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Commit bfb5d2e6 authored by XChy's avatar XChy Committed by Noah Goldstein
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[InstCombine] Transform (A > 0) | (A < 0) -> zext (A != 0) fold

[InstCombine] Transform (A > 0) | (A < 0) -> zext (A != 0) fold

This extends **foldCastedBitwiseLogic** to handle the similar cases.

Actually, for `(A > B) | (A < B)`, when B != 0, it can be optimized to `zext( A != B )` by **foldAndOrOfICmpsUsingRanges**.
However, when B = 0, **transformZExtICmp** will transform `zext(A < 0) to i32` into `A << 31`,
which cannot be optimized by **foldAndOrOfICmpsUsingRanges**.

Because I'm new to LLVM and has no concise knowledge about how LLVM decides the order of optimization,
I choose to extend **foldCastedBitwiseLogic** to fold `( A << (X - 1) ) | ((A > 0) zext to iX) -> (A != 0) zext to iX`.

And the equivalent fold follows:
```
 A << (X - 1) ) | ((A > 0) zext to iX
  -> A < 0 | A > 0
  -> (A != 0) zext to iX
```

It's proved by [[https://alive2.llvm.org/ce/z/33HzjE|alive-tv]]

Related issue:
[[https://github.com/llvm/llvm-project/issues/62586  | (a > b) | (a < b) is not simplified only for the case b=0 ]]

Reviewed By: goldstein.w.n

Differential Revision: https://reviews.llvm.org/D154126
parent e8744ba3
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