https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78348
Bug ID: 78348
Summary: [7 REGRESSION] 15% performance drop for
coremark-pro/nnet-test after r242038
Product: gcc
Version: 7.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: ysrumyan at gmail dot com
Target Milestone: ---
We noticed huge (>15%) performance drop after fix in loop distribution phase.
Before fix fix distribution is not performed since loop contains anti (write
after read) dependence. But now distibution is performed and memmove & memset
built-in are generated. We don't have fast implemention of memmove on HASWELL
that results in leads to performance regression. But note that the dependence
analysis is very poor and does not detect simple copying one struct field to
another. I attached simple test-case to reproduce this issue.
Note also that fix to pg_add_dependence_edges is correct and must not be
removed.
