[all-commits] [llvm/llvm-project] 38a821: [Loop Fusion] Integrate Loop Peeling into Loop Fus...

[Sidharth Baveja via All-commits]

  Branch: refs/heads/master
  Home:   https://github.com/llvm/llvm-project
  Commit: 38a82179315c7cdd3f2bc0044cc29451fddf4bd8
      https://github.com/llvm/llvm-project/commit/38a82179315c7cdd3f2bc0044cc29451fddf4bd8
  Author: Sidharth Baveja <sidharth.baveja at ibm.com>
  Date:   2020-07-23 (Thu, 23 Jul 2020)

  Changed paths:
    M llvm/lib/Transforms/Scalar/LoopFuse.cpp
    A llvm/test/Transforms/LoopFusion/guarded_peel.ll
    A llvm/test/Transforms/LoopFusion/guarded_unsafeblock_peel.ll
    A llvm/test/Transforms/LoopFusion/nonadjacent_peel.ll
    A llvm/test/Transforms/LoopFusion/peel.ll

  Log Message:
  -----------
  [Loop Fusion] Integrate Loop Peeling into Loop Fusion (re-land after fixing ASAN build failures)

This patch adds the ability to peel off iterations of the first loop in loop
fusion. This can allow for both loops to have the same trip count, making it
legal for them to be fused together.

Here is a simple scenario peeling can be used in loop fusion:

for (i = 0; i < 10; ++i)
  a[i] = a[i] + 3;
for (j = 1; j < 10; ++j)
  b[j] = b[j] + 5;

Here is we can make use of peeling, and then fuse the two loops together. We
can peel off the 0th iteration of the loop i, and then combine loop i and j for
i = 1 to 10.

a[0] = a[0] +3;
for (i = 1; i < 10; ++i) {
  a[i] = a[i] + 3;
  b[i] = b[i] + 5;
}

Currently peeling with loop fusion is only supported for loops with constant
trip counts and a single exit point. Both unguarded and guarded loops are
supported.

Reviewed By: bmahjour (Bardia Mahjour), MaskRay (Fangrui Song)

Differential Revision: https://reviews.llvm.org/D82927