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Subject: [Bug tree-optimization/34043]  New: Missed optimization causing extra loads and stores when using x86_64 builtin function together with aggregate types.
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From: "jsjodin at gcc dot gnu dot org" <gcc-bugzilla@gcc.gnu.org>
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Compile the attached file test.cpp with the following flags:
g++ -DNDEBUG -m32 -msse2 -O2 -msse2 -DSHOW_BUG gcc_bug.cpp -S

In the generated code there are useless stores and loads of %xmm0 to
-40(%eps) and -56(%eps).  If the code is compiled without -DSHOW_BUG
it will generate a more optimal version without the extra memory
accesses. See the attached generated files test_bad.s and test_good.s
for the resulting code. This is an old problem existing in 4.1.x.


-- 
           Summary: Missed optimization causing extra loads and stores when
                    using x86_64 builtin function together with aggregate
                    types.
           Product: gcc
           Version: 4.3.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: normal
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: jsjodin at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34043