Question

我正在尝试在llvm backend（llc）中添加对新arch的支持。但是我发现添加一个有2个结果的新SDNode很困难。我在sparc arch中看到UMUL / SMUL有2个结果（第二个是Y）所以他们定义了：

let Defs = [Y] in {
  defm UMUL : ...
  defm SMUL : ...
}

和

let Uses = [Y], ... in
  def RDY : ...

并在select函数中看起来像：

 SDNode *Mul = CurDAG->getMachineNode(Opcode, dl, MVT::i32, MVT::Glue,
                                     MulLHS, MulRHS);
// The high part is in the Y register.
return CurDAG->SelectNodeTo(N, SP::RDY, MVT::i32, SDValue(Mul, 1));

所以他们正在使用结果1 - 我认为是Y ...

在我的情况下，我有一个影响cc位的指令。所以我试着用同样的方法。我在Xinstr中定义了：

def SUBCri : ...>{
  let Defs = [CRZ];
}

。

let Uses = [CRZ] in {
  def BRC_Z : ... (outs), (ins target:$dst),
}

并在select函数中：

    SDVTList VTs = CurDAG->getVTList(MVT::i32, MVT::Glue);
    SDNode * CondCode = CurDAG->getMachineNode(X::SUBCri, dl, VTs, ops);
    SDNode * ResNode = CurDAG->SelectNodeTo(Node, X::BRC_Z, MVT::Other, Dst,
            SDValue(CondCode, 1));

但我得到了下一个错误：

Assertion `NumMIOperands >= II.getNumOperands() && NumMIOperands <= II.getNumOperands() + II.getNumImplicitDefs() + NumImpUses && "#operands for dag node doesn't match .td file!"' failed.

所以我的问题是：

定义SDNode的正确方法是什么？
SDVTList VT是什么意思？是结果吗？（SDVTList VTs）的顺序是什么意思？
什么是OpsArray？是投入吗？插入输入的正确顺序是什么？我在＆＃34; countOperands＆＃34;他们检查功能，看看最后一个是胶水。什么意思胶水是最后的？在同一个函数中，他们检查MVT :: Other是否也存在？这意味着什么？
最后 - 我做错了什么？为什么我得不到第二个结果？为什么我一直都会收到这个错误？

Answer 1

This should really be a comment, but I have no rep. Some hints that may hopefully help:

VT stands for ValueType. LLVM needs to know the type(s) of the return values of each SDNode. By passing VTs into getMachineNode, you create a new SDNode that returns as many values as there are in the SDVTList, with the specified types.
"Glue" is a special ValueType that doesn't actually hold a value. It's just used to ensure that two glued SDNodes don't get separated when instruction scheduling happens.
"ops" are indeed the incoming inputs.
The order of inputs and return values should be exactly the order specified in TableGen.
I'm not sure about this, but I don't think Defs are turned into implicit return values. You might have to manually create a CopyFromReg node, to grab the register that is written to.
MVT::Other represents a "chain", a way to ensure that instructions with side effects are not reordered relative to each other.

Do read the doxygen docs, they're fairly good at explaining the individual functions (even if a bit lacking in the bigger-picture).

Try starting here: http://llvm.org/docs/doxygen/html/classllvm_1_1SelectionDAG.html

如何在llvm中构建新的SDNode？

1 个答案: