Re: [C/C++ PATCH] Fix merge_decls/duplicate_decls DECL_USER_ALIGN/DECL_ALIGN handling (PR c/52181)

[Richard Guenther <richard dot guenther at gmail dot com>]

On Thu, Feb 9, 2012 at 12:38 PM, Jakub Jelinek <jakub@redhat.com> wrote:
> Hi!
>
> DECL_USER_ALIGN bit used to be formerly in tree_decl_common structure
> directly, thus the memcpy merge_decls performs used to copy also the
> DECL_USER_ALIGN (newdecl) bit to DECL_USER_ALIGN (olddecl). ?But
> it has been moved into tree_base, which is not copied that way.
> This means that in C if olddecl has normal alignment and newdecl has bigger
> alignment and DECL_USER_ALIGN, it will have the bigger DECL_ALIGN (which
> is copied with memcpy), but won't have DECL_USER_ALIGN set, so when we call
> relayout_decl on it this DECL_ALIGN is reset back to the smaller value.
> Fixed by copying that bit.
>
> After writing a larger testcase for this I've noticed that the C++ FE
> has a bug in this too, but the other way around, i.e. if olddecl had
> user alignment and newdecl does not, newdecl will not inherit the user
> alignment.
>
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

I'd say this needs to be backported to at least the point where we moved
the align fields.

Richard.

> 2012-02-09 ?Jakub Jelinek ?<jakub@redhat.com>
>
> ? ? ? ?PR c/52181
> ? ? ? ?* c-decl.c (merge_decls): Copy DECL_USER_ALIGN bit from olddecl to
> ? ? ? ?newdecl.
>
> ? ? ? ?* decl.c (duplicate_decls): If olddecl has bigger DECL_ALIGN than
> ? ? ? ?newdecl, copy DECL_ALIGN to newdecl and or DECL_USER_ALIGN bits.
>
> ? ? ? ?* c-c++-common/pr52181.c: New test.
>
> --- gcc/c-decl.c.jj ? ? 2012-01-15 20:59:56.000000000 +0100
> +++ gcc/c-decl.c ? ? ? ?2012-02-09 09:33:35.955067726 +0100
> @@ -2449,6 +2449,7 @@ merge_decls (tree newdecl, tree olddecl,
> ? ? memcpy ((char *) olddecl + sizeof (struct tree_common),
> ? ? ? ? ? ?(char *) newdecl + sizeof (struct tree_common),
> ? ? ? ? ? ?sizeof (struct tree_decl_common) - sizeof (struct tree_common));
> + ? ?DECL_USER_ALIGN (olddecl) = DECL_USER_ALIGN (newdecl);
> ? ? switch (TREE_CODE (olddecl))
> ? ? ? {
> ? ? ? case FUNCTION_DECL:
> --- gcc/cp/decl.c.jj ? ?2012-01-26 09:22:19.000000000 +0100
> +++ gcc/cp/decl.c ? ? ? 2012-02-09 09:56:42.129108618 +0100
> @@ -2214,7 +2214,12 @@ duplicate_decls (tree newdecl, tree oldd
> ? ? ? SET_DECL_INIT_PRIORITY (olddecl, DECL_INIT_PRIORITY (newdecl));
> ? ? ? DECL_HAS_INIT_PRIORITY_P (olddecl) = 1;
> ? ? }
> - ?/* Likewise for DECL_USER_ALIGN and DECL_PACKED. ?*/
> + ?/* Likewise for DECL_ALIGN, DECL_USER_ALIGN and DECL_PACKED. ?*/
> + ?if (DECL_ALIGN (olddecl) > DECL_ALIGN (newdecl))
> + ? ?{
> + ? ? ?DECL_ALIGN (newdecl) = DECL_ALIGN (olddecl);
> + ? ? ?DECL_USER_ALIGN (newdecl) |= DECL_USER_ALIGN (olddecl);
> + ? ?}
> ? DECL_USER_ALIGN (olddecl) = DECL_USER_ALIGN (newdecl);
> ? if (TREE_CODE (newdecl) == FIELD_DECL)
> ? ? DECL_PACKED (olddecl) = DECL_PACKED (newdecl);
> --- gcc/testsuite/c-c++-common/pr52181.c.jj ? ? 2012-02-09 09:36:36.332028377 +0100
> +++ gcc/testsuite/c-c++-common/pr52181.c ? ? ? ?2012-02-09 09:36:04.000000000 +0100
> @@ -0,0 +1,13 @@
> +/* PR c/52181 */
> +/* { dg-do compile } */
> +
> +extern const int v1[];
> +const int __attribute__((aligned(16))) v1[] = { 1 };
> +extern const int __attribute__((aligned(16))) v2[];
> +const int v2[] = { 1 };
> +extern const int __attribute__((aligned(16))) v3[];
> +const int __attribute__((aligned(16))) v3[] = { 1 };
> +const int __attribute__((aligned(16))) v4[] = { 1 };
> +int test[(__alignof__ (v4) != __alignof__ (v1) ? ? ? ? /* { dg-bogus "is negative" } */
> + ? ? ? ?|| __alignof__ (v4) != __alignof__ (v2)
> + ? ? ? ?|| __alignof__ (v4) != __alignof__ (v3)) ? -1 : 0];
>
> ? ? ? ?Jakub