//===- LoopStrengthReduce.cpp - Strength Reduce GEPs in Loops -------------===//
-//
+//
// The LLVM Compiler Infrastructure
//
// This file was developed by Nate Begeman and is distributed under the
// University of Illinois Open Source License. See LICENSE.TXT for details.
-//
+//
//===----------------------------------------------------------------------===//
//
// This pass performs a strength reduction on array references inside loops that
// access for the first iteration, and then creating a new GEP instruction in
// the loop to increment the value by the appropriate amount.
//
-// There are currently several deficiencies in the implementation, marked with
-// FIXME in the code.
-//
//===----------------------------------------------------------------------===//
+#define DEBUG_TYPE "loop-reduce"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Constants.h"
#include "llvm/Instructions.h"
#include "llvm/DerivedTypes.h"
#include "llvm/Analysis/Dominators.h"
#include "llvm/Analysis/LoopInfo.h"
+#include "llvm/Analysis/LoopPass.h"
+#include "llvm/Analysis/ScalarEvolutionExpander.h"
#include "llvm/Support/CFG.h"
+#include "llvm/Support/GetElementPtrTypeIterator.h"
+#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Target/TargetData.h"
#include "llvm/ADT/Statistic.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/Compiler.h"
+#include "llvm/Target/TargetLowering.h"
+#include <algorithm>
#include <set>
using namespace llvm;
+STATISTIC(NumReduced , "Number of GEPs strength reduced");
+STATISTIC(NumInserted, "Number of PHIs inserted");
+STATISTIC(NumVariable, "Number of PHIs with variable strides");
+
namespace {
- Statistic<> NumReduced ("loop-reduce", "Number of GEPs strength reduced");
- class GEPCache {
- public:
- GEPCache() : CachedPHINode(0), Map() {}
+ struct BasedUser;
- GEPCache *get(Value *v) {
- std::map<Value *, GEPCache>::iterator I = Map.find(v);
- if (I == Map.end())
- I = Map.insert(std::pair<Value *, GEPCache>(v, GEPCache())).first;
- return &I->second;
+ /// IVStrideUse - Keep track of one use of a strided induction variable, where
+ /// the stride is stored externally. The Offset member keeps track of the
+ /// offset from the IV, User is the actual user of the operand, and 'Operand'
+ /// is the operand # of the User that is the use.
+ struct VISIBILITY_HIDDEN IVStrideUse {
+ SCEVHandle Offset;
+ Instruction *User;
+ Value *OperandValToReplace;
+
+ // isUseOfPostIncrementedValue - True if this should use the
+ // post-incremented version of this IV, not the preincremented version.
+ // This can only be set in special cases, such as the terminating setcc
+ // instruction for a loop or uses dominated by the loop.
+ bool isUseOfPostIncrementedValue;
+
+ IVStrideUse(const SCEVHandle &Offs, Instruction *U, Value *O)
+ : Offset(Offs), User(U), OperandValToReplace(O),
+ isUseOfPostIncrementedValue(false) {}
+ };
+
+ /// IVUsersOfOneStride - This structure keeps track of all instructions that
+ /// have an operand that is based on the trip count multiplied by some stride.
+ /// The stride for all of these users is common and kept external to this
+ /// structure.
+ struct VISIBILITY_HIDDEN IVUsersOfOneStride {
+ /// Users - Keep track of all of the users of this stride as well as the
+ /// initial value and the operand that uses the IV.
+ std::vector<IVStrideUse> Users;
+
+ void addUser(const SCEVHandle &Offset,Instruction *User, Value *Operand) {
+ Users.push_back(IVStrideUse(Offset, User, Operand));
}
+ };
+
+ /// IVInfo - This structure keeps track of one IV expression inserted during
+ /// StrengthReduceStridedIVUsers. It contains the stride, the common base, as
+ /// well as the PHI node and increment value created for rewrite.
+ struct VISIBILITY_HIDDEN IVExpr {
+ SCEVHandle Stride;
+ SCEVHandle Base;
+ PHINode *PHI;
+ Value *IncV;
+
+ IVExpr()
+ : Stride(SCEVUnknown::getIntegerSCEV(0, Type::Int32Ty)),
+ Base (SCEVUnknown::getIntegerSCEV(0, Type::Int32Ty)) {}
+ IVExpr(const SCEVHandle &stride, const SCEVHandle &base, PHINode *phi,
+ Value *incv)
+ : Stride(stride), Base(base), PHI(phi), IncV(incv) {}
+ };
+
+ /// IVsOfOneStride - This structure keeps track of all IV expression inserted
+ /// during StrengthReduceStridedIVUsers for a particular stride of the IV.
