[all-commits] [llvm/llvm-project] c0d9bf: [indvars] Allow rotation (narrowing) of exit test ...

[Philip Reames via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: c0d9bf2f6afdceca53cda1a294ceeb74385142d1
      https://github.com/llvm/llvm-project/commit/c0d9bf2f6afdceca53cda1a294ceeb74385142d1
  Author: Philip Reames <listmail at philipreames.com>
  Date:   2021-11-04 (Thu, 04 Nov 2021)

  Changed paths:
    M llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
    M llvm/test/Transforms/IndVarSimplify/finite-exit-comparisons.ll

  Log Message:
  -----------
  [indvars] Allow rotation (narrowing) of exit test when discovering trip count

This relaxes the one-use requirement on the rotation transform specifically for the case where we know we're zexting an IV of the loop.  This allows us to discover trip count information in SCEV, which seems worth a single extra loop invariant truncate.  Honestly, I'd prefer if SCEV could just compute the trip count directly (e.g. D109457), but this unblocks practical benefit.