From 06a52ce65151c6de4046283f718589d42197e8fe Mon Sep 17 00:00:00 2001
From: Stella Stamenova <stilis@microsoft.com>
Date: Mon, 17 May 2021 20:26:59 -0700
Subject: [PATCH] Revert "[ADT] Add new type traits for type pack indexes"

This reverts commit a6d3987b8ef3b7616f0835b89515c4264f2a7a64.
---
 include/llvm/ADT/PointerUnion.h | 25 ++++++++++++---
 include/llvm/ADT/STLExtras.h    | 54 ---------------------------------
 unittests/ADT/STLExtrasTest.cpp | 36 ----------------------
 3 files changed, 20 insertions(+), 95 deletions(-)

diff --git a/include/llvm/ADT/PointerUnion.h b/include/llvm/ADT/PointerUnion.h
index 5c3ef01f1b0..c39691061b7 100644
--- a/include/llvm/ADT/PointerUnion.h
+++ b/include/llvm/ADT/PointerUnion.h
@@ -64,6 +64,21 @@ namespace pointer_union_detail {
     return std::min<int>({PointerLikeTypeTraits<Ts>::NumLowBitsAvailable...});
   }
 
+  /// Find the index of a type in a list of types. TypeIndex<T, Us...>::Index
+  /// is the index of T in Us, or sizeof...(Us) if T does not appear in the
+  /// list.
+  template <typename T, typename ...Us> struct TypeIndex;
+  template <typename T, typename ...Us> struct TypeIndex<T, T, Us...> {
+    static constexpr int Index = 0;
+  };
+  template <typename T, typename U, typename... Us>
+  struct TypeIndex<T, U, Us...> {
+    static constexpr int Index = 1 + TypeIndex<T, Us...>::Index;
+  };
+  template <typename T> struct TypeIndex<T> {
+    static constexpr int Index = 0;
+  };
+
   /// Find the first type in a list of types.
   template <typename T, typename...> struct GetFirstType {
     using type = T;
@@ -130,7 +145,6 @@ namespace pointer_union_detail {
 ///    P = (float*)0;
 ///    Y = P.get<float*>();   // ok.
 ///    X = P.get<int*>();     // runtime assertion failure.
-///    PointerUnion<int*, int*> Q; // compile time failure.
 template <typename... PTs>
 class PointerUnion
     : public pointer_union_detail::PointerUnionMembers<
@@ -139,14 +153,12 @@ class PointerUnion
               void *, pointer_union_detail::bitsRequired(sizeof...(PTs)), int,
               pointer_union_detail::PointerUnionUIntTraits<PTs...>>,
           0, PTs...> {
-  static_assert(TypesAreDistinct<PTs...>(),
-                "PointerUnion alternative types cannot be repeated");
   // The first type is special because we want to directly cast a pointer to a
   // default-initialized union to a pointer to the first type. But we don't
   // want PointerUnion to be a 'template <typename First, typename ...Rest>'
   // because it's much more convenient to have a name for the whole pack. So
   // split off the first type here.
-  using First = TypeAtIndex<0, PTs...>;
+  using First = typename pointer_union_detail::GetFirstType<PTs...>::type;
   using Base = typename PointerUnion::PointerUnionMembers;
 
 public:
@@ -163,7 +175,10 @@ public:
 
   /// Test if the Union currently holds the type matching T.
   template <typename T> bool is() const {
-    return this->Val.getInt() == FirstIndexOfType<T, PTs...>{};
+    constexpr int Index = pointer_union_detail::TypeIndex<T, PTs...>::Index;
+    static_assert(Index < sizeof...(PTs),
+                  "PointerUnion::is<T> given type not in the union");
+    return this->Val.getInt() == Index;
   }
 
   /// Returns the value of the specified pointer type.
diff --git a/include/llvm/ADT/STLExtras.h b/include/llvm/ADT/STLExtras.h
index fad62a5f7c9..182451c25e3 100644
--- a/include/llvm/ADT/STLExtras.h
+++ b/include/llvm/ADT/STLExtras.h
@@ -144,60 +144,6 @@ template <typename ReturnType, typename... Args>
 struct function_traits<ReturnType (&)(Args...), false>
     : public function_traits<ReturnType (*)(Args...)> {};
 
