Index: llvm/docs/CommandGuide/FileCheck.rst
===================================================================
--- llvm/docs/CommandGuide/FileCheck.rst
+++ llvm/docs/CommandGuide/FileCheck.rst
@@ -71,6 +71,11 @@
  The :option:`--strict-whitespace` argument disables this behavior. End-of-line
  sequences are canonicalized to UNIX-style ``\n`` in all modes.
 
+.. option:: --ignore-case
+
+  By default, FileCheck uses case-sensitive matching. This option causes
+  FileCheck to use case-insensitive matching.
+
 .. option:: --implicit-check-not check-pattern
 
   Adds implicit negative checks for the specified patterns between positive
Index: llvm/include/llvm/Support/FileCheck.h
===================================================================
--- llvm/include/llvm/Support/FileCheck.h
+++ llvm/include/llvm/Support/FileCheck.h
@@ -30,6 +30,7 @@
   std::vector<std::string> GlobalDefines;
   bool AllowEmptyInput = false;
   bool MatchFullLines = false;
+  bool IgnoreCase = false;
   bool EnableVarScope = false;
   bool AllowDeprecatedDagOverlap = false;
   bool Verbose = false;
Index: llvm/lib/Support/FileCheck.cpp
===================================================================
--- llvm/lib/Support/FileCheck.cpp
+++ llvm/lib/Support/FileCheck.cpp
@@ -320,6 +320,7 @@
                                     SourceMgr &SM,
                                     const FileCheckRequest &Req) {
   bool MatchFullLinesHere = Req.MatchFullLines && CheckTy != Check::CheckNot;
+  IgnoreCase = Req.IgnoreCase;
 
   PatternLoc = SMLoc::getFromPointer(PatternStr.data());
 
@@ -619,7 +620,8 @@
   // If this is a fixed string pattern, just match it now.
   if (!FixedStr.empty()) {
     MatchLen = FixedStr.size();
-    size_t Pos = Buffer.find(FixedStr);
+    size_t Pos = IgnoreCase ? Buffer.find_lower(FixedStr)
+                            : Buffer.find(FixedStr);
     if (Pos == StringRef::npos)
       return make_error<FileCheckNotFoundError>();
     return Pos;
@@ -657,7 +659,10 @@
   }
 
   SmallVector<StringRef, 4> MatchInfo;
-  if (!Regex(RegExToMatch, Regex::Newline).match(Buffer, &MatchInfo))
+  unsigned int Flags = Regex::Newline;
+  if (IgnoreCase)
+    Flags |= Regex::IgnoreCase;
+  if (!Regex(RegExToMatch, Flags).match(Buffer, &MatchInfo))
     return make_error<FileCheckNotFoundError>();
 
   // Successful regex match.
Index: llvm/lib/Support/FileCheckImpl.h
===================================================================
--- llvm/lib/Support/FileCheckImpl.h
+++ llvm/lib/Support/FileCheckImpl.h
@@ -428,6 +428,9 @@
   /// line to the one with this CHECK.
   Optional<size_t> LineNumber;
 
+  /// Ignore case while matching if set to true.
+  bool IgnoreCase = false;
+
 public:
   FileCheckPattern(Check::FileCheckType Ty, FileCheckPatternContext *Context,
                    Optional<size_t> Line = None)
Index: llvm/test/FileCheck/check-ignore-case.txt
===================================================================
--- /dev/null
+++ llvm/test/FileCheck/check-ignore-case.txt
@@ -0,0 +1,22 @@
+# RUN: FileCheck -ignore-case -match-full-lines -check-prefix=FULL -input-file %s %s
+# RUN: FileCheck -ignore-case -check-prefix=REGEX -input-file %s %s
+# RUN: FileCheck -ignore-case -check-prefix=PAT -DPATTERN="THIS is the" -input-file %s %s
+# RUN: FileCheck -ignore-case -input-file %s %s
+
+this is the STRING to be matched
+
+# FULL: tHis iS The String TO be matched
+# REGEX: s{{TRing}}
+# PAT: [[PATTERN]] string
+
+Loop 1
+lOop 2
+loOp 3
+looP 4
+loop 5
+LOOP 5
+BREAK
+
+# CHECK-COUNT-6: LOop {{[0-9]}}
+# CHECK-NOT: loop
+# CHECK-NEXT: break
\ No newline at end of file
Index: llvm/utils/FileCheck/FileCheck.cpp
===================================================================
--- llvm/utils/FileCheck/FileCheck.cpp
+++ llvm/utils/FileCheck/FileCheck.cpp
@@ -48,6 +48,10 @@
     "strict-whitespace",
     cl::desc("Do not treat all horizontal whitespace as equivalent"));
 
+static cl::opt<bool> IgnoreCase(
+    "ignore-case",
+    cl::desc("Ignore case in comparisons"));
+
 static cl::list<std::string> ImplicitCheckNot(
     "implicit-check-not",
     cl::desc("Add an implicit negative check with this pattern to every\n"
@@ -555,6 +559,7 @@
   Req.VerboseVerbose = VerboseVerbose;
   Req.NoCanonicalizeWhiteSpace = NoCanonicalizeWhiteSpace;
   Req.MatchFullLines = MatchFullLines;
+  Req.IgnoreCase = IgnoreCase;
 
   if (VerboseVerbose)
     Req.Verbose = true;