llvm-mirror/lib/Analysis/IRSimilarityIdentifier.cpp

//===- IRSimilarityIdentifier.cpp - Find similarity in a module -----------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// \file
// Implementation file for the IRSimilarityIdentifier for identifying
// similarities in IR including the IRInstructionMapper.
//
//===----------------------------------------------------------------------===//

#include "llvm/Analysis/IRSimilarityIdentifier.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/IR/Intrinsics.h"
#include "llvm/IR/User.h"

using namespace llvm;
using namespace IRSimilarity;

IRInstructionData::IRInstructionData(Instruction &I, bool Legality,
                                     IRInstructionDataList &IDList)
    : Inst(&I), Legal(Legality), IDL(&IDList) {
  // Here we collect the operands to be used to determine whether two
  // instructions are similar to one another.
  for (Use &OI : I.operands())
    OperVals.push_back(OI.get());
}

bool IRSimilarity::isClose(const IRInstructionData &A,
                           const IRInstructionData &B) {
  return A.Legal && A.Inst->isSameOperationAs(B.Inst);
}

// TODO: This is the same as the MachineOutliner, and should be consolidated
// into the same interface.
void IRInstructionMapper::convertToUnsignedVec(
    BasicBlock &BB, std::vector<IRInstructionData *> &InstrList,
    std::vector<unsigned> &IntegerMapping) {
  BasicBlock::iterator It = BB.begin();

  std::vector<unsigned> IntegerMappingForBB;
  std::vector<IRInstructionData *> InstrListForBB;

  HaveLegalRange = false;
  CanCombineWithPrevInstr = false;
  AddedIllegalLastTime = true;

  for (BasicBlock::iterator Et = BB.end(); It != Et; ++It) {
    switch (InstClassifier.visit(*It)) {
    case InstrType::Legal:
      mapToLegalUnsigned(It, IntegerMappingForBB, InstrListForBB);
      break;
    case InstrType::Illegal:
      mapToIllegalUnsigned(It, IntegerMappingForBB, InstrListForBB);
      break;
    case InstrType::Invisible:
      AddedIllegalLastTime = false;
      break;
    }
  }

  if (HaveLegalRange) {
    mapToIllegalUnsigned(It, IntegerMappingForBB, InstrListForBB, true);
    for_each(InstrListForBB,
             [this](IRInstructionData *ID) { this->IDL->push_back(*ID); });
    InstrList.insert(InstrList.end(), InstrListForBB.begin(),
                     InstrListForBB.end());
    IntegerMapping.insert(IntegerMapping.end(), IntegerMappingForBB.begin(),
                          IntegerMappingForBB.end());
  }
}

// TODO: This is the same as the MachineOutliner, and should be consolidated
// into the same interface.
unsigned IRInstructionMapper::mapToLegalUnsigned(
    BasicBlock::iterator &It, std::vector<unsigned> &IntegerMappingForBB,
    std::vector<IRInstructionData *> &InstrListForBB) {
  // We added something legal, so we should unset the AddedLegalLastTime
  // flag.
  AddedIllegalLastTime = false;

  // If we have at least two adjacent legal instructions (which may have
  // invisible instructions in between), remember that.
  if (CanCombineWithPrevInstr)
    HaveLegalRange = true;
  CanCombineWithPrevInstr = true;

  // Get the integer for this instruction or give it the current
  // LegalInstrNumber.
  IRInstructionData *ID = allocateIRInstructionData(*It, true, *IDL);
  InstrListForBB.push_back(ID);

  // Add to the instruction list
  bool WasInserted;
  DenseMap<IRInstructionData *, unsigned, IRInstructionDataTraits>::iterator
      ResultIt;
  std::tie(ResultIt, WasInserted) =
      InstructionIntegerMap.insert(std::make_pair(ID, LegalInstrNumber));
  unsigned INumber = ResultIt->second;

  // There was an insertion.
  if (WasInserted)
    LegalInstrNumber++;

  IntegerMappingForBB.push_back(INumber);

