ptr")) {
           AsmTypeInfo Info;
           if (Parser.lookUpType(Identifier, Info))
             return Error(Tok.getLoc(), "unknown type");
@@ -3068,13 +3068,13 @@
     }
     // Parse MASM style pseudo prefixes.
     if (isParsingMSInlineAsm()) {
-      if (Name.equals_lower("vex"))
+      if (Name.equals_insensitive("vex"))
         ForcedVEXEncoding = VEXEncoding_VEX;
-      else if (Name.equals_lower("vex2"))
+      else if (Name.equals_insensitive("vex2"))
         ForcedVEXEncoding = VEXEncoding_VEX2;
-      else if (Name.equals_lower("vex3"))
+      else if (Name.equals_insensitive("vex3"))
         ForcedVEXEncoding = VEXEncoding_VEX3;
-      else if (Name.equals_lower("evex"))
+      else if (Name.equals_insensitive("evex"))
         ForcedVEXEncoding = VEXEncoding_EVEX;
 
       if (ForcedVEXEncoding != VEXEncoding_Default) {
@@ -3105,7 +3105,7 @@
        (PatchedName.startswith("j") &&
         ParseConditionCode(PatchedName.substr(1)) != X86::COND_INVALID))) {
     StringRef NextTok = Parser.getTok().getString();
-    if (Parser.isParsingMasm() ? NextTok.equals_lower("short")
+    if (Parser.isParsingMasm() ? NextTok.equals_insensitive("short")
                                : NextTok == "short") {
       SMLoc NameEndLoc =
           NameLoc.getFromPointer(NameLoc.getPointer() + Name.size());
@@ -4649,19 +4649,19 @@
   else if (IDVal == ".cv_fpo_endproc")
     return parseDirectiveFPOEndProc(DirectiveID.getLoc());
   else if (IDVal == ".seh_pushreg" ||
-           (Parser.isParsingMasm() && IDVal.equals_lower(".pushreg")))
+           (Parser.isParsingMasm() && IDVal.equals_insensitive(".pushreg")))
     return parseDirectiveSEHPushReg(DirectiveID.getLoc());
   else if (IDVal == ".seh_setframe" ||
-           (Parser.isParsingMasm() && IDVal.equals_lower(".setframe")))
+           (Parser.isParsingMasm() && IDVal.equals_insensitive(".setframe")))
     return parseDirectiveSEHSetFrame(DirectiveID.getLoc());
   else if (IDVal == ".seh_savereg" ||
-           (Parser.isParsingMasm() && IDVal.equals_lower(".savereg")))
+           (Parser.isParsingMasm() && IDVal.equals_insensitive(".savereg")))
     return parseDirectiveSEHSaveReg(DirectiveID.getLoc());
   else if (IDVal == ".seh_savexmm" ||
-           (Parser.isParsingMasm() && IDVal.equals_lower(".savexmm128")))
+           (Parser.isParsingMasm() && IDVal.equals_insensitive(".savexmm128")))
     return parseDirectiveSEHSaveXMM(DirectiveID.getLoc());
   else if (IDVal == ".seh_pushframe" ||
-           (Parser.isParsingMasm() && IDVal.equals_lower(".pushframe")))
+           (Parser.isParsingMasm() && IDVal.equals_insensitive(".pushframe")))
     return parseDirectiveSEHPushFrame(DirectiveID.getLoc());
 
   return true;
diff --git a/llvm/lib/Target/X86/MCTargetDesc/X86MCTargetDesc.cpp b/llvm/lib/Target/X86/MCTargetDesc/X86MCTargetDesc.cpp
--- a/llvm/lib/Target/X86/MCTargetDesc/X86MCTargetDesc.cpp
+++ b/llvm/lib/Target/X86/MCTargetDesc/X86MCTargetDesc.cpp
@@ -332,7 +332,7 @@
     MAI = new X86ELFMCAsmInfo(TheTriple);
   } else if (TheTriple.isWindowsMSVCEnvironment() ||
              TheTriple.isWindowsCoreCLREnvironment()) {
-    if (Options.getAssemblyLanguage().equals_lower("masm"))
+    if (Options.getAssemblyLanguage().equals_insensitive("masm"))
       MAI = new X86MCAsmInfoMicrosoftMASM(TheTriple);
     else
       MAI = new X86MCAsmInfoMicrosoft(TheTriple);
diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -51968,21 +51968,21 @@
       }
 
       // GCC allows "st(0)" to be called just plain "st".
-      if (StringRef("{st}").equals_lower(Constraint))
+      if (StringRef("{st}").equals_insensitive(Constraint))
         return std::make_pair(X86::FP0, &X86::RFP80RegClass);
     }
 
     // flags -> EFLAGS
-    if (StringRef("{flags}").equals_lower(Constraint))
+    if (StringRef("{flags}").equals_insensitive(Constraint))
       return std::make_pair(X86::EFLAGS, &X86::CCRRegClass);
 
