From 8d0422b6f33d05bdc634c75eabd8f5eaba81d148 Mon Sep 17 00:00:00 2001
From: "Alex Lam S.L" <alexlamsl@gmail.com>
Date: Fri, 31 Dec 2021 23:53:47 +0000
Subject: [PATCH] enhance `reduce_vars` (#5248)

---
 lib/compress.js              | 19 ++++++++++---------
 test/compress/evaluate.js    |  3 +--
 test/compress/merge_vars.js  |  4 ++--
 test/compress/reduce_vars.js |  4 ++--
 4 files changed, 15 insertions(+), 15 deletions(-)

diff --git a/lib/compress.js b/lib/compress.js
index c54a8f3a..ab930ffa 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -492,7 +492,6 @@ Compressor.prototype.compress = function(node) {
             def.reassigned = 0;
             def.recursive_refs = 0;
             def.references = [];
-            def.should_replace = undefined;
             def.single_use = undefined;
         }
 
@@ -11599,8 +11598,8 @@ Compressor.prototype.compress = function(node) {
                 def.replaced++;
                 return value;
             }
-            var local = self.fixed !== def.fixed;
-            if (fixed && (local || def.should_replace !== false)) {
+            var state;
+            if (fixed && (state = self.fixed || def.fixed).should_replace !== false) {
                 var ev, init;
                 if (fixed instanceof AST_This) {
                     if (!is_funarg(def) && same_scope(def)) init = fixed;
@@ -11613,20 +11612,22 @@ Compressor.prototype.compress = function(node) {
                     init = make_node_from_constant(ev, fixed);
                 }
                 if (init) {
-                    if (!local && def.should_replace === undefined) {
+                    if (state.should_replace === undefined) {
                         var value_length = init.optimize(compressor).print_to_string().length;
                         if (!has_symbol_ref(fixed)) {
                             value_length = Math.min(value_length, fixed.print_to_string().length);
                         }
                         var name_length = def.name.length;
                         if (compressor.option("unused") && !compressor.exposed(def)) {
-                            var referenced = def.references.length - def.replaced;
-                            name_length += (name_length + 2 + value_length) / (referenced - def.assignments);
+                            var refs = def.references.length - def.replaced - def.assignments;
+                            refs = Math.min(refs, def.references.filter(function(ref) {
+                                return ref.fixed === state;
+                            }).length);
+                            name_length += (name_length + 2 + value_length) / Math.max(1, refs);
                         }
-                        var delta = value_length - Math.floor(name_length);
-                        def.should_replace = delta < compressor.eval_threshold;
+                        state.should_replace = value_length - Math.floor(name_length) < compressor.eval_threshold;
                     }
-                    if (local || def.should_replace) {
+                    if (state.should_replace) {
                         var value;
                         if (has_symbol_ref(fixed)) {
                             value = init.optimize(compressor);
diff --git a/test/compress/evaluate.js b/test/compress/evaluate.js
index c479a534..acd218ed 100644
--- a/test/compress/evaluate.js
+++ b/test/compress/evaluate.js
@@ -2752,8 +2752,7 @@ issue_3944: {
     }
     expect: {
         void function f() {
-            while (a = 0 == (a = void 0), console.log(a), void 0);
-            var a;
+            while (0 == void 0, console.log(false), void 0);
             f;
         }();
     }
diff --git a/test/compress/merge_vars.js b/test/compress/merge_vars.js
index 9f89efe5..a0ece252 100644
--- a/test/compress/merge_vars.js
+++ b/test/compress/merge_vars.js
@@ -3228,10 +3228,10 @@ issue_4653: {
         f(a++ + (b = b), b |= console.log(a));
     }
     expect: {
-        var b = 1;
+        var b, a = 1;
         (function(c, d) {
             c || console.log(d);
-        })(+b + (b = void 0), b |= console.log(2));
+        })(+a + (b = b), b |= console.log(2));
     }
     expect_stdout: [
         "2",
diff --git a/test/compress/reduce_vars.js b/test/compress/reduce_vars.js
index 7a150afa..0e232eee 100644
--- a/test/compress/reduce_vars.js
+++ b/test/compress/reduce_vars.js
@@ -905,7 +905,7 @@ use_before_var: {
     }
     expect: {
         function f(){
-            console.log(void 0);
+            console.log(t);
             var t = 1;
         }
     }
@@ -981,7 +981,7 @@ inner_var_for_1: {
     expect: {
         function f() {
             var a = 1;
-            x(1, void 0, d);
+            x(1, b, d);
             for (var b = 2, c = 3; x(1, 2, 3, d); x(1, 2, 3, d)) {
                 var d = 4, e = 5;
                 x(1, 2, 3, d, e);