[PGO] Create weak alias for the renamed Comdat function

Add a weak alias to the renamed Comdat function in IR level instrumentation,
using it's original name. This ensures the same behavior w/ and w/o IR
instrumentation, even for non standard conforming code.

Differential Revision: http://reviews.llvm.org/D25339


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@283490 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/Instrumentation/PGOInstrumentation.cpp

@@ -439,9 +439,11 @@ template <class Edge, class BBInfo>
 void FuncPGOInstrumentation<Edge, BBInfo>::renameComdatFunction() {
   if (!canRenameComdat(F, ComdatMembers))
     return;
+  std::string OrigName = F.getName().str();
   std::string NewFuncName =
       Twine(F.getName() + "." + Twine(FunctionHash)).str();
   F.setName(Twine(NewFuncName));
+  GlobalAlias::create(GlobalValue::WeakAnyLinkage, OrigName, &F);
   FuncName = Twine(FuncName + "." + Twine(FunctionHash)).str();
   Comdat *NewComdat;
   Module *M = F.getParent();
@@ -467,7 +469,9 @@ void FuncPGOInstrumentation<Edge, BBInfo>::renameComdatFunction() {
     if (GlobalAlias *GA = dyn_cast<GlobalAlias>(CM.second)) {
       // For aliases, change the name directly.
       assert(dyn_cast<Function>(GA->getAliasee()->stripPointerCasts()) == &F);
+      std::string OrigGAName = GA->getName().str();
       GA->setName(Twine(GA->getName() + "." + Twine(FunctionHash)));
+      GlobalAlias::create(GlobalValue::WeakAnyLinkage, OrigGAName, GA);
       continue;
     }
     // Must be a function.

test/Transforms/PGOProfile/comdat_rename.ll

@@ -50,6 +50,12 @@ define linkonce_odr void @f_with_alias() comdat($f_with_alias) {
 
 ; Rename AvailableExternallyLinkage functions
 ; ELFONLY-DAG: $aef.[[SINGLEBB_HASH]] = comdat any
+
+; ELFONLY: @f = weak alias void (), void ()* @f.[[SINGLEBB_HASH]]
+; ELFONLY: @f_with_alias = weak alias void (), void ()* @f_with_alias.[[SINGLEBB_HASH]]
+; ELFONLY: @af = weak alias void (...), void (...)* @af.[[SINGLEBB_HASH]]
+; ELFONLY: @aef = weak alias void (), void ()* @aef.[[SINGLEBB_HASH]]
+
 define available_externally void @aef() {
 ; ELFONLY: define linkonce_odr void @aef.[[SINGLEBB_HASH]]() comdat {
 ; COFFONLY: define available_externally void @aef() {