llvm/lib/Target/BPF/BPFISelDAGToDAG.cpp

   1 //===-- BPFISelDAGToDAG.cpp - A dag to dag inst selector for BPF ----------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 //
   9 // This file defines a DAG pattern matching instruction selector for BPF,
  10 // converting from a legalized dag to a BPF dag.
  11 //
  12 //===----------------------------------------------------------------------===//
  13
  14 #include "BPF.h"
  15 #include "BPFRegisterInfo.h"
  16 #include "BPFSubtarget.h"
  17 #include "BPFTargetMachine.h"
  18 #include "llvm/CodeGen/FunctionLoweringInfo.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/Constants.h"
  26 #include "llvm/IR/IntrinsicInst.h"
  27 #include "llvm/IR/IntrinsicsBPF.h"
  28 #include "llvm/Support/Debug.h"
  29 #include "llvm/Support/Endian.h"
  30 #include "llvm/Support/ErrorHandling.h"
  31 #include "llvm/Support/raw_ostream.h"
  32 #include "llvm/Target/TargetMachine.h"
  33
  34 using namespace llvm;
  35
  36 #define DEBUG_TYPE "bpf-isel"
  37
  38 // Instruction Selector Implementation
  39 namespace {
  40
  41 class BPFDAGToDAGISel : public SelectionDAGISel {
  42
  43   /// Subtarget - Keep a pointer to the BPFSubtarget around so that we can
  44   /// make the right decision when generating code for different subtargets.
  45   const BPFSubtarget *Subtarget;
  46
  47 public:
  48   explicit BPFDAGToDAGISel(BPFTargetMachine &TM)
  49       : SelectionDAGISel(TM), Subtarget(nullptr) {}
  50
  51   StringRef getPassName() const override {
  52     return "BPF DAG->DAG Pattern Instruction Selection";
  53   }
  54
  55   bool runOnMachineFunction(MachineFunction &MF) override {
  56     // Reset the subtarget each time through.
  57     Subtarget = &MF.getSubtarget<BPFSubtarget>();
  58     return SelectionDAGISel::runOnMachineFunction(MF);
  59   }
  60
  61   void PreprocessISelDAG() override;
  62
  63   bool SelectInlineAsmMemoryOperand(const SDValue &Op, unsigned ConstraintCode,
  64                                     std::vector<SDValue> &OutOps) override;
  65
  66
  67 private:
  68 // Include the pieces autogenerated from the target description.
  69 #include "BPFGenDAGISel.inc"
  70
  71   void Select(SDNode *N) override;
  72
  73   // Complex Pattern for address selection.
  74   bool SelectAddr(SDValue Addr, SDValue &Base, SDValue &Offset);
  75   bool SelectFIAddr(SDValue Addr, SDValue &Base, SDValue &Offset);
  76
  77   // Node preprocessing cases
  78   void PreprocessLoad(SDNode *Node, SelectionDAG::allnodes_iterator &I);
  79   void PreprocessCopyToReg(SDNode *Node);
  80   void PreprocessTrunc(SDNode *Node, SelectionDAG::allnodes_iterator &I);
  81
  82   // Find constants from a constant structure
  83   typedef std::vector<unsigned char> val_vec_type;
  84   bool fillGenericConstant(const DataLayout &DL, const Constant *CV,
  85                            val_vec_type &Vals, uint64_t Offset);
  86   bool fillConstantDataArray(const DataLayout &DL, const ConstantDataArray *CDA,
  87                              val_vec_type &Vals, int Offset);
  88   bool fillConstantArray(const DataLayout &DL, const ConstantArray *CA,
  89                          val_vec_type &Vals, int Offset);
  90   bool fillConstantStruct(const DataLayout &DL, const ConstantStruct *CS,
  91                           val_vec_type &Vals, int Offset);
  92   bool getConstantFieldValue(const GlobalAddressSDNode *Node, uint64_t Offset,
  93                              uint64_t Size, unsigned char *ByteSeq);
  94   // Mapping from ConstantStruct global value to corresponding byte-list values
  95   std::map<const void *, val_vec_type> cs_vals_;
  96 };
  97 } // namespace
  98
  99 // ComplexPattern used on BPF Load/Store instructions
 100 bool BPFDAGToDAGISel::SelectAddr(SDValue Addr, SDValue &Base, SDValue &Offset) {
 101   // if Address is FI, get the TargetFrameIndex.
