llvm/lib/Analysis/PHITransAddr.cpp - rust-lang/llvm-project - Git at Google

 //===- PHITransAddr.cpp - PHI Translation for Addresses -------------------===//
 //
 // 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
 //
 //===----------------------------------------------------------------------===//
 //
 // This file implements the PHITransAddr class.
 //
 //===----------------------------------------------------------------------===//

 #include "llvm/Analysis/PHITransAddr.h"
 #include "llvm/Analysis/InstructionSimplify.h"
 #include "llvm/Analysis/ValueTracking.h"
 #include "llvm/Config/llvm-config.h"
 #include "llvm/IR/Constants.h"
 #include "llvm/IR/Dominators.h"
 #include "llvm/IR/Instructions.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/raw_ostream.h"
 using namespace llvm;

 static cl::opt<bool> EnableAddPhiTranslation(
     "gvn-add-phi-translation", cl::init(false), cl::Hidden,
     cl::desc("Enable phi-translation of add instructions"));

 static bool canPHITrans(Instruction *Inst) {
   if (isa<PHINode>(Inst) || isa<GetElementPtrInst>(Inst) || isa<CastInst>(Inst))
     return true;

   if (Inst->getOpcode() == Instruction::Add &&
       isa<ConstantInt>(Inst->getOperand(1)))
     return true;

   return false;
 }

 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
 LLVM_DUMP_METHOD void PHITransAddr::dump() const {
   if (!Addr) {
     dbgs() << "PHITransAddr: null\n";
     return;
   }
   dbgs() << "PHITransAddr: " << *Addr << "\n";
   for (unsigned i = 0, e = InstInputs.size(); i != e; ++i)
     dbgs() << "  Input #" << i << " is " << *InstInputs[i] << "\n";
 }
 #endif

 static bool verifySubExpr(Value *Expr,
                           SmallVectorImpl<Instruction *> &InstInputs) {
   // If this is a non-instruction value, there is nothing to do.
   Instruction *I = dyn_cast<Instruction>(Expr);
   if (!I) return true;

   // If it's an instruction, it is either in Tmp or its operands recursively
   // are.
   if (auto Entry = find(InstInputs, I); Entry != InstInputs.end()) {
     InstInputs.erase(Entry);
     return true;
   }

   // If it isn't in the InstInputs list it is a subexpr incorporated into the
   // address.  Validate that it is phi translatable.
   if (!canPHITrans(I)) {
     errs() << "Instruction in PHITransAddr is not phi-translatable:\n";
     errs() << *I << '\n';
     llvm_unreachable("Either something is missing from InstInputs or "
                      "canPHITrans is wrong.");
   }

   // Validate the operands of the instruction.
   return all_of(I->operands(),
                 [&](Value *Op) { return verifySubExpr(Op, InstInputs); });
 }

 /// verify - Check internal consistency of this data structure.  If the
 /// structure is valid, it returns true.  If invalid, it prints errors and
 /// returns false.
 bool PHITransAddr::verify() const {
   if (!Addr) return true;

   SmallVector<Instruction*, 8> Tmp(InstInputs.begin(), InstInputs.end());

   if (!verifySubExpr(Addr, Tmp))
     return false;

   if (!Tmp.empty()) {
     errs() << "PHITransAddr contains extra instructions:\n";
     for (unsigned i = 0, e = InstInputs.size(); i != e; ++i)
       errs() << "  InstInput #" << i << " is " << *InstInputs[i] << "\n";
     llvm_unreachable("This is unexpected.");
   }

   // a-ok.
   return true;
 }

 /// isPotentiallyPHITranslatable - If this needs PHI translation, return true
 /// if we have some hope of doing it.  This should be used as a filter to
 /// avoid calling PHITranslateValue in hopeless situations.
 bool PHITransAddr::isPotentiallyPHITranslatable() const {
   // If the input value is not an instruction, or if it is not defined in CurBB,
   // then we don't need to phi translate it.
   Instruction *Inst = dyn_cast<Instruction>(Addr);
   return !Inst || canPHITrans(Inst);
 }

 static void RemoveInstInputs(Value *V,
                              SmallVectorImpl<Instruction*> &InstInputs) {
   Instruction *I = dyn_cast<Instruction>(V);
   if (!I) return;

