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 #define PASS_NAME "BPF DAG->DAG Pattern Instruction Selection"
38 
39 // Instruction Selector Implementation
40 namespace {
41 
42 class BPFDAGToDAGISel : public SelectionDAGISel {
43 
44   /// Subtarget - Keep a pointer to the BPFSubtarget around so that we can
45   /// make the right decision when generating code for different subtargets.
46   const BPFSubtarget *Subtarget;
47 
48 public:
49   static char ID;
50 
51   BPFDAGToDAGISel() = delete;
52 
53   explicit BPFDAGToDAGISel(BPFTargetMachine &TM)
54       : SelectionDAGISel(ID, TM), Subtarget(nullptr) {}
55 
56   bool runOnMachineFunction(MachineFunction &MF) override {
57     // Reset the subtarget each time through.
58     Subtarget = &MF.getSubtarget<BPFSubtarget>();
59     return SelectionDAGISel::runOnMachineFunction(MF);
60   }
61 
62   void PreprocessISelDAG() override;
63 
64   bool SelectInlineAsmMemoryOperand(const SDValue &Op, unsigned ConstraintCode,
65                                     std::vector<SDValue> &OutOps) override;
66 
67 
68 private:
69 // Include the pieces autogenerated from the target description.
70 #include "BPFGenDAGISel.inc"
71 
72   void Select(SDNode *N) override;
73 
74   // Complex Pattern for address selection.
75   bool SelectAddr(SDValue Addr, SDValue &Base, SDValue &Offset);
76   bool SelectFIAddr(SDValue Addr, SDValue &Base, SDValue &Offset);
77 
78   // Node preprocessing cases
79   void PreprocessLoad(SDNode *Node, SelectionDAG::allnodes_iterator &I);
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 char BPFDAGToDAGISel::ID = 0;
100 
101 INITIALIZE_PASS(BPFDAGToDAGISel, DEBUG_TYPE, PASS_NAME, false, false)
102 
103 // ComplexPattern used on BPF Load/Store instructions
104 bool BPFDAGToDAGISel::SelectAddr(SDValue Addr, SDValue &Base, SDValue &Offset) {
105   // if Address is FI, get the TargetFrameIndex.
106   SDLoc DL(Addr);
107   if (auto *FIN = dyn_cast<FrameIndexSDNode>(Addr)) {
108     Base = CurDAG->getTargetFrameIndex(FIN->getIndex(), MVT::i64);
109     Offset = CurDAG->getTargetConstant(0, DL, MVT::i64);
110     return true;
111   }
112 
113   if (Addr.getOpcode() == ISD::TargetExternalSymbol ||
114       Addr.getOpcode() == ISD::TargetGlobalAddress)
115     return false;
116 
117   // Addresses of the form Addr+const or Addr|const
118   if (CurDAG->isBaseWithConstantOffset(Addr)) {
119     auto *CN = cast<ConstantSDNode>(Addr.getOperand(1));
120     if (isInt<16>(CN->getSExtValue())) {
121       // If the first operand is a FI, get the TargetFI Node
122       if (auto *FIN = dyn_cast<FrameIndexSDNode>(Addr.getOperand(0)))
123         Base = CurDAG->getTargetFrameIndex(FIN->getIndex(), MVT::i64);
124       else
125         Base = Addr.getOperand(0);
126 
127       Offset = CurDAG->getTargetConstant(CN->getSExtValue(), DL, MVT::i64);
128       return true;
129     }
130   }
131 
132   Base = Addr;
133   Offset = CurDAG->getTargetConstant(0, DL, MVT::i64);
134   return true;
135 }
136 
137 // ComplexPattern used on BPF FI instruction
138 bool BPFDAGToDAGISel::SelectFIAddr(SDValue Addr, SDValue &Base,
139                                    SDValue &Offset) {
140   SDLoc DL(Addr);
141 
142   if (!CurDAG->isBaseWithConstantOffset(Addr))
143     return false;
144 
145   // Addresses of the form Addr+const or Addr|const
146   auto *CN = cast<ConstantSDNode>(Addr.getOperand(1));
