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Subject: [Bug tree-optimization/47538] [4.6 Regression] GNU Scientific Library miscompiled by gcc 4.6
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47538

--- Comment #13 from Richard Guenther <rguenth at gcc dot gnu.org> 2011-01-31 11:55:03 UTC ---
Can we use sth like

Index: tree-ssa-ccp.c
===================================================================
--- tree-ssa-ccp.c      (revision 169434)
+++ tree-ssa-ccp.c      (working copy)
@@ -1770,9 +1770,38 @@ bit_value_binop_1 (enum tree_code code,
 {
   bool uns = (TREE_CODE (r1type) == INTEGER_TYPE
              && TYPE_IS_SIZETYPE (r1type) ? 0 : TYPE_UNSIGNED (r1type));
+
   /* Assume we'll get a constant result.  Use an initial varying value,
      we fall back to varying in the end if necessary.  */
   *mask = double_int_minus_one;
+
+  /* We have some sizetype issues, drop to varying in case there are
+     mismatches.  */
+  switch (code)
+    {
+    case LSHIFT_EXPR:
+    case RSHIFT_EXPR:
+    case LROTATE_EXPR:
+    case RROTATE_EXPR:
+      if ((TREE_CODE (type) == INTEGER_TYPE
+          && TYPE_IS_SIZETYPE (type) ? 0 : TYPE_UNSIGNED (type)) != uns)
+       return;
+      break;
+
+    case EQ_EXPR:
+    case NE_EXPR:
+    case LT_EXPR:
+    case LE_EXPR:
+    case GE_EXPR:
+    case GT_EXPR:
+      if ((TREE_CODE (r2type) == INTEGER_TYPE
+          && TYPE_IS_SIZETYPE (r2type) ? 0 : TYPE_UNSIGNED (r2type)) != uns)
+       return;
+      break;
+
+    default:;
+    }
+

instead?  It makes it more obvious what happens (IMHO).