   // If the instruction is in the InstInputs list, remove it.
   if (auto Entry = find(InstInputs, I); Entry != InstInputs.end()) {
     InstInputs.erase(Entry);
     return;
   }

   assert(!isa<PHINode>(I) && "Error, removing something that isn't an input");

   // Otherwise, it must have instruction inputs itself.  Zap them recursively.
   for (Value *Op : I->operands())
     if (Instruction *OpInst = dyn_cast<Instruction>(Op))
       RemoveInstInputs(OpInst, InstInputs);
 }

 Value *PHITransAddr::translateSubExpr(Value *V, BasicBlock *CurBB,
                                       BasicBlock *PredBB,
                                       const DominatorTree *DT) {
   // If this is a non-instruction value, it can't require PHI translation.
   Instruction *Inst = dyn_cast<Instruction>(V);
   if (!Inst) return V;

   // Determine whether 'Inst' is an input to our PHI translatable expression.
   bool isInput = is_contained(InstInputs, Inst);

   // Handle inputs instructions if needed.
   if (isInput) {
     if (Inst->getParent() != CurBB) {
       // If it is an input defined in a different block, then it remains an
       // input.
       return Inst;
     }

     // If 'Inst' is defined in this block and is an input that needs to be phi
     // translated, we need to incorporate the value into the expression or fail.

     // In either case, the instruction itself isn't an input any longer.
     InstInputs.erase(find(InstInputs, Inst));

     // If this is a PHI, go ahead and translate it.
     if (PHINode *PN = dyn_cast<PHINode>(Inst))
       return addAsInput(PN->getIncomingValueForBlock(PredBB));

     // If this is a non-phi value, and it is analyzable, we can incorporate it
     // into the expression by making all instruction operands be inputs.
     if (!canPHITrans(Inst))
       return nullptr;

     // All instruction operands are now inputs (and of course, they may also be
     // defined in this block, so they may need to be phi translated themselves.
     for (Value *Op : Inst->operands())
       addAsInput(Op);
   }

   // Ok, it must be an intermediate result (either because it started that way
   // or because we just incorporated it into the expression).  See if its
   // operands need to be phi translated, and if so, reconstruct it.

   if (CastInst *Cast = dyn_cast<CastInst>(Inst)) {
     Value *PHIIn = translateSubExpr(Cast->getOperand(0), CurBB, PredBB, DT);
     if (!PHIIn) return nullptr;
     if (PHIIn == Cast->getOperand(0))
       return Cast;

     // Find an available version of this cast.

     // Try to simplify cast first.
     if (Value *V = simplifyCastInst(Cast->getOpcode(), PHIIn, Cast->getType(),
                                     {DL, TLI, DT, AC})) {
       RemoveInstInputs(PHIIn, InstInputs);
       return addAsInput(V);
     }

     // Otherwise we have to see if a casted version of the incoming pointer
     // is available.  If so, we can use it, otherwise we have to fail.
     for (User *U : PHIIn->users()) {
       if (CastInst *CastI = dyn_cast<CastInst>(U))
         if (CastI->getOpcode() == Cast->getOpcode() &&
             CastI->getType() == Cast->getType() &&
             (!DT || DT->dominates(CastI->getParent(), PredBB)))
           return CastI;
     }
     return nullptr;
   }

   // Handle getelementptr with at least one PHI translatable operand.
   if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Inst)) {
     SmallVector<Value*, 8> GEPOps;
     bool AnyChanged = false;
     for (Value *Op : GEP->operands()) {
       Value *GEPOp = translateSubExpr(Op, CurBB, PredBB, DT);
       if (!GEPOp) return nullptr;

       AnyChanged |= GEPOp != Op;
       GEPOps.push_back(GEPOp);
     }

     if (!AnyChanged)
       return GEP;