147   if (isInt<16>(CN->getSExtValue())) {
148     // If the first operand is a FI, get the TargetFI Node
149     if (auto *FIN = dyn_cast<FrameIndexSDNode>(Addr.getOperand(0)))
150       Base = CurDAG->getTargetFrameIndex(FIN->getIndex(), MVT::i64);
151     else
152       return false;
153 
154     Offset = CurDAG->getTargetConstant(CN->getSExtValue(), DL, MVT::i64);
155     return true;
156   }
157 
158   return false;
159 }
160 
161 bool BPFDAGToDAGISel::SelectInlineAsmMemoryOperand(
162     const SDValue &Op, unsigned ConstraintCode, std::vector<SDValue> &OutOps) {
163   SDValue Op0, Op1;
164   switch (ConstraintCode) {
165   default:
166     return true;
167   case InlineAsm::Constraint_m: // memory
168     if (!SelectAddr(Op, Op0, Op1))
169       return true;
170     break;
171   }
172 
173   SDLoc DL(Op);
174   SDValue AluOp = CurDAG->getTargetConstant(ISD::ADD, DL, MVT::i32);
175   OutOps.push_back(Op0);
176   OutOps.push_back(Op1);
177   OutOps.push_back(AluOp);
178   return false;
179 }
180 
181 void BPFDAGToDAGISel::Select(SDNode *Node) {
182   unsigned Opcode = Node->getOpcode();
183 
184   // If we have a custom node, we already have selected!
185   if (Node->isMachineOpcode()) {
186     LLVM_DEBUG(dbgs() << "== "; Node->dump(CurDAG); dbgs() << '\n');
187     return;
188   }
189 
190   // tablegen selection should be handled here.
191   switch (Opcode) {
192   default:
193     break;
194   case ISD::SDIV: {
195     DebugLoc Empty;
196     const DebugLoc &DL = Node->getDebugLoc();
197     if (DL != Empty)
198       errs() << "Error at line " << DL.getLine() << ": ";
199     else
200       errs() << "Error: ";
201     errs() << "Unsupport signed division for DAG: ";
202     Node->print(errs(), CurDAG);
203     errs() << "Please convert to unsigned div/mod.\n";
204     break;
205   }
206   case ISD::INTRINSIC_W_CHAIN: {
207     unsigned IntNo = cast<ConstantSDNode>(Node->getOperand(1))->getZExtValue();
208     switch (IntNo) {
209     case Intrinsic::bpf_load_byte:
210     case Intrinsic::bpf_load_half:
211     case Intrinsic::bpf_load_word: {
212       SDLoc DL(Node);
213       SDValue Chain = Node->getOperand(0);
214       SDValue N1 = Node->getOperand(1);
215       SDValue Skb = Node->getOperand(2);
216       SDValue N3 = Node->getOperand(3);
217 
218       SDValue R6Reg = CurDAG->getRegister(BPF::R6, MVT::i64);
219       Chain = CurDAG->getCopyToReg(Chain, DL, R6Reg, Skb, SDValue());
220       Node = CurDAG->UpdateNodeOperands(Node, Chain, N1, R6Reg, N3);
221       break;
222     }
223     }
224     break;
225   }
226 
227   case ISD::FrameIndex: {
228     int FI = cast<FrameIndexSDNode>(Node)->getIndex();
229     EVT VT = Node->getValueType(0);
230     SDValue TFI = CurDAG->getTargetFrameIndex(FI, VT);
231     unsigned Opc = BPF::MOV_rr;
232     if (Node->hasOneUse()) {
233       CurDAG->SelectNodeTo(Node, Opc, VT, TFI);
234       return;
235     }
236     ReplaceNode(Node, CurDAG->getMachineNode(Opc, SDLoc(Node), VT, TFI));
237     return;
238   }
239   }
240 
241   // Select the default instruction
242   SelectCode(Node);
243 }
244 
245 void BPFDAGToDAGISel::PreprocessLoad(SDNode *Node,
246                                      SelectionDAG::allnodes_iterator &I) {
247   union {
248     uint8_t c[8];
249     uint16_t s;
250     uint32_t i;
251     uint64_t d;
252   } new_val; // hold up the constant values replacing loads.
