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Re: [PATCH 1/2] Don't warn function alignment if warn_if_not_aligned_p is true

On 08/21/2017 06:21 AM, H.J. Lu wrote:
When warn_if_not_aligned_p is true, a warning will be issued on function
declaration later.  There is no need to warn function alignment when
warn_if_not_aligned_p is true.

OK for trunk?

	* c-attribs.c (common_handle_aligned_attribute): Don't warn
	function alignment if warn_if_not_aligned_p is true.
 gcc/c-family/c-attribs.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/gcc/c-family/c-attribs.c b/gcc/c-family/c-attribs.c
index 5f79468407f..78969532543 100644
--- a/gcc/c-family/c-attribs.c
+++ b/gcc/c-family/c-attribs.c
@@ -1754,9 +1754,12 @@ common_handle_aligned_attribute (tree *node, tree args, int flags,
       This formally comes from the c++11 specification but we are
       doing it for the GNU attribute syntax as well.  */
     *no_add_attrs = true;
-  else if (TREE_CODE (decl) == FUNCTION_DECL
+  else if (!warn_if_not_aligned_p
+	   && TREE_CODE (decl) == FUNCTION_DECL
 	   && DECL_ALIGN (decl) > (1U << i) * BITS_PER_UNIT)
+      /* Don't warn function alignment here if warn_if_not_aligned_p is
+	 true.  It will be warned later.  */
       if (DECL_USER_ALIGN (decl))
 	error ("alignment for %q+D was previously specified as %d "
 	       "and may not be decreased", decl,

Your comment refers to warning but the code here uses error().
That raises two questions for me: a) will the later diagnostic
really be a warning or an error, and if a warning, under what
option will it be issued? and b) why is an error appropriate
here when a warning is appropriate elsewhere (most other
attribute conflicts are at present diagnosed with -Wattributes).

My main motivation for these questions is to understand the
rationale for warning for vs rejecting conflicts so that
a consistent general solution can be implemented for all
attributes (i.e., along the lines of my patch here:


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