     // dirflag -> DF
     // Only allow for clobber.
-    if (StringRef("{dirflag}").equals_lower(Constraint) && VT == MVT::Other)
+    if (StringRef("{dirflag}").equals_insensitive(Constraint) && VT == MVT::Other)
       return std::make_pair(X86::DF, &X86::DFCCRRegClass);
 
     // fpsr -> FPSW
-    if (StringRef("{fpsr}").equals_lower(Constraint))
+    if (StringRef("{fpsr}").equals_insensitive(Constraint))
       return std::make_pair(X86::FPSW, &X86::FPCCRRegClass);
 
     return Res;
diff --git a/llvm/lib/ToolDrivers/llvm-dlltool/DlltoolDriver.cpp b/llvm/lib/ToolDrivers/llvm-dlltool/DlltoolDriver.cpp
--- a/llvm/lib/ToolDrivers/llvm-dlltool/DlltoolDriver.cpp
+++ b/llvm/lib/ToolDrivers/llvm-dlltool/DlltoolDriver.cpp
@@ -99,10 +99,10 @@
   // llvm-dlltool -> None
   // aarch64-w64-mingw32-llvm-dlltool-10.exe -> aarch64-w64-mingw32
   ProgName = ProgName.rtrim("0123456789.-");
-  if (!ProgName.consume_back_lower("dlltool"))
+  if (!ProgName.consume_back_insensitive("dlltool"))
     return None;
-  ProgName.consume_back_lower("llvm-");
-  ProgName.consume_back_lower("-");
+  ProgName.consume_back_insensitive("llvm-");
+  ProgName.consume_back_insensitive("-");
   return ProgName.str();
 }
 
diff --git a/llvm/tools/bugpoint/ToolRunner.cpp b/llvm/tools/bugpoint/ToolRunner.cpp
--- a/llvm/tools/bugpoint/ToolRunner.cpp
+++ b/llvm/tools/bugpoint/ToolRunner.cpp
@@ -607,12 +607,12 @@
 
 static bool IsARMArchitecture(std::vector<StringRef> Args) {
   for (size_t I = 0; I < Args.size(); ++I) {
-    if (!Args[I].equals_lower("-arch"))
+    if (!Args[I].equals_insensitive("-arch"))
       continue;
     ++I;
     if (I == Args.size())
       break;
-    if (Args[I].startswith_lower("arm"))
+    if (Args[I].startswith_insensitive("arm"))
       return true;
   }
 
diff --git a/llvm/tools/llvm-ar/llvm-ar.cpp b/llvm/tools/llvm-ar/llvm-ar.cpp
--- a/llvm/tools/llvm-ar/llvm-ar.cpp
+++ b/llvm/tools/llvm-ar/llvm-ar.cpp
@@ -126,9 +126,9 @@
 )";
 
 static void printHelpMessage() {
-  if (Stem.contains_lower("ranlib"))
+  if (Stem.contains_insensitive("ranlib"))
     outs() << RanlibHelp;
-  else if (Stem.contains_lower("ar"))
+  else if (Stem.contains_insensitive("ar"))
     outs() << ArHelp;
 }
 
@@ -1276,7 +1276,7 @@
     // Lib.exe -> lib (see D44808, MSBuild runs Lib.exe)
     // dlltool.exe -> dlltool
     // arm-pokymllib32-linux-gnueabi-llvm-ar-10 -> ar
-    auto I = Stem.rfind_lower(Tool);
+    auto I = Stem.rfind_insensitive(Tool);
     return I != StringRef::npos &&
            (I + Tool.size() == Stem.size() || !isAlnum(Stem[I + Tool.size()]));
   };
diff --git a/llvm/tools/llvm-cov/llvm-cov.cpp b/llvm/tools/llvm-cov/llvm-cov.cpp
--- a/llvm/tools/llvm-cov/llvm-cov.cpp
+++ b/llvm/tools/llvm-cov/llvm-cov.cpp
@@ -60,7 +60,7 @@
   InitLLVM X(argc, argv);
 
   // If argv[0] is or ends with 'gcov', always be gcov compatible
-  if (sys::path::stem(argv[0]).endswith_lower("gcov"))
+  if (sys::path::stem(argv[0]).endswith_insensitive("gcov"))
     return gcovMain(argc, argv);
 
   // Check if we are invoking a specific tool command.
diff --git a/llvm/tools/llvm-jitlink/llvm-jitlink.cpp b/llvm/tools/llvm-jitlink/llvm-jitlink.cpp
--- a/llvm/tools/llvm-jitlink/llvm-jitlink.cpp
+++ b/llvm/tools/llvm-jitlink/llvm-jitlink.cpp
@@ -479,12 +479,12 @@
 
   uint64_t Units = 1024;
 
