| Issue |
130088
|
| Summary |
Failure to recognise unnecessary sext for add+cmp
|
| Labels |
llvm:instcombine,
missed-optimization
|
| Assignees |
|
| Reporter |
RKSimon
|
Pulled out #76524 - we fail to recognize that extension is unnecessary and that the trunc is nsw
```ll
define i8 @src(i16 noundef %x) {
entry:
%conv = sext i16 noundef %x to i128
%add = add i128 %conv, 128
%or.cond.i = icmp ult i128 %add, 256
assume i1 %or.cond.i
%conv1 = trunc i16 noundef %x to i8
ret i8 %conv1
}
=>
define i8 @tgt(i16 noundef %x) {
entry:
%add = add i16 noundef %x, 128
%or.cond.i = icmp ult i16 %add, 256
assume i1 %or.cond.i
%conv1 = trunc nsw i16 noundef %x to i8
ret i8 %conv1
}
Transformation seems to be correct!
```
https://alive2.llvm.org/ce/z/epn8hd
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