[libcxx-commits] [PATCH] D152208: [libc++] Introduce __make_uninitialized_buffer and use it instead of get_temporary_buffer

[Mingming Liu via Phabricator via libcxx-commits]

mingmingl added inline comments.


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Comment at: libcxx/include/__memory/uninitialized_buffer.h:71-73
+#else
+  _Tp* __ptr = static_cast<_Tp*>(::operator new(sizeof(_Tp) * __count, align_val_t(_LIBCPP_ALIGNOF(_Tp)), nothrow));
+#endif
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Hi, a regression is observed in a benchmark that uses `std::stable_sort` intensively. 

Comparing baseline and the regressed case, the baseline (using `get_temporary_buffer`) uses unaligned alloc ( `void* operator new[](size_t size) `) when objects are not over aligned, and the regressed uses aligned alloc for all objects. This may increase the memory usage as well.

Given `std::stable_sort` is pretty important, I wonder if this regression warrants a fix to have consistent usage of (aligned or unaligned) new operator?


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D152208/new/

https://reviews.llvm.org/D152208