Commit Graph

4 Commits

Author SHA1 Message Date
Eric Christopher cee313d288 Revert "Temporarily Revert "Add basic loop fusion pass.""
The reversion apparently deleted the test/Transforms directory.

Will be re-reverting again.

llvm-svn: 358552
2019-04-17 04:52:47 +00:00
Eric Christopher a863435128 Temporarily Revert "Add basic loop fusion pass."
As it's causing some bot failures (and per request from kbarton).

This reverts commit r358543/ab70da07286e618016e78247e4a24fcb84077fda.

llvm-svn: 358546
2019-04-17 02:12:23 +00:00
Vedant Kumar 32a014d048 [HotColdSplit] Simplify tests by lowering their splitting thresholds
This gets rid of the brittle/mysterious calls to @sink()/@sideeffect()
peppered throughout the test cases. They are no longer needed to force
splitting to occur.

llvm-svn: 351480
2019-01-17 21:29:34 +00:00
Vedant Kumar c299006879 [HotColdSplitting] Identify larger cold regions using domtree queries
The current splitting algorithm works in three stages:

  1) Identify cold blocks, then
  2) Use forward/backward propagation to mark hot blocks, then
  3) Grow a SESE region of blocks *outside* of the set of hot blocks and
  start outlining.

While testing this pass on Apple internal frameworks I noticed that some
kinds of control flow (e.g. loops) are never outlined, even though they
unconditionally lead to / follow cold blocks. I noticed two other issues
related to how cold regions are identified:

  - An inconsistency can arise in the internal state of the hotness
  propagation stage, as a block may end up in both the ColdBlocks set
  and the HotBlocks set. Further inconsistencies can arise as these sets
  do not match what's in ProfileSummaryInfo.

  - It isn't necessary to limit outlining to single-exit regions.

This patch teaches the splitting algorithm to identify maximal cold
regions and outline them. A maximal cold region is defined as the set of
blocks post-dominated by a cold sink block, or dominated by that sink
block. This approach can successfully outline loops in the cold path. As
a side benefit, it maintains less internal state than the current
approach.

Due to a limitation in CodeExtractor, blocks within the maximal cold
region which aren't dominated by a single entry point (a so-called "max
ancestor") are filtered out.

Results:
  - X86 (LNT + -Os + externals): 134KB of TEXT were outlined compared to
  47KB pre-patch, or a ~3x improvement. Did not see a performance impact
  across two runs.
  - AArch64 (LNT + -Os + externals + Apple-internal benchmarks): 149KB
  of TEXT were outlined. Ditto re: performance impact.
  - Outlining results improve marginally in the internal frameworks I
  tested.

Follow-ups:
  - Outline more than once per function, outline large single basic
  blocks, & try to remove unconditional branches in outlined functions.

Differential Revision: https://reviews.llvm.org/D53627

llvm-svn: 345209
2018-10-24 22:15:41 +00:00