[PATCH] D29034: [Guards] Introduce loop-predication pass

[Artur Pilipenko via Phabricator via llvm-commits]

apilipenko created this revision.
Herald added subscribers: mgorny, mzolotukhin.

This patch introduces guard based loop predication optimization. The new LoopPredication pass tries to convert loop variant range checks to loop invariant by widening checks across loop iterations. For example, it will convert

  for (i = 0; i < n; i++) {
    guard(i < len);
    ...
  }

to

  for (i = 0; i < n; i++) {
    guard(n - 1 < len);
    ...
  }

After this transformation the condition of the guard is loop invariant, so loop-unswitch can later unswitch the loop by this condition which basically predicates the loop by the widened condition:

  if (n - 1 < len)
    for (i = 0; i < n; i++) {
      ...
    }
  else
    deoptimize


https://reviews.llvm.org/D29034

Files:
  include/llvm/InitializePasses.h
  include/llvm/LinkAllPasses.h
  include/llvm/Transforms/Scalar.h
  lib/Transforms/Scalar/CMakeLists.txt
  lib/Transforms/Scalar/LoopPredication.cpp
  lib/Transforms/Scalar/Scalar.cpp
  test/Transforms/LoopPredication/basic.ll
  test/Transforms/LoopPredication/nested.ll
  test/Transforms/LoopPredication/visited.ll

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