Re: [PATCH] Fold x/x to 1, 0/x to 0 and 0%x to 0 consistently

[Jakub Jelinek <jakub@redhat.com>]

On Wed, Jun 08, 2016 at 01:43:56PM -0400, Jason Merrill wrote:
> > A few random ideas I was considering:
> > * restrict it to GIMPLE, so we can't have a regression in the front-ends.
> > * fold x/0 to 0 with TREE_OVERFLOW set, to tell the front-end that something
> > is going on.
> > * fold to (x/y,0) or (x/y,1) so the division by 0 is still there, but C++11
> > constexpr might give a strange message about it, and folding might not be
> > idempotent.
> 
> Any of these would avoid the constexpr regression, though the second
> would make the diagnostic worse.  Or the front end could copy
> constexpr function bodies before folding.

Or, both cxx_eval_binary_expression and cp_fold would need to
not fold if the divisor is integer_zerop.

	Jakub