3b76874834
Ulrich Weigand identified two bugs in this code due to it falsely claiming there were unreachable rules in the s390x backend. The fixes are: - Add constraints for pure constructors. I didn't notice that a constructor which is declared pure (which currently implies that it is fallible), when used on the left-hand side of a rule, can cause the rule to fail to match. Therefore, any constructors on the left-hand side must be noted as additional constraints on the rule, so that overlap checking can see them. - Ignore subset-overlaps for rules with equality constraints This eliminates false positives when checking for unreachable rules. It introduces false negatives instead but we prefer to fail to detect an error instead of claiming that valid input is wrong. We can implement a more accurate check later.
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.