> You mean this piece of nice code:
>
> /* Step 4: Close chains for registers that die here, unless
> the register is mentioned in a REG_UNUSED note. In that
> case we keep the chain open until step #7 below to ensure
> it conflicts with other output operands of this insn.
> See PR 52573. Arguably the insn should not have both
> notes; it has proven difficult to fix that without
> other undesirable side effects. */
> for (note = REG_NOTES (insn); note; note = XEXP (note, 1))
> if (REG_NOTE_KIND (note) == REG_DEAD
> && !find_regno_note (insn, REG_UNUSED, REGNO (XEXP (note,
> 0)))) {
> remove_from_hard_reg_set (&live_hard_regs,
> GET_MODE (XEXP (note, 0)),
> REGNO (XEXP (note, 0)));
> scan_rtx (insn, &XEXP (note, 0), NO_REGS, terminate_dead,
> OP_IN);
> }
>
> ?
That one is fairly recent, but I was rather referring to:
/* Process the insn, determining its effect on the def-use
chains and live hard registers. We perform the following
steps with the register references in the insn, simulating
its effect:
(1) Deal with earlyclobber operands and CLOBBERs of non-operands
by creating chains and marking hard regs live.
[...]
(7) For any REG_UNUSED, close any chains we just opened.
(7) does actually more than advertised above:
/* Step 7: Close chains for registers that were never
really used here. */
for (note = REG_NOTES (insn); note; note = XEXP (note, 1))
if (REG_NOTE_KIND (note) == REG_UNUSED)
{
remove_from_hard_reg_set (&live_hard_regs,
GET_MODE (XEXP (note, 0)),
REGNO (XEXP (note, 0)));
So (7) also closes the live ranges of hard regs opened in (1).
--
Eric Botcazou
