libgcc/config/i386/crtfastmath.c

   1 /*
   2  * Copyright (C) 2005-2014 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 #ifndef _SOFT_FLOAT
  25 #define MXCSR_DAZ (1 << 6)      /* Enable denormals are zero mode */
  26 #define MXCSR_FTZ (1 << 15)     /* Enable flush to zero mode */
  27
  28 #ifndef __x86_64__
  29 /* All 64-bit targets have SSE and DAZ;
  30    only check them explicitly for 32-bit ones. */
  31 #include "cpuid.h"
  32 #endif
  33
  34 static void __attribute__((constructor))
  35 #ifndef __x86_64__
  36 /* The i386 ABI only requires 4-byte stack alignment, so this is necessary
  37    to make sure the fxsave struct gets correct alignment.
  38    See PR27537 and PR28621.  */
  39 __attribute__ ((force_align_arg_pointer))
  40 #endif
  41 set_fast_math (void)
  42 {
  43 #ifndef __x86_64__
  44   unsigned int eax, ebx, ecx, edx;
  45
  46   if (!__get_cpuid (1, &eax, &ebx, &ecx, &edx))
  47     return;
  48
  49   if (edx & bit_SSE)
  50     {
  51       unsigned int mxcsr;
  52
  53       if (edx & bit_FXSAVE)
  54         {
  55           /* Check if DAZ is available.  */
  56           struct
  57             {
  58               unsigned short cwd;
  59               unsigned short swd;
  60               unsigned short twd;
  61               unsigned short fop;
  62               unsigned int fip;
  63               unsigned int fcs;
  64               unsigned int foo;
  65               unsigned int fos;
  66               unsigned int mxcsr;
  67               unsigned int mxcsr_mask;
  68               unsigned int st_space[32];
  69               unsigned int xmm_space[32];
  70               unsigned int padding[56];
  71             } __attribute__ ((aligned (16))) fxsave;
  72
  73           /* This is necessary since some implementations of FXSAVE
  74              do not modify reserved areas within the image.  */
  75           fxsave.mxcsr_mask = 0;
  76
  77           __builtin_ia32_fxsave (&fxsave);
  78
  79           mxcsr = fxsave.mxcsr;
  80
  81           if (fxsave.mxcsr_mask & MXCSR_DAZ)
  82             mxcsr |= MXCSR_DAZ;
  83         }
  84       else
  85         mxcsr = __builtin_ia32_stmxcsr ();
  86
  87       mxcsr |= MXCSR_FTZ;
  88       __builtin_ia32_ldmxcsr (mxcsr);
  89     }
  90 #else
  91   unsigned int mxcsr = __builtin_ia32_stmxcsr ();
  92   mxcsr |= MXCSR_DAZ | MXCSR_FTZ;
  93   __builtin_ia32_ldmxcsr (mxcsr);
  94 #endif
  95 }
  96 #endif