[es7] implement |do| expressions proposal

src/compiler/ast-graph-builder.cc

 // Copyright 2014 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/compiler/ast-graph-builder.h"
 
 #include "src/compiler.h"
 #include "src/compiler/ast-loop-assignment-analyzer.h"
 #include "src/compiler/control-builders.h"
 #include "src/compiler/js-type-feedback.h"
@@ skipping 1639 matching lines @@
   }
   ast_context()->ProduceValue(literal);
 }
 
 
 void AstGraphBuilder::VisitNativeFunctionLiteral(NativeFunctionLiteral* expr) {
   UNREACHABLE();
 }
 
 
+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());
   Node* condition = environment()->Pop();
   compare_if.If(condition);
   compare_if.Then();
   Visit(expr->then_expression());
   compare_if.Else();
   Visit(expr->else_expression());
   compare_if.End();
@@ skipping 2618 matching lines @@
     // Phi does not exist yet, introduce one.
     value = NewPhi(inputs, value, control);
     value->ReplaceInput(inputs - 1, other);
   }
   return value;
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8