tree e0e8a88e13f1908abc26dd996a5869f295d4eb76
parent 7d8cf48c8d1bfd526841db01075c802fef61f93e
author Kit Barton <kbarton@ca.ibm.com> 1555465020 +0000
committer Kit Barton <kbarton@ca.ibm.com> 1555465020 +0000

Add basic loop fusion pass.

This patch adds a basic loop fusion pass. It will fuse loops that conform to the
following 4 conditions:
  1. Adjacent (no code between them)
  2. Control flow equivalent (if one loop executes, the other loop executes)
  3. Identical bounds (both loops iterate the same number of iterations)
  4. No negative distance dependencies between the loop bodies.

The pass does not make any changes to the IR to create opportunities for fusion.
Instead, it checks if the necessary conditions are met and if so it fuses two
loops together.

The pass has not been added to the pass pipeline yet, and thus is not enabled by
default. It can be run stand alone using the -loop-fusion option.

Phabricator: https://reviews.llvm.org/D55851

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@358543 91177308-0d34-0410-b5e6-96231b3b80d8