[llvm] 656ebd5 - [SimplifyLibCalls] Don't change alignment when creating memset

[via llvm-commits]

Author: sstefan1
Date: 2021-04-21T20:34:13+02:00
New Revision: 656ebd519e3fd52050e1c8abeacafcf94d1fa260

URL: https://github.com/llvm/llvm-project/commit/656ebd519e3fd52050e1c8abeacafcf94d1fa260
DIFF: https://github.com/llvm/llvm-project/commit/656ebd519e3fd52050e1c8abeacafcf94d1fa260.diff

LOG: [SimplifyLibCalls] Don't change alignment when creating memset

Fix for PR49984
This was discovered during Attributor testing.
Memset was always created with alignment of 1
and in case when strncpy alignment was changed
it triggered an assertion in the AttrBuilder.
Memset will now be created with appropriate alignment.

Differential Revision: https://reviews.llvm.org/D100875

Added: 
    

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

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp b/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
index 2e440511d6fde..ab181be20964d 100644
--- a/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
@@ -575,8 +575,10 @@ Value *LibCallSimplifier::optimizeStrNCpy(CallInst *CI, IRBuilderBase &B) {
   }
 
   if (SrcLen == 0) {
-    // strncpy(x, "", y) -> memset(align 1 x, '\0', y)
-    CallInst *NewCI = B.CreateMemSet(Dst, B.getInt8('\0'), Size, Align(1));
+    // strncpy(x, "", y) -> memset(x, '\0', y)
+    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));

diff  --git a/llvm/test/Transforms/InstCombine/strncpy-1.ll b/llvm/test/Transforms/InstCombine/strncpy-1.ll
index bc104cab081ae..210df0e7c1ea4 100644
--- a/llvm/test/Transforms/InstCombine/strncpy-1.ll
+++ b/llvm/test/Transforms/InstCombine/strncpy-1.ll
@@ -144,6 +144,16 @@ define i8* @test3(i8* %dst, i32 %n) {
   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() {