Improve VRP of BIT_AND_EXPR

Hi!

Looking at PR44858, I was surprised VRP doesn't figure out
for
x = (a > b);
y = x & 2;
that y is 0.  Similarly say for x & y when
x is [1024, 1039] and y is [2048, 2063], we can count
on the result being [0, 15] (the 0x400 and 0x800 bits are both cleared),
etc.

The following patch improves handling of BIT_AND_EXPR.

Bootstrapped/regtested on x86_64-linux and i686-linux.  Ok for trunk?

In the testsuite slp-perm-4.c was the only failure, because in
for (i = 0; i < 16; i++)
  {
    i %= 256;
    if (i > 200)
      abort ();
    ...
  }
with the patch the conditional and abort is now optimized away - previously
i &= 255; was VARYING, now is [0, 15].

As next step, I guess VRP should be able to optimize that &= 255 away
completely, because the argument is known to be [0, 15], so doesn't need
any masking.

2010-07-08  Jakub Jelinek  <jakub@redhat.com>

	* tree-vrp.c (extract_range_from_binary_expr) <BIT_AND_EXPR>: If
	both ranges are range_int_cst_p with non-negative minimum,
	try harder to derive smaller range.

	* gcc.dg/tree-ssa/vrp50.c: New test.
	* gcc.dg/vect/slp-perm-4.c (main): Make sure loop isn't vectorized.



	Jakub

On Thu, Jul 8, 2010 at 7:07 PM, Jakub Jelinek <jakub@redhat.com> wrote:
> Hi!
>
> Looking at PR44858, I was surprised VRP doesn't figure out
> for
> x = (a > b);
> y = x & 2;
> that y is 0.  Similarly say for x & y when
> x is [1024, 1039] and y is [2048, 2063], we can count
> on the result being [0, 15] (the 0x400 and 0x800 bits are both cleared),
> etc.
>
> The following patch improves handling of BIT_AND_EXPR.
>
> Bootstrapped/regtested on x86_64-linux and i686-linux.  Ok for trunk?
>
> In the testsuite slp-perm-4.c was the only failure, because in
> for (i = 0; i < 16; i++)
>  {
>    i %= 256;
>    if (i > 200)
>      abort ();
>    ...
>  }
> with the patch the conditional and abort is now optimized away - previously
> i &= 255; was VARYING, now is [0, 15].
>
> As next step, I guess VRP should be able to optimize that &= 255 away
> completely, because the argument is known to be [0, 15], so doesn't need
> any masking.

Ok.

Thanks,
Richard.

