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48b6a79b2d
Review by Chandler Carruth. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@163944 91177308-0d34-0410-b5e6-96231b3b80d8
171 lines
6.4 KiB
C++
171 lines
6.4 KiB
C++
//===--- AlignOf.h - Portable calculation of type alignment -----*- C++ -*-===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file defines the AlignOf function that computes alignments for
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// arbitrary types.
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_SUPPORT_ALIGNOF_H
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#define LLVM_SUPPORT_ALIGNOF_H
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#include "llvm/Support/Compiler.h"
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#include <cstddef>
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namespace llvm {
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template <typename T>
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struct AlignmentCalcImpl {
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char x;
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T t;
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private:
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AlignmentCalcImpl() {} // Never instantiate.
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};
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/// AlignOf - A templated class that contains an enum value representing
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/// the alignment of the template argument. For example,
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/// AlignOf<int>::Alignment represents the alignment of type "int". The
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/// alignment calculated is the minimum alignment, and not necessarily
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/// the "desired" alignment returned by GCC's __alignof__ (for example). Note
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/// that because the alignment is an enum value, it can be used as a
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/// compile-time constant (e.g., for template instantiation).
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template <typename T>
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struct AlignOf {
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enum { Alignment =
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static_cast<unsigned int>(sizeof(AlignmentCalcImpl<T>) - sizeof(T)) };
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enum { Alignment_GreaterEqual_2Bytes = Alignment >= 2 ? 1 : 0 };
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enum { Alignment_GreaterEqual_4Bytes = Alignment >= 4 ? 1 : 0 };
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enum { Alignment_GreaterEqual_8Bytes = Alignment >= 8 ? 1 : 0 };
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enum { Alignment_GreaterEqual_16Bytes = Alignment >= 16 ? 1 : 0 };
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enum { Alignment_LessEqual_2Bytes = Alignment <= 2 ? 1 : 0 };
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enum { Alignment_LessEqual_4Bytes = Alignment <= 4 ? 1 : 0 };
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enum { Alignment_LessEqual_8Bytes = Alignment <= 8 ? 1 : 0 };
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enum { Alignment_LessEqual_16Bytes = Alignment <= 16 ? 1 : 0 };
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};
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/// alignOf - A templated function that returns the minimum alignment of
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/// of a type. This provides no extra functionality beyond the AlignOf
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/// class besides some cosmetic cleanliness. Example usage:
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/// alignOf<int>() returns the alignment of an int.
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template <typename T>
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inline unsigned alignOf() { return AlignOf<T>::Alignment; }
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/// \brief Helper for building an aligned character array type.
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///
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/// This template is used to explicitly build up a collection of aligned
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/// character types. We have to build these up using a macro and explicit
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/// specialization to cope with old versions of MSVC and GCC where only an
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/// integer literal can be used to specify an alignment constraint. Once built
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/// up here, we can then begin to indirect between these using normal C++
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/// template parameters.
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template <size_t Alignment> struct AlignedCharArrayImpl;
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// MSVC requires special handling here.
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#ifndef _MSC_VER
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#if __has_feature(cxx_alignas)
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#define LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(x) \
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template <> struct AlignedCharArrayImpl<x> { \
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char alignas(x) aligned; \
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}
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#elif defined(__GNUC__)
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#define LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(x) \
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template <> struct AlignedCharArrayImpl<x> { \
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char aligned __attribute__((aligned(x))); \
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}
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#else
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# error No supported align as directive.
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#endif
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LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(1);
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LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(2);
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LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(4);
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LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(8);
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LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(16);
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LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(32);
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LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(64);
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LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(128);
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LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(512);
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LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(1024);
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LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(2048);
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LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(4096);
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LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(8192);
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#undef LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT
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#else // _MSC_VER
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// We provide special variations of this template for the most common
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// alignments because __declspec(align(...)) doesn't actually work when it is
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// a member of a by-value function argument in MSVC, even if the alignment
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// request is something reasonably like 8-byte or 16-byte.
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template <> struct AlignedCharArrayImpl<1> { char aligned; };
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template <> struct AlignedCharArrayImpl<2> { short aligned; };
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template <> struct AlignedCharArrayImpl<4> { int aligned; };
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template <> struct AlignedCharArrayImpl<8> { double aligned; };
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#define LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(x) \
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template <> struct AlignedCharArrayImpl<x> { \
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__declspec(align(x)) char aligned; \
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}
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LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(16);
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LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(32);
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LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(64);
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LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(128);
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LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(512);
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LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(1024);
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LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(2048);
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LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(4096);
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LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(8192);
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// Any larger and MSVC complains.
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#undef LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT
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#endif // _MSC_VER
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/// \brief This union template exposes a suitably aligned and sized character
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/// array member which can hold elements of any of up to four types.
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///
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/// These types may be arrays, structs, or any other types. The goal is to
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/// produce a union type containing a character array which, when used, forms
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/// storage suitable to placement new any of these types over. Support for more
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/// than four types can be added at the cost of more boiler plate.
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template <typename T1,
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typename T2 = char, typename T3 = char, typename T4 = char>
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union AlignedCharArrayUnion {
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private:
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class AlignerImpl {
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T1 t1; T2 t2; T3 t3; T4 t4;
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AlignerImpl(); // Never defined or instantiated.
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};
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union SizerImpl {
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char arr1[sizeof(T1)], arr2[sizeof(T2)], arr3[sizeof(T3)], arr4[sizeof(T4)];
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};
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public:
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/// \brief The character array buffer for use by clients.
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///
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/// No other member of this union should be referenced. The exist purely to
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/// constrain the layout of this character array.
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char buffer[sizeof(SizerImpl)];
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private:
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// Tests seem to indicate that both Clang and GCC will properly register the
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// alignment of a struct containing an aligned member, and this alignment
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// should carry over to the character array in the union.
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llvm::AlignedCharArrayImpl<AlignOf<AlignerImpl>::Alignment> nonce_member;
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};
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} // end namespace llvm
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#endif
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