  // Make sure we don't overflow or use any integers reserved by the DenseMap.
  assert(LegalInstrNumber < IllegalInstrNumber &&
         "Instruction mapping overflow!");

  assert(LegalInstrNumber != DenseMapInfo<unsigned>::getEmptyKey() &&
         "Tried to assign DenseMap tombstone or empty key to instruction.");
  assert(LegalInstrNumber != DenseMapInfo<unsigned>::getTombstoneKey() &&
         "Tried to assign DenseMap tombstone or empty key to instruction.");

  return INumber;
}

IRInstructionData *
IRInstructionMapper::allocateIRInstructionData(Instruction &I, bool Legality,
                                               IRInstructionDataList &IDL) {
  return new (InstDataAllocator->Allocate()) IRInstructionData(I, Legality, IDL);
}

IRInstructionDataList *
IRInstructionMapper::allocateIRInstructionDataList() {
  return new (IDLAllocator->Allocate()) IRInstructionDataList();
}

// TODO: This is the same as the MachineOutliner, and should be consolidated
// into the same interface.
unsigned IRInstructionMapper::mapToIllegalUnsigned(
    BasicBlock::iterator &It, std::vector<unsigned> &IntegerMappingForBB,
    std::vector<IRInstructionData *> &InstrListForBB, bool End) {
  // Can't combine an illegal instruction. Set the flag.
  CanCombineWithPrevInstr = false;

  // Only add one illegal number per range of legal numbers.
  if (AddedIllegalLastTime)
    return IllegalInstrNumber;

  IRInstructionData *ID = nullptr;
  if (!End)
    ID = allocateIRInstructionData(*It, false, *IDL);
  InstrListForBB.push_back(ID);

  // Remember that we added an illegal number last time.
  AddedIllegalLastTime = true;
  unsigned INumber = IllegalInstrNumber;
  IntegerMappingForBB.push_back(IllegalInstrNumber--);

  assert(LegalInstrNumber < IllegalInstrNumber &&
         "Instruction mapping overflow!");

  assert(IllegalInstrNumber != DenseMapInfo<unsigned>::getEmptyKey() &&
         "IllegalInstrNumber cannot be DenseMap tombstone or empty key!");

  assert(IllegalInstrNumber != DenseMapInfo<unsigned>::getTombstoneKey() &&
         "IllegalInstrNumber cannot be DenseMap tombstone or empty key!");

  return INumber;
}

IRSimilarityCandidate::IRSimilarityCandidate(unsigned StartIdx, unsigned Len,
                                             IRInstructionData *FirstInstIt,
                                             IRInstructionData *LastInstIt)
    : StartIdx(StartIdx), Len(Len) {

  assert(FirstInstIt != nullptr && "Instruction is nullptr!");
  assert(LastInstIt != nullptr && "Instruction is nullptr!");
  assert(StartIdx + Len > StartIdx &&
         "Overflow for IRSimilarityCandidate range?");
  assert(Len - 1 ==
             std::distance(iterator(FirstInstIt), iterator(LastInstIt)) &&
         "Length of the first and last IRInstructionData do not match the "
         "given length");

  // We iterate over the given instructions, and map each unique value
  // to a unique number in the IRSimilarityCandidate ValueToNumber and
  // NumberToValue maps.  A constant get its own value globally, the individual
  // uses of the constants are not considered to be unique.
  //
  // IR:                    Mapping Added:
  // %add1 = add i32 %a, c1    %add1 -> 3, %a -> 1, c1 -> 2
  // %add2 = add i32 %a, %1    %add2 -> 4
  // %add3 = add i32 c2, c1    %add3 -> 6, c2 -> 5
  //
  // when replace with global values, starting from 1, would be
  //
  // 3 = add i32 1, 2
  // 4 = add i32 1, 3
  // 6 = add i32 5, 2
  unsigned LocalValNumber = 1;
  IRInstructionDataList::iterator ID = iterator(*FirstInstIt);
  for (unsigned Loc = StartIdx; Loc < StartIdx + Len; Loc++, ID++) {
    // Map the operand values to an unsigned integer if it does not already
    // have an unsigned integer assigned to it.
    for (Value *Arg : ID->OperVals)
      if (ValueToNumber.find(Arg) == ValueToNumber.end()) {
        ValueToNumber.try_emplace(Arg, LocalValNumber);
        NumberToValue.try_emplace(LocalValNumber, Arg);
        LocalValNumber++;
      }

