transform function calls to IIFEs (#1560)

- expose function body to call sites for potential optimisations
- suppress substitution of variable used within `AST_Defun`

lib/compress.js

@@ -245,7 +245,8 @@ merge(Compressor.prototype, {
                 if (node instanceof AST_SymbolRef) {
                     var d = node.definition();
                     d.references.push(node);
-                    if (!d.fixed || isModified(node, 0) || !is_safe(d)) {
+                    if (!d.fixed || !is_safe(d)
+                        || is_modified(node, 0, d.fixed instanceof AST_Lambda)) {
                         d.fixed = false;
                     }
                 }
@@ -261,6 +262,21 @@ merge(Compressor.prototype, {
                         d.fixed = false;
                     }
                 }
+                if (node instanceof AST_Defun) {
+                    var d = node.name.definition();
+                    if (!toplevel && d.global || is_safe(d)) {
+                        d.fixed = false;
+                    } else {
+                        d.fixed = node;
+                        mark_as_safe(d);
+                    }
+                    var save_ids = safe_ids;
+                    safe_ids = [];
+                    push();
+                    descend();
+                    safe_ids = save_ids;
+                    return true;
+                }
                 var iife;
                 if (node instanceof AST_Function
                     && (iife = tw.parent()) instanceof AST_Call
@@ -344,13 +360,13 @@ merge(Compressor.prototype, {
             def.should_replace = undefined;
         }
 
-        function isModified(node, level) {
+        function is_modified(node, level, func) {
             var parent = tw.parent(level);
             if (isLHS(node, parent)
-                || parent instanceof AST_Call && parent.expression === node) {
+                || !func && parent instanceof AST_Call && parent.expression === node) {
                 return true;
             } else if (parent instanceof AST_PropAccess && parent.expression === node) {
-                return isModified(parent, level + 1);
+                return !func && is_modified(parent, level + 1);
             }
         }
     });
@@ -1307,14 +1323,7 @@ merge(Compressor.prototype, {
         def(AST_Statement, function(){
             throw new Error(string_template("Cannot evaluate a statement [{file}:{line},{col}]", this.start));
         });
-        // XXX: AST_Accessor and AST_Function both inherit from AST_Scope,
-        // which itself inherits from AST_Statement; however, they aren't
-        // really statements.  This could bite in other places too. :-(
-        // Wish JS had multiple inheritance.
-        def(AST_Accessor, function(){
-            throw def;
-        });
-        def(AST_Function, function(){
+        def(AST_Lambda, function(){
             throw def;
         });
         function ev(node, compressor) {
@@ -2590,6 +2599,24 @@ merge(Compressor.prototype, {
 
     OPT(AST_Call, function(self, compressor){
         var exp = self.expression;
+        if (compressor.option("reduce_vars")
+            && exp instanceof AST_SymbolRef) {
+            var def = exp.definition();
+            if (def.fixed instanceof AST_Defun) {
+                def.fixed = make_node(AST_Function, def.fixed, def.fixed).clone(true);
+            }
+            if (def.fixed instanceof AST_Function) {
+                exp = def.fixed;
+                if (compressor.option("unused")
+                    && def.references.length == 1
+                    && compressor.find_parent(AST_Scope) === def.scope) {
+                    if (!compressor.option("keep_fnames")) {
+                        exp.name = null;
+                    }
+                    self.expression = exp;
+                }
+            }
+        }
         if (compressor.option("unused")
             && exp instanceof AST_Function
             && !exp.uses_arguments