     // Simplify the GEP to handle 'gep x, 0' -> x etc.
     if (Value *V = simplifyGEPInst(GEP->getSourceElementType(), GEPOps[0],
                                    ArrayRef<Value *>(GEPOps).slice(1),
                                    GEP->isInBounds(), {DL, TLI, DT, AC})) {
       for (unsigned i = 0, e = GEPOps.size(); i != e; ++i)
         RemoveInstInputs(GEPOps[i], InstInputs);

       return addAsInput(V);
     }

     // Scan to see if we have this GEP available.
     Value *APHIOp = GEPOps[0];
     for (User *U : APHIOp->users()) {
       if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(U))
         if (GEPI->getType() == GEP->getType() &&
             GEPI->getSourceElementType() == GEP->getSourceElementType() &&
             GEPI->getNumOperands() == GEPOps.size() &&
             GEPI->getParent()->getParent() == CurBB->getParent() &&
             (!DT || DT->dominates(GEPI->getParent(), PredBB))) {
           if (std::equal(GEPOps.begin(), GEPOps.end(), GEPI->op_begin()))
             return GEPI;
         }
     }
     return nullptr;
   }

   // Handle add with a constant RHS.
   if (Inst->getOpcode() == Instruction::Add &&
       isa<ConstantInt>(Inst->getOperand(1))) {
     // PHI translate the LHS.
     Constant *RHS = cast<ConstantInt>(Inst->getOperand(1));
     bool isNSW = cast<BinaryOperator>(Inst)->hasNoSignedWrap();
     bool isNUW = cast<BinaryOperator>(Inst)->hasNoUnsignedWrap();

     Value *LHS = translateSubExpr(Inst->getOperand(0), CurBB, PredBB, DT);
     if (!LHS) return nullptr;

     // If the PHI translated LHS is an add of a constant, fold the immediates.
     if (BinaryOperator *BOp = dyn_cast<BinaryOperator>(LHS))
       if (BOp->getOpcode() == Instruction::Add)
         if (ConstantInt *CI = dyn_cast<ConstantInt>(BOp->getOperand(1))) {
           LHS = BOp->getOperand(0);
           RHS = ConstantExpr::getAdd(RHS, CI);
           isNSW = isNUW = false;

           // If the old 'LHS' was an input, add the new 'LHS' as an input.
           if (is_contained(InstInputs, BOp)) {
             RemoveInstInputs(BOp, InstInputs);
             addAsInput(LHS);
           }
         }

     // See if the add simplifies away.
     if (Value *Res = simplifyAddInst(LHS, RHS, isNSW, isNUW, {DL, TLI, DT, AC})) {
       // If we simplified the operands, the LHS is no longer an input, but Res
       // is.
       RemoveInstInputs(LHS, InstInputs);
       return addAsInput(Res);
     }

     // If we didn't modify the add, just return it.
     if (LHS == Inst->getOperand(0) && RHS == Inst->getOperand(1))
       return Inst;

     // Otherwise, see if we have this add available somewhere.
     for (User *U : LHS->users()) {
       if (BinaryOperator *BO = dyn_cast<BinaryOperator>(U))
         if (BO->getOpcode() == Instruction::Add &&
             BO->getOperand(0) == LHS && BO->getOperand(1) == RHS &&
             BO->getParent()->getParent() == CurBB->getParent() &&
             (!DT || DT->dominates(BO->getParent(), PredBB)))
           return BO;
     }

     return nullptr;
   }

   // Otherwise, we failed.
   return nullptr;
 }

 /// PHITranslateValue - PHI translate the current address up the CFG from
 /// CurBB to Pred, updating our state to reflect any needed changes.  If
 /// 'MustDominate' is true, the translated value must dominate PredBB.
 Value *PHITransAddr::translateValue(BasicBlock *CurBB, BasicBlock *PredBB,
                                     const DominatorTree *DT,
                                     bool MustDominate) {
   assert(DT || !MustDominate);
   assert(verify() && "Invalid PHITransAddr!");
   if (DT && DT->isReachableFromEntry(PredBB))
     Addr = translateSubExpr(Addr, CurBB, PredBB, DT);
   else
     Addr = nullptr;
   assert(verify() && "Invalid PHITransAddr!");

   if (MustDominate)
     // Make sure the value is live in the predecessor.
     if (Instruction *Inst = dyn_cast_or_null<Instruction>(Addr))
       if (!DT->dominates(Inst->getParent(), PredBB))
         Addr = nullptr;

   return Addr;
 }

 /// PHITranslateWithInsertion - PHI translate this value into the specified
 /// predecessor block, inserting a computation of the value if it is
 /// unavailable.
 ///
 /// All newly created instructions are added to the NewInsts list.  This
 /// returns null on failure.
 ///
 Value *
 PHITransAddr::translateWithInsertion(BasicBlock *CurBB, BasicBlock *PredBB,
                                      const DominatorTree &DT,
                                      SmallVectorImpl<Instruction *> &NewInsts) {
   unsigned NISize = NewInsts.size();

