[Bug sanitizer/80536] [6/7/8 Regression] UBSAN: compile time segfault

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80536

--- Comment #18 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
(In reply to Marek Polacek from comment #17)
> (In reply to Jakub Jelinek from comment #16)
> > (In reply to Marek Polacek from comment #15)
> > > In C I don't think so, because we mostly call c_save_expr and c_fully_fold
> > > therein would fold that expression to 0.  And when we call save_expr, it's
> > 
> > Yeah, I know that, and I think it is a serious bug.  With the c_fully_fold
> > in c_save_expr the C FE is not doing anything close to delayed folding, it
> > folds immediately whenever we might need a save_expr, the old trees gone.
> > So I think it would be nice to kill c_save_expr, just use save_expr, and let
> > c_fully_fold fold SAVE_EXPR operand (just once, not many times).
> 
> I agree.  I'll try (guess we'll need the fold cache).  That can be a
> separate project, though.

See above, if it is just about SAVE_EXPR, the C FE could just grab one of the
many spare bits on SAVE_EXPR for a flag whether the operand has been
c_fully_folded already.