Hi!
On Wed, Nov 01, 2017 at 04:35:52PM +0000, Segher Boessenkool wrote:
> When we have a REG_DEAD note for a reg that is set in the new I2, we
> drop the note on the floor (we cannot find whether to place it on I2
> or on I3). But the code I added to do this has a bug and does not
> always actually drop it. This patch fixes it.
>
> But that on its own is too pessimistic, it turns out, and we generate
> worse code. One case where we do know where to place the note is if
> it came from I3 (it should go to I3 again). Doing this fixes all of
> the regressions.
>
> Tested on an aarch64 cross-compiler with the PR82683 test; tested on
> powerpc64-linux {-m32,-m64}. Committing to trunk, will backport later.
I now backported this to 7 and 6.
Segher
> 2017-11-01 Segher Boessenkool <seg...@kernel.crashing.org>
>
> PR rtl-optimization/64682
> PR rtl-optimization/69567
> PR rtl-optimization/69737
> PR rtl-optimization/82683
> * combine.c (distribute_notes) <REG_DEAD>: If the new I2 sets the same
> register mentioned in the note, drop the note, unless it came from I3,
> in which case it should go to I3 again.
>
> ---
> gcc/combine.c | 16 +++++++++++-----
> 1 file changed, 11 insertions(+), 5 deletions(-)
>
> diff --git a/gcc/combine.c b/gcc/combine.c
> index 4fba2c1..5782013 100644
> --- a/gcc/combine.c
> +++ b/gcc/combine.c
> @@ -14388,6 +14388,17 @@ distribute_notes (rtx notes, rtx_insn *from_insn,
> rtx_insn *i3, rtx_insn *i2,
> && CALL_P (from_insn)
> && find_reg_fusage (from_insn, USE, XEXP (note, 0)))
> place = from_insn;
> + else if (i2 && reg_set_p (XEXP (note, 0), PATTERN (i2)))
> + {
> + /* If the new I2 sets the same register that is marked
> + dead in the note, we do not in general know where to
> + put the note. One important case we _can_ handle is
> + when the note comes from I3. */
> + if (from_insn == i3)
> + place = i3;
> + else
> + break;
> + }
> else if (reg_referenced_p (XEXP (note, 0), PATTERN (i3)))
> place = i3;
> else if (i2 != 0 && next_nonnote_nondebug_insn (i2) == i3
> @@ -14401,11 +14412,6 @@ distribute_notes (rtx notes, rtx_insn *from_insn,
> rtx_insn *i3, rtx_insn *i2,
> || rtx_equal_p (XEXP (note, 0), elim_i0))
> break;
> tem_insn = i3;
> - /* If the new I2 sets the same register that is marked dead
> - in the note, we do not know where to put the note.
> - Give up. */
> - if (i2 != 0 && reg_set_p (XEXP (note, 0), PATTERN (i2)))
> - break;
> }
>
> if (place == 0)
> --
> 1.8.3.1