    // Mapping the instructions to an unsigned integer if it is not already
    // exist in the mapping.
    if (ValueToNumber.find(ID->Inst) == ValueToNumber.end()) {
      ValueToNumber.try_emplace(ID->Inst, LocalValNumber);
      NumberToValue.try_emplace(LocalValNumber, ID->Inst);
      LocalValNumber++;
    }
  }

  // Setting the first and last instruction data pointers for the candidate.  If
  // we got through the entire for loop without hitting an assert, we know
  // that both of these instructions are not nullptrs.
  FirstInst = FirstInstIt;
  LastInst = LastInstIt;
}

bool IRSimilarityCandidate::isSimilar(const IRSimilarityCandidate &A,
                                      const IRSimilarityCandidate &B) {
  if (A.getLength() != B.getLength())
    return false;

  auto InstrDataForBoth =
      zip(make_range(A.begin(), A.end()), make_range(B.begin(), B.end()));

  return all_of(InstrDataForBoth,
                [](std::tuple<IRInstructionData &, IRInstructionData &> R) {
                  IRInstructionData &A = std::get<0>(R);
                  IRInstructionData &B = std::get<1>(R);
                  if (!A.Legal || !B.Legal)
                    return false;
                  return isClose(A, B);
                });
}

/// Determine if operand number \p TargetArgVal is in the current mapping set
/// for operand number \p SourceArgVal.
///
/// \param [in, out] CurrentSrcTgtNumberMapping current mapping of global
/// value numbers from source IRSimilarityCandidate to target
/// IRSimilarityCandidate.
/// \param [in] SourceArgVal The global value number for an operand in the
/// in the original candidate.
/// \param [in] TargetArgVal The global value number for the corresponding
/// operand in the other candidate.
/// \returns True if there exists a mapping and false if not.
bool checkNumberingAndReplace(
    DenseMap<unsigned, DenseSet<unsigned>> &CurrentSrcTgtNumberMapping,
    unsigned SourceArgVal, unsigned TargetArgVal) {
  // We are given two unsigned integers representing the global values of
  // the operands in different IRSimilarityCandidates and a current mapping
  // between the two.
  //
  // Source Operand GVN: 1
  // Target Operand GVN: 2
  // CurrentMapping: {1: {1, 2}}
  //
  // Since we have mapping, and the target operand is contained in the set, we
  // update it to:
  // CurrentMapping: {1: {2}}
  // and can return true. But, if the mapping was
  // CurrentMapping: {1: {3}}
  // we would return false.

  bool WasInserted;
  DenseMap<unsigned, DenseSet<unsigned>>::iterator Val;

  std::tie(Val, WasInserted) = CurrentSrcTgtNumberMapping.insert(
      std::make_pair(SourceArgVal, DenseSet<unsigned>({TargetArgVal})));

  // If we created a new mapping, then we are done.
  if (WasInserted)
    return true;

  // If there is more than one option in the mapping set, and the target value
  // is included in the mapping set replace that set with one that only includes
  // the target value, as it is the only valid mapping via the non commutative
  // instruction.

  DenseSet<unsigned> &TargetSet = Val->second;
  if (TargetSet.size() > 1 && TargetSet.find(TargetArgVal) != TargetSet.end()) {
    TargetSet.clear();
    TargetSet.insert(TargetArgVal);
    return true;
  }

  // Return true if we can find the value in the set.
  return TargetSet.find(TargetArgVal) != TargetSet.end();
}

bool IRSimilarityCandidate::compareOperandMapping(OperandMapping A,
                                                  OperandMapping B) {
  // Iterators to keep track of where we are in the operands for each
  // Instruction.
  ArrayRef<Value *>::iterator VItA = A.OperVals.begin();
  ArrayRef<Value *>::iterator VItB = B.OperVals.begin();
  unsigned OperandLength = A.OperVals.size();

