[all-commits] [llvm/llvm-project] df9ba1: [LV] Handle scalable VFs in optimizeForVFAndUF (#8...

[Philip Reames via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: df9ba13579e298fcb57aa59c5c187ce6729881d6
      https://github.com/llvm/llvm-project/commit/df9ba13579e298fcb57aa59c5c187ce6729881d6
  Author: Philip Reames <preames at rivosinc.com>
  Date:   2024-03-04 (Mon, 04 Mar 2024)

  Changed paths:
    M llvm/include/llvm/Analysis/ScalarEvolution.h
    M llvm/lib/Analysis/ScalarEvolution.cpp
    M llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp

  Log Message:
  -----------
  [LV] Handle scalable VFs in optimizeForVFAndUF (#82669)

Given a scalable VF of the form <NumElts * VScale>, this patch adds the
ability to discharge a backedge test for a loop whose trip count is
between (NumElts, MinVScale*NumElts).

A couple of notes on this:
* Annoyingly, I could not figure out to write a test for this case. My
attempt is checked in as test32_i8 in f67ef1a, but LV uses a fixed
vector in that case, and ignored the force flags.
* This depends on 9eb5f94f to avoid appearing like a regression. Since
SCEV doesn't know any upper bound on vscale without the vscale_range
attribute (it doesn't query TTI), the ranges overflow on the multiply.
Arguably, this is fixing a bug in the current LV code since in theory
vscale can be large enough to overflow for real, but no actual target is
going to see that case.



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