[ignition] handle catch prediction tracking entirely in BytecodeGenerator

Remove catch prediction tracking from AstNumbering, and replace it with
a similar mechanism in the BytecodeGenerator visitor.

BUG=v8:4483, v8:5855

Change-Id: I6351ba311716102fa55cd9ef29b9955ab4b11027
Reviewed-on: https://chromium-review.googlesource.com/559006Reviewed-by: Georg Neis <neis@chromium.org>
Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Commit-Queue: Caitlin Potter <caitp@igalia.com>
Cr-Commit-Position: refs/heads/master@{#46419}

src/ast/ast-numbering.cc

@@ -26,7 +26,6 @@ class AstNumberingVisitor final : public AstVisitor<AstNumberingVisitor> {
         slot_cache_(zone),
         disable_fullcodegen_reason_(kNoReason),
         dont_optimize_reason_(kNoReason),
-        catch_prediction_(HandlerTable::UNCAUGHT),
         collect_type_profile_(collect_type_profile) {
     InitializeAstVisitor(stack_limit);
   }
@@ -102,7 +101,6 @@ class AstNumberingVisitor final : public AstVisitor<AstNumberingVisitor> {
   FeedbackSlotCache slot_cache_;
   BailoutReason disable_fullcodegen_reason_;
   BailoutReason dont_optimize_reason_;
-  HandlerTable::CatchPrediction catch_prediction_;
   bool collect_type_profile_;
 
   DEFINE_AST_VISITOR_SUBCLASS_MEMBERS();
@@ -296,34 +294,6 @@ void AstNumberingVisitor::VisitFunctionDeclaration(FunctionDeclaration* node) {
 void AstNumberingVisitor::VisitCallRuntime(CallRuntime* node) {
   IncrementNodeCount();
   VisitArguments(node->arguments());
-  // To support catch prediction within async/await:
-  //
-  // The AstNumberingVisitor is when catch prediction currently occurs, and it
-  // is the only common point that has access to this information. The parser
-  // just doesn't know yet. Take the following two cases of catch prediction:
-  //
-  // try { await fn(); } catch (e) { }
-  // try { await fn(); } finally { }
-  //
-  // When parsing the await that we want to mark as caught or uncaught, it's
-  // not yet known whether it will be followed by a 'finally' or a 'catch.
-  // The AstNumberingVisitor is what learns whether it is caught. To make
-  // the information available later to the runtime, the AstNumberingVisitor
-  // has to stash it somewhere. Changing the runtime function into another
-  // one in ast-numbering seemed like a simple and straightforward solution to
-  // that problem.
-  if (node->is_jsruntime() && catch_prediction_ == HandlerTable::ASYNC_AWAIT) {
-    switch (node->context_index()) {
-      case Context::ASYNC_FUNCTION_AWAIT_CAUGHT_INDEX:
-        node->set_context_index(Context::ASYNC_FUNCTION_AWAIT_UNCAUGHT_INDEX);
-        break;
-      case Context::ASYNC_GENERATOR_AWAIT_CAUGHT:
-        node->set_context_index(Context::ASYNC_GENERATOR_AWAIT_UNCAUGHT);
-        break;
-      default:
-        break;
-    }
-  }
 }
 
 
@@ -361,18 +331,7 @@ void AstNumberingVisitor::VisitTryCatchStatement(TryCatchStatement* node) {
   DCHECK(node->scope() == nullptr || !node->scope()->HasBeenRemoved());
   IncrementNodeCount();
   DisableFullCodegen(kTryCatchStatement);
-  {
-    const HandlerTable::CatchPrediction old_prediction = catch_prediction_;
-    // This node uses its own prediction, unless it's "uncaught", in which case
-    // we adopt the prediction of the outer try-block.
-    HandlerTable::CatchPrediction catch_prediction = node->catch_prediction();
-    if (catch_prediction != HandlerTable::UNCAUGHT) {
-      catch_prediction_ = catch_prediction;
-    }
-    node->set_catch_prediction(catch_prediction_);
-    Visit(node->try_block());
-    catch_prediction_ = old_prediction;
-  }
+  Visit(node->try_block());
   Visit(node->catch_block());
 }
 
@@ -380,9 +339,6 @@ void AstNumberingVisitor::VisitTryCatchStatement(TryCatchStatement* node) {
 void AstNumberingVisitor::VisitTryFinallyStatement(TryFinallyStatement* node) {
   IncrementNodeCount();
   DisableFullCodegen(kTryFinallyStatement);
-  // We can't know whether the finally block will override ("catch") an
-  // exception thrown in the try block, so we just adopt the outer prediction.
-  node->set_catch_prediction(catch_prediction_);
   Visit(node->try_block());
   Visit(node->finally_block());
 }

src/ast/ast.h

@@ -971,30 +971,9 @@ class TryStatement : public Statement {
   Block* try_block() const { return try_block_; }
   void set_try_block(Block* b) { try_block_ = b; }
 
