https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84743
Bug ID: 84743
Summary: default widths for parallel reassociation now hurt
rather than help
Product: gcc
Version: 8.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: acsawdey at gcc dot gnu.org
Reporter: acsawdey at gcc dot gnu.org
Target Milestone: ---
Target: powerpc64le power8
The width settings in rs6000_reassociation_width() were chosen to help
performance for SPEC CPU in gcc 7.
Testing on power8 shows that in gcc 8 (258101) there are now major degradations
in CPU2017 int with the default reassociation widths as compared to using
--param tree-reassoc-width=1 to disable reassociation.
Benchmark
500.perlbench_r -5.98%
502.gcc_r -1.16%
505.mcf_r -12.44%
520.omnetpp_r -39.00%
523.xalancbmk_r -9.78%
525.x264_r -1.76%
531.deepsjeng_r -4.23%
548.exchange2_r -0.66%
557.xz_r -2.04%
