HI,why the VFP vector mode can not be used in cortex-a series processors?
why VFP instructions with the arity set above 1 on ARMv7/NEON processors will perform much slower?
Support for arity > 1 is deprecated, and provided only for backwards compatibility with legacy code bases. It is known to be relatively slow. Either use the new NEON instructions, or write scalar VFP sequences with arity=1.
i still do not understand the reason why became slower int cortex-a processors using VFP vector mode,can you explain it in more details ?
There isn't really any more detail that will be useful; it's deprecated, slower on ARMv7, and totally removed in ARMv8. There are at least two fast non-deprecated alternatives; write non-vector VFP code with multiple instructions or use NEON.
HTH, Pete