253   bool to_replace = false;
254   SDLoc DL(Node);
255   const LoadSDNode *LD = cast<LoadSDNode>(Node);
256   uint64_t size = LD->getMemOperand()->getSize();
257 
258   if (!size || size > 8 || (size & (size - 1)) || !LD->isSimple())
259     return;
260 
261   SDNode *LDAddrNode = LD->getOperand(1).getNode();
262   // Match LDAddr against either global_addr or (global_addr + offset)
263   unsigned opcode = LDAddrNode->getOpcode();
264   if (opcode == ISD::ADD) {
265     SDValue OP1 = LDAddrNode->getOperand(0);
266     SDValue OP2 = LDAddrNode->getOperand(1);
267 
268     // We want to find the pattern global_addr + offset
269     SDNode *OP1N = OP1.getNode();
270     if (OP1N->getOpcode() <= ISD::BUILTIN_OP_END || OP1N->getNumOperands() == 0)
271       return;
272 
273     LLVM_DEBUG(dbgs() << "Check candidate load: "; LD->dump(); dbgs() << '\n');
274 
275     const GlobalAddressSDNode *GADN =
276         dyn_cast<GlobalAddressSDNode>(OP1N->getOperand(0).getNode());
277     const ConstantSDNode *CDN = dyn_cast<ConstantSDNode>(OP2.getNode());
278     if (GADN && CDN)
279       to_replace =
280           getConstantFieldValue(GADN, CDN->getZExtValue(), size, new_val.c);
281   } else if (LDAddrNode->getOpcode() > ISD::BUILTIN_OP_END &&
282              LDAddrNode->getNumOperands() > 0) {
283     LLVM_DEBUG(dbgs() << "Check candidate load: "; LD->dump(); dbgs() << '\n');
284 
285     SDValue OP1 = LDAddrNode->getOperand(0);
286     if (const GlobalAddressSDNode *GADN =
287             dyn_cast<GlobalAddressSDNode>(OP1.getNode()))
288       to_replace = getConstantFieldValue(GADN, 0, size, new_val.c);
289   }
290 
291   if (!to_replace)
292     return;
293 
294   // replacing the old with a new value
295   uint64_t val;
296   if (size == 1)
297     val = new_val.c[0];
298   else if (size == 2)
299     val = new_val.s;
300   else if (size == 4)
301     val = new_val.i;
302   else {
303     val = new_val.d;
304   }
305 
306   LLVM_DEBUG(dbgs() << "Replacing load of size " << size << " with constant "
307                     << val << '\n');
308   SDValue NVal = CurDAG->getConstant(val, DL, LD->getValueType(0));
309 
310   // After replacement, the current node is dead, we need to
311   // go backward one step to make iterator still work
312   I--;
313   SDValue From[] = {SDValue(Node, 0), SDValue(Node, 1)};
314   SDValue To[] = {NVal, NVal};
315   CurDAG->ReplaceAllUsesOfValuesWith(From, To, 2);
316   I++;
317   // It is safe to delete node now
318   CurDAG->DeleteNode(Node);
319 }
320 
321 void BPFDAGToDAGISel::PreprocessISelDAG() {
322   // Iterate through all nodes, interested in the following case:
323   //
324   //  . loads from ConstantStruct or ConstantArray of constructs
325   //    which can be turns into constant itself, with this we can
326   //    avoid reading from read-only section at runtime.
327   //
328   //  . Removing redundant AND for intrinsic narrow loads.
