Fuzzer generates invalid code for table initializers

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Assessment

Difficulty
3/5
Estimated time
1-2 days
Newbie friendliness
68/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Quiet
Tech stack
wasm
Domain
compilers

Research direction

Run the supplied bin/wasm-opt command with the seed.wast module and --translate-to-fuzz, then inspect the table-initializer path and the code discussed in the linked pull request. Done means fuzz translation no longer emits ref.as_non_null in the constant table initializer and the resulting module passes validation.

Written by the indexing model from the issue text.

Description

I ran --translate-to-fuzz on the following seed file:

(module
  (import "env" "table" (table 1 1 (ref exn)))
)

 bin/wasm-opt -ttf -if seed.wast -all /dev/null -o /dev/null

And hit a fatal error that validation failed, since a ref.as_non_null was generated in a constant expression (the table initializer):

[wasm-validator error in module] unexpected false: table initializer value must be constant, on
...
 (table $timport$0 1 1 (ref exn) (ref.as_non_null
  (ref.null noexn)
 ))

It looks like it's caused by the code described here.

Dominant language
WebAssembly
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