> 2010-07-08  Jakub Jelinek  <jakub@redhat.com>
>
>        * tree-vrp.c (extract_range_from_binary_expr) <BIT_AND_EXPR>: If
>        both ranges are range_int_cst_p with non-negative minimum,
>        try harder to derive smaller range.
>
>        * gcc.dg/tree-ssa/vrp50.c: New test.
>        * gcc.dg/vect/slp-perm-4.c (main): Make sure loop isn't vectorized.
>
> --- gcc/tree-vrp.c.jj   2010-07-05 12:37:01.000000000 +0200
> +++ gcc/tree-vrp.c      2010-07-08 16:03:11.000000000 +0200
> @@ -2577,6 +2577,58 @@ extract_range_from_binary_expr (value_ra
>
>       if (vr0_int_cst_singleton_p && vr1_int_cst_singleton_p)
>        min = max = int_const_binop (code, vr0.max, vr1.max, 0);
> +      else if (range_int_cst_p (&vr0)
> +              && range_int_cst_p (&vr1)
> +              && tree_int_cst_sgn (vr0.min) >= 0
> +              && tree_int_cst_sgn (vr1.min) >= 0)
> +       {
> +         double_int vr0_mask = tree_to_double_int (vr0.min);
> +         double_int vr1_mask = tree_to_double_int (vr1.min);
> +         double_int maxd, diff;
> +         tree mask;
> +
> +         min = build_int_cst (expr_type, 0);
> +         /* Compute non-zero bits mask from both ranges.  */
> +         if (!vr0_int_cst_singleton_p)
> +           {
> +             maxd = tree_to_double_int (vr0.max);
> +             diff = double_int_sub (maxd, vr0_mask);
> +             if (diff.high)
> +               {
> +                 diff.low = ~(unsigned HOST_WIDE_INT)0;
> +                 diff.high = ((HOST_WIDE_INT) 2
> +                              << floor_log2 (diff.high)) - 1;
> +               }
> +             else
> +               diff.low = ((HOST_WIDE_INT) 2 << floor_log2 (diff.low)) - 1;
> +             vr0_mask = double_int_ior (vr0_mask,
> +                                        double_int_ior (maxd, diff));
> +           }
> +         if (!vr1_int_cst_singleton_p)
> +           {
> +             maxd = tree_to_double_int (vr1.max);
> +             diff = double_int_sub (maxd, vr1_mask);
> +             if (diff.high)
> +               {
> +                 diff.low = ~(unsigned HOST_WIDE_INT)0;
> +                 diff.high = ((HOST_WIDE_INT) 2
> +                              << floor_log2 (diff.high)) - 1;
> +               }
> +             else
> +               diff.low = ((HOST_WIDE_INT) 2 << floor_log2 (diff.low)) - 1;
> +             vr1_mask = double_int_ior (vr1_mask,
> +                                        double_int_ior (maxd, diff));
> +           }
> +         mask = double_int_to_tree (expr_type,
> +                                    double_int_and (vr0_mask, vr1_mask));
> +         max = vr0.max;
> +         if (tree_int_cst_lt (vr1.max, max))
> +           max = vr1.max;
> +         if (!TREE_OVERFLOW (mask)
> +             && tree_int_cst_lt (mask, max)
> +             && tree_int_cst_sgn (mask) >= 0)
> +           max = mask;
> +       }
>       else if (vr0_int_cst_singleton_p
>               && tree_int_cst_sgn (vr0.max) >= 0)
>        {
> --- gcc/testsuite/gcc.dg/tree-ssa/vrp50.c.jj    2010-07-08 16:24:42.000000000 +0200
> +++ gcc/testsuite/gcc.dg/tree-ssa/vrp50.c       2010-07-08 16:32:26.000000000 +0200
> @@ -0,0 +1,36 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -fdump-tree-vrp1" } */
> +
> +int
> +foo (unsigned int i, unsigned int j)
> +{
> +  i &= 15;
> +  j &= 15;
> +  i += 1024;
> +  j += 2048;
> +  i &= j;
> +  return i < 16;
> +}
> +
> +int
> +bar (int i)
> +{
> +  int c = 2;
> +  c &= i > 6;
> +  return c == 0;
> +}
> +
> +int baz (int x, int y)
> +{
> +  x &= 15;
> +  y &= 15;
> +  x += 4;
> +  y += 16;
> +  x &= y;
> +  return x < 20;
> +}
> +
> +/* { dg-final { scan-tree-dump "Folding predicate i_\[^\n\r\]* to 1" "vrp1" } } */
> +/* { dg-final { scan-tree-dump "Folding predicate c_\[^\n\r\]* to 1" "vrp1" } } */
> +/* { dg-final { scan-tree-dump "Folding predicate x_\[^\n\r\]* to 1" "vrp1" } } */
> +/* { dg-final { cleanup-tree-dump "vrp1" } } */
> --- gcc/testsuite/gcc.dg/vect/slp-perm-4.c.jj   2010-06-11 11:00:46.000000000 +0200
> +++ gcc/testsuite/gcc.dg/vect/slp-perm-4.c      2010-07-08 18:53:40.102558207 +0200
> @@ -69,6 +69,7 @@ int main (int argc, const char* argv[])
>       if (input[i] > 200)
>         abort();
>       output[i] = 0;
> +      __asm__ volatile ("");
>     }
>
>   foo (input, output);
>
>
>        Jakub
>