   // Attempt to PHI translate with insertion.
   Addr = insertTranslatedSubExpr(Addr, CurBB, PredBB, DT, NewInsts);

   // If successful, return the new value.
   if (Addr) return Addr;

   // If not, destroy any intermediate instructions inserted.
   while (NewInsts.size() != NISize)
     NewInsts.pop_back_val()->eraseFromParent();
   return nullptr;
 }

 /// insertTranslatedSubExpr - Insert a computation of the PHI translated
 /// version of 'V' for the edge PredBB->CurBB into the end of the PredBB
 /// block.  All newly created instructions are added to the NewInsts list.
 /// This returns null on failure.
 ///
 Value *PHITransAddr::insertTranslatedSubExpr(
     Value *InVal, BasicBlock *CurBB, BasicBlock *PredBB,
     const DominatorTree &DT, SmallVectorImpl<Instruction *> &NewInsts) {
   // See if we have a version of this value already available and dominating
   // PredBB.  If so, there is no need to insert a new instance of it.
   PHITransAddr Tmp(InVal, DL, AC);
   if (Value *Addr =
           Tmp.translateValue(CurBB, PredBB, &DT, /*MustDominate=*/true))
     return Addr;

   // We don't need to PHI translate values which aren't instructions.
   auto *Inst = dyn_cast<Instruction>(InVal);
   if (!Inst)
     return nullptr;

   // Handle cast of PHI translatable value.
   if (CastInst *Cast = dyn_cast<CastInst>(Inst)) {
     Value *OpVal = insertTranslatedSubExpr(Cast->getOperand(0), CurBB, PredBB,
                                            DT, NewInsts);
     if (!OpVal) return nullptr;

     // Otherwise insert a cast at the end of PredBB.
     CastInst *New = CastInst::Create(Cast->getOpcode(), OpVal, InVal->getType(),
                                      InVal->getName() + ".phi.trans.insert",
                                      PredBB->getTerminator());
     New->setDebugLoc(Inst->getDebugLoc());
     NewInsts.push_back(New);
     return New;
   }

   // Handle getelementptr with at least one PHI operand.
   if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Inst)) {
     SmallVector<Value*, 8> GEPOps;
     BasicBlock *CurBB = GEP->getParent();
     for (Value *Op : GEP->operands()) {
       Value *OpVal = insertTranslatedSubExpr(Op, CurBB, PredBB, DT, NewInsts);
       if (!OpVal) return nullptr;
       GEPOps.push_back(OpVal);
     }

     GetElementPtrInst *Result = GetElementPtrInst::Create(
         GEP->getSourceElementType(), GEPOps[0], ArrayRef(GEPOps).slice(1),
         InVal->getName() + ".phi.trans.insert", PredBB->getTerminator());
     Result->setDebugLoc(Inst->getDebugLoc());
     Result->setIsInBounds(GEP->isInBounds());
     NewInsts.push_back(Result);
     return Result;
   }

   // Handle add with a constant RHS.
   if (EnableAddPhiTranslation && Inst->getOpcode() == Instruction::Add &&
       isa<ConstantInt>(Inst->getOperand(1))) {

     // FIXME: This code works, but it is unclear that we actually want to insert
     // a big chain of computation in order to make a value available in a block.
     // This needs to be evaluated carefully to consider its cost trade offs.

     // PHI translate the LHS.
     Value *OpVal = insertTranslatedSubExpr(Inst->getOperand(0), CurBB, PredBB,
                                            DT, NewInsts);
     if (OpVal == nullptr)
       return nullptr;

     BinaryOperator *Res = BinaryOperator::CreateAdd(OpVal, Inst->getOperand(1),
                                            InVal->getName()+".phi.trans.insert",
                                                     PredBB->getTerminator());
     Res->setHasNoSignedWrap(cast<BinaryOperator>(Inst)->hasNoSignedWrap());
     Res->setHasNoUnsignedWrap(cast<BinaryOperator>(Inst)->hasNoUnsignedWrap());
     NewInsts.push_back(Res);
     return Res;
   }

   return nullptr;
 }
	//===- PHITransAddr.cpp - PHI Translation for Addresses -------------------===//
	//
	// 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
	//
	//===----------------------------------------------------------------------===//
	//
	// This file implements the PHITransAddr class.
	//
	//===----------------------------------------------------------------------===//

