[PATCH] D25339: [PGO] Create weak alias for the renamed Comdat function

[Rong Xu via llvm-commits]

xur created this revision.
xur added a reviewer: davidxl.
xur added a subscriber: llvm-commits.

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.


https://reviews.llvm.org/D25339

Files:
  lib/Transforms/Instrumentation/PGOInstrumentation.cpp
  test/Transforms/PGOProfile/comdat_rename.ll


Index: test/Transforms/PGOProfile/comdat_rename.ll
===================================================================
--- test/Transforms/PGOProfile/comdat_rename.ll
+++ test/Transforms/PGOProfile/comdat_rename.ll
@@ -50,6 +50,12 @@
 
 ; 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() {
Index: lib/Transforms/Instrumentation/PGOInstrumentation.cpp
===================================================================
--- lib/Transforms/Instrumentation/PGOInstrumentation.cpp
+++ lib/Transforms/Instrumentation/PGOInstrumentation.cpp
@@ -439,9 +439,11 @@
 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 @@
     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.


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