[llvm-dev] Which assumptions do llvm.memcpy/memmove/memset.* make when the count is 0?
John Regehr via llvm-dev
llvm-dev at lists.llvm.org
Thu Jul 20 21:06:08 PDT 2017
Also note that whereas GCC exploits the tricky definition of memcpy(),
LLVM at present doesn't appear to:
In fact LLVM doesn't even assume the pointer is non-null in a case where
I'd argue that it should:
On 07/20/2017 10:00 PM, John Regehr via llvm-dev wrote:
>> 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).
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