	#include "llvm/Analysis/PHITransAddr.h"
	#include "llvm/Analysis/InstructionSimplify.h"
	#include "llvm/Analysis/ValueTracking.h"
	#include "llvm/Config/llvm-config.h"
	#include "llvm/IR/Constants.h"
	#include "llvm/IR/Dominators.h"
	#include "llvm/IR/Instructions.h"
	#include "llvm/Support/ErrorHandling.h"
	#include "llvm/Support/raw_ostream.h"
	using namespace llvm;

	static cl::opt<bool> EnableAddPhiTranslation(
	"gvn-add-phi-translation", cl::init(false), cl::Hidden,
	cl::desc("Enable phi-translation of add instructions"));

	static bool canPHITrans(Instruction *Inst) {
	if (isa<PHINode>(Inst) \|\| isa<GetElementPtrInst>(Inst) \|\| isa<CastInst>(Inst))
	return true;

	if (Inst->getOpcode() == Instruction::Add &&
	isa<ConstantInt>(Inst->getOperand(1)))
	return true;

	return false;
	}

	#if !defined(NDEBUG) \|\| defined(LLVM_ENABLE_DUMP)
	LLVM_DUMP_METHOD void PHITransAddr::dump() const {
	if (!Addr) {
	dbgs() << "PHITransAddr: null\n";
	return;
	}
	dbgs() << "PHITransAddr: " << *Addr << "\n";
	for (unsigned i = 0, e = InstInputs.size(); i != e; ++i)
	dbgs() << " Input #" << i << " is " << *InstInputs[i] << "\n";
	}
	#endif

	static bool verifySubExpr(Value *Expr,
	SmallVectorImpl<Instruction *> &InstInputs) {
	// If this is a non-instruction value, there is nothing to do.
	Instruction *I = dyn_cast<Instruction>(Expr);
	if (!I) return true;

	// If it's an instruction, it is either in Tmp or its operands recursively
	// are.
	if (auto Entry = find(InstInputs, I); Entry != InstInputs.end()) {
	InstInputs.erase(Entry);
	return true;
	}

	// If it isn't in the InstInputs list it is a subexpr incorporated into the
	// address. Validate that it is phi translatable.
	if (!canPHITrans(I)) {
	errs() << "Instruction in PHITransAddr is not phi-translatable:\n";
	errs() << *I << '\n';
	llvm_unreachable("Either something is missing from InstInputs or "
	"canPHITrans is wrong.");
	}

	// Validate the operands of the instruction.
	return all_of(I->operands(),
	[&](Value *Op) { return verifySubExpr(Op, InstInputs); });
	}

	/// verify - Check internal consistency of this data structure. If the
	/// structure is valid, it returns true. If invalid, it prints errors and
	/// returns false.
	bool PHITransAddr::verify() const {
	if (!Addr) return true;

	SmallVector<Instruction*, 8> Tmp(InstInputs.begin(), InstInputs.end());

	if (!verifySubExpr(Addr, Tmp))
	return false;

	if (!Tmp.empty()) {
	errs() << "PHITransAddr contains extra instructions:\n";
	for (unsigned i = 0, e = InstInputs.size(); i != e; ++i)
	errs() << " InstInput #" << i << " is " << *InstInputs[i] << "\n";
	llvm_unreachable("This is unexpected.");
	}

	// a-ok.
	return true;
	}

	/// isPotentiallyPHITranslatable - If this needs PHI translation, return true
	/// if we have some hope of doing it. This should be used as a filter to
	/// avoid calling PHITranslateValue in hopeless situations.
	bool PHITransAddr::isPotentiallyPHITranslatable() const {
	// If the input value is not an instruction, or if it is not defined in CurBB,
	// then we don't need to phi translate it.
	Instruction *Inst = dyn_cast<Instruction>(Addr);
	return !Inst \|\| canPHITrans(Inst);
	}

	static void RemoveInstInputs(Value *V,
	SmallVectorImpl<Instruction*> &InstInputs) {
	Instruction *I = dyn_cast<Instruction>(V);
	if (!I) return;

