On Tue, Apr 18, 2023 at 07:35:44AM -0600, Jeff Law wrote:
>
>
> On 4/18/23 03:06, Jakub Jelinek wrote:
> > Hi!
> >
> > While we've agreed this is not the right fix for the PR109040 bug,
> > the patch clearly improves generated code (at least on the testcase from the
> > PR), so I'd like to propose this as optimization heuristics improvement
> > for GCC 14.
> >
> > Ok for trunk?
> >
> > 2023-04-18 Jakub Jelinek <ja...@redhat.com>
> >
> > PR target/109040
> > * dse.cc (replace_read): If read_reg is a SUBREG of a word mode
> > REG, for WORD_REGISTER_OPERATIONS copy SUBREG_REG of it into
> > a new REG rather than the SUBREG.
> Doesn't the new behavior need to be conditional on can_create_pseudos_p
> since the call to copy_to_mode_reg can ultimately call gen_reg_rtx.
Why? copy_to_mode_reg was used before as well and it unconditionally does
rtx temp = gen_reg_rtx (mode);
as the first thing in the function.
So, if replace_read is used during post-RA DSE instance, it would already
ICE before.
All the patch changes is it will in some cases do copy_to_mode_reg
on SUBREG_REG and create a new SUBREG instead of doing copy_to_mode_reg
on the original.
I think
/* No place to keep the value after ra. */
&& !reload_completed
in record_store prevents recording the rhs values in DSE2 and so
replace_read should never trigger there.
Jakub
