[LoopRotate] Restructuring LoopRotation.cpp to create Loop Rotation Pass with Loop Rotation Utility Interface

The existing LoopRotation.cpp is implemented as one of loop passes instead of
being a utility. The user cannot easily perform the loop rotation selectively
(or on demand) under different optimization level. For example, the loop
rotation is needed as part of the logic to convert a loop into a loop with
bottom test for a transformation. If the loop rotation is simply added as a
loop pass before the transformation, the pass is skipped if it is compiled at
–O0 or if it is explicitly disabled by the user, causing the compiler to
generate incorrect code. Furthermore, as a loop pass it will rotate all loops
instead of just the relevant loops.

We provide a utility interface for the loop rotation so that the loop rotation
can be called on demand. The changeset is as follows:

- Create a new file lib/Transforms/Utils/LoopRotationUtils.cpp and move the main
  implementation of class LoopRotate into this file.
- Create a new file llvm/include/Transform/Utils/LoopRotationUtils.h with the
  interface LoopRotation(...).
- Original LoopRotation.cpp is changed to use the utility function LoopRotation
  in LoopRotationUtils.cpp. This is done in the same way community did for
  mem-to-reg implementation.

Patch by Jin Lin!

Differential Revision: https://reviews.llvm.org/D44595

llvm-svn: 328766

0 files changed, 0 insertions, 0 deletions