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      1 //===-- BPFISelDAGToDAG.cpp - A dag to dag inst selector for BPF ----------===//
      2 //
      3 //                     The LLVM Compiler Infrastructure
      4 //
      5 // This file is distributed under the University of Illinois Open Source
      6 // License. See LICENSE.TXT for details.
      7 //
      8 //===----------------------------------------------------------------------===//
      9 //
     10 // This file defines a DAG pattern matching instruction selector for BPF,
     11 // converting from a legalized dag to a BPF dag.
     12 //
     13 //===----------------------------------------------------------------------===//
     14 
     15 #include "BPF.h"
     16 #include "BPFRegisterInfo.h"
     17 #include "BPFSubtarget.h"
     18 #include "BPFTargetMachine.h"
     19 #include "llvm/CodeGen/MachineConstantPool.h"
     20 #include "llvm/CodeGen/MachineFrameInfo.h"
     21 #include "llvm/CodeGen/MachineFunction.h"
     22 #include "llvm/CodeGen/MachineInstrBuilder.h"
     23 #include "llvm/CodeGen/MachineRegisterInfo.h"
     24 #include "llvm/CodeGen/SelectionDAGISel.h"
     25 #include "llvm/IR/IntrinsicInst.h"
     26 #include "llvm/Support/Debug.h"
     27 #include "llvm/Support/ErrorHandling.h"
     28 #include "llvm/Support/raw_ostream.h"
     29 #include "llvm/Target/TargetMachine.h"
     30 using namespace llvm;
     31 
     32 #define DEBUG_TYPE "bpf-isel"
     33 
     34 // Instruction Selector Implementation
     35 namespace {
     36 
     37 class BPFDAGToDAGISel : public SelectionDAGISel {
     38 public:
     39   explicit BPFDAGToDAGISel(BPFTargetMachine &TM) : SelectionDAGISel(TM) {}
     40 
     41   const char *getPassName() const override {
     42     return "BPF DAG->DAG Pattern Instruction Selection";
     43   }
     44 
     45 private:
     46 // Include the pieces autogenerated from the target description.
     47 #include "BPFGenDAGISel.inc"
     48 
     49   SDNode *Select(SDNode *N) override;
     50 
     51   // Complex Pattern for address selection.
     52   bool SelectAddr(SDValue Addr, SDValue &Base, SDValue &Offset);
     53   bool SelectFIAddr(SDValue Addr, SDValue &Base, SDValue &Offset);
     54 };
     55 }
     56 
     57 // ComplexPattern used on BPF Load/Store instructions
     58 bool BPFDAGToDAGISel::SelectAddr(SDValue Addr, SDValue &Base, SDValue &Offset) {
     59   // if Address is FI, get the TargetFrameIndex.
     60   SDLoc DL(Addr);
     61   if (FrameIndexSDNode *FIN = dyn_cast<FrameIndexSDNode>(Addr)) {
     62     Base   = CurDAG->getTargetFrameIndex(FIN->getIndex(), MVT::i64);
     63     Offset = CurDAG->getTargetConstant(0, DL, MVT::i64);
     64     return true;
     65   }
     66 
     67   if (Addr.getOpcode() == ISD::TargetExternalSymbol ||
     68       Addr.getOpcode() == ISD::TargetGlobalAddress)
     69     return false;
     70 
     71   // Addresses of the form Addr+const or Addr|const
     72   if (CurDAG->isBaseWithConstantOffset(Addr)) {
     73     ConstantSDNode *CN = dyn_cast<ConstantSDNode>(Addr.getOperand(1));
     74     if (isInt<32>(CN->getSExtValue())) {
     75 
     76       // If the first operand is a FI, get the TargetFI Node
     77       if (FrameIndexSDNode *FIN =
     78               dyn_cast<FrameIndexSDNode>(Addr.getOperand(0)))
     79         Base = CurDAG->getTargetFrameIndex(FIN->getIndex(), MVT::i64);
     80       else
     81         Base = Addr.getOperand(0);
     82 
