drop assignment in `AST_VarDef.value` (#2522)

fixes #2516

3 files changed, 118 insertions, 37 deletions

diff --git a/lib/compress.js b/lib/compress.js
index 22415f4d..b51fdfc7 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -1088,6 +1088,7 @@ merge(Compressor.prototype, {
             function get_lhs(expr) {
                 if (expr instanceof AST_VarDef) {
                     var def = expr.name.definition();
+                    if (!member(expr.name, def.orig)) return;
                     var declared = def.orig.length - def.eliminated;
                     var referenced = def.references.length - def.replaced;
                     if (declared > 1 && !(expr.name instanceof AST_SymbolFunarg)
@@ -2434,47 +2435,18 @@ merge(Compressor.prototype, {
                 });
                 return true;
             }
-            var sym;
-            if (scope === self
-                && (sym = assign_as_unused(node)) instanceof AST_SymbolRef
-                && self.variables.get(sym.name) === sym.definition()) {
-                if (node instanceof AST_Assign) node.right.walk(tw);
-                return true;
-            }
-            if (node instanceof AST_SymbolRef) {
-                var node_def = node.definition();
-                if (!(node_def.id in in_use_ids)) {
-                    in_use_ids[node_def.id] = true;
-                    in_use.push(node_def);
-                }
-                return true;
-            }
-            if (node instanceof AST_Scope) {
-                var save_scope = scope;
-                scope = node;
-                descend();
-                scope = save_scope;
-                return true;
-            }
+            return scan_ref_scoped(node, descend);
         });
         self.walk(tw);
         // pass 2: for every used symbol we need to walk its
         // initialization code to figure out if it uses other
         // symbols (that may not be in_use).
+        tw = new TreeWalker(scan_ref_scoped);
         for (var i = 0; i < in_use.length; ++i) {
             in_use[i].orig.forEach(function(decl){
                 // undeclared globals will be instanceof AST_SymbolRef
                 var init = initializations.get(decl.name);
                 if (init) init.forEach(function(init){
-                    var tw = new TreeWalker(function(node){
-                        if (node instanceof AST_SymbolRef) {
-                            var node_def = node.definition();
-                            if (!(node_def.id in in_use_ids)) {
-                                in_use_ids[node_def.id] = true;
-                                in_use.push(node_def);
-                            }
-                        }
-                    });
                     init.walk(tw);
                 });
             });
@@ -2663,6 +2635,31 @@ merge(Compressor.prototype, {
             }
         );
         self.transform(tt);
+
+        function scan_ref_scoped(node, descend) {
+            var sym;
+            if (scope === self
+                && (sym = assign_as_unused(node)) instanceof AST_SymbolRef
+                && self.variables.get(sym.name) === sym.definition()) {
+                if (node instanceof AST_Assign) node.right.walk(tw);
+                return true;
+            }
+            if (node instanceof AST_SymbolRef) {
+                var node_def = node.definition();
+                if (!(node_def.id in in_use_ids)) {
+                    in_use_ids[node_def.id] = true;
+                    in_use.push(node_def);
+                }
+                return true;
+            }
+            if (node instanceof AST_Scope) {
+                var save_scope = scope;
+                scope = node;
+                descend();
+                scope = save_scope;
+                return true;
+            }
+        }
     });
 
