[Intrinsics] Added writeonly attribute to the first arg of llvm.memmove

D18714 introduced writeonly attribute:

"Also start using the attribute for memset, memcpy, and memmove intrinsics,
and remove their special-casing in BasicAliasAnalysis."

But actually, writeonly was not attached to memmove - oversight, it seems.

So let's add it. As we can see, this helps DSE to eliminate redundant stores.

Reviewed By: jdoerfert

Differential Revision: https://reviews.llvm.org/D89724

Author: davidbolvansky

llvm/include/llvm/IR/Intrinsics.td

@@ -583,7 +583,8 @@ def int_memmove : Intrinsic<[],
                              llvm_i1_ty],
                             [IntrArgMemOnly, IntrWillReturn,
                              NoCapture<ArgIndex<0>>, NoCapture<ArgIndex<1>>,
-                             ReadOnly<ArgIndex<1>>, ImmArg<ArgIndex<3>>]>;
+                             WriteOnly<ArgIndex<0>>, ReadOnly<ArgIndex<1>>,
+                             ImmArg<ArgIndex<3>>]>;
 def int_memset  : Intrinsic<[],
                             [llvm_anyptr_ty, llvm_i8_ty, llvm_anyint_ty,
                              llvm_i1_ty],

llvm/test/Bitcode/upgrade-memory-intrinsics.ll

@@ -29,8 +29,8 @@ define void @test2(i8* %p1, i8* %p2, i8* %p3) {
 
 ; CHECK: declare void @llvm.memset.p0i8.i64(i8* nocapture writeonly, i8, i64, i1 immarg)
 ; CHECK: declare void @llvm.memcpy.p0i8.p0i8.i64(i8* noalias nocapture writeonly, i8* noalias nocapture readonly, i64, i1 immarg)
-; CHECK: declare void @llvm.memmove.p0i8.p0i8.i64(i8* nocapture, i8* nocapture readonly, i64, i1 immarg)
+; CHECK: declare void @llvm.memmove.p0i8.p0i8.i64(i8* nocapture writeonly, i8* nocapture readonly, i64, i1 immarg)
 declare void @llvm.memset.p0i8.i64(i8* nocapture writeonly, i8, i64, i32, i1)
 declare void @llvm.memcpy.p0i8.p0i8.i64(i8* nocapture writeonly , i8* nocapture readonly, i64, i32, i1)
-declare void @llvm.memmove.p0i8.p0i8.i64(i8* nocapture, i8* nocapture readonly, i64, i32, i1)
+declare void @llvm.memmove.p0i8.p0i8.i64(i8* nocapture writeonly, i8* nocapture readonly, i64, i32, i1)
 

llvm/test/Transforms/DeadStoreElimination/MSSA/memintrinsics.ll

@@ -18,10 +18,8 @@ define void @test1(i8* noalias %A, i8* noalias %B) {
   ret void
 }
 
-; FIXME: We should eliminate this dead store.
 define void @test2(i8* noalias %A, i8* noalias %B) {
 ; CHECK-LABEL: @test2(
-; CHECK-NEXT:    store i8 0, i8* [[A:%.*]], align 1
 ; CHECK-NEXT:    call void @llvm.memmove.p0i8.p0i8.i8(i8* [[A]], i8* [[B:%.*]], i8 12, i1 false)
 ; CHECK-NEXT:    ret void
 ;