commit 7489a9400cffa4c1010debaf2d86dcd286ce1cfd
Author: Jason Merrill <jason@redhat.com>
Date:   Tue Nov 17 12:56:00 2015 -0500

    	PR bootstrap/68346
    
    	* c-common.c (warn_tautological_cmp): Fold before checking for
    	constants.

diff --git a/gcc/c-family/c-common.c b/gcc/c-family/c-common.c
index 06d857c..f50ca48 100644
--- a/gcc/c-family/c-common.c
+++ b/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.
diff --git a/gcc/testsuite/g++.dg/warn/Wtautological-compare2.C b/gcc/testsuite/g++.dg/warn/Wtautological-compare2.C
new file mode 100644
index 0000000..9d9060d
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/Wtautological-compare2.C
@@ -0,0 +1,11 @@
+// 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();
+}