Use profile info to set function section prefix to group hot/cold functions.

Summary:
The original implementation is in r261607, which was reverted in r269726 to accomendate the ProfileSummaryInfo analysis pass. The new implementation:
1. add a new metadata for function section prefix
2. query against ProfileSummaryInfo in CGP to set the correct section prefix for each function
3. output the section prefix set by CGP

Reviewers: davidxl, eraman

Subscribers: vsk, llvm-commits

Differential Revision: https://reviews.llvm.org/D24989

llvm-svn: 284533

1 files changed, 6 insertions, 2 deletions

diff --git a/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp b/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
index edaa778a605..91cee337c98 100644
--- a/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
+++ b/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
@@ -296,8 +296,12 @@ selectELFSectionForGlobal(MCContext &Ctx, const GlobalValue *GV,
   } else {
     Name = getSectionPrefixForGlobal(Kind);
   }
-  // FIXME: Extend the section prefix to include hotness catagories such as .hot
-  //  or .unlikely for functions.
+
+  if (const Function *F = dyn_cast<Function>(GV)) {
+    const auto &OptionalPrefix = F->getSectionPrefix();
+    if (OptionalPrefix)
+      Name += *OptionalPrefix;
+  }
 
   if (EmitUniqueSection && UniqueSectionNames) {
     Name.push_back('.');