-  // Prediction of whether exceptions thrown into the handler for this try block
-  // will be caught.
-  //
-  // This is set in ast-numbering and later compiled into the code's handler
-  // table.  The runtime uses this information to implement a feature that
-  // notifies the debugger when an uncaught exception is thrown, _before_ the
-  // exception propagates to the top.
-  //
-  // Since it's generally undecidable whether an exception will be caught, our
-  // prediction is only an approximation.
-  HandlerTable::CatchPrediction catch_prediction() const {
-    return catch_prediction_;
-  }
-  void set_catch_prediction(HandlerTable::CatchPrediction prediction) {
-    catch_prediction_ = prediction;
-  }
-
  protected:
   TryStatement(Block* try_block, int pos, NodeType type)
-      : Statement(pos, type),
-        catch_prediction_(HandlerTable::UNCAUGHT),
-        try_block_(try_block) {}
-
-  HandlerTable::CatchPrediction catch_prediction_;
+      : Statement(pos, type), try_block_(try_block) {}
 
  private:
   Block* try_block_;
@@ -1007,18 +986,52 @@ class TryCatchStatement final : public TryStatement {
   Block* catch_block() const { return catch_block_; }
   void set_catch_block(Block* b) { catch_block_ = b; }
 
-  // The clear_pending_message flag indicates whether or not to clear the
-  // isolate's pending exception message before executing the catch_block.  In
-  // the normal use case, this flag is always on because the message object
-  // is not needed anymore when entering the catch block and should not be kept
-  // alive.
-  // The use case where the flag is off is when the catch block is guaranteed to
-  // rethrow the caught exception (using %ReThrow), which reuses the pending
-  // message instead of generating a new one.
+  // Prediction of whether exceptions thrown into the handler for this try block
+  // will be caught.
+  //
+  // BytecodeGenerator tracks the state of catch prediction, which can change
+  // with each TryCatchStatement encountered. The tracked catch prediction is
+  // later compiled into the code's handler table. The runtime uses this
+  // information to implement a feature that notifies the debugger when an
+  // uncaught exception is thrown, _before_ the exception propagates to the top.
+  //
+  // If this try/catch statement is meant to rethrow (HandlerTable::UNCAUGHT),
+  // the catch prediction value is set to the same value as the surrounding
+  // catch prediction.
+  //
+  // Since it's generally undecidable whether an exception will be caught, our
+  // prediction is only an approximation.
+  // ---------------------------------------------------------------------------
+  inline HandlerTable::CatchPrediction GetCatchPrediction(
+      HandlerTable::CatchPrediction outer_catch_prediction) const {
+    if (catch_prediction_ == HandlerTable::UNCAUGHT) {
+      return outer_catch_prediction;
+    }
+    return catch_prediction_;
+  }
+
+  // Indicates whether or not code should be generated to clear the pending
+  // exception. The pending exception is cleared for cases where the exception
+  // is not guaranteed to be rethrown, indicated by the value
+  // HandlerTable::UNCAUGHT. If both the current and surrounding catch handler's
+  // are predicted uncaught, the exception is not cleared.
+  //
+  // If this handler is not going to simply rethrow the exception, this method
+  // indicates that the isolate's pending exception message should be cleared
+  // before executing the catch_block.
+  // In the normal use case, this flag is always on because the message object
+  // is not needed anymore when entering the catch block and should not be
+  // kept alive.
+  // The use case where the flag is off is when the catch block is guaranteed
+  // to rethrow the caught exception (using %ReThrow), which reuses the
+  // pending message instead of generating a new one.
   // (When the catch block doesn't rethrow but is guaranteed to perform an
-  // ordinary throw, not clearing the old message is safe but not very useful.)
-  bool clear_pending_message() const {
-    return catch_prediction_ != HandlerTable::UNCAUGHT;
+  // ordinary throw, not clearing the old message is safe but not very
+  // useful.)
+  inline bool ShouldClearPendingException(
+      HandlerTable::CatchPrediction outer_catch_prediction) const {
+    return catch_prediction_ != HandlerTable::UNCAUGHT ||
+           outer_catch_prediction != HandlerTable::UNCAUGHT;
   }
 
  private:
@@ -1028,12 +1041,12 @@ class TryCatchStatement final : public TryStatement {
                     HandlerTable::CatchPrediction catch_prediction, int pos)
       : TryStatement(try_block, pos, kTryCatchStatement),
         scope_(scope),
-        catch_block_(catch_block) {
-    catch_prediction_ = catch_prediction;
-  }
+        catch_block_(catch_block),
+        catch_prediction_(catch_prediction) {}
 
