[all-commits] [llvm/llvm-project] 6ff439: [SimplifyCFG] Use a (trivially) dominanting widena...

[Philip Reames via All-commits]

  Branch: refs/heads/master
  Home:   https://github.com/llvm/llvm-project
  Commit: 6ff439b57f0fc2b1a2193ae37637c531ff652b1c
      https://github.com/llvm/llvm-project/commit/6ff439b57f0fc2b1a2193ae37637c531ff652b1c
  Author: Philip Reames <listmail at philipreames.com>
  Date:   2019-11-04 (Mon, 04 Nov 2019)

  Changed paths:
    M llvm/lib/Transforms/Utils/SimplifyCFG.cpp
    A llvm/test/Transforms/SimplifyCFG/wc-widen-block.ll

  Log Message:
  -----------
  [SimplifyCFG] Use a (trivially) dominanting widenable branch to remove later slow path blocks

This transformation is a variation on the GuardWidening transformation we have checked in as it's own pass. Instead of focusing on merge (i.e. hoisting and simplifying) two widenable branches, this transform makes the observation that simply removing a second slowpath block (by reusing an existing one) is often a very useful canonicalization. This may lead to later merging, or may not. This is a useful generalization when the intermediate block has loads whose dereferenceability is hard to establish.

As noted in the patch, this can be generalized further, and will be.

Differential Revision: https://reviews.llvm.org/D69689