From b6ff4d6f717dfb4bd41c62c7085e15ace868f296 Mon Sep 17 00:00:00 2001
From: Niklas Mischkulnig <4586894+mischnic@users.noreply.github.com>
Date: Mon, 3 May 2021 11:12:15 +0200
Subject: [PATCH] fix(es/transforms/optimization): Preserve `x instanceof
 Object` (#1630)

---
 .../transforms/optimization/src/simplify/expr/mod.rs | 12 +++++++++++-
 .../optimization/src/simplify/expr/tests.rs          |  2 ++
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/ecmascript/transforms/optimization/src/simplify/expr/mod.rs b/ecmascript/transforms/optimization/src/simplify/expr/mod.rs
index 4a19b25fb13c..d7a332a78139 100644
--- a/ecmascript/transforms/optimization/src/simplify/expr/mod.rs
+++ b/ecmascript/transforms/optimization/src/simplify/expr/mod.rs
@@ -466,12 +466,22 @@ impl SimplifyExpr {
                     }
                 }
 
+                fn is_obj(e: &Expr) -> bool {
+                    match *e {
+                        Expr::Array { .. }
+                        | Expr::Object { .. }
+                        | Expr::Fn { .. }
+                        | Expr::New { .. } => true,
+                        _ => false,
+                    }
+                }
+
                 // Non-object types are never instances.
                 if is_non_obj(&left) {
                     return make_bool_expr(span, false, iter::once(right));
                 }
 
-                if right.is_ident_ref_to(js_word!("Object")) {
+                if is_obj(&left) && right.is_ident_ref_to(js_word!("Object")) {
                     return make_bool_expr(span, true, iter::once(left));
                 }
 
diff --git a/ecmascript/transforms/optimization/src/simplify/expr/tests.rs b/ecmascript/transforms/optimization/src/simplify/expr/tests.rs
index d6afd2724670..a60b5d48aa9d 100644
--- a/ecmascript/transforms/optimization/src/simplify/expr/tests.rs
+++ b/ecmascript/transforms/optimization/src/simplify/expr/tests.rs
@@ -1140,6 +1140,7 @@ fn test_fold_instance_of() {
 
     // These cases is foldable, but no handled currently.
     fold("new Foo() instanceof Object", "new Foo(), true;");
+
     // These would require type information to fold.
     fold_same("[] instanceof Foo");
     fold_same("({}) instanceof Foo");
@@ -1148,6 +1149,7 @@ fn test_fold_instance_of() {
 
     // An unknown value should never be folded.
     fold_same("x instanceof Foo");
+    fold_same("x instanceof Object");
 }
 
 #[test]