   Scope* scope_;
   Block* catch_block_;
+  HandlerTable::CatchPrediction catch_prediction_;
 };
 
 

src/ast/prettyprinter.cc

@@ -875,24 +875,9 @@ void AstPrinter::VisitForOfStatement(ForOfStatement* node) {
 
 void AstPrinter::VisitTryCatchStatement(TryCatchStatement* node) {
   IndentedScope indent(this, "TRY CATCH", node->position());
-  PrintTryStatement(node);
-  PrintLiteralWithModeIndented("CATCHVAR", node->scope()->catch_variable(),
-                               node->scope()->catch_variable()->name());
-  PrintIndentedVisit("CATCH", node->catch_block());
-}
-
-
-void AstPrinter::VisitTryFinallyStatement(TryFinallyStatement* node) {
-  IndentedScope indent(this, "TRY FINALLY", node->position());
-  PrintTryStatement(node);
-  PrintIndentedVisit("FINALLY", node->finally_block());
-}
-
-void AstPrinter::PrintTryStatement(TryStatement* node) {
-  PrintIndentedVisit("TRY", node->try_block());
   PrintIndented("CATCH PREDICTION");
   const char* prediction = "";
-  switch (node->catch_prediction()) {
+  switch (node->GetCatchPrediction(HandlerTable::UNCAUGHT)) {
     case HandlerTable::UNCAUGHT:
       prediction = "UNCAUGHT";
       break;
@@ -911,6 +896,14 @@ void AstPrinter::PrintTryStatement(TryStatement* node) {
       UNREACHABLE();
   }
   Print(" %s\n", prediction);
+  PrintLiteralWithModeIndented("CATCHVAR", node->scope()->catch_variable(),
+                               node->scope()->catch_variable()->name());
+  PrintIndentedVisit("CATCH", node->catch_block());
+}
+
+void AstPrinter::VisitTryFinallyStatement(TryFinallyStatement* node) {
+  IndentedScope indent(this, "TRY FINALLY", node->position());
+  PrintIndentedVisit("FINALLY", node->finally_block());
 }
 
 void AstPrinter::VisitDebuggerStatement(DebuggerStatement* node) {

src/ast/prettyprinter.h

@@ -96,7 +96,6 @@ class AstPrinter final : public AstVisitor<AstPrinter> {
   void PrintLabelsIndented(ZoneList<const AstRawString*>* labels);
   void PrintObjectProperties(ZoneList<ObjectLiteral::Property*>* properties);
   void PrintClassProperties(ZoneList<ClassLiteral::Property*>* properties);
-  void PrintTryStatement(TryStatement* try_statement);
 
   void inc_indent() { indent_++; }
   void dec_indent() { indent_--; }

src/interpreter/bytecode-generator.cc

@@ -798,7 +798,8 @@ BytecodeGenerator::BytecodeGenerator(CompilationInfo* info)
       generator_jump_table_(nullptr),
       generator_object_(),
       generator_state_(),
-      loop_depth_(0) {
+      loop_depth_(0),
+      catch_prediction_(HandlerTable::UNCAUGHT) {
   DCHECK_EQ(closure_scope(), closure_scope()->GetClosureScope());
   if (info->is_block_coverage_enabled()) {
     DCHECK(FLAG_block_coverage);
@@ -1576,7 +1577,13 @@ void BytecodeGenerator::VisitForOfStatement(ForOfStatement* stmt) {
 }
 
 void BytecodeGenerator::VisitTryCatchStatement(TryCatchStatement* stmt) {
-  TryCatchBuilder try_control_builder(builder(), stmt->catch_prediction());
+  // Update catch prediction tracking. The updated catch_prediction value lasts
+  // until the end of the try_block in the AST node, and does not apply to the
+  // catch_block.
+  HandlerTable::CatchPrediction outer_catch_prediction = catch_prediction();
+  set_catch_prediction(stmt->GetCatchPrediction(outer_catch_prediction));
+
+  TryCatchBuilder try_control_builder(builder(), catch_prediction());
 
   // Preserve the context in a dedicated register, so that it can be restored
   // when the handler is entered by the stack-unwinding machinery.
@@ -1590,6 +1597,7 @@ void BytecodeGenerator::VisitTryCatchStatement(TryCatchStatement* stmt) {
   {
     ControlScopeForTryCatch scope(this, &try_control_builder);
     Visit(stmt->try_block());
+    set_catch_prediction(outer_catch_prediction);
   }
   try_control_builder.EndTry();
 
@@ -1598,7 +1606,7 @@ void BytecodeGenerator::VisitTryCatchStatement(TryCatchStatement* stmt) {
   builder()->StoreAccumulatorInRegister(context);
 
