[SampleFDO] Add use-sample-profile function attribute.

When sampleFDO is enabled, people may expect they can use
-fno-profile-sample-use to opt-out using sample profile for a certain file.
That could be either for debugging purpose or for performance tuning purpose.
However, when thinlto is enabled, if a function in file A compiled with
-fno-profile-sample-use is imported to another file B compiled with
-fprofile-sample-use, the inlined copy of the function in file B may still
get its profile annotated.

The inconsistency may even introduce profile unused warning because if the
target is not compiled with explicit debug information flag, the function
in file A won't have its debug information enabled (debug information will
be enabled implicitly only when -fprofile-sample-use is used). After it is
imported into file B which is compiled with -fprofile-sample-use, profile
annotation for the outline copy of the function will fail because the
function has no debug information, and that will trigger  profile unused
warning.

We add a new attribute use-sample-profile to control whether a function
will use its sample profile no matter for its outline or inline copies.
That will make the behavior of -fno-profile-sample-use consistent.

Differential Revision: https://reviews.llvm.org/D79959

1 files changed, 3 insertions, 0 deletions

diff --git a/clang/lib/CodeGen/CodeGenFunction.cpp b/clang/lib/CodeGen/CodeGenFunction.cpp
index d6622a4..0fa795d 100644
--- a/clang/lib/CodeGen/CodeGenFunction.cpp
+++ b/clang/lib/CodeGen/CodeGenFunction.cpp
@@ -791,6 +791,9 @@ void CodeGenFunction::StartFunction(GlobalDecl GD, QualType RetTy,
   if (CGM.getCodeGenOpts().ProfileSampleAccurate)
     Fn->addFnAttr("profile-sample-accurate");
 
+  if (!CGM.getCodeGenOpts().SampleProfileFile.empty())
+    Fn->addFnAttr("use-sample-profile");
+
   if (D && D->hasAttr<CFICanonicalJumpTableAttr>())
     Fn->addFnAttr("cfi-canonical-jump-table");