+ // Setup the builder so we can create any PHIs we need.
+ Builder.SetInsertPoint(ExitBB, ExitBB->begin());
+ PHINode *Success = Builder.CreatePHI(Type::getInt1Ty(Ctx), 2);
+ Success->addIncoming(ConstantInt::getTrue(Ctx), SuccessBB);
+ Success->addIncoming(ConstantInt::getFalse(Ctx), FailureBB);
+
+ // Look for any users of the cmpxchg that are just comparing the loaded value
+ // against the desired one, and replace them with the CFG-derived version.
+ SmallVector<ExtractValueInst *, 2> PrunedInsts;
+ for (auto User : CI->users()) {
+ ExtractValueInst *EV = dyn_cast<ExtractValueInst>(User);
+ if (!EV)
+ continue;
+
+ assert(EV->getNumIndices() == 1 && EV->getIndices()[0] <= 1 &&
+ "weird extraction from { iN, i1 }");
+
+ if (EV->getIndices()[0] == 0)
+ EV->replaceAllUsesWith(Loaded);
+ else
+ EV->replaceAllUsesWith(Success);
+
+ PrunedInsts.push_back(EV);
+ }
+
+ // We can remove the instructions now we're no longer iterating through them.
+ for (auto EV : PrunedInsts)
+ EV->eraseFromParent();
+
+ if (!CI->use_empty()) {
+ // Some use of the full struct return that we don't understand has happened,
+ // so we've got to reconstruct it properly.
+ Value *Res;
+ Res = Builder.CreateInsertValue(UndefValue::get(CI->getType()), Loaded, 0);
+ Res = Builder.CreateInsertValue(Res, Success, 1);
+
+ CI->replaceAllUsesWith(Res);
+ }
+
+ CI->eraseFromParent();