	// If the instruction is in the InstInputs list, remove it.
	if (auto Entry = find(InstInputs, I); Entry != InstInputs.end()) {
	InstInputs.erase(Entry);
	return;
	}

	assert(!isa<PHINode>(I) && "Error, removing something that isn't an input");

	// Otherwise, it must have instruction inputs itself. Zap them recursively.
	for (Value *Op : I->operands())
	if (Instruction *OpInst = dyn_cast<Instruction>(Op))
	RemoveInstInputs(OpInst, InstInputs);
	}

	Value PHITransAddr::translateSubExpr(Value V, BasicBlock *CurBB,
	BasicBlock *PredBB,
	const DominatorTree *DT) {
	// If this is a non-instruction value, it can't require PHI translation.
	Instruction *Inst = dyn_cast<Instruction>(V);
	if (!Inst) return V;

	// Determine whether 'Inst' is an input to our PHI translatable expression.
	bool isInput = is_contained(InstInputs, Inst);

	// Handle inputs instructions if needed.
	if (isInput) {
	if (Inst->getParent() != CurBB) {
	// If it is an input defined in a different block, then it remains an
	// input.
	return Inst;
	}

	// If 'Inst' is defined in this block and is an input that needs to be phi
	// translated, we need to incorporate the value into the expression or fail.

	// In either case, the instruction itself isn't an input any longer.
	InstInputs.erase(find(InstInputs, Inst));

	// If this is a PHI, go ahead and translate it.
	if (PHINode *PN = dyn_cast<PHINode>(Inst))
	return addAsInput(PN->getIncomingValueForBlock(PredBB));

	// If this is a non-phi value, and it is analyzable, we can incorporate it
	// into the expression by making all instruction operands be inputs.
	if (!canPHITrans(Inst))
	return nullptr;

	// All instruction operands are now inputs (and of course, they may also be
	// defined in this block, so they may need to be phi translated themselves.
	for (Value *Op : Inst->operands())
	addAsInput(Op);
	}

	// Ok, it must be an intermediate result (either because it started that way
	// or because we just incorporated it into the expression). See if its
	// operands need to be phi translated, and if so, reconstruct it.

	if (CastInst *Cast = dyn_cast<CastInst>(Inst)) {
	Value *PHIIn = translateSubExpr(Cast->getOperand(0), CurBB, PredBB, DT);
	if (!PHIIn) return nullptr;
	if (PHIIn == Cast->getOperand(0))
	return Cast;

	// Find an available version of this cast.

	// Try to simplify cast first.
	if (Value *V = simplifyCastInst(Cast->getOpcode(), PHIIn, Cast->getType(),
	{DL, TLI, DT, AC})) {
	RemoveInstInputs(PHIIn, InstInputs);
	return addAsInput(V);
	}

	// Otherwise we have to see if a casted version of the incoming pointer
	// is available. If so, we can use it, otherwise we have to fail.
	for (User *U : PHIIn->users()) {
	if (CastInst *CastI = dyn_cast<CastInst>(U))
	if (CastI->getOpcode() == Cast->getOpcode() &&
	CastI->getType() == Cast->getType() &&
	(!DT \|\| DT->dominates(CastI->getParent(), PredBB)))
	return CastI;
	}
	return nullptr;
	}

	// Handle getelementptr with at least one PHI translatable operand.
	if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Inst)) {
	SmallVector<Value*, 8> GEPOps;
	bool AnyChanged = false;
	for (Value *Op : GEP->operands()) {
	Value *GEPOp = translateSubExpr(Op, CurBB, PredBB, DT);
	if (!GEPOp) return nullptr;

	AnyChanged \|= GEPOp != Op;
	GEPOps.push_back(GEPOp);
	}

	if (!AnyChanged)
	return GEP;

