enhance unused (#4922)

mishoo · May 11, 2021 · b1cfa71 · b1cfa71
1 parent 7b8570f
commit b1cfa71
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Showing 2 changed files with 16 additions and 14 deletions.
diff --git a/lib/compress.js b/lib/compress.js
@@ -6057,7 +6057,7 @@ merge(Compressor.prototype, {
                                 if (!side_effects) {
                                     initializations.add(def.id, value);
                                 } else if (shared) {
-                                    verify_safe_usage(def, true, value_modified[def.id]);
+                                    verify_safe_usage(def, name, value_modified[def.id]);
                                 }
                                 assignments.add(def.id, defn);
                             }
@@ -6200,19 +6200,13 @@ merge(Compressor.prototype, {
             if (drop_vars) {
                 var props = [], sym = assign_as_unused(node, props);
                 if (sym) {
-                    var def = sym.definition();
-                    var in_use = def.id in in_use_ids;
                     var value;
-                    if (node instanceof AST_Assign) {
-                        if (!in_use || node.left === sym && indexOf_assign(def, node) < 0) {
+                    if (can_drop_lhs(sym, node)) {
+                        if (node instanceof AST_Assign) {
                             value = get_rhs(node);
-                            if (node.write_only === true) {
-                                value = value.drop_side_effect_free(compressor)
-                                    || make_node(AST_Number, node, { value: 0 });
-                            }
+                            if (node.write_only === true) value = value.drop_side_effect_free(compressor);
                         }
-                    } else if (!in_use || node.expression === sym && indexOf_assign(def, node) < 0) {
-                        value = make_node(AST_Number, node, { value: 0 });
+                        if (!value) value = make_node(AST_Number, node, { value: 0 });
                     }
                     if (value) {
                         if (props.assign) {
@@ -6705,14 +6699,22 @@ merge(Compressor.prototype, {
         function verify_safe_usage(def, read, modified) {
             if (def.id in in_use_ids) return;
             if (read && modified) {
-                in_use_ids[def.id] = true;
+                in_use_ids[def.id] = read;
                 in_use.push(def);
             } else {
                 value_read[def.id] = read;
                 value_modified[def.id] = modified;
             }
         }
 
+        function can_drop_lhs(sym, node) {
+            var def = sym.definition();
+            var in_use = in_use_ids[def.id];
+            if (!in_use) return true;
+            if (node[node instanceof AST_Assign ? "left" : "expression"] !== sym) return false;
+            return in_use === sym && def.references.length - def.replaced == 1 || indexOf_assign(def, node) < 0;
+        }
+
         function get_rhs(assign) {
             var rhs = assign.right;
             if (!assign.write_only) return rhs;
@@ -6775,7 +6777,7 @@ merge(Compressor.prototype, {
                     }
                     if (node.left === sym) {
                         if (!node.write_only || shared) {
-                            verify_safe_usage(node_def, true, value_modified[node_def.id]);
+                            verify_safe_usage(node_def, sym, value_modified[node_def.id]);
                         }
                     } else {
                         var fixed = sym.fixed_value();

diff --git a/test/compress/drop-unused.js b/test/compress/drop-unused.js
@@ -3436,7 +3436,7 @@ issue_4912_2: {
         console.log(function() {
             var g, f = function() {};
             f.p = {};
-            (g = f.p.q = function() {}).r = "PASS";
+            (f.p.q = function() {}).r = "PASS";
             return f;
         }().p.q.r);
     }