On 6/12/19 10:40 AM, Jakub Jelinek wrote: > On Wed, Jun 12, 2019 at 10:13:57AM -0600, Martin Sebor wrote: >> But GCC doesn't support such an implementation, does it? > > Why would that be relevant? The warning would cause people to make portable > code less portable (by removing the alloca (0) calls that were added there > for portability reasons), or add hacks to work around the warning (whether > #pragma GCC diagnostic or something else). That is something we do not > want people to do. I'd like to move C-alloca support to the ash heap of history. But I'm not sure we can realistically do that. Given that reality I think we need to honor the intent of alloca(0).
I also understand Martin's point that not warning on it could easily miss programming errors. I wonder if we could set TREE_NOWARNING on the CALL_EXPR early in the front-end of the argument is a constant 0 (before simplification, folding, etc). That way we'd be able to support alloca(0), but also capture cases where 0 flows into alloca via other mechansisms (which are likely programming errors). Jeff
