| Issue |
148388
|
| Summary |
`@llvm.abs.i64` optimizes differently versus target-specific `@llvm.aarch64.neon.abs.i64`
|
| Labels |
new issue
|
| Assignees |
|
| Reporter |
folkertdev
|
I'm not sure one is really better than the other, but it's the difference that is weird. My reading of https://llvm.org/docs/LangRef.html#llvm-abs-intrinsic is that the second argument being false means that the behavior is in fact wrapping, like the neon instruction.
https://godbolt.org/z/fTvxc4z3z
```llvm
target triple = "aarch64-unknown-linux-gnu"
define noundef i64 @foo(i64 noundef %a) unnamed_addr {
start:
%_0.sroa.0.0 = tail call i64 @llvm.abs.i64(i64 %a, i1 false)
ret i64 %_0.sroa.0.0
}
define noundef i64 @bar(i64 noundef %a) unnamed_addr {
start:
%_0.i = tail call noundef i64 @llvm.aarch64.neon.abs.i64(i64 noundef %a) #3
ret i64 %_0.i
}
declare i64 @llvm.aarch64.neon.abs.i64(i64) unnamed_addr #1
declare i64 @llvm.abs.i64(i64, i1 immarg) #2
```
At `-O0` they produce the same instructions, but at `-O3` they do not
```asm
foo: // @foo
cmp x0, #0
cneg x0, x0, mi
ret
bar: // @bar
fmov d0, x0
abs d0, d0
fmov x0, d0
ret
```
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