[PATCH] D133362: [InstCombine] Fold x + (x | -x) to x & (x - 1)

[Sanjay Patel via Phabricator via llvm-commits]

spatel added inline comments.


================
Comment at: llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp:1425-1428
+  // (add A (or A, -A)) --> (and (add A, -1) A)
+  // (add A (or -A, A)) --> (and (add A, -1) A)
+  // (add (or A, -A) A) --> (and (add A, -1) A)
+  // (add (or -A, A) A) --> (and (add A, -1) A)
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This shows the expected set of commuted variants of the general pattern, but I don't think the match is handling all of them.

You'll want to add tests for each of these variations, and that's going to require some bonus instructions to make the patterns stick until we reach this point in visitAdd().

Here are some tests that I recently added that can serve as templates - note especially the lines with "thwart complexity-based canoinicalization":
d4a4004c0f9d3070


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D133362/new/

https://reviews.llvm.org/D133362