[wasm] Simplify unwinding of interpreter activations.

R=clemensh@chromium.org

Change-Id: I3c5f38c33d5fdb08f927e5417d4d85652d0125ac
Reviewed-on: https://chromium-review.googlesource.com/c/1454603Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59366}

src/isolate.cc

@@ -1747,10 +1747,6 @@ Object Isolate::UnwindAndFindHandler() {
         if (trap_handler::IsThreadInWasm()) {
           trap_handler::ClearThreadInWasm();
         }
-        WasmInterpreterEntryFrame* interpreter_frame =
-            WasmInterpreterEntryFrame::cast(frame);
-        // TODO(wasm): Implement try-catch in the interpreter.
-        interpreter_frame->debug_info()->Unwind(frame->fp());
       } break;
 
       case StackFrame::JAVA_SCRIPT_BUILTIN_CONTINUATION_WITH_CATCH: {

src/wasm/wasm-debug.cc

@@ -216,15 +216,21 @@ class InterpreterHandle {
           Handle<Object> exception =
               isolate_->factory()->NewWasmRuntimeError(message_id);
           isolate_->Throw(*exception);
-          // Handle this exception. Return without trying to read back the
-          // return value.
+          // Handle this exception locally within the activation.
           auto result = thread->HandleException(isolate_);
-          return result == WasmInterpreter::Thread::HANDLED;
-        } break;
+          if (result == WasmInterpreter::Thread::HANDLED) break;
+          // If no local handler was found, we fall-thru to {STOPPED}.
+          DCHECK_EQ(WasmInterpreter::State::STOPPED, thread->state());
+          V8_FALLTHROUGH;
+        }
         case WasmInterpreter::State::STOPPED:
-          // An exception happened, and the current activation was unwound.
+          // An exception happened, and the current activation was unwound
+          // without hitting a local exception handler. All that remains to be
+          // done is finish the activation and let the exception propagate.
           DCHECK_EQ(thread->ActivationFrameBase(activation_id),
                     thread->GetFrameCount());
+          DCHECK(isolate_->has_pending_exception());
+          FinishActivation(frame_pointer, activation_id);
           return false;
         // RUNNING should never occur here.
         case WasmInterpreter::State::RUNNING:
@@ -379,20 +385,6 @@ class InterpreterHandle {
     return thread->GetFrame(frame_range.first + idx);
   }
 
-  void Unwind(Address frame_pointer) {
-    // Find the current activation.
-    DCHECK_EQ(1, activations_.count(frame_pointer));
-    // Activations must be properly stacked:
-    DCHECK_EQ(activations_.size() - 1, activations_[frame_pointer]);
-    uint32_t activation_id = static_cast<uint32_t>(activations_.size() - 1);
-    // The top activation must have no active frames. The interpreter already
-    // had a chance to handle exceptions and hence dropped all frames.
-    DCHECK_EQ(interpreter()->GetThread(0)->GetFrameCount(),
-              interpreter()->GetThread(0)->ActivationFrameBase(activation_id));
-    // All that remains to be done is finish the activation.
-    FinishActivation(frame_pointer, activation_id);
-  }
-
   uint64_t NumInterpretedCalls() {
     DCHECK_EQ(1, interpreter()->GetThreadCount());
     return interpreter()->GetThread(0)->NumInterpretedCalls();
@@ -626,10 +618,6 @@ wasm::WasmInterpreter::FramePtr WasmDebugInfo::GetInterpretedFrame(
   return GetInterpreterHandle(*this)->GetInterpretedFrame(frame_pointer, idx);
 }
 
-void WasmDebugInfo::Unwind(Address frame_pointer) {
-  return GetInterpreterHandle(*this)->Unwind(frame_pointer);
-}
-
 uint64_t WasmDebugInfo::NumInterpretedCalls() {
   auto* handle = GetInterpreterHandleOrNull(*this);
   return handle ? handle->NumInterpretedCalls() : 0;

src/wasm/wasm-objects.h

@@ -710,10 +710,6 @@ class WasmDebugInfo : public Struct {
   std::unique_ptr<wasm::InterpretedFrame, wasm::InterpretedFrameDeleter>
   GetInterpretedFrame(Address frame_pointer, int frame_index);
 
-  // Unwind the interpreted stack belonging to the passed interpreter entry
-  // frame.
-  void Unwind(Address frame_pointer);
-
   // Returns the number of calls / function frames executed in the interpreter.
   uint64_t NumInterpretedCalls();