[llvm-commits] [llvm] r85697 - in /llvm/trunk: lib/Target/ARM/ARMInstrNEON.td test/CodeGen/ARM/fmacs.ll test/CodeGen/ARM/fnmacs.ll test/CodeGen/Thumb2/cross-rc-coalescing-2.ll

[David Conrad]

On Nov 3, 2009, at 5:07 PM, Jim Grosbach wrote:

>
> On Nov 2, 2009, at 1:53 AM, David Conrad wrote:
>
>> Thus even without modeling the special behaviour of vmla it's always
>> better to use it: it'll always be at least as fast as a separate vmul
>> +vadd. This applies to the integer versions as well.
>
>
> Hi David,
>
> Unfortunately, this turns out not to be the case. The NEON unit will  
> stall adjacent instructions in the presence of vmla to preserve in- 
> order retirement. If a RAW hazard is present, the stall is 8  
> (possibly 7) cycles, otherwise it is 4 cycles.

You're correct, sorry for the noise and wrong information.