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 <seg...@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