[PATCH] D86993: Document Clang's expectations of the C standard library.

[John McCall via Phabricator via cfe-commits]

rjmccall added a comment.

In D86993#4474267 <https://reviews.llvm.org/D86993#4474267>, @RalfJung wrote:

> The first point is important for LLVM's own memcpy/memmove intrinsics, which are documented as NOPs on size 0 (and e.g. Rust relies on that).

Right, I understand that these assumptions come directly from the stronger semantics offered by the LLVM intrinsics.  The C committee is not going to find that compelling, though — we don't get to default-win arguments just because we've defined an IR with stronger semantics than necessary.  They are going to want to see arguments about why it's valuable for the C library to have these stronger semantics, which for us means talking about code patterns in user programs that take advantage of those stronger semantics and the benefits they see from that.


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