On Mon, Oct 29, 2012 at 3:44 PM, H.J. Lu <hjl.to...@gmail.com> wrote:
> On Mon, Oct 29, 2012 at 8:15 AM, Richard Sandiford
> <rdsandif...@googlemail.com> wrote:
>> "H.J. Lu" <hjl.to...@gmail.com> writes:
>>> Hi,
>>>
>>> This patch changes get_elimination to check register number instead of
>>> RTX. Tested on Linux/x32 with -maddress-mode=long. OK to install?
>>
>> FWIW, this doesn't sound right to me, at least not without more
>> justification.
>> The idea is that things like frame_pointer_rtx are supposed to be unique,
>> so the original code:
>>
>>> if ((ep = elimination_map[hard_regno]) != NULL)
>>> - return ep->from_rtx != reg ? NULL : ep;
>>> from != hard_regno ? NULL : ep;
>>
>> ought to be correct in itself. reload did the same thing:
>>
>> for (ep = reg_eliminate; ep < ®_eliminate[NUM_ELIMINABLE_REGS];
>> ep++)
>> if (ep->from_rtx == x && ep->can_eliminate)
>> return plus_constant (Pmode, ep->to_rtx, ep->previous_offset);
>>
>> It sounds on the face of it like the bug is elsewhere.
>>
>
> LRA has
>
> if (REG_P (reg) && (ep = get_elimination (reg)) != NULL)
> {
> rtx to_rtx = replace_p ? ep->to_rtx : ep->from_rtx;
>
> if (! replace_p)
> {
> offset += (ep->offset - ep->previous_offset);
> offset = trunc_int_for_mode (offset, GET_MODE (plus_cst_src));
> }
>
> if (GET_CODE (XEXP (plus_cst_src, 0)) == SUBREG)
> to_rtx = gen_lowpart (GET_MODE (XEXP (plus_cst_src, 0)), to_rtx);
>
> Reload has
>
> rtx to_rtx = ep->to_rtx;
> offset += ep->offset;
> offset = trunc_int_for_mode (offset, GET_MODE (plus_cst_src));
>
> if (GET_CODE (XEXP (plus_cst_src, 0)) == SUBREG)
> to_rtx = gen_lowpart (GET_MODE (XEXP (plus_cst_src, 0)),
> to_rtx);
>
> (gdb) call debug_rtx (ep->to_rtx)
> (reg/f:DI 7 sp)
> (gdb) call debug_rtx (ep->from_rtx)
> (reg/f:DI 16 argp)
> (gdb)
>
> gen_lowpart returns (reg/f:DI 7 sp) for reload and (reg:SI 16 argp)
> for LRA. They are caused by
>
> if (FRAME_POINTER_REGNUM != ARG_POINTER_REGNUM
> /* We should convert arg register in LRA after the elimination
> if it is possible. */
> && xregno == ARG_POINTER_REGNUM
> && ! lra_in_progress)
> return -1;
>
> It doesn't work in this case.
>
This testcase shows that LRA can't convert arg register after
the elimination.
--
H.J.
