[PING 6, PATCH] PR/68089: C++-11: Ingore "alignas(0)".

Dominik Vogt vogt@linux.vnet.ibm.com
Tue Apr 12 09:04:00 GMT 2016


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?
> 
> > Also, in the test, I noticed the definition of the first struct
> > is missing the terminating semicolon.
> 
> Yeah.

> 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 <vogt@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




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