https://bugs.llvm.org/show_bug.cgi?id=44388
Bug ID: 44388
Summary: memcpyopt adds incorrect align to memset
Product: libraries
Version: trunk
Hardware: PC
OS: All
Status: NEW
Severity: normal
Priority: P
Component: Scalar Optimizations
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected]
Created attachment 22966
--> https://bugs.llvm.org/attachment.cgi?id=22966&action=edit
memset.src.ll
```
$ cat memset.src.ll
; Transforms/MemCpyOpt/form-memset.ll
define void @test6(i32* nocapture %P) nounwind ssp {
entry:
%0 = bitcast i32* %P to i8*
tail call void @llvm.memset.p0i8.i64(i8* %0, i8 0, i64 12, i1 false)
%add.ptr = getelementptr inbounds i32, i32* %P, i64 3
%1 = bitcast i32* %add.ptr to i8*
tail call void @llvm.memset.p0i8.i64(i8* %1, i8 0, i64 12, i1 false)
ret void
}
declare void @llvm.memset.p0i8.i64(i8* nocapture, i8, i64, i1) nounwind
$ ../llvm/build/bin/opt -memcpyopt memset.src.ll -S -o -
; ModuleID = 'memset.src.ll'
source_filename = "memset.src.ll"
; Function Attrs: nounwind ssp
define void @test6(i32* nocapture %P) #0 {
entry:
%0 = bitcast i32* %P to i8*
%add.ptr = getelementptr inbounds i32, i32* %P, i64 3
%1 = bitcast i32* %add.ptr to i8*
%2 = bitcast i32* %P to i8*
call void @llvm.memset.p0i8.i64(i8* align 4 %2, i8 0, i64 24, i1 false)
ret void
}
; Function Attrs: argmemonly nounwind willreturn
declare void @llvm.memset.p0i8.i64(i8* nocapture writeonly, i8, i64, i1 immarg)
#1
attributes #0 = { nounwind ssp }
attributes #1 = { argmemonly nounwind willreturn }
```
memcpyopt merges two memsets if they overlap and write the same value.
After merging, align 4 is added, which is incorrect because %P is not
guaranteed to have alignment 4.
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