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Add an LLVM_PTR_SIZE macro to make LLVM_ALIGNAS more useful

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MSVC 2013 requires the argument to __declspec(align()) to be an integer
constant expression that doesn't involve any identifiers like sizeof.

For GCC and Clang, LLVM_PTR_SIZE is equivalent to __SIZEOF_POINTER__,
which dates back to GCC 4.6 and Clang 2010. If that's not available, we
get sizeof(void*), which works with alignas() and
__attribute__((aligned())).

For MSVC, LLVM_PTR_SIZE is 4 or 8 depending on _WIN64.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@233929 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Reid Kleckner 2015-04-02 17:43:35 +00:00
parent 5e66a2ab59
commit 2647380f59
1 changed files with 18 additions and 1 deletions
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19
include/llvm/Support/Compiler.h
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@ -283,7 +283,8 @@
/// \macro LLVM_ALIGNAS
/// \brief Used to specify a minimum alignment for a structure or variable. The
/// alignment must be a constant integer.
/// alignment must be a constant integer. Use LLVM_PTR_SIZE to compute
/// alignments in terms of the size of a pointer.
///
/// Note that __declspec(align) has special quirks, it's not legal to pass a
/// structure with __declspec(align) as a formal parameter.
@ -295,6 +296,22 @@
# define LLVM_ALIGNAS(x) alignas(x)
#endif
/// \macro LLVM_PTR_SIZE
/// \brief A constant integer equivalent to the value of sizeof(void*).
/// Generally used in combination with LLVM_ALIGNAS or when doing computation in
/// the preprocessor.
#ifdef __SIZEOF_POINTER__
# define LLVM_PTR_SIZE __SIZEOF_POINTER__
#elif defined(_WIN64)
# define LLVM_PTR_SIZE 8
#elif defined(_WIN32)
# define LLVM_PTR_SIZE 4
#elif defined(_MSC_VER)
# error "could not determine LLVM_PTR_SIZE as a constant int for MSVC"
#else
# define LLVM_PTR_SIZE sizeof(void *)
#endif
/// \macro LLVM_FUNCTION_NAME
/// \brief Expands to __func__ on compilers which support it. Otherwise,
/// expands to a compiler-dependent replacement.