r300: better 1-x presubtract pattern matching
Right now we only check for 1 - x
patterns, but we can also convert -x + 1
just fine and also x - 1
or -1 + x
when we add extra negate.
This can be done in the backend, but would be so much easier with a late algebraic rule to just shuffle it to the expected form in NIR, so just another thing on the todo list after ntt merge.