rsmith created this revision. rsmith added reviewers: fhahn, rjmccall. Herald added a project: clang. Herald added a subscriber: cfe-commits. rsmith requested review of this revision.
As suggested in https://reviews.llvm.org/D86815 Repository: rG LLVM Github Monorepo https://reviews.llvm.org/D86993 Files: clang/docs/Toolchain.rst Index: clang/docs/Toolchain.rst =================================================================== --- clang/docs/Toolchain.rst +++ clang/docs/Toolchain.rst @@ -276,6 +276,19 @@ `C standard library <https://en.cppreference.com/w/c>`_ implementations. +Clang and LLVM make some assumptions about the behavior of the C standard +library beyond those required by the C standard: + +* ``memcpy(p, q, 0)`` and ``memmove(p, q, 0)`` are expected to have no effect, + even if ``p`` or ``q`` is a null or otherwise-invalid (but correctly-aligned) + pointer. +* ``memcpy(p, p, n)`` is expected to leave the contents of the memory pointed + to by ``p`` unchanged, but may perform (redundant) loads and stores through + the ``n`` bytes pointed to by ``p``. + +C standard library implementations that do not guarantee these properties +incompatible with Clang and LLVM (and with several other major compilers). + C++ ABI library ---------------
Index: clang/docs/Toolchain.rst =================================================================== --- clang/docs/Toolchain.rst +++ clang/docs/Toolchain.rst @@ -276,6 +276,19 @@ `C standard library <https://en.cppreference.com/w/c>`_ implementations. +Clang and LLVM make some assumptions about the behavior of the C standard +library beyond those required by the C standard: + +* ``memcpy(p, q, 0)`` and ``memmove(p, q, 0)`` are expected to have no effect, + even if ``p`` or ``q`` is a null or otherwise-invalid (but correctly-aligned) + pointer. +* ``memcpy(p, p, n)`` is expected to leave the contents of the memory pointed + to by ``p`` unchanged, but may perform (redundant) loads and stores through + the ``n`` bytes pointed to by ``p``. + +C standard library implementations that do not guarantee these properties +incompatible with Clang and LLVM (and with several other major compilers). + C++ ABI library ---------------
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