     AST_Scope.DEFMETHOD("hoist_declarations", function(compressor){
diff --git a/test/compress/collapse_vars.js b/test/compress/collapse_vars.js
index 844d5b0f..f968ff20 100644
--- a/test/compress/collapse_vars.js
+++ b/test/compress/collapse_vars.js
@@ -705,7 +705,7 @@ collapse_vars_lvalues_drop_assign: {
         function f2(x) { var z = x, a = ++z; return z += a; }
         function f3(x) { var a = (x -= 3); return x + a; }
         function f4(x) { var a = (x -= 3); return x + a; }
-        function f5(x) { e1(); var v = e2(), c = v = --x; return x - c; }
+        function f5(x) { e1(), e2(); var c = --x; return x - c; }
         function f6(x) { e1(), e2(); return --x - x; }
         function f7(x) { e1(); return x - (e2() - x); }
         function f8(x) { e1(); return x - (e2() - x); }
@@ -2386,6 +2386,7 @@ duplicate_argname: {
 issue_2298: {
     options = {
         collapse_vars: true,
+        passes: 2,
         reduce_funcs: true,
         reduce_vars: true,
         unused: true,
@@ -3087,13 +3088,14 @@ issue_2437: {
     }
     expect: {
         !function() {
-            if (xhrDesc)
-                return result = !!(req = new XMLHttpRequest()).onreadystatechange,
-                    Object.defineProperty(XMLHttpRequest.prototype, "onreadystatechange", xhrDesc || {}),
+            if (xhrDesc) {
+                var result = !!(req = new XMLHttpRequest()).onreadystatechange;
+                return Object.defineProperty(XMLHttpRequest.prototype, "onreadystatechange", xhrDesc || {}),
                     result;
+            }
             var req = new XMLHttpRequest(), detectFunc = function() {};
-            req.onreadystatechange = detectFunc;
-            var result = req[SYMBOL_FAKE_ONREADYSTATECHANGE_1] === detectFunc;
+            req.onreadystatechange = detectFunc,
+            result = req[SYMBOL_FAKE_ONREADYSTATECHANGE_1] === detectFunc,
             req.onreadystatechange = null;
         }();
     }
@@ -3522,6 +3524,7 @@ issue_2436_12: {
 issue_2436_13: {
     options = {
         collapse_vars: true,
+        passes: 2,
         reduce_vars: true,
         unused: true,
     }
@@ -3622,6 +3625,7 @@ issue_2497: {
 issue_2506: {
     options = {
         collapse_vars: true,
+        passes: 2,
         reduce_vars: true,
         unused: true,
     }
diff --git a/test/compress/drop-unused.js b/test/compress/drop-unused.js
index 33241d67..eb6f9df4 100644
--- a/test/compress/drop-unused.js
+++ b/test/compress/drop-unused.js
@@ -1299,3 +1299,83 @@ issue_2288: {
         }
     }
 }
+
+issue_2516_1: {
+    options = {
+        collapse_vars: true,
+        reduce_funcs: true,
+        reduce_vars: true,
+        unused: true,
+    }
+    input: {
+        function foo() {
+            function qux(x) {
+                bar.call(null, x);
+            }
+            function bar(x) {
+                var FOUR = 4;
+                var trouble = x || never_called();
+                var value = (FOUR - 1) * trouble;
+                console.log(value == 6 ? "PASS" : value);
+            }
+            Baz = qux;
+        }
+        var Baz;
+        foo();
+        Baz(2);
+    }
+    expect: {
+        function foo() {
+            Baz = function(x) {
+                (function(x) {
+                    var trouble = x || never_called();
+                    var value = (4 - 1) * trouble;
+                    console.log(6 == value ? "PASS" : value);
+                }).call(null, x);
+            };
+        }
+        var Baz;
+        foo();
+        Baz(2);
+    }
+}
+
+issue_2516_2: {
+    options = {
+        collapse_vars: true,
+        reduce_funcs: true,
+        reduce_vars: true,
+        passes: 2,
+        unused: true,
+    }
+    input: {
+        function foo() {
+            function qux(x) {
+                bar.call(null, x);
+            }
+            function bar(x) {
+                var FOUR = 4;
+                var trouble = x || never_called();
+                var value = (FOUR - 1) * trouble;
+                console.log(value == 6 ? "PASS" : value);
+            }
+            Baz = qux;
+        }
+        var Baz;
+        foo();
+        Baz(2);
+    }
+    expect: {
+        function foo() {
+            Baz = function(x) {
+                (function(x) {
+                    var value = (4 - 1) * (x || never_called());
+                    console.log(6 == value ? "PASS" : value);
+                }).call(null, x);
+            };
+        }
+        var Baz;
+        foo();
+        Baz(2);
+    }
+}