[llvm] [AArch64] Improve lowering of scalar abs(sub(a, b)). (PR #151180)
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    Mon Sep  8 10:36:36 PDT 2025
    
    
  
AZero13 wrote:
I would like to revisit this.
Mostly because honestly, I don't think that selection lowering should deal with only this specific case.
So I'm wondering: I want to do one of two things:
either make the transform (subs (sub (x, y) 0) -> subs (x, y) if one use and not using overflow or carry flags, in general, not just for this case:
Or have peephole catch these cases.
I tried implementing the first one in global-isel and it had mixed results: many regressions but some improvements.
There's also the fact that peephole should be catching this anyway but isn't. 
https://github.com/llvm/llvm-project/pull/151180
    
    
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