C++ SelectInst::getFalseValue方法代码示例

SizeOffsetType ObjectSizeOffsetVisitor::visitSelectInst(SelectInst &I) {
  SizeOffsetType TrueSide  = compute(I.getTrueValue());
  SizeOffsetType FalseSide = compute(I.getFalseValue());
  if (bothKnown(TrueSide) && bothKnown(FalseSide) && TrueSide == FalseSide)
    return TrueSide;
  return unknown();
}

SizeOffsetType ObjectSizeOffsetVisitor::visitSelectInst(SelectInst &I) {
  SizeOffsetType TrueSide  = compute(I.getTrueValue());
  SizeOffsetType FalseSide = compute(I.getFalseValue());
  if (bothKnown(TrueSide) && bothKnown(FalseSide)) {
    if (TrueSide == FalseSide) {
        return TrueSide;
    }

    APInt TrueResult = getSizeWithOverflow(TrueSide);
    APInt FalseResult = getSizeWithOverflow(FalseSide);

    if (TrueResult == FalseResult) {
      return TrueSide;
    }
    if (Options.EvalMode == ObjectSizeOpts::Mode::Min) {
      if (TrueResult.slt(FalseResult))
        return TrueSide;
      return FalseSide;
    }
    if (Options.EvalMode == ObjectSizeOpts::Mode::Max) {
      if (TrueResult.sgt(FalseResult))
        return TrueSide;
      return FalseSide;
    }
  }
  return unknown();
}

/// MatchSelectPattern - Pattern match integer [SU]MIN, [SU]MAX, and ABS idioms,
/// returning the kind and providing the out parameter results if we
/// successfully match.
static SelectPatternFlavor
MatchSelectPattern(Value *V, Value *&LHS, Value *&RHS) {
  SelectInst *SI = dyn_cast<SelectInst>(V);
  if (SI == 0) return SPF_UNKNOWN;

  ICmpInst *ICI = dyn_cast<ICmpInst>(SI->getCondition());
  if (ICI == 0) return SPF_UNKNOWN;

  LHS = ICI->getOperand(0);
  RHS = ICI->getOperand(1);

  // (icmp X, Y) ? X : Y
  if (SI->getTrueValue() == ICI->getOperand(0) &&
      SI->getFalseValue() == ICI->getOperand(1)) {
    switch (ICI->getPredicate()) {
    default: return SPF_UNKNOWN; // Equality.
    case ICmpInst::ICMP_UGT:
    case ICmpInst::ICMP_UGE: return SPF_UMAX;
    case ICmpInst::ICMP_SGT:
    case ICmpInst::ICMP_SGE: return SPF_SMAX;
    case ICmpInst::ICMP_ULT:
    case ICmpInst::ICMP_ULE: return SPF_UMIN;
    case ICmpInst::ICMP_SLT:
    case ICmpInst::ICMP_SLE: return SPF_SMIN;
    }
  }

  // (icmp X, Y) ? Y : X
  if (SI->getTrueValue() == ICI->getOperand(1) &&
      SI->getFalseValue() == ICI->getOperand(0)) {
    switch (ICI->getPredicate()) {
      default: return SPF_UNKNOWN; // Equality.
      case ICmpInst::ICMP_UGT:
      case ICmpInst::ICMP_UGE: return SPF_UMIN;
      case ICmpInst::ICMP_SGT:
      case ICmpInst::ICMP_SGE: return SPF_SMIN;
      case ICmpInst::ICMP_ULT:
      case ICmpInst::ICMP_ULE: return SPF_UMAX;
      case ICmpInst::ICMP_SLT:
      case ICmpInst::ICMP_SLE: return SPF_SMAX;
    }
  }

  // TODO: (X > 4) ? X : 5   -->  (X >= 5) ? X : 5  -->  MAX(X, 5)

  return SPF_UNKNOWN;
}

bool CorrelatedValuePropagation::processPHI(PHINode *P) {
  bool Changed = false;

  BasicBlock *BB = P->getParent();
  for (unsigned i = 0, e = P->getNumIncomingValues(); i < e; ++i) {
    Value *Incoming = P->getIncomingValue(i);
    if (isa<Constant>(Incoming)) continue;

    Value *V = LVI->getConstantOnEdge(Incoming, P->getIncomingBlock(i), BB);

