From 9911589f5d4abd9994f294816eb5aa522f4d0458 Mon Sep 17 00:00:00 2001
From: "Duncan P. N. Exon Smith" <dexonsmith@apple.com>
Date: Wed, 8 Dec 2021 13:41:31 -0800
Subject: [PATCH] ADT: Make StringRef::size() and StringRef::empty() constexpr

This unblocks using `StringLiteral::size()` for a SmallVector size in
another patch.

Differential Revision: https://reviews.llvm.org/D115395
---
 llvm/include/llvm/ADT/StringRef.h    | 4 ++--
 llvm/unittests/ADT/StringRefTest.cpp | 4 ++++
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/llvm/include/llvm/ADT/StringRef.h b/llvm/include/llvm/ADT/StringRef.h
index 9f4b89218042..3950910f0635 100644
--- a/llvm/include/llvm/ADT/StringRef.h
+++ b/llvm/include/llvm/ADT/StringRef.h
@@ -149,11 +149,11 @@ namespace llvm {
 
     /// empty - Check if the string is empty.
     LLVM_NODISCARD
-    bool empty() const { return Length == 0; }
+    constexpr bool empty() const { return Length == 0; }
 
     /// size - Get the string size.
     LLVM_NODISCARD
-    size_t size() const { return Length; }
+    constexpr size_t size() const { return Length; }
 
     /// front - Get the first character in the string.
     LLVM_NODISCARD
diff --git a/llvm/unittests/ADT/StringRefTest.cpp b/llvm/unittests/ADT/StringRefTest.cpp
index 87285e0e61ce..41c35804f122 100644
--- a/llvm/unittests/ADT/StringRefTest.cpp
+++ b/llvm/unittests/ADT/StringRefTest.cpp
@@ -1092,10 +1092,14 @@ TEST(StringRefTest, DropWhileUntil) {
 TEST(StringRefTest, StringLiteral) {
   constexpr StringRef StringRefs[] = {"Foo", "Bar"};
   EXPECT_EQ(StringRef("Foo"), StringRefs[0]);
+  EXPECT_EQ(3u, (std::integral_constant<size_t, StringRefs[0].size()>::value));
+  EXPECT_EQ(false, (std::integral_constant<bool, StringRefs[0].empty()>::value));
   EXPECT_EQ(StringRef("Bar"), StringRefs[1]);
 
   constexpr StringLiteral Strings[] = {"Foo", "Bar"};
   EXPECT_EQ(StringRef("Foo"), Strings[0]);
+  EXPECT_EQ(3u, (std::integral_constant<size_t, Strings[0].size()>::value));
+  EXPECT_EQ(false, (std::integral_constant<bool, Strings[0].empty()>::value));
   EXPECT_EQ(StringRef("Bar"), Strings[1]);
 }