-  if (SizeString.endswith_lower("kb"))
+  if (SizeString.endswith_insensitive("kb"))
     SizeString = SizeString.drop_back(2).rtrim();
-  else if (SizeString.endswith_lower("mb")) {
+  else if (SizeString.endswith_insensitive("mb")) {
     Units = 1024 * 1024;
     SizeString = SizeString.drop_back(2).rtrim();
-  } else if (SizeString.endswith_lower("gb")) {
+  } else if (SizeString.endswith_insensitive("gb")) {
     Units = 1024 * 1024 * 1024;
     SizeString = SizeString.drop_back(2).rtrim();
   }
diff --git a/llvm/tools/llvm-objcopy/llvm-objcopy.cpp b/llvm/tools/llvm-objcopy/llvm-objcopy.cpp
--- a/llvm/tools/llvm-objcopy/llvm-objcopy.cpp
+++ b/llvm/tools/llvm-objcopy/llvm-objcopy.cpp
@@ -81,7 +81,7 @@
     // strip-10.exe -> strip
     // powerpc64-unknown-freebsd13-objcopy -> objcopy
     // llvm-install-name-tool -> install-name-tool
-    auto I = Stem.rfind_lower(Tool);
+    auto I = Stem.rfind_insensitive(Tool);
     return I != StringRef::npos &&
            (I + Tool.size() == Stem.size() || !isAlnum(Stem[I + Tool.size()]));
   };
diff --git a/llvm/tools/llvm-objdump/llvm-objdump.cpp b/llvm/tools/llvm-objdump/llvm-objdump.cpp
--- a/llvm/tools/llvm-objdump/llvm-objdump.cpp
+++ b/llvm/tools/llvm-objdump/llvm-objdump.cpp
@@ -2527,7 +2527,7 @@
     // llvm-objdump -> objdump
     // llvm-otool-10.exe -> otool
     // powerpc64-unknown-freebsd13-objdump -> objdump
-    auto I = Stem.rfind_lower(Tool);
+    auto I = Stem.rfind_insensitive(Tool);
     return I != StringRef::npos &&
            (I + Tool.size() == Stem.size() || !isAlnum(Stem[I + Tool.size()]));
   };
diff --git a/llvm/tools/llvm-pdbutil/DumpOutputStyle.cpp b/llvm/tools/llvm-pdbutil/DumpOutputStyle.cpp
--- a/llvm/tools/llvm-pdbutil/DumpOutputStyle.cpp
+++ b/llvm/tools/llvm-pdbutil/DumpOutputStyle.cpp
@@ -350,13 +350,13 @@
   StringRef Name = Group.name();
   if (Name.startswith("Import:"))
     return false;
-  if (Name.endswith_lower(".dll"))
+  if (Name.endswith_insensitive(".dll"))
     return false;
-  if (Name.equals_lower("* linker *"))
+  if (Name.equals_insensitive("* linker *"))
     return false;
-  if (Name.startswith_lower("f:\\binaries\\Intermediate\\vctools"))
+  if (Name.startswith_insensitive("f:\\binaries\\Intermediate\\vctools"))
     return false;
-  if (Name.startswith_lower("f:\\dd\\vctools\\crt"))
+  if (Name.startswith_insensitive("f:\\dd\\vctools\\crt"))
     return false;
   return true;
 }
diff --git a/llvm/tools/llvm-rc/ResourceFileWriter.cpp b/llvm/tools/llvm-rc/ResourceFileWriter.cpp
--- a/llvm/tools/llvm-rc/ResourceFileWriter.cpp
+++ b/llvm/tools/llvm-rc/ResourceFileWriter.cpp
@@ -99,7 +99,7 @@
     return false;
 
   // Just take the contents of the string, checking if it's been marked long.
-  IsLongString = Str.startswith_lower("L");
+  IsLongString = Str.startswith_insensitive("L");
   if (IsLongString)
     Str = Str.drop_front();
 
diff --git a/llvm/tools/llvm-rc/ResourceScriptCppFilter.cpp b/llvm/tools/llvm-rc/ResourceScriptCppFilter.cpp
--- a/llvm/tools/llvm-rc/ResourceScriptCppFilter.cpp
+++ b/llvm/tools/llvm-rc/ResourceScriptCppFilter.cpp
@@ -91,7 +91,7 @@
 
   StringRef Ext = Line.rsplit('.').second;
 