 102   SDLoc DL(Addr);
 103   if (auto *FIN = dyn_cast<FrameIndexSDNode>(Addr)) {
 104     Base = CurDAG->getTargetFrameIndex(FIN->getIndex(), MVT::i64);
 105     Offset = CurDAG->getTargetConstant(0, DL, MVT::i64);
 106     return true;
 107   }
 108
 109   if (Addr.getOpcode() == ISD::TargetExternalSymbol ||
 110       Addr.getOpcode() == ISD::TargetGlobalAddress)
 111     return false;
 112
 113   // Addresses of the form Addr+const or Addr|const
 114   if (CurDAG->isBaseWithConstantOffset(Addr)) {
 115     auto *CN = cast<ConstantSDNode>(Addr.getOperand(1));
 116     if (isInt<16>(CN->getSExtValue())) {
 117       // If the first operand is a FI, get the TargetFI Node
 118       if (auto *FIN = dyn_cast<FrameIndexSDNode>(Addr.getOperand(0)))
 119         Base = CurDAG->getTargetFrameIndex(FIN->getIndex(), MVT::i64);
 120       else
 121         Base = Addr.getOperand(0);
 122
 123       Offset = CurDAG->getTargetConstant(CN->getSExtValue(), DL, MVT::i64);
 124       return true;
 125     }
 126   }
 127
 128   Base = Addr;
 129   Offset = CurDAG->getTargetConstant(0, DL, MVT::i64);
 130   return true;
 131 }
 132
 133 // ComplexPattern used on BPF FI instruction
 134 bool BPFDAGToDAGISel::SelectFIAddr(SDValue Addr, SDValue &Base,
 135                                    SDValue &Offset) {
 136   SDLoc DL(Addr);
 137
 138   if (!CurDAG->isBaseWithConstantOffset(Addr))
 139     return false;
 140
 141   // Addresses of the form Addr+const or Addr|const
 142   auto *CN = cast<ConstantSDNode>(Addr.getOperand(1));
 143   if (isInt<16>(CN->getSExtValue())) {
 144     // If the first operand is a FI, get the TargetFI Node
 145     if (auto *FIN = dyn_cast<FrameIndexSDNode>(Addr.getOperand(0)))
 146       Base = CurDAG->getTargetFrameIndex(FIN->getIndex(), MVT::i64);
 147     else
 148       return false;
 149
 150     Offset = CurDAG->getTargetConstant(CN->getSExtValue(), DL, MVT::i64);
 151     return true;
 152   }
 153
 154   return false;
 155 }
 156
 157 bool BPFDAGToDAGISel::SelectInlineAsmMemoryOperand(
 158     const SDValue &Op, unsigned ConstraintCode, std::vector<SDValue> &OutOps) {
 159   SDValue Op0, Op1;
 160   switch (ConstraintCode) {
 161   default:
 162     return true;
 163   case InlineAsm::Constraint_m: // memory
 164     if (!SelectAddr(Op, Op0, Op1))
 165       return true;
 166     break;
 167   }
 168
 169   SDLoc DL(Op);
 170   SDValue AluOp = CurDAG->getTargetConstant(ISD::ADD, DL, MVT::i32);;
 171   OutOps.push_back(Op0);
 172   OutOps.push_back(Op1);
 173   OutOps.push_back(AluOp);
 174   return false;
 175 }
 176
 177 void BPFDAGToDAGISel::Select(SDNode *Node) {
 178   unsigned Opcode = Node->getOpcode();
 179
 180   // If we have a custom node, we already have selected!
 181   if (Node->isMachineOpcode()) {
 182     LLVM_DEBUG(dbgs() << "== "; Node->dump(CurDAG); dbgs() << '\n');
 183     return;
 184   }
 185
 186   // tablegen selection should be handled here.
