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[Bug tree-optimization/82604] [8 Regression] SPEC CPU2006 410.bwaves ~50% performance regression with trunk@253679 when ftree-parallelize-loops is used
- From: "rguenth at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: Fri, 17 Nov 2017 10:50:43 +0000
- Subject: [Bug tree-optimization/82604] [8 Regression] SPEC CPU2006 410.bwaves ~50% performance regression with trunk@253679 when ftree-parallelize-loops is used
- Auto-submitted: auto-generated
- References: <bug-82604-4@http.gcc.gnu.org/bugzilla/>
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82604
--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
So it still parallelizes the loop(s) but at one level deeper (line 176 vs.
173).
This is because dependence analysis does not handle calls and loop distribution
distributed a memset. ISL dependence analysis will have the same issue.
I've quickly tried replacing memset with *p = {} which somewhat works
when wrapping the LHS with a WITH_SIZE_EXPR. It later ICEs, but well.
RTL expansion suggests we expect it on the RHS, so *p = WITH_SIZE_EXPR <{}, n}
but that doesn't parallelize again (dependence analysis is confused).
I think the proper fix is to dependence analysis in get_references_in_stmt,
similar to how we handle masked loads/stores.