libgcc/config/i386/crtfastmath.c

   1 /*
   2  * Copyright (C) 2005-2020 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
  33 __attribute__ ((target("fxsr,sse")))
  34 static void
  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 set_fast_math_sse (unsigned int edx)
  40 {
  41   unsigned int mxcsr;
  42
  43   if (edx & bit_FXSAVE)
  44     {
  45       /* Check if DAZ is available.  */
  46       struct
  47       {
  48         unsigned short cwd;
  49         unsigned short swd;
  50         unsigned short twd;
  51         unsigned short fop;
  52         unsigned int fip;
  53         unsigned int fcs;
  54         unsigned int foo;
  55         unsigned int fos;
  56         unsigned int mxcsr;
  57         unsigned int mxcsr_mask;
  58         unsigned int st_space[32];
  59         unsigned int xmm_space[32];
  60         unsigned int padding[56];
  61       } __attribute__ ((aligned (16))) fxsave;
  62
  63       /* This is necessary since some implementations of FXSAVE
  64          do not modify reserved areas within the image.  */
  65       fxsave.mxcsr_mask = 0;
  66
  67       __builtin_ia32_fxsave (&fxsave);
  68
  69       mxcsr = fxsave.mxcsr;
  70
  71       if (fxsave.mxcsr_mask & MXCSR_DAZ)
  72         mxcsr |= MXCSR_DAZ;
  73     }
  74   else
  75     mxcsr = __builtin_ia32_stmxcsr ();
  76
  77   mxcsr |= MXCSR_FTZ;
  78   __builtin_ia32_ldmxcsr (mxcsr);
  79 }
  80 #endif
  81
  82 static void __attribute__((constructor))
  83 set_fast_math (void)
  84 {
  85 #ifndef __x86_64__
  86   unsigned int eax, ebx, ecx, edx;
  87
  88   if (!__get_cpuid (1, &eax, &ebx, &ecx, &edx))
  89     return;
  90
  91   if (edx & bit_SSE)
  92     set_fast_math_sse (edx);
  93 #else
  94   unsigned int mxcsr = __builtin_ia32_stmxcsr ();
  95   mxcsr |= MXCSR_DAZ | MXCSR_FTZ;
  96   __builtin_ia32_ldmxcsr (mxcsr);
  97 #endif
  98 }
  99 #endif