On Thu, 19 Jul 2012, Markus Trippelsdorf wrote:
> On 2012.07.17 at 15:10 +0200, Richard Guenther wrote:
> > Comments welcome, of course.
>
> This patch apparently miscompiles the Linux kernel, which just
> hangs during early boot:
>
> ...
> SLUB: Genslabs=15, HWalign=64, Order=0-3, MinObjects=0, CPUs=4, Nodes=1
> Hierarchical RCU implementation.
> NR_IRQS:4352 nr_irqs:712 16
> Extended CMOS year: 2000
> Console: colour VGA+ 80x25
> console [tty0] enabled
> (hang)
>
> See: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54031
The following fixes one issue (but reportedly does not fix the above
issue).
Bootstrapped and tested on x86_64-unknown-linux-gnu, applied to trunk.
Richard.
2012-07-20 Richard Guenther <rguent...@suse.de>
* builtins.c (get_object_alignment_2): Correct offset handling
when using type alignment of a MEM_REF kind base.
Index: gcc/builtins.c
===================================================================
--- gcc/builtins.c (revision 189656)
+++ gcc/builtins.c (working copy)
@@ -346,12 +346,10 @@ get_object_alignment_2 (tree exp, unsign
known_alignment
= get_pointer_alignment_1 (addr, &ptr_align, &ptr_bitpos);
- bitpos += ptr_bitpos;
align = MAX (ptr_align, align);
- if (TREE_CODE (exp) == MEM_REF
- || TREE_CODE (exp) == TARGET_MEM_REF)
- bitpos += mem_ref_offset (exp).low * BITS_PER_UNIT;
+ /* The alignment of the pointer operand in a TARGET_MEM_REF
+ has to take the variable offset parts into account. */
if (TREE_CODE (exp) == TARGET_MEM_REF)
{
if (TMR_INDEX (exp))
@@ -369,9 +367,19 @@ get_object_alignment_2 (tree exp, unsign
/* When EXP is an actual memory reference then we can use
TYPE_ALIGN of a pointer indirection to derive alignment.
Do so only if get_pointer_alignment_1 did not reveal absolute
- alignment knowledge. */
- if (!addr_p && !known_alignment)
- align = MAX (TYPE_ALIGN (TREE_TYPE (exp)), align);
+ alignment knowledge and if using that alignment would
+ improve the situation. */
+ if (!addr_p && !known_alignment
+ && TYPE_ALIGN (TREE_TYPE (exp)) > align)
+ align = TYPE_ALIGN (TREE_TYPE (exp));
+ else
+ {
+ /* Else adjust bitpos accordingly. */
+ bitpos += ptr_bitpos;
+ if (TREE_CODE (exp) == MEM_REF
+ || TREE_CODE (exp) == TARGET_MEM_REF)
+ bitpos += mem_ref_offset (exp).low * BITS_PER_UNIT;
+ }
}
else if (TREE_CODE (exp) == STRING_CST)
{
