1 files changed, 90 insertions, 0 deletions
diff --git a/include/llvm/Support/AlignOf.h b/include/llvm/Support/AlignOf.h
index cebfa7982d..b63e75fd66 100644
--- a/include/llvm/Support/AlignOf.h
+++ b/include/llvm/Support/AlignOf.h
@@ -15,6 +15,9 @@
 #ifndef LLVM_SUPPORT_ALIGNOF_H
 #define LLVM_SUPPORT_ALIGNOF_H
 
+#include "llvm/Support/Compiler.h"
+#include <cstddef>
+
 namespace llvm {
 
 template <typename T>
@@ -56,5 +59,92 @@ struct AlignOf {
 template <typename T>
 static inline unsigned alignOf() { return AlignOf<T>::Alignment; }
 
+
+/// \brief Helper for building an aligned character array type.
+///
+/// This template is used to explicitly build up a collection of aligned
+/// character types. We have to build these up using a macro and explicit
+/// specialization to cope with old versions of MSVC and GCC where only an
+/// integer literal can be used to specify an alignment constraint. Once built
+/// up here, we can then begin to indirect between these using normal C++
+/// template parameters.
+template <size_t Alignment> struct AlignedCharArrayImpl {};
+template <> struct AlignedCharArrayImpl<0> {
+  typedef char type;
+};
+#if __cplusplus == 201103L || __has_feature(cxx_alignas)
+#define LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(x) \
+  template <> struct AlignedCharArrayImpl<x> { \
+    typedef char alignas(x) type; \
+  }
+#elif defined(__clang__) || defined(__GNUC__)
+#define LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(x) \
+  template <> struct AlignedCharArrayImpl<x> { \
+    typedef char type __attribute__((aligned(x))); \
+  }
+#elif defined(_MSC_VER)
+#define LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(x) \
+  template <> struct AlignedCharArrayImpl<x> { \
+    typedef __declspec(align(x)) char type; \
+  }
+#else
+# error No supported align as directive.
+#endif
+
+LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(1);
+LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(2);
+LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(4);
+LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(8);
+LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(16);
+LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(32);
+LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(64);
+LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(128);
+LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(512);
+LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(1024);
+LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(2048);
+LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(4096);
+LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(8192);
+// Any larger and MSVC complains.
+#undef LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT
+
+/// \brief This class template exposes a typedef for type containing a suitable
+/// aligned character array to hold elements of any of up to four types.
+///
+/// These types may be arrays, structs, or any other types. The goal is to
+/// produce a union type containing a character array which, when used, forms
+/// storage suitable to placement new any of these types over. Support for more
+/// than four types can be added at the cost of more boiler plate.
+template <typename T1,
+          typename T2 = char, typename T3 = char, typename T4 = char>
+class AlignedCharArray {
+  class AlignerImpl {
+    T1 t1; T2 t2; T3 t3; T4 t4;
+
+    AlignerImpl(); // Never defined or instantiated.
+  };
+  union SizerImpl {
+    char arr1[sizeof(T1)], arr2[sizeof(T2)], arr3[sizeof(T3)], arr4[sizeof(T4)];
+  };
+
+public:
+  // Sadly, Clang and GCC both fail to align a character array properly even
+  // with an explicit alignment attribute. To work around this, we union
+  // the character array that will actually be used with a struct that contains
+  // a single aligned character member. Tests seem to indicate that both Clang
+  // and GCC will properly register the alignment of a struct containing an
+  // aligned member, and this alignment should carry over to the character
+  // array in the union.
+  union union_type {
+    // This is the only member of the union which should be used by clients:
+    char buffer[sizeof(SizerImpl)];
+
+    // This member of the union only exists to force the alignment.
+    struct {
+      typename llvm::AlignedCharArrayImpl<AlignOf<AlignerImpl>::Alignment>::type
+        nonce_inner_member;
+    } nonce_member;
+  };
+};
+
 } // end namespace llvm
 #endif