Set MemoryEffects of call only if called function is nomem

It make call close to constrained calls, where memory effects of the
calls do not define memory effects. It helps migration to operand
bundles.

Author: spavloff

llvm/lib/IR/IRBuilder.cpp

@@ -139,12 +139,13 @@ CallInst *IRBuilderBase::CreateCall(FunctionType *FTy, Value *Callee,
   // If the builder is in strictfp mode and has non-default options (like
   // non-dynamic rounding), add corresponding operand bundle. If such bundle is
   // already present, assume it overwrites defaults.
-  bool doesTheCallAccessFPEnv = false;
+  bool NeedUpdateMemoryEffects = false;
   if (IsFPConstrained) {
     if (const auto *Func = dyn_cast<Function>(Callee)) {
       if (Intrinsic::ID ID = Func->getIntrinsicID()) {
         if (IntrinsicInst::isFloatingPointOperation(ID)) {
-          doesTheCallAccessFPEnv = true;
+          MemoryEffects FME = Func->getMemoryEffects();
+          NeedUpdateMemoryEffects = !FME.doesAccessInaccessibleMem();
           bool NeedRound = DefaultConstrainedRounding != RoundingMode::Dynamic;
           bool NeedExcept = DefaultConstrainedExcept != fp::ebStrict;
           for (const auto &Item : OpBundles) {
@@ -166,10 +167,8 @@ CallInst *IRBuilderBase::CreateCall(FunctionType *FTy, Value *Callee,
 
   // If the call accesses FPE, update memory effects accordingly.
   CallInst *CI = CallInst::Create(FTy, Callee, Args, OpBundles);
-  if (doesTheCallAccessFPEnv) {
+  if (NeedUpdateMemoryEffects) {
     MemoryEffects ME = MemoryEffects::inaccessibleMemOnly();
-    if (CI->getAttributes().hasFnAttr(Attribute::Memory))
-      ME |= CI->getAttributes().getMemoryEffects();
     auto A = Attribute::getWithMemoryEffects(getContext(), ME);
     CI->addFnAttr(A);
   }