"Moore, Catherine" <[email protected]> writes:
>> >> -----Original Message-----
>> >> From: Richard Sandiford [mailto:[email protected]]
>> >> Sent: Tuesday, March 05, 2013 4:06 PM
>> >> To: Moore, Catherine
>> >> Cc: [email protected]; Rozycki, Maciej
>> >> Subject: Re: FW: [PATCH] [MIPS] microMIPS gcc support:
>> >>
>> >> We have a few internal-only undocumented constraints that aren't used
>> >> much, so we should be able to move them to the "Y" space instead.
>> >> The patch below does this for "T" and "U". Then we could use "U" for
>> >> new, longer constraints.
>> >>
>> >>
>> >> U<type><factor><bits>
>> >>
>> >> where <type> is:
>> >>
>> >> s for signed
>> >> u for unsigned
>> >> d for decremented unsigned (-1 ... N)
>> >> i for incremented unsigned (1 ... N)
>> >>
>> >> where <factor> is:
>> >>
>> >> b for "byte" (*1)
>> >> h for "halfwords" (*2)
>> >> w for "words" (*4)
>> >> d for "doublewords" (*8) -- useful for 64-bit MIPS16 but probably not
>> >> needed for 32-bit microMIPS
>> >>
>> >> and where <bits> is the number of bits. <type> and <factor> could be
>> >> replaced with an ad-hoc two-letter combination for special cases.
>> >> E.g. "Uas9" ("add stack") for ADDISUP.
>> >>
>> >> Just a suggestion though. I'm not saying these names are totally
>> >> intuitive or anything, but they should at least be better than arbitrary
>> letters.
>> >>
>> >> Also, <bits> could be two digits if necessary, or we could just use hex
>> digits.
>> >
>> > I extended this proposal a bit by:
>> > 1. Adding a <type> e for encoded. The constraint will start with Ue,
>> > when the operand is an encoded value.
>> > 2. I decided to use two digits for <bits>.
>> > 3. The ad-hoc combination is used for anything else.
>>
>> First of all, thanks for coming up with a counter-suggestion. I'm hopeless
>> at
>> naming things, so I was hoping there would be at least some pushback.
>>
>> "e" for "encoded" sounds good. I'm less keen on the mixture of single- and
>> double-digit widths though (single digit for some "Ue"s, double digits for
>> other "U"s.) I think we should either:
>>
>> (a) use the same number of digits for all "U" constraints. That leaves
>> one character for the "Ue" type, which isn't as mnemonic, but is in
>> line with what we do elsewhere.
>>
>> (b) avoid digits in the "Ue" forms and just have an ad-hoc letter
>> combination.
FWIW, as far as this point goes, the patch still has "Uea4".
>> > +/* Return true if X is a legitimate address that conforms to the
>> requirements
>> > + for any of the short microMIPS LOAD or STORE instructions except LWSP
>> > + or SWSP. */
>> > +
>> > +bool
>> > +umips_address_p (rtx x, bool load, enum machine_mode mode) {
>> > +
>> > + struct mips_address_info addr;
>> > + bool ok = mips_classify_address (&addr, x, mode, false)
>> > + && addr.type == ADDRESS_REG
>> > + && M16_REG_P (REGNO (addr.reg))
>> > + && CONST_INT_P (addr.offset);
>> > +
>> > + if (!ok)
>> > + return false;
>> > +
>> > + if (mips_unsigned_immediate_p (INTVAL (addr.offset), 4, 2)
>> > + || mips_unsigned_immediate_p (INTVAL (addr.offset), 4, 1))
>> > + return true;
>> > +
>> > + if (load && IN_RANGE (INTVAL (addr.offset), -1, 14))
>> > + return true;
>> > +
>> > + if (!load && IN_RANGE (INTVAL (addr.offset), 0, 15))
>> > + return true;
>> > +
>> > + return false;
>> > +
>> > +}
>>
>> No blank lines after "{" and before "}".
>>
>> More importantly, what cases are these range tests covering?
>> Both binutils and qemu seem to think that LW and SW need offsets that
>> exactly match:
>>
>> mips_unsigned_immediate_p (INTVAL (addr.offset), 4, 2)
>>
>
> Those range tests are for the LBU16 and SB16 instructions. LBU16
> supports offsets from -1 to 14 (encodes -1 as 15) while the SB16 insn
> supports offsets from 0-15.
They need to use separate constraints in that case. The patch as written
allows -1 offsets for LW16 too. (In rare cases, offsets like -1 can be
used even with aligned word loads.)
E.g. we could have:
/* Return true if X is legitimate for accessing values of mode MODE,
if it is based on a MIPS16 register, and if the offset satisfies
OFFSET_PREDICATE. */
bool
m16_based_address_p (rtx x, enum machine_mode mode,
insn_operand_predicate_fn predicate)
{
struct mips_address_info addr;
return (mips_classify_address (&addr, x, mode, false)
&& addr.type == ADDRESS_REG
&& M16_REG_P (REGNO (addr.reg))
&& offset_predicate (addr.offset));
}
Perhaps if there are so many of these, we should define "T???" to be
a memory constraint in which the base register is an M16_REG and in
which "???" has the same format as for "U". E.g. "Tuw4" for LW and SW.
That's just a suggestion though.
Thanks,
Richard
