[RFA][PATCH] Fix tree-optimization/57144

[Richard Biener]

On Fri, May 3, 2013 at 6:30 AM, Jeff Law <law@redhat.com> wrote:
>
> When we have
>
> x = (T) y;
> if (x > CONST)
>   true arm
> else
>   false arm
>
> Assume CONST is larger than what can be represented in T.  If we use
> fold_convert, any bits not not in T will be dropped.  So if CONST is say
> 0x100000000 and T is a 32 bit type, the returned constant will be 0x0. So we
> change the code to
>
> x = (T) y;
> if (y > 0)
>   true arm
> else
>   false arm
>
> If y happens to have a value such as "1" we end up taking the true arm when
> we should have taken the false arm.
>
> The astute reader will note that VRP should have simply eliminated the
> condition because it can never be true, at least not in the testcase which
> is derived from real code in mpfr.  Probably we're too conservative when
> propagating a [0..INF(OV)] through a widening conversion.
>
> Bootstrapped and regression tested on x86_64-unknown-linux-gnu, OK for
> trunk?

Ok with the testcase changes suggested by Jakub.

Thanks,
Richard.

> Note this fixes the mpfr-2.x testsuite failures on x86_64.  While I believe
> this fix will address 57144 (ia64), I haven't directly confirmed that's
> true.
>
>
>
>
>
>
> commit baf070f82c7c6f19fd0a9e72514cc0ce03920c29
> Author: Jeff Law <law@redhat.com>
> Date:   Thu May 2 22:19:37 2013 -0600
>
>         PR tree-optimization/57411
>         * tree-vrp.c (simplify_cond_using_ranges): Verify the constant
>         operand of the condition will bit into the new type when eliminating
>         a cast feeding a condition.
>
>         PR tree-optimization/57411
>         * gcc.c-torture/execute/pr57144.c: New test.
>
> diff --git a/gcc/ChangeLog b/gcc/ChangeLog
> index 9e3d783..f245097 100644
> --- a/gcc/ChangeLog
> +++ b/gcc/ChangeLog
> @@ -1,3 +1,10 @@
> +2013-05-02  Jeff Law  <law@redhat.com>
> +
> +       PR tree-optimization/57411
> +       * tree-vrp.c (simplify_cond_using_ranges): Verify the constant
> +       operand of the condition will bit into the new type when eliminating
> +       a cast feeding a condition.
> +
>  2013-05-02  Richard Biener  <rguenther@suse.de>
>
>         * tree-eh.c (cleanup_empty_eh_merge_phis): Remove rename_virts
> diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
> index c8dc189..be30c51 100644
> --- a/gcc/testsuite/ChangeLog
> +++ b/gcc/testsuite/ChangeLog
> @@ -1,3 +1,8 @@
> +2013-05-02  Jeff Law  <law@redhat.com>
> +
> +       PR tree-optimization/57411
> +       * gcc.c-torture/execute/pr57144.c: New test.
> +
>  2013-05-02  Tobias Burnus  <burnus@net-b.de>
>
>         PR fortran/57142
> diff --git a/gcc/testsuite/gcc.c-torture/execute/pr57144.c
> b/gcc/testsuite/gcc.c-torture/execute/pr57144.c
> new file mode 100644
> index 0000000..e96c749
> --- /dev/null
> +++ b/gcc/testsuite/gcc.c-torture/execute/pr57144.c
> @@ -0,0 +1,15 @@
> +__attribute__ ((noinline))
> +foo(int a)
> +{
> +  int z = a > 0 ? a : -a;
> +  long x = z;
> +  if (x > 0x100000000)
> +    abort ();
> +  else
> +    exit (0);
> +}
> +
> +main()
> +{
> +  foo (1);
> +}
> diff --git a/gcc/tree-vrp.c b/gcc/tree-vrp.c
> index 6ed353f..b5de683 100644
> --- a/gcc/tree-vrp.c
> +++ b/gcc/tree-vrp.c
> @@ -8668,7 +8668,8 @@ simplify_cond_using_ranges (gimple stmt)
>           if (range_int_cst_p (vr)
>               && range_fits_type_p (vr,
>                                     TYPE_PRECISION (TREE_TYPE (op0)),
> -                                   TYPE_UNSIGNED (TREE_TYPE (op0))))
> +                                   TYPE_UNSIGNED (TREE_TYPE (op0)))
> +             && int_fits_type_p (op1, TREE_TYPE (innerop)))
>             {
>               tree newconst = fold_convert (TREE_TYPE (innerop), op1);
>               gimple_cond_set_lhs (stmt, innerop);
>