[GR-54677] Support new exception handling proposal

[graalvmbot]

The new exception handling proposal as opposed to the legacy one uses a new try_table block for exception catching, if inside that block an exception is thrown, Wasm breaks to the block specified in the try_table's catch clauses. This makes exception control-flow the same as any other break-based control-flow, but makes it a bit harder for us.

This required support for Wasm blocks that return a result, which also made the validator more complex.

The new exception handling is used by default. The legacy proposal can be re-enabled using -H:+LegacyExceptions. In node (before version 25), the new exceptions are behind the --experimental-wasm-exnref flag.

---

WithExceptionNodes are now lowered to the following (see WasmIRWalker#lowerWithException for more details):

(block $exnBlock (result $throwable)
    (try_table (catch $exc_tag $exnBlock)
        WithExceptionNode();
        br Successor
    )
)
(local.set $exc_var)
ExceptionEdge();

This is optimal in terms of number of required blocks.

This does not seem to have an effect on code size.

[reneleonhardt]

All 3 features of WASM 3 mentioned as implemented are specifically shown as unimplemented by the latest news:
https://webassembly.org/news/2025-09-17-wasm-3.0/

Have Garbage Collection, Exception Handling and Typed Function References been implemented?
If they are, can they be marked as implemented in the WASM 3 news and the features overview?

https://webassembly.org/features/

[patrick96]

This PR is about Web Image, a JVM bytecode to Wasm compiler, not the GraalWasm runtime.

Though WasmGC support seems to be on its way for GraalWasm as well: #12701

[reneleonhardt]

Should Web Image be added to the webassembly.org implementations then, separate from GraalWasm?