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[AlignOf] Add AlignedCharArray and refactor AlignedCharArrayUnion.

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This adds AlignedCharArray<Alignment, Size>. A templated struct that contains
a member named buffer of type char[Size] that is aligned to Alignment.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@171319 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Michael J. Spencer 2012-12-31 19:54:45 +00:00
parent 44365353a4
commit 3c6f89aa2e
2 changed files with 107 additions and 74 deletions
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168
include/llvm/Support/AlignOf.h
View File

@ -19,7 +19,6 @@
#include <cstddef>
namespace llvm {
template <typename T>
struct AlignmentCalcImpl {
char x;
@ -49,7 +48,6 @@ struct AlignOf {
enum { Alignment_LessEqual_4Bytes = Alignment <= 4 ? 1 : 0 };
enum { Alignment_LessEqual_8Bytes = Alignment <= 8 ? 1 : 0 };
enum { Alignment_LessEqual_16Bytes = Alignment <= 16 ? 1 : 0 };
};
/// alignOf - A templated function that returns the minimum alignment of
@ -59,112 +57,138 @@ struct AlignOf {
template <typename T>
inline unsigned alignOf() { return AlignOf<T>::Alignment; }
/// \struct AlignedCharArray
/// \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
/// character array 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;
// MSVC requires special handling here.
#ifndef _MSC_VER
#if __has_feature(cxx_alignas)
#define LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(x) \
template <> struct AlignedCharArrayImpl<x> { \
char alignas(x) aligned; \
}
template<std::size_t Alignment, std::size_t Size>
struct AlignedCharArray {
alignas(Alignment) char buffer[Size];
};
#elif defined(__GNUC__) || defined(__IBM_ATTRIBUTES)
/// \brief Create a type with an aligned char buffer.
template<std::size_t Alignment, std::size_t Size>
struct AlignedCharArray;
#define LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(x) \
template <> struct AlignedCharArrayImpl<x> { \
char aligned __attribute__((aligned(x))); \
}
template<std::size_t Size> \
struct AlignedCharArray<x, Size> { \
__attribute__((aligned(x))) char buffer[Size]; \
};
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)
#undef LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT
#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);
#undef LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT
#else // _MSC_VER
/// \brief Create a type with an aligned char buffer.
template<std::size_t Alignment, std::size_t Size>
struct AlignedCharArray;
// We provide special variations of this template for the most common
// alignments because __declspec(align(...)) doesn't actually work when it is
// a member of a by-value function argument in MSVC, even if the alignment
// request is something reasonably like 8-byte or 16-byte.
template <> struct AlignedCharArrayImpl<1> { char aligned; };
template <> struct AlignedCharArrayImpl<2> { short aligned; };
template <> struct AlignedCharArrayImpl<4> { int aligned; };
template <> struct AlignedCharArrayImpl<8> { double aligned; };
template<std::size_t Size>
struct AlignedCharArray<1, Size> {
union {
char aligned;
__declspec(align(1)) char buffer[Size];
};
};
template<std::size_t Size>
struct AlignedCharArray<2, Size> {
union {
short aligned;
__declspec(align(2)) char buffer[Size];
};
};
template<std::size_t Size>
struct AlignedCharArray<4, Size> {
union {
int aligned;
__declspec(align(4)) char buffer[Size];
};
};
template<std::size_t Size>
struct AlignedCharArray<8, Size> {
union {
double aligned;
__declspec(align(8)) char buffer[Size];
};
};
#define LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(x) \
template <> struct AlignedCharArrayImpl<x> { \
__declspec(align(x)) char aligned; \
}
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.
template<std::size_t Size> \
struct AlignedCharArray<x, Size> { \
__declspec(align(x)) char buffer[Size]; \
};
LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(16)
LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(32)
LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(64)
LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(128)
#undef LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT
#endif // _MSC_VER
namespace detail {
template <typename T1,
typename T2 = char, typename T3 = char, typename T4 = char>
class AlignerImpl {
T1 t1; T2 t2; T3 t3; T4 t4;
AlignerImpl(); // Never defined or instantiated.
};
template <typename T1,
typename T2 = char, typename T3 = char, typename T4 = char>
union SizerImpl {
char arr1[sizeof(T1)], arr2[sizeof(T2)], arr3[sizeof(T3)], arr4[sizeof(T4)];
};
} // 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 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.
/// 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 four types can
/// be added at the cost of more boiler plate.
template <typename T1,
typename T2 = char, typename T3 = char, typename T4 = char>
union AlignedCharArrayUnion {
private:
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:
/// \brief The character array buffer for use by clients.
///
/// No other member of this union should be referenced. The exist purely to
/// constrain the layout of this character array.
char buffer[sizeof(SizerImpl)];
private:
// 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.
llvm::AlignedCharArrayImpl<AlignOf<AlignerImpl>::Alignment> nonce_member;
struct AlignedCharArrayUnion :
llvm::AlignedCharArray<AlignOf<detail::AlignerImpl<T1, T2, T3, T4> >
::Alignment,
sizeof(detail::SizerImpl<T1, T2, T3, T4>)> {
};
} // end namespace llvm
#endif

13
unittests/Support/AlignOfTest.cpp
View File

@ -14,7 +14,6 @@
using namespace llvm;
namespace {
// Disable warnings about questionable type definitions.
// We're testing that even questionable types work with the alignment utilities.
#ifdef _MSC_VER
@ -321,6 +320,16 @@ TEST(AlignOfTest, BasicAlignedArray) {
#ifndef _MSC_VER
EXPECT_EQ(sizeof(V8), sizeof(AlignedCharArrayUnion<V8>));
#endif
}
EXPECT_EQ(1u, (alignOf<AlignedCharArray<1, 1> >()));
EXPECT_EQ(2u, (alignOf<AlignedCharArray<2, 1> >()));
EXPECT_EQ(4u, (alignOf<AlignedCharArray<4, 1> >()));
EXPECT_EQ(8u, (alignOf<AlignedCharArray<8, 1> >()));
EXPECT_EQ(16u, (alignOf<AlignedCharArray<16, 1> >()));
EXPECT_EQ(1u, sizeof(AlignedCharArray<1, 1>));
EXPECT_EQ(7u, sizeof(AlignedCharArray<1, 7>));
EXPECT_EQ(2u, sizeof(AlignedCharArray<2, 2>));
EXPECT_EQ(16u, sizeof(AlignedCharArray<2, 16>));
}
}