fix corner case in inline

fixes #3821

lib/compress.js

@@ -6130,8 +6130,12 @@ merge(Compressor.prototype, {
                     return;
                 }
                 if (node instanceof AST_Scope) return abort = true;
-                var def;
-                if (node instanceof AST_SymbolRef && fn.variables.get(node.name) === (def = node.definition())) {
+                if (node instanceof AST_SymbolRef) {
+                    var def = node.definition();
+                    if (fn.variables.get(node.name) !== def) {
+                        in_order = null;
+                        return;
+                    }
                     if (def.init instanceof AST_Defun) return abort = true;
                     if (is_lhs(node, this.parent())) return abort = true;
                     var index = resolve_index(def);

test/compress/functions.js

@@ -4062,3 +4062,49 @@ issue_3777_2: {
     }
     expect_stdout: "PASS"
 }
+
+issue_3821_1: {
+    options = {
+        inline: true,
+    }
+    input: {
+        var a = 0;
+        console.log(function(b) {
+            return +a + b;
+        }(--a));
+    }
+    expect: {
+        var a = 0;
+        console.log(function(b) {
+            return +a + b;
+        }(--a));
+    }
+    expect_stdout: "-2"
+}
+
+issue_3821_2: {
+    options = {
+        inline: true,
+        reduce_vars: true,
+        toplevel: true,
+    }
+    input: {
+        var a = "PASS";
+        function f(g, b) {
+            return g(), b;
+        }
+        console.log(f(function() {
+            a = "FAIL";
+        }, a));
+    }
+    expect: {
+        var a = "PASS";
+        function f(g, b) {
+            return g(), b;
+        }
+        console.log(f(function() {
+            a = "FAIL";
+        }, a));
+    }
+    expect_stdout: "PASS"
+}