We can remove the restriction that the narrow type needs to be exactly
EEW / 2 for scalable ISD::{ADD,SUB,MUL} nodes. This allows us to perform
the combine even if we can't fully fold the extend into the widening op.
VP intrinsics already do this, since they are lowered to _VL nodes which
don't have this restriction.
The "exactly EEW / 2" narrow type restriction prevented us from emitting
V{S,Z}EXT_VL nodes with i1 element types which crash when we try to
select them, since no other legal type is double the size of i1, see the
test case added in this PR `i1_zext`. So to preserve this, this adds a
check for i1 narrow types instead.
These test cases show (op (ext a), (ext b)) patterns where the dest EEW is
more than 2 * source EEW. These could be lowered into widening ops where we
still have extend the operands, but at a smaller EEW.
This changes the default value used for mask policy from mask undisturbed to mask agnostic. In hardware, there may be a minor preference for ta/ma, but since this is only going to apply to instructions which don't use the mask policy bit, this is functionally mostly a nop. The main value is to make future changes to using MA when legal for masked instructions easier to review by reducing test churn.
The prior code was motivated by a desire to minimize state transitions between masked and unmasked code. This patch achieves the same effect using the demanded field logic (landed in afb45ff), and there are no regressions I spotted in the test diffs. (Given the size, I have only been able to skim.) I do want to call out that regressions are possible here; the demanded analysis only works on a block local scope right now, so e.g. a tight loop mixing masked and unmasked computation might see an extra vsetvli or two.
Differential Revision: https://reviews.llvm.org/D133803
One of the sources is the same size as the destination so that source
doesn't have an overlap with the destination register. By using the _TIED
form we avoid an early clobber contraint for that source.
This matches what was already done for instrinsics. ConvertToThreeAddress
will fix it if it can't stay tied.