 187   switch (Opcode) {
 188   default:
 189     break;
 190   case ISD::SDIV: {
 191     DebugLoc Empty;
 192     const DebugLoc &DL = Node->getDebugLoc();
 193     if (DL != Empty)
 194       errs() << "Error at line " << DL.getLine() << ": ";
 195     else
 196       errs() << "Error: ";
 197     errs() << "Unsupport signed division for DAG: ";
 198     Node->print(errs(), CurDAG);
 199     errs() << "Please convert to unsigned div/mod.\n";
 200     break;
 201   }
 202   case ISD::INTRINSIC_W_CHAIN: {
 203     unsigned IntNo = cast<ConstantSDNode>(Node->getOperand(1))->getZExtValue();
 204     switch (IntNo) {
 205     case Intrinsic::bpf_load_byte:
 206     case Intrinsic::bpf_load_half:
 207     case Intrinsic::bpf_load_word: {
 208       SDLoc DL(Node);
 209       SDValue Chain = Node->getOperand(0);
 210       SDValue N1 = Node->getOperand(1);
 211       SDValue Skb = Node->getOperand(2);
 212       SDValue N3 = Node->getOperand(3);
 213
 214       SDValue R6Reg = CurDAG->getRegister(BPF::R6, MVT::i64);
 215       Chain = CurDAG->getCopyToReg(Chain, DL, R6Reg, Skb, SDValue());
 216       Node = CurDAG->UpdateNodeOperands(Node, Chain, N1, R6Reg, N3);
 217       break;
 218     }
 219     }
 220     break;
 221   }
 222
 223   case ISD::FrameIndex: {
 224     int FI = cast<FrameIndexSDNode>(Node)->getIndex();
 225     EVT VT = Node->getValueType(0);
 226     SDValue TFI = CurDAG->getTargetFrameIndex(FI, VT);
 227     unsigned Opc = BPF::MOV_rr;
 228     if (Node->hasOneUse()) {
 229       CurDAG->SelectNodeTo(Node, Opc, VT, TFI);
 230       return;
 231     }
 232     ReplaceNode(Node, CurDAG->getMachineNode(Opc, SDLoc(Node), VT, TFI));
 233     return;
 234   }
 235   }
 236
 237   // Select the default instruction
 238   SelectCode(Node);
 239 }
 240
 241 void BPFDAGToDAGISel::PreprocessLoad(SDNode *Node,
 242                                      SelectionDAG::allnodes_iterator &I) {
 243   union {
 244     uint8_t c[8];
 245     uint16_t s;
 246     uint32_t i;
 247     uint64_t d;
 248   } new_val; // hold up the constant values replacing loads.
 249   bool to_replace = false;
 250   SDLoc DL(Node);
 251   const LoadSDNode *LD = cast<LoadSDNode>(Node);
 252   uint64_t size = LD->getMemOperand()->getSize();
 253
 254   if (!size || size > 8 || (size & (size - 1)) || !LD->isSimple())
 255     return;
 256
 257   SDNode *LDAddrNode = LD->getOperand(1).getNode();
 258   // Match LDAddr against either global_addr or (global_addr + offset)
 259   unsigned opcode = LDAddrNode->getOpcode();
 260   if (opcode == ISD::ADD) {
 261     SDValue OP1 = LDAddrNode->getOperand(0);
 262     SDValue OP2 = LDAddrNode->getOperand(1);
 263
 264     // We want to find the pattern global_addr + offset
 265     SDNode *OP1N = OP1.getNode();
 266     if (OP1N->getOpcode() <= ISD::BUILTIN_OP_END || OP1N->getNumOperands() == 0)
 267       return;
 268
 269     LLVM_DEBUG(dbgs() << "Check candidate load: "; LD->dump(); dbgs() << '\n');
 270
 271     const GlobalAddressSDNode *GADN =
 272         dyn_cast<GlobalAddressSDNode>(OP1N->getOperand(0).getNode());
 273     const ConstantSDNode *CDN = dyn_cast<ConstantSDNode>(OP2.getNode());
 274     if (GADN && CDN)
 275       to_replace =
 276           getConstantFieldValue(GADN, CDN->getZExtValue(), size, new_val.c);
 277   } else if (LDAddrNode->getOpcode() > ISD::BUILTIN_OP_END &&
 278              LDAddrNode->getNumOperands() > 0) {
 279     LLVM_DEBUG(dbgs() << "Check candidate load: "; LD->dump(); dbgs() << '\n');
 280
 281     SDValue OP1 = LDAddrNode->getOperand(0);
 282     if (const GlobalAddressSDNode *GADN =
 283             dyn_cast<GlobalAddressSDNode>(OP1.getNode()))
 284       to_replace = getConstantFieldValue(GADN, 0, size, new_val.c);
 285   }
 286
 287   if (!to_replace)
 288     return;
 289
 290   // replacing the old with a new value
 291   uint64_t val;
 292   if (size == 1)
 293     val = new_val.c[0];
 294   else if (size == 2)
 295     val = new_val.s;
 296   else if (size == 4)
 297     val = new_val.i;
 298   else {
 299     val = new_val.d;
 300   }
 301
 302   LLVM_DEBUG(dbgs() << "Replacing load of size " << size << " with constant "
 303                     << val << '\n');
 304   SDValue NVal = CurDAG->getConstant(val, DL, LD->getValueType(0));
 305
 306   // After replacement, the current node is dead, we need to
 307   // go backward one step to make iterator still work
 308   I--;
 309   SDValue From[] = {SDValue(Node, 0), SDValue(Node, 1)};
 310   SDValue To[] = {NVal, NVal};
 311   CurDAG->ReplaceAllUsesOfValuesWith(From, To, 2);
 312   I++;
 313   // It is safe to delete node now
 314   CurDAG->DeleteNode(Node);
 315 }
 316
 317 void BPFDAGToDAGISel::PreprocessISelDAG() {
 318   // Iterate through all nodes, interested in the following case:
 319   //
 320   //  . loads from ConstantStruct or ConstantArray of constructs
 321   //    which can be turns into constant itself, with this we can
 322   //    avoid reading from read-only section at runtime.
