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

[Eli Friedman]

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?

-Eli