commit 7a29aa5984cb7c46408a04c09b4eefb1d1bb9c48
author Ömer Sinan Ağacan <omersa@google.com> Thu Aug 17 11:18:39 2023 +0000
committer Commit Queue <dart-scoped@luci-project-accounts.iam.gserviceaccount.com> Thu Aug 17 11:18:39 2023 +0000
tree 9c11890508a0fc708821490b31e9c2dea3bb1f89
parent 51ac43644d153a778097fe4f82b8e3a1902750f4

[dart2wasm] Simplify Error._throw

I can't find a public documentation of Binaryen's type merging pass, but
the code clearly states in [1] that merging isn't observable.

So we can remove the assumption in `Error._throw` that type merging can
merge unrelated struct types, and use a Wasm type test for checking if
the thrown object is an `Error`.

After this, Binaryen inlines all `Error._throw`s in some programs and
removes the definition.

Inlining `Error._throw` in turn removes some `unreachable`s. Example:

Before:

    (func $IndexError.check ...
      ...
      (if
        ...
        (call $Error._throw
         (local.get $3)
         (call $StackTrace.current))
        (unreachable)))

After:

     (func $IndexError.check ...
      ...
      (if
        ...
        (local.set $4
         (call $StackTrace.current))
        (if
         (ref.is_null
          (struct.get $IndexError 2
           (local.get $3)))
         (struct.set $IndexError 2
          (local.get $3)
          (local.get $4)))
        (throw $tag$0
         (local.get $3)
         (local.get $4))))

[1]: https://github.com/WebAssembly/binaryen/blob/0fc7b883d373924717ceccf71a6a759c97a8fb08/src/passes/TypeMerging.cpp#L18-L19

Change-Id: Ic635cf008435829043cd19306039659d894b0149
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/319401
Reviewed-by: Aske Simon Christensen <askesc@google.com>
Commit-Queue: Ömer Ağacan <omersa@google.com>