Help understanding "VFP magic dust" in cortex-strings memcpy

Hi!

I've attempted to study the implementation of memcpy for 32-bit Arm cores in Glibc (which is also found in arm-optimized-routines and first appeared in Linaro's cortex-strings project), and I came across a peculiar snippet:

#ifdef USE_VFP /* Magic dust alert! Force VFP on Cortex-A9. Experiments show that the FP pipeline is much better at streaming loads and stores. This is outside the critical loop. */ vmov.f32 s0, s0 #endif

This seems to imply that this NOP-like instruction affects CPU state and makes the vldr/vstr instructions that follow use different datapaths that they might otherwise? Can anyone shed more light on this, please?

I was able to trace history of this code back to revision 100 in cortex-strings repository, where it appeared as part of a large rewrite by Will Newton:

https://bazaar.launchpad.net/~linaro-toolchain-dev/cortex-strings/trunk/revi...

The entire memcpy.S file in Arm optimized-routines repo can be found here:

https://github.com/ARM-software/optimized-routines/blob/master/string/arm/me...

Thanks! Alexander