From: Jakub Jelinek <jakub@redhat.com>
To: Segher Boessenkool <segher@kernel.crashing.org>
Cc: gcc-patches@gcc.gnu.org
Subject: Re: [PATCH] combine: Don't create REG_UNUSED notes if the reg already died (PR99927)
Date: Sun, 18 Apr 2021 17:24:50 +0200 [thread overview]
Message-ID: <20210418152450.GY1179226@tucnak> (raw)
In-Reply-To: <b412ce8e961052e6becea3bc783a53e1d5feaa0f.1618758103.git.segher@kernel.crashing.org>
On Sun, Apr 18, 2021 at 03:03:07PM +0000, Segher Boessenkool wrote:
> If the register named in an existing REG_UNUSED note dies somewhere
> between where the note used to be and I3, we should just drop it.
>
> 2021-04-21 Segher Boessenkool <segher@kernel.crashing.org>
>
> PR rtl-optimization/99927
> * combine.c (distribute_notes) [REG_UNUSED]: If the register already
> is dead, just drop it.
> ---
>
> Committed to trunk. This will need backports to all open branches.
Thanks for working on this. Just some nits but note that I don't know much
about the combiner...
> gcc/combine.c | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/gcc/combine.c b/gcc/combine.c
> index 9063a07bd009..62bf4aeaabae 100644
> --- a/gcc/combine.c
> +++ b/gcc/combine.c
> @@ -14366,6 +14366,11 @@ distribute_notes (rtx notes, rtx_insn *from_insn, rtx_insn *i3, rtx_insn *i2,
> we keep notes from i2 or i1 if they will turn into REG_DEAD
> notes. */
>
> + /* If this register is set or clobbered between FROM_INSN and I3,
> + we should not create a note for it. */
> + if (reg_set_between_p (XEXP (note, 0), from_insn, i3))
> + break;
> +
> /* If this register is set or clobbered in I3, put the note there
> unless there is one already. */
> if (reg_set_p (XEXP (note, 0), PATTERN (i3)))
Doesn't this make the
if (from_insn != i3 && i2 && INSN_P (i2)
&& reg_referenced_p (XEXP (note, 0), PATTERN (i2)))
{
if (!reg_set_p (XEXP (note, 0), PATTERN (i2)))
PUT_REG_NOTE_KIND (note, REG_DEAD);
if (! (REG_P (XEXP (note, 0))
? find_regno_note (i2, REG_NOTE_KIND (note),
REGNO (XEXP (note, 0)))
: find_reg_note (i2, REG_NOTE_KIND (note),
XEXP (note, 0))))
place = i2;
}
case unreachable (the reg_set_p stuff at least; I mean if
reg_set_p is true on i2 and i2 is in between from_ins and i3, then
reg_set_between_p will surely be true)?
And, shouldn't the
record_value_for_reg (XEXP (note, 0), NULL, NULL_RTX);
be called in some cases?
To me it would make more sense to add the if (reg_set_between_p (...)) break;
to the individual cases later, so before
if (! (REG_P (XEXP (note, 0))
? find_regno_note (i3, REG_UNUSED, REGNO (XEXP (note, 0)))
: find_reg_note (i3, REG_UNUSED, XEXP (note, 0))))
place = i3;
and before
PUT_REG_NOTE_KIND (note, REG_DEAD);
place = i3;
and into the
if (from_insn != i3 && i2 && INSN_P (i2)
&& reg_referenced_p (XEXP (note, 0), PATTERN (i2)))
but there just checking if it isn't set in between from_insn and i2
Jakub
next prev parent reply other threads:[~2021-04-18 15:24 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-18 15:03 Segher Boessenkool
2021-04-18 15:24 ` Jakub Jelinek [this message]
2021-04-18 17:03 ` Segher Boessenkool
2021-04-19 17:59 ` Segher Boessenkool
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