enhance `collapse_vars` (#3801)

1 files changed, 10 insertions, 6 deletions

diff --git a/lib/compress.js b/lib/compress.js
index b7a91ea5..b0e25dde 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -1122,7 +1122,10 @@ merge(Compressor.prototype, {
         function collapse(statements, compressor) {
             if (scope.pinned()) return statements;
             var args;
+            var assignments = Object.create(null);
             var candidates = [];
+            var declare_only = Object.create(null);
+            var force_single;
             var stat_index = statements.length;
             var scanner = new TreeTransformer(function(node, descend) {
                 if (abort) return node;
@@ -1255,7 +1258,6 @@ merge(Compressor.prototype, {
                 // Skip (non-executed) functions and (leading) default case in switch statements
                 if (node instanceof AST_Default || node instanceof AST_Scope) return node;
             }, patch_sequence);
-            var force_single;
             while (--stat_index >= 0) {
                 // Treat parameters as collapsible in IIFE, i.e.
                 //   function(a, b){ ... }(x());
@@ -1264,7 +1266,6 @@ merge(Compressor.prototype, {
                 if (stat_index == 0 && compressor.option("unused")) extract_args();
                 // Find collapsible assignments
                 var hit_stack = [];
-                var declare_only = Object.create(null);
                 extract_candidates(statements[stat_index]);
                 while (candidates.length > 0) {
                     hit_stack = candidates.pop();
@@ -1501,6 +1502,9 @@ merge(Compressor.prototype, {
                     candidates.push(hit_stack.slice());
                     extract_candidates(expr.left);
                     extract_candidates(expr.right);
+                    if (expr.left instanceof AST_SymbolRef) {
+                        assignments[expr.left.name] = (assignments[expr.left.name] || 0) + 1;
+                    }
                 } else if (expr instanceof AST_Binary) {
                     extract_candidates(expr.left);
                     extract_candidates(expr.right);
@@ -1740,14 +1744,13 @@ merge(Compressor.prototype, {
                 if (expr instanceof AST_VarDef) {
                     var def = expr.name.definition();
                     if (!member(expr.name, def.orig)) return;
-                    var referenced = def.references.length - def.replaced;
-                    var declared = def.orig.length - def.eliminated;
-                    declared -= declare_only[def.name] || 0;
+                    var declared = def.orig.length - def.eliminated - (declare_only[def.name] || 0);
+                    var referenced = def.references.length - def.replaced - (assignments[def.name] || 0);
                     if (declared > 1 && !(expr.name instanceof AST_SymbolFunarg)) {
                         mangleable_var(expr.value);
                         return make_node(AST_SymbolRef, expr.name, expr.name);
                     }
-                    if (referenced > 1 ? mangleable_var(expr.value) : !compressor.exposed(def)) {
+                    if (mangleable_var(expr.value) || referenced == 1 && !compressor.exposed(def)) {
                         return make_node(AST_SymbolRef, expr.name, expr.name);
                     }
                 } else if (expr instanceof AST_Assign) {
@@ -1871,6 +1874,7 @@ merge(Compressor.prototype, {
                     found = true;
                     if (node instanceof AST_VarDef) {
                         node.value = null;
+                        declare_only[node.name.name] = (declare_only[node.name.name] || 0) + 1;
                         if (value_def) value_def.replaced++;
                         return node;
                     }