On Thu, Nov 30, 2023 at 12:07 PM Ties Klappe via Gcc <gcc@gcc.gnu.org> wrote: > > When reading section 6.7.3.1 of the C standard (quoted below) about > the *restrict > *type qualifier, the first section talks about *ordinary identifiers*. > These are defined in section 6.2.3, and exclude members of structures. > > Let D be a declaration of an ordinary identifier that provides a means of > > designating an object P as a restrict-qualified pointer to type T. > > > I would assume that this means that in the code excerpt below the function > *h* cannot be optimized by substituting the load of *b.p *for *10*, as the > standard does not specify what it means for a struct member to be restrict > qualified. However, the code is still optimized by gcc (but not Clang), as > can be seen here: https://godbolt.org/z/hEnKKoaae > > struct bar { > int* restrict p; > int* restrict q; > }; > > int h(struct bar b) { > *b.p = 10; > *b.q = 11; > return *b.p; > } > > Was this a deliberate choice, or does it simply follow from how restrict is > supported in gcc (and could this be considered a bug w.r.t. the standard)?
Hmm, this was a deliberate choice (it also works for global 'b'), I didn't think the standard would exclude that. Note GCCs C++ standard library makes use of restrict qualified pointers as structure members for example. Richard.
