On Thu, 2021-11-18 at 14:08 -0600, Segher Boessenkool wrote: > On Wed, Nov 17, 2021 at 10:43:58PM +0000, Joseph Myers wrote: > > On Wed, 17 Nov 2021, Prathamesh Kulkarni via Gcc-patches wrote: > > > More generally, would it be a good idea to provide attributes for > > > mod/ref anaylsis ? > > > So sth like: > > > void foo(void) __attribute__((modifies(errno))); > > > which would state that foo modifies errno, but neither reads nor > > > modifies any other global var. > > > and > > > void bar(void) __attribute__((reads(errno))) > > > which would state that bar only reads errno, and doesn't modify > > > or > > > read any other global var. > > > > Many math.h functions are const except for possibly setting errno, > > possibly raising floating-point exceptions (which might have other > > effects > > when using alternate exception handling) and possibly reading the > > rounding > > mode. To represent that, it might be useful for such attributes to > > be > > able to describe state (such as the floating-point environment) > > that > > doesn't correspond to a C identifier. (errno tends to be a macro, > > so > > referring to it as such in an attribute may be awkward as well.) > > We need some way to describe these things in Gimple and RTL as well, > and not just on function calls: also on other expressions. Adding > attributes that allow to describe this (partially, only per function) > in > C source code does not bring us closer to where we need to be.
Right, but those IR concerns are orthogonal to the needs of the patch kit, which is a way to express certain *other* things per-function in the C frontend. As noted in my other replies, this thread seems to be turning into something of a scope-creep pile-on, when I have some specific things I need for the rest of the patch kit, and they're unrelated to the problems of errno or floating-point handling. Dave
