fix corner case in collapse_vars (#3139)

lib/compress.js

@@ -1240,7 +1240,10 @@ merge(Compressor.prototype, {
             }
 
             function should_stop(node, parent) {
-                if (node instanceof AST_Assign) return node.operator != "=" && lhs.equivalent_to(node.left);
+                if (parent instanceof AST_For) return node !== parent.init;
+                if (node instanceof AST_Assign) {
+                    return node.operator != "=" && lhs.equivalent_to(node.left);
+                }
                 if (node instanceof AST_Call) {
                     return lhs instanceof AST_PropAccess && lhs.equivalent_to(node.expression);
                 }
@@ -1249,7 +1252,6 @@ merge(Compressor.prototype, {
                 if (node instanceof AST_LoopControl) return true;
                 if (node instanceof AST_Try) return true;
                 if (node instanceof AST_With) return true;
-                if (parent instanceof AST_For) return node !== parent.init;
                 if (replace_all) return false;
                 return node instanceof AST_SymbolRef && !node.is_declared(compressor);
             }

test/compress/collapse_vars.js

@@ -4931,6 +4931,27 @@ collapse_rhs_lhs_2: {
     expect_stdout: "PASS"
 }
 
+collapse_rhs_loop: {
+    options = {
+        collapse_vars: true,
+    }
+    input: {
+        var s;
+        s = "<tpl>PASS</tpl>";
+        for (var m, r = /<tpl>(.*)<\/tpl>/; m = s.match(r);)
+            s = s.replace(m[0], m[1]);
+        console.log(s);
+    }
+    expect: {
+        var s;
+        s = "<tpl>PASS</tpl>";
+        for (var m, r = /<tpl>(.*)<\/tpl>/; m = s.match(r);)
+            s = s.replace(m[0], m[1]);
+        console.log(s);
+    }
+    expect_stdout: "PASS"
+}
+
 collapse_rhs_side_effects: {
     options = {
         collapse_vars: true,