Asmc Macro Assembler Reference
RETM [[textitem]]
Terminates expansion of the current repeat or macro block and begins assembly of the next statement outside the block. In a macro function, textitem is the value returned.
RETM deviates from EXITM by skipping the return value if not used.
In this case the latter returns a value but the former do not:
_mm_sqrt_ss( _mm_min_ss( a, b ) )
_mm_min_ss( _mm_sqrt_ss( a ), b )