[llvm] [MemCpyOpt] Always create gep instructions in `processMemCpyMemCpyDependence` (PR #98686)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-transforms

Author: Yingwei Zheng (dtcxzyw)

<details>
<summary>Changes</summary>

Fixes https://github.com/llvm/llvm-project/issues/98675.


---
Full diff: https://github.com/llvm/llvm-project/pull/98686.diff


2 Files Affected:

- (modified) llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp (+3-2) 
- (modified) llvm/test/Transforms/MemCpyOpt/memcpy-memcpy-offset.ll (+18) 


``````````diff
diff --git a/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp b/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
index 1c65219585e5a..c542084c1ad2f 100644
--- a/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
+++ b/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
@@ -1188,8 +1188,9 @@ bool MemCpyOptPass::processMemCpyMemCpyDependence(MemCpyInst *M,
     if (MDestOffset == MForwardOffset)
       CopySource = M->getDest();
     else {
-      NewCopySource = cast<Instruction>(Builder.CreateInBoundsPtrAdd(
-          CopySource, Builder.getInt64(MForwardOffset)));
+      NewCopySource = GetElementPtrInst::CreateInBounds(
+          Builder.getInt8Ty(), CopySource, Builder.getInt64(MForwardOffset), "",
+          Builder.GetInsertPoint());
       CopySource = NewCopySource;
     }
     // We need to update `MCopyLoc` if an offset exists.
diff --git a/llvm/test/Transforms/MemCpyOpt/memcpy-memcpy-offset.ll b/llvm/test/Transforms/MemCpyOpt/memcpy-memcpy-offset.ll
index 6abb0da827990..455a06045ab8d 100644
--- a/llvm/test/Transforms/MemCpyOpt/memcpy-memcpy-offset.ll
+++ b/llvm/test/Transforms/MemCpyOpt/memcpy-memcpy-offset.ll
@@ -197,6 +197,24 @@ define void @do_not_forward_offset_and_store(ptr %src, ptr %dest) {
   ret void
 }
 
+; Make sure we don't crash when the copy source is a constant.
+ at buf = external global [32 x i8]
+
+define void @pr98675(ptr noalias %p1, ptr noalias %p2) {
+; CHECK-LABEL: define void @pr98675(
+; CHECK-SAME: ptr noalias [[P1:%.*]], ptr noalias [[P2:%.*]]) {
+; CHECK-NEXT:    call void @llvm.memcpy.p0.p0.i64(ptr [[P1]], ptr @buf, i64 26, i1 false)
+; CHECK-NEXT:    [[GEP:%.*]] = getelementptr i8, ptr [[P1]], i64 10
+; CHECK-NEXT:    [[TMP1:%.*]] = getelementptr inbounds i8, ptr @buf, i64 10
+; CHECK-NEXT:    call void @llvm.memcpy.p0.p0.i64(ptr [[P2]], ptr [[TMP1]], i64 1, i1 false)
+; CHECK-NEXT:    ret void
+;
+  call void @llvm.memcpy.p0.p0.i64(ptr %p1, ptr @buf, i64 26, i1 false)
+  %gep = getelementptr i8, ptr %p1, i64 10
+  call void @llvm.memmove.p0.p0.i64(ptr %p2, ptr %gep, i64 1, i1 false)
+  ret void
+}
+
 declare void @use(ptr)
 
 declare void @llvm.memcpy.p0.p0.i64(ptr nocapture, ptr nocapture, i64, i1)

``````````

</details>


https://github.com/llvm/llvm-project/pull/98686