     83       Offset = CurDAG->getTargetConstant(CN->getSExtValue(), DL, MVT::i64);
     84       return true;
     85     }
     86   }
     87 
     88   Base   = Addr;
     89   Offset = CurDAG->getTargetConstant(0, DL, MVT::i64);
     90   return true;
     91 }
     92 
     93 // ComplexPattern used on BPF FI instruction
     94 bool BPFDAGToDAGISel::SelectFIAddr(SDValue Addr, SDValue &Base, SDValue &Offset) {
     95   SDLoc DL(Addr);
     96 
     97   if (!CurDAG->isBaseWithConstantOffset(Addr))
     98     return false;
     99 
    100   // Addresses of the form Addr+const or Addr|const
    101   ConstantSDNode *CN = dyn_cast<ConstantSDNode>(Addr.getOperand(1));
    102   if (isInt<32>(CN->getSExtValue())) {
    103 
    104     // If the first operand is a FI, get the TargetFI Node
    105     if (FrameIndexSDNode *FIN =
    106             dyn_cast<FrameIndexSDNode>(Addr.getOperand(0)))
    107       Base = CurDAG->getTargetFrameIndex(FIN->getIndex(), MVT::i64);
    108     else
    109       return false;
    110 
    111     Offset = CurDAG->getTargetConstant(CN->getSExtValue(), DL, MVT::i64);
    112     return true;
    113   }
    114 
    115   return false;
    116 }
    117 
    118 SDNode *BPFDAGToDAGISel::Select(SDNode *Node) {
    119   unsigned Opcode = Node->getOpcode();
    120 
    121   // Dump information about the Node being selected
    122   DEBUG(dbgs() << "Selecting: "; Node->dump(CurDAG); dbgs() << '\n');
    123 
    124   // If we have a custom node, we already have selected!
    125   if (Node->isMachineOpcode()) {
    126     DEBUG(dbgs() << "== "; Node->dump(CurDAG); dbgs() << '\n');
    127     return NULL;
    128   }
    129 
    130   // tablegen selection should be handled here.
    131   switch (Opcode) {
    132   default: break;
    133   case ISD::INTRINSIC_W_CHAIN: {
    134     unsigned IntNo = cast<ConstantSDNode>(Node->getOperand(1))->getZExtValue();
    135     switch (IntNo) {
    136     case Intrinsic::bpf_load_byte:
    137     case Intrinsic::bpf_load_half:
    138     case Intrinsic::bpf_load_word: {
    139       SDLoc DL(Node);
    140       SDValue Chain = Node->getOperand(0);
    141       SDValue N1 = Node->getOperand(1);
    142       SDValue Skb = Node->getOperand(2);
    143       SDValue N3 = Node->getOperand(3);
    144 
    145       SDValue R6Reg = CurDAG->getRegister(BPF::R6, MVT::i64);
    146       Chain = CurDAG->getCopyToReg(Chain, DL, R6Reg, Skb, SDValue());
    147       Node = CurDAG->UpdateNodeOperands(Node, Chain, N1, R6Reg, N3);
    148       break;
    149     }
    150     }
    151     break;
    152   }
    153 
    154   case ISD::FrameIndex: {
    155     int FI = cast<FrameIndexSDNode>(Node)->getIndex();
    156     EVT VT = Node->getValueType(0);
    157     SDValue TFI = CurDAG->getTargetFrameIndex(FI, VT);
    158     unsigned Opc = BPF::MOV_rr;
    159     if (Node->hasOneUse())
    160       return CurDAG->SelectNodeTo(Node, Opc, VT, TFI);
    161     return CurDAG->getMachineNode(Opc, SDLoc(Node), VT, TFI);
    162   }
    163   }
    164 
    165   // Select the default instruction
    166   SDNode *ResNode = SelectCode(Node);
    167 
    168   DEBUG(dbgs() << "=> ";
    169         if (ResNode == nullptr || ResNode == Node)
    170           Node->dump(CurDAG);
    171         else
    172           ResNode->dump(CurDAG);
    173         dbgs() << '\n');
    174   return ResNode;
    175 }
    176 
    177 FunctionPass *llvm::createBPFISelDag(BPFTargetMachine &TM) {
    178   return new BPFDAGToDAGISel(TM);
    179 }
    180