Index: cfe/trunk/include/clang/Driver/Options.td
===================================================================
--- cfe/trunk/include/clang/Driver/Options.td
+++ cfe/trunk/include/clang/Driver/Options.td
@@ -1858,6 +1858,8 @@
   Flags<[CC1Option]>,
   HelpText<"Use copy relocations support for PIE builds">;
 def mno_pie_copy_relocations : Flag<["-"], "mno-pie-copy-relocations">, Group<m_Group>;
+def mfentry : Flag<["-"], "mfentry">, HelpText<"insert calls to fentry at function entry (x86 only)">,
+  Flags<[CC1Option]>, Group<m_Group>;
 def mx87 : Flag<["-"], "mx87">, Group<m_x86_Features_Group>;
 def m80387 : Flag<["-"], "m80387">, Alias<mx87>;
 def msse2 : Flag<["-"], "msse2">, Group<m_x86_Features_Group>;
Index: cfe/trunk/include/clang/Frontend/CodeGenOptions.def
===================================================================
--- cfe/trunk/include/clang/Frontend/CodeGenOptions.def
+++ cfe/trunk/include/clang/Frontend/CodeGenOptions.def
@@ -83,6 +83,7 @@
 VALUE_CODEGENOPT(XRayInstructionThreshold , 32, 200)
 
 CODEGENOPT(InstrumentForProfiling , 1, 0) ///< Set when -pg is enabled.
+CODEGENOPT(CallFEntry , 1, 0) ///< Set when -mfentry is enabled.
 CODEGENOPT(LessPreciseFPMAD  , 1, 0) ///< Enable less precise MAD instructions to
                                      ///< be generated.
 CODEGENOPT(PrepareForLTO     , 1, 0) ///< Set when -flto is enabled on the
Index: cfe/trunk/lib/CodeGen/CodeGenFunction.cpp
===================================================================
--- cfe/trunk/lib/CodeGen/CodeGenFunction.cpp
+++ cfe/trunk/lib/CodeGen/CodeGenFunction.cpp
@@ -860,8 +860,12 @@
   // inlining, we just add an attribute to insert a mcount call in backend.
   // The attribute "counting-function" is set to mcount function name which is
   // architecture dependent.
-  if (CGM.getCodeGenOpts().InstrumentForProfiling)
-    Fn->addFnAttr("counting-function", getTarget().getMCountName());
+  if (CGM.getCodeGenOpts().InstrumentForProfiling) {
+    if (CGM.getCodeGenOpts().CallFEntry)
+      Fn->addFnAttr("fentry-call", "true");
+    else
+      Fn->addFnAttr("counting-function", getTarget().getMCountName());
+  }
 
   if (RetTy->isVoidType()) {
     // Void type; nothing to return.
Index: cfe/trunk/lib/Driver/Tools.cpp
===================================================================
--- cfe/trunk/lib/Driver/Tools.cpp
+++ cfe/trunk/lib/Driver/Tools.cpp
@@ -5483,6 +5483,9 @@
   if (getToolChain().SupportsProfiling())
     Args.AddLastArg(CmdArgs, options::OPT_pg);
 
+  if (getToolChain().SupportsProfiling())
+    Args.AddLastArg(CmdArgs, options::OPT_mfentry);
+
   // -flax-vector-conversions is default.
   if (!Args.hasFlag(options::OPT_flax_vector_conversions,
                     options::OPT_fno_lax_vector_conversions))
Index: cfe/trunk/lib/Frontend/CompilerInvocation.cpp
===================================================================
--- cfe/trunk/lib/Frontend/CompilerInvocation.cpp
+++ cfe/trunk/lib/Frontend/CompilerInvocation.cpp
@@ -717,6 +717,7 @@
   Opts.XRayInstructionThreshold =
       getLastArgIntValue(Args, OPT_fxray_instruction_threshold_, 200, Diags);
   Opts.InstrumentForProfiling = Args.hasArg(OPT_pg);
+  Opts.CallFEntry = Args.hasArg(OPT_mfentry);
   Opts.EmitOpenCLArgMetadata = Args.hasArg(OPT_cl_kernel_arg_info);
   Opts.CompressDebugSections = Args.hasArg(OPT_compress_debug_sections);
   Opts.RelaxELFRelocations = Args.hasArg(OPT_mrelax_relocations);
Index: cfe/trunk/test/CodeGen/fentry.c
===================================================================
--- cfe/trunk/test/CodeGen/fentry.c
+++ cfe/trunk/test/CodeGen/fentry.c
@@ -0,0 +1,11 @@
+// RUN: %clang_cc1 -pg -mfentry -triple i386-unknown-unknown -emit-llvm -o - %s | FileCheck  %s
+// RUN: %clang_cc1 -pg -mfentry -triple x86_64-unknown-linux-gnu -emit-llvm -o - %s | FileCheck %s
+// RUN: %clang_cc1 -mfentry -triple i386-unknown-unknown -emit-llvm -o - %s | FileCheck -check-prefix=NOPG %s
+// RUN: %clang_cc1 -mfentry -triple x86_64-unknown-linux-gnu -emit-llvm -o - %s | FileCheck -check-prefix=NOPG %s
+
+int foo(void) {
+  return 0;
+}
+
+//CHECK: attributes #{{[0-9]+}} = { {{.*}}"fentry-call"="true"{{.*}} }
+//NOPG-NOT: attributes #{{[0-9]+}} = { {{.*}}"fentry-call"{{.*}} }