[Bug target/55941] New: [4.8 Regression] Strange copy of double (in struct) to stack

[Bug target/55941] New: [4.8 Regression] Strange copy of double (in struct) to stack

[glisse at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55941

             Bug #: 55941
           Summary: [4.8 Regression] Strange copy of double (in struct) to
                    stack
    Classification: Unclassified
           Product: gcc
           Version: 4.8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: glisse@gcc.gnu.org
            Target: x86_64-linux-gnu


typedef struct A { double a, b; } A;
double f(A x,double y){return x.a+y;}

generates with gcc -Ofast -S:

    addsd    %xmm0, %xmm2
    movsd    %xmm0, -8(%rsp)
    movapd    %xmm2, %xmm0
    ret

I don't understand what that movsd is doing there?

Note that gcc-4.7 generates the expected:

    addsd    %xmm2, %xmm0
    ret

[Bug target/55941] [4.8 Regression] Strange copy of double (in struct) to stack

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55941

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2013-01-11
                 CC|                            |jakub at gcc dot gnu.org
     Ever Confirmed|0                           |1

--- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> 2013-01-11 14:44:23 UTC ---
This first regressed with:
http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=190492
into:
        movsd   %xmm0, -8(%rsp)
        addsd   %xmm2, %xmm0
and then we regress again with:
http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=190847
into:
        addsd   %xmm0, %xmm2
        movsd   %xmm0, -8(%rsp)
        movapd  %xmm2, %xmm0

[Bug target/55941] [4.8 Regression] Strange copy of double (in struct) to stack

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55941

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |rth at gcc dot gnu.org

--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> 2013-01-11 15:01:18 UTC ---
I'd hope that the subreg pass could be able to figure out something out of:
(insn 4 3 5 2 (set (reg:TI 63 [ x ])
        (const_int 0 [0])) pr55941.c:2 85 {*movti_internal_rex64}
     (nil))
(insn 5 4 6 2 (set (subreg:DF (reg:TI 63 [ x ]) 0)
        (reg:DF 64 [ x ])) pr55941.c:2 131 {*movdf_internal_rex64}
     (expr_list:REG_DEAD (reg:DF 64 [ x ])
        (nil)))
(insn 6 5 8 2 (set (subreg:DF (reg:TI 63 [ x ]) 8)
        (reg:DF 22 xmm1 [ x+8 ])) pr55941.c:2 131 {*movdf_internal_rex64}
     (expr_list:REG_DEAD (reg:DF 22 xmm1 [ x+8 ])
        (nil)))
(insn 8 6 9 2 (set (reg:DF 67 [ D.1730 ])
        (reg:DF 23 xmm2 [ y ])) pr55941.c:2 131 {*movdf_internal_rex64}
     (expr_list:REG_DEAD (reg:DF 23 xmm2 [ y ])
        (nil)))
(note 9 8 12 2 NOTE_INSN_FUNCTION_BEG)
(insn 12 9 17 2 (set (reg:DF 67 [ D.1730 ])
        (plus:DF (reg:DF 67 [ D.1730 ])
            (subreg:DF (reg:TI 63 [ x ]) 0))) pr55941.c:2 785
{*fop_df_comm_sse}
     (expr_list:REG_DEAD (reg:TI 63 [ x ])
        (nil)))
(all accesses to pseudo 63 in the listed insns), but it only drops the insn 6,
but doesn't figure out the only user uses the low part and thus propagate the
setter.  Or perhaps should forwprop propagate something like that?

[Bug target/55941] [4.8 Regression] Strange copy of double (in struct) to stack

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55941

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P1
   Target Milestone|---                         |4.8.0

[Bug target/55941] [4.8 Regression] Strange copy of double (in struct) to stack

[rth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55941

Richard Henderson <rth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
         AssignedTo|unassigned at gcc dot       |rth at gcc dot gnu.org
                   |gnu.org                     |

--- Comment #3 from Richard Henderson <rth at gcc dot gnu.org> 2013-02-14 20:40:34 UTC ---
Mine.

[Bug target/55941] [4.8 Regression] Strange copy of double (in struct) to stack

[rth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55941

--- Comment #4 from Richard Henderson <rth at gcc dot gnu.org> 2013-02-15 01:41:33 UTC ---
Author: rth
Date: Fri Feb 15 01:41:29 2013
New Revision: 196071

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=196071
Log:
PR target/55941
        * lower-subreg.c (simple_move): Check dest mode instead of src mode.

Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/lower-subreg.c

[Bug target/55941] [4.8 Regression] Strange copy of double (in struct) to stack

[rth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55941

Richard Henderson <rth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |FIXED

--- Comment #5 from Richard Henderson <rth at gcc dot gnu.org> 2013-02-15 06:07:21 UTC ---
Fixed.

[Bug target/55941] [4.8 Regression] Strange copy of double (in struct) to stack

[ubizjak at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55941

--- Comment #6 from Uros Bizjak <ubizjak at gmail dot com> 2013-02-15 08:55:05 UTC ---
With a fix, testcase compiles to (-O2):

f:
        addsd   %xmm0, %xmm2
        movapd  %xmm2, %xmm0
        ret

gcc-4.7 generates:

f:
        addsd   %xmm2, %xmm0
        ret

I have opened PR56339 for this problem.