Re: [PATCH] Fix PR47801, fold references in debug stmts

[Jakub Jelinek <jakub at redhat dot com>]

On Sat, Feb 19, 2011 at 09:57:06PM +0100, Richard Guenther wrote:
> > I'd say this is done in a wrong spot, because if gimple_debug_bind_get_value
> > is say PLUS_EXPR of a VAR_DECL and INTEGER_CST, you wouldn't fold the
> > VAR_DECL.
> 
> I thought we have the same restrictions on debug stmt RHS as on
> gimple RHS, thus memory refs always get a debug temp?

Not sure if always, but probably at least most of the time.
int m = 7;
int main (void)
{
  int a = m;
  int b = m + 1;
  int c = m * 4;
  int *d = &m;
  return 6;
}

(wonder if we shouldn't do some simple CSE on the debug temporaries...).

> > Can't this be done at the beginning of expand_debug_expr instead (in the
> > switch based on TREE_CODE_CLASS you'd for
> >   case tcc_declaration:
> >   case tcc_reference:
> > do this folding and if you decide to use the folded value, you'd just
> > return expand_debug_expr (folded);
> 
> Well, from a quick look I think we'll end up recursing from ADDR_EXPRs
> which will break.

It wouldn't break, we'd just generate DW_OP_GNU_implicit_ptr, but if the
const has a memory it is of course preferrable to use real address of the
object.  We'd have to pass an extra bool whether we are in ADDR_EXPR or not
(i.e. whether we are trying hard to get a MEM or not).  Anyway, given the
above I guess your patch is better (Alex, do you agree?).

	Jakub