Fixes preprocessor testing and adds deadcode removal.

external/builder/fixtures_esprima/deadcode-expected.js

@@ -0,0 +1,13 @@
+function f1() {
+}
+function f2() {
+ return 1;
+}
+function f3() {
+ var i = 0;
+ throw "test";
+}
+function f4() {
+ var i = 0;
+}
+

external/builder/fixtures_esprima/deadcode.js

@@ -0,0 +1,25 @@
+function f1() {
+  return;
+  var i = 0;
+}
+
+function f2() {
+  return 1;
+  var i = 0;
+}
+
+function f3() {
+  var i = 0;
+  throw "test";
+  var j = 0;
+}
+
+function f4() {
+  var i = 0;
+  if (true) {
+    return;
+  }
+  throw "test";
+  var j = 0;
+}
+

external/builder/preprocessor2.js

@@ -169,22 +169,38 @@ function postprocessNode(ctx, node) {
     case 'BlockStatement':
       var subExpressionIndex = 0;
       while (subExpressionIndex < node.body.length) {
-        if (node.body[subExpressionIndex].type === 'EmptyStatement') {
+        switch (node.body[subExpressionIndex].type) {
+          case 'EmptyStatement':
             // Removing empty statements from the blocks.
             node.body.splice(subExpressionIndex, 1);
             continue;
-        }
-        if (node.body[subExpressionIndex].type === 'BlockStatement') {
+          case 'BlockStatement':
             // Block statements inside a block are moved to the parent one.
             var subChildren = node.body[subExpressionIndex].body;
             Array.prototype.splice.apply(node.body,
               [subExpressionIndex, 1].concat(subChildren));
-          subExpressionIndex += subChildren.length;
+            subExpressionIndex += Math.max(subChildren.length - 1, 0);
             continue;
+          case 'ReturnStatement':
+          case 'ThrowStatement':
+            // Removing dead code after return or throw.
+            node.body.splice(subExpressionIndex + 1,
+                             node.body.length - subExpressionIndex - 1);
+            break;
         }
         subExpressionIndex++;
       }
       break;
+    case 'FunctionDeclaration':
+    case 'FunctionExpression':
+      var block = node.body;
+      if (block.body.length > 0 &&
+          block.body[block.body.length - 1].type === 'ReturnStatement' &&
+          !block.body[block.body.length - 1].argument) {
+        // Function body ends with return without arg -- removing it.
+        block.body.pop();
+      }
+      break;
   }
   return node;
 }