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Re: avx runtime check


On May 15, 2014, at 11:52 PM, Richard Biener <richard.guenther@gmail.com> wrote:
> On May 16, 2014 4:47:11 AM CEST, Mike Stump <mikestump@comcast.net> wrote:
>> This reorders the avx checks and gates on a target triplet check before
>> compiling any code.
> 
> Can you explain why?

Sure, because check_avx_hw_available runs [istarget x86_64-*-*] || [istarget i?86-*-*] before doing anything, like compiling:

       typedef double __m512d __attribute__ ((__vector_size__ (64)));

        __m512d _mm512_add (__m512d a)
        {
          return __builtin_ia32_addpd512_mask (a, a, a, 1, 4);
        }

with -mavx512f, which my target doesn’t have, but even running a compilation of that seems wrong.  The other possibility would be to add in a:

        # If this is not the right target then we can skip the test.                                                                                                                  
        if { !([istarget x86_64-*-*] || [istarget i?86-*-*]) } {
            expr 0
        } else {

into the test for check_effective_target_avx512f.


proc check_effective_target_avx512f { } {
    return [check_no_compiler_messages avx512f object {
        typedef double __m512d __attribute__ ((__vector_size__ (64)));

        __m512d _mm512_add (__m512d a)
        {
          return __builtin_ia32_addpd512_mask (a, a, a, 1, 4);
        }
    } "-O2 -mavx512f" ]
}

proc check_avx_hw_available { } {
    return [check_cached_effective_target avx_hw_available {
        # If this is not the right target then we can skip the test.                                                                                                                  
        if { !([istarget x86_64-*-*] || [istarget i?86-*-*]) } {
            expr 0
        } else {
            check_runtime_nocache avx_hw_available {
                #include "cpuid.h"                                                                                                                                                    
                int main ()
                {
	          unsigned int eax, ebx, ecx, edx;
                  if (__get_cpuid (1, &eax, &ebx, &ecx, &edx))
	            return ((ecx & (bit_AVX | bit_OSXSAVE))
                            != (bit_AVX | bit_OSXSAVE));
                  return 1;
                }
            } ""
        }
    }]
}


>> diff --git a/gcc/testsuite/lib/target-supports.exp
>> b/gcc/testsuite/lib/target-supports.exp
>> index 40b5414..103a28a 100644
>> --- a/gcc/testsuite/lib/target-supports.exp
>> +++ b/gcc/testsuite/lib/target-supports.exp
>> @@ -1353,8 +1353,8 @@ proc check_effective_target_sse2_runtime { } {
>> # Return 1 if the target supports running AVX executables, 0 otherwise.
>> 
>> proc check_effective_target_avx_runtime { } {
>> -    if { [check_effective_target_avx]
>> -        && [check_avx_hw_available]
>> +    if { [check_avx_hw_available]
>> +        && [check_effective_target_avx]
>>        && [check_avx_os_support_available] } {
>>       return 1
>>    }


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