gcc/config/i386/crtfastmath.c

   1 /*
   2  * Copyright (C) 2005, 2007, 2009 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 3, or (at your option) any
   7  * later version.
   8  *
   9  * This file is distributed in the hope that it will be useful, but
  10  * WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12  * General Public License for more details.
  13  *
  14  * Under Section 7 of GPL version 3, you are granted additional
  15  * permissions described in the GCC Runtime Library Exception, version
  16  * 3.1, as published by the Free Software Foundation.
  17  *
  18  * You should have received a copy of the GNU General Public License and
  19  * a copy of the GCC Runtime Library Exception along with this program;
  20  * see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
  21  * <http://www.gnu.org/licenses/>.
  22  */
  23
  24 #define MXCSR_DAZ (1 << 6)      /* Enable denormals are zero mode */
  25 #define MXCSR_FTZ (1 << 15)     /* Enable flush to zero mode */
  26
  27 #ifndef __x86_64__
  28 /* All 64-bit targets have SSE and DAZ;
  29    only check them explicitly for 32-bit ones. */
  30 #include "cpuid.h"
  31 #endif
  32
  33 static void __attribute__((constructor))
  34 #ifndef __x86_64__
  35 /* The i386 ABI only requires 4-byte stack alignment, so this is necessary
  36    to make sure the fxsave struct gets correct alignment.
  37    See PR27537 and PR28621.  */
  38 __attribute__ ((force_align_arg_pointer))
  39 #endif
  40 set_fast_math (void)
  41 {
  42 #ifndef __x86_64__
  43   unsigned int eax, ebx, ecx, edx;
  44
  45   if (!__get_cpuid (1, &eax, &ebx, &ecx, &edx))
  46     return;
  47
  48   if (edx & bit_SSE)
  49     {
  50       unsigned int mxcsr = __builtin_ia32_stmxcsr ();
  51
  52       mxcsr |= MXCSR_FTZ;
  53
  54       if (edx & bit_FXSAVE)
  55         {
  56           /* Check if DAZ is available.  */
  57           struct
  58             {
  59               unsigned short int cwd;
  60               unsigned short int swd;
  61               unsigned short int twd;
  62               unsigned short int fop;
  63               long int fip;
  64               long int fcs;
  65               long int foo;
  66               long int fos;
  67               long int mxcsr;
  68               long int mxcsr_mask;
  69               long int st_space[32];
  70               long int xmm_space[32];
  71               long int padding[56];
  72             } __attribute__ ((aligned (16))) fxsave;
  73
  74           __builtin_memset (&fxsave, 0, sizeof (fxsave));
  75
  76           asm volatile ("fxsave %0" : "=m" (fxsave) : "m" (fxsave));
  77
  78           if (fxsave.mxcsr_mask & MXCSR_DAZ)
  79             mxcsr |= MXCSR_DAZ;
  80         }
  81
  82       __builtin_ia32_ldmxcsr (mxcsr);
  83     }
  84 #else
  85   unsigned int mxcsr = __builtin_ia32_stmxcsr ();
  86   mxcsr |= MXCSR_DAZ | MXCSR_FTZ;
  87   __builtin_ia32_ldmxcsr (mxcsr);
  88 #endif
  89 }