	// Simplify the GEP to handle 'gep x, 0' -> x etc.
	if (Value *V = simplifyGEPInst(GEP->getSourceElementType(), GEPOps[0],
	ArrayRef<Value *>(GEPOps).slice(1),
	GEP->isInBounds(), {DL, TLI, DT, AC})) {
	for (unsigned i = 0, e = GEPOps.size(); i != e; ++i)
	RemoveInstInputs(GEPOps[i], InstInputs);

	return addAsInput(V);
	}

	// Scan to see if we have this GEP available.
	Value *APHIOp = GEPOps[0];
	for (User *U : APHIOp->users()) {
	if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(U))
	if (GEPI->getType() == GEP->getType() &&
	GEPI->getSourceElementType() == GEP->getSourceElementType() &&
	GEPI->getNumOperands() == GEPOps.size() &&
	GEPI->getParent()->getParent() == CurBB->getParent() &&
	(!DT \|\| DT->dominates(GEPI->getParent(), PredBB))) {
	if (std::equal(GEPOps.begin(), GEPOps.end(), GEPI->op_begin()))
	return GEPI;
	}
	}
	return nullptr;
	}

	// Handle add with a constant RHS.
	if (Inst->getOpcode() == Instruction::Add &&
	isa<ConstantInt>(Inst->getOperand(1))) {
	// PHI translate the LHS.
	Constant *RHS = cast<ConstantInt>(Inst->getOperand(1));
	bool isNSW = cast<BinaryOperator>(Inst)->hasNoSignedWrap();
	bool isNUW = cast<BinaryOperator>(Inst)->hasNoUnsignedWrap();

	Value *LHS = translateSubExpr(Inst->getOperand(0), CurBB, PredBB, DT);
	if (!LHS) return nullptr;

	// If the PHI translated LHS is an add of a constant, fold the immediates.
	if (BinaryOperator *BOp = dyn_cast<BinaryOperator>(LHS))
	if (BOp->getOpcode() == Instruction::Add)
	if (ConstantInt *CI = dyn_cast<ConstantInt>(BOp->getOperand(1))) {
	LHS = BOp->getOperand(0);
	RHS = ConstantExpr::getAdd(RHS, CI);
	isNSW = isNUW = false;

	// If the old 'LHS' was an input, add the new 'LHS' as an input.
	if (is_contained(InstInputs, BOp)) {
	RemoveInstInputs(BOp, InstInputs);
	addAsInput(LHS);
	}
	}

	// See if the add simplifies away.
	if (Value *Res = simplifyAddInst(LHS, RHS, isNSW, isNUW, {DL, TLI, DT, AC})) {
	// If we simplified the operands, the LHS is no longer an input, but Res
	// is.
	RemoveInstInputs(LHS, InstInputs);
	return addAsInput(Res);
	}

	// If we didn't modify the add, just return it.
	if (LHS == Inst->getOperand(0) && RHS == Inst->getOperand(1))
	return Inst;

	// Otherwise, see if we have this add available somewhere.
	for (User *U : LHS->users()) {
	if (BinaryOperator *BO = dyn_cast<BinaryOperator>(U))
	if (BO->getOpcode() == Instruction::Add &&
	BO->getOperand(0) == LHS && BO->getOperand(1) == RHS &&
	BO->getParent()->getParent() == CurBB->getParent() &&
	(!DT \|\| DT->dominates(BO->getParent(), PredBB)))
	return BO;
	}

	return nullptr;
	}

	// Otherwise, we failed.
	return nullptr;
	}

	/// PHITranslateValue - PHI translate the current address up the CFG from
	/// CurBB to Pred, updating our state to reflect any needed changes. If
	/// 'MustDominate' is true, the translated value must dominate PredBB.
	Value PHITransAddr::translateValue(BasicBlock CurBB, BasicBlock *PredBB,
	const DominatorTree *DT,
	bool MustDominate) {
	assert(DT \|\| !MustDominate);
	assert(verify() && "Invalid PHITransAddr!");
	if (DT && DT->isReachableFromEntry(PredBB))
	Addr = translateSubExpr(Addr, CurBB, PredBB, DT);
	else
	Addr = nullptr;
	assert(verify() && "Invalid PHITransAddr!");

	if (MustDominate)
	// Make sure the value is live in the predecessor.
	if (Instruction *Inst = dyn_cast_or_null<Instruction>(Addr))
	if (!DT->dominates(Inst->getParent(), PredBB))
	Addr = nullptr;

	return Addr;
	}

	/// PHITranslateWithInsertion - PHI translate this value into the specified
	/// predecessor block, inserting a computation of the value if it is
	/// unavailable.
	///
	/// All newly created instructions are added to the NewInsts list. This
	/// returns null on failure.
	///
	Value *
	PHITransAddr::translateWithInsertion(BasicBlock CurBB, BasicBlock PredBB,
	const DominatorTree &DT,
	SmallVectorImpl<Instruction *> &NewInsts) {
	unsigned NISize = NewInsts.size();

