| Issue |
161493
|
| Summary |
[InstCombine] Missing freeze when reusing existing value in def-use chain
|
| Labels |
miscompilation,
llvm:instcombine,
generated by fuzzer
|
| Assignees |
dtcxzyw
|
| Reporter |
dtcxzyw
|
Reproducer: https://alive2.llvm.org/ce/z/H_tcBV
```
define i16 @src(i4 %x, i12 %y) {
%x.fr = freeze i4 %x
%zext.x = zext i4 %x.fr to i16
%slx = shl nuw nsw i16 %zext.x, 12
%zext.y = zext i12 %y to i16
%xy = or disjoint i16 %slx, %zext.y
call void @use(i16 %xy)
%sly = shl nuw i16 %zext.y, 4
%yx = or disjoint i16 %sly, %zext.x
ret i16 %yx
}
define i16 @tgt(i4 %x, i12 %y) {
%x.fr = freeze i4 %x
%zext.x = zext i4 %x.fr to i16
%slx = shl nuw nsw i16 %zext.x, 12
%zext.y = zext i12 %y to i16
%xy = or disjoint i16 %slx, %zext.y
call void @use(i16 %xy)
;%sly = shl nuw i16 %zext.y, 4
;%yx = or disjoint i16 %sly, %zext.x
%yx = call i16 @llvm.fshl.i16(i16 %xy, i16 %xy, i16 4)
ret i16 %yx
}
declare void @use(i16)
```
```
Transformation doesn't verify!
ERROR: Target is more poisonous than source
Example:
i4 %x = #x8 (8, -8)
i12 %y = #x000 (0)
Source:
i4 %x.fr = #x8 (8, -8)
i16 %zext.x = #x0008 (8)
i16 %slx = poison
i16 %zext.y = #x0000 (0)
i16 %xy = poison
Function @use returned
i16 %sly = #x0000 (0)
i16 %yx = #x0008 (8)
SOURCE MEMORY STATE
===================
NON-LOCAL BLOCKS:
Block 0 > size: 0 align: 1 alloc type: 0 alive: false address: #x0
Block 1 > size: 0 align: 1 alloc type: 0 alive: true address: #x1
Target:
i4 %x.fr = #x8 (8, -8)
i16 %zext.x = #x0008 (8)
i16 %slx = poison
i16 %zext.y = #x0000 (0)
i16 %xy = poison
Function @use returned
i16 %yx = poison
TARGET MEMORY STATE
===================
NON-LOCAL BLOCKS:
Block 0 > size: 0 align: 1 alloc type: 0 alive: false address: #x0
Block 1 > size: 0 align: 1 alloc type: 0 alive: true address: #x1
Source value: #x0008 (8)
Target value: poison
```
It is caused by https://github.com/llvm/llvm-project/pull/68502.
![]()
_______________________________________________
llvm-bugs mailing list
[email protected]
https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-bugs
