http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52283
--- Comment #6 from Manuel López-Ibáñez <manu at gcc dot gnu.org> 2012-02-16 18:25:30 UTC --- (In reply to comment #5) > On Thu, 16 Feb 2012, manu at gcc dot gnu.org wrote: > > > What is the problem with stripping the nops *before giving the error* and > > if it > > still fails, give an error? > > NOPs are used to represent an intermediate expression that folded to an > integer constant but is not an integer constant expression and cannot > appear in one, as well as to carry TREE_NO_WARNING. So you need to be > careful about where you strip them to avoid making something into an > integer constant expression that should not be one; don't strip them too > early. Is this folding actually necessary for anything beyond diagnostics? I thought it was agreed that folding in the FEs was EVIL and we should stop doing it. > I think it would be OK to have a c_fully_fold_no_nop (which removes any > TREE_NO_WARNING nop from the return from c_fully_fold) that is used in the > relevant places (set_init_index, do_case, check_bitfield_type_and_width, > build_enumerator at least) which have the pedwarn-if-pedantic logic for > things folding to an integer constant where an integer constant expression > is required. I wouldn't be surprised if the compiler got noticeably faster by removing all early folding and all the workarounds and hacks that come with it, and replacing it by doing a temporary c_fully_fold at those specific places that needed it (and throwing away the result and keeping the original code around).
