[llvm-commits] [llvm] r140319 - /llvm/trunk/lib/Target/Mips/MipsRegisterInfo.td

[Akira Hatanaka]

Okay, I will create two register files and two sets of instructions.

Thank you for your comments.

On Thu, Sep 22, 2011 at 3:42 PM, Bruno Cardoso Lopes
<bruno.cardoso at gmail.com> wrote:
> On Thu, Sep 22, 2011 at 3:35 PM, Jakob Stoklund Olesen <stoklund at 2pi.dk> wrote:
>>
>> On Sep 22, 2011, at 3:10 PM, Akira Hatanaka wrote:
>>
>> > Mips64 and Mips32 have the same set of floating point instructions but
>> > the organization of the floating point register file is different:
>> > Mips64's register file consists of 32 x 64-bit registers, whilie
>> > Mips32's register file consists of 16 x 64-bit registers (each 64-bit
>> > register consist of a pair of single precision registers).
>>
>> OK, so the same set of instructions use different register banks depending on the target configuration.
>>
>> > I was considering making only one out of the two sets of registers
>> > available for the register allocator to pick at any time by changing
>> > the set of reserved registers. For example, if the target is Mips32,
>> > D*_64 registers are reserved, while D* registers are available.
>> >
>> > Does this make sense?
>>
>> I think I understand now.
>>
>> I think your scheme could work, but it is quite confusing to have D1_64 and D1 in the same register class. It would be better to create two separate register classes for f64. One containing D*_64, and one containing D*.
>>
>> That would require duplicate f64 instruction definitions for 64-bit and 32-bit mode. This is what you want to avoid, right?
>>
>> An alternative is to use the TRI::getPointerRegClass() hook.  It should really be called getDynamicRegClass(), it is not just for pointers. You can:
>>
>>  def f64_rc : PointerLikeRegClass<1>;
>>
>> Then use f64_rc instead of AFGR64 in your f64 FPU instruction definitions, and add a TRI::getPointerRegClass() hook.
>>
>>
>> If you are planning to add MC support, you should know that the MC layer doesn't understand dynamic register classes.  In that case, I think it would be better to duplicate the f64 instructions for 64-bit and 32-bit mode.
>
> +1 for having 2 different reg classes and duplicating the instructions!
>
>
> --
> Bruno Cardoso Lopes
> http://www.brunocardoso.cc
>