improve reduce_vars and fix a bug

- update modified flag between compress() passes
- support IIFE arguments
- fix corner case with multiple definitions

closes #1473

1 files changed, 34 insertions, 7 deletions

diff --git a/lib/compress.js b/lib/compress.js
index 345a414a..72afe92a 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -108,7 +108,8 @@ merge(Compressor.prototype, {
     compress: function(node) {
         var passes = +this.options.passes || 1;
         for (var pass = 0; pass < passes && pass < 3; ++pass) {
-            if (pass > 0) node.clear_opt_flags();
+            if (pass > 0 || this.option("reduce_vars"))
+                node.reset_opt_flags(this);
             node = node.transform(this);
         }
         return node;
@@ -167,19 +168,45 @@ merge(Compressor.prototype, {
         return this.print_to_string() == node.print_to_string();
     });
 
-    AST_Node.DEFMETHOD("clear_opt_flags", function(){
-        this.walk(new TreeWalker(function(node){
+    AST_Node.DEFMETHOD("reset_opt_flags", function(compressor){
+        var reduce_vars = compressor.option("reduce_vars");
+        var tw = new TreeWalker(function(node){
+            if (reduce_vars && node instanceof AST_Scope) {
+                node.variables.each(function(def) {
+                    delete def.modified;
+                });
+            }
             if (node instanceof AST_SymbolRef) {
                 var d = node.definition();
-                if (d && d.init) {
+                if (d.init) {
                     delete d.init._evaluated;
                 }
+                if (reduce_vars && (d.orig.length > 1 || isModified(node, 0))) {
+                    d.modified = true;
+                }
+            }
+            if (reduce_vars && node instanceof AST_Call && node.expression instanceof AST_Function) {
+                node.expression.argnames.forEach(function(arg, i) {
+                    arg.definition().init = node.args[i] || make_node(AST_Undefined, node);
+                });
             }
             if (!(node instanceof AST_Directive || node instanceof AST_Constant)) {
                 node._squeezed = false;
                 node._optimized = false;
             }
-        }));
+        });
+        this.walk(tw);
+
+        function isModified(node, level) {
+            var parent = tw.parent(level);
+            if (parent instanceof AST_Unary && (parent.operator === "++" || parent.operator === "--")
+                || parent instanceof AST_Assign && parent.left === node
+                || parent instanceof AST_Call && parent.expression === node) {
+                return true;
+            } else if (parent instanceof AST_PropAccess && parent.expression === node) {
+                return isModified(parent, level + 1);
+            }
+        }
     });
 
     function make_node(ctor, orig, props) {
@@ -459,7 +486,7 @@ merge(Compressor.prototype, {
                     var_defs_removed = true;
                 }
                 // Further optimize statement after substitution.
-                stat.clear_opt_flags();
+                stat.reset_opt_flags(compressor);
 
                 compressor.warn("Replacing " + (is_constant ? "constant" : "variable") +
                     " " + var_name + " [{file}:{line},{col}]", node.start);
@@ -1158,7 +1185,7 @@ merge(Compressor.prototype, {
             this._evaluating = true;
             try {
                 var d = this.definition();
-                if (d && (d.constant || compressor.option("reduce_vars") && !d.modified) && d.init) {
+                if ((d.constant || compressor.option("reduce_vars") && !d.modified) && d.init) {
                     if (compressor.option("unsafe")) {
                         if (!HOP(d.init, '_evaluated')) {
                             d.init._evaluated = ev(d.init, compressor);