[wasm][eh] Update delegate behavior

Update the behavior of 'delegate' according to:
https://github.com/WebAssembly/exception-handling/issues/176

Summary: delegate can target any block, which just rethrows to the next
outer try/catch.

R=clemensb@chromium.org

Bug: v8:8091
Change-Id: I967db9ab1cbb1a15b2c5e0a1a20f64fa19a3f769
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3140603
Commit-Queue: Thibaud Michaud <thibaudm@chromium.org>
Reviewed-by: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/main@{#76677}

src/wasm/function-body-decoder-impl.h

@@ -2635,19 +2635,15 @@ class WasmFullDecoder : public WasmDecoder<validate, decoding_mode> {
       return 0;
     }
     // +1 because the current try block is not included in the count.
-    Control* target = control_at(imm.depth + 1);
-    if (imm.depth + 1 < control_depth() - 1 && !target->is_try()) {
-      this->DecodeError(
-          "delegate target must be a try block or the function block");
-      return 0;
-    }
-    if (target->is_try_catch() || target->is_try_catchall()) {
-      this->DecodeError(
-          "cannot delegate inside the catch handler of the target");
-      return 0;
+    uint32_t target_depth = imm.depth + 1;
+    while (target_depth < control_depth() - 1 &&
+           (!control_at(target_depth)->is_try() ||
+            control_at(target_depth)->is_try_catch() ||
+            control_at(target_depth)->is_try_catchall())) {
+      target_depth++;
     }
     FallThrough();
-    CALL_INTERFACE_IF_OK_AND_PARENT_REACHABLE(Delegate, imm.depth + 1, c);
+    CALL_INTERFACE_IF_OK_AND_PARENT_REACHABLE(Delegate, target_depth, c);
     current_catch_ = c->previous_catch;
     EndControl();
     PopControl();

test/mjsunit/wasm/exceptions.js

@@ -1073,3 +1073,41 @@ d8.file.execute("test/mjsunit/wasm/exceptions-utils.js");
   assertDoesNotThrow(() => instance.exports.catchless_try(0));
   assertWasmThrows(instance, except, [], () => instance.exports.catchless_try(1));
 })();
+
+// Delegate to a regular block inside a try block.
+(function TestDelegateToBlock() {
+  print(arguments.callee.name);
+  let builder = new WasmModuleBuilder();
+  let except = builder.addTag(kSig_v_v);
+  builder.addFunction('test', kSig_i_v)
+      .addBody([
+        kExprTry, kWasmI32,
+          kExprBlock, kWasmI32,
+            kExprTry, kWasmI32,
+              kExprThrow, except,
+            kExprDelegate, 0,
+          kExprEnd,
+        kExprCatch, except,
+          kExprI32Const, 2,
+        kExprEnd,
+      ]).exportFunc();
+  instance = builder.instantiate();
+  assertEquals(2, instance.exports.test());
+})();
+
+// Delegate to a regular block with no outer try (delegate to caller).
+(function TestDelegateToCallerWithBlock() {
+  print(arguments.callee.name);
+  let builder = new WasmModuleBuilder();
+  let except = builder.addTag(kSig_v_v);
+  builder.addFunction('test', kSig_v_v)
+      .addBody([
+        kExprBlock, kWasmVoid,
+          kExprTry, kWasmVoid,
+            kExprThrow, except,
+          kExprDelegate, 0,
+        kExprEnd
+      ]).exportFunc();
+  instance = builder.instantiate();
+  assertThrows(() => instance.exports.test(), WebAssembly.Exception);
+})();

test/unittests/wasm/function-body-decoder-unittest.cc

@@ -2990,18 +2990,16 @@ TEST_F(FunctionBodyDecoderTest, TryDelegate) {
       sigs.v_v(),
       {WASM_BLOCK(WASM_TRY_OP, WASM_TRY_DELEGATE(WASM_STMTS(kExprThrow, ex), 2),
                   kExprCatch, ex, kExprEnd)});
+  ExpectValidates(sigs.v_v(),
+                  {WASM_TRY_OP, kExprCatch, ex,
+                   WASM_TRY_DELEGATE(WASM_STMTS(kExprThrow, ex), 0), kExprEnd},
+                  kAppendEnd);
+  ExpectValidates(sigs.v_v(),
+                  {WASM_TRY_OP,
+                   WASM_BLOCK(WASM_TRY_DELEGATE(WASM_STMTS(kExprThrow, ex), 0)),
+                   kExprCatch, ex, kExprEnd},
+                  kAppendEnd);
 
-  ExpectFailure(sigs.v_v(),
-                {WASM_TRY_OP,
-                 WASM_BLOCK(WASM_TRY_DELEGATE(WASM_STMTS(kExprThrow, ex), 0)),
-                 kExprCatch, ex, kExprEnd},
-                kAppendEnd,
-                "delegate target must be a try block or the function block");
-  ExpectFailure(sigs.v_v(),
-                {WASM_TRY_OP, kExprCatch, ex,
-                 WASM_TRY_DELEGATE(WASM_STMTS(kExprThrow, ex), 0), kExprEnd},
-                kAppendEnd,
-                "cannot delegate inside the catch handler of the target");
   ExpectFailure(
       sigs.v_v(),
       {WASM_BLOCK(WASM_TRY_OP, WASM_TRY_DELEGATE(WASM_STMTS(kExprThrow, ex), 3),