[Interpreter] Basic flow control.

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 <stack>
 
 #include "src/compiler.h"
 #include "src/objects.h"
@@ skipping 27 matching lines @@
   if (scope()->is_function_scope() && scope()->function() != NULL) {
     VisitVariableDeclaration(scope()->function());
   }
 
   // Visit declarations within the function scope.
   VisitDeclarations(scope()->declarations());
 
   // Visit statements in the function body.
   VisitStatements(info->literal()->body());
 
-  // If the last bytecode wasn't a return, then return 'undefined' to avoid
-  // falling off the end.
-  if (!builder_.HasExplicitReturn()) {
-    builder_.LoadUndefined();
-    builder_.Return();
-  }
-
   set_scope(nullptr);
   set_info(nullptr);
   return builder_.ToBytecodeArray();
 }
 
 
 void BytecodeGenerator::VisitBlock(Block* node) {
+  builder().EnterBlock();
   if (node->scope() == NULL) {
     // Visit statements in the same scope, no declarations.
     VisitStatements(node->statements());
   } else {
     // Visit declarations and statements in a block scope.
     if (node->scope()->ContextLocalCount() > 0) {
       UNIMPLEMENTED();
     } else {
       VisitDeclarations(node->scope()->declarations());
       VisitStatements(node->statements());
     }
   }
+  builder().LeaveBlock();
 }
 
 
 void BytecodeGenerator::VisitVariableDeclaration(VariableDeclaration* decl) {
   Variable* variable = decl->proxy()->var();
   switch (variable->location()) {
     case VariableLocation::GLOBAL:
     case VariableLocation::UNALLOCATED:
       UNIMPLEMENTED();
       break;
@@ skipping 23 matching lines @@
   UNIMPLEMENTED();
 }
 
 
 void BytecodeGenerator::VisitExpressionStatement(ExpressionStatement* stmt) {
   Visit(stmt->expression());
 }
 
 
 void BytecodeGenerator::VisitEmptyStatement(EmptyStatement* stmt) {
-  UNIMPLEMENTED();
+  // For control-flow it could be useful to signal empty paths here.

[rmcilroy, 2015/09/23 14:00:29]

nit - TODO(oth): 

[oth, 2015/09/24 11:15:27]

Done.

 }
 
 
-void BytecodeGenerator::VisitIfStatement(IfStatement* stmt) { UNIMPLEMENTED(); }
+void BytecodeGenerator::VisitIfStatement(IfStatement* stmt) {
+  // TODO(oth): spot easy cases if (true/1/false/0)?

[rmcilroy, 2015/09/23 14:00:29]

nit - clarify comment please - e.g.: spot easy cases where we wouldn't need to
emit the then or else block, e.g., if (true/1/false/0).

[oth, 2015/09/24 11:15:27]

Done.

+  BytecodeLabel else_start, else_end;
+  Visit(stmt->condition());
+  builder().CastAccumulatorToBoolean();
+  builder().JumpIfFalse(&else_start);
+  Visit(stmt->then_statement());
+  builder().Jump(&else_end);
+  builder().Bind(&else_start);
+  Visit(stmt->else_statement());
+  builder().Bind(&else_end);

[rmcilroy, 2015/09/23 14:00:29]

nit - maybe some whitespace between condition, then, else, etc.

[oth, 2015/09/24 11:15:27]

Done.

+}
 
 
 void BytecodeGenerator::VisitSloppyBlockFunctionStatement(
     SloppyBlockFunctionStatement* stmt) {
   Visit(stmt->statement());
 }
 
 
 void BytecodeGenerator::VisitContinueStatement(ContinueStatement* stmt) {
   UNIMPLEMENTED();
@@ skipping 319 matching lines @@
       UNIMPLEMENTED();
       break;
     default:
       VisitArithmeticExpression(binop);
       break;
   }
 }
 
 
 void BytecodeGenerator::VisitCompareOperation(CompareOperation* expr) {
-  UNIMPLEMENTED();
+  Token::Value op = expr->op();
+  Expression* left = expr->left();
+  Expression* right = expr->right();
+
+  TemporaryRegisterScope temporary_register_scope(&builder_);
+  Register temporary = temporary_register_scope.NewRegister();
+
+  Visit(left);
+  builder().StoreAccumulatorInRegister(temporary);
+  Visit(right);
+  builder().CompareOperation(op, temporary, language_mode());
 }
 
 
 void BytecodeGenerator::VisitSpread(Spread* expr) { UNREACHABLE(); }
 
 
 void BytecodeGenerator::VisitEmptyParentheses(EmptyParentheses* expr) {
   UNREACHABLE();
 }
 
@@ skipping 34 matching lines @@
 }
 
 
 int BytecodeGenerator::feedback_index(FeedbackVectorICSlot slot) const {
   return info()->feedback_vector()->GetIndex(slot);
 }
 
 }  // namespace interpreter
 }  // namespace internal
 }  // namespace v8