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From: "tprince at computer dot org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/66740] New: omp simd reduction miscompiles at -O3 with AVX (recent regression)
Date: Thu, 02 Jul 2015 12:42:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66740

            Bug ID: 66740
           Summary: omp simd reduction miscompiles at -O3 with AVX (recent
                    regression)
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: tprince at computer dot org
  Target Milestone: ---

Created attachment 35897
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=35897&action=edit
f2c include file

This regression is new in the last 2 weeks.
gcc -O3 -march=sandybridge -std=c99 -D__assume_aligned=  -fopenmp -c s115.c
is miscompiled (bad numerical results when run under test harness).
It is OK at -O2 or with -march=westmere, or with the omp directive disabled.
It doesn't vectorize without the omp directive.  It fails the same with
-march=haswell.
Similar versions using inner_product or Fortran dot_product are vectorizing
correctly without omp simd.