+ struct VISIBILITY_HIDDEN IVsOfOneStride {
+ std::vector<IVExpr> IVs;
- PHINode *CachedPHINode;
- std::map<Value *, GEPCache> Map;
+ void addIV(const SCEVHandle &Stride, const SCEVHandle &Base, PHINode *PHI,
+ Value *IncV) {
+ IVs.push_back(IVExpr(Stride, Base, PHI, IncV));
+ }
};
- class LoopStrengthReduce : public FunctionPass {
+ class VISIBILITY_HIDDEN LoopStrengthReduce : public LoopPass {
LoopInfo *LI;
- DominatorSet *DS;
+ ETForest *EF;
+ ScalarEvolution *SE;
+ const TargetData *TD;
+ const Type *UIntPtrTy;
bool Changed;
- unsigned MaxTargetAMSize;
- public:
- LoopStrengthReduce(unsigned MTAMS = 1)
- : MaxTargetAMSize(MTAMS) {
- }
- virtual bool runOnFunction(Function &) {
- LI = &getAnalysis<LoopInfo>();
- DS = &getAnalysis<DominatorSet>();
- Changed = false;
+ /// IVUsesByStride - Keep track of all uses of induction variables that we
+ /// are interested in. The key of the map is the stride of the access.
+ std::map<SCEVHandle, IVUsersOfOneStride> IVUsesByStride;
+
+ /// IVsByStride - Keep track of all IVs that have been inserted for a
+ /// particular stride.
+ std::map<SCEVHandle, IVsOfOneStride> IVsByStride;
+
+ /// StrideOrder - An ordering of the keys in IVUsesByStride that is stable:
+ /// We use this to iterate over the IVUsesByStride collection without being
+ /// dependent on random ordering of pointers in the process.
+ std::vector<SCEVHandle> StrideOrder;
+
+ /// CastedValues - As we need to cast values to uintptr_t, this keeps track
+ /// of the casted version of each value. This is accessed by
+ /// getCastedVersionOf.
+ std::map<Value*, Value*> CastedPointers;
- for (LoopInfo::iterator I = LI->begin(), E = LI->end(); I != E; ++I)
- runOnLoop(*I);
- return Changed;
+ /// DeadInsts - Keep track of instructions we may have made dead, so that
+ /// we can remove them after we are done working.
+ std::set<Instruction*> DeadInsts;
+
+ /// TLI - Keep a pointer of a TargetLowering to consult for determining
+ /// transformation profitability.
+ const TargetLowering *TLI;
+
+ public:
+ LoopStrengthReduce(const TargetLowering *tli = NULL)
+ : TLI(tli) {
}
+ bool runOnLoop(Loop *L, LPPassManager &LPM);
+
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
- AU.setPreservesCFG();
+ // We split critical edges, so we change the CFG. However, we do update
+ // many analyses if they are around.
+ AU.addPreservedID(LoopSimplifyID);
+ AU.addPreserved<LoopInfo>();
+ AU.addPreserved<DominatorSet>();
+ AU.addPreserved<ETForest>();
+ AU.addPreserved<ImmediateDominators>();
+ AU.addPreserved<DominanceFrontier>();
+ AU.addPreserved<DominatorTree>();
+
AU.addRequiredID(LoopSimplifyID);
AU.addRequired<LoopInfo>();
- AU.addRequired<DominatorSet>();
+ AU.addRequired<ETForest>();
AU.addRequired<TargetData>();
+ AU.addRequired<ScalarEvolution>();
}
- private:
- void runOnLoop(Loop *L);
- void strengthReduceGEP(GetElementPtrInst *GEPI, Loop *L,
- GEPCache* GEPCache,
- Instruction *InsertBefore,
- std::set<Instruction*> &DeadInsts);
+
+ /// getCastedVersionOf - Return the specified value casted to uintptr_t.
