Belatedly, here's an updated version, using Martin Sebor's suggested wording from "https://gcc.gnu.org/pipermail/gcc-patches/2020-July/549580.html". I added two commas, hopefully helpfully. Albeit ok'd by Richard Biener in "https://gcc.gnu.org/pipermail/gcc-patches/2020-July/549922.html", better have this reviewed properly, including markup (none added).
Ok for trunk (gcc-11) and gcc-10? --- We say very little about reads and writes to aggregate / compound objects, just scalar objects (i.e. assignments don't cause reads). Let's lets say something safe about aggregate objects, but only for those that are the same size as a scalar type. There's an equal-sounding section (Volatiles) in extend.texi, but this seems a more appropriate place, as specifying the behavior of a standard qualifier. gcc: 2020-12-02 Hans-Peter Nilsson <h...@axis.com> Martin Sebor <mse...@redhat.com> PR middle-end/94600 * doc/implement-c.texi (Qualifiers implementation): Add blurb about access to the whole of a volatile aggregate object, only for same-size as a scalar object. --- gcc/doc/implement-c.texi | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/gcc/doc/implement-c.texi b/gcc/doc/implement-c.texi index 692297b69c4..2e9158a2a45 100644 --- a/gcc/doc/implement-c.texi +++ b/gcc/doc/implement-c.texi @@ -576,6 +576,11 @@ are of scalar types, the expression is interpreted by GCC as a read of the volatile object; in the other cases, the expression is only evaluated for its side effects. +When an object of an aggregate type, with the same size and alignment as a +scalar type S, is the subject of a volatile access by an assignment +expression or an atomic function, the access to it is performed as if the +object's declared type were volatile S. + @end itemize @node Declarators implementation -- 2.11.0