-  if (Ext.equals_lower("h") || Ext.equals_lower("c")) {
+  if (Ext.equals_insensitive("h") || Ext.equals_insensitive("c")) {
     Outputting = false;
   } else {
     Outputting = true;
diff --git a/llvm/tools/llvm-rc/ResourceScriptParser.cpp b/llvm/tools/llvm-rc/ResourceScriptParser.cpp
--- a/llvm/tools/llvm-rc/ResourceScriptParser.cpp
+++ b/llvm/tools/llvm-rc/ResourceScriptParser.cpp
@@ -215,7 +215,7 @@
   }
 
   case Kind::Identifier: {
-    if (!read().value().equals_lower("not"))
+    if (!read().value().equals_insensitive("not"))
       return getExpectedError(ErrorMsg, true);
     ASSIGN_OR_RETURN(Result, parseIntExpr2());
     return IntWithNotMask(0, (*Result).getValue());
@@ -330,7 +330,7 @@
     bool FoundFlag = false;
 
     for (size_t FlagId = 0; FlagId < FlagDesc.size(); ++FlagId) {
-      if (!FlagResult->equals_lower(FlagDesc[FlagId]))
+      if (!FlagResult->equals_insensitive(FlagDesc[FlagId]))
         continue;
 
       Result |= FlagValues[FlagId];
@@ -351,23 +351,23 @@
     if (Token.kind() != Kind::Identifier)
       return Flags;
     const StringRef Ident = Token.value();
-    if (Ident.equals_lower("PRELOAD"))
+    if (Ident.equals_insensitive("PRELOAD"))
       Flags |= MfPreload;
-    else if (Ident.equals_lower("LOADONCALL"))
+    else if (Ident.equals_insensitive("LOADONCALL"))
       Flags &= ~MfPreload;
-    else if (Ident.equals_lower("FIXED"))
+    else if (Ident.equals_insensitive("FIXED"))
       Flags &= ~(MfMoveable | MfDiscardable);
-    else if (Ident.equals_lower("MOVEABLE"))
+    else if (Ident.equals_insensitive("MOVEABLE"))
       Flags |= MfMoveable;
-    else if (Ident.equals_lower("DISCARDABLE"))
+    else if (Ident.equals_insensitive("DISCARDABLE"))
       Flags |= MfDiscardable | MfMoveable | MfPure;
-    else if (Ident.equals_lower("PURE"))
+    else if (Ident.equals_insensitive("PURE"))
       Flags |= MfPure;
-    else if (Ident.equals_lower("IMPURE"))
+    else if (Ident.equals_insensitive("IMPURE"))
       Flags &= ~(MfPure | MfDiscardable);
-    else if (Ident.equals_lower("SHARED"))
+    else if (Ident.equals_insensitive("SHARED"))
       Flags |= MfPure;
-    else if (Ident.equals_lower("NONSHARED"))
+    else if (Ident.equals_insensitive("NONSHARED"))
       Flags &= ~(MfPure | MfDiscardable);
     else
       return Flags;
@@ -392,23 +392,23 @@
 Expected<std::unique_ptr<OptionalStmt>>
 RCParser::parseSingleOptionalStatement(OptStmtType StmtsType) {
   ASSIGN_OR_RETURN(TypeToken, readIdentifier());
-  if (TypeToken->equals_lower("CHARACTERISTICS"))
+  if (TypeToken->equals_insensitive("CHARACTERISTICS"))
     return parseCharacteristicsStmt();
-  if (TypeToken->equals_lower("LANGUAGE"))
+  if (TypeToken->equals_insensitive("LANGUAGE"))
     return parseLanguageStmt();
-  if (TypeToken->equals_lower("VERSION"))
+  if (TypeToken->equals_insensitive("VERSION"))
     return parseVersionStmt();
 
   if (StmtsType != OptStmtType::BasicStmt) {
-    if (TypeToken->equals_lower("CAPTION"))
+    if (TypeToken->equals_insensitive("CAPTION"))
       return parseCaptionStmt();
-    if (TypeToken->equals_lower("CLASS"))
+    if (TypeToken->equals_insensitive("CLASS"))
       return parseClassStmt();
-    if (TypeToken->equals_lower("EXSTYLE"))
+    if (TypeToken->equals_insensitive("EXSTYLE"))
       return parseExStyleStmt();
-    if (TypeToken->equals_lower("FONT"))
+    if (TypeToken->equals_insensitive("FONT"))
       return parseFontStmt(StmtsType);
-    if (TypeToken->equals_lower("STYLE"))
+    if (TypeToken->equals_insensitive("STYLE"))
       return parseStyleStmt();
   }
 
@@ -635,15 +635,15 @@
   while (!consumeOptionalType(Kind::BlockEnd)) {
     ASSIGN_OR_RETURN(ItemTypeResult, readIdentifier());
 