 323   //
 324   //  . Removing redundant AND for intrinsic narrow loads.
 325   for (SelectionDAG::allnodes_iterator I = CurDAG->allnodes_begin(),
 326                                        E = CurDAG->allnodes_end();
 327        I != E;) {
 328     SDNode *Node = &*I++;
 329     unsigned Opcode = Node->getOpcode();
 330     if (Opcode == ISD::LOAD)
 331       PreprocessLoad(Node, I);
 332     else if (Opcode == ISD::AND)
 333       PreprocessTrunc(Node, I);
 334   }
 335 }
 336
 337 bool BPFDAGToDAGISel::getConstantFieldValue(const GlobalAddressSDNode *Node,
 338                                             uint64_t Offset, uint64_t Size,
 339                                             unsigned char *ByteSeq) {
 340   const GlobalVariable *V = dyn_cast<GlobalVariable>(Node->getGlobal());
 341
 342   if (!V || !V->hasInitializer() || !V->isConstant())
 343     return false;
 344
 345   const Constant *Init = V->getInitializer();
 346   const DataLayout &DL = CurDAG->getDataLayout();
 347   val_vec_type TmpVal;
 348
 349   auto it = cs_vals_.find(static_cast<const void *>(Init));
 350   if (it != cs_vals_.end()) {
 351     TmpVal = it->second;
 352   } else {
 353     uint64_t total_size = 0;
 354     if (const ConstantStruct *CS = dyn_cast<ConstantStruct>(Init))
 355       total_size =
 356           DL.getStructLayout(cast<StructType>(CS->getType()))->getSizeInBytes();
 357     else if (const ConstantArray *CA = dyn_cast<ConstantArray>(Init))
 358       total_size = DL.getTypeAllocSize(CA->getType()->getElementType()) *
 359                    CA->getNumOperands();
 360     else
 361       return false;
 362
 363     val_vec_type Vals(total_size, 0);
 364     if (fillGenericConstant(DL, Init, Vals, 0) == false)
 365       return false;
 366     cs_vals_[static_cast<const void *>(Init)] = Vals;
 367     TmpVal = std::move(Vals);
 368   }
 369
 370   // test whether host endianness matches target
 371   union {
 372     uint8_t c[2];
 373     uint16_t s;
 374   } test_buf;
 375   uint16_t test_val = 0x2345;
 376   if (DL.isLittleEndian())
 377     support::endian::write16le(test_buf.c, test_val);
 378   else
 379     support::endian::write16be(test_buf.c, test_val);
 380
 381   bool endian_match = test_buf.s == test_val;
 382   for (uint64_t i = Offset, j = 0; i < Offset + Size; i++, j++)
 383     ByteSeq[j] = endian_match ? TmpVal[i] : TmpVal[Offset + Size - 1 - j];
 384
 385   return true;
 386 }
 387
 388 bool BPFDAGToDAGISel::fillGenericConstant(const DataLayout &DL,
 389                                           const Constant *CV,
 390                                           val_vec_type &Vals, uint64_t Offset) {
 391   uint64_t Size = DL.getTypeAllocSize(CV->getType());
 392
 393   if (isa<ConstantAggregateZero>(CV) || isa<UndefValue>(CV))
 394     return true; // already done
 395
 396   if (const ConstantInt *CI = dyn_cast<ConstantInt>(CV)) {
 397     uint64_t val = CI->getZExtValue();
 398     LLVM_DEBUG(dbgs() << "Byte array at offset " << Offset << " with value "
 399                       << val << '\n');
 400
 401     if (Size > 8 || (Size & (Size - 1)))
 402       return false;
 403
 404     // Store based on target endian
 405     for (uint64_t i = 0; i < Size; ++i) {
 406       Vals[Offset + i] = DL.isLittleEndian()
 407                              ? ((val >> (i * 8)) & 0xFF)
 408                              : ((val >> ((Size - i - 1) * 8)) & 0xFF);
 409     }
 410     return true;
 411   }
 412
 413   if (const ConstantDataArray *CDA = dyn_cast<ConstantDataArray>(CV))
