[PATCH] D13611: [Polly] Create virtual independent blocks

[Johannes Doerfert via llvm-commits]

jdoerfert created this revision.
jdoerfert added reviewers: grosser, Meinersbur.
jdoerfert added a subscriber: Polly.
Herald added a subscriber: sanjoy.

  Even with the scalar/PHI modeling and code generation we still
  utilized the independent blocks pass to move scalars around in order to
  decrease the dependences caused by them. However, this has two major
  drawbacks:
    o Polly could not be used as analysis only pass by default and
      without the independent blocks pass the result suffered.
    o The independent blocks pass had limited knowledge about domains
      as well as accesses. Both limited the pass to simple
      movement/re-computation of scalars that can be trivially moved.

  This patch is a drop-in replacement for the independent blocks pass
  that first virtually moves/re-computes scalars in the SCoP description.
  Only in the code generation re-computation will actually take place.

  The logic is split in three traversals of the scalars in the SCoP:
    1) Collect interesting operands for each scalar definition that
       escapes the block it resides in.
    2) For each scalar use, check if the definition can be recomputed
       in its statement based on the interesting operands of the
       definition. If so, remove the access and remember that the
       definition has to be recomputed later.
    3) For each scalar definition, check if all uses have been
       eliminated through virtual re-computation. If so, remove the
       access as it does not need to be communicated anymore.

  Subsequent patches can increase the capabilities easily as the domain
  and access information is already available.

    --------------------------  REVIEW NOTES  --------------------------

      - lnt & unit tests are green
      - We had 245 scalar access in the test suite before, now 236. In
        total this logic eliminated 54 trivially recomputable scalars
        and allowed to eliminate 54 instead of 49 statements.
      - The buildbots show the following compile/execution time changes for
        a similar but prior version of this patch:

        Compile time:
          Improvements           : Δ       : Previous : Current : σ
          .../bmm                : -71.43% : 0.6440   : 0.1840  : 0.0054
          .../paq8p              : -12.48% : 5.8644   : 5.1323  : 0.0181
          .../consumer-lame      : -10.13% : 10.3444  : 9.2961  : 0.0376
          .../sieve              : -5.61%  : 0.4280   : 0.4040  : 0.0093
          .../espresso           : -1.35%  : 10.3841  : 10.2441 : 0.0395
          ..//Recurrences-dbl    : -1.24%  : 4.1923   : 4.1403  : 0.0150
          .../471_omnetpp        : -1.08%  : 42.1606  : 41.7046 : 0.1013

        Execution time:
          Regressions            : Δ       : Previous : Current : σ
          .../salsa20            : 4.32%   : 6.6684   : 6.9564  : 0.0059
          .../GlobalDataFlow-dbl : 1.53%   : 4.6963   : 4.7683  : 0.0047

          Improvements           : Δ       : Previous : Current : σ
          ..//viterbi            : -1.61%  : 2.7402   : 2.6962  : 0.0072

http://reviews.llvm.org/D13611

Files:
  include/polly/CodeGen/BlockGenerators.h
  include/polly/LinkAllPasses.h
  include/polly/ScopInfo.h
  lib/Analysis/ScopInfo.cpp
  lib/CMakeLists.txt
  lib/CodeGen/BlockGenerators.cpp
  lib/CodeGen/CodeGeneration.cpp
  lib/Makefile
  lib/Support/RegisterPasses.cpp
  lib/Transform/IndependentBlocks.cpp
  test/IndependentBlocks/inter_bb_scalar_dep.ll
  test/IndependentBlocks/intra_and_inter_bb_scalar_dep.ll
  test/IndependentBlocks/intra_bb_scalar_dep.ll
  test/IndependentBlocks/phi_outside_scop.ll
  test/IndependentBlocks/scalar_to_array.ll
  test/IndependentBlocks/scev-invalidated.ll
  test/Isl/CodeGen/20110312-Fail-without-basicaa.ll
  test/Isl/CodeGen/OpenMP/invariant_base_pointer_preloaded_different_bb.ll
  test/Isl/CodeGen/eliminate-multiple-scalar-fp-reads.ll
  test/Isl/CodeGen/eliminate-multiple-scalar-reads.ll
  test/Isl/CodeGen/eliminate-scalars-with-outside-load.ll
  test/Isl/CodeGen/non-affine-phi-node-expansion-3.ll
  test/Isl/CodeGen/srem-in-other-bb.ll
  test/ScopInfo/eliminate-scalar-caused-by-load-reduction-2.ll
  test/ScopInfo/eliminate-scalar-caused-by-load-reduction.ll
  test/ScopInfo/independent-blocks-never-stop-on-big-scop.ll
  test/ScopInfo/inter_bb_scalar_dep.ll
  test/ScopInfo/intra_and_inter_bb_scalar_dep.ll
  test/ScopInfo/scalar_dependence_cond_br.ll
  test/ScopInfo/tempscop-printing.ll
  test/ScopInfo/unneeded_scalar_dependences-1.ll
  test/ScopInfo/unneeded_scalar_dependences-2.ll
  test/ScopInfo/unneeded_scalar_dependences-3.ll
  test/ScopInfo/unneeded_scalar_dependences-4.ll
  test/ScopInfo/unneeded_scalar_dependences-5.ll
  test/ScopInfo/unneeded_scalar_dependences-6.ll
  test/ScopInfo/unneeded_scalar_dependences-7.ll
  test/ScopInfo/unneeded_scalar_dependences-8.ll
  test/ScopInfo/unneeded_scalar_dependences-9.ll

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