-namespace detail {
-template <typename T, typename... Ts>
-constexpr size_t getFirstIndexOfTypeImpl() {
-  constexpr bool Matches[] = {false, std::is_same<T, Ts>{}...};
-  // TODO: use llvm::find once it's constexpr (std::find is constexpr in C++20)
-  for (size_t I = 1; I <= sizeof...(Ts); ++I)
-    if (Matches[I])
-      return I - 1;
-  return sizeof...(Ts);
-}
-template <typename T, typename... Ts> constexpr size_t getFirstIndexOfType() {
-  constexpr size_t Index = getFirstIndexOfTypeImpl<T, Ts...>();
-  static_assert(Index != sizeof...(Ts),
-                "type T is not present in type pack Ts");
-  return Index;
-}
-template <typename... Ts> static constexpr bool areTypesDistinct() {
-  constexpr size_t IndexOf[] = {0, getFirstIndexOfType<Ts, Ts...>()...};
-  // TODO: use llvm::find once it's constexpr (std::find is constexpr in C++20)
-  for (size_t I = 1; I <= sizeof...(Ts); ++I)
-    if (I - 1 != IndexOf[I])
-      return false;
-  return true;
-}
-} // namespace detail
-
-/// Determine if all types in Ts are distinct.
-///
-/// Useful to statically assert when Ts is intended to describe a non-multi set
-/// of types.
-template <typename... Ts>
-using TypesAreDistinct =
-    std::integral_constant<bool, detail::areTypesDistinct<Ts...>()>;
-
-/// Find the first index where a type appears in a list of types.
-///
-/// FirstIndexOfType<T, Ts...>::value is the first index of T in Ts.
-///
-/// Typically only meaningful when it is otherwise statically known that the
-/// type pack has no duplicate types. This should be guaranteed explicitly with
-/// static_assert(TypesAreDistinct<Ts...>{}).
-///
-/// It is a compile-time error to instantiate when T is not present in Ts, i.e.
-/// if is_one_of<T, Ts...>::value is false.
-template <typename T, typename... Ts>
-using FirstIndexOfType =
-    std::integral_constant<size_t, detail::getFirstIndexOfType<T, Ts...>()>;
-
-/// Find the type at a given index in a list of types.
-///
-/// TypeAtIndex<I, Ts...> is the type at index I in Ts.
-template <size_t I, typename... Ts>
-using TypeAtIndex = std::tuple_element_t<I, std::tuple<Ts...>>;
-
 //===----------------------------------------------------------------------===//
 //     Extra additions to <functional>
 //===----------------------------------------------------------------------===//
diff --git a/unittests/ADT/STLExtrasTest.cpp b/unittests/ADT/STLExtrasTest.cpp
index a80c6ce7730..86265305541 100644
--- a/unittests/ADT/STLExtrasTest.cpp
+++ b/unittests/ADT/STLExtrasTest.cpp
@@ -711,40 +711,4 @@ TEST(STLExtras, MoveRange) {
   EXPECT_EQ(V4.size(), 4U);
   EXPECT_TRUE(llvm::all_of(V4, HasVal));
 }
-
-TEST(STLExtrasTest, TypesAreDistinct) {
-  EXPECT_TRUE((llvm::TypesAreDistinct<>::value));
-  EXPECT_TRUE((llvm::TypesAreDistinct<int>::value));
-  EXPECT_FALSE((llvm::TypesAreDistinct<int, int>::value));
-  EXPECT_TRUE((llvm::TypesAreDistinct<int, float>::value));
-  EXPECT_FALSE((llvm::TypesAreDistinct<int, float, int>::value));
-  EXPECT_TRUE((llvm::TypesAreDistinct<int, float, double>::value));
-  EXPECT_FALSE((llvm::TypesAreDistinct<int, float, double, float>::value));
-  EXPECT_TRUE((llvm::TypesAreDistinct<int, int *>::value));
-  EXPECT_TRUE((llvm::TypesAreDistinct<int, int &>::value));
-  EXPECT_TRUE((llvm::TypesAreDistinct<int, int &&>::value));
-  EXPECT_TRUE((llvm::TypesAreDistinct<int, const int>::value));
-}
-
-TEST(STLExtrasTest, FirstIndexOfType) {
-  EXPECT_EQ((llvm::FirstIndexOfType<int, int>::value), 0u);
-  EXPECT_EQ((llvm::FirstIndexOfType<int, int, int>::value), 0u);
-  EXPECT_EQ((llvm::FirstIndexOfType<int, float, int>::value), 1u);
-  EXPECT_EQ((llvm::FirstIndexOfType<int const *, float, int, int const *,
-                                    const int>::value),
-            2u);
-}
-
-TEST(STLExtrasTest, TypeAtIndex) {
-  EXPECT_TRUE((std::is_same<int, llvm::TypeAtIndex<0, int>>::value));
-  EXPECT_TRUE((std::is_same<int, llvm::TypeAtIndex<0, int, float>>::value));
-  EXPECT_TRUE((std::is_same<float, llvm::TypeAtIndex<1, int, float>>::value));
-  EXPECT_TRUE(
-      (std::is_same<float, llvm::TypeAtIndex<1, int, float, double>>::value));
-  EXPECT_TRUE(
-      (std::is_same<float, llvm::TypeAtIndex<1, int, float, double>>::value));
-  EXPECT_TRUE(
-      (std::is_same<double, llvm::TypeAtIndex<2, int, float, double>>::value));
-}
-
 } // namespace