 414     return fillConstantDataArray(DL, CDA, Vals, Offset);
 415
 416   if (const ConstantArray *CA = dyn_cast<ConstantArray>(CV))
 417     return fillConstantArray(DL, CA, Vals, Offset);
 418
 419   if (const ConstantStruct *CVS = dyn_cast<ConstantStruct>(CV))
 420     return fillConstantStruct(DL, CVS, Vals, Offset);
 421
 422   return false;
 423 }
 424
 425 bool BPFDAGToDAGISel::fillConstantDataArray(const DataLayout &DL,
 426                                             const ConstantDataArray *CDA,
 427                                             val_vec_type &Vals, int Offset) {
 428   for (unsigned i = 0, e = CDA->getNumElements(); i != e; ++i) {
 429     if (fillGenericConstant(DL, CDA->getElementAsConstant(i), Vals, Offset) ==
 430         false)
 431       return false;
 432     Offset += DL.getTypeAllocSize(CDA->getElementAsConstant(i)->getType());
 433   }
 434
 435   return true;
 436 }
 437
 438 bool BPFDAGToDAGISel::fillConstantArray(const DataLayout &DL,
 439                                         const ConstantArray *CA,
 440                                         val_vec_type &Vals, int Offset) {
 441   for (unsigned i = 0, e = CA->getNumOperands(); i != e; ++i) {
 442     if (fillGenericConstant(DL, CA->getOperand(i), Vals, Offset) == false)
 443       return false;
 444     Offset += DL.getTypeAllocSize(CA->getOperand(i)->getType());
 445   }
 446
 447   return true;
 448 }
 449
 450 bool BPFDAGToDAGISel::fillConstantStruct(const DataLayout &DL,
 451                                          const ConstantStruct *CS,
 452                                          val_vec_type &Vals, int Offset) {
 453   const StructLayout *Layout = DL.getStructLayout(CS->getType());
 454   for (unsigned i = 0, e = CS->getNumOperands(); i != e; ++i) {
 455     const Constant *Field = CS->getOperand(i);
 456     uint64_t SizeSoFar = Layout->getElementOffset(i);
 457     if (fillGenericConstant(DL, Field, Vals, Offset + SizeSoFar) == false)
 458       return false;
 459   }
 460   return true;
 461 }
 462
 463 void BPFDAGToDAGISel::PreprocessTrunc(SDNode *Node,
 464                                       SelectionDAG::allnodes_iterator &I) {
 465   ConstantSDNode *MaskN = dyn_cast<ConstantSDNode>(Node->getOperand(1));
 466   if (!MaskN)
 467     return;
 468
 469   // The Reg operand should be a virtual register, which is defined
 470   // outside the current basic block. DAG combiner has done a pretty
 471   // good job in removing truncating inside a single basic block except
 472   // when the Reg operand comes from bpf_load_[byte | half | word] for
 473   // which the generic optimizer doesn't understand their results are
 474   // zero extended.
 475   SDValue BaseV = Node->getOperand(0);
 476   if (BaseV.getOpcode() != ISD::INTRINSIC_W_CHAIN)
 477     return;
 478
 479   unsigned IntNo = cast<ConstantSDNode>(BaseV->getOperand(1))->getZExtValue();
 480   uint64_t MaskV = MaskN->getZExtValue();
 481
 482   if (!((IntNo == Intrinsic::bpf_load_byte && MaskV == 0xFF) ||
 483         (IntNo == Intrinsic::bpf_load_half && MaskV == 0xFFFF) ||
 484         (IntNo == Intrinsic::bpf_load_word && MaskV == 0xFFFFFFFF)))
 485     return;
 486
 487   LLVM_DEBUG(dbgs() << "Remove the redundant AND operation in: ";
 488              Node->dump(); dbgs() << '\n');
 489
 490   I--;
 491   CurDAG->ReplaceAllUsesWith(SDValue(Node, 0), BaseV);
 492   I++;
 493   CurDAG->DeleteNode(Node);
 494 }
 495
 496 FunctionPass *llvm::createBPFISelDag(BPFTargetMachine &TM) {
 497   return new BPFDAGToDAGISel(TM);
 498 }