[LLVMdev] selecting ISD node - help

[DaAn]

Hi Tim,


Tim Northover-2 wrote
> The code used for DIV is around X86ISelDAGToDAG.cpp:2415, but from a
> glance the key points seem to be:
> 1. use the second result of getCopyToReg (i.e. SDValue(setIdNode, 1))
> in the RDMSR node.
> 2. Give your RDMSR node type MVT::Glue instead of MVT::Other

I tried doing what you said, and the DAG looks like how I think it supposed
to look like (attached the picture below). 

	  if(Subtarget->is64Bit())
	  {
		  idReg = X86::RCX;
		  resultReg = MF.addLiveIn(X86::RAX, &X86::GR64RegClass);
	  }
	  else
	  {
		  idReg = X86::ECX;
		  resultReg = MF.addLiveIn(X86::EAX, &X86::GR32RegClass);
	  }

	  idRegValue = CurDAG->getRegister(idReg, resultType);

	  SDValue setIdNode = CurDAG->getCopyToReg(CurDAG->getEntryNode(), dl,
idRegValue, id, SDValue());
	  SDValue rdmsrNode = SDValue(CurDAG->getMachineNode(X86::RDMSR, dl,
MVT::Glue, setIdNode.getValue(1)), 0);
	  SDValue resultNode = CurDAG->getCopyFromReg(CurDAG->getEntryNode(), dl,
X86::EAX, MVT::i32, rdmsrNode);
	  
	  return resultNode.getNode();

but I've a couple of problems:

getCopyToReg doesn't show on the final assembly
	  __Z5test2v proc near
	  push    ebp
	  mov     ebp, esp
	  rdmsr
	  pop     ebp
	  retn
	  __Z5test2v endp

When I add rdmsr + rdmsr, first the rdmsr calls are made and only then he
adds eax, eax.
	  __Z5test3v proc near
	  push    ebp
	  mov     ebp, esp
	  rdmsr
	  rdmsr
	  add     eax, eax
	  pop     ebp
	  retn
	  __Z5test3v endp
Maybe it's because I use MF.addLiveIn but when I tried using X86::EAX it
failed with the message: 
	  # Machine code for function _Z5test2v: Post SSA

	  BB#0: derived from LLVM BB %entry
	          %vreg2<def> = COPY %EAX; GR32:%vreg2
 	         RDMSR
 	         %EAX<def> = COPY %vreg2; GR32:%vreg2
  	        RET %EAX<kill>

	  # End machine code for function _Z5test2v.

	  *** Bad machine code: Using an undefined physical register ***
	  - function:    _Z5test2v
	  - basic block: BB#0 entry (0x2ff8228)
	  - instruction: %vreg2<def> = COPY %EAX; GR32:%vreg2
	  - operand 1:   %EAX
	  LLVM ERROR: Found 1 machine code errors.
	  Stack dump:
	  0.      Program arguments:
C:\Users\DaAn\Documents\Projects\llvm-3.4\build\bin\Debug\llc.exe
-filetype=obj -view-sched-dags
C:\Users\DaAn\Documents\Projects\llvm-3.4\build\bin\Debug\test.bc
	  1.      Running pass 'Function Pass Manager' on module
'C:\Users\DaAn\Documents\Projects\llvm-3.4\build\bin\Debug\test.bc'.
	  2.      Running pass 'Greedy Register Allocator' on function '@_Z5test2v'

<http://llvm.1065342.n5.nabble.com/file/n65821/dag._Z5test2v-4ac530.png> 
<http://llvm.1065342.n5.nabble.com/file/n65821/dag._Z5test3v-e16193.png> 



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