| Issue |
109455
|
| Summary |
Opportunity to reuse overflow flag in `min/max(a, add/sub(a, b))`
|
| Labels |
backend:AArch64,
backend:X86,
missed-optimization,
llvm:SelectionDAG
|
| Assignees |
|
| Reporter |
Kmeakin
|
Expressions like `a + b > a ? a : a + b` can reuse the overflow flag from `a + b` to avoid a second comparison.
[C++ examples](https://godbolt.org/z/W5Yjq5rGT)
[Alive proofs](https://alive2.llvm.org/ce/z/ft4Yar)
```asm
; AArch64
src_umax_add:
add w8, w1, w0
cmp w0, w8
csel w0, w0, w8, hi
ret
tgt_umax_add:
adds w8, w0, w1
csel w0, w0, w8, hs
ret
```
```asm
; x86-64
src_umax_add:
lea eax, [rsi + rdi]
cmp edi, eax
cmova eax, edi
ret
tgt_umax_add:
mov eax, esi
add eax, edi
cmovb eax, edi
ret
```
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