On Sun, 26 Jun 2011, Martin Jambor wrote:
> Hi,
>
> under some circumstances involving user specified alignment and/or
> packed attributes, SRA can create a misaligned MEM_REF. As the
> testcase demonstrates, it is not enough to not consider variables with
> these type attributes, mainly because we might attempt to load/store
> the scalar replacements from/to right/left sides of original aggregate
> assignments which might be misaligned.
>
> I'm wondering whether this approach isn't too heavy-handed but I have
> not been able to convince myself that anything short of this is
> sufficient, esp. in presence of the all-time-SRA-favorite type-casts,
> one-field-structures and unions. At the very least I therefore do
> this only for strict-alignment architectures, where this is actually
> an issue.
>
> I have verified the testcase fails with a "bus error" on sparc64 and
> passes when the patch is applied. I have run make -k test for c and
> c++ on sparc64-linux without any issues as well as traditional
> bootstrap and full testsuite run on x86_64-linux. OK for trunk and
> for 4.6 when unfrozen?
>
> Thanks,
>
> Martin
>
>
> 2011-06-24 Martin Jambor <[email protected]>
>
> PR tree-optimization/49094
> * tree-sra.c (potential_alignment_issues): New function.
> (build_accesses_from_assign): Use it.
>
> * testsuite/gcc.dg/tree-ssa/pr49094.c: New test.
>
>
> Index: src/gcc/tree-sra.c
> ===================================================================
> --- src.orig/gcc/tree-sra.c
> +++ src/gcc/tree-sra.c
> @@ -1023,6 +1023,33 @@ disqualify_ops_if_throwing_stmt (gimple
> return false;
> }
>
> +/* Return true iff type of EXP or any of the types it is based on are
> + user-aligned and packed. */
> +
> +static bool
> +potential_alignment_issues (tree exp)
> +{
> + if (!STRICT_ALIGNMENT)
> + return false;
> +
> + while (true)
> + {
> + tree type = TREE_TYPE (exp);
> +
> + if (TYPE_USER_ALIGN (type)
> + || TYPE_PACKED (type))
> + return true;
> +
> + if (handled_component_p (exp))
> + exp = TREE_OPERAND (exp, 0);
> + else
> + break;
> + }
I think you want something like
static bool
tree_non_mode_aligned_mem_p (tree exp)
{
enum machine_mode mode = TYPE_MODE (TREE_TYPE (exp));
unsigned int align;
if (mode == BLKmode
|| !STRICT_ALIGNMENT)
return false;
align = get_object_alignment (exp, BIGGEST_ALIGNMENT);
if (GET_MODE_ALIGNMENT (mode) > align)
return true;
return false;
}
as for STRICT_ALIGNMENT targets we assume that the loads/stores SRA
inserts have the alignment of the mode.
Richard.
> + return false;
> +}
> +
> +
> /* Scan expressions occuring in STMT, create access structures for all
> accesses
> to candidates for scalarization and remove those candidates which occur in
> statements or expressions that prevent them from being split apart.
> Return
> @@ -1047,7 +1074,10 @@ build_accesses_from_assign (gimple stmt)
> lacc = build_access_from_expr_1 (lhs, stmt, true);
>
> if (lacc)
> - lacc->grp_assignment_write = 1;
> + {
> + lacc->grp_assignment_write = 1;
> + lacc->grp_unscalarizable_region |= potential_alignment_issues (rhs);
> + }
>
> if (racc)
> {
> @@ -1055,6 +1085,7 @@ build_accesses_from_assign (gimple stmt)
> if (should_scalarize_away_bitmap && !gimple_has_volatile_ops (stmt)
> && !is_gimple_reg_type (racc->type))
> bitmap_set_bit (should_scalarize_away_bitmap, DECL_UID (racc->base));
> + racc->grp_unscalarizable_region |= potential_alignment_issues (lhs);
> }
>
> if (lacc && racc
> Index: src/gcc/testsuite/gcc.dg/tree-ssa/pr49094.c
> ===================================================================
> --- /dev/null
> +++ src/gcc/testsuite/gcc.dg/tree-ssa/pr49094.c
> @@ -0,0 +1,38 @@
> +/* { dg-do run } */
> +/* { dg-options "-O" } */
> +
> +struct in_addr {
> + unsigned int s_addr;
> +};
> +
> +struct ip {
> + unsigned char ip_p;
> + unsigned short ip_sum;
> + struct in_addr ip_src,ip_dst;
> +} __attribute__ ((aligned(1), packed));
> +
> +struct ip ip_fw_fwd_addr;
> +
> +int test_alignment( char *m )
> +{
> + struct ip *ip = (struct ip *) m;
> + struct in_addr pkt_dst;
> + pkt_dst = ip->ip_dst ;
> + if( pkt_dst.s_addr == 0 )
> + return 1;
> + else
> + return 0;
> +}
> +
> +int __attribute__ ((noinline, noclone))
> +intermediary (char *p)
> +{
> + return test_alignment (p);
> +}
> +
> +int
> +main (int argc, char *argv[])
> +{
> + ip_fw_fwd_addr.ip_dst.s_addr = 1;
> + return intermediary ((void *) &ip_fw_fwd_addr);
> +}
>
>
--
Richard Guenther <[email protected]>
Novell / SUSE Labs
SUSE LINUX Products GmbH - Nuernberg - AG Nuernberg - HRB 16746
GF: Jeff Hawn, Jennifer Guild, Felix Imendörffer
