Re: [RFC][PR68217] Improve value range for signed & sign-bit-CST

[kugan]

On 27/04/16 00:14, Richard Biener wrote:
On Fri, Apr 15, 2016 at 12:44 PM, kugan
<kugan.vivekanandara...@linaro.org> wrote:
As pointed out by Richard, for signed & sign-bit-CST value range should be
[-INF, 0] range, not a [-INF, INF] range as happens now.

This patch fixes this. I bootstrapped and regression tested for
x86-64-linux-gnu with no new regression. Is this OK for statege-1.

I think you need to check vr0 for singleton-constant == sign_bit as well,
there is nothing that canonicalizes this during propagation.

Thanks for the review. Here is the updated patch. I will bootstrap again 
and commit if this is OK.

Thanks,
Kugan


Otherwise ok.

Thanks,
Richard.

Thanks,
Kugan


gcc/ChangeLog:

2016-04-14  Kugan Vivekanandarajah  <kug...@linaro.org>

         PR middle-end/68217
         * tree-vrp.c (extract_range_from_binary_expr_1): In case of signed &
sign-bit-CST,
          generate [-INF, 0] instead of [-INF, INF].


gcc/testsuite/ChangeLog:

2016-04-14  Kugan Vivekanandarajah  <kug...@linaro.org>

         PR middle-end/68217
         * gcc.dg/pr68217.c: New test.
diff --git a/gcc/testsuite/gcc.dg/pr68217.c b/gcc/testsuite/gcc.dg/pr68217.c
index e69de29..8197363 100644
--- a/gcc/testsuite/gcc.dg/pr68217.c
+++ b/gcc/testsuite/gcc.dg/pr68217.c
@@ -0,0 +1,14 @@
+
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-vrp1" } */
+
+int foo (void)
+{
+    volatile int a = -1;
+    long long b = -9223372036854775807LL - 1; // LLONG_MIN
+    long long x = (a & b); // x == 0x8000000000000000
+    if (x < 1LL) { ; } else { __builtin_abort(); }
+    return 0;
+}
+
+/* { dg-final { scan-tree-dump "x_*: \\[-INF, 0\\]" "vrp1" } } */
diff --git a/gcc/tree-vrp.c b/gcc/tree-vrp.c
index bbdf9ce..a86d6dd 100644
--- a/gcc/tree-vrp.c
+++ b/gcc/tree-vrp.c
@@ -3115,6 +3115,24 @@ extract_range_from_binary_expr_1 (value_range *vr,
          if (int_cst_range1 && tree_int_cst_sgn (vr1.min) >= 0)
            wmax = wi::min (wmax, vr1.max, TYPE_SIGN (expr_type));
          max = wide_int_to_tree (expr_type, wmax);
+         cmp = compare_values (min, max);
+         /* PR68217: In case of signed & sign-bit-CST should
+            result in [-INF, 0] instead of [-INF, INF].  */
+         if (cmp == -2 || cmp == 1)
+           {
+             wide_int sign_bit
+               = wi::set_bit_in_zero (TYPE_PRECISION (expr_type) - 1,
+                                      TYPE_PRECISION (expr_type));
+             if (!TYPE_UNSIGNED (expr_type)
+                 && ((value_range_constant_singleton (&vr0)
+                      && !wi::cmps (vr0.min, sign_bit))
+                     || (value_range_constant_singleton (&vr1)
+                         && !wi::cmps (vr1.min, sign_bit))))
+               {
+                 min = TYPE_MIN_VALUE (expr_type);
+                 max = build_int_cst (expr_type, 0);
+               }
+           }
        }
       else if (code == BIT_IOR_EXPR)
        {