Re: compile warnings when including avltree-list and gcc-warnings is enabled

[Dylan Cali <calid1984@gmail.com>]

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On Mon, Sep 8, 2014 at 10:04 AM, Dylan Cali <calid1984@gmail.com> wrote:
> On Sep 8, 2014 9:27 AM, "Eric Blake" <eblake@redhat.com> wrote:
>> Does this work for all supported versions of gcc? Or do you need to make
>> it conditional on new enough gcc (it's okay if warnings have to be
>> disabled to compile with older gcc, but not okay if the way to disable
>> warnings for newer gcc causes compilation failure in older gcc).
>
> Yep you're right, looking at some other code of mine I have a conditional
> checking for gcc > 3.7 before doing the push/pop, so it looks like that is
> the min version for this pragma.  So wrap the pragma in a conditional, and
> add a conditional in the Makefile turning off warnings altogether for gcc <=
> 3.7?

Ok cool, it looks like this is mostly already implemented.  First, I
was wrong about the version of gcc that supports these pragmas, it's
4.6 [1].  And gnulib already uses the diagnostic pragmas elsewhere, so
I mimicked the conditional format used in other files.  Finally, the
makefile conditional is already done in the coreutils configure.ac
[2].

I've attached a patch with the updates, let me know if you see any
further issues.

Thanks,
Dylan

[1] https://gcc.gnu.org/ml/gcc-help/2011-01/msg00113.html
[2] https://github.com/coreutils/coreutils/blob/master/configure.ac#L97

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From 71f4f452e4768606c6f81300887e3e9c6ca74a93 Mon Sep 17 00:00:00 2001
From: Dylan Cali <calid1984@gmail.com>
Date: Sat, 6 Sep 2014 01:52:31 -0500
Subject: [PATCH] build: fix gcc warnings

* tests/test-avltree_list.c: Remove gl_avltree_list_check_invariants
declaration
* lib/gl_avltree_list.c: Add gl_avltree_list_check_invariants
declaration from test-avltree_list.c. Fixes gcc warning about missing
declaration.
* lib/gl_avltree_list.c: (check_invariants): Add pure attribute.
(gl_avltree_list_check_invariants): Add const attribute. Also use a gcc
pragma to ignore a false positive warning about check_invariants being a
statement with no effect (only for gcc >= 4.6).
* lib/gl_anytree_list2.h: Add pure attribute to (gl_tree_node_value),
(gl_tree_next_node), (gl_tree_previous_node), (node_at),
(gl_tree_get_at)
---
 lib/gl_anytree_list2.h    | 10 +++++-----
 lib/gl_avltree_list.c     | 18 ++++++++++++++++--
 tests/test-avltree_list.c |  2 --
 3 files changed, 21 insertions(+), 9 deletions(-)

diff --git a/lib/gl_anytree_list2.h b/lib/gl_anytree_list2.h
index 70e59a5..05fde15 100644
--- a/lib/gl_anytree_list2.h
+++ b/lib/gl_anytree_list2.h
@@ -59,7 +59,7 @@ gl_tree_size (gl_list_t list)
   return (list->root != NULL ? list->root->branch_size : 0);
 }
 
-static const void *
+static const void * _GL_ATTRIBUTE_PURE
 gl_tree_node_value (gl_list_t list, gl_list_node_t node)
 {
   return node->value;
@@ -100,7 +100,7 @@ gl_tree_node_nx_set_value (gl_list_t list, gl_list_node_t node, const void *elt)
   return 0;
 }
 
-static gl_list_node_t
+static gl_list_node_t _GL_ATTRIBUTE_PURE
 gl_tree_next_node (gl_list_t list, gl_list_node_t node)
 {
   if (node->right != NULL)
@@ -118,7 +118,7 @@ gl_tree_next_node (gl_list_t list, gl_list_node_t node)
   return node;
 }
 
-static gl_list_node_t
+static gl_list_node_t _GL_ATTRIBUTE_PURE
 gl_tree_previous_node (gl_list_t list, gl_list_node_t node)
 {
   if (node->left != NULL)
@@ -137,7 +137,7 @@ gl_tree_previous_node (gl_list_t list, gl_list_node_t node)
 }
 
 /* Return the node at the given position < gl_tree_size (list).  */
-static gl_list_node_t
+static gl_list_node_t _GL_ATTRIBUTE_PURE
 node_at (gl_list_node_t root, size_t position)
 {
   /* Here we know that root != NULL.  */
@@ -162,7 +162,7 @@ node_at (gl_list_node_t root, size_t position)
   return node;
 }
 
-static const void *
+static const void * _GL_ATTRIBUTE_PURE
 gl_tree_get_at (gl_list_t list, size_t position)
 {
   gl_list_node_t node = list->root;
diff --git a/lib/gl_avltree_list.c b/lib/gl_avltree_list.c
index 1afe5ca..0466029 100644
--- a/lib/gl_avltree_list.c
+++ b/lib/gl_avltree_list.c
@@ -36,8 +36,10 @@
 /* Generic binary tree code.  */
 #include "gl_anytree_list2.h"
 
+extern void gl_avltree_list_check_invariants (gl_list_t list);
+
 /* For debugging.  */
-static unsigned int
+static unsigned int _GL_ATTRIBUTE_PURE
 check_invariants (gl_list_node_t node, gl_list_node_t parent)
 {
   unsigned int left_height =
@@ -59,13 +61,25 @@ check_invariants (gl_list_node_t node, gl_list_node_t parent)
 
   return 1 + (left_height > right_height ? left_height : right_height);
 }
-void
+
+/* GCC warns that check_invariants has no effect, but it does. Ignore
+   the false positive. */
+#if (__GNUC__ == 4 && 6 <= __GNUC_MINOR__) || 4 < __GNUC__
+# pragma GCC diagnostic push
+# pragma GCC diagnostic ignored "-Wunused-value"
+#endif
+
+void _GL_ATTRIBUTE_CONST
 gl_avltree_list_check_invariants (gl_list_t list)
 {
   if (list->root != NULL)
     check_invariants (list->root, NULL);
 }
 
+#if (__GNUC__ == 4 && 6 <= __GNUC_MINOR__) || 4 < __GNUC__
+# pragma GCC diagnostic pop
+#endif
+
 const struct gl_list_implementation gl_avltree_list_implementation =
   {
     gl_tree_nx_create_empty,
diff --git a/tests/test-avltree_list.c b/tests/test-avltree_list.c
index 1c0331a..c877c09 100644
--- a/tests/test-avltree_list.c
+++ b/tests/test-avltree_list.c
@@ -25,8 +25,6 @@
 #include "progname.h"
 #include "macros.h"
 
-extern void gl_avltree_list_check_invariants (gl_list_t list);
-
 static const char *objects[15] =
   {
     "a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m", "n", "o"
-- 
2.1.0