b69fede72f
Currently, a variable can be named in two different ways in an ISLE pattern. One can write a pattern like `(T x y)` that binds the two args of `T` with the subpatterns `x` and `y`, each of which match anything and capture the value as a bound variable. Or, one can write a pattern like `(T x =x)`, where the first arg pattern `x` captures the value in `x` and the second arg pattern `=x` matches only the same value that was already captured. It turns out (thanks to @fitzgen for this insight here [1]) that this distinction can actually be inferred easily: if `x` isn't bound, then mentioning it binds it; otherwise, it matches only the already-bound variable. There's no concern about ordering (one mention binding vs. the other) because (i) the value is equal either way, and (ii) the types at both sites must be the same. This language tweak seems like it should simplify things nicely! We can remove the `=x` syntax later if we want, but this PR doesn't do so. [1] https://github.com/bytecodealliance/wasmtime/pull/4071#discussion_r859111513
7 lines
90 B
Common Lisp
7 lines
90 B
Common Lisp
(type u32 (primitive u32))
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(decl A (u32 u32) u32)
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(rule 1 (A x x) x)
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(rule 0 (A x _) 0)
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