[InstCombine] Transform to undef incorrect atomic unordered mem intri…

…nsics

According to LangRef:
If len is not a positive integer multiple of element_size, then the behaviour of the intrinsic is undefined.

Add InstCombine rule to transform intrinsic to undef operation.

This is a follow-up for D76116.

Reviewers: reames
Reviewed By: reames
Subscribers: hiraditya, jfb, dantrushin, llvm-commits
Differential Revision: https://reviews.llvm.org/D76215

llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp

@@ -1806,6 +1806,18 @@ Instruction *InstCombiner::visitCallInst(CallInst &CI) {
   IntrinsicInst *II = dyn_cast<IntrinsicInst>(&CI);
   if (!II) return visitCallBase(CI);
 
+  // For atomic unordered mem intrinsics if len is not a positive or
+  // not a multiple of element size then behavior is undefined.
+  if (auto *AMI = dyn_cast<AtomicMemIntrinsic>(II))
+    if (ConstantInt *NumBytes = dyn_cast<ConstantInt>(AMI->getLength()))
+      if (NumBytes->getSExtValue() < 0 ||
+          (NumBytes->getZExtValue() % AMI->getElementSizeInBytes() != 0)) {
+        CreateNonTerminatorUnreachable(AMI);
+        assert(AMI->getType()->isVoidTy() &&
+               "non void atomic unordered mem intrinsic");
+        return eraseInstFromFunction(*AMI);
+      }
+
   // Intrinsics cannot occur in an invoke or a callbr, so handle them here
   // instead of in visitCallBase.
   if (auto *MI = dyn_cast<AnyMemIntrinsic>(II)) {

llvm/test/Transforms/InstCombine/element-atomic-memintrins.ll

@@ -415,4 +415,23 @@ define void @test_memcpy_loadstore_16(i8* %dest, i8* %src) {
   ret void
 }
 
+define void @test_undefined(i8* %dest, i8* %src) {
+; CHECK-LABEL: @test_undefined(
+entry:
+  br i1 undef, label %ok, label %undefined
+undefined:
+; CHECK: undefined:
+; CHECK-NEXT:    store i1 true, i1* undef
+; CHECK-NEXT:    br label %ok
+  call void @llvm.memcpy.element.unordered.atomic.p0i8.p0i8.i32(i8* align 16 %dest, i8* align 16 %src, i32 7, i32 4)
+  call void @llvm.memcpy.element.unordered.atomic.p0i8.p0i8.i32(i8* align 16 %dest, i8* align 16 %src, i32 -8, i32 4)
+  call void @llvm.memmove.element.unordered.atomic.p0i8.p0i8.i32(i8* align 16 %dest, i8* align 16 %src, i32 7, i32 4)
+  call void @llvm.memmove.element.unordered.atomic.p0i8.p0i8.i32(i8* align 16 %dest, i8* align 16 %src, i32 -8, i32 4)
+  call void @llvm.memset.element.unordered.atomic.p0i8.i32(i8* align 16 %dest, i8 1, i32 7, i32 4)
+  call void @llvm.memset.element.unordered.atomic.p0i8.i32(i8* align 16 %dest, i8 1, i32 -8, i32 4)
+  br label %ok
+ok:
+  ret void
+}
+
 declare void @llvm.memcpy.element.unordered.atomic.p0i8.p0i8.i32(i8* nocapture writeonly, i8* nocapture readonly, i32, i32) nounwind argmemonly