-    bool IsMenuItem = ItemTypeResult->equals_lower("MENUITEM");
-    bool IsPopup = ItemTypeResult->equals_lower("POPUP");
+    bool IsMenuItem = ItemTypeResult->equals_insensitive("MENUITEM");
+    bool IsPopup = ItemTypeResult->equals_insensitive("POPUP");
     if (!IsMenuItem && !IsPopup)
       return getExpectedError("MENUITEM, POPUP, END or '}'", true);
 
     if (IsMenuItem && isNextTokenKind(Kind::Identifier)) {
       // Now, expecting SEPARATOR.
       ASSIGN_OR_RETURN(SeparatorResult, readIdentifier());
-      if (SeparatorResult->equals_lower("SEPARATOR")) {
+      if (SeparatorResult->equals_insensitive("SEPARATOR")) {
         List.addDefinition(std::make_unique<MenuSeparator>());
         continue;
       }
@@ -731,12 +731,12 @@
   // Expect either BLOCK or VALUE, then a name or a key (a string).
   ASSIGN_OR_RETURN(TypeResult, readIdentifier());
 
-  if (TypeResult->equals_lower("BLOCK")) {
+  if (TypeResult->equals_insensitive("BLOCK")) {
     ASSIGN_OR_RETURN(NameResult, readString());
     return parseVersionInfoBlockContents(*NameResult);
   }
 
-  if (TypeResult->equals_lower("VALUE")) {
+  if (TypeResult->equals_insensitive("VALUE")) {
     ASSIGN_OR_RETURN(KeyResult, readString());
     // Read a non-empty list of strings and/or ints, each
     // possibly preceded by a comma. Unfortunately, the tool behavior depends
diff --git a/llvm/tools/llvm-rc/ResourceScriptStmt.h b/llvm/tools/llvm-rc/ResourceScriptStmt.h
--- a/llvm/tools/llvm-rc/ResourceScriptStmt.h
+++ b/llvm/tools/llvm-rc/ResourceScriptStmt.h
@@ -145,7 +145,7 @@
       : Data(Token), IsInt(Token.kind() == RCToken::Kind::Int) {}
 
   bool equalsLower(const char *Str) {
-    return !IsInt && Data.String.equals_lower(Str);
+    return !IsInt && Data.String.equals_insensitive(Str);
   }
 
   bool isInt() const { return IsInt; }
diff --git a/llvm/tools/llvm-rc/ResourceScriptToken.cpp b/llvm/tools/llvm-rc/ResourceScriptToken.cpp
--- a/llvm/tools/llvm-rc/ResourceScriptToken.cpp
+++ b/llvm/tools/llvm-rc/ResourceScriptToken.cpp
@@ -350,9 +350,9 @@
   assert(Token.kind() == Kind::Identifier);
   StringRef Name = Token.value();
 
-  if (Name.equals_lower("begin"))
+  if (Name.equals_insensitive("begin"))
     Token = RCToken(Kind::BlockBegin, Name);
-  else if (Name.equals_lower("end"))
+  else if (Name.equals_insensitive("end"))
     Token = RCToken(Kind::BlockEnd, Name);
 }
 
diff --git a/llvm/tools/llvm-rc/llvm-rc.cpp b/llvm/tools/llvm-rc/llvm-rc.cpp
--- a/llvm/tools/llvm-rc/llvm-rc.cpp
+++ b/llvm/tools/llvm-rc/llvm-rc.cpp
@@ -262,10 +262,10 @@
   // llvm-rc -> "", llvm-rc
   // aarch64-w64-mingw32-llvm-windres-10.exe -> aarch64-w64-mingw32, llvm-windres
   ProgName = ProgName.rtrim("0123456789.-");
-  if (!ProgName.consume_back_lower("windres"))
+  if (!ProgName.consume_back_insensitive("windres"))
     return std::make_pair<bool, std::string>(false, "");
-  ProgName.consume_back_lower("llvm-");
-  ProgName.consume_back_lower("-");
+  ProgName.consume_back_insensitive("llvm-");
+  ProgName.consume_back_insensitive("-");
   return std::make_pair<bool, std::string>(true, ProgName.str());
 }
 
diff --git a/llvm/unittests/ADT/SmallStringTest.cpp b/llvm/unittests/ADT/SmallStringTest.cpp
--- a/llvm/unittests/ADT/SmallStringTest.cpp
+++ b/llvm/unittests/ADT/SmallStringTest.cpp
@@ -210,12 +210,12 @@
   EXPECT_EQ( 1, SmallString<10>("aab").compare("aa"));
   EXPECT_EQ( 1, SmallString<10>("\xFF").compare("\1"));
 
-  EXPECT_EQ(-1, SmallString<10>("AaB").compare_lower("aAd"));
-  EXPECT_EQ( 0, SmallString<10>("AaB").compare_lower("aab"));
-  EXPECT_EQ( 1, SmallString<10>("AaB").compare_lower("AAA"));
-  EXPECT_EQ(-1, SmallString<10>("AaB").compare_lower("aaBb"));
-  EXPECT_EQ( 1, SmallString<10>("AaB").compare_lower("aA"));
-  EXPECT_EQ( 1, SmallString<10>("\xFF").compare_lower("\1"));
+  EXPECT_EQ(-1, SmallString<10>("AaB").compare_insensitive("aAd"));
+  EXPECT_EQ( 0, SmallString<10>("AaB").compare_insensitive("aab"));
+  EXPECT_EQ( 1, SmallString<10>("AaB").compare_insensitive("AAA"));
+  EXPECT_EQ(-1, SmallString<10>("AaB").compare_insensitive("aaBb"));
+  EXPECT_EQ( 1, SmallString<10>("AaB").compare_insensitive("aA"));
+  EXPECT_EQ( 1, SmallString<10>("\xFF").compare_insensitive("\1"));
 
