fix corner case in reduce_vars (#4997)

fixes #4996

lib/compress.js

@@ -606,7 +606,11 @@ merge(Compressor.prototype, {
             var safe = tw.safe_ids[def.id];
             if (!HOP(tw.safe_ids, def.id)) {
                 if (!safe) return false;
-                if (safe.read && def.scope.resolve() !== tw.find_parent(AST_Scope)) return false;
+                if (safe.read) {
+                    var scope = tw.find_parent(AST_BlockScope);
+                    if (scope instanceof AST_Class) return false;
+                    if (def.scope.resolve() !== scope.resolve()) return false;
+                }
                 safe.assign = safe.assign && safe.assign !== tw.safe_ids ? true : tw.safe_ids;
             }
             if (def.fixed != null && safe.read) {

test/compress/classes.js

@@ -1748,3 +1748,47 @@ issue_4992: {
     expect_stdout: "function"
     node_version: ">=12"
 }
+
+issue_4996_1: {
+    options = {
+        evaluate: true,
+        reduce_vars: true,
+        toplevel: true,
+    }
+    input: {
+        var a = 1;
+        console.log(new class A {
+            p = a-- && new A();
+        }().p.p);
+    }
+    expect: {
+        var a = 1;
+        console.log(new class A {
+            p = a-- && new A();
+        }().p.p);
+    }
+    expect_stdout: "0"
+    node_version: ">=12"
+}
+
+issue_4996_2: {
+    options = {
+        reduce_vars: true,
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        var a = 1;
+        console.log(new class A {
+            p = a-- && new A();
+        }().p.p);
+    }
+    expect: {
+        var a = 1;
+        console.log(new class A {
+            p = a-- && new A();
+        }().p.p);
+    }
+    expect_stdout: "0"
+    node_version: ">=12"
+}