[PATCH] Improving LowerSwitch behavior for contiguous ranges

[Joerg Sonnenberger]

On Wed, Jun 11, 2014 at 04:32:52PM +0100, Marcello Maggioni wrote:
> Looks like it gives the same result

Looks suboptimal?

> 2014-06-11 14:18 GMT+01:00 Joerg Sonnenberger <joerg at britannica.bec.de>:
> 
> > On Wed, Jun 11, 2014 at 02:05:23AM +0100, Marcello Maggioni wrote:
> > > Hello Joerg,
> > >
> > > by unreachable default you mean something like this?
> > >
> > > int foo(int a) {
> > >   switch (a) {
> > >   case 0:
> > >     return 10;
> > >   case 1:
> > >     return 20;
> > >   case 2:
> > >     return 2;
> > >   case 8:
> > >     return 3;
> > >   case 9:
> > >     return 4;
> > >   case 10:
> > >     return 5;
> > >   default:
> > >     abort();
> > >   }
> > > }
> >
> > More like explicit __builtin_unreachable(), since abort() still has side
> > effects. Practical use case is switching over an enum.

I would expect something like:

if (a >= 8) {
  if (a >= 9) {
    if (a >= 10)
      return 5;
    else
      return 4;
  } else {
    return 3;
  }
} else {
  if (a >= 1) {
    if (a >= 2)
      return 20;
    return 2;
  } else {
    return 10;
  }
}

Joerg