Index: include/clang/Basic/Sanitizers.def
===================================================================
--- include/clang/Basic/Sanitizers.def
+++ include/clang/Basic/Sanitizers.def
@@ -114,6 +114,11 @@
 SANITIZER("local-bounds", LocalBounds)
 SANITIZER_GROUP("bounds", Bounds, ArrayBounds | LocalBounds)
 
+// EfficiencySanitizer
+SANITIZER("efficiency-cache-frag", EfficiencyCacheFrag)
+// Meta-group only used internally.
+SANITIZER_GROUP("efficiency-all", Efficiency, EfficiencyCacheFrag)
+
 // Magic group, containing all sanitizers. For example, "-fno-sanitize=all"
 // can be used to disable all the sanitizers.
 SANITIZER_GROUP("all", All, ~0ULL)
Index: include/clang/Driver/SanitizerArgs.h
===================================================================
--- include/clang/Driver/SanitizerArgs.h
+++ include/clang/Driver/SanitizerArgs.h
@@ -58,6 +58,9 @@
   bool needsCfiRt() const;
   bool needsCfiDiagRt() const;
   bool needsStatsRt() const { return Stats; }
+  bool needsEsanRt() const {
+    return Sanitizers.hasOneOf(SanitizerKind::Efficiency);
+  }
 
   bool requiresPIE() const;
   bool needsUnwindTables() const;
Index: lib/CodeGen/BackendUtil.cpp
===================================================================
--- lib/CodeGen/BackendUtil.cpp
+++ lib/CodeGen/BackendUtil.cpp
@@ -248,6 +248,17 @@
   PM.add(createDataFlowSanitizerPass(LangOpts.SanitizerBlacklistFiles));
 }
 
+static void addEfficiencySanitizerPass(const PassManagerBuilder &Builder,
+                                       legacy::PassManagerBase &PM) {
+  const PassManagerBuilderWrapper &BuilderWrapper =
+      static_cast<const PassManagerBuilderWrapper&>(Builder);
+  const LangOptions &LangOpts = BuilderWrapper.getLangOpts();
+  EfficiencySanitizerOptions Opts;
+  if (LangOpts.Sanitize.has(SanitizerKind::EfficiencyCacheFrag))
+    Opts.ToolType = EfficiencySanitizerOptions::ESAN_CacheFrag;
+  PM.add(createEfficiencySanitizerPass(Opts));
+}
+
 static TargetLibraryInfoImpl *createTLII(llvm::Triple &TargetTriple,
                                          const CodeGenOptions &CodeGenOpts) {
   TargetLibraryInfoImpl *TLII = new TargetLibraryInfoImpl(TargetTriple);
@@ -407,6 +418,13 @@
                            addDataFlowSanitizerPass);
   }
 
+  if (LangOpts.Sanitize.hasOneOf(SanitizerKind::Efficiency)) {
+    PMBuilder.addExtension(PassManagerBuilder::EP_OptimizerLast,
+                           addEfficiencySanitizerPass);
+    PMBuilder.addExtension(PassManagerBuilder::EP_EnabledOnOptLevel0,
+                           addEfficiencySanitizerPass);
+  }
+
   // Set up the per-function pass manager.
   legacy::FunctionPassManager *FPM = getPerFunctionPasses();
   if (CodeGenOpts.VerifyModule)
Index: lib/Driver/SanitizerArgs.cpp
===================================================================
--- lib/Driver/SanitizerArgs.cpp
+++ lib/Driver/SanitizerArgs.cpp
@@ -693,6 +693,10 @@
     if (A->getOption().matches(options::OPT_fsanitize_EQ) &&
         0 == strcmp("all", Value))
       Kind = 0;
+    // Similarly, don't accept -fsanitize=efficiency-all.
+    else if (A->getOption().matches(options::OPT_fsanitize_EQ) &&
+        0 == strcmp("efficiency-all", Value))
+      Kind = 0;
     else
       Kind = parseSanitizerValue(Value, /*AllowGroups=*/true);
 
Index: lib/Driver/ToolChains.cpp
===================================================================
--- lib/Driver/ToolChains.cpp
+++ lib/Driver/ToolChains.cpp
@@ -422,6 +422,8 @@
                       /*AlwaysLink=*/true);
     AddLinkSanitizerLibArgs(Args, CmdArgs, "stats");
   }
+  if (Sanitize.needsEsanRt())
+    AddLinkSanitizerLibArgs(Args, CmdArgs, "esan");
 
   // Otherwise link libSystem, then the dynamic runtime library, and finally any
   // target specific static runtime library.
@@ -4149,6 +4151,8 @@
     Res |= SanitizerKind::Thread;
   if (IsX86_64 || IsMIPS64 || IsPowerPC64 || IsAArch64)
     Res |= SanitizerKind::Memory;
+  if (IsX86_64)
+    Res |= SanitizerKind::Efficiency;
   if (IsX86 || IsX86_64) {
     Res |= SanitizerKind::Function;
   }
Index: lib/Driver/Tools.cpp
===================================================================
--- lib/Driver/Tools.cpp
+++ lib/Driver/Tools.cpp
@@ -3006,6 +3006,8 @@
     NonWholeStaticRuntimes.push_back("stats");
     RequiredSymbols.push_back("__sanitizer_stats_register");
   }
+  if (SanArgs.needsEsanRt())
+    StaticRuntimes.push_back("esan");
 }
 
 // Should be called before we add system libraries (C++ ABI, libstdc++/libc++,
Index: lib/Lex/PPMacroExpansion.cpp
===================================================================
--- lib/Lex/PPMacroExpansion.cpp
+++ lib/Lex/PPMacroExpansion.cpp
@@ -1100,6 +1100,8 @@
       .Case("memory_sanitizer", LangOpts.Sanitize.has(SanitizerKind::Memory))
       .Case("thread_sanitizer", LangOpts.Sanitize.has(SanitizerKind::Thread))
       .Case("dataflow_sanitizer", LangOpts.Sanitize.has(SanitizerKind::DataFlow))
+      .Case("efficiency_sanitizer",
+            LangOpts.Sanitize.hasOneOf(SanitizerKind::Efficiency))
       // Objective-C features
       .Case("objc_arr", LangOpts.ObjCAutoRefCount) // FIXME: REMOVE?
       .Case("objc_arc", LangOpts.ObjCAutoRefCount)