[Interpreter] Basic flow control.

src/interpreter/bytecode-generator.cc

Index: src/interpreter/bytecode-generator.cc
diff --git a/src/interpreter/bytecode-generator.cc b/src/interpreter/bytecode-generator.cc
index 2a330ca87059de709f9d3ab3c91039b6738ee064..b561b7fcb118ad983a0b2672ac40fd12cd355685 100644
--- a/src/interpreter/bytecode-generator.cc
+++ b/src/interpreter/bytecode-generator.cc
@@ -114,11 +114,25 @@ void BytecodeGenerator::VisitExpressionStatement(ExpressionStatement* stmt) {
 
 
 void BytecodeGenerator::VisitEmptyStatement(EmptyStatement* stmt) {
-  UNIMPLEMENTED();
+  // For control-flow it could be useful to signal empty paths here.
 }
 
 
-void BytecodeGenerator::VisitIfStatement(IfStatement* stmt) { UNIMPLEMENTED(); }
+void BytecodeGenerator::VisitIfStatement(IfStatement* stmt) {
+  // TODO(oth): spot easy cases if (true/1/false/0)?
+  BytecodeLabel else_start, else_end;
+  Visit(stmt->condition());
+  // TODO(oth) This cast may need to be pushed down the evaluation stack
+  // when logical connectives are implemented, e.g. &&, ||, etc. Optimization

[Michael Starzinger, 2015/09/23 08:46:24]

I am not sure what this TODO refers to exactly, but I think the coercion is in
the correct position here. The evaluation order of [[ToBoolean]] coercions
within if-statements and and binary logical operators is fully specified.
Short-circuiting for example can provide uncoerced value of {c} for {a || b ||
c}. So in general the if-statement needs to coerce before testing.

[oth, 2015/09/23 10:46:56]

Sorry about the wording here.

Basically, the goal would be that BytecodeArrayBuilder is more selective about
whether it emits the CastToBoolean bytecode. Specifically, if the previous
bytecode is in the same block and that bytecode would have put a boolean value
in the accumulator then CastToBoolean is not emitted.

Implemented this in patch set 16.

+  // opportunities too in bytecode-array-builder.cc.
+  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);
+}
 
 
 void BytecodeGenerator::VisitContinueStatement(ContinueStatement* stmt) {
@@ -452,7 +466,17 @@ void BytecodeGenerator::VisitBinaryOperation(BinaryOperation* binop) {
 
 
 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());
 }