[LLVMdev] Passing return values on the stack & storing arbitrary sized integers

[Fabian Scheler]

Hi Eli,

thank you for the information.

>> thanks to kind help of the LLVM-community I was able to bring my
>> TriCore back-end a huge step forward, however I am not done, so far. I
>> still miss the following features and maybe you could again provide me
>> some help:
>>
>> 1. Passing return values on the stack
>>
>> Describing the calling conventions in tablegen so that first registers
>> are used and to fall back to the stack if these do not suffice.
>> However, this is not enough and lowering calls and returns have to
>> reflect this, too.  Currently, most targets also do not support this
>> (there is assertion: assert(VA.isRegLoc() && "Can only return in
>> registers!")).
>>
>> How important is this feature? Is it save to ignore it? Is there some
>> guide how to implement such a hybrid passing of return values (partly
>> in registers, partly on the stack)? Currently, the TriCore back-end is
>> not able to compile functions returning e.g. {i128,i1}.
>
> This isn't very important; you won't run into it compiling C code.

OK, fine :-)

>> 2. Storing arbitrary sized integers
>>
>> The testcase "test/CodeGen/Generic/APIntLoadStore.ll" checks for
>> loading/storing e.g. i33 integers from/into global variable. The
>> questions are the same as regarding feature 1: How important is this
>> feature? Is it save to ignore it? Is there some guide how to implement
>> this?
>
> If you're using the LLVM CodeGen infrastructure and have everything
> else implemented correctly, this should be taken care of for you.  We
> have infrastructure generally referred to as "legalization" that will
> transform this into something sane for your target automatically.  I
> would suggest not ignoring this because the optimizers will
> occasionally generate unusual loads and stores.

Hm, my problem is that the TriCore does not really support i64 only
paired 32.bit registers, but I need such a register class as some
instructions require them. So, the Legalizer thinks i64-instructions
are legal and integer types above i32 are not legalized automatically.
For the most operations I used setOperationAction, setLoadExtAction,
... and now I have to handle loads/stores for i33. Maybe you can guide
me, where I shall look at inside LLVM how to do that.

Ciao, Fabian