In the SSAT instruction description it says:
ASR #32 Arithmetic right shift by 32 bits, permitted only for encoding A1. Encoded as sh = 1, immsh = 0b00000.
ASR #32 Arithmetic right shift by 32 bits, permitted only for encoding A1.
Encoded as sh = 1, immsh = 0b00000.
What does that mean?
Isn't ASR #32 the same as ASR #31?
I understand that it shifts (with "sign extension") the whole 32-bit value out and leaves only the sign extension bits
that are "copies" of the highest bit of the original value.
What am I missing here?
That definitely qualifies for a cool trick. If you want to avoid branching, you could combine it with the sbcs instruction like SBCS r3,r3,r3 after a BMI.
(or of course use conditional execution). Using it as a mask for a conditional AND would probably also be useful.
... MVNS r0,r1,asr#31 might also prove useful, if you need to invert the sign.