mutate breaks semantics: i32.eq is not associative #2766

With --preserve-semantics, the peephole mutator can rewrite with the rule i32.eq-associates:

This identity does not hold, because i32.eq returns 0 or 1 rather than one of its operands. For example, with x = 1, y = z = 0x80000000:

• (i32.eq x (i32.eq y z)) = (i32.eq 1 1) = 1
• (i32.eq (i32.eq x y) z) = (i32.eq 0 0x80000000) = 0

The rule right below it, i64.eq-associates, is ill-typed. The inner i64.eq produces an i32, but the outer i64.eq expects i64 operands. Neither side can appear in a valid module, so it never fires. Even with the types fixed, it would be wrong for the same reason.

Repro

test.wat:

(module
  (func (export "f") (param i32 i32 i32) (result i32)
    (i32.eq (local.get 0) (i32.eq (local.get 1) (local.get 2)))))

$ wasm-tools parse test.wat -o test.wasm
$ wasm-tools mutate --preserve-semantics -s 211 test.wasm -o mutated.wasm
$ wasmtime run --invoke f test.wasm 1 -2147483648 -2147483648
1
$ wasmtime run --invoke f mutated.wasm 1 -2147483648 -2147483648
0

Suggested fix

Both i32.eq-associates and i64.eq-associates should be removed.

Version

• wasm-tools 1.261.0 (96376d3 2026-10-08).