[EH] Improve catch validation (#4315)

This improves validation of `catch` bodies mostly by checking the
validity of `pop`s.

For every `catch` body:
- Checks if its tag exists
- If the tag's type is none:
  - Ensures there shouldn't be any `pop`s
- If the tag's type is not none:
  - Checks if there's a single `pop` within the catch body
  - Checks if the tag type matches the `pop`'s type
  - Checks if the `pop`'s location is valid

For every `catch_all` body:
- Ensures there shuldn't be any `pop`s

This uncovers several bugs related to `pop`s in existing tests, which
this PR also fixes.

1 files changed, 26 insertions, 0 deletions

diff --git a/test/exception-handling.wast b/test/exception-handling.wast
index c608e860a..cd436296b 100644
--- a/test/exception-handling.wast
+++ b/test/exception-handling.wast
@@ -2,6 +2,7 @@
   (tag $e-i32 (param i32))
   (tag $e-i64 (param i64))
   (tag $e-i32-i64 (param i32 i64))
+  (tag $e-anyref (param anyref))
   (tag $e-empty)
 
   (func $foo)
@@ -311,4 +312,29 @@
       )
     )
   )
+
+  (func $pop_test
+    (try
+      (do)
+      (catch $e-i32
+        (throw $e-i32
+          (if (result i32)
+            ;; pop is within an if condition, so this is OK.
+            (pop i32)
+            (i32.const 0)
+            (i32.const 3)
+          )
+        )
+      )
+    )
+
+    (try
+      (do)
+      (catch $e-anyref
+        (drop
+          (pop funcref) ;; pop can be subtype
+        )
+      )
+    )
+  )
 )