+ ///
+ Value *getCastedVersionOf(Instruction::CastOps opcode, Value *V);
+private:
+ bool AddUsersIfInteresting(Instruction *I, Loop *L,
+ std::set<Instruction*> &Processed);
+ SCEVHandle GetExpressionSCEV(Instruction *E, Loop *L);
+
+ void OptimizeIndvars(Loop *L);
+
+ unsigned CheckForIVReuse(const SCEVHandle&, IVExpr&, const Type*,
+ const std::vector<BasedUser>& UsersToProcess);
+
+ bool ValidStride(int64_t, const std::vector<BasedUser>& UsersToProcess);
+
+ void StrengthReduceStridedIVUsers(const SCEVHandle &Stride,
+ IVUsersOfOneStride &Uses,
+ Loop *L, bool isOnlyStride);
void DeleteTriviallyDeadInstructions(std::set<Instruction*> &Insts);
};
- RegisterOpt<LoopStrengthReduce> X("loop-reduce",
- "Strength Reduce GEP Uses of Ind. Vars");
+ RegisterPass<LoopStrengthReduce> X("loop-reduce", "Loop Strength Reduction");
}
-FunctionPass *llvm::createLoopStrengthReducePass(unsigned MaxTargetAMSize) {
- return new LoopStrengthReduce(MaxTargetAMSize);
+LoopPass *llvm::createLoopStrengthReducePass(const TargetLowering *TLI) {
+ return new LoopStrengthReduce(TLI);
}
+/// getCastedVersionOf - Return the specified value casted to uintptr_t. This
+/// assumes that the Value* V is of integer or pointer type only.
+///
+Value *LoopStrengthReduce::getCastedVersionOf(Instruction::CastOps opcode,
+ Value *V) {
+ if (V->getType() == UIntPtrTy) return V;
+ if (Constant *CB = dyn_cast<Constant>(V))
+ return ConstantExpr::getCast(opcode, CB, UIntPtrTy);
+
+ Value *&New = CastedPointers[V];
+ if (New) return New;
+
+ New = SCEVExpander::InsertCastOfTo(opcode, V, UIntPtrTy);
+ DeadInsts.insert(cast<Instruction>(New));
+ return New;
+}
+
+
/// DeleteTriviallyDeadInstructions - If any of the instructions is the
/// specified set are trivially dead, delete them and see if this makes any of
/// their operands subsequently dead.
for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
if (Instruction *U = dyn_cast<Instruction>(I->getOperand(i)))
Insts.insert(U);
- I->getParent()->getInstList().erase(I);
+ SE->deleteInstructionFromRecords(I);
+ I->eraseFromParent();
Changed = true;
}
}
}
-void LoopStrengthReduce::strengthReduceGEP(GetElementPtrInst *GEPI, Loop *L,
- GEPCache *Cache,
- Instruction *InsertBefore,
- std::set<Instruction*> &DeadInsts) {
- // We will strength reduce the GEP by splitting it into two parts. The first
- // is a GEP to hold the initial value of the non-strength-reduced GEP upon
- // entering the loop, which we will insert at the end of the loop preheader.
- // The second is a GEP to hold the incremented value of the initial GEP.
- // The LoopIndVarSimplify pass guarantees that loop counts start at zero, so
- // we will replace the indvar with a constant zero value to create the first
- // GEP.
- //
- // We currently only handle GEP instructions that consist of zero or more
- // constants or loop invariable expressions prior to an instance of the
- // canonical induction variable.
- unsigned indvar = 0;
- std::vector<Value *> pre_op_vector;
- std::vector<Value *> inc_op_vector;
- const Type *ty = GEPI->getOperand(0)->getType();
- Value *CanonicalIndVar = L->getCanonicalInductionVariable();
- BasicBlock *Header = L->getHeader();
- BasicBlock *Preheader = L->getLoopPreheader();
- bool AllConstantOperands = true;
- Cache = Cache->get(GEPI->getOperand(0));
-
- for (unsigned op = 1, e = GEPI->getNumOperands(); op != e; ++op) {
- Value *operand = GEPI->getOperand(op);
- if (ty->getTypeID() == Type::StructTyID) {
- assert(isa<ConstantUInt>(operand));
- ConstantUInt *c = dyn_cast<ConstantUInt>(operand);
- ty = ty->getContainedType(unsigned(c->getValue()));
+
+/// GetExpressionSCEV - Compute and return the SCEV for the specified
+/// instruction.
