wasm-reduce crash on WasmValidator (non-nullable domination)

[kripken]

Similar to #8713, I see this when I disable quiet validation:

[wasm-validator error in function 6] unexpected false: non-nullable local's sets must dominate gets, on 
5
wasm-reduce: src/tools/wasm-reduce/wasm-reduce.cpp:1131: void Reducer::reduceFunctions(): Assertion `WasmValidator().validate( *module, WasmValidator::Globally)' failed.

@tlively sounds like the code there is adding non-nullable locals in a way that doesn't validate?

[tlively]

Thanks, I'll take a look.

[tlively]

The obvious fix is to change FunctionReplacer::requiresNonNullableLocalFixups to return true, but Gemini and I are having a hard time coming up with a way to make the current code trigger this validation error in the first place. Do you still have the reproducer handy? In the worst case we can upload a fix without a test.

[kripken]

A fix without a test sgtm. This is from a very large testcase.