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 }
499