[Bug c++/56961] stack overflow in gimplifier with volatile field

["rguenth at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=56961

--- Comment #6 from Richard Biener <rguenth at gcc dot gnu.org> ---
The C++ gimplify langhook gimplifies the gimplifier generated

  vol.1 = b.fields

as

  vol.1, b.fields;

so it isn't a manifestation of the issue but a fallout of the attempt to
fix it in the C++ gimplifier...  it drops the assignment but leaves the
load from the volatile in place (as side-effect to be preserved?).  But
then we gimplify that again ... producing vol.2 = b.fields ... and on we go.