[all-commits] [llvm/llvm-project] 88241f: [Passes] Move ADCE before DSE & LICM.

[Florian Hahn via All-commits]

  Branch: refs/heads/master
  Home:   https://github.com/llvm/llvm-project
  Commit: 88241ffb5636ebc0579d3ab8eeec78446a769c54
      https://github.com/llvm/llvm-project/commit/88241ffb5636ebc0579d3ab8eeec78446a769c54
  Author: Florian Hahn <flo at fhahn.com>
  Date:   2020-10-21 (Wed, 21 Oct 2020)

  Changed paths:
    M llvm/lib/Passes/PassBuilder.cpp
    M llvm/lib/Transforms/IPO/PassManagerBuilder.cpp
    M llvm/test/CodeGen/AMDGPU/opt-pipeline.ll
    M llvm/test/Other/new-pm-defaults.ll
    M llvm/test/Other/new-pm-thinlto-defaults.ll
    M llvm/test/Other/new-pm-thinlto-postlink-pgo-defaults.ll
    M llvm/test/Other/new-pm-thinlto-postlink-samplepgo-defaults.ll
    M llvm/test/Other/new-pm-thinlto-prelink-pgo-defaults.ll
    M llvm/test/Other/new-pm-thinlto-prelink-samplepgo-defaults.ll
    M llvm/test/Other/opt-O2-pipeline.ll
    M llvm/test/Other/opt-O3-pipeline-enable-matrix.ll
    M llvm/test/Other/opt-O3-pipeline.ll
    M llvm/test/Other/opt-Os-pipeline.ll

  Log Message:
  -----------
  [Passes] Move ADCE before DSE & LICM.

The adjustment seems to have very little impact on optimizations.
The only binary change with -O3 MultiSource/SPEC2000/SPEC2006 on X86 is
in consumer-typeset and the size there actually decreases by -0.1%, with
not significant changes in the stats.

On its own, it is mildly positive in terms of compile-time, most likely
due to LICM & DSE having to process slightly less instructions. It
should also be unlikely that DSE/LICM make much new code dead.

http://llvm-compile-time-tracker.com/compare.php?from=df63eedef64d715ce1f31843f7de9c11fe1e597f&to=e3bdfcf94a9eeae6e006d010464f0c1b3550577d&stat=instructions

With DSE & MemorySSA, it gives some nice compile-time improvements, due
to the fact that DSE can re-use the PDT from ADCE, if it does not make
any changes:

http://llvm-compile-time-tracker.com/compare.php?from=15fdd6cd7c24c745df1bb419e72ff66fd138aa7e&to=481f494515fc89cb7caea8d862e40f2c910dc994&stat=instructions

Reviewed By: xbolva00

Differential Revision: https://reviews.llvm.org/D87322