[PATCH] D45856: [InstCombine] Support BitTests in ThreeWayComparison. General case, part 2

[Max Kazantsev via Phabricator via llvm-commits]

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

In this patch we continue supporting BitTests of the highest bit in the ThreeWayComparison
matcher in the InstCombine (see problem's description in the message of https://reviews.llvm.org/D45854).

This patch adds support for the transform of

  %c2 = icmp slt %a, 0
  %select1 = select %c2, %Less, %Greater

to

  (%a s>> 31) - (%Less - %Greater) | %Greater

which is an alternative to

  (%a s>> 31) - (%Less - %Greater) + %Greater

which applies if `(%Less - %Greater) & %Greater == 0`.

This is a part of fix of the bug 37147.


https://reviews.llvm.org/D45856

Files:
  lib/Transforms/InstCombine/InstCombineCompares.cpp
  test/Transforms/InstCombine/three-way-comparison.ll

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