+SCEVHandle LoopStrengthReduce::GetExpressionSCEV(Instruction *Exp, Loop *L) {
+ // Pointer to pointer bitcast instructions return the same value as their
+ // operand.
+ if (BitCastInst *BCI = dyn_cast<BitCastInst>(Exp)) {
+ if (SE->hasSCEV(BCI) || !isa<Instruction>(BCI->getOperand(0)))
+ return SE->getSCEV(BCI);
+ SCEVHandle R = GetExpressionSCEV(cast<Instruction>(BCI->getOperand(0)), L);
+ SE->setSCEV(BCI, R);
+ return R;
+ }
+
+ // Scalar Evolutions doesn't know how to compute SCEV's for GEP instructions.
+ // If this is a GEP that SE doesn't know about, compute it now and insert it.
+ // If this is not a GEP, or if we have already done this computation, just let
+ // SE figure it out.
+ GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Exp);
+ if (!GEP || SE->hasSCEV(GEP))
+ return SE->getSCEV(Exp);
+
+ // Analyze all of the subscripts of this getelementptr instruction, looking
+ // for uses that are determined by the trip count of L. First, skip all
+ // operands the are not dependent on the IV.
+
+ // Build up the base expression. Insert an LLVM cast of the pointer to
+ // uintptr_t first.
+ SCEVHandle GEPVal = SCEVUnknown::get(
+ getCastedVersionOf(Instruction::PtrToInt, GEP->getOperand(0)));
+
+ gep_type_iterator GTI = gep_type_begin(GEP);
+
+ for (unsigned i = 1, e = GEP->getNumOperands(); i != e; ++i, ++GTI) {
+ // If this is a use of a recurrence that we can analyze, and it comes before
+ // Op does in the GEP operand list, we will handle this when we process this
+ // operand.
+ if (const StructType *STy = dyn_cast<StructType>(*GTI)) {
+ const StructLayout *SL = TD->getStructLayout(STy);
+ unsigned Idx = cast<ConstantInt>(GEP->getOperand(i))->getZExtValue();
+ uint64_t Offset = SL->getElementOffset(Idx);
+ GEPVal = SCEVAddExpr::get(GEPVal,
+ SCEVUnknown::getIntegerSCEV(Offset, UIntPtrTy));
} else {
- ty = ty->getContainedType(0);
+ unsigned GEPOpiBits =
+ GEP->getOperand(i)->getType()->getPrimitiveSizeInBits();
+ unsigned IntPtrBits = UIntPtrTy->getPrimitiveSizeInBits();
+ Instruction::CastOps opcode = (GEPOpiBits < IntPtrBits ?
+ Instruction::SExt : (GEPOpiBits > IntPtrBits ? Instruction::Trunc :
+ Instruction::BitCast));
+ Value *OpVal = getCastedVersionOf(opcode, GEP->getOperand(i));
+ SCEVHandle Idx = SE->getSCEV(OpVal);
+
+ uint64_t TypeSize = TD->getTypeSize(GTI.getIndexedType());
+ if (TypeSize != 1)
+ Idx = SCEVMulExpr::get(Idx,
+ SCEVConstant::get(ConstantInt::get(UIntPtrTy,
+ TypeSize)));
+ GEPVal = SCEVAddExpr::get(GEPVal, Idx);
}
+ }
+
+ SE->setSCEV(GEP, GEPVal);
+ return GEPVal;
+}
+
+/// getSCEVStartAndStride - Compute the start and stride of this expression,
+/// returning false if the expression is not a start/stride pair, or true if it
+/// is. The stride must be a loop invariant expression, but the start may be
+/// a mix of loop invariant and loop variant expressions.
+static bool getSCEVStartAndStride(const SCEVHandle &SH, Loop *L,
+ SCEVHandle &Start, SCEVHandle &Stride) {
+ SCEVHandle TheAddRec = Start; // Initialize to zero.
