[all-commits] [llvm/llvm-project] 5de1bc: [🍒] Unconditionally lower std::string's alignment ...

[Eric via All-commits]

  Branch: refs/heads/release/18.x
  Home:   https://github.com/llvm/llvm-project
  Commit: 5de1bcb70db21cfd2c28ef70c67fd1833ce1e6da
      https://github.com/llvm/llvm-project/commit/5de1bcb70db21cfd2c28ef70c67fd1833ce1e6da
  Author: Eric <eric at efcs.ca>
  Date:   2024-02-06 (Tue, 06 Feb 2024)

  Changed paths:
    M libcxx/docs/ReleaseNotes/18.rst
    M libcxx/include/__config
    M libcxx/include/string
    M libcxx/test/libcxx/strings/basic.string/string.capacity/allocation_size.pass.cpp
    M libcxx/test/libcxx/strings/basic.string/string.capacity/max_size.pass.cpp
    M libcxx/test/std/strings/basic.string/string.capacity/max_size.pass.cpp

  Log Message:
  -----------
  [🍒] Unconditionally lower std::string's alignment requirement from 16 to 8 (#68925) (#79480)

This change saves memory by providing the allocator more freedom to
allocate the most
efficient size class by dropping the alignment requirements for
std::string's
pointer from 16 to 8. This changes the output of std::string::max_size,
which makes it ABI breaking.

That said, the discussion concluded that we don't care about this ABI
break. and would like this change enabled universally.

The ABI break isn't one of layout or "class size", but rather the value
of "max_size()" changes, which in turn changes whether `std::bad_alloc`
or `std::length_error` is thrown for large allocations.

This change is the child of PR #68807, which enabled the change behind
an ABI flag.