[LLVMdev] A few questions from a newbie

[Peter Bacon]

Hi Jacob, thank you for your reply.

Your suggestion works! But instead of using the Pat<>, I am using

def MOVE_ADDR : MYInst<(outs Int32Regs:$dst), (ins i32mem:$a),
                     "move $dst, $a;",
                     [(set Int32Regs:$dst, (Wrapper tglobaladdr:$a))]>;


I don't quite understand what the semantics of Pat in general. Could you
please explain what

def : Pat<(BfinWrapper (i32 tglobaladdr:$addr)),
          (LOAD32imm tglobaladdr:$addr)>;

means?

And I totally agree it would be better if someone can explain why the
Wrapper is needed here.

Regards,

P.B.


On Sun, Apr 19, 2009 at 11:01 PM, Jakob Stoklund Olesen <stoklund at 2pi.dk>wrote:

>
> On 20/04/2009, at 07.35, Peter Bacon wrote:
>
> > Hello, I am learning to write a new backend for LLVM and have a few
> > simple questions.
>
> Hi Peter,
>
> I am a newbie too, but I have recently dealt with the same issues.
>
> > 1) What are the differences between 'constant' and 'targetconstant',
> > 'globaladdress' and 'targetglobaladdress'? It is not clear from the
> > document when and which should be used.
>
> The target* variants are 'done' and will not be changed further by the
> instruction selection. After instruction selection, everything should
> be converted to the target* variants.
>
> > 2) On the processor I am working on, there is a 'move reg, mem_addr'
> > instruction.
> >
> > When I try to match it using the pattern  [(set Int32Regs::reg,
> > tglobaladdr::mem_addr)]. the code generated by tblgen cannot be
> > compiled because there will be a switch statement that contains two
> > cases for the 'tglobaladdr', one is hard-coded in by tblgen and the
> > other is generated by tbglen following the pattern I specified. The
> > compilation fails because of the two duplicated and conflicting cases.
>
> This happened to me too. I stole a solution from the other targets -
> create a wrapper node:
>
> def BfinWrapper: SDNode<"BfinISD::Wrapper", SDTIntUnaryOp>;
>
> Then custom lower ISD::GlobalAddress, converting it to a wrapped
> TargetGlobalAddress:
>
> SDValue
> BlackfinTargetLowering::LowerGlobalAddress(SDValue Op, SelectionDAG
> &DAG)
> {
>   DebugLoc DL = Op.getDebugLoc();
>   GlobalValue *GV = cast<GlobalAddressSDNode>(Op)->getGlobal();
>
>   Op = DAG.getTargetGlobalAddress(GV, MVT::i32);
>   return DAG.getNode(BfinISD::Wrapper, DL, MVT::i32, Op);
> }
>
> Now you can pattern match on the wrapper:
>
> def : Pat<(BfinWrapper (i32 tglobaladdr:$addr)),
>           (LOAD32imm tglobaladdr:$addr)>;
>
> If you think this is overly complicated, I agree.
> Does anybody know why this is necessary?
>
> /jakob
>
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20090420/7210538e/attachment.html>