[Profile] Use a flag to enable PGO rather than the profraw filename.

[jakev]

Summary

Enable instrumentation using a flag rather than the profile filename.

This is the other half of:
https://reviews.llvm.org/D22607

[davidxl]

lgtm

lib/CodeGen/BackendUtil.cpp

void EmitAssemblyHelper::CreatePasses(legacy::PassManager &MPM,
 
   if (CodeGenOpts.hasProfileClangInstr()) {
     InstrProfOptions Options;
     Options.NoRedZone = CodeGenOpts.DisableRedZone;
     Options.InstrProfileOutput = CodeGenOpts.InstrProfileOutput;
     MPM.add(createInstrProfilingLegacyPass(Options));
   }
   if (CodeGenOpts.hasProfileIRInstr()) {
+    PMBuilder.EnablePGOInstrGen = true;
     if (!CodeGenOpts.InstrProfileOutput.empty())
       PMBuilder.PGOInstrGen = CodeGenOpts.InstrProfileOutput;
-    else
-      PMBuilder.PGOInstrGen = "default.profraw";
   }
   if (CodeGenOpts.hasProfileIRUse())
     PMBuilder.PGOInstrUse = CodeGenOpts.ProfileInstrumentUsePath;
 
   if (!CodeGenOpts.SampleProfileFile.empty()) {
     MPM.add(createPruneEHPass());
     MPM.add(createSampleProfileLoaderPass(CodeGenOpts.SampleProfileFile));
     PMBuilder.addExtension(PassManagerBuilder::EP_EarlyAsPossible,

test/Profile/gcc-flag-compatibility.c

 // Tests for -fprofile-generate and -fprofile-use flag compatibility. These two
 // flags behave similarly to their GCC counterparts:
 //
 // -fprofile-generate         Generates the profile file ./default.profraw
 // -fprofile-generate=<dir>   Generates the profile file <dir>/default.profraw
 // -fprofile-use              Uses the profile file ./default.profdata
 // -fprofile-use=<dir>        Uses the profile file <dir>/default.profdata
 // -fprofile-use=<dir>/file   Uses the profile file <dir>/file
 
-// FIXME: IRPGO shouldn't use the override API when no profraw name is given.
-// Check that -fprofile-generate overrides the default profraw.
+// Check that -fprofile-generate doesn't use the override API.
 // RUN: %clang %s -c -S -o - -emit-llvm -fprofile-generate | FileCheck -check-prefix=PROFILE-GEN %s
-// PROFILE-GEN: call void @__llvm_profile_override_default_filename
-// PROFILE-GEN: declare void @__llvm_profile_override_default_filename(i8*)
+// PROFILE-GEN-NOT: call void @__llvm_profile_override_default_filename
+// PROFILE-GEN-NOT: declare void @__llvm_profile_override_default_filename(i8*)
 
 // Check that -fprofile-generate=/path/to generates /path/to/default.profraw
 // RUN: %clang %s -c -S -o - -emit-llvm -fprofile-generate=/path/to | FileCheck -check-prefix=PROFILE-GEN-EQ %s
 // PROFILE-GEN-EQ: private constant [25 x i8] c"/path/to{{/|\\5C}}default.profraw\00"
 // PROFILE-GEN-EQ: call void @__llvm_profile_override_default_filename(i8* getelementptr inbounds ([25 x i8], [25 x i8]* @0, i32 0, i32 0))
 // PROFILE-GEN-EQ: declare void @__llvm_profile_override_default_filename(i8*)
 
 // Check that -fprofile-use=some/path reads some/path/default.profdata