[PATCH] D98222: [SCEV] Use trip count information to improve shift recurrence ranges

[Philip Reames via Phabricator via llvm-commits]

reames created this revision.
reames added reviewers: fhahn, nikic, gilr, mkazantsev.
Herald added subscribers: dantrushin, javed.absar, hiraditya, mcrosier.
Herald added a reviewer: bollu.
reames requested review of this revision.
Herald added a project: LLVM.

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.

In my motivating example (a multiple dimension loop nest w/a shl recurrence at the outer level), this results in a massive improvement in scev-aa results.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D98222

Files:
  llvm/include/llvm/Analysis/ScalarEvolution.h
  llvm/lib/Analysis/ScalarEvolution.cpp
  llvm/test/Analysis/ScalarEvolution/shift-recurrences.ll

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