[EH] Support try-delegate in interpreter (#4408)

Author: aheejin

src/wasm-interpreter.h

@@ -2697,6 +2697,9 @@ template<typename GlobalManager, typename SubType> class ModuleInstanceBase {
     FunctionScope& scope;
     // Stack of <caught exception, caught catch's try label>
     SmallVector<std::pair<WasmException, Name>, 4> exceptionStack;
+    // The current delegate target, if delegation of an exception is in
+    // progress. If no delegation is in progress, this will be an empty Name.
+    Name currDelegateTarget;
 
   protected:
     // Returns the instance that defines the memory used by this one.
@@ -3443,6 +3446,16 @@ template<typename GlobalManager, typename SubType> class ModuleInstanceBase {
       try {
         return this->visit(curr->body);
       } catch (const WasmException& e) {
+        // If delegation is in progress and the current try is not the target of
+        // the delegation, don't handle it and just rethrow.
+        if (currDelegateTarget.is()) {
+          if (currDelegateTarget == curr->name) {
+            currDelegateTarget.clear();
+          } else {
+            throw;
+          }
+        }
+
         auto processCatchBody = [&](Expression* catchBody) {
           // Push the current exception onto the exceptionStack in case
           // 'rethrow's use it
@@ -3469,6 +3482,9 @@ template<typename GlobalManager, typename SubType> class ModuleInstanceBase {
         if (curr->hasCatchAll()) {
           return processCatchBody(curr->catchBodies.back());
         }
+        if (curr->isDelegate()) {
+          currDelegateTarget = curr->delegateTarget;
+        }
         // This exception is not caught by this try-catch. Rethrow it.
         throw;
       }

test/spec/exception-handling.wast

@@ -201,6 +201,88 @@
       )
     )
   )
+
+  (func (export "try_delegate_caught") (result i32)
+    (try $l0 (result i32)
+      (do
+        (try (result i32)
+          (do
+            (try (result i32)
+              (do
+                 (throw $e-i32 (i32.const 3))
+              )
+              (delegate $l0)
+            )
+          )
+          (catch_all
+            (i32.const 0)
+          )
+        )
+      )
+      (catch $e-i32
+        (pop i32)
+      )
+    )
+  )
+
+  (func (export "try_delegate_to_catchless_try") (result i32)
+    (try $l0 (result i32)
+      (do
+        (try (result i32)
+          (do
+            (try (result i32)
+              (do
+                 (throw $e-i32 (i32.const 3))
+              )
+              (delegate $l0)
+            )
+          )
+          (catch_all
+            (i32.const 0)
+          )
+        )
+      )
+    )
+  )
+
+  (func (export "try_delegate_to_delegate") (result i32)
+    (try $l0 (result i32)
+      (do
+        (try $l1 (result i32)
+          (do
+            (try (result i32)
+              (do
+                 (throw $e-i32 (i32.const 3))
+              )
+              (delegate $l1)
+            )
+          )
+          (delegate $l0)
+        )
+      )
+      (catch $e-i32
+        (pop i32)
+      )
+    )
+  )
+
+  (func (export "try_delegate_to_caller")
+    (try $l0
+      (do
+        (try $l1
+          (do
+            (try
+              (do
+                 (throw $e-i32 (i32.const 3))
+              )
+              (delegate 2) ;; to caller
+            )
+          )
+        )
+      )
+      (catch_all)
+    )
+  )
 )
 
 (assert_trap (invoke "throw_single_value"))
@@ -216,6 +298,10 @@
 (assert_return (invoke "rethrow_target_test1") (i32.const 2))
 (assert_return (invoke "rethrow_target_test2") (i32.const 1))
 (assert_return (invoke "rethrow_target_test3") (i32.const 1))
+(assert_return (invoke "try_delegate_caught") (i32.const 3))
+(assert_trap (invoke "try_delegate_to_catchless_try"))
+(assert_return (invoke "try_delegate_to_delegate") (i32.const 3))
+(assert_trap (invoke "try_delegate_to_caller"))
 
 (assert_invalid
   (module