[Bug target/28074] New: -mstackrealign generates very inefficient code

[hjl at lucon dot org]

[hjl@gnu-3 xmm]$ cat x.c
#include <emmintrin.h>
extern char *e1 (void);
char *e1 (void)
{
  volatile __m128 dummy = _mm_set_ps1(0.f);
  return "OK";
}
[hjl@gnu-3 xmm]$ /usr/gcc-4.2/bin/gcc -m32 -O -msse2 -S -mstackrealign x.c     
[hjl@gnu-3 xmm]$ cat x.s
        .file   "x.c"
        .section        .rodata.str1.1,"aMS",@progbits,1
.LC0:
        .string "OK"
        .text
.globl e1
        .type   e1, @function
e1:
        leal    4(%esp), %ecx
        andl    $-16, %esp
        pushl   -4(%ecx)
        pushl   %ebp
        movl    %esp, %ebp
        pushl   %ecx
        subl    $20, %esp
        xorps   %xmm0, %xmm0
        movaps  %xmm0, -24(%ebp)
        movl    $.LC0, %eax
        addl    $20, %esp
        popl    %ecx
        popl    %ebp
        leal    -4(%ecx), %esp
        ret
        .size   e1, .-e1
        .ident  "GCC: (GNU) 4.2.0 20060613 (experimental) [trunk revision
114620 clean]"
        .section        .note.GNU-stack,"",@progbits
[hjl@gnu-3 xmm]$

Icc 9.1 generates:

        .globl e1
e1:
..B1.1:                         # Preds ..B1.0
        pushl     %ebp                                          #4.1
        movl      %esp, %ebp                                    #4.1
        andl      $-16, %esp                                    #4.1
        subl      $16, %esp                                     #4.1
        xorps     %xmm0, %xmm0                                  #5.27
        movaps    %xmm0, (%esp)                                 #5.19
        movl      $__STRING.0, %eax                             #6.10
        movl      %ebp, %esp                                    #6.10
        popl      %ebp                                          #6.10
        ret                                                     #6.10

It doesn't waste ecx to align the stack.


-- 
           Summary: -mstackrealign generates very inefficient code
           Product: gcc
           Version: 4.2.0
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: target
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: hjl at lucon dot org
 GCC build triplet: i686-pc-linux-gnu
  GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28074