[all-commits] [llvm/llvm-project] 8ef4b9: [knownbits] Preserve known bits for small shift re...

[Philip Reames via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 8ef4b961a3af6e6839b487ba3962ddad133629fc
      https://github.com/llvm/llvm-project/commit/8ef4b961a3af6e6839b487ba3962ddad133629fc
  Author: Philip Reames <listmail at philipreames.com>
  Date:   2021-02-11 (Thu, 11 Feb 2021)

  Changed paths:
    M llvm/lib/Analysis/ValueTracking.cpp
    M llvm/test/Analysis/ValueTracking/shift-recurrence-knownbits.ll

  Log Message:
  -----------
  [knownbits] Preserve known bits for small shift recurrences

The motivation for this is that I'm looking at an example that uses shifts as induction variables. There's lots of other omissions, but one of the first I noticed is that we can't compute tight known bits. (This indirectly causes SCEV's range analysis to produce very poor results as well.)

Differential Revision: https://reviews.llvm.org/D96440