  // For each operand, get the value numbering and ensure it is consistent.
  for (unsigned Idx = 0; Idx < OperandLength; Idx++, VItA++, VItB++) {
    unsigned OperValA = A.IRSC.ValueToNumber.find(*VItA)->second;
    unsigned OperValB = B.IRSC.ValueToNumber.find(*VItB)->second;

    // Attempt to add a set with only the target value.  If there is no mapping
    // we can create it here.
    //
    // For an instruction like a subtraction:
    // IRSimilarityCandidateA:  IRSimilarityCandidateB:
    // %resultA = sub %a, %b    %resultB = sub %d, %e
    //
    // We map %a -> %d and %b -> %e.
    //
    // And check to see whether their mapping is consistent in
    // checkNumberingAndReplace.

    if (!checkNumberingAndReplace(A.ValueNumberMapping, OperValA, OperValB))
      return false;

    if (!checkNumberingAndReplace(B.ValueNumberMapping, OperValB, OperValA))
      return false;
  }
  return true;
}

bool IRSimilarityCandidate::compareStructure(const IRSimilarityCandidate &A,
                                             const IRSimilarityCandidate &B) {
  if (A.getLength() != B.getLength())
    return false;

  if (A.ValueToNumber.size() != B.ValueToNumber.size())
    return false;

  iterator ItA = A.begin();
  iterator ItB = B.begin();

  // These sets create a create a mapping between the values in one candidate
  // to values in the other candidate.  If we create a set with one element,
  // and that same element maps to the original element in the candidate
  // we have a good mapping.
  DenseMap<unsigned, DenseSet<unsigned>> ValueNumberMappingA;
  DenseMap<unsigned, DenseSet<unsigned>> ValueNumberMappingB;
  DenseMap<unsigned, DenseSet<unsigned>>::iterator ValueMappingIt;

  bool WasInserted;

  // Iterate over the instructions contained in each candidate
  unsigned SectionLength = A.getStartIdx() + A.getLength();
  for (unsigned Loc = A.getStartIdx(); Loc < SectionLength;
       ItA++, ItB++, Loc++) {
    // Make sure the instructions are similar to one another.
    if (!isClose(*ItA, *ItB))
      return false;

    Instruction *IA = ItA->Inst;
    Instruction *IB = ItB->Inst;

    if (!ItA->Legal || !ItB->Legal)
      return false;

    // Get the operand sets for the instructions.
    ArrayRef<Value *> OperValsA = ItA->OperVals;
    ArrayRef<Value *> OperValsB = ItB->OperVals;

    unsigned InstValA = A.ValueToNumber.find(IA)->second;
    unsigned InstValB = B.ValueToNumber.find(IB)->second;

    // Ensure that the mappings for the instructions exists.
    std::tie(ValueMappingIt, WasInserted) = ValueNumberMappingA.insert(
        std::make_pair(InstValA, DenseSet<unsigned>({InstValB})));
    if (!WasInserted && ValueMappingIt->second.find(InstValB) ==
                            ValueMappingIt->second.end())
      return false;

    std::tie(ValueMappingIt, WasInserted) = ValueNumberMappingB.insert(
        std::make_pair(InstValB, DenseSet<unsigned>({InstValA})));
    if (!WasInserted && ValueMappingIt->second.find(InstValA) ==
                            ValueMappingIt->second.end())
      return false;

    // TODO: Handle commutative instructions by mapping one operand to many
    // operands instead only mapping a single operand to a single operand.
    if (!compareOperandMapping({A, OperValsA, ValueNumberMappingA},
                               {B, OperValsB, ValueNumberMappingB}))
      return false;
  }

  return true;
}

bool IRSimilarityCandidate::overlap(const IRSimilarityCandidate &A,
                                    const IRSimilarityCandidate &B) {
  auto DoesOverlap = [](const IRSimilarityCandidate &X,
                        const IRSimilarityCandidate &Y) {
    // Check:
    // XXXXXX        X starts before Y ends
    //      YYYYYYY  Y starts after X starts
    return X.StartIdx <= Y.getEndIdx() && Y.StartIdx >= X.StartIdx;
  };

  return DoesOverlap(A, B) || DoesOverlap(B, A);
}