| Issue |
60957
|
| Summary |
[InstCombine] fold signbit test of a pow2-or-zero
|
| Labels |
new issue
|
| Assignees |
|
| Reporter |
rotateright
|
This probably isn't worth the compile-time cost of using ValueTracking, but we could add a direct pattern match for this and similar icmp patterns:
```ll
define i1 @src(i8 %x) {
%negx = sub i8 0, %x
%pow2_or_zero = and i8 %negx, %x
%cmp = icmp slt i8 %pow2_or_zero, 0
ret i1 %cmp
}
define i1 @tgt(i8 %x) {
%cmp = icmp eq i8 %x, -128
ret i1 %cmp
}
```
https://alive2.llvm.org/ce/z/_J5q3S
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