[PATCH] D100875: [SimplifyLibCalls] Don't change alignment when creating memset Fix for PR49984

[Stefan Stipanovic via Phabricator via llvm-commits]

sstefan1 created this revision.
sstefan1 added reviewers: jdoerfert, xbolva00.
Herald added a subscriber: hiraditya.
sstefan1 requested review of this revision.
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Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D100875

Files:
  llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
  llvm/test/Transforms/InstCombine/strncpy-1.ll


Index: llvm/test/Transforms/InstCombine/strncpy-1.ll
===================================================================
--- llvm/test/Transforms/InstCombine/strncpy-1.ll
+++ llvm/test/Transforms/InstCombine/strncpy-1.ll
@@ -144,6 +144,16 @@
   ret i8* %ret
 }
 
+define i8* @test4(i8* %dst, i32 %n) {
+; CHECK-LABEL: @test4(
+; CHECK-NEXT:    call void @llvm.memset.p0i8.i32(i8* noalias noundef nonnull align 16 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* align(16) noalias nonnull %dst, i8* nonnull %src, i32 5);
+  ret i8* %ret
+}
+
 ; Check cases that shouldn't be simplified.
 
 define void @test_no_simplify1() {
Index: llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
===================================================================
--- llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
+++ llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
@@ -576,7 +576,9 @@
 
   if (SrcLen == 0) {
     // strncpy(x, "", y) -> memset(align 1 x, '\0', y)
-    CallInst *NewCI = B.CreateMemSet(Dst, B.getInt8('\0'), Size, Align(1));
+    Align MemSetAlign =
+        CI->getAttributes().getParamAttributes(0).getAlignment().valueOrOne();
+    CallInst *NewCI = B.CreateMemSet(Dst, B.getInt8('\0'), Size, MemSetAlign);
     AttrBuilder ArgAttrs(CI->getAttributes().getParamAttributes(0));
     NewCI->setAttributes(NewCI->getAttributes().addParamAttributes(
         CI->getContext(), 0, ArgAttrs));


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