[Bug c/65672] New: type attribute "aligned" can decrease alignment

[Bug c/65672] New: type attribute "aligned" can decrease alignment

[glisse at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65672

            Bug ID: 65672
           Summary: type attribute "aligned" can decrease alignment
           Product: gcc
           Version: 5.0
            Status: UNCONFIRMED
          Keywords: documentation
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: glisse at gcc dot gnu.org

https://gcc.gnu.org/onlinedocs/gcc/Type-Attributes.html states that 
"The aligned attribute can only increase the alignment"

However, on x86_64:

typedef float vec __attribute__((vector_size(16)));
typedef float vecu __attribute__((vector_size(16),aligned(8)));

alignof(vec) says 16 and alignof(vecu) says 8. And indeed,

vec f(vecu*p){
  return *p;
}

compiles to movups (while regular loads use movaps), so this behavior is
useful. Assuming it is meant to work and not just an accident, it would be nice
to document this (otherwise it is a wrong code bug).

[Bug c/65672] type attribute "aligned" can decrease alignment

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65672

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---


*** This bug has been marked as a duplicate of bug 89950 ***

[Bug c/65672] type attribute "aligned" can decrease alignment

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65672

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|DUPLICATE                   |---
             Status|RESOLVED                    |NEW

--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
actually let's reopen this one and close the other one as a dup of this one.

[Bug c/65672] type attribute "aligned" can decrease alignment

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65672

--- Comment #5 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
*** Bug 89950 has been marked as a duplicate of this bug. ***

[Bug c/65672] type attribute "aligned" can decrease alignment

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65672

--- Comment #6 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Note I see Martin has argued both ways :).

Anyways I the issue is in reconstruct_complex_type (either
cp_reconstruct_complex_type in gcc/cp/decl2.cc or reconstruct_complex_type in
gcc/tree.cc).