[C/C++ PATCH, committed] Fix -Wtautological-compare (PR bootstrap/67030)

[Marek Polacek]

This PR exposed a defect in my -Wtautological-compare warning: we don't
want to warn when the expression comes from a macro expansion.

Bootstrapped/regtested on x86_64-linux, applying to trunk.

2015-07-27  Marek Polacek  <pola...@redhat.com>

        PR bootstrap/67030
        * c-common.c (warn_tautological_cmp): Don't warn for macro expansion.

        * c-c++-common/Wtautological-compare-2.c: New test.

diff --git gcc/c-family/c-common.c gcc/c-family/c-common.c
index 6a79b95..caa801e 100644
--- gcc/c-family/c-common.c
+++ gcc/c-family/c-common.c
@@ -1890,6 +1890,12 @@ warn_tautological_cmp (location_t loc, enum tree_code 
code, tree lhs, tree rhs)
   if (TREE_CODE_CLASS (code) != tcc_comparison)
     return;
 
+  /* Don't warn for various macro expansions.  */
+  if (from_macro_expansion_at (loc)
+      || from_macro_expansion_at (EXPR_LOCATION (lhs))
+      || from_macro_expansion_at (EXPR_LOCATION (rhs)))
+    return;
+
   /* 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))
diff --git gcc/testsuite/c-c++-common/Wtautological-compare-2.c 
gcc/testsuite/c-c++-common/Wtautological-compare-2.c
index e69de29..c8aecef 100644
--- gcc/testsuite/c-c++-common/Wtautological-compare-2.c
+++ gcc/testsuite/c-c++-common/Wtautological-compare-2.c
@@ -0,0 +1,15 @@
+/* PR bootstrap/67030 */
+/* { dg-do compile } */
+/* { dg-options "-Wtautological-compare" } */
+
+extern int foo (void);
+
+#define A a
+#define B A
+#define FOO (A > B)
+
+void
+fn1 (int a)
+{
+  if (FOO);
+}

        Marek