| Issue |
80880
|
| Summary |
Constant reusing fails to understand when bits are irrelevant
|
| Labels |
new issue
|
| Assignees |
|
| Reporter |
Validark
|
In my code, I had a snippet like this:
```zig
export fn foo(x: u64) u64 {
return ((x ^ 0x1111111111111111) * 0x1111111111111111) << 4;
}
```
Unfortunately, this gets optimized to the equivalent of this:
```zig
export fn foo(x: u64) u64 {
return (x ^ 0x0111111111111111) * 0x1111111111111110;
}
```
```asm
foo:
movabs rcx, 76861433640456465
movabs rax, 1229782938247303440
xor rcx, rdi
imul rax, rcx
ret
```
Rather than:
```zig
export fn bar(x: u64) u64 {
return (x ^ 0x1111111111111111) * 0x1111111111111110;
}
```
```asm
bar:
movabs rcx, 1229782938247303440
lea rax, [rcx + 1]
xor rax, rdi
imul rax, rcx
ret
```
It would be nice if the constant reusing feature recognized that I don't actually need `0x0111111111111111`, but `0xZ111111111111111`, where `Z` is any bitstring. That means that even if I had written `(x ^ 0xF111111111111111) * 0x1111111111111110;`, the same optimization could be applied.
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