improve synergy between `collapse_vars` & `unused` (#2521)

4 files changed, 48 insertions, 49 deletions

diff --git a/lib/compress.js b/lib/compress.js
index b51fdfc7..f49f0b24 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -800,14 +800,6 @@ merge(Compressor.prototype, {
             || compressor.option("unsafe") && global_names(this.name);
     });
 
-    function drop_decl(def) {
-        def.eliminated++;
-        if (def.orig.length == def.eliminated) {
-            def.scope.functions.del(def.name);
-            def.scope.variables.del(def.name);
-        }
-    }
-
     function is_identifier_atom(node) {
         return node instanceof AST_Infinity
             || node instanceof AST_NaN
@@ -1138,7 +1130,6 @@ merge(Compressor.prototype, {
                     if (node === expr || node.body === expr) {
                         found = true;
                         if (node instanceof AST_VarDef) {
-                            drop_decl(node.name.definition());
                             node.value = null;
                             return node;
                         }
@@ -2484,7 +2475,7 @@ merge(Compressor.prototype, {
                     var def = node.name.definition();
                     if (!(def.id in in_use_ids)) {
                         compressor[node.name.unreferenced() ? "warn" : "info"]("Dropping unused function {name} [{file}:{line},{col}]", template(node.name));
-                        drop_decl(def);
+                        def.eliminated++;
                         return make_node(AST_EmptyStatement, node);
                     }
                     return node;
@@ -2503,10 +2494,17 @@ merge(Compressor.prototype, {
                         if (!drop_vars || sym.id in in_use_ids) {
                             if (def.name instanceof AST_SymbolVar) {
                                 var var_defs = var_defs_by_id.get(sym.id);
-                                if (var_defs.length > 1 && !def.value) {
+                                if (var_defs.length > 1 && (!def.value || sym.orig.indexOf(def.name) > sym.eliminated)) {
                                     compressor.warn("Dropping duplicated definition of variable {name} [{file}:{line},{col}]", template(def.name));
+                                    if (def.value) {
+                                        merge_sequence(side_effects, make_node(AST_Assign, def, {
+                                            operator: "=",
+                                            left: make_node(AST_SymbolRef, def.name, def.name),
+                                            right: def.value
+                                        }));
+                                    }
                                     remove(var_defs, def);
-                                    drop_decl(sym);
+                                    sym.eliminated++;
                                     return;
                                 }
                             }
@@ -2539,25 +2537,9 @@ merge(Compressor.prototype, {
                             } else {
                                 compressor[def.name.unreferenced() ? "warn" : "info"]("Dropping unused variable {name} [{file}:{line},{col}]", template(def.name));
                             }
-                            drop_decl(sym);
+                            sym.eliminated++;
                         }
                     });
-                    if (head.length == 0 && tail.length == 1 && tail[0].name instanceof AST_SymbolVar) {
-                        var var_defs = var_defs_by_id.get(tail[0].name.definition().id);
-                        if (var_defs.length > 1) {
-                            var def = tail.pop();
-                            compressor.warn("Converting duplicated definition of variable {name} to assignment [{file}:{line},{col}]", template(def.name));
-                            remove(var_defs, def);
-                            side_effects.unshift(make_node(AST_Assign, def, {
-                                operator: "=",
-                                left: make_node(AST_SymbolRef, def.name, def.name),
-                                right: def.value
-                            }));
-                            def = def.name.definition();
-                            drop_decl(def);
-                            def.replaced--;
-                        }
-                    }
                     if (head.length > 0 || tail.length > 0) {
                         node.definitions = head.concat(tail);
                         body.push(node);
@@ -3385,7 +3367,9 @@ merge(Compressor.prototype, {
                 }));
                 if (reduce_vars) name.definition().fixed = false;
             }
-            drop_decl(def.name.definition());
+            def = def.name.definition();
+            def.eliminated++;
+            def.replaced--;
             return a;
         }, []);
         if (assignments.length == 0) return null;
diff --git a/test/compress/collapse_vars.js b/test/compress/collapse_vars.js
index f968ff20..68313354 100644
--- a/test/compress/collapse_vars.js
+++ b/test/compress/collapse_vars.js
@@ -2013,7 +2013,8 @@ chained_3: {
     }
     expect: {
         console.log(function(a, b) {
-            var c = 1, c = b;
+            var c = 1;
+            c = b;
             b++;
             return c;
         }(0, 2));
@@ -2081,7 +2082,7 @@ inner_lvalues: {
     expect_stdout: true
 }
 
