[llvm] [ADT] Add and use (for AArch64) `ValueWithSentinel<T, Sentinel>` (PR #158120)

[Jakub Kuderski via llvm-commits]

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@@ -0,0 +1,37 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/ADT/ValueWithSentinel.h"
+#include "gtest/gtest.h"
+
+using namespace llvm;
+
+namespace {
+
+TEST(ValueWithSentinelTest, Basic) {
+  ValueWithSentinelNumericMax<int> Value;
+  EXPECT_FALSE(Value.has_value());
+
+  Value = 1000;
+  EXPECT_TRUE(Value.has_value());
+
+  EXPECT_EQ(Value, 1000);
+  EXPECT_EQ(Value.value(), 1000);
+
+  Value.clear();
+  EXPECT_FALSE(Value.has_value());
+
+  ValueWithSentinelNumericMax<int> OtherValue(99);
+  EXPECT_TRUE(OtherValue.has_value());
+  EXPECT_NE(Value, OtherValue);
+
+  Value = OtherValue;
+  EXPECT_EQ(Value, OtherValue);
+}
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kuhar wrote:

This doesn't exercise all the operators. Would be also nice to test with some other data type. For example, I think this allows pointer values with a nullptr sentinel?

https://github.com/llvm/llvm-project/pull/158120