[RFA] [PR tree-optimization/79095][PATCH 3/4] Improve ASSERT_EXPRs and simplification of overflow tests V2

[Richard Biener]

On Tue, Feb 7, 2017 at 7:32 PM, Jeff Law <law@redhat.com> wrote:
> This patch addresses issues Richi raised from V1.  Specifically the users of
> overflow_comparison_1 don't need to worry about trying both the original
> comparison and the reversed comparison.  This slightly simplifies the
> callers.
>
> Bootstrapped and regression tested as part of the full patch series.
>
> OK for the trunk?

Ok.

Richard.

> Jeff
>
>         * tree-vrp.c (register_edge_assert_for_2): Register additional
> asserts
>         if NAME is used in an overflow test.
>         (vrp_evaluate_conditional_warnv_with_ops): If the ops represent an
>         overflow check that can be expressed as an equality test, then
> adjust
>         ops to be that equality test.
>
> diff --git a/gcc/tree-vrp.c b/gcc/tree-vrp.c
> index 2c03a74..21c459c 100644
> --- a/gcc/tree-vrp.c
> +++ b/gcc/tree-vrp.c
> @@ -5319,7 +5319,17 @@ register_edge_assert_for_2 (tree name, edge e,
> gimple_stmt_iterator bsi,
>    /* Only register an ASSERT_EXPR if NAME was found in the sub-graph
>       reachable from E.  */
>    if (live_on_edge (e, name))
> -    register_new_assert_for (name, name, comp_code, val, NULL, e, bsi);
> +    {
> +      tree x;
> +      if (overflow_comparison_p (comp_code, name, val, false, &x))
> +       {
> +         enum tree_code new_code
> +           = ((comp_code == GT_EXPR || comp_code == GE_EXPR)
> +              ? GT_EXPR : LE_EXPR);
> +         register_new_assert_for (name, name, new_code, x, NULL, e, bsi);
> +       }
> +      register_new_assert_for (name, name, comp_code, val, NULL, e, bsi);
> +    }
>
>    /* In the case of NAME <= CST and NAME being defined as
>       NAME = (unsigned) NAME2 + CST2 we can assert NAME2 >= -CST2
> @@ -7678,6 +7688,39 @@ vrp_evaluate_conditional_warnv_with_ops (enum
> tree_code code, tree op0,
>        && !POINTER_TYPE_P (TREE_TYPE (op0)))
>      return NULL_TREE;
>
> +  /* If OP0 CODE OP1 is an overflow comparison, if it can be expressed
> +     as a simple equality test, then prefer that over its current form
> +     for evaluation.
> +
> +     An overflow test which collapses to an equality test can always be
> +     expressed as a comparison of one argument against zero.  Overflow
> +     occurs when the chosen argument is zero and does not occur if the
> +     chosen argument is not zero.  */
> +  tree x;
> +  if (overflow_comparison_p (code, op0, op1, use_equiv_p, &x))
> +    {
> +      wide_int max = wi::max_value (TYPE_PRECISION (TREE_TYPE (op0)),
> UNSIGNED);
> +      /* B = A - 1; if (A < B) -> B = A - 1; if (A == 0)
> +         B = A - 1; if (A > B) -> B = A - 1; if (A != 0)
> +         B = A + 1; if (B < A) -> B = A + 1; if (B == 0)
> +         B = A + 1; if (B > A) -> B = A + 1; if (B != 0) */
> +      if (integer_zerop (x))
> +       {
> +         op1 = x;
> +         code = (code == LT_EXPR || code == LE_EXPR) ? EQ_EXPR : NE_EXPR;
> +       }
> +      /* B = A + 1; if (A > B) -> B = A + 1; if (B == 0)
> +         B = A + 1; if (A < B) -> B = A + 1; if (B != 0)
> +         B = A - 1; if (B > A) -> B = A - 1; if (A == 0)
> +         B = A - 1; if (B < A) -> B = A - 1; if (A != 0) */
> +      else if (wi::eq_p (x, max - 1))
> +       {
> +         op0 = op1;
> +         op1 = wide_int_to_tree (TREE_TYPE (op0), 0);
> +         code = (code == GT_EXPR || code == GE_EXPR) ? EQ_EXPR : NE_EXPR;
> +       }
> +    }
> +
>    if ((ret = vrp_evaluate_conditional_warnv_with_ops_using_ranges
>                (code, op0, op1, strict_overflow_p)))
>      return ret;
>