On Fri, Aug 22, 2014 at 2:21 PM, Ilya Enkovich <enkovich....@gmail.com> wrote:
> Hi,
>
> On Cauldron 2014 we had a couple of talks about relaxation of ebx usage in
> 32bit PIC mode. It was decided that the best approach would be to not fix
> ebx register, use speudo register for GOT base address and let allocator do
> the rest. This should be similar to how clang and icc work with GOT base
> address. I've been working for some time on such patch and now want to share
> my results.
+#define PIC_OFFSET_TABLE_REGNUM
\
+ ((TARGET_64BIT && (ix86_cmodel == CM_SMALL_PIC \
+ || TARGET_PECOFF))
\
+ || !flag_pic ? INVALID_REGNUM \
+ : X86_TUNE_RELAX_PIC_REG ? (pic_offset_table_rtx ? INVALID_REGNUM \
+ : REAL_PIC_OFFSET_TABLE_REGNUM) \
+ : reload_completed ? REGNO (pic_offset_table_rtx) \
: REAL_PIC_OFFSET_TABLE_REGNUM)
I'd like to avoid X86_TUNE_RELAX_PIC_REG and always treat EBX as an
allocatable register. This way, we can avoid all mess with implicit
xchgs in atomic_compare_and_swap<dwi>_doubleword. Also, having
allocatable EBX would allow us to introduce __builtin_cpuid builtin
and cleanup cpiud.h.
