[PGO] Make needsComdatForCounter() available (NFC)

Move needsComdatForCounter() to lib/ProfileData/InstrProf.cpp from
lib/Transforms/Instrumentation/InstrProfiling.cpp to make is available for
other files.

Differential Revision: https://reviews.llvm.org/D22643

llvm-svn: 276330

1 files changed, 26 insertions, 0 deletions

diff --git a/llvm/lib/ProfileData/InstrProf.cpp b/llvm/lib/ProfileData/InstrProf.cpp
index 6962f82a5ef..a0400721166 100644
--- a/llvm/lib/ProfileData/InstrProf.cpp
+++ b/llvm/lib/ProfileData/InstrProf.cpp
@@ -14,6 +14,7 @@
 
 #include "llvm/ProfileData/InstrProf.h"
 #include "llvm/ADT/StringExtras.h"
+#include "llvm/ADT/Triple.h"
 #include "llvm/IR/Constants.h"
 #include "llvm/IR/Function.h"
 #include "llvm/IR/GlobalVariable.h"
@@ -780,4 +781,29 @@ void createPGOFuncNameMetadata(Function &F, StringRef PGOFuncName) {
   F.setMetadata(getPGOFuncNameMetadataName(), N);
 }
 
+bool needsComdatForCounter(const Function &F, const Module &M) {
+  if (F.hasComdat())
+    return true;
+
+  Triple TT(M.getTargetTriple());
+  if (!TT.isOSBinFormatELF())
+    return false;
+
+  // See createPGOFuncNameVar for more details. To avoid link errors, profile
+  // counters for function with available_externally linkage needs to be changed
+  // to linkonce linkage. On ELF based systems, this leads to weak symbols to be
+  // created. Without using comdat, duplicate entries won't be removed by the
+  // linker leading to increased data segement size and raw profile size. Even
+  // worse, since the referenced counter from profile per-function data object
+  // will be resolved to the common strong definition, the profile counts for
+  // available_externally functions will end up being duplicated in raw profile
+  // data. This can result in distorted profile as the counts of those dups
+  // will be accumulated by the profile merger.
+  GlobalValue::LinkageTypes Linkage = F.getLinkage();
+  if (Linkage != GlobalValue::ExternalWeakLinkage &&
+      Linkage != GlobalValue::AvailableExternallyLinkage)
+    return false;
+
+  return true;
+}
 } // end namespace llvm