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Subject: [Bug rtl-optimization/56151] [4.8 Regression] Performance degradation after r194054 on x86 Atom.
Date: Mon, 04 Feb 2013 12:04:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56151

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org,
                   |                            |uros at gcc dot gnu.org

--- Comment #6 from Jakub Jelinek <jakub at gcc dot gnu.org> 2013-02-04 12:03:52 UTC ---
Well, we already have peephole2s for MEM op= ARG (the TARGET_READ_MODIFY_WRITE
guarded peephole2s), the reason why it doesn't trigger in this case is that ARG
in this case ends up being a MEM, and
MEM op= MEM2 isn't a valid insn:

(insn 95 94 96 11 (set (reg:SI 3 bx [orig:135 D.1801 ] [135])
        (mem:SI (reg/f:SI 4 si [orig:86 D.1803 ] [86]) [2 *_41+0 S4 A32]))
pr56151.c:32 89 {*movsi_internal}
     (nil))
(insn 96 95 97 11 (parallel [
            (set (reg:SI 3 bx [orig:135 D.1801 ] [135])
                (ior:SI (reg:SI 3 bx [orig:135 D.1801 ] [135])
                    (mem:SI (plus:SI (mult:SI (reg:SI 6 bp [orig:132 D.1801 ]
[132])
                                (const_int 4 [0x4]))
                            (symbol_ref:SI ("setmask")  <var_decl
0x7f587927a390 setmask>)) [2 setmask S4 A32])))
            (clobber (reg:CC 17 flags))
        ]) pr56151.c:32 421 {*iorsi_1}
     (expr_list:REG_DEAD (reg:SI 6 bp [orig:132 D.1801 ] [132])
        (nil)))
(insn 97 96 98 11 (set (mem:SI (reg/f:SI 4 si [orig:86 D.1803 ] [86]) [2 *_41+0
S4 A32])
        (reg:SI 3 bx [orig:135 D.1801 ] [135])) pr56151.c:32 89
{*movsi_internal}
     (expr_list:REG_DEAD (reg:SI 3 bx [orig:135 D.1801 ] [135])
        (expr_list:REG_DEAD (reg/f:SI 4 si [orig:86 D.1803 ] [86])
            (nil))))

I guess for temp = MEM; temp op= MEM2; MEM = temp; for temp dead afterwards
(this case), we could as well just add another set of the (up to 3?)
peephole2's, that would transform that into
temp = MEM2;
MEM op= temp;
instead.