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 40static void __attribute__((constructor)) 41#ifndef __x86_64__ 42/* The i386 ABI only requires 4-byte stack alignment, so this is necessary 43 to make sure the fxsave struct gets correct alignment. 44 See PR27537 and PR28621. */ 45__attribute__ ((force_align_arg_pointer)) 46#endif 47set_fast_math (void) 48{ 49#ifndef __x86_64__ 50 /* All 64-bit targets have SSE and DAZ; only check them explicitly 51 for 32-bit ones. */ 52 unsigned int eax, ebx, ecx, edx; 53 54 /* See if we can use cpuid. */ 55 asm volatile ("pushfl; pushfl; popl %0; movl %0,%1; xorl %2,%0;" 56 "pushl %0; popfl; pushfl; popl %0; popfl" 57 : "=&r" (eax), "=&r" (ebx) 58 : "i" (0x00200000)); 59 60 if (((eax ^ ebx) & 0x00200000) == 0) 61 return; 62 63 /* Check the highest input value for eax. */ 64 asm volatile ("xchgl %%ebx, %1; cpuid; xchgl %%ebx, %1" 65 : "=a" (eax), "=r" (ebx), "=c" (ecx), "=d" (edx) 66 : "0" (0)); 67 68 if (eax == 0) 69 return; 70 71 asm volatile ("xchgl %%ebx, %1; cpuid; xchgl %%ebx, %1" 72 : "=a" (eax), "=r" (ebx), "=c" (ecx), "=d" (edx) 73 : "0" (1)); 74 75 if (edx & SSE) 76 { 77 unsigned int mxcsr = __builtin_ia32_stmxcsr (); 78 79 mxcsr |= MXCSR_FTZ; 80 81 if (edx & FXSAVE) 82 { 83 /* Check if DAZ is available. */ 84 struct 85 { 86 unsigned short int cwd; 87 unsigned short int swd; 88 unsigned short int twd; 89 unsigned short int fop; 90 long int fip; 91 long int fcs; 92 long int foo; 93 long int fos; 94 long int mxcsr; 95 long int mxcsr_mask; 96 long int st_space[32]; 97 long int xmm_space[32]; 98 long int padding[56]; 99 } __attribute__ ((aligned (16))) fxsave; 100 101 __builtin_memset (&fxsave, 0, sizeof (fxsave)); 102 103 asm volatile ("fxsave %0" : "=m" (fxsave) : "m" (fxsave)); 104 105 if (fxsave.mxcsr_mask & MXCSR_DAZ) 106 mxcsr |= MXCSR_DAZ; 107 } 108 109 __builtin_ia32_ldmxcsr (mxcsr); 110 } 111#else 112 unsigned int mxcsr = __builtin_ia32_stmxcsr (); 113 mxcsr |= MXCSR_DAZ | MXCSR_FTZ; 114 __builtin_ia32_ldmxcsr (mxcsr); 115#endif 116} 117