   EXPECT_EQ(-1, SmallString<10>("aab").compare_numeric("aad"));
   EXPECT_EQ( 0, SmallString<10>("aab").compare_numeric("aab"));
diff --git a/llvm/unittests/ADT/StringRefTest.cpp b/llvm/unittests/ADT/StringRefTest.cpp
--- a/llvm/unittests/ADT/StringRefTest.cpp
+++ b/llvm/unittests/ADT/StringRefTest.cpp
@@ -98,15 +98,15 @@
   EXPECT_EQ( 1, StringRef("aab").compare("aa"));
   EXPECT_EQ( 1, StringRef("\xFF").compare("\1"));
 
-  EXPECT_EQ(-1, StringRef("AaB").compare_lower("aAd"));
-  EXPECT_EQ( 0, StringRef("AaB").compare_lower("aab"));
-  EXPECT_EQ( 1, StringRef("AaB").compare_lower("AAA"));
-  EXPECT_EQ(-1, StringRef("AaB").compare_lower("aaBb"));
-  EXPECT_EQ(-1, StringRef("AaB").compare_lower("bb"));
-  EXPECT_EQ( 1, StringRef("aaBb").compare_lower("AaB"));
-  EXPECT_EQ( 1, StringRef("bb").compare_lower("AaB"));
-  EXPECT_EQ( 1, StringRef("AaB").compare_lower("aA"));
-  EXPECT_EQ( 1, StringRef("\xFF").compare_lower("\1"));
+  EXPECT_EQ(-1, StringRef("AaB").compare_insensitive("aAd"));
+  EXPECT_EQ( 0, StringRef("AaB").compare_insensitive("aab"));
+  EXPECT_EQ( 1, StringRef("AaB").compare_insensitive("AAA"));
+  EXPECT_EQ(-1, StringRef("AaB").compare_insensitive("aaBb"));
+  EXPECT_EQ(-1, StringRef("AaB").compare_insensitive("bb"));
+  EXPECT_EQ( 1, StringRef("aaBb").compare_insensitive("AaB"));
+  EXPECT_EQ( 1, StringRef("bb").compare_insensitive("AaB"));
+  EXPECT_EQ( 1, StringRef("AaB").compare_insensitive("aA"));
+  EXPECT_EQ( 1, StringRef("\xFF").compare_insensitive("\1"));
 
   EXPECT_EQ(-1, StringRef("aab").compare_numeric("aad"));
   EXPECT_EQ( 0, StringRef("aab").compare_numeric("aab"));
@@ -366,14 +366,14 @@
   EXPECT_FALSE(Str.startswith("hi"));
 }
 
-TEST(StringRefTest, StartsWithLower) {
+TEST(StringRefTest, StartsWithInsensitive) {
   StringRef Str("heLLo");
-  EXPECT_TRUE(Str.startswith_lower(""));
-  EXPECT_TRUE(Str.startswith_lower("he"));
-  EXPECT_TRUE(Str.startswith_lower("hell"));
-  EXPECT_TRUE(Str.startswith_lower("HELlo"));
-  EXPECT_FALSE(Str.startswith_lower("helloworld"));
-  EXPECT_FALSE(Str.startswith_lower("hi"));
+  EXPECT_TRUE(Str.startswith_insensitive(""));
+  EXPECT_TRUE(Str.startswith_insensitive("he"));
+  EXPECT_TRUE(Str.startswith_insensitive("hell"));
+  EXPECT_TRUE(Str.startswith_insensitive("HELlo"));
+  EXPECT_FALSE(Str.startswith_insensitive("helloworld"));
+  EXPECT_FALSE(Str.startswith_insensitive("hi"));
 }
 
 TEST(StringRefTest, ConsumeFront) {
@@ -392,22 +392,22 @@
   EXPECT_TRUE(Str.consume_front(""));
 }
 
