[PATCH] D134415: [InstCombine] Improve fold icmp of truncated left shift

[Chenbing.Zheng via Phabricator via llvm-commits]

Chenbing.Zheng created this revision.
Chenbing.Zheng added reviewers: spatel, RKSimon, hasyimibhar, benshi001.
Chenbing.Zheng added a project: LLVM.
Herald added a subscriber: hiraditya.
Herald added a project: All.
Chenbing.Zheng requested review of this revision.
Herald added subscribers: llvm-commits, jacquesguan.

Original version only solve shifted constant 1, this patch expend it to PowerOf2
(trunc (2**Z << Y) to iN) == 0 -> Y u>  N - Z + 1
(trunc (2**Z << Y) to iN) != 0 -> Y u<= N - Z + 1
and
(trunc (2**Z << Y) to iN) == 2**C --> Y == C - Z
(trunc (2**Z << Y) to iN) != 2**C --> Y != C - Z


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D134415

Files:
  llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
  llvm/test/Transforms/InstCombine/icmp-trunc.ll

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