[interpreter] Implement support for the --trace flag.

src/interpreter/bytecode-generator.cc

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/interpreter/bytecode-generator.h"
 
 #include "src/ast/compile-time-value.h"
 #include "src/ast/scopes.h"
 #include "src/code-stubs.h"
 #include "src/compilation-info.h"
@@ skipping 199 matching lines @@
   explicit ControlScopeForTopLevel(BytecodeGenerator* generator)
       : ControlScope(generator) {}
 
  protected:
   bool Execute(Command command, Statement* statement) override {
     switch (command) {
       case CMD_BREAK:  // We should never see break/continue in top-level.
       case CMD_CONTINUE:
         UNREACHABLE();
       case CMD_RETURN:
-        generator()->builder()->Return();
+        generator()->BuildReturn();
         return true;
       case CMD_RETHROW:
-        generator()->builder()->ReThrow();
+        generator()->BuildReThrow();
         return true;
     }
     return false;
   }
 };
 
 // Scoped class for enabling break inside blocks and switch blocks.
 class BytecodeGenerator::ControlScopeForBreakable final
     : public BytecodeGenerator::ControlScope {
  public:
@@ skipping 70 matching lines @@
       : ControlScope(generator) {}
 
  protected:
   bool Execute(Command command, Statement* statement) override {
     switch (command) {
       case CMD_BREAK:
       case CMD_CONTINUE:
       case CMD_RETURN:
         break;
       case CMD_RETHROW:
-        generator()->builder()->ReThrow();
+        generator()->BuildReThrow();
         return true;
     }
     return false;
   }
 };
 
 // Scoped class for enabling control flow through try-finally constructs.
 class BytecodeGenerator::ControlScopeForTryFinally final
     : public BytecodeGenerator::ControlScope {
  public:
@@ skipping 317 matching lines @@
   }
 
   // In generator functions, we may not have visited every yield in the AST
   // since we skip some obviously dead code. Hence the generated bytecode may
   // contain jumps to unbound labels (resume points that will never be used).
   // We bind these now.
   for (auto& label : generator_resume_points_) {
     if (!label.is_bound()) builder()->Bind(&label);
   }
 
-  builder()->EnsureReturn();
+  // Emit an implicit return instruction in case control flow can fall off the
+  // end of the function without an explicit return being present on all paths.
+  if (builder()->RequiresImplicitReturn()) {
+    builder()->LoadUndefined();
+    BuildReturn();
+  }
+  DCHECK(!builder()->RequiresImplicitReturn());
 }
 
 void BytecodeGenerator::GenerateBytecodeBody() {
   // Build the arguments object if it is used.
   VisitArgumentsObject(scope()->arguments());
 
   // Build rest arguments array if it is used.
   Variable* rest_parameter = scope()->rest_parameter();
   VisitRestArgumentsArray(rest_parameter);
 
   // Build assignment to {.this_function} variable if it is used.
   VisitThisFunctionVariable(scope()->this_function_var());
 
   // Build assignment to {new.target} variable if it is used.
   VisitNewTargetVariable(scope()->new_target_var());
 
-  // TODO(rmcilroy): Emit tracing call if requested to do so.
-  if (FLAG_trace) {
-    UNIMPLEMENTED();
-  }
+  // Emit tracing call if requested to do so.
+  if (FLAG_trace) builder()->CallRuntime(Runtime::kTraceEnter);
 
   // Visit declarations within the function scope.
   VisitDeclarations(scope()->declarations());
 
   // Perform a stack-check before the body.
   builder()->StackCheck(info()->literal()->start_position());
 
   // Visit statements in the function body.
   VisitStatements(info()->literal()->body());
 }
@@ skipping 1165 matching lines @@
     }
   }
 }
 
 void BytecodeGenerator::VisitVariableLoadForAccumulatorValue(
     Variable* variable, FeedbackVectorSlot slot, TypeofMode typeof_mode) {
   ValueResultScope accumulator_result(this);
   VisitVariableLoad(variable, slot, typeof_mode);
 }
 
+void BytecodeGenerator::BuildReturn() {
+  if (FLAG_trace) {
+    RegisterAllocationScope register_scope(this);
+    Register result = register_allocator()->NewRegister();
+    // Runtime returns {result} value, preserving accumulator.
+    builder()->StoreAccumulatorInRegister(result).CallRuntime(
+        Runtime::kTraceExit, result);
+  }
+  builder()->Return();
+}
+
+void BytecodeGenerator::BuildReThrow() { builder()->ReThrow(); }
+
 void BytecodeGenerator::BuildAbort(BailoutReason bailout_reason) {
   RegisterAllocationScope register_scope(this);
   Register reason = register_allocator()->NewRegister();
   builder()
       ->LoadLiteral(Smi::FromInt(static_cast<int>(bailout_reason)))
       .StoreAccumulatorInRegister(reason)
       .CallRuntime(Runtime::kAbort, reason);
 }
 
 void BytecodeGenerator::BuildThrowReferenceError(Handle<String> name) {
@@ skipping 1278 matching lines @@
 }
 
 Runtime::FunctionId BytecodeGenerator::StoreKeyedToSuperRuntimeId() {
   return is_strict(language_mode()) ? Runtime::kStoreKeyedToSuper_Strict
                                     : Runtime::kStoreKeyedToSuper_Sloppy;
 }
 
 }  // namespace interpreter
 }  // namespace internal
 }  // namespace v8