    // Look if the incoming value is a select with a constant but LVI tells us
    // that the incoming value can never be that constant. In that case replace
    // the incoming value with the other value of the select. This often allows
    // us to remove the select later.
    if (!V) {
      SelectInst *SI = dyn_cast<SelectInst>(Incoming);
      if (!SI) continue;

      Constant *C = dyn_cast<Constant>(SI->getFalseValue());
      if (!C) continue;

      if (LVI->getPredicateOnEdge(ICmpInst::ICMP_EQ, SI, C,
                                  P->getIncomingBlock(i), BB) !=
          LazyValueInfo::False)
        continue;

      DEBUG(dbgs() << "CVP: Threading PHI over " << *SI << '\n');
      V = SI->getTrueValue();
    }

    P->setIncomingValue(i, V);
    Changed = true;
  }

  if (Value *V = SimplifyInstruction(P)) {
    P->replaceAllUsesWith(V);
    P->eraseFromParent();
    Changed = true;
  }

  if (Changed)
    ++NumPhis;

  return Changed;
}

/// Returns true if the select instruction has users in the compare-and-add
/// reduction pattern below. The select instruction argument is the last one
/// in the sequence.
///
/// %sum.1 = phi ...
/// ...
/// %cmp = fcmp pred %0, %CFP
/// %add = fadd %0, %sum.1
/// %sum.2 = select %cmp, %add, %sum.1
RecurrenceDescriptor::InstDesc
RecurrenceDescriptor::isConditionalRdxPattern(
    RecurrenceKind Kind, Instruction *I) {
  SelectInst *SI = dyn_cast<SelectInst>(I);
  if (!SI)
    return InstDesc(false, I);

  CmpInst *CI = dyn_cast<CmpInst>(SI->getCondition());
  // Only handle single use cases for now.
  if (!CI || !CI->hasOneUse())
    return InstDesc(false, I);

  Value *TrueVal = SI->getTrueValue();
  Value *FalseVal = SI->getFalseValue();
  // Handle only when either of operands of select instruction is a PHI
  // node for now.
  if ((isa<PHINode>(*TrueVal) && isa<PHINode>(*FalseVal)) ||
      (!isa<PHINode>(*TrueVal) && !isa<PHINode>(*FalseVal)))
    return InstDesc(false, I);

  Instruction *I1 =
      isa<PHINode>(*TrueVal) ? dyn_cast<Instruction>(FalseVal)
                             : dyn_cast<Instruction>(TrueVal);
  if (!I1 || !I1->isBinaryOp())
    return InstDesc(false, I);

  Value *Op1, *Op2;
  if ((m_FAdd(m_Value(Op1), m_Value(Op2)).match(I1)  ||
       m_FSub(m_Value(Op1), m_Value(Op2)).match(I1)) &&
      I1->isFast())
    return InstDesc(Kind == RK_FloatAdd, SI);

  if (m_FMul(m_Value(Op1), m_Value(Op2)).match(I1) && (I1->isFast()))
    return InstDesc(Kind == RK_FloatMult, SI);

  return InstDesc(false, I);
}

bool SelectInstrumenter::CheckAndInstrument(Instruction* inst) {
  SelectInst* selectInst = dyn_cast<SelectInst>(inst);

  if (selectInst != NULL) {

    safe_assert(parent_ != NULL);

    count_++;

    InstrPtrVector instrs;

    Constant* iidC = IID_CONSTANT(selectInst);

    Constant* inxC = computeIndex(selectInst);

    Value* condition = KVALUE_VALUE(selectInst->getCondition(), instrs, NOSIGN);
    if(condition == NULL) return false;

    Value* tvalue = KVALUE_VALUE(selectInst->getTrueValue(), instrs, NOSIGN);
    if(tvalue == NULL) return false;
    
    Value* fvalue = KVALUE_VALUE(selectInst->getFalseValue(), instrs, NOSIGN);
    if(fvalue == NULL) return false;
    
    Instruction* call = CALL_IID_KVALUE_KVALUE_KVALUE_INT("llvm_select", iidC, condition, tvalue, fvalue, inxC);
    
    instrs.push_back(call);