329   for (SelectionDAG::allnodes_iterator I = CurDAG->allnodes_begin(),
330                                        E = CurDAG->allnodes_end();
331        I != E;) {
332     SDNode *Node = &*I++;
333     unsigned Opcode = Node->getOpcode();
334     if (Opcode == ISD::LOAD)
335       PreprocessLoad(Node, I);
336     else if (Opcode == ISD::AND)
337       PreprocessTrunc(Node, I);
338   }
339 }
340 
341 bool BPFDAGToDAGISel::getConstantFieldValue(const GlobalAddressSDNode *Node,
342                                             uint64_t Offset, uint64_t Size,
343                                             unsigned char *ByteSeq) {
344   const GlobalVariable *V = dyn_cast<GlobalVariable>(Node->getGlobal());
345 
346   if (!V || !V->hasInitializer() || !V->isConstant())
347     return false;
348 
349   const Constant *Init = V->getInitializer();
350   const DataLayout &DL = CurDAG->getDataLayout();
351   val_vec_type TmpVal;
352 
353   auto it = cs_vals_.find(static_cast<const void *>(Init));
354   if (it != cs_vals_.end()) {
355     TmpVal = it->second;
356   } else {
357     uint64_t total_size = 0;
358     if (const ConstantStruct *CS = dyn_cast<ConstantStruct>(Init))
359       total_size =
360           DL.getStructLayout(cast<StructType>(CS->getType()))->getSizeInBytes();
361     else if (const ConstantArray *CA = dyn_cast<ConstantArray>(Init))
362       total_size = DL.getTypeAllocSize(CA->getType()->getElementType()) *
363                    CA->getNumOperands();
364     else
365       return false;
366 
367     val_vec_type Vals(total_size, 0);
368     if (fillGenericConstant(DL, Init, Vals, 0) == false)
369       return false;
370     cs_vals_[static_cast<const void *>(Init)] = Vals;
371     TmpVal = std::move(Vals);
372   }
373 
374   // test whether host endianness matches target
375   union {
376     uint8_t c[2];
377     uint16_t s;
378   } test_buf;
379   uint16_t test_val = 0x2345;
380   if (DL.isLittleEndian())
381     support::endian::write16le(test_buf.c, test_val);
382   else
383     support::endian::write16be(test_buf.c, test_val);
384 
385   bool endian_match = test_buf.s == test_val;
386   for (uint64_t i = Offset, j = 0; i < Offset + Size; i++, j++)
387     ByteSeq[j] = endian_match ? TmpVal[i] : TmpVal[Offset + Size - 1 - j];
388 
389   return true;
390 }
391 
392 bool BPFDAGToDAGISel::fillGenericConstant(const DataLayout &DL,
393                                           const Constant *CV,
394                                           val_vec_type &Vals, uint64_t Offset) {
395   uint64_t Size = DL.getTypeAllocSize(CV->getType());
396 
397   if (isa<ConstantAggregateZero>(CV) || isa<UndefValue>(CV))
398     return true; // already done
399 
400   if (const ConstantInt *CI = dyn_cast<ConstantInt>(CV)) {
401     uint64_t val = CI->getZExtValue();
402     LLVM_DEBUG(dbgs() << "Byte array at offset " << Offset << " with value "
403                       << val << '\n');
404 
405     if (Size > 8 || (Size & (Size - 1)))
406       return false;
407 
408     // Store based on target endian
409     for (uint64_t i = 0; i < Size; ++i) {
410       Vals[Offset + i] = DL.isLittleEndian()
411                              ? ((val >> (i * 8)) & 0xFF)
412                              : ((val >> ((Size - i - 1) * 8)) & 0xFF);
413     }
414     return true;
415   }
416 
417   if (const ConstantDataArray *CDA = dyn_cast<ConstantDataArray>(CV))
418     return fillConstantDataArray(DL, CDA, Vals, Offset);
