> On Jun 8, 2024, at 1:12 PM, Jeff Law <jeffreya...@gmail.com> wrote:
>
>
>
> On 6/8/24 10:45 AM, Paul Koning via Gcc wrote:
>>> On Jun 8, 2024, at 5:32 AM, Mikael Pettersson via Gcc <gcc@gcc.gnu.org>
>>> wrote:
>>>
>>> On Thu, Jun 6, 2024 at 8:59 PM Dimitar Dimitrov <dimi...@dinux.eu> wrote:
>>>> Have you tried defining TARGET_LEGITIMIZE_ADDRESS for your target? From
>>>> a quick search I see that the iq2000 and rx backends are rewriting some
>>>> PLUS expression addresses with insn sequence to calculate the address.
>>>
>>> I have partial success.
>>>
>>> The key was to define both TARGET_LEGITIMATE_ADDRESS_P and an
>>> addptr<Pmode>3 insn.
>>>
>>> I had tried TARGET_LEGITIMATE_ADDRESS_P before, together with various
>>> combinations of TARGET_LEGITIMIZE_ADDRESS and
>>> LEGITIMIZE_RELOAD_ADDRESS, but they all threw gcc into reload loops.
>>>
>>> My add<Pmode>3 insn clobbers the CC register. The docs say to define
>>> addptr<Pmode>3 in this case, and that eliminated the reload loops.
>>>
>>> The issue now is that the machine cannot perform an add without
>>> clobbering the CC register, so I'll have to hide that somehow. When
>>> emitting the asm code, can one check if the CC register is LIVE-OUT
>>> from the insn? If it isn't I shouldn't have to generate code to
>>> preserve it.
>>>
>>> /Mikael
>> I'm not sure why add that clobbers CC requires anything special (other than
>> of course showing the CC register as clobbered in the definition). pdp11 is
>> another target that only has a CC-clobbering add. Admittedly, it does have
>> register+offset addressing modes, but still the reload machinery deals just
>> fine with add operations like that.
> If he's got a CC register exposed prior to LRA and LRA needs to insert any
> code, that inserted code may clobber the CC state. This is discussed in the
> reload-to-LRA transition wiki page.
>
> jeff
I remember working through all that in the CC0 to CCmode transition, though I
didn't notice any new issues with LRA (in pdp11, LRA conversion simply amounted
to turning it on). The CC0 conversion documentation, as I recall, speaks of
two flavors of targets, and two different ways of managing CC in the MD file.
PDP11 is the type of target where all ALU operations update CC, so in
particular there is no way to do address arithmetic beyond what the addressing
modes do, without affecting CC. The style of CC description I used given that
guidance works just fine.
paul
