https://bugs.llvm.org/show_bug.cgi?id=49208
Bug ID: 49208
Summary: Wrong optimization around memset
Product: new-bugs
Version: unspecified
Hardware: PC
OS: Windows NT
Status: NEW
Severity: normal
Priority: P
Component: new bugs
Assignee: unassignedb...@nondot.org
Reporter: bogdan.gur...@gmail.com
CC: htmldevelo...@gmail.com, llvm-bugs@lists.llvm.org
Created attachment 24539
--> https://bugs.llvm.org/attachment.cgi?id=24539&action=edit
The input llvm code
The attached example should be run with the O2 optimization level. The 'memset'
memory pointer argument is replaced by the 'undef' which causes unexpected
behavior at runtime. I don't see any reason to replace it with 'undef' since
there are writers and external function calls that are related to this memory
pointer.
Command line:
"C:\Program Files\LLVM\bin\clang.exe" -S -emit-llvm d:\work\test.bc -o
d:\work\test_out.bc -O2
I compared the input and output and the only replacement is:
from:
```
%15 = load i8*, i8** %4, align 8, !tbaa !6
%16 = shl nsw i64 %14, 1
call void @llvm.memset.p0i8.i64(i8* align 2 %15, i8 0, i64 %16, i1 false) #0
```
to:
```
%15 = shl nsw i64 %14, 1
call void @llvm.memset.p0i8.i64(i8* align 2 undef, i8 0, i64 %15, i1 false)
#0
```
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