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Subject: [Bug rtl-optimization/55845] [4.8 Regression] 454.calculix miscompares with -march=btver2 -O3 -ffastmath -fschedule-insns -mvzeroupper for test data run
Date: Sun, 06 Jan 2013 13:24:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55845

Uros Bizjak <ubizjak at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |bonzini at gnu dot org

--- Comment #9 from Uros Bizjak <ubizjak at gmail dot com> 2013-01-06 13:23:54 UTC ---
It is try_head_merge_bb that moves unspec_volatile to the wrong place. However,
the core of the problem lies in can_move_insns_accross, which does not
special-case unspec_volatiles.

The untested df-problems.c patch that fixes the failing testcase:

--cut here--
Index: df-problems.c
===================================================================
--- df-problems.c       (revision 194945)
+++ df-problems.c       (working copy)
@@ -3916,6 +3916,10 @@ can_move_insns_across (rtx from, rtx to, rtx acros
        break;
       if (NONDEBUG_INSN_P (insn))
        {
+         /* Do not move unspec_volatile insns.  */
+         if (GET_CODE (PATTERN (insn)) == UNSPEC_VOLATILE)
+           break;
+
          if (may_trap_or_fault_p (PATTERN (insn))
              && (trapping_insns_in_across || other_branch_live != NULL))
            break;
--cut here--

Adding Paolo B. to CC.