-Wtautological-compare: fix comparison of macro expansions

gcc/c-family/ChangeLog:
	PR c++/87504
	* c-warn.c (get_outermost_macro_expansion): New function.
	(spelled_the_same_p): Use it to unwind the macro expansions, and
	compare the outermost macro in each nested expansion, rather than
	the innermost.

gcc/testsuite/ChangeLog:
	PR c++/87504
	* c-c++-common/Wtautological-compare-8.c: New test.

From-SVN: r267299

gcc/c-family/ChangeLog

+2018-12-20  David Malcolm  <dmalcolm@redhat.com>
+
+	PR c++/87504
+	* c-warn.c (get_outermost_macro_expansion): New function.
+	(spelled_the_same_p): Use it to unwind the macro expansions, and
+	compare the outermost macro in each nested expansion, rather than
+	the innermost.
+
 2018-12-19  David Malcolm  <dmalcolm@redhat.com>
 
 	PR c++/87504

gcc/c-family/c-warn.c

@@ -399,6 +399,25 @@ warn_tautological_bitwise_comparison (const op_location_t &loc, tree_code code,
 		"bitwise comparison always evaluates to true");
 }
 
+/* Given LOC from a macro expansion, return the map for the outermost
+   macro in the nest of expansions.  */
+
+static const line_map_macro *
+get_outermost_macro_expansion (location_t loc)
+{
+  gcc_assert (from_macro_expansion_at (loc));
+
+  const line_map *map = linemap_lookup (line_table, loc);
+  const line_map_macro *macro_map;
+  do
+    {
+      macro_map = linemap_check_macro (map);
+      loc = linemap_unwind_toward_expansion (line_table, loc, &map);
+    } while (linemap_macro_expansion_map_p (map));
+
+  return macro_map;
+}
+
 /* Given LOC_A and LOC_B from macro expansions, return true if
    they are "spelled the same" i.e. if they are both directly from
    expansion of the same non-function-like macro.  */
@@ -409,11 +428,8 @@ spelled_the_same_p (location_t loc_a, location_t loc_b)
   gcc_assert (from_macro_expansion_at (loc_a));
   gcc_assert (from_macro_expansion_at (loc_b));
 
-  const line_map_macro *map_a
-    = linemap_check_macro (linemap_lookup (line_table, loc_a));
-
-  const line_map_macro *map_b
-    = linemap_check_macro (linemap_lookup (line_table, loc_b));
+  const line_map_macro *map_a = get_outermost_macro_expansion (loc_a);
+  const line_map_macro *map_b = get_outermost_macro_expansion (loc_b);
 
   if (map_a->macro == map_b->macro)
     if (!cpp_fun_like_macro_p (map_a->macro))

gcc/testsuite/ChangeLog

+2018-12-20  David Malcolm  <dmalcolm@redhat.com>
+
+	PR c++/87504
+	* c-c++-common/Wtautological-compare-8.c: New test.
+
 2018-12-20  Richard Biener  <rguenther@suse.de>
 
 	PR tree-optimization/84362

gcc/testsuite/c-c++-common/Wtautological-compare-8.c

+/* { dg-options "-Wtautological-compare" } */
+
+int foo;
+#define INCOMING_FRAME_SP_OFFSET foo
+#define DEFAULT_INCOMING_FRAME_SP_OFFSET INCOMING_FRAME_SP_OFFSET
+
+int test (void)
+{
+  if (DEFAULT_INCOMING_FRAME_SP_OFFSET != INCOMING_FRAME_SP_OFFSET) /* { dg-warning "self-comparison" "" { target c } } */
+    return 1;
+  else
+    return 0;
+}
+
+#define BYTES_BIG_ENDIAN foo
+#define WORDS_BIG_ENDIAN foo
+
+int test_2 (void)
+{
+  if (BYTES_BIG_ENDIAN != WORDS_BIG_ENDIAN) /* { dg-warning "self-comparison" "" { target c } } */
+    return 1;
+  else
+    return 0;
+}
+
+#define COND DEFAULT_INCOMING_FRAME_SP_OFFSET != INCOMING_FRAME_SP_OFFSET
+int test_3 (void)
+{
+  if (COND)
+    return 1;
+  else
+    return 0;
+}