[es7] implement |do| expressions proposal

src/compiler/ast-graph-builder.cc

Index: src/compiler/ast-graph-builder.cc
diff --git a/src/compiler/ast-graph-builder.cc b/src/compiler/ast-graph-builder.cc
index f2e10ecfe5354e71c159f151c40dd48fccfb48a7..8e98ea4d04f71c0f4180685eb87091ac90aa47db 100644
--- a/src/compiler/ast-graph-builder.cc
+++ b/src/compiler/ast-graph-builder.cc
@@ -1657,6 +1657,28 @@ void AstGraphBuilder::VisitNativeFunctionLiteral(NativeFunctionLiteral* expr) {
 }
 
 
+void AstGraphBuilder::VisitDoExpression(DoExpression* expr) {
+  BlockBuilder block(this);
+  ControlScopeForBreakable scope(
+      this, reinterpret_cast<BreakableStatement*>(expr), &block);
+  // Visit declarations and statements in a block scope.
+  if (expr->scope()->NeedsContext()) {
+    Node* context = BuildLocalBlockContext(expr->scope());
+    ContextScope scope(this, expr->scope(), context);
+    VisitDeclarations(expr->scope()->declarations());
+    VisitStatements(expr->statements());
+  } else {
+    VisitDeclarations(expr->scope()->declarations());
+    VisitStatements(expr->statements());
+  }
+  if (expr->result()->is_assigned()) {

[rossberg, 2015/10/12 13:52:39]

It's better to avoid this case distinction in back-ends and simply make sure in
the rewriter that it always gets assigned, with undefined if necessary.

[caitp (gmail), 2015/10/12 18:22:59]

Done.

It seems like it could potentially save a bit of space if the variable never got
allocated, though.

[rossberg, 2015/10/13 10:44:32]

Such an optimsation comes for free with SSA form.

+    VisitVariableProxy(expr->result());
+  } else {
+    ast_context()->ProduceValue(jsgraph()->UndefinedConstant());
+  }
+}
+
+
 void AstGraphBuilder::VisitConditional(Conditional* expr) {
   IfBuilder compare_if(this);
   VisitForTest(expr->condition());