419 
420   if (const ConstantArray *CA = dyn_cast<ConstantArray>(CV))
421     return fillConstantArray(DL, CA, Vals, Offset);
422 
423   if (const ConstantStruct *CVS = dyn_cast<ConstantStruct>(CV))
424     return fillConstantStruct(DL, CVS, Vals, Offset);
425 
426   return false;
427 }
428 
429 bool BPFDAGToDAGISel::fillConstantDataArray(const DataLayout &DL,
430                                             const ConstantDataArray *CDA,
431                                             val_vec_type &Vals, int Offset) {
432   for (unsigned i = 0, e = CDA->getNumElements(); i != e; ++i) {
433     if (fillGenericConstant(DL, CDA->getElementAsConstant(i), Vals, Offset) ==
434         false)
435       return false;
436     Offset += DL.getTypeAllocSize(CDA->getElementAsConstant(i)->getType());
437   }
438 
439   return true;
440 }
441 
442 bool BPFDAGToDAGISel::fillConstantArray(const DataLayout &DL,
443                                         const ConstantArray *CA,
444                                         val_vec_type &Vals, int Offset) {
445   for (unsigned i = 0, e = CA->getNumOperands(); i != e; ++i) {
446     if (fillGenericConstant(DL, CA->getOperand(i), Vals, Offset) == false)
447       return false;
448     Offset += DL.getTypeAllocSize(CA->getOperand(i)->getType());
449   }
450 
451   return true;
452 }
453 
454 bool BPFDAGToDAGISel::fillConstantStruct(const DataLayout &DL,
455                                          const ConstantStruct *CS,
456                                          val_vec_type &Vals, int Offset) {
457   const StructLayout *Layout = DL.getStructLayout(CS->getType());
458   for (unsigned i = 0, e = CS->getNumOperands(); i != e; ++i) {
459     const Constant *Field = CS->getOperand(i);
460     uint64_t SizeSoFar = Layout->getElementOffset(i);
461     if (fillGenericConstant(DL, Field, Vals, Offset + SizeSoFar) == false)
462       return false;
463   }
464   return true;
465 }
466 
467 void BPFDAGToDAGISel::PreprocessTrunc(SDNode *Node,
468                                       SelectionDAG::allnodes_iterator &I) {
469   ConstantSDNode *MaskN = dyn_cast<ConstantSDNode>(Node->getOperand(1));
470   if (!MaskN)
471     return;
472 
473   // The Reg operand should be a virtual register, which is defined
474   // outside the current basic block. DAG combiner has done a pretty
475   // good job in removing truncating inside a single basic block except
476   // when the Reg operand comes from bpf_load_[byte | half | word] for
477   // which the generic optimizer doesn't understand their results are
478   // zero extended.
479   SDValue BaseV = Node->getOperand(0);
480   if (BaseV.getOpcode() != ISD::INTRINSIC_W_CHAIN)
481     return;
482 
483   unsigned IntNo = cast<ConstantSDNode>(BaseV->getOperand(1))->getZExtValue();
484   uint64_t MaskV = MaskN->getZExtValue();
485 
486   if (!((IntNo == Intrinsic::bpf_load_byte && MaskV == 0xFF) ||
487         (IntNo == Intrinsic::bpf_load_half && MaskV == 0xFFFF) ||
488         (IntNo == Intrinsic::bpf_load_word && MaskV == 0xFFFFFFFF)))
489     return;
490 
491   LLVM_DEBUG(dbgs() << "Remove the redundant AND operation in: ";
492              Node->dump(); dbgs() << '\n');
493 
494   I--;
495   CurDAG->ReplaceAllUsesWith(SDValue(Node, 0), BaseV);
496   I++;
497   CurDAG->DeleteNode(Node);
498 }
499 
500 FunctionPass *llvm::createBPFISelDag(BPFTargetMachine &TM) {
501   return new BPFDAGToDAGISel(TM);
502 }
503