If there are spare bits it would be very good to look at using some of them to specify the mode, because otherwise a SPR has to be used which will need to be set and unset. This can get costly.
+Idea: 2 bits for clamping mode? similar to elwidth:
+
+* 0b00 default (no clamp)
+* 0b01 8 bit (sel: -128/127, us:0/255)
+* 0b10 16 bit
+* 0b11 32 bit
+
+not the same *as* elwidth.
+
# Notes about Swizzle
Basically, there isn't enough room to try to fit two src src1/2 swizzle, and SV, even into 64 bit (actually 24) without severely compromising on the number of bits allocated to either swizzle, or SV, or both.