fix corner case in side_effects (#3984)

fixes #3983

lib/compress.js

@@ -5279,7 +5279,8 @@ merge(Compressor.prototype, {
         });
         def(AST_SymbolRef, function(compressor) {
             if (!this.is_declared(compressor)) return this;
-            this.definition().replaced++;
+            var def = this.definition();
+            if (member(this, def.references)) def.replaced++;
             return null;
         });
         def(AST_This, return_null);
@@ -7575,9 +7576,8 @@ merge(Compressor.prototype, {
     function recursive_ref(compressor, def) {
         var level = 0, node = compressor.self();
         do {
-            if (node instanceof AST_Lambda && node.name && node.name.definition() === def) break;
+            if (node instanceof AST_Lambda && node.name && node.name.definition() === def) return node;
         } while (node = compressor.parent(level++));
-        return node;
     }
 
     OPT(AST_SymbolRef, function(self, compressor) {

test/compress/side_effects.js

@@ -297,3 +297,33 @@ operator_in: {
     }
     expect_stdout: "PASS"
 }
+
+issue_3983: {
+    options = {
+        collapse_vars: true,
+        conditionals: true,
+        evaluate: true,
+        inline: true,
+        reduce_vars: true,
+        side_effects: true,
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        var a = "PASS";
+        function f() {
+            g && g();
+        }
+        f();
+        function g() {
+            0 ? a : 0;
+        }
+        var b = a;
+        console.log(a);
+    }
+    expect: {
+        var a = "PASS";
+        console.log(a);
+    }
+    expect_stdout: "PASS"
+}