| Issue |
168828
|
| Summary |
[x86] Eliminate `movzx` when upper part of register is irrelevant or overwritten
|
| Labels |
new issue
|
| Assignees |
|
| Reporter |
Validark
|
```zig
export fn foo(x: u8) u32 {
return @ctz(x >> 1);
}
```
```asm
foo:
shr dil
movzx eax, dil
or eax, 256
tzcnt eax, eax
ret
```
Could be:
```asm
foo:
shr dil
or edi, 256
tzcnt eax, edi
ret
```
The compiler could also look for things like `or eax, -256` and eliminate `movzx eax, al` since the relevant bits are overwritten anyway.
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