| Issue |
97475
|
| Summary |
integer vector miscompile from instcombine
|
| Labels |
miscompilation,
llvm:instcombine
|
| Assignees |
|
| Reporter |
regehr
|
I believe this is being mis-optimized:
```lllvm
define <4 x i32> @f(<4 x i32> %0) {
%2 = icmp eq <4 x i32> %0, zeroinitializer
%3 = shufflevector <4 x i32> %0, <4 x i32> zeroinitializer, <4 x i32> <i32 1, i32 1, i32 0, i32 3>
%4 = select <4 x i1> %2, <4 x i32> %3, <4 x i32> zeroinitializer
ret <4 x i32> %4
}
```
I'll just give Alive's reasoning, which is pretty easy to follow and seems correct:
```
regehr@ohm:~$ ~/alive2-regehr/build/alive-tv -passes=instcombine foo.ll
----------------------------------------
define <4 x i32> @f(<4 x i32> %#0) {
#1:
%#2 = icmp eq <4 x i32> %#0, { 0, 0, 0, 0 }
%#3 = shufflevector <4 x i32> %#0, <4 x i32> { 0, 0, 0, 0 }, 1, 1, 0, 3
%#4 = select <4 x i1> %#2, <4 x i32> %#3, <4 x i32> { 0, 0, 0, 0 }
ret <4 x i32> %#4
}
=>
define <4 x i32> @f(<4 x i32> %#0) {
#1:
ret <4 x i32> { 0, 0, 0, 0 }
}
Transformation doesn't verify!
ERROR: Value mismatch
Example:
<4 x i32> %#0 = < #x00000000 (0), #x00000001 (1), #x00000000 (0), poison >
Source:
<4 x i1> %#2 = < #x1 (1), #x0 (0), #x1 (1), poison >
<4 x i32> %#3 = < #x00000001 (1), #x00000001 (1), #x00000000 (0), poison >
<4 x i32> %#4 = < #x00000001 (1), #x00000000 (0), #x00000000 (0), poison >
Target:
Source value: < #x00000001 (1), #x00000000 (0), #x00000000 (0), poison >
Target value: < #x00000000 (0), #x00000000 (0), #x00000000 (0), #x00000000 (0) >
Summary:
0 correct transformations
1 incorrect transformations
0 failed-to-prove transformations
0 Alive2 errors
regehr@ohm:~$
```
cc @nunoplopes
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