armv8 NEON if condition

问题

I would like to realize if condition in armv8 NEON inline assembly code. In armv7 this was possible through checking overflow bit like this:

  VMRS r4, FPSCR            
  BIC r4, r4, #(1<<27)      
  VMSR FPSCR, r4     

  vtst.16  d30, d30, d30    
  vqadd.u16  d30, d30, d30 

  vmrs r4, FPSCR            
  tst  r4, #(1<<27)         
  bne label1

But I am not able to achieve this in armv8 equivalent code. It seems that SQADD doesnt affect overflow bit in FPSR or I cannot check it like this. Is it possible or is there better approach how to skip long part of code?

Thank you

回答1:

The same information is available in Aarch64. You just need to replace:

VMSR r4, FPSCR VMRS FPSCR, r4

by:

MRS w4, FPSR MSR FPSR, w4

来源：https://stackoverflow.com/questions/38145583/armv8-neon-if-condition