[llvm-dev] Which assumptions do llvm.memcpy/memmove/memset.* make when the count is 0?

[John Regehr via llvm-dev]

> So, the pointer arguments of memcpy *shall* (a violation of a shall 
> clause is UB, per §4/2) have valid values, even though the function will 
> copy zero characters.

This is true in C but the question was about LLVM intrinsics.

Since the LangRef does not mention any such restriction, I would assume 
that memcpy(0,0,0) is not UB in LLVM.  If it is UB then we must update 
the LangRef to be clear on this point (actually we should update the 
LangRef either way since this is a question that'll come up again).

John