[C++ PATCH] Handle CASE_HIGH in constexpr evaluation (PR c++/72868)

[Jakub Jelinek]

Hi!

As mentioned in the PR, constexpr.c has been handling cases with ranges
just as the lowest value of the range.

Fixed thusly, bootstrapped/regtested on x86_64-linux and i686-linux, ok for
trunk?  What about 6.2 (not a regression, but low risk fix for wrong-code)?

2016-08-11  Jakub Jelinek  <ja...@redhat.com>

        PR c++/72868
        * constexpr.c (label_matches): Handle case range expressions.

        * g++.dg/cpp1y/constexpr-switch4.C: New test.

--- gcc/cp/constexpr.c.jj       2016-08-10 00:21:07.000000000 +0200
+++ gcc/cp/constexpr.c  2016-08-10 22:17:16.577041975 +0200
@@ -3448,6 +3448,12 @@ label_matches (tree *jump_target, tree_s
        {
          if (!CASE_LOW (stmt))
            default_label = i;
+         else if (CASE_HIGH (stmt))
+           {
+             if (tree_int_cst_le (CASE_LOW (stmt), *jump_target)
+                 && tree_int_cst_le (*jump_target, CASE_HIGH (stmt)))
+               return true;
+           }
          else if (tree_int_cst_equal (*jump_target, CASE_LOW (stmt)))
            return true;
        }
--- gcc/testsuite/g++.dg/cpp1y/constexpr-switch4.C.jj   2016-08-10 
22:22:29.567129868 +0200
+++ gcc/testsuite/g++.dg/cpp1y/constexpr-switch4.C      2016-08-10 
22:23:25.104435699 +0200
@@ -0,0 +1,27 @@
+// PR c++/72868
+// { dg-do compile }
+// { dg-options "-std=gnu++14" }
+
+constexpr int
+foo (int i)
+{
+  switch (i)
+    {
+    case 11 ... 12:
+      return 4;
+    case 0 ... 9:
+      return 3;
+    default:
+      return 7;
+    }
+}
+
+#define SA(X) static_assert((X),#X)
+SA (foo (-1) == 7);
+SA (foo (0) == 3);
+SA (foo (3) == 3);
+SA (foo (9) == 3);
+SA (foo (10) == 7);
+SA (foo (11) == 4);
+SA (foo (12) == 4);
+SA (foo (13) == 7);

        Jakub