enhance merge_vars (#4125)

lib/compress.js

@@ -4322,7 +4322,7 @@ merge(Compressor.prototype, {
 
     AST_Scope.DEFMETHOD("merge_variables", function(compressor) {
         if (!compressor.option("merge_vars")) return;
-        var self = this, segment = null;
+        var self = this, segment = {};
         var first = [], last = [], index = 0;
         var declarations = new Dictionary();
         var references = Object.create(null);
@@ -4331,9 +4331,9 @@ merge(Compressor.prototype, {
             if (node instanceof AST_Assign) {
                 var sym = node.left;
                 if (!(sym instanceof AST_SymbolRef)) return;
-                if (node.operator != "=") mark(sym);
+                if (node.operator != "=") mark(sym, true, false);
                 node.right.walk(tw);
-                mark(sym, true);
+                mark(sym, false, true);
                 return true;
             }
             if (node instanceof AST_Binary) {
@@ -4357,6 +4357,7 @@ merge(Compressor.prototype, {
             if (node instanceof AST_For) {
                 if (node.init) node.init.walk(tw);
                 push();
+                segment.block = node;
                 if (node.condition) node.condition.walk(tw);
                 node.body.walk(tw);
                 if (node.step) node.step.walk(tw);
@@ -4366,6 +4367,7 @@ merge(Compressor.prototype, {
             if (node instanceof AST_ForIn) {
                 node.object.walk(tw);
                 push();
+                segment.block = node;
                 node.init.walk(tw);
                 node.body.walk(tw);
                 pop();
@@ -4385,12 +4387,14 @@ merge(Compressor.prototype, {
             }
             if (node instanceof AST_IterationStatement) {
                 push();
+                segment.block = node;
                 descend();
                 pop();
                 return true;
             }
             if (node instanceof AST_LabeledStatement) {
                 push();
+                segment.block = node;
                 node.body.walk(tw);
                 pop();
                 return true;
@@ -4401,6 +4405,7 @@ merge(Compressor.prototype, {
                     if (node.name) references[node.name.definition().id] = false;
                 }
                 push();
+                segment.block = node;
                 descend();
                 pop();
                 return true;
@@ -4422,11 +4427,11 @@ merge(Compressor.prototype, {
                 return true;
             }
             if (node instanceof AST_SymbolFunarg) {
-                if (!node.__unused) mark(node, true);
+                if (!node.__unused) mark(node, false, true);
                 return true;
             }
             if (node instanceof AST_SymbolRef) {
-                mark(node);
+                mark(node, true, false);
                 return true;
             }
             if (node instanceof AST_Try) {
@@ -4446,13 +4451,13 @@ merge(Compressor.prototype, {
                 if (!unary_arithmetic[node.operator]) return;
                 var sym = node.expression;
                 if (!(sym instanceof AST_SymbolRef)) return;
-                mark(sym);
+                mark(sym, true, true);
                 return true;
             }
             if (node instanceof AST_VarDef) {
                 if (node.value) {
                     node.value.walk(tw);
-                    mark(node.name, true);
+                    mark(node.name, false, true);
                 } else {
                     var id = node.name.definition().id;
                     if (!(id in references)) {
@@ -4479,7 +4484,7 @@ merge(Compressor.prototype, {
                 if (tail.index > head.index) continue;
                 var id = tail.definition.id;
                 if (!references[id]) continue;
-                if (references[def.id].segment !== references[id].segment) {
+                if (!mergeable()) {
                     skipped.unshift(tail);
                     continue;
                 }
@@ -4510,7 +4515,36 @@ merge(Compressor.prototype, {
             segment = Object.getPrototypeOf(segment);
         }
 
-        function read(def) {
+        function mark(sym, read, write) {
+            var def = sym.definition();
+            if (def.id in references) {
+                var refs = references[def.id];
+                if (!refs) return;
+                if (write ? refs.start !== segment : refs.start.block !== segment.block) {
+                    return references[def.id] = false;
+                }
+                refs.push(sym);
+                refs.end = segment;
+                if (def.id in prev) {
+                    last[prev[def.id]] = null;
+                } else if (!read) {
+                    return;
+                }
+            } else if (self.variables.get(def.name) !== def || compressor.exposed(def)) {
+                return references[def.id] = false;
+            } else {
+                var refs = declarations.get(def.id) || [];
+                refs.push(sym);
+                references[def.id] = refs;
+                if (!read) {
+                    refs.start = segment;
+                    return first.push({
+                        index: index++,
+                        definition: def,
+                    });
+                }
+                refs.start = self;
+            }
             prev[def.id] = last.length;
             last.push({
                 index: index++,
@@ -4518,32 +4552,15 @@ merge(Compressor.prototype, {
             });
         }
 
-        function mark(sym, write_only) {
+        function must_visit(base, segment) {
-            var def = sym.definition();
+            return base === segment || base.isPrototypeOf(segment);
-            if (def.id in references) {
-                var refs = references[def.id];
-                if (!refs) return;
-                if (refs.segment !== segment) return references[def.id] = false;
-                refs.push(sym);
-                if (def.id in prev) last[prev[def.id]] = null;
-                read(def);
-            } else if (self.variables.get(def.name) !== def || compressor.exposed(def)) {
-                references[def.id] = false;
-            } else {
-                var refs = declarations.get(def.id) || [];
-                refs.push(sym);
-                references[def.id] = refs;
-                if (write_only) {
-                    refs.segment = segment;
-                    first.push({
-                        index: index++,
-                        definition: def,
-                    });
-                } else {
-                    refs.segment = self;
-                    read(def);
-                }
         }
+
+        function mergeable() {
+            var head = references[def.id];
+            var tail = references[id];
+            if (head.start.block !== tail.start.block) return false;
+            return must_visit(head.start, head.end) || must_visit(head.start, tail.start);
         }
     });