[Bug other/55527] New: Passing structures containing floats by value in calls are underoptimized

[alex.gaynor at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55527



             Bug #: 55527

           Summary: Passing structures containing floats by value in calls

                    are underoptimized

    Classification: Unclassified

           Product: gcc

           Version: 4.7.2

            Status: UNCONFIRMED

          Severity: normal

          Priority: P3

         Component: other

        AssignedTo: unassig...@gcc.gnu.org

        ReportedBy: alex.gay...@gmail.com





This can be reproduced with the following code:



agaynor@tannit:~$ gcc --version

gcc (Ubuntu/Linaro 4.7.2-4precise1) 4.7.2

Copyright (C) 2012 Free Software Foundation, Inc.

This is free software; see the source for copying conditions.  There is NO

warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.



agaynor@tannit:~$ cat t.c 

struct x {

    float a;

    float b;

};





void f(struct x);



void g(float x, float y) {

    struct x z = {x, y};

    f(z);

}

agaynor@tannit:~$ gcc -O3 -S t.c 

agaynor@tannit:~$ cat t.s 

    .file    "t.c"

    .text

    .p2align 4,,15

    .globl    g

    .type    g, @function

g:

.LFB0:

    .cfi_startproc

    subq    $24, %rsp

    .cfi_def_cfa_offset 32

    movss    %xmm0, 12(%rsp)

    movq    %xmm1, (%rsp)

    movq    (%rsp), %rdx

    movl    12(%rsp), %eax

    salq    $32, %rdx

    movl    %eax, %eax

    orq    %rdx, %rax

    movq    %rax, (%rsp)

    movq    (%rsp), %xmm0

    call    f

    addq    $24, %rsp

    .cfi_def_cfa_offset 8

    ret

    .cfi_endproc

.LFE0:

    .size    g, .-g

    .ident    "GCC: (Ubuntu/Linaro 4.7.2-4precise1) 4.7.2"

    .section    .note.GNU-stack,"",@progbits





It would be more efficient to compile this using the PUNPCKLD instruction,

rather than all these moves and conversions from XMM to GPR registers.