From 48a2a277e60e9a1a2b563f37cc7e0c5b9680872f Mon Sep 17 00:00:00 2001
From: Sean Callanan <scallanan@apple.com>
Date: Mon, 9 Jan 2017 23:23:25 +0000
Subject: [PATCH] Lift the 10-type limit for AlignedCharArrayUnion

This patch uses C++11 parameter packs and constexpr functions
to allow AlignedCharArrayUnion to hold an arbitrary number of
types.

Differential Revision: https://reviews.llvm.org/D28429


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@291503 91177308-0d34-0410-b5e6-96231b3b80d8
---
 include/llvm/Support/AlignOf.h    | 51 +++++++++++++------------------
 unittests/Support/AlignOfTest.cpp | 18 +++++++++++
 2 files changed, 40 insertions(+), 29 deletions(-)

diff --git a/include/llvm/Support/AlignOf.h b/include/llvm/Support/AlignOf.h
index abd19afa22f..5fda901a100 100644
--- a/include/llvm/Support/AlignOf.h
+++ b/include/llvm/Support/AlignOf.h
@@ -102,45 +102,38 @@ LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(128)
 
 #endif // _MSC_VER
 
-namespace detail {
-template <typename T1,
-          typename T2 = char, typename T3 = char, typename T4 = char,
-          typename T5 = char, typename T6 = char, typename T7 = char,
-          typename T8 = char, typename T9 = char, typename T10 = char>
-class AlignerImpl {
-  T1 t1; T2 t2; T3 t3; T4 t4; T5 t5; T6 t6; T7 t7; T8 t8; T9 t9; T10 t10;
+// This code implements the equivalent of std::aligned_union from C++11.
+// That is supported by Visual Studio 2015 and GCC 5.1.
+// Once these are the baselines for LLVM, we can use std::aligned_union instead.
 
+namespace detail {
+template <typename... Ts> class AlignerImpl;
+
+template <typename T1, typename... Ts>
+class AlignerImpl<T1, Ts...> : AlignerImpl<Ts...> {
+  T1 t;
   AlignerImpl() = delete;
 };
 
-template <typename T1,
-          typename T2 = char, typename T3 = char, typename T4 = char,
-          typename T5 = char, typename T6 = char, typename T7 = char,
-          typename T8 = char, typename T9 = char, typename T10 = char>
-union SizerImpl {
-  char arr1[sizeof(T1)], arr2[sizeof(T2)], arr3[sizeof(T3)], arr4[sizeof(T4)],
-       arr5[sizeof(T5)], arr6[sizeof(T6)], arr7[sizeof(T7)], arr8[sizeof(T8)],
-       arr9[sizeof(T9)], arr10[sizeof(T10)];
-};
+template <> class AlignerImpl<> { AlignerImpl() = delete; };
+
+template <typename T1> constexpr size_t sizer() { return sizeof(T1); }
+
+template <typename T1, typename T2, typename... Ts> constexpr size_t sizer() {
+  return (sizeof(T1) > sizer<T2, Ts...>()) ? sizeof(T1) : sizer<T2, Ts...>();
+}
 } // end namespace detail
 
 /// \brief This union template exposes a suitably aligned and sized character
-/// array member which can hold elements of any of up to ten types.
+/// array member which can hold elements of any of a number of types.
 ///
 /// These types may be arrays, structs, or any other types. The goal is to
 /// expose a char array buffer member which can be used as suitable storage for
-/// a placement new of any of these types. Support for more than ten types can
-/// be added at the cost of more boilerplate.
-template <typename T1,
-          typename T2 = char, typename T3 = char, typename T4 = char,
-          typename T5 = char, typename T6 = char, typename T7 = char,
-          typename T8 = char, typename T9 = char, typename T10 = char>
-struct AlignedCharArrayUnion : llvm::AlignedCharArray<
-    alignof(llvm::detail::AlignerImpl<T1, T2, T3, T4, T5,
-                                      T6, T7, T8, T9, T10>),
-    sizeof(::llvm::detail::SizerImpl<T1, T2, T3, T4, T5,
-                                     T6, T7, T8, T9, T10>)> {
-};
+/// a placement new of any of these types.
+template <typename... Ts>
+struct AlignedCharArrayUnion
+    : llvm::AlignedCharArray<alignof(llvm::detail::AlignerImpl<Ts...>),
+                             detail::sizer<Ts...>()> {};
 } // end namespace llvm
 
 #endif // LLVM_SUPPORT_ALIGNOF_H
diff --git a/unittests/Support/AlignOfTest.cpp b/unittests/Support/AlignOfTest.cpp
index 388ca11b776..dfcdc1484b3 100644
--- a/unittests/Support/AlignOfTest.cpp
+++ b/unittests/Support/AlignOfTest.cpp
@@ -91,6 +91,24 @@ V8::~V8() {}
 
 template <typename M> struct T { M m; };
 
+typedef uint8_t t1;
+typedef uint16_t t2;
+typedef uint32_t t3;
+typedef uint64_t t4;
+typedef int8_t t5;
+typedef int16_t t6;
+typedef int32_t t7;
+typedef int64_t t8;
+typedef struct { uint8_t bytes[16]; } t9;
+typedef struct { uint16_t words[16]; } t10;
+typedef struct { uint32_t words[16]; } t11;
+typedef struct { uint64_t words[16]; } t12;
+
+typedef AlignedCharArrayUnion<t1, t2, t3, t4, t5, t6, t7, t8, t9, t10, t11, t12> U;
+
+static_assert(sizeof(U) == sizeof(uint64_t[16]), "Statically-computed size must be right");
+static_assert(alignof(U) == alignof(uint64_t), "Statically-computed alignment must be right");
+
 TEST(AlignOfTest, BasicAlignedArray) {
   EXPECT_LE(1u, alignof(AlignedCharArrayUnion<A1>));
   EXPECT_LE(2u, alignof(AlignedCharArrayUnion<A2>));