There are two different syntaxes for mask register.

[JerryShih]

@aswaterman
Why we have two different usage for mask?
Here are the example:

1. vfsgnjn.vf vd, vs2, rs1, v0.t
2. vmerge.vxm vd, vs2, rs1, v0

[hanna-kruppe]

IIRC the rationale in the meeting where this was decided was:

• v0.t syntax should be reserved for when the mask controls writeback, i.e., destination elements are undisturbed where the mask has 0s
• For vmerge, the mask register is not used in that way, instead all destination elements (up to vl) are written unconditionally (only which values are written depends on the mask bits)

[hanna-kruppe]

See also discussion in #189

[aswaterman]

Sounds like a good explanation to me.

[JerryShih]

@rkruppe
Thank you.