| Issue |
114752
|
| Summary |
[InstCombine] an element is overwritten as a `poison`
|
| Labels |
new issue
|
| Assignees |
|
| Reporter |
bongjunj
|
The optimizer overwrites the second element of the second operand of `add` as `poison` for no reason.
Alive2 report: https://alive2.llvm.org/ce/z/qka3d8
```llvm
----------------------------------------
define <4 x i8> @sel_shuf_commute3.2(<4 x i8> %x, <4 x i8> %y, i1 %cmp) {
#0:
%#1 = add <4 x i8> %x, { 0, 1, 2, 3 }
%blend = shufflevector <4 x i8> %#1, <4 x i8> %y, 0, 5, 2, 3
%r = select i1 %cmp, <4 x i8> %y, <4 x i8> %blend
ret <4 x i8> %r
}
=>
define <4 x i8> @sel_shuf_commute3.2(<4 x i8> %x, <4 x i8> %y, i1 %cmp) {
#0:
%#1 = add <4 x i8> %x, { 0, poison, 2, 3 }
%sel = select i1 %cmp, <4 x i8> %y, <4 x i8> %#1
%r = shufflevector <4 x i8> %sel, <4 x i8> %y, 0, 5, 2, 3
ret <4 x i8> %r
}
Transformation doesn't verify!
ERROR: Target's return value is more undefined
Example:
<4 x i8> %x = < #x03 (3), #x00 (0) [based on undef value], #x00 (0), #x00 (0) >
<4 x i8> %y = < undef, #x00 (0), #x03 (3), #x00 (0) >
i1 %cmp = undef
Source:
<4 x i8> %#1 = < #x03 (3), #x01 (1), #x02 (2), #x03 (3) >
<4 x i8> %blend = < #x03 (3), #x00 (0), #x02 (2), #x03 (3) >
<4 x i8> %r = < #x03 (3) [based on undef value], #x00 (0), #x02 (2), #x03 (3) >
Target:
<4 x i8> %#1 = < #x03 (3), poison, #x02 (2), #x03 (3) >
<4 x i8> %sel = < #x54 (84), #x00 (0), #x03 (3), #x00 (0) >
<4 x i8> %r = < #x54 (84), #x00 (0), #x02 (2), #x03 (3) >
Source value: < #x03 (3), #x00 (0), #x02 (2), #x03 (3) >
Target value: < #x54 (84), #x00 (0), #x02 (2), #x03 (3) >
Summary:
0 correct transformations
1 incorrect transformations
0 failed-to-prove transformations
0 Alive2 errors
```
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