http://gcc.gnu.org/ml/gcc-patches/2008-02/msg00110.html

	PR 33738
	* tree-vrp.c (vrp_evaluate_conditional): With
	-Wtype-limits, emit a warning when comparing against a
	constant outside the natural range of OP0's type.

testsuite/ChangeLog

	PR 33738
	* testsuite/g++.dg/warn/pr33738.C: New.

From-SVN: r132111

1 files changed, 42 insertions, 0 deletions

diff --git a/gcc/tree-vrp.c b/gcc/tree-vrp.c
index 5f9a327..9b9cc03 100644
--- a/gcc/tree-vrp.c
+++ b/gcc/tree-vrp.c
@@ -5073,6 +5073,48 @@ vrp_evaluate_conditional (tree cond, tree stmt)
 	}
     }
 
+  if (warn_type_limits
+      && ret
+      && TREE_CODE_CLASS (TREE_CODE (cond)) == tcc_comparison)
+    {
+      /* If the comparison is being folded and the operand on the LHS
+	 is being compared against a constant value that is outside of
+	 the natural range of OP0's type, then the predicate will
+	 always fold regardless of the value of OP0.  If -Wtype-limits
+	 was specified, emit a warning.  */
+      const char *warnmsg = NULL;
+      tree op0 = TREE_OPERAND (cond, 0);
+      tree op1 = TREE_OPERAND (cond, 1);
+      tree type = TREE_TYPE (op0);
+      value_range_t *vr0 = get_value_range (op0);
+
+      if (vr0->type != VR_VARYING
+	  && INTEGRAL_TYPE_P (type)
+	  && vrp_val_is_min (vr0->min)
+	  && vrp_val_is_max (vr0->max)
+	  && is_gimple_min_invariant (op1))
+	{
+	  if (integer_zerop (ret))
+	    warnmsg = G_("comparison always false due to limited range of "
+		         "data type");
+	  else
+	    warnmsg = G_("comparison always true due to limited range of "
+			 "data type");
+	}
+
+      if (warnmsg)
+	{
+	  location_t locus;
+
+	  if (!EXPR_HAS_LOCATION (stmt))
+	    locus = input_location;
+	  else
+	    locus = EXPR_LOCATION (stmt);
+
+	  warning (OPT_Wextra, "%H%s", &locus, warnmsg);
+	}
+    }
+
   return ret;
 }