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Re: -mfpmath=sse,387 is experimental ?
Zuxy Meng wrote:
> Hi,
>
> "Timothy Madden" <terminatorul@gmail.com> ååææ
!
>> I am sure having twice the number of registers (sse+387) would make a
>> big difference.
You're not counting the rename registers, you're talking about 32-bit mode
only, and you're discounting the different mode of accessing the registers.
>>
>> How would I know if my AMD Sempron 2200+ has separate execution units
>> for SSE and
>> FPU instructions, with independent registers ?
>
> Most CPU use the same FP unit for both x87 and SIMD operations so it
> wouldn't give you double the performance. The only exception I know of
> is K6-2/3, whose x87 and 3DNow! units are separate.
>
-march=pentium-m observed the preference of those CPUs for mixing the
types of code. This was due more to the limited issue rate for SSE
instructions than to the expanded number of registers in use. You are
welcome to test it on your CPU; however, AMD CPUs were designed to perform
well with SSE alone, particularly in 64-bit mode.