	// Attempt to PHI translate with insertion.
	Addr = insertTranslatedSubExpr(Addr, CurBB, PredBB, DT, NewInsts);

	// If successful, return the new value.
	if (Addr) return Addr;

	// If not, destroy any intermediate instructions inserted.
	while (NewInsts.size() != NISize)
	NewInsts.pop_back_val()->eraseFromParent();
	return nullptr;
	}

	/// insertTranslatedSubExpr - Insert a computation of the PHI translated
	/// version of 'V' for the edge PredBB->CurBB into the end of the PredBB
	/// block. All newly created instructions are added to the NewInsts list.
	/// This returns null on failure.
	///
	Value *PHITransAddr::insertTranslatedSubExpr(
	Value InVal, BasicBlock CurBB, BasicBlock *PredBB,
	const DominatorTree &DT, SmallVectorImpl<Instruction *> &NewInsts) {
	// See if we have a version of this value already available and dominating
	// PredBB. If so, there is no need to insert a new instance of it.
	PHITransAddr Tmp(InVal, DL, AC);
	if (Value *Addr =
	Tmp.translateValue(CurBB, PredBB, &DT, /MustDominate=/true))
	return Addr;

	// We don't need to PHI translate values which aren't instructions.
	auto *Inst = dyn_cast<Instruction>(InVal);
	if (!Inst)
	return nullptr;

	// Handle cast of PHI translatable value.
	if (CastInst *Cast = dyn_cast<CastInst>(Inst)) {
	Value *OpVal = insertTranslatedSubExpr(Cast->getOperand(0), CurBB, PredBB,
	DT, NewInsts);
	if (!OpVal) return nullptr;

	// Otherwise insert a cast at the end of PredBB.
	CastInst *New = CastInst::Create(Cast->getOpcode(), OpVal, InVal->getType(),
	InVal->getName() + ".phi.trans.insert",
	PredBB->getTerminator());
	New->setDebugLoc(Inst->getDebugLoc());
	NewInsts.push_back(New);
	return New;
	}

	// Handle getelementptr with at least one PHI operand.
	if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Inst)) {
	SmallVector<Value*, 8> GEPOps;
	BasicBlock *CurBB = GEP->getParent();
	for (Value *Op : GEP->operands()) {
	Value *OpVal = insertTranslatedSubExpr(Op, CurBB, PredBB, DT, NewInsts);
	if (!OpVal) return nullptr;
	GEPOps.push_back(OpVal);
	}

	GetElementPtrInst *Result = GetElementPtrInst::Create(
	GEP->getSourceElementType(), GEPOps[0], ArrayRef(GEPOps).slice(1),
	InVal->getName() + ".phi.trans.insert", PredBB->getTerminator());
	Result->setDebugLoc(Inst->getDebugLoc());
	Result->setIsInBounds(GEP->isInBounds());
	NewInsts.push_back(Result);
	return Result;
	}

	// Handle add with a constant RHS.
	if (EnableAddPhiTranslation && Inst->getOpcode() == Instruction::Add &&
	isa<ConstantInt>(Inst->getOperand(1))) {

	// FIXME: This code works, but it is unclear that we actually want to insert
	// a big chain of computation in order to make a value available in a block.
	// This needs to be evaluated carefully to consider its cost trade offs.

	// PHI translate the LHS.
	Value *OpVal = insertTranslatedSubExpr(Inst->getOperand(0), CurBB, PredBB,
	DT, NewInsts);
	if (OpVal == nullptr)
	return nullptr;

	BinaryOperator *Res = BinaryOperator::CreateAdd(OpVal, Inst->getOperand(1),
	InVal->getName()+".phi.trans.insert",
	PredBB->getTerminator());
	Res->setHasNoSignedWrap(cast<BinaryOperator>(Inst)->hasNoSignedWrap());
	Res->setHasNoUnsignedWrap(cast<BinaryOperator>(Inst)->hasNoUnsignedWrap());
	NewInsts.push_back(Res);
	return Res;
	}

	return nullptr;
	}