implement hoist_props (#2396)

fixes #2377

lib/compress.js

@@ -60,6 +60,7 @@ function Compressor(options, false_by_default) {
         expression    : false,
         global_defs   : {},
         hoist_funs    : !false_by_default,
+        hoist_props   : false,
         hoist_vars    : false,
         ie8           : false,
         if_return     : !false_by_default,
@@ -190,6 +191,7 @@ merge(Compressor.prototype, {
         if (node._squeezed) return node;
         var was_scope = false;
         if (node instanceof AST_Scope) {
+            node = node.hoist_properties(this);
             node = node.hoist_declarations(this);
             was_scope = true;
         }
@@ -547,6 +549,7 @@ merge(Compressor.prototype, {
         }
 
         function reset_def(def) {
+            def.direct_access = false;
             def.escaped = false;
             if (def.scope.uses_eval) {
                 def.fixed = false;
@@ -604,15 +607,19 @@ merge(Compressor.prototype, {
                 || parent instanceof AST_Return && node === parent.value && node.scope !== d.scope
                 || parent instanceof AST_VarDef && node === parent.value) {
                 d.escaped = true;
+                return;
             } else if (parent instanceof AST_Array || parent instanceof AST_Object) {
                 mark_escaped(d, parent, parent, level + 1);
             } else if (parent instanceof AST_PropAccess && node === parent.expression) {
-                mark_escaped(d, parent, read_property(value, parent.property), level + 1);
+                value = read_property(value, parent.property);
+                mark_escaped(d, parent, value, level + 1);
+                if (value) return;
             }
+            if (level == 0) d.direct_access = true;
         }
     });
 
-    AST_SymbolRef.DEFMETHOD("fixed_value", function() {
+    AST_Symbol.DEFMETHOD("fixed_value", function() {
         var fixed = this.definition().fixed;
         if (!fixed || fixed instanceof AST_Node) return fixed;
         return fixed();
@@ -2478,11 +2485,11 @@ merge(Compressor.prototype, {
                         }));
                     }
                     switch (body.length) {
-                        case 0:
+                      case 0:
                         return in_list ? MAP.skip : make_node(AST_EmptyStatement, node);
-                        case 1:
+                      case 1:
                         return body[0];
-                        default:
+                      default:
                         return in_list ? MAP.splice(body) : make_node(AST_BlockStatement, node, {
                             body: body
                         });
@@ -2678,6 +2685,71 @@ merge(Compressor.prototype, {
         return self;
     });
 
+    AST_Scope.DEFMETHOD("hoist_properties", function(compressor){
+        var self = this;
+        if (!compressor.option("hoist_props") || compressor.has_directive("use asm")) return self;
+        var defs_by_id = Object.create(null);
+        var var_names = Object.create(null);
+        self.enclosed.forEach(function(def) {
+            var_names[def.name] = true;
+        });
+        self.variables.each(function(def, name) {
+            var_names[name] = true;
+        });
+        return self.transform(new TreeTransformer(function(node) {
+            if (node instanceof AST_VarDef) {
+                var sym = node.name, def, value;
+                if (sym.scope === self
+                    && !(def = sym.definition()).escaped
+                    && !def.single_use
+                    && !def.direct_access
+                    && (value = sym.fixed_value()) === node.value
+                    && value instanceof AST_Object) {
+                    var defs = new Dictionary();
+                    var assignments = [];
+                    value.properties.forEach(function(prop) {
+                        assignments.push(make_node(AST_VarDef, node, {
+                            name: make_sym(prop.key),
+                            value: prop.value
+                        }));
+                    });
+                    defs_by_id[def.id] = defs;
+                    return MAP.splice(assignments);
+                }
+            }
+            if (node instanceof AST_PropAccess && node.expression instanceof AST_SymbolRef) {
+                var defs = defs_by_id[node.expression.definition().id];
+                if (defs) {
+                    var key = node.property;
+                    if (key instanceof AST_Node) key = key.getValue();
+                    var def = defs.get(key);
+                    var sym = make_node(AST_SymbolRef, node, {
+                        name: def.name,
+                        scope: node.expression.scope,
+                        thedef: def
+                    });
+                    sym.reference({});
+                    return sym;
+                }
+            }
+
+            function make_sym(key) {
+                var prefix = sym.name + "_" + key.toString().replace(/[^a-z_$]+/ig, "_");
+                var name = prefix;
+                for (var i = 0; var_names[name]; i++) name = prefix + "$" + i;
+                var new_var = make_node(sym.CTOR, sym, {
+                    name: name,
+                    scope: self
+                });
+                var def = self.def_variable(new_var);
+                defs.set(key, def);
+                self.enclosed.push(def);
+                var_names[name] = true;
+                return new_var;
+            }
+        }));
+    });
+
     // drop_side_effect_free()
     // remove side-effect-free parts which only affects return value
     (function(def){