> On Oct 14, 2022, at 12:18 PM, Segher Boessenkool <seg...@kernel.crashing.org>
> wrote:
>
> On Fri, Oct 14, 2022 at 12:36:47AM +0000, Koning, Paul wrote:
>> I guess I'll have to look harder to see if it's possible to make LRA handle
>> CISC addressing modes like memory indirect, autoincrement, autodecrement,
>> and others that the old reload handles at least somewhat. Ideally LRA
>> should do a better job; right now I believe it doesn't really do these
>> things at all. Targets like pdp11 and vax would like these.
>
> So what does it do now? Break every more complex addressing mode apart
> again? Or ICE? Or something in between?
The former. LRA does handle some cases but not all that the target permits and
not as many as the old reload.
Example:
unsigned int cksum (unsigned int *buf, unsigned int len)
{
unsigned int ret = 0;
do {
ret += *buf++;
} while (--len != 0);
return ret;
}
The loop looks like this:
L_2:
add (r2)+,r0
sob r1,L_2
which is what I would expect. Now throw in an indirection:
Old reload produces this loop:
L_2:
add @(r2)+,r0
sob r1,L_2
while LRA doesn't understand it can use the autoincrement indirect mode:
L_2:
mov (r2)+,r3
add (r3),r0
sob r1,L_2
This is from a GCC 13.0 test build of last June, with -O2 -m45, with and
without -mlra.
paul
