Henri Cloetens <henri.cloetens@xxxxxxxxxx> writes:
> Hello Segher, all,
>
> - It is indeed true subreg only works on bytes.
> - So, I changed the declaration:
> a. I declared all 12 condition code bits as BYTES (QI)
> b. I split it in 4 CC fields (cfr below), and declared each of these
> as SI.
> - Then, the compare addresses the CC field in SI mode, the branch in QI
> mode, and all goes well. I mean, it does not matter if I declare SI
> or BI, because
> the compare instruction only writes 0 or 1, and the branch
> instruction tests only
> for 0 or 1.
> - With all goes well, I mean, gcc-9.2.0 correctly writes the CC field,
> and then correctly
> picks the correct subreg for the branch.
> - BUT ... the test still fails. I refer here to "emit-rtl.c", function
> validate_subreg() in gcc-9.2.0
> the test on line 1024. It is commented why it fails :
> OSIZE is not a multiple of REGSIZE. The intend here is to have
> REGSIZE as byte, but the
> routine calculates REGSIZE as REGMODE_NATURAL_SIZE(imode).
> I do not understand this. I mean, imode is SImode, but in the backend
> description, it is
> described that 4 registers of the CC field are necessary to hold an
> operand of type SImode.
> - Is this a bug ?, or, what did I wrong ?.
Sorry if this was already suggested downthread (didn't see it), but:
what's UNITS_PER_WORD on your target? Normally it's not possible
to split hard registers into smaller chunks than that and still
refer to each chunk using a subreg. So under the normal scheme,
each individually-addressable register would need to be word_mode
or bigger. But that of course leaves the composite registers being
ridiculously big.
Another unfortunate assumption from the old days is:
case MODE_CC:
/* Again, nothing more need be said. For historical reasons,
the size of a CC mode is four units. */
validate_mode (m, UNSET, UNSET, UNSET, UNSET, UNSET);
m->bytesize = 4;
m->ncomponents = 1;
m->component = 0;
break;
(genmodes.c). Nothing much should depend on this behaviour though.
So one option might be to:
- Add a new genmodes.c macro (e.g. CC_MODE_WITH_SIZE) that creates a CC
mode with a specific byte size.
- Create a 1-byte CC mode for the individual registers.
- Create a larger CC modes for the composite forms.
- Define REGMODE_NATURAL_SIZE to 1 for these CC modes (but leave it at
UNITS_PER_WORD for other modes.
Thanks,
Richard
