Re: [PATCH] PR c++/80544 strip cv-quals from cast results

[Jonathan Wakely <jwakely at redhat dot com>]

On 25/05/17 16:11 +0200, Jakub Jelinek wrote:
> On Thu, May 25, 2017 at 03:02:42PM +0100, Jonathan Wakely wrote:
> > On 25/05/17 11:07 +0100, Jonathan Wakely wrote:
> > > On 25/05/17 10:05 +0200, Andreas Schwab wrote:
> > > > ../../gcc/ada/gcc-interface/utils2.c: In function 'int compare_elmt_bitpos(const void*, const void*)':
> > > > ../../gcc/ada/gcc-interface/utils2.c:1937:73: error: type qualifiers ignored on cast result type [-Werror=ignored-qualifiers]
> > > >  const constructor_elt * const elmt1 = (const constructor_elt * const) rt1;
> > > >                                                                        ^~~
> > > > ../../gcc/ada/gcc-interface/utils2.c:1938:73: error: type qualifiers ignored on cast result type [-Werror=ignored-qualifiers]
> > > >  const constructor_elt * const elmt2 = (const constructor_elt * const) rt2;
> > >
> > > I'm testing this obvious fix.
> >
> > Committed as r248458 because it gets bootstrap past the error above,
> > although now Ada fails for me with:
> >
> > /home/jwakely/src/gcc/bootstrap/./gcc/xgcc -B/home/jwakely/src/gcc/bootstrap/./gcc/ -B/usr/local/x86_64-pc-linux-gnu/bin/ -B/usr/local/x86_64-pc-linux-gnu/lib/ -isystem /usr/local/x86_64-pc-linux-gnu/include -isystem /usr/local/x86_64-pc-linux-gnu/sys-include    -c -g -O2 -m32 -fpic  -W -Wall -gnatpg -nostdinc -m32  s-regpat.adb -o s-regpat.o
> >
> > raised STORAGE_ERROR : stack overflow or erroneous memory access
> > ../gcc-interface/Makefile:296: recipe for target 's-regpat.o' failed
> >
> >
> > > diff --git a/gcc/ada/gcc-interface/utils2.c b/gcc/ada/gcc-interface/utils2.c
> > > index fc6f1b8..cd37791 100644
> > > --- a/gcc/ada/gcc-interface/utils2.c
> > > +++ b/gcc/ada/gcc-interface/utils2.c
> > > @@ -1934,8 +1934,8 @@ build_call_raise_range (int msg, Node_Id gnat_node, char kind,
> > > static int
> > > compare_elmt_bitpos (const PTR rt1, const PTR rt2)
> > > {
> > > -  const constructor_elt * const elmt1 = (const constructor_elt * const) rt1;
> > > -  const constructor_elt * const elmt2 = (const constructor_elt * const) rt2;
> > > +  const constructor_elt * const elmt1 = (const constructor_elt *) rt1;
> > > +  const constructor_elt * const elmt2 = (const constructor_elt *) rt2;
> > >   const_tree const field1 = elmt1->index;
> > >   const_tree const field2 = elmt2->index;
> > >   const int ret
>
> So, what can one do with typeof or similar to avoid the warning?
>
> void
> foo (const void *p)
> {
>  const int *const q = (const int *const) p;
>  typeof (q) r = (typeof (q)) p;
>  (void) q;
>  (void) r;
> }

I'd probably write that like this instead:

void
foo (const void *p)
{
 typedef const int* ptr_type;
 ptr_type const q = (ptr_type) p;
 ptr_type const r = (ptr_type) p;
 (void) q;
 (void) r;
}

It names the type only once, not twice as in your example, and doesn't
need to use typeof to refer to that type again.

The variables p and q are defined const, which is what's wanted. The
cast is to ptr_type, not ptr_type const.