Typed continuations: suspend instructions (#6393)

This PR is part of a series that adds basic support for the [typed
continuations/wasmfx proposal](https://github.com/wasmfx/specfx).

This particular PR adds support for the `suspend` instruction for suspending
with a given tag, documented
[here](https://github.com/wasmfx/specfx/blob/main/proposals/continuations/Overview.md#instructions).
These instructions are of the form `(suspend $tag)`. Assuming that `$tag` is
defined with _n_ `param` types `t_1` to `t_n`, the instruction consumes _n_
arguments of types  `t_1` to `t_n`. Its result type is the same as the `result`
type of the tag. Thus, the folded textual representation looks like
`(suspend $tag arg1 ... argn)`.

Support for the instruction is implemented in both the old and the new wat
parser.

Note that this PR does not implement validation of the new instruction.

This PR also fixes finalization of `cont.new`, `cont.bind` and `resume` nodes in
those cases where any  of their children are unreachable.

1 files changed, 4 insertions, 0 deletions

diff --git a/src/wasm2js.h b/src/wasm2js.h
index 5f0305877..3ac4d2b4d 100644
--- a/src/wasm2js.h
+++ b/src/wasm2js.h
@@ -2440,6 +2440,10 @@ Ref Wasm2JSBuilder::processFunctionBody(Module* m,
       unimplemented(curr);
       WASM_UNREACHABLE("unimp");
     }
+    Ref visitSuspend(Suspend* curr) {
+      unimplemented(curr);
+      WASM_UNREACHABLE("unimp");
+    }
 
   private:
     Ref makePointer(Expression* ptr, Address offset) {