[LLVMdev] Can llvm support a target backend without function call ?

[Justin Holewinski]

On Thu, Sep 15, 2011 at 6:51 AM, Peng Wang <paulart.wang at gmail.com> wrote:

> Hi all,
>
> I am writing a llvm backend for a small stream processor. Because of its
> special application field, the processor does not support function. When I
> built the llvm backend for the new target, I leave the calling convention
> and frame lowering part blank. It compilered correctly, but I encountered
> execution errors, like
>
> *[xxx at localhost ex]$ llc test.ll -march=SSP -o test.s
> 0  llc       0x08f7ee49
> 1  llc       0x08f7f41a
> 2            0x003b1420 __kernel_sigreturn + 0
> 3  llc       0x08de0d52 llvm::TargetData::getAlignment(llvm::Type const*,
> bool) const + 44
> 4  llc       0x08de108a llvm::TargetData::getABITypeAlignment(llvm::Type
> const*) const + 44
> 5  llc       0x0863e289 llvm::TargetData::getTypeAllocSize(llvm::Type
> const*) const + 37
> 6  llc       0x08a707ed llvm::GetReturnInfo(llvm::Type const*, unsigned
> int, llvm::SmallVectorImpl<llvm::ISD::OutputArg>&, llvm::TargetLowering
> const&, llvm::SmallVectorImpl<unsigned long long>*) + 573
> 7  llc       0x089b59be llvm::FunctionLoweringInfo::set(llvm::Function
> const&, llvm::MachineFunction&) + 156
> 8  llc       0x08a4ec8a
> llvm::SelectionDAGISel::runOnMachineFunction(llvm::MachineFunction&) + 280
> 9  llc       0x08b7c191
> llvm::MachineFunctionPass::runOnFunction(llvm::Function&) + 89
> 10 llc       0x08eb92f1 llvm::FPPassManager::runOnFunction(llvm::Function&)
> + 315
> 11 llc       0x08eb94bb llvm::FPPassManager::runOnModule(llvm::Module&) +
> 121
> 12 llc       0x08eb8fbf llvm::MPPassManager::runOnModule(llvm::Module&) +
> 413
> 13 llc       0x08eba3b0 llvm::PassManagerImpl::run(llvm::Module&) + 124
> 14 llc       0x08eba415 llvm::PassManager::run(llvm::Module&) + 39
> 15 llc       0x0859a610 main + 2470
> 16 libc.so.6 0x0097de9c __libc_start_main + 220
> 17 llc       0x08598b61
> Stack dump:
> 0.      Program arguments: llc test.ll -march=SSP -o test.s
> 1.      Running pass 'Function Pass Manager' on module 'test.ll'.
> 2.      Running pass 'SSP DAG->DAG Pattern Instruction Selection' on
> function '@add'
> Segmentation fault
> *
>

This error seems to suggest there is something wrong with how you implement
your TargetData field in your TargetMachine subclass.


> **
> I think the error comes from the lacking support of function call. Should I
> write some fake codes to walk around, or I have some ways to tell LLVM that
> I do not want function call?
>

You do not need to handle call instructions, but you do need to handle
parameter passing.  A function is the basic unit of compilation in LLVM, and
a function can have zero or more parameters, and an output parameter.  You
need to specify how to lower these parameters.  If you always have a
function that takes no arguments, and returns nothing, then you can just
omit the implementation.


>
> Actually, I tried to write LLVM IR without the function form of define
> @main(..., but with function body directly. Unfortunately, everything seems
> must work with a function call, otherwise llc will not work.
>

Yes, LLVM requires all instructions to be within a block within a function.


>
>
> Best wishes!
>
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>
>


-- 

Thanks,

Justin Holewinski
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20110915/7797a8b2/attachment.html>