Re: [PATCH (3/7)] Widening multiply-and-accumulate pattern matching

[Andrew Stubbs <ams at codesourcery dot com>]

On 07/07/11 13:37, Richard Guenther wrote:
> > I'll cook up a quick patch for VRP.
>
> Like the attached.  I'll finish and properly test it.

Your patch appears to do the wrong thing for this test case:

int
foo (int a, short b, short c)
{
  int bc = b * c;
  return a + (short)bc;
}

With your patch, the input to the widening-mult pass now looks like this:

foo (int a, short int b, short int c)
{
  int bc;
  int D.2016;
  int D.2015;
  int D.2014;

<bb 2>:
  D.2014_2 = (int) b_1(D);
  D.2015_4 = (int) c_3(D);
  bc_5 = D.2014_2 * D.2015_4;
  D.2016_9 = bc_5 + a_8(D);
  return D.2016_9;

}

It looks like when the user tries to deliberately break the maths your 
patch seems to unbreak it.

Andrew