Hi Joshua,
> For th.vmadc/th.vmsbc as well as narrowing arithmetic instructions
> and floating-point compare instructions, an illegal instruction
> exception will be raised if the destination vector register overlaps
> a source vector register group.
>
> To handle this issue, we use "group_overlap" and "enabled" attribute
> to disable some alternatives for xtheadvector.
> ;; Widening instructions have group-overlap constraints. Those are only
> ;; valid for certain register-group sizes. This attribute marks the
> ;; alternatives not matching the required register-group size as disabled.
> -(define_attr "group_overlap" "none,W21,W42,W84,W43,W86,W87,W0"
> +(define_attr "group_overlap"
> "none,W21,W42,W84,W43,W86,W87,W0,thv_disabled,rvv_disabled"
> (const_string "none"))
I realize there have been some discussions before but I find the naming
misleading. The group_overlap attribute is supposed to specify whether
groups overlap (and mark the respective alternatives accepting
only this overlap).
Then we check if the groups overlap and disable all non-matching
alternatives. "none" i.e. "no overlap" always matches.
Your first goal seems to be to disable existing non-early-clobber
alternatives for thv. For this, maybe "full", "same" (or "any"?) would
work? Please also add a comment in group_overlap_valid then that we
need not actually check for register equality.
For the other insns, I wonder if we could get away with not really
disabling the newly added early-clobber alternatives for RVV but
just disparaging ("?") them? That way we could re-use "full" for
the thv-disabled alternatives and "none" for the newly added ones.
("none" will still be misleading then, though :/)
If this doesn't work or others feel the separation is not strict
enough, I'd prefer a separate attribute rather than overloading
group_overlap. Maybe something like "spec_restriction" or similar
with two values "rvv" and "thv"?
Regards
Robin
