[SLC] Preserve attrs for strncpy(x, "", y) -> memset(align 1 x, '\0', y)

llvm-svn: 372101

Author: davidbolvansky

llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp

@@ -610,7 +610,10 @@ Value *LibCallSimplifier::optimizeStrNCpy(CallInst *CI, IRBuilder<> &B) {
 
   if (SrcLen == 0) {
     // strncpy(x, "", y) -> memset(align 1 x, '\0', y)
-    B.CreateMemSet(Dst, B.getInt8('\0'), Size, 1);
+    CallInst *NewCI = B.CreateMemSet(Dst, B.getInt8('\0'), Size, 1);
+    AttrBuilder ArgAttrs(CI->getAttributes().getParamAttributes(0));
+    NewCI->setAttributes(NewCI->getAttributes().addParamAttributes(
+        CI->getContext(), 0, ArgAttrs));
     return Dst;
   }
 

llvm/test/Transforms/InstCombine/strncpy-1.ll

@@ -134,6 +134,16 @@ define i8* @test2(i8* %dst) {
   ret i8* %ret
 }
 
+define i8* @test3(i8* %dst, i32 %n) {
+; CHECK-LABEL: @test3(
+; CHECK-NEXT:    call void @llvm.memset.p0i8.i32(i8* noalias nonnull align 1 dereferenceable(5) [[DST:%.*]], i8 0, i32 5, i1 false)
+; CHECK-NEXT:    ret i8* [[DST]]
+;
+  %src = getelementptr [1 x i8], [1 x i8]* @null, i32 0, i32 0
+  %ret = call i8* @strncpy(i8* noalias nonnull %dst, i8* nonnull %src, i32 5);
+  ret i8* %ret
+}
+
 ; Check cases that shouldn't be simplified.
 
 define void @test_no_simplify1() {