Can this be approved?
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69089
On Mon, Jan 04, 2016 at 12:33:21PM +0100, Dominik Vogt wrote:
> On Fri, Jan 01, 2016 at 05:53:08PM -0700, Martin Sebor wrote:
> > On 12/31/2015 04:50 AM, Dominik Vogt wrote:
> > >The attached patch fixes C++-11 handling of "alignas(0)" which
> > >should be ignored but currently generates an error message. A
> > >test case is included; the patch has been tested on S390x. Since
> > >it's a language issue it should be independent of the backend
> > >used.
> >
> > The patch doesn't handle value-dependent expressions(*).
>
> > It
> > seems that the problem is in handle_aligned_attribute() calling
> > check_user_alignment() with the second argument (ALLOW_ZERO)
> > set to false. Calling it with true fixes the problem and handles
> > value-dependent expressions (I haven't done any more testing beyond
> > that).
>
> Like the attached patch? (Passes the testsuite on s390x.)
>
> But wouldn't an "aligned" attribute be added, allowing the backend
> to possibly generate an error or a warning?
> gcc/c-family/ChangeLog
>
> PR/69089
> * c-common.c (handle_aligned_attribute): Allow 0 as an argument to the
> "aligned" attribute.
>
> gcc/testsuite/ChangeLog
>
> PR/69089
> * g++.dg/cpp0x/alignas5.C: New test.
> >From 2461293b9070da74950fd0ae055d1239cc69ce67 Mon Sep 17 00:00:00 2001
> From: Dominik Vogt <v...@de.ibm.com>
> Date: Wed, 30 Dec 2015 15:08:52 +0100
> Subject: [PATCH] C++-11: Ingore "alignas(0)" instead of generating an
> error message.
>
> This is required by the C++-11 standard.
> ---
> gcc/c-family/c-common.c | 2 +-
> gcc/testsuite/g++.dg/cpp0x/alignas5.C | 29 +++++++++++++++++++++++++++++
> 2 files changed, 30 insertions(+), 1 deletion(-)
> create mode 100644 gcc/testsuite/g++.dg/cpp0x/alignas5.C
>
> diff --git a/gcc/c-family/c-common.c b/gcc/c-family/c-common.c
> index 653d1dc..9eb25a9 100644
> --- a/gcc/c-family/c-common.c
> +++ b/gcc/c-family/c-common.c
> @@ -7804,7 +7804,7 @@ handle_aligned_attribute (tree *node, tree ARG_UNUSED
> (name), tree args,
> else if (TYPE_P (*node))
> type = node, is_type = 1;
>
> - if ((i = check_user_alignment (align_expr, false)) == -1
> + if ((i = check_user_alignment (align_expr, true)) == -1
> || !check_cxx_fundamental_alignment_constraints (*node, i, flags))
> *no_add_attrs = true;
> else if (is_type)
> diff --git a/gcc/testsuite/g++.dg/cpp0x/alignas5.C
> b/gcc/testsuite/g++.dg/cpp0x/alignas5.C
> new file mode 100644
> index 0000000..f3252a9
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp0x/alignas5.C
> @@ -0,0 +1,29 @@
> +// PR c++/69089
> +// { dg-do compile { target c++11 } }
> +// { dg-options "-Wno-attributes" }
> +
> +alignas (0) int valid1;
> +alignas (1 - 1) int valid2;
> +struct Tvalid
> +{
> + alignas (0) int i;
> + alignas (2 * 0) int j;
> +};
> +
> +alignas (-1) int invalid1; /* { dg-error "not a positive power of 2" } */
> +alignas (1 - 2) int invalid2; /* { dg-error "not a positive power of 2" } */
> +struct Tinvalid
> +{
> + alignas (-1) int i; /* { dg-error "not a positive power of 2" } */
> + alignas (2 * 0 - 1) int j; /* { dg-error "not a positive power of 2" } */
> +};
> +
> +template <int N> struct TNvalid1 { alignas (N) int i; };
> +TNvalid1<0> SNvalid1;
> +template <int N> struct TNvalid2 { alignas (N) int i; };
> +TNvalid2<1 - 1> SNvalid2;
> +
> +template <int N> struct TNinvalid1 { alignas (N) int i; }; /* { dg-error
> "not a positive power of 2" } */
> +TNinvalid1<-1> SNinvalid1;
> +template <int N> struct TNinvalid2 { alignas (N) int i; }; /* { dg-error
> "not a positive power of 2" } */
> +TNinvalid2<1 - 2> SNinvalid2;
> --
> 2.3.0
>
Ciao
Dominik ^_^ ^_^
--
Dominik Vogt
IBM Germany
