[PATCH] D55745: [InstCombine] Simplify cttz/ctlz + icmp eq/ne into mask check

[Nikita Popov via Phabricator via llvm-commits]

nikic created this revision.
nikic added reviewers: spatel, RKSimon.
Herald added subscribers: llvm-commits, JDevlieghere.

Related to https://bugs.llvm.org/show_bug.cgi?id=28668.

Checking whether a number has a certain number of trailing / leading zeros means checking whether it is of the form 0001XXXX or XXXX1000, which can be done with an and+icmp.

This is the first step, handling only eq/ne predicates, as that's what the existing code does. I'd like to extend this to handle all predicate types in the next step, which would resolve https://github.com/rust-lang/rust/issues/43024.


Repository:
  rL LLVM

https://reviews.llvm.org/D55745

Files:
  lib/Transforms/InstCombine/InstCombineCompares.cpp
  test/Transforms/InstCombine/cmp-intrinsic.ll
  test/Transforms/InstCombine/intrinsics.ll

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