    // instrument
    InsertAllBefore(instrs, selectInst);

    return true;
  } 

  return false;
}

/// Tests whether this function is known to not return null.
///
/// Requires that the function returns a pointer.
///
/// Returns true if it believes the function will not return a null, and sets
/// \p Speculative based on whether the returned conclusion is a speculative
/// conclusion due to SCC calls.
static bool isReturnNonNull(Function *F, const SCCNodeSet &SCCNodes,
                            bool &Speculative) {
  assert(F->getReturnType()->isPointerTy() &&
         "nonnull only meaningful on pointer types");
  Speculative = false;

  SmallSetVector<Value *, 8> FlowsToReturn;
  for (BasicBlock &BB : *F)
    if (auto *Ret = dyn_cast<ReturnInst>(BB.getTerminator()))
      FlowsToReturn.insert(Ret->getReturnValue());

  for (unsigned i = 0; i != FlowsToReturn.size(); ++i) {
    Value *RetVal = FlowsToReturn[i];

    // If this value is locally known to be non-null, we're good
    if (isKnownNonNull(RetVal))
      continue;

    // Otherwise, we need to look upwards since we can't make any local
    // conclusions.
    Instruction *RVI = dyn_cast<Instruction>(RetVal);
    if (!RVI)
      return false;
    switch (RVI->getOpcode()) {
    // Extend the analysis by looking upwards.
    case Instruction::BitCast:
    case Instruction::GetElementPtr:
    case Instruction::AddrSpaceCast:
      FlowsToReturn.insert(RVI->getOperand(0));
      continue;
    case Instruction::Select: {
      SelectInst *SI = cast<SelectInst>(RVI);
      FlowsToReturn.insert(SI->getTrueValue());
      FlowsToReturn.insert(SI->getFalseValue());
      continue;
    }
    case Instruction::PHI: {
      PHINode *PN = cast<PHINode>(RVI);
      for (int i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
        FlowsToReturn.insert(PN->getIncomingValue(i));
      continue;
    }
    case Instruction::Call:
    case Instruction::Invoke: {
      CallSite CS(RVI);
      Function *Callee = CS.getCalledFunction();
      // A call to a node within the SCC is assumed to return null until
      // proven otherwise
      if (Callee && SCCNodes.count(Callee)) {
        Speculative = true;
        continue;
      }
      return false;
    }
    default:
      return false; // Unknown source, may be null
    };
    llvm_unreachable("should have either continued or returned");
  }

  return true;
}

/// Tests whether a function is "malloc-like".
///
/// A function is "malloc-like" if it returns either null or a pointer that
/// doesn't alias any other pointer visible to the caller.
static bool isFunctionMallocLike(Function *F, const SCCNodeSet &SCCNodes) {
  SmallSetVector<Value *, 8> FlowsToReturn;
  for (BasicBlock &BB : *F)
    if (ReturnInst *Ret = dyn_cast<ReturnInst>(BB.getTerminator()))
      FlowsToReturn.insert(Ret->getReturnValue());

  for (unsigned i = 0; i != FlowsToReturn.size(); ++i) {
    Value *RetVal = FlowsToReturn[i];

    if (Constant *C = dyn_cast<Constant>(RetVal)) {
      if (!C->isNullValue() && !isa<UndefValue>(C))
        return false;

      continue;
    }

    if (isa<Argument>(RetVal))
      return false;

    if (Instruction *RVI = dyn_cast<Instruction>(RetVal))
      switch (RVI->getOpcode()) {
      // Extend the analysis by looking upwards.
      case Instruction::BitCast:
      case Instruction::GetElementPtr:
      case Instruction::AddrSpaceCast:
        FlowsToReturn.insert(RVI->getOperand(0));
        continue;
      case Instruction::Select: {
        SelectInst *SI = cast<SelectInst>(RVI);
        FlowsToReturn.insert(SI->getTrueValue());
        FlowsToReturn.insert(SI->getFalseValue());
        continue;
      }
      case Instruction::PHI: {
        PHINode *PN = cast<PHINode>(RVI);
        for (Value *IncValue : PN->incoming_values())
          FlowsToReturn.insert(IncValue);
        continue;
      }

