On 28/06/12 10:03, Carrot Wei wrote:
> Hi Ramana
>
> Thanks for the review, please see my inlined comments.
>
> On Thu, Jun 28, 2012 at 12:02 AM, Ramana Radhakrishnan
> <ramana.radhakrish...@linaro.org> wrote:
>>
>> On 8 June 2012 10:12, Carrot Wei <car...@google.com> wrote:
>>> Hi
>>>
>>> In rtl expression, substract a constant c is expressed as add a value -c,
>>> so it
>>> is alse processed by adddi3, and I extend it more to handle a subtraction of
>>> 64bit constant. I created an insn pattern arm_subdi3_immediate to
>>> specifically
>>> represent substraction with 64bit constant while continue keeping the add
>>> rtl
>>> expression.
>>>
>>
>> Sorry about the time it has taken to review this patch -Thanks for
>> tackling this but I'm not convinced that this patch is correct and
>> definitely can be more efficient.
>>
>> The range of valid 64 bit constants allowed would be in my opinion are
>> the following- obtained by dividing the 64 bit constant into 2 32 bit
>> halves (upper32 and lower32 referred to as upper and lower below)
>>
>> arm_not_operand (upper) && arm_add_operand (lower) which boils down
>> to the valid combination of
>>
>> adds lo : adc hi - both positive constants.
>> adds lo ; sbc hi - lower positive, upper negative
> I assume you mean "sbc -hi" or "sbc abs(hi)", similar for following
> instructions
>
No, it's sbc ~hi -- bitwise inversion
It all falls out from the specification, where
adc == X + Y + C
and
sbc == X + ~Y + C.
Hence the need to use arm_not_operand.
R.
