[all-commits] [llvm/llvm-project] 8bd9ad: [InstCombine] Fold `fcmp pred sqrt(X), 0.0 -> fcmp...

[Yingwei Zheng via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 8bd9ade6284a793c898da133723121c3bcc49ef7
      https://github.com/llvm/llvm-project/commit/8bd9ade6284a793c898da133723121c3bcc49ef7
  Author: Yingwei Zheng <dtcxzyw2333 at gmail.com>
  Date:   2024-08-03 (Sat, 03 Aug 2024)

  Changed paths:
    M llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
    M llvm/test/Transforms/InstCombine/fcmp.ll
    M llvm/test/Transforms/InstCombine/known-never-nan.ll

  Log Message:
  -----------
  [InstCombine] Fold `fcmp pred sqrt(X), 0.0 -> fcmp pred2 X, 0.0` (#101626)

Proof (Please run alive-tv with larger smt-to):
https://alive2.llvm.org/ce/z/-aqixk
FMF propagation: https://alive2.llvm.org/ce/z/zyKK_p

```
sqrt(X) < 0.0 --> false
sqrt(X) u>= 0.0 --> true
sqrt(X) u< 0.0 --> X u< 0.0
sqrt(X) u<= 0.0 --> X u<= 0.0
sqrt(X) > 0.0 --> X > 0.0
sqrt(X) >= 0.0 --> X >= 0.0
sqrt(X) == 0.0 --> X == 0.0
sqrt(X) u!= 0.0 --> X u!= 0.0
sqrt(X) <= 0.0 --> X == 0.0
sqrt(X) u> 0.0 --> X u!= 0.0
sqrt(X) u== 0.0 --> X u<= 0.0
sqrt(X) != 0.0 --> X > 0.0
!isnan(sqrt(X)) --> X >= 0.0
isnan(sqrt(X)) --> X u< 0.0
```

In most cases, `sqrt` cannot be eliminated since it has multiple uses.
But this patch will break data dependencies and allow optimizer to sink
expensive `sqrt` calls into successor blocks.



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