      // Check whether the pointer came from an allocation.
      case Instruction::Alloca:
        break;
      case Instruction::Call:
      case Instruction::Invoke: {
        CallSite CS(RVI);
        if (CS.hasRetAttr(Attribute::NoAlias))
          break;
        if (CS.getCalledFunction() && SCCNodes.count(CS.getCalledFunction()))
          break;
        LLVM_FALLTHROUGH;
      }
      default:
        return false; // Did not come from an allocation.
      }

    if (PointerMayBeCaptured(RetVal, false, /*StoreCaptures=*/false))
      return false;
  }

  return true;
}

bool CorrelatedValuePropagation::processPHI(PHINode *P) {
  bool Changed = false;

  BasicBlock *BB = P->getParent();
  for (unsigned i = 0, e = P->getNumIncomingValues(); i < e; ++i) {
    Value *Incoming = P->getIncomingValue(i);
    if (isa<Constant>(Incoming)) continue;

    Value *V = LVI->getConstantOnEdge(Incoming, P->getIncomingBlock(i), BB, P);

    // Look if the incoming value is a select with a scalar condition for which
    // LVI can tells us the value. In that case replace the incoming value with
    // the appropriate value of the select. This often allows us to remove the
    // select later.
    if (!V) {
      SelectInst *SI = dyn_cast<SelectInst>(Incoming);
      if (!SI) continue;

      Value *Condition = SI->getCondition();
      if (!Condition->getType()->isVectorTy()) {
        if (Constant *C = LVI->getConstantOnEdge(
                Condition, P->getIncomingBlock(i), BB, P)) {
          if (C->isOneValue()) {
            V = SI->getTrueValue();
          } else if (C->isZeroValue()) {
            V = SI->getFalseValue();
          }
          // Once LVI learns to handle vector types, we could also add support
          // for vector type constants that are not all zeroes or all ones.
        }
      }

      // Look if the select has a constant but LVI tells us that the incoming
      // value can never be that constant. In that case replace the incoming
      // value with the other value of the select. This often allows us to
      // remove the select later.
      if (!V) {
        Constant *C = dyn_cast<Constant>(SI->getFalseValue());
        if (!C) continue;

        if (LVI->getPredicateOnEdge(ICmpInst::ICMP_EQ, SI, C,
              P->getIncomingBlock(i), BB, P) !=
            LazyValueInfo::False)
          continue;
        V = SI->getTrueValue();
      }

      DEBUG(dbgs() << "CVP: Threading PHI over " << *SI << '\n');
    }

    P->setIncomingValue(i, V);
    Changed = true;
  }

  // FIXME: Provide TLI, DT, AT to SimplifyInstruction.
  const DataLayout &DL = BB->getModule()->getDataLayout();
  if (Value *V = SimplifyInstruction(P, DL)) {
    P->replaceAllUsesWith(V);
    P->eraseFromParent();
    Changed = true;
  }

  if (Changed)
    ++NumPhis;

  return Changed;
}

//.........这里部分代码省略.........
      if (W == Y) {
        Value *NewAdd = Builder->CreateAdd(X, Z, LHS->getName());
        return BinaryOperator::CreateMul(W, NewAdd);
      }
    }
  }

  if (ConstantInt *CRHS = dyn_cast<ConstantInt>(RHS)) {
    Value *X = 0;
    if (match(LHS, m_Not(m_Value(X))))    // ~X + C --> (C-1) - X
      return BinaryOperator::CreateSub(SubOne(CRHS), X);

    // (X & FF00) + xx00  -> (X+xx00) & FF00
    if (LHS->hasOneUse() &&
        match(LHS, m_And(m_Value(X), m_ConstantInt(C2))) &&
        CRHS->getValue() == (CRHS->getValue() & C2->getValue())) {
      // See if all bits from the first bit set in the Add RHS up are included
      // in the mask.  First, get the rightmost bit.
      const APInt &AddRHSV = CRHS->getValue();
      
      // Form a mask of all bits from the lowest bit added through the top.
      APInt AddRHSHighBits(~((AddRHSV & -AddRHSV)-1));

      // See if the and mask includes all of these bits.
      APInt AddRHSHighBitsAnd(AddRHSHighBits & C2->getValue());

      if (AddRHSHighBits == AddRHSHighBitsAnd) {
        // Okay, the xform is safe.  Insert the new add pronto.
        Value *NewAdd = Builder->CreateAdd(X, CRHS, LHS->getName());
        return BinaryOperator::CreateAnd(NewAdd, C2);
      }
    }