-double_def: {
+double_def_1: {
     options = {
         collapse_vars: true,
         unused: true,
@@ -2091,8 +2092,23 @@ double_def: {
         a();
     }
     expect: {
-        var a = x;
-        (a = a && y)();
+        var a;
+        (a = (a = x) && y)();
+    }
+}
+
+double_def_2: {
+    options = {
+        collapse_vars: true,
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        var a = x, a = a && y;
+        a();
+    }
+    expect: {
+        (x && y)();
     }
 }
 
@@ -2201,7 +2217,7 @@ lvalues_def: {
     }
     expect: {
         var a = 0, b = 1;
-        var a = b++, b = +void 0;
+        a = b++, b = +void 0;
         a && a[a++];
         console.log(a, b);
     }
@@ -3074,10 +3090,9 @@ issue_2437: {
                 var result = !!req.onreadystatechange;
                 Object.defineProperty(XMLHttpRequest.prototype, 'onreadystatechange', xhrDesc || {});
                 return result;
-            }
-            else {
+            } else {
                 var req = new XMLHttpRequest();
-                var detectFunc = function () { };
+                var detectFunc = function () {};
                 req.onreadystatechange = detectFunc;
                 var result = req[SYMBOL_FAKE_ONREADYSTATECHANGE_1] === detectFunc;
                 req.onreadystatechange = null;
@@ -3093,9 +3108,9 @@ issue_2437: {
                 return Object.defineProperty(XMLHttpRequest.prototype, "onreadystatechange", xhrDesc || {}),
                     result;
             }
-            var req = new XMLHttpRequest(), detectFunc = function() {};
-            req.onreadystatechange = detectFunc,
-            result = req[SYMBOL_FAKE_ONREADYSTATECHANGE_1] === detectFunc,
+            var req, detectFunc = function() {};
+            (req = new XMLHttpRequest()).onreadystatechange = detectFunc;
+            result = req[SYMBOL_FAKE_ONREADYSTATECHANGE_1] === detectFunc;
             req.onreadystatechange = null;
         }();
     }
@@ -3609,15 +3624,15 @@ issue_2497: {
     expect: {
         function sample() {
             if (true)
-                for (i = 0; i < 1; ++i)
-                    for (k = 0; k < 1; ++k) {
+                for (var i = 0; i < 1; ++i)
+                    for (var k = 0; k < 1; ++k) {
                         value = 1;
                         value = value ? value + 1 : 0;
                     }
             else
-                for (var i = 0; i < 1; ++i)
-                    for (var k = 0; k < 1; ++k)
-                        var value=1;
+                for (i = 0; i < 1; ++i)
+                    for (k = 0; k < 1; ++k)
+                        var value = 1;
         }
     }
 }
diff --git a/test/compress/drop-unused.js b/test/compress/drop-unused.js
index eb6f9df4..189a0008 100644
--- a/test/compress/drop-unused.js
+++ b/test/compress/drop-unused.js
@@ -1294,8 +1294,8 @@ issue_2288: {
     expect: {
         function foo(o) {
             o.a;
-            for (i = 0; i < 0; i++);
             for (var i = 0; i < 0; i++);
+            for (i = 0; i < 0; i++);
         }
     }
 }
diff --git a/test/compress/reduce_vars.js b/test/compress/reduce_vars.js
index 02ff5e43..82b5ad6d 100644
--- a/test/compress/reduce_vars.js
+++ b/test/compress/reduce_vars.js
@@ -972,8 +972,8 @@ inner_var_for_2: {
     }
     expect: {
         !function() {
-            a = 1;
-            for (var b = 1; --b;) var a = 2;
+            var a = 1;
+            for (var b = 1; --b;) a = 2;
             console.log(a);
         }();
     }