   // If requested, clear message object as we enter the catch block.
-  if (stmt->clear_pending_message()) {
+  if (stmt->ShouldClearPendingException(outer_catch_prediction)) {
     builder()->LoadTheHole().SetPendingMessage();
   }
 
@@ -1611,7 +1619,9 @@ void BytecodeGenerator::VisitTryCatchStatement(TryCatchStatement* stmt) {
 }
 
 void BytecodeGenerator::VisitTryFinallyStatement(TryFinallyStatement* stmt) {
-  TryFinallyBuilder try_control_builder(builder(), stmt->catch_prediction());
+  // We can't know whether the finally block will override ("catch") an
+  // exception thrown in the try bblock, so we just adopt the outer prediction.
+  TryFinallyBuilder try_control_builder(builder(), catch_prediction());
 
   // We keep a record of all paths that enter the finally-block to be able to
   // dispatch to the correct continuation point after the statements in the
@@ -3249,15 +3259,49 @@ void BytecodeGenerator::VisitCallNew(CallNew* expr) {
   }
 }
 
+int BytecodeGenerator::UpdateRuntimeFunctionForAsyncAwait(int context_index) {
+  // To support catch prediction within async/await:
+  //
+  // BytecodeGenerator models catch prediction (see VisitTryCatchstatement).
+  // Certain runtime calls need to be rewritten to invoke different functions,
+  // depending on the currently tracked catch prediction state. Take the
+  // following two cases of catch prediction:
+  //
+  // try { await fn(); } catch (e) { }
+  // try { await fn(); } finally { }
+  //
+  // When parsing the await that we want to mark as caught or uncaught, it's
+  // not yet known whether it will be followed by a 'finally' or a 'catch.
+  // The BytecodeGenerator has learned whether or not this Await is caught or
+  // not, and is responsible for invoking the correct function depending on
+  // those findings. It does that here.
+  if (catch_prediction() == HandlerTable::ASYNC_AWAIT) {
+    switch (context_index) {
+      case Context::ASYNC_FUNCTION_AWAIT_CAUGHT_INDEX:
+        context_index = Context::ASYNC_FUNCTION_AWAIT_UNCAUGHT_INDEX;
+        break;
+      case Context::ASYNC_GENERATOR_AWAIT_CAUGHT:
+        context_index = Context::ASYNC_GENERATOR_AWAIT_UNCAUGHT;
+        break;
+      default:
+        break;
+    }
+  }
+  return context_index;
+}
+
 void BytecodeGenerator::VisitCallRuntime(CallRuntime* expr) {
   if (expr->is_jsruntime()) {
+    int context_index =
+        UpdateRuntimeFunctionForAsyncAwait(expr->context_index());
+
     RegisterList args = register_allocator()->NewGrowableRegisterList();
     // Allocate a register for the receiver and load it with undefined.
     // TODO(leszeks): If CallJSRuntime always has an undefined receiver, use the
     // same mechanism as CallUndefinedReceiver.
     BuildPushUndefinedIntoRegisterList(&args);
     VisitArguments(expr->arguments(), &args);
-    builder()->CallJSRuntime(expr->context_index(), args);
+    builder()->CallJSRuntime(context_index, args);
   } else {
     // Evaluate all arguments to the runtime call.
     RegisterList args = register_allocator()->NewGrowableRegisterList();

src/interpreter/bytecode-generator.h

@@ -214,6 +214,8 @@ class BytecodeGenerator final : public AstVisitor<BytecodeGenerator> {
                                      Register* out_register));
   void VisitInSameTestExecutionScope(Expression* expr);
 
+  int UpdateRuntimeFunctionForAsyncAwait(int context_index);
+
   // Returns the runtime function id for a store to super for the function's
   // language mode.
   inline Runtime::FunctionId StoreToSuperRuntimeId();
@@ -258,6 +260,13 @@ class BytecodeGenerator final : public AstVisitor<BytecodeGenerator> {
   inline LanguageMode language_mode() const;
   int feedback_index(FeedbackSlot slot) const;
 
+  inline HandlerTable::CatchPrediction catch_prediction() const {
+    return catch_prediction_;
+  }
+  inline void set_catch_prediction(HandlerTable::CatchPrediction value) {
+    catch_prediction_ = value;
+  }
+
   Zone* zone_;
   BytecodeArrayBuilder* builder_;
   CompilationInfo* info_;
@@ -282,6 +291,8 @@ class BytecodeGenerator final : public AstVisitor<BytecodeGenerator> {
   Register generator_object_;
   Register generator_state_;
   int loop_depth_;
+
+  HandlerTable::CatchPrediction catch_prediction_;
 };
 
 }  // namespace interpreter