[all-commits] [llvm/llvm-project] 7ef2c6: [InstSimplify] improve efficiency for detecting no...

[RotateRight via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 7ef2c68a3d24af0b0d540e748e8b564180f4e18a
      https://github.com/llvm/llvm-project/commit/7ef2c68a3d24af0b0d540e748e8b564180f4e18a
  Author: Sanjay Patel <spatel at rotateright.com>
  Date:   2021-04-14 (Wed, 14 Apr 2021)

  Changed paths:
    M llvm/lib/Analysis/InstructionSimplify.cpp

  Log Message:
  -----------
  [InstSimplify] improve efficiency for detecting non-zero value

Stepping through callstacks in the example from D99759 reveals
this potential compile-time improvement.

The savings come from avoiding ValueTracking's computing known
bits if we have already dealt with special-case patterns.

Further improvements in this direction seem possible.

This makes a degenerate test based on PR49785 about 40x faster
(25 sec -> 0.6 sec), but it does not address the larger question
of how to limit computeKnownBitsFromAssume(). Ie, the original
test there is still infinite-time for all practical purposes.

Differential Revision: https://reviews.llvm.org/D100408