mbox series

[v2,0/3] reassoc: Propagate PHI_LOOP_BIAS along single uses

Message ID 20210921225429.326017-1-iii@linux.ibm.com
Headers
Series reassoc: Propagate PHI_LOOP_BIAS along single uses |

Message

Ilya Leoshkevich Sept. 21, 2021, 10:54 p.m. UTC 
  This is an update to my very old patch with the review comments
addressed.  Bootstrapped and regtested x86_64-redhat-linux,
ppc64le-redhat-linux and s390x-redhat-linux.

v1: https://gcc.gnu.org/pipermail/gcc-patches/2020-June/548785.html
Changes in v2:
* Disable PHI biasing in the early pass instance in a separate patch.
* Replace s390-specific tests with the generic tree-ssa ones.
* Replace the fragile (op_rank & PHI_LOOP_BIAS) test with auto_bitmap
  biased_names.  The review suggestion was to rather check whether op
  is defined by a loop-carried phi, but this would allow detecting only
  single assingments, and not assignment chains.  Another alternative
  that would make the check less fragile was to use saturating addition
  in order to prevent overflows into the PHI_LOOP_BIAS bit, but
  auto_bitmap of SSA_NAMEs allows graceful processing of large basic
  blocks, and its memory overhead looks acceptable.
* Restructure the code to make it a bit more readable.  The overall
  logic is the same as in v1.  I considered implementing an idea from
  [1], more specifically, detecting single-use chains in
  is_phi_for_stmt() so that swap_ops_for_binary_stmt() shifts the
  corresponding operand towards the end.  These two functions actually
  seem to serve a very related purpose.  However, for single-use chain
  detection we would still need to recursively traverse
  SSA_NAME_DEF_STMTs of operands, which propagate_rank() and friends
  already do.  So this would not have resulted in a significant code
  simplification.

[1] https://gcc.gnu.org/pipermail/gcc-patches/2020-June/549149.html

Ilya Leoshkevich (3):
  reassoc: Do not bias loop-carried PHIs early
  reassoc: Propagate PHI_LOOP_BIAS along single uses
  reassoc: Test rank biasing

 gcc/passes.def                             |   4 +-
 gcc/testsuite/gcc.dg/tree-ssa/reassoc-46.c |   7 ++
 gcc/testsuite/gcc.dg/tree-ssa/reassoc-46.h |  33 ++++++
 gcc/testsuite/gcc.dg/tree-ssa/reassoc-47.c |   9 ++
 gcc/testsuite/gcc.dg/tree-ssa/reassoc-48.c |   9 ++
 gcc/testsuite/gcc.dg/tree-ssa/reassoc-49.c |  11 ++
 gcc/testsuite/gcc.dg/tree-ssa/reassoc-50.c |  10 ++
 gcc/testsuite/gcc.dg/tree-ssa/reassoc-51.c |  11 ++
 gcc/tree-ssa-reassoc.c                     | 113 ++++++++++++++-------
 9 files changed, 170 insertions(+), 37 deletions(-)
 create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/reassoc-46.c
 create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/reassoc-46.h
 create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/reassoc-47.c
 create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/reassoc-48.c
 create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/reassoc-49.c
 create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/reassoc-50.c
 create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/reassoc-51.c