    // Try to fold constant add into select arguments.
    if (SelectInst *SI = dyn_cast<SelectInst>(LHS))
      if (Instruction *R = FoldOpIntoSelect(I, SI))
        return R;
  }

  // add (select X 0 (sub n A)) A  -->  select X A n
  {
    SelectInst *SI = dyn_cast<SelectInst>(LHS);
    Value *A = RHS;
    if (!SI) {
      SI = dyn_cast<SelectInst>(RHS);
      A = LHS;
    }
    if (SI && SI->hasOneUse()) {
      Value *TV = SI->getTrueValue();
      Value *FV = SI->getFalseValue();
      Value *N;

      // Can we fold the add into the argument of the select?
      // We check both true and false select arguments for a matching subtract.
      if (match(FV, m_Zero()) && match(TV, m_Sub(m_Value(N), m_Specific(A))))
        // Fold the add into the true select value.
        return SelectInst::Create(SI->getCondition(), N, A);
      
      if (match(TV, m_Zero()) && match(FV, m_Sub(m_Value(N), m_Specific(A))))
        // Fold the add into the false select value.
        return SelectInst::Create(SI->getCondition(), A, N);
    }
  }

  // Check for (add (sext x), y), see if we can merge this into an
  // integer add followed by a sext.
  if (SExtInst *LHSConv = dyn_cast<SExtInst>(LHS)) {
    // (add (sext x), cst) --> (sext (add x, cst'))
    if (ConstantInt *RHSC = dyn_cast<ConstantInt>(RHS)) {
      Constant *CI = 
        ConstantExpr::getTrunc(RHSC, LHSConv->getOperand(0)->getType());
      if (LHSConv->hasOneUse() &&
          ConstantExpr::getSExt(CI, I.getType()) == RHSC &&
          WillNotOverflowSignedAdd(LHSConv->getOperand(0), CI)) {
        // Insert the new, smaller add.
        Value *NewAdd = Builder->CreateNSWAdd(LHSConv->getOperand(0), 
                                              CI, "addconv");
        return new SExtInst(NewAdd, I.getType());
      }
    }
    
    // (add (sext x), (sext y)) --> (sext (add int x, y))
    if (SExtInst *RHSConv = dyn_cast<SExtInst>(RHS)) {
      // Only do this if x/y have the same type, if at last one of them has a
      // single use (so we don't increase the number of sexts), and if the
      // integer add will not overflow.
      if (LHSConv->getOperand(0)->getType()==RHSConv->getOperand(0)->getType()&&
          (LHSConv->hasOneUse() || RHSConv->hasOneUse()) &&
          WillNotOverflowSignedAdd(LHSConv->getOperand(0),
                                   RHSConv->getOperand(0))) {
        // Insert the new integer add.
        Value *NewAdd = Builder->CreateNSWAdd(LHSConv->getOperand(0), 
                                             RHSConv->getOperand(0), "addconv");
        return new SExtInst(NewAdd, I.getType());
      }
    }
  }

  return Changed ? &I : 0;
}

/// IsFunctionMallocLike - A function is malloc-like if it returns either null
/// or a pointer that doesn't alias any other pointer visible to the caller.
bool FunctionAttrs::IsFunctionMallocLike(Function *F,
                              SmallPtrSet<Function*, 8> &SCCNodes) const {
  UniqueVector<Value *> FlowsToReturn;
  for (Function::iterator I = F->begin(), E = F->end(); I != E; ++I)
    if (ReturnInst *Ret = dyn_cast<ReturnInst>(I->getTerminator()))
      FlowsToReturn.insert(Ret->getReturnValue());

  for (unsigned i = 0; i != FlowsToReturn.size(); ++i) {
    Value *RetVal = FlowsToReturn[i+1];   // UniqueVector[0] is reserved.

