[PR 87059] kludge over MIN_EXPR problem causing VRP failure in value ranges

[Aldy Hernandez <aldyh at redhat dot com>]

As discussed in the PR, the MIN_EXPR being passed to VRP has 
incompatible signs.  I expect MIN_EXPR to have the same type for all 
arguments plus the MIN_EXPR node itself, but this is not the case.

The culprit on PPC is expand_builtin_strncmp, but fixing it there causes 
other problems on x86-64 (see PR).  I believe Martin Sebor had some 
questions related to the x86 fallout 
(https://gcc.gnu.org/ml/gcc/2018-08/msg00164.html).

Since it seems this has been broken for a while, and I'd like to unbreak 
PPC without having to take my patch out, I suggest (for now) just 
passing the sign of the first argument as VRP had been doing all along 
(through int_const_binop):

int_const_binop():
...
  tree type = TREE_TYPE (arg1);
...
  if (TREE_CODE (arg1) == INTEGER_CST && TREE_CODE (arg2) == INTEGER_CST)
    {
      wide_int warg1 = wi::to_wide (arg1), res;
      wide_int warg2 = wi::to_wide (arg2, TYPE_PRECISION (type));
      success = wide_int_binop (res, code, warg1, warg2, sign, &overflow);
      poly_res = res;
    }

At some point later, if someone is sufficiently vexed by broken 
MIN_EXPR, we could fix it and the x86 fall out.

OK pending tests?

gcc/

	PR 87059/tree-optimization
	* tree-vrp.c (extract_range_from_binary_expr_1): Pass sign of
	first argument to wide_int_range_min_max.

diff --git a/gcc/tree-vrp.c b/gcc/tree-vrp.c
index 735b3646e81..7373011d901 100644
--- a/gcc/tree-vrp.c
+++ b/gcc/tree-vrp.c
@@ -1566,6 +1566,15 @@ extract_range_from_binary_expr_1 (value_range *vr,
       wide_int vr1_min, vr1_max;
       extract_range_into_wide_ints (&vr0, sign, prec, vr0_min, vr0_max);
       extract_range_into_wide_ints (&vr1, sign, prec, vr1_min, vr1_max);
+
+      /* FIXME: Currently the sign of MIN_EXPR and the sign of its
+	 arguments are not always the same.  Fixing the creators of
+	 these faulty nodes caused other problems.  For now use the
+	 sign of the first argument as VRP was previously doing.  See
+	 PR87059.  */
+      if (vr0.min)
+	sign = TYPE_SIGN (TREE_TYPE (vr0.min));
+
       if (wide_int_range_min_max (wmin, wmax, code, sign, prec,
 				  vr0_min, vr0_max, vr1_min, vr1_max))
 	set_value_range (vr, VR_RANGE,