re PR bootstrap/68346 (Bootstrap failure on i686-linux)

	PR bootstrap/68346

	* c-common.c (warn_tautological_cmp): Fold before checking for
	constants.

From-SVN: r230471

gcc/c-family/ChangeLog

+2015-11-17  Jason Merrill  <jason@redhat.com>
+
+	PR bootstrap/68346
+	* c-common.c (warn_tautological_cmp): Fold before checking for
+	constants.
+
 2015-11-16  Marek Polacek  <polacek@redhat.com>
 
 	PR c++/68362

gcc/c-family/c-common.c

@@ -1924,7 +1924,7 @@ warn_tautological_cmp (location_t loc, enum tree_code code, tree lhs, tree rhs)
 
   /* We do not warn for constants because they are typical of macro
      expansions that test for features, sizeof, and similar.  */
-  if (CONSTANT_CLASS_P (lhs) || CONSTANT_CLASS_P (rhs))
+  if (CONSTANT_CLASS_P (fold (lhs)) || CONSTANT_CLASS_P (fold (rhs)))
     return;
 
   /* Don't warn for e.g.

gcc/testsuite/g++.dg/warn/Wtautological-compare2.C

+// PR bootstrap/68346
+// { dg-options -Wtautological-compare }
+
+#define INVALID_REGNUM			(~(unsigned int) 0)
+#define PIC_OFFSET_TABLE_REGNUM INVALID_REGNUM
+
+int main()
+{
+  if ((unsigned) PIC_OFFSET_TABLE_REGNUM != INVALID_REGNUM)
+    __builtin_abort();
+}