54207d343e
In #5174 we decided it doesn't make sense for a rule to have a bind-pattern at the root of its left-hand side. There's no Rust value corresponding to the root value of such a term, because it actually represents a function declaration with one or more arguments. This commit takes that to its logical conclusion. `sema::Rule` previously had an `lhs` field whose value must always be a `Pattern::Term` variant, and anyone using that structure had to deal with the possibility of finding the wrong variant there. Now the relevant fields from that variant are stored directly in `Rule` instead. Also, the (tiny!) portion of `translate_pattern` which applied when the pattern was the root term is now inlined in `collect_rules`. Because `translate_pattern` no longer has to special-case the root term, we can delete its `rule_term` and `is_root` arguments. That brings it down to a more manageable four arguments, which means many calls fit on one line now.
ISLE: Instruction Selection / Lowering Expressions
ISLE is a domain specific language (DSL) for instruction selection and lowering
clif instructions to vcode's MachInsts in Cranelift.
ISLE is a statically-typed term-rewriting language. You define rewriting rules
that map input terms (clif instructions) into output terms (MachInsts). These
rules get compiled down into Rust source test that uses a tree of match
expressions that is as good or better than what you would have written by hand.