On Tue, 10 May 2011, Michael Matz wrote:
> Hi,
>
> On Tue, 10 May 2011, Richard Guenther wrote:
>
> > struct B {
> > unsigned bit0 : 1;
> > unsigned bit1 : 1;
> > };
> >
> > void
> > foo (struct B *b)
> > {
> > b->bit0 = b->bit0 | b->bit1;
> > }
> >
> > we with this patch generate
> >
> > D.2686_2 = b_1(D)->bit0;
> > D.2688_4 = b_1(D)->bit1;
> > D.2693_10 = D.2688_4 ^ D.2686_2;
> > b_1(D)->bit0 = D.2693_10;
>
> I assume that this generates a XOR instead of an OR is a typo not a
> feature of the patch ;-)
Yes ;)
> > + struct B {
> > + unsigned bit0 : 1;
> > + unsigned bit1 : 1;
> > + };
> > +
> > + void
> > + foo (struct B *b)
> > + {
> > + b->bit0 = b->bit0 | b->bit1;
> > + }
> > +
> > + /* { dg-final { scan-tree-dump-not "\\\(unsigned char\\\)" "optimized" }
> > } */
>
> Perhaps test for only '\\\(unsigned' ? Because I'm not sure if some
> targets don't extend to "unsigned int", after all that's the base type of
> the bitfields.
It's what some of the premature FE optimization does, shortening
the width of the operation. The C standard would have
int (or unsigned int) conversions. So in reality no conversion at all
should prevail, but I didn't want to try inventing a regexp for that ;)
But yes, matching \\\(unsigned should be enough.
Richard.
