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

[Fabian Scheler]

Hi everybody,

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}.

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?

When looking for some kind of guide, I am not looking for step-by-step
instructions to implement these issues, but a well documented back-end
would be really helpful, here. While being the most complete target,
the X86 target IMO is much too complex for that purpose.

BTW: are the testcases in test/CodeGen/Generic supposed to be
"must-haves" for all LLVM-targets or can/should I ignore some of them?

Ciao, Fabian