[PATCH] D49179: [InstCombine] Fold x & (-1 >> y) == x to x u<= (-1 >> y)

[Roman Lebedev via Phabricator via llvm-commits]

lebedev.ri created this revision.
lebedev.ri added reviewers: spatel, craig.topper.

https://bugs.llvm.org/show_bug.cgi?id=38123

This pattern will be produced by Implicit Integer Truncation sanitizer,
https://reviews.llvm.org/D48958
https://bugs.llvm.org/show_bug.cgi?id=21530
in unsigned case, therefore it is probably a good idea to improve it.

https://rise4fun.com/Alive/Rny
^ there are more opportunities for folds, i will follow up with them afterwards.

Caveat: this somehow exposes a missing opportunities
in `test/Transforms/InstCombine/icmp-logical.ll`
It seems, the problem is in `foldLogOpOfMaskedICmps()` in `InstCombineAndOrXor.cpp`.
But i'm not quite sure what is wrong, because it calls `getMaskedTypeForICmpPair()`,
which calls `decomposeBitTestICmp()` which should already work for these cases...
I would love to have some pointers on how to address it.


Repository:
  rL LLVM

https://reviews.llvm.org/D49179

Files:
  include/llvm/IR/PatternMatch.h
  lib/Transforms/InstCombine/InstCombineCompares.cpp
  test/Transforms/InstCombine/canonicalize-constant-low-bit-mask-and-icmp-eq-to-icmp-ule.ll
  test/Transforms/InstCombine/canonicalize-low-bit-mask-and-icmp-eq-to-icmp-ule.ll
  test/Transforms/InstCombine/icmp-logical.ll
  test/Transforms/InstCombine/icmp-mul-zext.ll

-------------- next part --------------
A non-text attachment was scrubbed...
Name: D49179.154978.patch
Type: text/x-patch
Size: 12059 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20180711/471a541e/attachment.bin>