http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58806
--- Comment #3 from Marc Glisse <glisse at gcc dot gnu.org> --- (In reply to Richard Biener from comment #2) > You cannot find the PR because it's already implemented via the "fn spec" > attribute (conveniently not user-accessible because bike-shedding about > whether separate attributes are required). The documentation resides > in gimple.c:gimple_call_arg_flags, Thanks, I knew of the EAF_* flags (none look that promising for my particular use), but not of this "fn spec" attribute. > and I _think_ it doesn't quite provide > what you want as it was designed to help the context and flow-insensitive > points-to analysis which doesn't benefit from "this call does not clobber > or read from escaped memory". But what it provides is "the argument to > this function does not escape" which is important. I locally changed the name to fn_spec so I could try it. Nothing helps for comment #0. The combination EAF_NOCLOBBER | EAF_NOESCAPE (aka 'r') is enough to optimize comment #1. However, EAF_NOCLOBBER is exactly the opposite of what I want since the whole point of g is to write to its argument, and I don't see why EAF_NOESCAPE should be necessary since there is no other call afterwards. So I guess more flags (ECF_* since they wouldn't apply to a specific argument) would be good. I tried the attributes nothrow,nonnull,leaf on comment #0 because that's what gcc puts on memcpy and gcc knows that memcpy(data,...) doesn't change *p, but that didn't work, I should look at where exactly the difference between memcpy and init plays a role.