On 10/30/2012 06:34 AM, Richard Sandiford wrote:
"H.J. Lu" <hjl.to...@gmail.com> writes:
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.
Here is a patch to remove ra_in_progress check for
ARG_POINTER_REGNUM. Tested on Linux.x86-64.
OK to install?
Thanks HJ. This looks good to me. As well as your testcase, I think
it would be dangerous to reduce this kind of subreg during non-final
elimination in cases where the argument pointer occupies more than one
hard register (like avr IIRC). We could end up with something like
ARG_POINTER_REGNUM+1, which wouldn't show up as an elimination register
during the rest of LRA.
It's important that we do get rid of the subreg during the final
elimination stage, but I think alter_subreg already handles that case.
Since this code is outside the LRA files: patch is OK if Vlad agrees.
I added this code for a reason probably to solve some target problems.
So I am not sure but let us try.
It is ok for me to commit the patch if there are no regressions on
x86/x86-64.
