[PGO] Delete dead comdat renaming code related to GlobalAlias. NFC

[MaskRay]

Summary

A GlobalAlias is an address-taken user of its aliased function.
canRenameComdatFunc has excluded such cases.

[davidxl]

lgtm

llvm/lib/Transforms/Instrumentation/PGOInstrumentation.cpp

 // Check if we can safely rename this Comdat function.
 static bool canRenameComdat(
     Function &F,
     std::unordered_multimap<Comdat *, GlobalValue *> &ComdatMembers) {
   if (!DoComdatRenaming || !canRenameComdatFunc(F, true))
     return false;
 
   // FIXME: Current only handle those Comdat groups that only containing one
-  // function and function aliases.
+  // function.
   // (1) For a Comdat group containing multiple functions, we need to have a
   // unique postfix based on the hashes for each function. There is a
   // non-trivial code refactoring to do this efficiently.
   // (2) Variables can not be renamed, so we can not rename Comdat function in a
   // group including global vars.
   Comdat *C = F.getComdat();
   for (auto &&CM : make_range(ComdatMembers.equal_range(C))) {
-    if (dyn_cast<GlobalAlias>(CM.second))
-      continue;
+    assert(!isa<GlobalAlias>(CM.second));
     Function *FM = dyn_cast<Function>(CM.second);
     if (FM != &F)
       return false;
   }
   return true;
 }
 
 // Append the CFGHash to the Comdat function name.
void FuncPGOInstrumentation<Edge, BBInfo>::renameComdatFunction() {
   // This function belongs to a single function Comdat group.
   Comdat *OrigComdat = F.getComdat();
   std::string NewComdatName =
       Twine(OrigComdat->getName() + "." + Twine(FunctionHash)).str();
   NewComdat = M->getOrInsertComdat(StringRef(NewComdatName));
   NewComdat->setSelectionKind(OrigComdat->getSelectionKind());
 
   for (auto &&CM : make_range(ComdatMembers.equal_range(OrigComdat))) {
-    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.
-    Function *CF = dyn_cast<Function>(CM.second);
-    assert(CF);
-    CF->setComdat(NewComdat);
+    cast<Function>(CM.second)->setComdat(NewComdat);
   }
 }
 
 // Collect all the BBs that will be instruments and return them in
 // InstrumentBBs and setup InEdges/OutEdge for UseBBInfo.
 template <class Edge, class BBInfo>
 void FuncPGOInstrumentation<Edge, BBInfo>::getInstrumentBBs(
     std::vector<BasicBlock *> &InstrumentBBs) {

llvm/test/Transforms/PGOProfile/comdat_rename.ll

 ; RUN: opt < %s -mtriple=x86_64-unknown-linux -pgo-instr-gen -do-comdat-renaming=true -S | FileCheck %s
 ; RUN: opt < %s -mtriple=x86_64-unknown-linux -passes=pgo-instr-gen -do-comdat-renaming=true -S | FileCheck %s
 ; RUN: opt < %s -mtriple=x86_64-pc-win32-coff -pgo-instr-gen -do-comdat-renaming=true -S | FileCheck %s
 ; RUN: opt < %s -mtriple=x86_64-pc-win32-coff -passes=pgo-instr-gen -do-comdat-renaming=true -S | FileCheck %s
 
 ; Rename Comdat group and its function.
 $f = comdat any
 ; CHECK: $f.[[SINGLEBB_HASH:[0-9]+]] = comdat any
 define linkonce_odr void @f() comdat($f) {
   ret void
 }
 
+; Not rename Comdat with an alias (an alias is an address-taken user).
+$f_with_alias = comdat any
+; CHECK: $f_with_alias = comdat any
+define linkonce_odr void @f_with_alias() comdat {
+  ret void
+}
+@f_alias = alias void (), void ()* @f_with_alias
+
 ; Not rename Comdat with right linkage.
 $nf = comdat any
 ; CHECK: $nf = comdat any
 define void @nf() comdat($nf) {
   ret void
 }
 
 ; Not rename Comdat with variable members.