[PATCH] D125717: [InstCombine] Optimize and of icmps with power-of-2 and contiguous masks

[John McIver via Phabricator via llvm-commits]

jmciver marked 2 inline comments as done.
jmciver added inline comments.


================
Comment at: llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp:494
+         "Expected equality predicates for masked type of icmps.");
+  if (!IsAnd || PredL != ICmpInst::ICMP_EQ || PredR != ICmpInst::ICMP_NE)
+    return nullptr;
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goldstein.w.n wrote:
> As a TODO (or here if you want to) you could also do:
> ```
> `(icmp (A & B) == B) & (icmp (A & D) == D)` -> `(icmp (A & (B | D) == (B | D)`
> ```
> https://alive2.llvm.org/ce/z/sFcvJP
This maybe already handled, but let me know if I am missing something: 

https://godbolt.org/z/WqnveefxP

https://github.com/llvm/llvm-project/blob/main/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp#L577



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Comment at: llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp:543
+          match(EElt, m_APInt(ECst)) && *DCst == *ECst &&
+          (isa<UndefValue>(BElt) ||
+           (BCst->countLeadingOnes() == DCst->countLeadingZeros()))) {
----------------
goldstein.w.n wrote:
> Can you add some tests with `undef` elements.
> 
> Also if `undef` is allowed in the non-vec case as well, this check and the scalar one could be done with a lambda. 
I added tests using undef splat vectors.

The conversion to a lambda is much cleaner. I have enabled support for undef/poison support in the scalar case. However, testing of this transformation using scalar undef or poison enables an earlier optimization path: 

https://godbolt.org/z/7c87ba45v

The following Alive2 output show the scalar use of undef and poison with this transformation to be correct:

https://alive2.llvm.org/ce/z/9_eQny


Repository:
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  https://reviews.llvm.org/D125717/new/

https://reviews.llvm.org/D125717