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Change the definition of MALLOC_ALIGN_MASK so it should always be correct on all platforms. #58495

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Merged
merged 1 commit into from
Apr 28, 2022
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Change the definition of MALLOC_ALIGN_MASK so it should always be correct on all platforms. #58495

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37 changes: 18 additions & 19 deletions stdlib/public/runtime/Heap.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -29,28 +29,27 @@
using namespace swift;

#if defined(__APPLE__)
// Apple malloc is always 16-byte aligned.
# define MALLOC_ALIGN_MASK 15

#elif defined(__linux__)
// Linux malloc is 16-byte aligned on 64-bit, and 8-byte aligned on 32-bit.
# if defined(__LP64)
# define MALLOC_ALIGN_MASK 15
# else
# define MALLOC_ALIGN_MASK 7
# endif

#elif defined(_WIN64)
// Windows malloc is 16-byte aligned on 64-bit and 8-byte aligned on 32-bit.
# define MALLOC_ALIGN_MASK 15
#elif defined(_WIN32)
# define MALLOC_ALIGN_MASK 7
/// On Apple platforms, \c malloc() is always 16-byte aligned.
static constexpr size_t MALLOC_ALIGN_MASK = 15;

#elif defined(__linux__) || defined(_WIN32)
/// On Linux and Windows, \c malloc() returns 16-byte aligned pointers on 64-bit
/// and 8-byte aligned pointers on 32-bit.
#if defined(__LP64) || defined(_WIN64)
static constexpr size_t MALLOC_ALIGN_MASK = 15;
#else
// Unknown alignment, but the standard requires alignment suitable for the largest
// standard types.
# define MALLOC_ALIGN_MASK std::max(alignof(void *), alignof(double))
static constexpr size_t MALLOC_ALIGN_MASK = 7;
#endif

#else
/// This platform's \c malloc() constraints are unknown, so fall back to a value
/// derived from \c std::max_align_t that will be sufficient, but is not
/// necessarily optimal.
///
/// The C and C++ standards defined \c max_align_t as a type whose alignment is
/// at least that of every scalar type. It is the lower bound for the alignment
/// of any pointer returned from \c malloc().
static constexpr size_t MALLOC_ALIGN_MASK = alignof(std::max_align_t) - 1;
#endif

// This assert ensures that manually allocated memory always uses the
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