From d6c8fe6f1a1135aa2528b775bbd4662c625c0088 Mon Sep 17 00:00:00 2001
From: Tzvetan Mikov <tmikov@meta.com>
Date: Tue, 7 Jan 2025 21:19:08 -0800
Subject: [PATCH] InstSimplify: optimize equality comparisons based on type

Summary:
Strict equality of non-overlapping types doesn't need to be performed.
Loose equality is trickier, so we constrain ourselves only to comparing
against `null|undefined`.

Reviewed By: davedets

Differential Revision: D67905084

fbshipit-source-id: ca0b7915973962de66ebddd9ecf61981e51d60c0
---
 lib/Optimizer/Scalar/InstSimplify.cpp        | 26 +++++++--
 test/Optimizer/simplify-eq-null-undefined.js | 56 ++++++++++++++++++++
 2 files changed, 78 insertions(+), 4 deletions(-)
 create mode 100644 test/Optimizer/simplify-eq-null-undefined.js

diff --git a/lib/Optimizer/Scalar/InstSimplify.cpp b/lib/Optimizer/Scalar/InstSimplify.cpp
index b7b1c15cd07..d6e4d700c0c 100644
--- a/lib/Optimizer/Scalar/InstSimplify.cpp
+++ b/lib/Optimizer/Scalar/InstSimplify.cpp
@@ -407,6 +407,14 @@ class InstSimplifyImpl {
           return builder_.createBinaryOperatorInst(
               lhs, rhs, ValueKind::BinaryStrictlyEqualInstKind);
         }
+
+        // ~(null|undefined) == null|undefined is always false.
+        if ((Type::intersectTy(leftTy, kNullOrUndef).isNoType() &&
+             rightTy.isSubsetOf(kNullOrUndef)) ||
+            (Type::intersectTy(rightTy, kNullOrUndef).isNoType() &&
+             leftTy.isSubsetOf(kNullOrUndef))) {
+          return builder_.getLiteralBool(false);
+        }
         break;
 
       case ValueKind::BinaryNotEqualInstKind: // !=
@@ -421,6 +429,14 @@ class InstSimplifyImpl {
           return builder_.createBinaryOperatorInst(
               lhs, rhs, ValueKind::BinaryStrictlyNotEqualInstKind);
         }
+
+        // ~(null|undefined) != null|undefined is always true.
+        if ((Type::intersectTy(leftTy, kNullOrUndef).isNoType() &&
+             rightTy.isSubsetOf(kNullOrUndef)) ||
+            (Type::intersectTy(rightTy, kNullOrUndef).isNoType() &&
+             leftTy.isSubsetOf(kNullOrUndef))) {
+          return builder_.getLiteralBool(true);
+        }
         break;
 
       case ValueKind::BinaryStrictlyEqualInstKind: // ===
@@ -430,10 +446,8 @@ class InstSimplifyImpl {
         }
 
         // Operands of different types can't be strictly equal.
-        if (leftTy.isPrimitive() && rightTy.isPrimitive()) {
-          if (Type::intersectTy(leftTy, rightTy).isNoType()) {
-            return builder_.getLiteralBool(false);
-          }
+        if (Type::intersectTy(leftTy, rightTy).isNoType()) {
+          return builder_.getLiteralBool(false);
         }
         break;
 
@@ -442,6 +456,10 @@ class InstSimplifyImpl {
         if (identicalForEquality) {
           return builder_.getLiteralBool(false);
         }
+        // Operands of different types can't be strictly equal.
+        if (Type::intersectTy(leftTy, rightTy).isNoType()) {
+          return builder_.getLiteralBool(true);
+        }
         break;
 
       case ValueKind::BinaryLessThanInstKind: // <
diff --git a/test/Optimizer/simplify-eq-null-undefined.js b/test/Optimizer/simplify-eq-null-undefined.js
new file mode 100644
index 00000000000..0c4a7379a8c
--- /dev/null
+++ b/test/Optimizer/simplify-eq-null-undefined.js
@@ -0,0 +1,56 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+// RUN: %hermesc -O -dump-ir %s | %FileCheckOrRegen %s
+
+// Test equality comparisons against null|undefined when the other type can
+// be neither type.
+
+let o = {};
+sink = o !== null;
+sink = o === null;
+sink = o != null;
+sink = o == null;
+sink = undefined !== o;
+sink = undefined === o;
+sink = undefined != o;
+sink = undefined == o;
+
+let n = +glob;
+sink = n !== undefined;
+sink = n === undefined;
+sink = n != undefined;
+sink = n == undefined;
+sink = null !== n;
+sink = null === n;
+sink = null != n;
+sink = null == n;
+
+// Auto-generated content below. Please do not modify manually.
+
+// CHECK:function global(): boolean
+// CHECK-NEXT:%BB0:
+// CHECK-NEXT:       StorePropertyLooseInst true: boolean, globalObject: object, "sink": string
+// CHECK-NEXT:       StorePropertyLooseInst false: boolean, globalObject: object, "sink": string
+// CHECK-NEXT:       StorePropertyLooseInst true: boolean, globalObject: object, "sink": string
+// CHECK-NEXT:       StorePropertyLooseInst false: boolean, globalObject: object, "sink": string
+// CHECK-NEXT:       StorePropertyLooseInst true: boolean, globalObject: object, "sink": string
+// CHECK-NEXT:       StorePropertyLooseInst false: boolean, globalObject: object, "sink": string
+// CHECK-NEXT:       StorePropertyLooseInst true: boolean, globalObject: object, "sink": string
+// CHECK-NEXT:       StorePropertyLooseInst false: boolean, globalObject: object, "sink": string
+// CHECK-NEXT:  %8 = TryLoadGlobalPropertyInst (:any) globalObject: object, "glob": string
+// CHECK-NEXT:  %9 = AsNumberInst (:number) %8: any
+// CHECK-NEXT:        StorePropertyLooseInst true: boolean, globalObject: object, "sink": string
+// CHECK-NEXT:        StorePropertyLooseInst false: boolean, globalObject: object, "sink": string
+// CHECK-NEXT:        StorePropertyLooseInst true: boolean, globalObject: object, "sink": string
+// CHECK-NEXT:        StorePropertyLooseInst false: boolean, globalObject: object, "sink": string
+// CHECK-NEXT:        StorePropertyLooseInst true: boolean, globalObject: object, "sink": string
+// CHECK-NEXT:        StorePropertyLooseInst false: boolean, globalObject: object, "sink": string
+// CHECK-NEXT:        StorePropertyLooseInst true: boolean, globalObject: object, "sink": string
+// CHECK-NEXT:        StorePropertyLooseInst false: boolean, globalObject: object, "sink": string
+// CHECK-NEXT:        ReturnInst false: boolean
+// CHECK-NEXT:function_end