[EH] Add exnref type back (#6149)

At the Oct hybrid CG meeting, we decided to add back `exnref`, which was
removed in 2020:
https://github.com/WebAssembly/meetings/blob/main/main/2023/CG-10.md

The new version of the proposal reflected in the explainer:
https://github.com/WebAssembly/exception-handling/blob/main/proposals/exception-handling/Exceptions.md

While adding support for `exnref` in the current codebase which has all
GC subtype hierarchies, I noticed we might need `noexn` heap type for
the bottom type of `exn`. We don't have it now so I just set it to 0xff
for the moment.

1 files changed, 14 insertions, 0 deletions

diff --git a/test/exception-handling.wast.fromBinary.noDebugInfo b/test/exception-handling.wast.fromBinary.noDebugInfo
index 4bc460630..beea8498b 100644
--- a/test/exception-handling.wast.fromBinary.noDebugInfo
+++ b/test/exception-handling.wast.fromBinary.noDebugInfo
@@ -4,6 +4,7 @@
  (type $2 (func (param i64)))
  (type $3 (func (param i32 i64)))
  (type $4 (func (param eqref)))
+ (type $5 (func (result exnref)))
  (tag $tag$0 (param i32))
  (tag $tag$1 (param i64))
  (tag $tag$2 (param i32 i64))
@@ -428,5 +429,18 @@
   )
   (nop)
  )
+ (func $8 (type $5) (result exnref)
+  (local $0 exnref)
+  (local $1 nullexnref)
+  (if (result exnref)
+   (i32.const 1)
+   (if (result nullexnref)
+    (i32.const 1)
+    (local.get $1)
+    (ref.null noexn)
+   )
+   (local.get $0)
+  )
+ )
 )