Fix return status of AtomicExpandPass

[serge-sans-paille]

Summary

Correctly reflect change in the return status.

Patch needed to land https://reviews.llvm.org/D80916

[foad]

Looks obviously correct. Might be slightly neater to change expandPartwordCmpXchg to return true, like expandAtomicCmpXchg does?

llvm/lib/CodeGen/AtomicExpandPass.cpp

insertRMWLLSCLoop(IRBuilder<> &Builder, Type *ResultTy, Value *Addr,
                       function_ref<Value *(IRBuilder<> &, Value *)> PerformOp);
     void expandAtomicOpToLLSC(
         Instruction *I, Type *ResultTy, Value *Addr, AtomicOrdering MemOpOrder,
         function_ref<Value *(IRBuilder<> &, Value *)> PerformOp);
     void expandPartwordAtomicRMW(
         AtomicRMWInst *I,
         TargetLoweringBase::AtomicExpansionKind ExpansionKind);
     AtomicRMWInst *widenPartwordAtomicRMW(AtomicRMWInst *AI);
-    void expandPartwordCmpXchg(AtomicCmpXchgInst *I);
+    bool expandPartwordCmpXchg(AtomicCmpXchgInst *I);
     void expandAtomicRMWToMaskedIntrinsic(AtomicRMWInst *AI);
     void expandAtomicCmpXchgToMaskedIntrinsic(AtomicCmpXchgInst *CI);
 
     AtomicCmpXchgInst *convertCmpXchgToIntegerType(AtomicCmpXchgInst *CI);
     static Value *insertRMWCmpXchgLoop(
         IRBuilder<> &Builder, Type *ResultType, Value *Addr,
         AtomicOrdering MemOpOrder,
         function_ref<Value *(IRBuilder<> &, Value *)> PerformOp,
AtomicRMWInst *NewAI = Builder.CreateAtomicRMW(Op, PMV.AlignedAddr,
                                                  NewOperand, AI->getOrdering());
 
   Value *FinalOldResult = extractMaskedValue(Builder, NewAI, PMV);
   AI->replaceAllUsesWith(FinalOldResult);
   AI->eraseFromParent();
   return NewAI;
 }
 
-void AtomicExpand::expandPartwordCmpXchg(AtomicCmpXchgInst *CI) {
+bool AtomicExpand::expandPartwordCmpXchg(AtomicCmpXchgInst *CI) {
   // The basic idea here is that we're expanding a cmpxchg of a
   // smaller memory size up to a word-sized cmpxchg. To do this, we
   // need to add a retry-loop for strong cmpxchg, so that
   // modifications to other parts of the word don't cause a spurious
   // failure.
 
   // This generates code like the following:
   //     [[Setup mask values PMV.*]]
bool AtomicExpand::expandPartwordCmpXchg(AtomicCmpXchgInst *CI) {
 
   Value *FinalOldVal = extractMaskedValue(Builder, OldVal, PMV);
   Value *Res = UndefValue::get(CI->getType());
   Res = Builder.CreateInsertValue(Res, FinalOldVal, 0);
   Res = Builder.CreateInsertValue(Res, Success, 1);
 
   CI->replaceAllUsesWith(Res);
   CI->eraseFromParent();
+  return true;
 }
 
 void AtomicExpand::expandAtomicOpToLLSC(
     Instruction *I, Type *ResultType, Value *Addr, AtomicOrdering MemOpOrder,
     function_ref<Value *(IRBuilder<> &, Value *)> PerformOp) {
   IRBuilder<> Builder(I);
   Value *Loaded =
       insertRMWLLSCLoop(Builder, ResultType, Addr, MemOpOrder, PerformOp);
bool AtomicExpand::tryExpandAtomicCmpXchg(AtomicCmpXchgInst *CI) {
   unsigned MinCASSize = TLI->getMinCmpXchgSizeInBits() / 8;
   unsigned ValueSize = getAtomicOpSize(CI);
 
   switch (TLI->shouldExpandAtomicCmpXchgInIR(CI)) {
   default:
     llvm_unreachable("Unhandled case in tryExpandAtomicCmpXchg");
   case TargetLoweringBase::AtomicExpansionKind::None:
     if (ValueSize < MinCASSize)
-      expandPartwordCmpXchg(CI);
+      return expandPartwordCmpXchg(CI);
     return false;
   case TargetLoweringBase::AtomicExpansionKind::LLSC: {
     return expandAtomicCmpXchg(CI);
   }
   case TargetLoweringBase::AtomicExpansionKind::MaskedIntrinsic:
     expandAtomicCmpXchgToMaskedIntrinsic(CI);
     return true;
   }