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Re: Using and clobbering hard regs in parallel
On Fri, Jul 20, 2001 at 11:53:04PM +0100, Joern Rennecke wrote:
> > ! This does not necessarily mean that the register @var{op} has no useful
> > ! value after this insn since it may also be an output of the insn.
> >
> > ! It does not follow that the register @var{op} has no useful value after
> > ! this insn since @var{op} is not necessarily modified by this insn.
>
> The first half of this sentence is true, but the reason stated is wrong.
> It is because @var{op} might be modified that it might contain a useful
> value. The original version had this right.
No, REG_DEAD talks about inputs only; REG_UNUSED talks about outputs only.
The reason that op might be useful is if we wish to extend the lifetime
of the original value.
r~