    if (Constant *C = dyn_cast<Constant>(RetVal)) {
      if (!C->isNullValue() && !isa<UndefValue>(C))
        return false;

      continue;
    }

    if (isa<Argument>(RetVal))
      return false;

    if (Instruction *RVI = dyn_cast<Instruction>(RetVal))
      switch (RVI->getOpcode()) {
        // Extend the analysis by looking upwards.
        case Instruction::BitCast:
        case Instruction::GetElementPtr:
          FlowsToReturn.insert(RVI->getOperand(0));
          continue;
        case Instruction::Select: {
          SelectInst *SI = cast<SelectInst>(RVI);
          FlowsToReturn.insert(SI->getTrueValue());
          FlowsToReturn.insert(SI->getFalseValue());
          continue;
        }
        case Instruction::PHI: {
          PHINode *PN = cast<PHINode>(RVI);
          for (int i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
            FlowsToReturn.insert(PN->getIncomingValue(i));
          continue;
        }

        // Check whether the pointer came from an allocation.
        case Instruction::Alloca:
          break;
        case Instruction::Call:
        case Instruction::Invoke: {
          CallSite CS(RVI);
          if (CS.paramHasNoAliasAttr(0))
            break;
          if (CS.getCalledFunction() &&
              SCCNodes.count(CS.getCalledFunction()))
            break;
        } // fall-through
        default:
          return false;  // Did not come from an allocation.
      }

    if (PointerMayBeCaptured(RetVal, false, /*StoreCaptures=*/false))
      return false;
  }

  return true;
}

/// FoldSPFofSPF - We have an SPF (e.g. a min or max) of an SPF of the form:
///   SPF2(SPF1(A, B), C)
Instruction *InstCombiner::FoldSPFofSPF(Instruction *Inner,
                                        SelectPatternFlavor SPF1,
                                        Value *A, Value *B,
                                        Instruction &Outer,
                                        SelectPatternFlavor SPF2, Value *C) {
  if (C == A || C == B) {
    // MAX(MAX(A, B), B) -> MAX(A, B)
    // MIN(MIN(a, b), a) -> MIN(a, b)
    if (SPF1 == SPF2)
      return ReplaceInstUsesWith(Outer, Inner);

    // MAX(MIN(a, b), a) -> a
    // MIN(MAX(a, b), a) -> a
    if ((SPF1 == SPF_SMIN && SPF2 == SPF_SMAX) ||
        (SPF1 == SPF_SMAX && SPF2 == SPF_SMIN) ||
        (SPF1 == SPF_UMIN && SPF2 == SPF_UMAX) ||
        (SPF1 == SPF_UMAX && SPF2 == SPF_UMIN))
      return ReplaceInstUsesWith(Outer, C);
  }

  if (SPF1 == SPF2) {
    if (ConstantInt *CB = dyn_cast<ConstantInt>(B)) {
      if (ConstantInt *CC = dyn_cast<ConstantInt>(C)) {
        APInt ACB = CB->getValue();
        APInt ACC = CC->getValue();

        // MIN(MIN(A, 23), 97) -> MIN(A, 23)
        // MAX(MAX(A, 97), 23) -> MAX(A, 97)
        if ((SPF1 == SPF_UMIN && ACB.ule(ACC)) ||
            (SPF1 == SPF_SMIN && ACB.sle(ACC)) ||
            (SPF1 == SPF_UMAX && ACB.uge(ACC)) ||
            (SPF1 == SPF_SMAX && ACB.sge(ACC)))
          return ReplaceInstUsesWith(Outer, Inner);

        // MIN(MIN(A, 97), 23) -> MIN(A, 23)
        // MAX(MAX(A, 23), 97) -> MAX(A, 97)
        if ((SPF1 == SPF_UMIN && ACB.ugt(ACC)) ||
            (SPF1 == SPF_SMIN && ACB.sgt(ACC)) ||
            (SPF1 == SPF_UMAX && ACB.ult(ACC)) ||
            (SPF1 == SPF_SMAX && ACB.slt(ACC))) {
          Outer.replaceUsesOfWith(Inner, A);
          return &Outer;
        }
      }
    }
  }

  // ABS(ABS(X)) -> ABS(X)
  // NABS(NABS(X)) -> NABS(X)
  if (SPF1 == SPF2 && (SPF1 == SPF_ABS || SPF1 == SPF_NABS)) {
    return ReplaceInstUsesWith(Outer, Inner);
  }

