[llvm] Use std::bool_constant (NFC) (#158520)

This patch replaces, std::integral_constant<bool, ...> with
std::bool_constant for brevity.  Note that std::bool_constant was
introduced as part of C++17.

There are cases where we could replace EXPECT_EQ(false, ...) with
EXPECT_FALSE(...), but I'm not doing that in this patch to avoid doing
multiple things in one patch.

Author: kazutakahirata

llvm/include/llvm/Support/YAMLTraits.h

@@ -668,17 +668,15 @@ inline QuotingType needsQuotes(StringRef S, bool ForcePreserveAsString = true) {
 
 template <typename T, typename Context>
 struct missingTraits
-    : public std::integral_constant<bool,
-                                    !has_ScalarEnumerationTraits<T>::value &&
-                                        !has_ScalarBitSetTraits<T>::value &&
-                                        !has_ScalarTraits<T>::value &&
-                                        !has_BlockScalarTraits<T>::value &&
-                                        !has_TaggedScalarTraits<T>::value &&
-                                        !has_MappingTraits<T, Context>::value &&
-                                        !has_SequenceTraits<T>::value &&
-                                        !has_CustomMappingTraits<T>::value &&
-                                        !has_DocumentListTraits<T>::value &&
-                                        !has_PolymorphicTraits<T>::value> {};
+    : public std::bool_constant<
+          !has_ScalarEnumerationTraits<T>::value &&
+          !has_ScalarBitSetTraits<T>::value && !has_ScalarTraits<T>::value &&
+          !has_BlockScalarTraits<T>::value &&
+          !has_TaggedScalarTraits<T>::value &&
+          !has_MappingTraits<T, Context>::value &&
+          !has_SequenceTraits<T>::value && !has_CustomMappingTraits<T>::value &&
+          !has_DocumentListTraits<T>::value &&
+          !has_PolymorphicTraits<T>::value> {};
 
 template <typename T, typename Context>
 struct validatedMappingTraits

llvm/lib/IR/Metadata.cpp

@@ -1007,8 +1007,7 @@ MDNode *MDNode::uniquify() {
 #define HANDLE_MDNODE_LEAF_UNIQUABLE(CLASS)                                    \
   case CLASS##Kind: {                                                          \
     CLASS *SubclassThis = cast<CLASS>(this);                                   \
-    std::integral_constant<bool, HasCachedHash<CLASS>::value>                  \
-        ShouldRecalculateHash;                                                 \
+    std::bool_constant<HasCachedHash<CLASS>::value> ShouldRecalculateHash;     \
     dispatchRecalculateHash(SubclassThis, ShouldRecalculateHash);              \
     return uniquifyImpl(SubclassThis, getContext().pImpl->CLASS##s);           \
   }
@@ -1065,7 +1064,7 @@ void MDNode::storeDistinctInContext() {
     llvm_unreachable("Invalid subclass of MDNode");
 #define HANDLE_MDNODE_LEAF(CLASS)                                              \
   case CLASS##Kind: {                                                          \
-    std::integral_constant<bool, HasCachedHash<CLASS>::value> ShouldResetHash; \
+    std::bool_constant<HasCachedHash<CLASS>::value> ShouldResetHash;           \
     dispatchResetHash(cast<CLASS>(this), ShouldResetHash);                     \
     break;                                                                     \
   }

llvm/unittests/ADT/StringRefTest.cpp

@@ -1124,14 +1124,13 @@ 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(false, (std::bool_constant<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(false, (std::bool_constant<Strings[0].empty()>::value));
   EXPECT_EQ(StringRef("Bar"), Strings[1]);
 }