-TEST(StringRefTest, ConsumeFrontLower) {
+TEST(StringRefTest, ConsumeFrontInsensitive) {
   StringRef Str("heLLo");
-  EXPECT_TRUE(Str.consume_front_lower(""));
+  EXPECT_TRUE(Str.consume_front_insensitive(""));
   EXPECT_EQ("heLLo", Str);
   EXPECT_FALSE(Str.consume_front("HEl"));
   EXPECT_EQ("heLLo", Str);
-  EXPECT_TRUE(Str.consume_front_lower("HEl"));
+  EXPECT_TRUE(Str.consume_front_insensitive("HEl"));
   EXPECT_EQ("Lo", Str);
-  EXPECT_FALSE(Str.consume_front_lower("loworld"));
+  EXPECT_FALSE(Str.consume_front_insensitive("loworld"));
   EXPECT_EQ("Lo", Str);
-  EXPECT_FALSE(Str.consume_front_lower("ol"));
+  EXPECT_FALSE(Str.consume_front_insensitive("ol"));
   EXPECT_EQ("Lo", Str);
-  EXPECT_TRUE(Str.consume_front_lower("lo"));
+  EXPECT_TRUE(Str.consume_front_insensitive("lo"));
   EXPECT_EQ("", Str);
-  EXPECT_FALSE(Str.consume_front_lower("o"));
-  EXPECT_TRUE(Str.consume_front_lower(""));
+  EXPECT_FALSE(Str.consume_front_insensitive("o"));
+  EXPECT_TRUE(Str.consume_front_insensitive(""));
 }
 
 TEST(StringRefTest, EndsWith) {
@@ -419,14 +419,14 @@
   EXPECT_FALSE(Str.endswith("so"));
 }
 
-TEST(StringRefTest, EndsWithLower) {
+TEST(StringRefTest, EndsWithInsensitive) {
   StringRef Str("heLLo");
-  EXPECT_TRUE(Str.endswith_lower(""));
-  EXPECT_TRUE(Str.endswith_lower("lo"));
-  EXPECT_TRUE(Str.endswith_lower("LO"));
-  EXPECT_TRUE(Str.endswith_lower("ELlo"));
-  EXPECT_FALSE(Str.endswith_lower("helloworld"));
-  EXPECT_FALSE(Str.endswith_lower("hi"));
+  EXPECT_TRUE(Str.endswith_insensitive(""));
+  EXPECT_TRUE(Str.endswith_insensitive("lo"));
+  EXPECT_TRUE(Str.endswith_insensitive("LO"));
+  EXPECT_TRUE(Str.endswith_insensitive("ELlo"));
+  EXPECT_FALSE(Str.endswith_insensitive("helloworld"));
+  EXPECT_FALSE(Str.endswith_insensitive("hi"));
 }
 
 TEST(StringRefTest, ConsumeBack) {
@@ -445,22 +445,22 @@
   EXPECT_TRUE(Str.consume_back(""));
 }
 
-TEST(StringRefTest, ConsumeBackLower) {
+TEST(StringRefTest, ConsumeBackInsensitive) {
   StringRef Str("heLLo");
-  EXPECT_TRUE(Str.consume_back_lower(""));
+  EXPECT_TRUE(Str.consume_back_insensitive(""));
   EXPECT_EQ("heLLo", Str);
   EXPECT_FALSE(Str.consume_back("lO"));
   EXPECT_EQ("heLLo", Str);
-  EXPECT_TRUE(Str.consume_back_lower("lO"));
+  EXPECT_TRUE(Str.consume_back_insensitive("lO"));
   EXPECT_EQ("heL", Str);
-  EXPECT_FALSE(Str.consume_back_lower("helhel"));
+  EXPECT_FALSE(Str.consume_back_insensitive("helhel"));
   EXPECT_EQ("heL", Str);
-  EXPECT_FALSE(Str.consume_back_lower("hle"));
+  EXPECT_FALSE(Str.consume_back_insensitive("hle"));
   EXPECT_EQ("heL", Str);
-  EXPECT_TRUE(Str.consume_back_lower("hEl"));
+  EXPECT_TRUE(Str.consume_back_insensitive("hEl"));
   EXPECT_EQ("", Str);
-  EXPECT_FALSE(Str.consume_back_lower("h"));
-  EXPECT_TRUE(Str.consume_back_lower(""));
+  EXPECT_FALSE(Str.consume_back_insensitive("h"));
+  EXPECT_TRUE(Str.consume_back_insensitive(""));
 }
 
 TEST(StringRefTest, Find) {
@@ -472,7 +472,7 @@
     char C;
     std::size_t From;
     std::size_t Pos;
-    std::size_t LowerPos;
+    std::size_t InsensitivePos;
   } CharExpectations[] = {
       {Str, 'h', 0U, 0U, 0U},
       {Str, 'e', 0U, 1U, 1U},
@@ -488,7 +488,7 @@
     llvm::StringRef S;
     std::size_t From;
     std::size_t Pos;
-    std::size_t LowerPos;
+    std::size_t InsensitivePos;
   } StrExpectations[] = {
       {Str, "helloword", 0, StringRef::npos, StringRef::npos},
       {Str, "hello", 0, 0U, 0U},
@@ -507,14 +507,14 @@
 
