[wasm][interpreter][eh] Add implicit rethrow

If the exception tag does not match any of the catch blocks and there is
no catch_all block, it should be rethrown.

R=clemensb@chromium.org

Bug: v8:8091
Change-Id: I8df80f51340fc6265f5ef4308ee3b0f892ee3a90
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2690599
Commit-Queue: Thibaud Michaud <thibaudm@chromium.org>
Reviewed-by: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#72713}

test/cctest/wasm/test-run-wasm-exceptions.cc

@@ -127,6 +127,37 @@ WASM_EXEC_TEST(TryCatchAllThrow) {
   }
 }
 
+WASM_EXEC_TEST(TryImplicitRethrow) {
+  TestSignatures sigs;
+  EXPERIMENTAL_FLAG_SCOPE(eh);
+  WasmRunner<uint32_t, uint32_t> r(execution_tier);
+  uint32_t except1 = r.builder().AddException(sigs.v_v());
+  uint32_t except2 = r.builder().AddException(sigs.v_v());
+  constexpr uint32_t kResult0 = 23;
+  constexpr uint32_t kResult1 = 42;
+  constexpr uint32_t kResult2 = 51;
+
+  // Build the main test function.
+  BUILD(r,
+        WASM_TRY_CATCH_T(
+            kWasmI32,
+            WASM_TRY_CATCH_T(kWasmI32,
+                             WASM_STMTS(WASM_I32V(kResult1),
+                                        WASM_IF(WASM_I32_EQZ(WASM_LOCAL_GET(0)),
+                                                WASM_THROW(except2))),
+                             WASM_STMTS(WASM_I32V(kResult2)), except1),
+            WASM_I32V(kResult0), except2));
+
+  if (execution_tier != TestExecutionTier::kInterpreter) {
+    // Need to call through JS to allow for creation of stack traces.
+    r.CheckCallViaJS(kResult0, 0);
+    r.CheckCallViaJS(kResult1, 1);
+  } else {
+    CHECK_EQ(kResult0, r.CallInterpreter(0));
+    CHECK_EQ(kResult1, r.CallInterpreter(1));
+  }
+}
+
 WASM_EXEC_TEST(TryCatchCallDirect) {
   TestSignatures sigs;
   EXPERIMENTAL_FLAG_SCOPE(eh);

test/common/wasm/wasm-interpreter.cc

@@ -561,6 +561,7 @@ int64_t ExecuteI64ReinterpretF64(WasmValue a) {
 
 constexpr int32_t kCatchInArity = 1;
 constexpr int32_t kCatchAllExceptionIndex = -1;
+constexpr int32_t kImplicitRethrowExceptionIndex = -2;
 
 }  // namespace
 
@@ -840,6 +841,8 @@ class SideTable : public ZoneObject {
             }
             DCHECK_NOT_NULL(c->else_label);
             c->else_label->Bind(i.pc() + 1, kCatchAllExceptionIndex);
+            c->else_label->Finish(&map_, code->start);
+            c->else_label = nullptr;
             DCHECK_IMPLIES(!unreachable,
                            stack_height >= c->end_label->target_stack_height);
             stack_height = c->end_label->target_stack_height;
@@ -899,6 +902,14 @@ class SideTable : public ZoneObject {
               if (*c->pc == kExprIf) {
                 // Bind else label for one-armed if.
                 c->else_label->Bind(i.pc());
+              } else if (!exception_stack.empty()) {
+                // No catch_all block, prepare for implicit rethrow.
+                DCHECK_EQ(*c->pc, kExprTry);
+                Control* next_try_block =
+                    &control_stack[exception_stack.back()];
+                c->else_label->Bind(i.pc(), kImplicitRethrowExceptionIndex);
+                next_try_block->else_label->Ref(
+                    i.pc(), c->else_label->target_stack_height);
               }
             }
             c->end_label->Bind(i.pc() + 1);
@@ -1366,9 +1377,14 @@ class WasmInterpreterInternals {
     auto it = code->side_table->map_.catch_map.find(*pc);
     DCHECK_NE(it, code->side_table->map_.catch_map.end());
     for (auto& entry : it->second) {
-      if (entry.exception_index == kCatchAllExceptionIndex) {
+      if (entry.exception_index < 0) {
         ResetStack(StackHeight() - entry.sp_diff);
         *pc += entry.pc_diff;
+        if (entry.exception_index == kImplicitRethrowExceptionIndex) {
+          // Recursively try to find a handler in the next enclosing try block.
+          return JumpToHandlerDelta(code, exception_object, pc);
+        }
+        DCHECK_EQ(entry.exception_index, kCatchAllExceptionIndex);
         return true;
       } else if (MatchingExceptionTag(exception_object,
                                       entry.exception_index)) {
@@ -1382,7 +1398,6 @@ class WasmInterpreterInternals {
         return true;
       }
     }
-    // TODO(thibaudm): Try rethrowing in the current frame before unwinding.
     return false;
   }