[all-commits] [llvm/llvm-project] d4648e: [SCEV] Use trip count information to improve shift...

[Philip Reames via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: d4648eeaa270fe787d8158596a0f58e0426ed498
      https://github.com/llvm/llvm-project/commit/d4648eeaa270fe787d8158596a0f58e0426ed498
  Author: Philip Reames <listmail at philipreames.com>
  Date:   2021-03-22 (Mon, 22 Mar 2021)

  Changed paths:
    M llvm/include/llvm/Analysis/ScalarEvolution.h
    M llvm/lib/Analysis/ScalarEvolution.cpp
    M llvm/test/Analysis/ScalarEvolution/shift-recurrences.ll

  Log Message:
  -----------
  [SCEV] Use trip count information to improve shift recurrence ranges

This patch exploits the knowledge that we may be running many fewer than bitwidth iterations of the loop, and may be able to disallow the overflow case. This patch specifically implements only the shl case, but this can be generalized to ashr and lshr without difficulty.

Differential Revision: https://reviews.llvm.org/D98222