   for (auto &E : CharExpectations) {
     EXPECT_EQ(E.Pos, E.Str.find(E.C, E.From));
-    EXPECT_EQ(E.LowerPos, E.Str.find_lower(E.C, E.From));
-    EXPECT_EQ(E.LowerPos, E.Str.find_lower(toupper(E.C), E.From));
+    EXPECT_EQ(E.InsensitivePos, E.Str.find_insensitive(E.C, E.From));
+    EXPECT_EQ(E.InsensitivePos, E.Str.find_insensitive(toupper(E.C), E.From));
   }
 
   for (auto &E : StrExpectations) {
     EXPECT_EQ(E.Pos, E.Str.find(E.S, E.From));
-    EXPECT_EQ(E.LowerPos, E.Str.find_lower(E.S, E.From));
-    EXPECT_EQ(E.LowerPos, E.Str.find_lower(E.S.upper(), E.From));
+    EXPECT_EQ(E.InsensitivePos, E.Str.find_insensitive(E.S, E.From));
+    EXPECT_EQ(E.InsensitivePos, E.Str.find_insensitive(E.S.upper(), E.From));
   }
 
   EXPECT_EQ(3U, Str.rfind('l'));
@@ -524,10 +524,10 @@
   EXPECT_EQ(1U, Str.rfind("ello"));
   EXPECT_EQ(StringRef::npos, Str.rfind("zz"));
 
-  EXPECT_EQ(8U, Str.rfind_lower('l'));
-  EXPECT_EQ(8U, Str.rfind_lower('L'));
-  EXPECT_EQ(StringRef::npos, Str.rfind_lower('z'));
-  EXPECT_EQ(StringRef::npos, Str.rfind_lower("HELLOWORLD"));
+  EXPECT_EQ(8U, Str.rfind_insensitive('l'));
+  EXPECT_EQ(8U, Str.rfind_insensitive('L'));
+  EXPECT_EQ(StringRef::npos, Str.rfind_insensitive('z'));
+  EXPECT_EQ(StringRef::npos, Str.rfind_insensitive("HELLOWORLD"));
   EXPECT_EQ(5U, Str.rfind("HELLO"));
   EXPECT_EQ(6U, Str.rfind("ELLO"));
   EXPECT_EQ(StringRef::npos, Str.rfind("ZZ"));
diff --git a/llvm/unittests/Support/CommandLineTest.cpp b/llvm/unittests/Support/CommandLineTest.cpp
--- a/llvm/unittests/Support/CommandLineTest.cpp
+++ b/llvm/unittests/Support/CommandLineTest.cpp
@@ -1123,7 +1123,7 @@
             llvm::sys::path::is_absolute(__argv[0]));
 
   EXPECT_TRUE(llvm::sys::path::filename(argv[0])
-              .equals_lower("supporttests.exe"))
+              .equals_insensitive("supporttests.exe"))
       << "Filename of test executable is "
       << llvm::sys::path::filename(argv[0]);
 }
diff --git a/llvm/utils/TableGen/AsmMatcherEmitter.cpp b/llvm/utils/TableGen/AsmMatcherEmitter.cpp
--- a/llvm/utils/TableGen/AsmMatcherEmitter.cpp
+++ b/llvm/utils/TableGen/AsmMatcherEmitter.cpp
@@ -612,7 +612,7 @@
   /// operator< - Compare two matchables.
   bool operator<(const MatchableInfo &RHS) const {
     // The primary comparator is the instruction mnemonic.
-    if (int Cmp = Mnemonic.compare_lower(RHS.Mnemonic))
+    if (int Cmp = Mnemonic.compare_insensitive(RHS.Mnemonic))
       return Cmp == -1;
 
     if (AsmOperands.size() != RHS.AsmOperands.size())
diff --git a/mlir/test/lib/Dialect/Test/TestTypes.cpp b/mlir/test/lib/Dialect/Test/TestTypes.cpp
--- a/mlir/test/lib/Dialect/Test/TestTypes.cpp
+++ b/mlir/test/lib/Dialect/Test/TestTypes.cpp
@@ -31,11 +31,11 @@
   auto loc = parser.getCurrentLocation();
   if (parser.parseKeyword(&signStr))
     return failure();
-  if (signStr.compare_lower("u") || signStr.compare_lower("unsigned"))
+  if (signStr.compare_insensitive("u") || signStr.compare_insensitive("unsigned"))
     result = TestIntegerType::SignednessSemantics::Unsigned;
-  else if (signStr.compare_lower("s") || signStr.compare_lower("signed"))
+  else if (signStr.compare_insensitive("s") || signStr.compare_insensitive("signed"))
     result = TestIntegerType::SignednessSemantics::Signed;
-  else if (signStr.compare_lower("n") || signStr.compare_lower("none"))
+  else if (signStr.compare_insensitive("n") || signStr.compare_insensitive("none"))
     result = TestIntegerType::SignednessSemantics::Signless;
   else
     return parser.emitError(loc, "expected signed, unsigned, or none");