"Dmitry" <mittie@xxxxxxx> writes:
> Yes but as you've said, it's a carry flag setter, but how could this example be transformed if I need to store not only carry flag but also for example a zero flag? Could you write such an example, please?
You do exactly the same thing, but you define a mode which means that
both the zero flag and the carry flag are valid. Then your test can
look for that mode in the flags register. Don't look at this insn in
isolation--look at it in conjunction with some conditional insn that
tests the value in the flags register. The conditional test is going to
be testing the result of the plus operation compared with zero, in some
mode.
The i386 backend uses CCmode to represent all the flags, and uses the
other modes to represent subsets of the flags.
Ian
> --- ÐÑÑÐÐÐÐÐ ÑÐÐÐÑÐÐÐÐ ---
> ÐÑ ÐÐÐÐ: "Ian Lance Taylor" <iant@xxxxxxxxxx>
> ÐÐÐÑ: "Dmitry" <mittie@xxxxxxx>
> ÐÐÑÐ: 5 ÐÐÑ 2011, 17:41:38
> ÐÐÐÐ: Re: Back end question.
>
>
>
>> "Dmitry" <mittie@xxxxxxx> writes:
>>
>> > Ok but if people do not set each status bit individually, how do they set several not related bits in one CC mode and in one set rtx?
>>
>> They represent the collection of bits as a mode, as you've been
>> discussing.
>>
>> E.g., from config/i386/i386.md
>>
>> (define_insn "*<plusminus_insn><mode>3_cc_overflow"
>> [(set (reg:CCC FLAGS_REG)
>> (compare:CCC
>> (plusminus:SWI
>> (match_operand:SWI 1 "nonimmediate_operand" "<comm>0,0")
>> (match_operand:SWI 2 "<general_operand>" "<r><i>,<r>m"))
>> (match_dup 1)))
>> (set (match_operand:SWI 0 "nonimmediate_operand" "=<r>m,<r>")
>> (plusminus:SWI (match_dup 1) (match_dup 2)))]
>> "ix86_binary_operator_ok (<CODE>, <MODE>mode, operands)"
>> "<plusminus_mnemonic>{<imodesuffix>}\t{%2, %0|%0, %2}"
>> [(set_attr "type" "alu")
>> (set_attr "mode" "<MODE>")])
>>
>>
>> Here the CCC mode (defined in i386-modes.def) means that the carry flag
>> is valid.
>>
>> Ian
>>
>>