  // ABS(NABS(X)) -> ABS(X)
  // NABS(ABS(X)) -> NABS(X)
  if ((SPF1 == SPF_ABS && SPF2 == SPF_NABS) ||
      (SPF1 == SPF_NABS && SPF2 == SPF_ABS)) {
    SelectInst *SI = cast<SelectInst>(Inner);
    Value *NewSI = Builder->CreateSelect(
        SI->getCondition(), SI->getFalseValue(), SI->getTrueValue());
    return ReplaceInstUsesWith(Outer, NewSI);
  }
  return nullptr;
}

/// MatchSelectPattern - Pattern match integer [SU]MIN, [SU]MAX, and ABS idioms,
/// returning the kind and providing the out parameter results if we
/// successfully match.
static SelectPatternFlavor
MatchSelectPattern(Value *V, Value *&LHS, Value *&RHS) {
  SelectInst *SI = dyn_cast<SelectInst>(V);
  if (!SI) return SPF_UNKNOWN;

  ICmpInst *ICI = dyn_cast<ICmpInst>(SI->getCondition());
  if (!ICI) return SPF_UNKNOWN;

  ICmpInst::Predicate Pred = ICI->getPredicate();
  Value *CmpLHS = ICI->getOperand(0);
  Value *CmpRHS = ICI->getOperand(1);
  Value *TrueVal = SI->getTrueValue();
  Value *FalseVal = SI->getFalseValue();

  LHS = CmpLHS;
  RHS = CmpRHS;

  // (icmp X, Y) ? X : Y
  if (TrueVal == CmpLHS && FalseVal == CmpRHS) {
    switch (Pred) {
    default: return SPF_UNKNOWN; // Equality.
    case ICmpInst::ICMP_UGT:
    case ICmpInst::ICMP_UGE: return SPF_UMAX;
    case ICmpInst::ICMP_SGT:
    case ICmpInst::ICMP_SGE: return SPF_SMAX;
    case ICmpInst::ICMP_ULT:
    case ICmpInst::ICMP_ULE: return SPF_UMIN;
    case ICmpInst::ICMP_SLT:
    case ICmpInst::ICMP_SLE: return SPF_SMIN;
    }
  }

  // (icmp X, Y) ? Y : X
  if (TrueVal == CmpRHS && FalseVal == CmpLHS) {
    switch (Pred) {
    default: return SPF_UNKNOWN; // Equality.
    case ICmpInst::ICMP_UGT:
    case ICmpInst::ICMP_UGE: return SPF_UMIN;
    case ICmpInst::ICMP_SGT:
    case ICmpInst::ICMP_SGE: return SPF_SMIN;
    case ICmpInst::ICMP_ULT:
    case ICmpInst::ICMP_ULE: return SPF_UMAX;
    case ICmpInst::ICMP_SLT:
    case ICmpInst::ICMP_SLE: return SPF_SMAX;
    }
  }

  if (ConstantInt *C1 = dyn_cast<ConstantInt>(CmpRHS)) {
    if ((CmpLHS == TrueVal && match(FalseVal, m_Neg(m_Specific(CmpLHS)))) ||
        (CmpLHS == FalseVal && match(TrueVal, m_Neg(m_Specific(CmpLHS))))) {

      // ABS(X) ==> (X >s 0) ? X : -X and (X >s -1) ? X : -X
      // NABS(X) ==> (X >s 0) ? -X : X and (X >s -1) ? -X : X
      if (Pred == ICmpInst::ICMP_SGT && (C1->isZero() || C1->isMinusOne())) {
        return (CmpLHS == TrueVal) ? SPF_ABS : SPF_NABS;
      }

      // ABS(X) ==> (X <s 0) ? -X : X and (X <s 1) ? -X : X
      // NABS(X) ==> (X <s 0) ? X : -X and (X <s 1) ? X : -X
      if (Pred == ICmpInst::ICMP_SLT && (C1->isZero() || C1->isOne())) {
        return (CmpLHS == FalseVal) ? SPF_ABS : SPF_NABS;
      }
    }
  }

