llvm/llvm-project
[x86] Eliminate `movzx` when upper part of register is irrelevant or overwritten
オープン
#168,828 opened on 2025/11/20
backend:X86good first issuellvm:SelectionDAGmissed-optimization
Repository metrics
- Stars
- (26,378 個のスター)
- PR merge metrics
- (PR metrics pending)
説明
export fn foo(x: u8) u32 {
return @ctz(x >> 1);
}
foo:
shr dil
movzx eax, dil
or eax, 256
tzcnt eax, eax
ret
Could be:
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.