On Thu, Dec 01, 2016 at 11:43:19PM -0700, Jeff Law wrote:
>
> Martin's alloca work flagged this code as problematical. Essentially if we
> had a statement with no operands and the statement was not in the hash
> table, then we could end up performing alloca (0), which is inadvisable.
I still don't understand why it is inadvisable. alloca(0) is not undefined
behavior. It can return NULL, or non-unique pointer, or a unique pointer,
and/or cause freeing of already left alloca blocks (like any other alloca
call).
None of that is a problem here. If num is 0, then copy is just set and
never used.
I expect most if not all gcc uses of alloca where the count can be 0 are
like that.
Jakub
