[cfe-commits] r166743 - in /cfe/trunk: lib/Headers/xmmintrin.h test/CodeGen/sse-builtins.c

[manman ren]

On Oct 30, 2012, at 4:13 PM, Michael Liao <michael.liao at intel.com> wrote:

> These unary insns are not modelled accurately to capture the hardware
> behavior (high parts of result is preserved in SSE variant). Even though
> the fix works here, it'd better to fix them in X86 backend. Bug is filed
> in PR14221.
I actually have a fix in backend, but thought it is cleaner to fix it in the front-end :)

Thanks,
Manman

> 
> Yours
> - Michael
> 
> On Tue, 2012-10-30 at 10:57 -0700, manman ren wrote:
>> On Oct 29, 2012, at 6:01 PM, Eli Friedman <eli.friedman at gmail.com> wrote:
>> 
>>> On Thu, Oct 25, 2012 at 8:23 PM, Manman Ren <mren at apple.com> wrote:
>>>> 
>>>> 
>>>> Sent from my iPhone
>>>> 
>>>> On Oct 25, 2012, at 7:54 PM, Eli Friedman <eli.friedman at gmail.com> wrote:
>>>> 
>>>>> On Thu, Oct 25, 2012 at 7:35 PM, Manman Ren <mren at apple.com> wrote:
>>>>>> 
>>>>>> 
>>>>>> Sent from my iPhone
>>>>>> 
>>>>>> On Oct 25, 2012, at 6:13 PM, Eli Friedman <eli.friedman at gmail.com> wrote:
>>>>>> 
>>>>>>> On Thu, Oct 25, 2012 at 5:25 PM, Manman Ren <mren at apple.com> wrote:
>>>>>>>> Author: mren
>>>>>>>> Date: Thu Oct 25 19:25:10 2012
>>>>>>>> New Revision: 166743
>>>>>>>> 
>>>>>>>> URL: http://llvm.org/viewvc/llvm-project?rev=166743&view=rev
>>>>>>>> Log:
>>>>>>>> X86 SSE Intrinsics: update header for sqrt_ss, rsqrt_ss and rcp_ss.
>>>>>>>> 
>>>>>>>> There intrinsics pass through the upper FP values from the input.
>>>>>>>> rdar://12558838
>>>>>>>> 
>>>>>>>> Modified:
>>>>>>>> cfe/trunk/lib/Headers/xmmintrin.h
>>>>>>>> cfe/trunk/test/CodeGen/sse-builtins.c
>>>>>>>> 
>>>>>>>> Modified: cfe/trunk/lib/Headers/xmmintrin.h
>>>>>>>> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Headers/xmmintrin.h?rev=166743&r1=166742&r2=166743&view=diff
>>>>>>>> ==============================================================================
>>>>>>>> --- cfe/trunk/lib/Headers/xmmintrin.h (original)
>>>>>>>> +++ cfe/trunk/lib/Headers/xmmintrin.h Thu Oct 25 19:25:10 2012
>>>>>>>> @@ -95,7 +95,8 @@
>>>>>>>> static __inline__ __m128 __attribute__((__always_inline__, __nodebug__))
>>>>>>>> _mm_sqrt_ss(__m128 a)
>>>>>>>> {
>>>>>>>> -  return __builtin_ia32_sqrtss(a);
>>>>>>>> +  __m128 c = __builtin_ia32_sqrtss(a);
>>>>>>>> +  return (__m128) { c[0], a[1], a[2], a[3] };
>>>>>>>> }
>>>>>>> 
>>>>>>> What does exactly does __builtin_ia32_sqrtss return, if not the result
>>>>>>> of a sqrtss instruction?
>>>>>> builtin returns the result of sqrtss instruction, which only updates the lowest FP. mm_sqrt_ss has the upper FPs pass through to the output.
>>>>> 
>>>>> What exactly is in the top 96 bits of the return value of
>>>>> __builtin_ia32_sqrtss, then?
>>>> Those bits are undefined with the current implementation, same goes for sqrt_sd.
>>> 
>>> Why are the intrinsics defined to take vectors in the first place, then?
>> Not sure why the builtins for sqrtss, rsqrtss, rcpss and sqrtsd take vectors.
>> Their top bits are undefined since they directly map to the corresponding instructions which have the top bits from the un-initialized destination registers.
>> 
>> Thanks,
>> Manman
>>> 
>>> -Eli
>> 
>> _______________________________________________
>> cfe-commits mailing list
>> cfe-commits at cs.uiuc.edu
>> http://lists.cs.uiuc.edu/mailman/listinfo/cfe-commits
> 
>