[PATCH] D124150: [InstCombine] Handle predicates for fold fcmp-of-copysign

[Sanjay Patel via Phabricator via llvm-commits]

spatel added inline comments.


================
Comment at: llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp:6762-6763
+    // copysign(non-zero constant, X) >  0.0 --> (bitcast X) >  0
+    // copysign(non-zero constant, X) <= 0.0 --> (bitcast X) <= 0
+    // copysign(non-zero constant, X) >= 0.0 --> (bitcast X) >= 0
+    switch (Pred) {
----------------
This is not correct if X is 0.0 (0x00000000).
copysign(1.0, 0.0) <= 0.0 is false
(bitcast 0.0) <= 0 is true

Similarly:
copysign(1.0, 0.0) > 0.0 is true
(bitcast 0.0) > 0 is false

I don't think we can verify copysign with Alive2, so please write a test program to check edge values so we know the transform is always correct.


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D124150/new/

https://reviews.llvm.org/D124150