enhance `collapse_vars` (#3572)

1 files changed, 31 insertions, 5 deletions

diff --git a/lib/compress.js b/lib/compress.js
index 87671d8e..ba789816 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -1235,7 +1235,7 @@ merge(Compressor.prototype, {
                     var lvalues = get_lvalues(candidate);
                     var lhs_local = is_lhs_local(lhs);
                     if (!side_effects) side_effects = value_has_side_effects(candidate);
-                    var replace_all = replace_all_symbols();
+                    var replace_all = replace_all_symbols(candidate);
                     var may_throw = candidate.may_throw(compressor) ? in_try ? function(node) {
                         return node.has_side_effects(compressor);
                     } : side_effects_external : return_false;
@@ -1312,6 +1312,7 @@ merge(Compressor.prototype, {
 
             function in_conditional(node, parent) {
                 if (parent instanceof AST_Binary) return lazy_op[parent.operator] && parent.left !== node;
+                if (parent instanceof AST_Case) return parent.expression !== node;
                 if (parent instanceof AST_Conditional) return parent.condition !== node;
                 return parent instanceof AST_If && parent.condition !== node;
             }
@@ -1477,19 +1478,43 @@ merge(Compressor.prototype, {
                 if (parent instanceof AST_Call) return node;
                 if (parent instanceof AST_Case) return node;
                 if (parent instanceof AST_Conditional) return node;
-                if (parent instanceof AST_Definitions) return find_stop(parent, level + 1);
+                if (parent instanceof AST_Definitions) return find_stop_unused(parent, level + 1);
                 if (parent instanceof AST_Exit) return node;
                 if (parent instanceof AST_If) return node;
                 if (parent instanceof AST_IterationStatement) return node;
                 if (parent instanceof AST_PropAccess) return node;
-                if (parent instanceof AST_Sequence) return find_stop(parent, level + 1);
-                if (parent instanceof AST_SimpleStatement) return find_stop(parent, level + 1);
+                if (parent instanceof AST_Sequence) {
+                    return (parent.tail_node() === node ? find_stop : find_stop_unused)(parent, level + 1);
+                }
+                if (parent instanceof AST_SimpleStatement) return find_stop_unused(parent, level + 1);
                 if (parent instanceof AST_Switch) return node;
                 if (parent instanceof AST_Unary) return node;
                 if (parent instanceof AST_VarDef) return node;
                 return null;
             }
 
+            function find_stop_unused(node, level) {
+                var parent = scanner.parent(level);
+                if (is_last_node(node, parent)) return node;
+                if (in_conditional(node, parent)) return node;
+                if (parent instanceof AST_Assign) return find_stop_unused(parent, level + 1);
+                if (parent instanceof AST_Binary) return find_stop_unused(parent, level + 1);
+                if (parent instanceof AST_Call) return find_stop_unused(parent, level + 1);
+                if (parent instanceof AST_Case) return find_stop_unused(parent, level + 1);
+                if (parent instanceof AST_Conditional) return find_stop_unused(parent, level + 1);
+                if (parent instanceof AST_Definitions) return find_stop_unused(parent, level + 1);
+                if (parent instanceof AST_Exit) return find_stop_unused(parent, level + 1);
+                if (parent instanceof AST_If) return find_stop_unused(parent, level + 1);
+                if (parent instanceof AST_IterationStatement) return node;
+                if (parent instanceof AST_PropAccess) return find_stop_unused(parent, level + 1);
+                if (parent instanceof AST_Sequence) return find_stop_unused(parent, level + 1);
+                if (parent instanceof AST_SimpleStatement) return find_stop_unused(parent, level + 1);
+                if (parent instanceof AST_Switch) return find_stop_unused(parent, level + 1);
+                if (parent instanceof AST_Unary) return find_stop_unused(parent, level + 1);
+                if (parent instanceof AST_VarDef) return find_stop_unused(parent, level + 1);
+                return null;
+            }
+
             function mangleable_var(var_def) {
                 var value = var_def.value;
                 if (!(value instanceof AST_SymbolRef)) return;
@@ -1656,7 +1681,8 @@ merge(Compressor.prototype, {
                 return get_rvalue(expr).has_side_effects(compressor);
             }
 
-            function replace_all_symbols() {
+            function replace_all_symbols(expr) {
+                if (expr instanceof AST_Unary) return false;
                 if (side_effects) return false;
                 if (value_def) return true;
                 if (lhs instanceof AST_SymbolRef) {