[PATCH] D55877: [LIR] Add CTTZ support part2

[Yuanfang Chen via Phabricator via llvm-commits]

tabloid.adroit created this revision.
Herald added a subscriber: llvm-commits.

Add a second idiom recognition (BitScan idiom) where bits of input
variable are scanned in order until hit a set bit:
scan-from-left-to-right means CTLZ; scan-from-right-to-left means CTTZ.
The starting bit index do not have to be first bit if we could prove
from CFG that preceding bits are zero.


Repository:
  rL LLVM

https://reviews.llvm.org/D55877

Files:
  lib/Transforms/Scalar/LoopIdiomRecognize.cpp
  test/Transforms/LoopIdiom/X86/ctlz.ll
  test/Transforms/LoopIdiom/X86/cttz.ll

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