  // TODO: (X > 4) ? X : 5   -->  (X >= 5) ? X : 5  -->  MAX(X, 5)

  return SPF_UNKNOWN;
}

//.........这里部分代码省略.........
  //  TODO:  Handle opposite shift by exact value.
  ConstantInt *CI = nullptr;
  if ((isLeftShift && match(I, m_LShr(m_Value(), m_ConstantInt(CI)))) ||
      (!isLeftShift && match(I, m_Shl(m_Value(), m_ConstantInt(CI))))) {
    if (CI->getZExtValue() == NumBits) {
      // TODO: Check that the input bits are already zero with MaskedValueIsZero
#if 0
      // If this is a truncate of a logical shr, we can truncate it to a smaller
      // lshr iff we know that the bits we would otherwise be shifting in are
      // already zeros.
      uint32_t OrigBitWidth = OrigTy->getScalarSizeInBits();
      uint32_t BitWidth = Ty->getScalarSizeInBits();
      if (MaskedValueIsZero(I->getOperand(0),
            APInt::getHighBitsSet(OrigBitWidth, OrigBitWidth-BitWidth)) &&
          CI->getLimitedValue(BitWidth) < BitWidth) {
        return CanEvaluateTruncated(I->getOperand(0), Ty);
      }
#endif

    }
  }

  // We can't mutate something that has multiple uses: doing so would
  // require duplicating the instruction in general, which isn't profitable.
  if (!I->hasOneUse()) return false;

  switch (I->getOpcode()) {
  default: return false;
  case Instruction::And:
  case Instruction::Or:
  case Instruction::Xor:
    // Bitwise operators can all arbitrarily be arbitrarily evaluated shifted.
    return CanEvaluateShifted(I->getOperand(0), NumBits, isLeftShift, IC) &&
           CanEvaluateShifted(I->getOperand(1), NumBits, isLeftShift, IC);

  case Instruction::Shl: {
    // We can often fold the shift into shifts-by-a-constant.
    CI = dyn_cast<ConstantInt>(I->getOperand(1));
    if (!CI) return false;

    // We can always fold shl(c1)+shl(c2) -> shl(c1+c2).
    if (isLeftShift) return true;

    // We can always turn shl(c)+shr(c) -> and(c2).
    if (CI->getValue() == NumBits) return true;

    unsigned TypeWidth = I->getType()->getScalarSizeInBits();

    // We can turn shl(c1)+shr(c2) -> shl(c3)+and(c4), but it isn't
    // profitable unless we know the and'd out bits are already zero.
    if (CI->getZExtValue() > NumBits) {
      unsigned LowBits = TypeWidth - CI->getZExtValue();
      if (MaskedValueIsZero(I->getOperand(0),
                       APInt::getLowBitsSet(TypeWidth, NumBits) << LowBits))
        return true;
    }

    return false;
  }
  case Instruction::LShr: {
    // We can often fold the shift into shifts-by-a-constant.
    CI = dyn_cast<ConstantInt>(I->getOperand(1));
    if (!CI) return false;

    // We can always fold lshr(c1)+lshr(c2) -> lshr(c1+c2).
    if (!isLeftShift) return true;

    // We can always turn lshr(c)+shl(c) -> and(c2).
    if (CI->getValue() == NumBits) return true;

    unsigned TypeWidth = I->getType()->getScalarSizeInBits();

    // We can always turn lshr(c1)+shl(c2) -> lshr(c3)+and(c4), but it isn't
    // profitable unless we know the and'd out bits are already zero.
    if (CI->getValue().ult(TypeWidth) && CI->getZExtValue() > NumBits) {
      unsigned LowBits = CI->getZExtValue() - NumBits;
      if (MaskedValueIsZero(I->getOperand(0),
                          APInt::getLowBitsSet(TypeWidth, NumBits) << LowBits))
        return true;
    }

    return false;
  }
  case Instruction::Select: {
    SelectInst *SI = cast<SelectInst>(I);
    return CanEvaluateShifted(SI->getTrueValue(), NumBits, isLeftShift, IC) &&
           CanEvaluateShifted(SI->getFalseValue(), NumBits, isLeftShift, IC);
  }
  case Instruction::PHI: {
    // We can change a phi if we can change all operands.  Note that we never
    // get into trouble with cyclic PHIs here because we only consider
    // instructions with a single use.
    PHINode *PN = cast<PHINode>(I);
    for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
      if (!CanEvaluateShifted(PN->getIncomingValue(i), NumBits, isLeftShift,IC))
        return false;
    return true;
  }
  }
}