gcc/config/i386/crtfastmath.c

   1 /*
   2  * Copyright (C) 2005 Free Software Foundation, Inc.
   3  *
   4  * This file is free software; you can redistribute it and/or modify it
   5  * under the terms of the GNU General Public License as published by the
   6  * Free Software Foundation; either version 2, or (at your option) any
   7  * later version.
   8  *
   9  * In addition to the permissions in the GNU General Public License, the
  10  * Free Software Foundation gives you unlimited permission to link the
  11  * compiled version of this file with other programs, and to distribute
  12  * those programs without any restriction coming from the use of this
  13  * file.  (The General Public License restrictions do apply in other
  14  * respects; for example, they cover modification of the file, and
  15  * distribution when not linked into another program.)
  16  *
  17  * This file is distributed in the hope that it will be useful, but
  18  * WITHOUT ANY WARRANTY; without even the implied warranty of
  19  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  20  * General Public License for more details.
  21  *
  22  * You should have received a copy of the GNU General Public License
  23  * along with this program; see the file COPYING.  If not, write to
  24  * the Free Software Foundation, 51 Franklin Street, Fifth Floor,
  25  * Boston, MA 02110-1301, USA.
  26  *
  27  *    As a special exception, if you link this library with files
  28  *    compiled with GCC to produce an executable, this does not cause
  29  *    the resulting executable to be covered by the GNU General Public License.
  30  *    This exception does not however invalidate any other reasons why
  31  *    the executable file might be covered by the GNU General Public License.
  32  */
  33
  34 #define MXCSR_DAZ (1 << 6)      /* Enable denormals are zero mode */
  35 #define MXCSR_FTZ (1 << 15)     /* Enable flush to zero mode */
  36
  37 #define FXSAVE  (1 << 24)
  38 #define SSE     (1 << 25)
  39
  40 static void __attribute__((constructor))
  41 set_fast_math (void)
  42 {
  43 #ifndef __x86_64__
  44   /* All 64-bit targets have SSE and DAZ; only check them explicitly
  45      for 32-bit ones. */
  46   unsigned int eax, ebx, ecx, edx;
  47
  48   /* See if we can use cpuid.  */
  49   asm volatile ("pushfl; pushfl; popl %0; movl %0,%1; xorl %2,%0;"
  50                 "pushl %0; popfl; pushfl; popl %0; popfl"
  51                 : "=&r" (eax), "=&r" (ebx)
  52                 : "i" (0x00200000));
  53
  54   if (((eax ^ ebx) & 0x00200000) == 0)
  55     return;
  56
  57   /* Check the highest input value for eax.  */
  58   asm volatile ("xchgl %%ebx, %1; cpuid; xchgl %%ebx, %1"
  59                 : "=a" (eax), "=r" (ebx), "=c" (ecx), "=d" (edx)
  60                 : "0" (0));
  61
  62   if (eax == 0)
  63     return;
  64
  65   asm volatile ("xchgl %%ebx, %1; cpuid; xchgl %%ebx, %1"
  66                 : "=a" (eax), "=r" (ebx), "=c" (ecx), "=d" (edx)
  67                 : "0" (1));
  68
  69   if (edx & SSE)
  70     {
  71       unsigned int mxcsr = __builtin_ia32_stmxcsr ();
  72
  73       mxcsr |= MXCSR_FTZ;
  74
  75       if (edx & FXSAVE)
  76         {
  77           /* Check if DAZ is available.  */
  78           struct
  79             {
  80               unsigned short int cwd;
  81               unsigned short int swd;
  82               unsigned short int twd;
  83               unsigned short int fop;
  84               long int fip;
  85               long int fcs;
  86               long int foo;
  87               long int fos;
  88               long int mxcsr;
  89               long int mxcsr_mask;
  90               long int st_space[32];
  91               long int xmm_space[32];
  92               long int padding[56];
  93             } __attribute__ ((aligned (16))) fxsave;
  94
  95           __builtin_memset (&fxsave, 0, sizeof (fxsave));
  96
  97           asm volatile ("fxsave %0" : "=m" (fxsave) : "m" (fxsave));
  98
  99           if (fxsave.mxcsr_mask & MXCSR_DAZ)
 100             mxcsr |= MXCSR_DAZ;
 101         }
 102
 103       __builtin_ia32_ldmxcsr (mxcsr);
 104     }
 105 #else
 106   unsigned int mxcsr = __builtin_ia32_stmxcsr ();
 107   mxcsr |= MXCSR_DAZ | MXCSR_FTZ;
 108   __builtin_ia32_ldmxcsr (mxcsr);
 109 #endif
 110 }