| Issue |
141360
|
| Summary |
LLVM fails to reduce zext(op(zext)) in some cases
|
| Labels |
new issue
|
| Assignees |
|
| Reporter |
AZero13
|
In the benchmark, I noticed
%30 = zext i16 %.promoted47 to i32
%31 = mul nuw nsw i32 %30, 20
%32 = zext nneg i32 %31 to i64
%31 is not used at all elsewhere.
It should be
%30 = zext i16 %.promoted47 to i64
%31 = mul nuw nsw i64 %30, 20
https://alive2.llvm.org/ce/z/XpJe59
I noticed that LLVM did in fact do this properly when I did an unrelated change: https://github.com/llvm/llvm-project/pull/140178
But that is because the DAG was different, meaning there is an edge case where this is not happening when it should be.
<img width="1067" alt="Image" src="" />
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