new compress swtich for inlining const variables.

lib/compress.js

@@ -59,6 +59,8 @@ function Compressor(options, false_by_default) {
         evaluate      : !false_by_default,
         booleans      : !false_by_default,
         loops         : !false_by_default,
+        inlineconst   : false,
+        inlinestr     : false,
         unused        : !false_by_default,
         hoist_funs    : !false_by_default,
         hoist_vars    : false,
@@ -83,6 +85,7 @@ merge(Compressor.prototype, {
     before: function(node, descend, in_list) {
         if (node._squeezed) return node;
         if (node instanceof AST_Scope) {
+            node.inline_const_primitive(this);
             node.drop_unused(this);
             node = node.hoist_declarations(this);
         }
@@ -593,8 +596,8 @@ merge(Compressor.prototype, {
         // of the array is always an AST_Node descendant; when
         // evaluation was successful it's a node that represents the
         // constant; otherwise it's the original node.
-        AST_Node.DEFMETHOD("evaluate", function(compressor){
-            if (!compressor.option("evaluate")) return [ this ];
+        AST_Node.DEFMETHOD("evaluate", function(compressor, ignore_setting){
+            if (!compressor.option("evaluate") && !ignore_setting) return [ this ];
             try {
                 var val = this._eval(), ast = make_node_from_constant(compressor, val, this);
                 return [ best_of(ast, this), val ];
@@ -886,6 +889,64 @@ merge(Compressor.prototype, {
         return self;
     });
 
+    AST_Scope.DEFMETHOD("inline_const_primitive", function(compressor){
+        var self = this;
+        var inlineStringThreshold = compressor.option("inlinestr");
+        if (compressor.option("inlineconst")
+            && !(self instanceof AST_Toplevel)
+            && !self.uses_eval
+           ) {
+            var in_use = [];
+            var definitions = {};
+            // pass 1: find out symbols defined for only once and has
+            // could be evaluate as number or bool constant.
+            var scope = this;
+            var tw = new TreeWalker(function(node, descend){
+                if (node !== self) {
+                    if (node instanceof AST_Definitions && scope === self) {
+                        node.definitions.forEach(function(def){
+                            if (def.value) {
+                                var value = def.value.evaluate(compressor, true);
+                                def.value = value[0];
+                                if (value.length > 1) {
+                                    if (!(typeof value[1] === 'string' && value[1].length >= inlineStringThreshold))
+                                        definitions[def.name.name] = value[1];
+                                }
+                            }
+                        });
+                        return true;
+                    }
+                    if (node instanceof AST_Assign) {
+                        if (definitions.hasOwnProperty(node.left.name))
+                            delete definitions[node.left.name];
+                        return true;
+                    }
+                    if (node instanceof AST_Scope) {
+                        var save_scope = scope;
+                        scope = node;
+                        descend();
+                        scope = save_scope;
+                        return true;
+                    }
+                }
+            });
+            self.walk(tw);
+
+            // pass 2: we should replace symbols refer to constants
+            // with corresponding values.
+            var tt = new TreeTransformer(
+                function before(node, descend, in_list) {
+                    if (node instanceof AST_SymbolRef) {
+                        if (definitions.hasOwnProperty(node.name)) {
+                            return make_node_from_constant(compressor, definitions[node.name], node.orig);
+                        }
+                    }
+                }
+            );
+            self.transform(tt);
+        }
+    });
+
     AST_Scope.DEFMETHOD("drop_unused", function(compressor){
         var self = this;
         if (compressor.option("unused")

test/compress/inlineconst.js

@@ -0,0 +1,67 @@
+inlineconst_number: {
+    options = { inlineconst: true };
+    input: {
+        function f(c) {
+            var a = 5, b = 10;
+            return a + b + c;
+        }
+    }
+    expect: {
+        function f(c) {
+            var a = 5, b = 10;
+            return 5 + 10 + c;
+        }
+    }
+}
+
+inlineconst_bool_and_null: {
+    options = { inlineconst: true };
+    input: {
+        function f(c) {
+            var a = true, b = false, n = null;
+            return (n || b || a) ^ c;
+        }
+    }
+    expect: {
+        function f(c) {
+            var a = true, b = false, n = null;
+            return (null || false || true) ^ c;
+        }
+    }
+}
+
+inlineconst_string: {
+    options = { inlineconst: true, inlinestr: 2 };
+    input: {
+        function f() {
+            var s1 = "1", s2 = "12";
+            return s1 + s2;
+        }
+    }
+    expect: {
+        function f() {
+            var s1 = "1", s2 = "12";
+            return "1" + s2;
+        }
+    }
+}
+
+inlineconst_in_nested_function: {
+    options = { inlineconst: true };
+    input: {
+        function f() {
+            var x = 1;
+            return function t() {
+                return x + 1;
+            };
+        }
+    }
+    expect: {
+        function f() {
+            var x = 1;
+            return function t() {
+                return 1 + 1;
+            };
+        }
+    }
+}