PR libstdc++/90046 fix build failure on epiphany-elf
The epiphany-elf target aligns structs to 8 bytes, which causes the static_assert(alignof(_Chunk) == 1) to fail. Instead of requiring _Chunks to be positionable at any alignment, ensure new buffers are aligned to alignof(_Chunk). Because the buffer size is a power of two, we know that both the buffer size and sizeof(_Chunk) are multiples of alignof(_Chunk). So is p is aligned to alignof(_Chunk) then so is (p + size - sizeof(_Chunk)). So just ensure the new buffer is aligned to at least alignof(_Chunk), which should already be true because the caller requests at least alignof(max_align_t). PR libstdc++/90046 * src/c++17/memory_resource.cc (monotonic_buffer_resource::_Chunk::allocate): Increase alignment if needed to allow placing a _Chunk at the end of the buffer. (monotonic_buffer_resource::_M_new_buffer): Remove static_assert. From-SVN: r270291
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@ -1,3 +1,11 @@
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2019-04-11 Jonathan Wakely <jwakely@redhat.com>
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PR libstdc++/90046
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* src/c++17/memory_resource.cc
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(monotonic_buffer_resource::_Chunk::allocate): Increase alignment if
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needed to allow placing a _Chunk at the end of the buffer.
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(monotonic_buffer_resource::_M_new_buffer): Remove static_assert.
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2019-04-10 Jonathan Wakely <jwakely@redhat.com>
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* doc/xml/faq.xml: Add information about emergency EH pool.
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@ -182,7 +182,21 @@ namespace pmr
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_Chunk*& __head)
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{
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__size = std::__ceil2(__size + sizeof(_Chunk));
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if constexpr (alignof(_Chunk) > 1)
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{
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// PR libstdc++/90046
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// For targets like epiphany-elf where alignof(_Chunk) != 1
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// ensure that the last sizeof(_Chunk) bytes in the buffer
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// are suitably-aligned for a _Chunk.
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// This should be unnecessary, because the caller already
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// passes in max(__align, alignof(max_align_t)).
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if (__align < alignof(_Chunk))
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__align = alignof(_Chunk);
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}
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void* __p = __r->allocate(__size, __align);
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// Add a chunk defined by (__p, __size, __align) to linked list __head.
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void* const __back = (char*)__p + __size - sizeof(_Chunk);
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__head = ::new(__back) _Chunk(__size, __align, __head);
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@ -231,9 +245,6 @@ namespace pmr
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void
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monotonic_buffer_resource::_M_new_buffer(size_t bytes, size_t alignment)
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{
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// Need to check this somewhere, so put it here:
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static_assert(alignof(monotonic_buffer_resource::_Chunk) == 1);
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const size_t n = std::max(bytes, _M_next_bufsiz);
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const size_t m = std::max(alignment, alignof(std::max_align_t));
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auto [p, size] = _Chunk::allocate(_M_upstream, n, m, _M_head);
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