- if (operand == CanonicalIndVar) {
- // FIXME: use getCanonicalInductionVariableIncrement to choose between
- // one and neg one maybe? We need to support int *foo = GEP base, -1
- const Type *Ty = CanonicalIndVar->getType();
- pre_op_vector.push_back(Constant::getNullValue(Ty));
- inc_op_vector.push_back(ConstantInt::get(Ty, 1));
- indvar = op;
- break;
- } else if (isa<Constant>(operand) || isa<Argument>(operand)) {
- pre_op_vector.push_back(operand);
- } else if (Instruction *inst = dyn_cast<Instruction>(operand)) {
- if (!DS->dominates(inst, Preheader->getTerminator()))
- return;
- pre_op_vector.push_back(operand);
- AllConstantOperands = false;
- } else
- return;
- Cache = Cache->get(operand);
+ // If the outer level is an AddExpr, the operands are all start values except
+ // for a nested AddRecExpr.
+ if (SCEVAddExpr *AE = dyn_cast<SCEVAddExpr>(SH)) {
+ for (unsigned i = 0, e = AE->getNumOperands(); i != e; ++i)
+ if (SCEVAddRecExpr *AddRec =
+ dyn_cast<SCEVAddRecExpr>(AE->getOperand(i))) {
+ if (AddRec->getLoop() == L)
+ TheAddRec = SCEVAddExpr::get(AddRec, TheAddRec);
+ else
+ return false; // Nested IV of some sort?
+ } else {
+ Start = SCEVAddExpr::get(Start, AE->getOperand(i));
+ }
+
+ } else if (isa<SCEVAddRecExpr>(SH)) {
+ TheAddRec = SH;
+ } else {
+ return false; // not analyzable.
}
- assert(indvar > 0 && "Indvar used by GEP not found in operand list");
- // Ensure the pointer base is loop invariant. While strength reduction
- // makes sense even if the pointer changed on every iteration, there is no
- // realistic way of handling it unless GEPs were completely decomposed into
- // their constituent operations so we have explicit multiplications to work
- // with.
- if (Instruction *GepPtrOp = dyn_cast<Instruction>(GEPI->getOperand(0)))
- if (!DS->dominates(GepPtrOp, Preheader->getTerminator()))
- return;
-
- // Don't reduce multiplies that the target can handle via addressing modes.
- uint64_t sz = getAnalysis<TargetData>().getTypeSize(ty);
- if (sz && (sz & (sz-1)) == 0) // Power of two?
- if (sz <= (1ULL << (MaxTargetAMSize-1)))
- return;
+ SCEVAddRecExpr *AddRec = dyn_cast<SCEVAddRecExpr>(TheAddRec);
+ if (!AddRec || AddRec->getLoop() != L) return false;
- // If all operands of the GEP we are going to insert into the preheader
- // are constants, generate a GEP ConstantExpr instead.
- //
- // If there is only one operand after the initial non-constant one, we know
- // that it was the induction variable, and has been replaced by a constant
- // null value. In this case, replace the GEP with a use of pointer directly.
- PHINode *NewPHI;
- if (1) {
- Value *PreGEP;
- if (AllConstantOperands && isa<Constant>(GEPI->getOperand(0))) {
- Constant *C = dyn_cast<Constant>(GEPI->getOperand(0));
- PreGEP = ConstantExpr::getGetElementPtr(C, pre_op_vector);
- } else if (pre_op_vector.size() == 1) {
- PreGEP = GEPI->getOperand(0);
- } else {
- PreGEP = new GetElementPtrInst(GEPI->getOperand(0),
- pre_op_vector, GEPI->getName()+".pre",
- Preheader->getTerminator());
+ // FIXME: Generalize to non-affine IV's.
+ if (!AddRec->isAffine()) return false;
+
+ Start = SCEVAddExpr::get(Start, AddRec->getOperand(0));
+
+ if (!isa<SCEVConstant>(AddRec->getOperand(1)))
+ DOUT << "[" << L->getHeader()->getName()
+ << "] Variable stride: " << *AddRec << "\n";
+
+ Stride = AddRec->getOperand(1);
+ return true;
+}
+
+/// IVUseShouldUsePostIncValue - We have discovered a "User" of an IV expression
+/// and now we need to decide whether the user should use the preinc or post-inc
+/// value. If this user should use the post-inc version of the IV, return true.
+///
+/// Choosing wrong here can break dominance properties (if we choose to use the
+/// post-inc value when we cannot) or it can end up adding extra live-ranges to
+/// the loop, resulting in reg-reg copies (if we use the pre-inc value when we
+/// should use the post-inc value).
+static bool IVUseShouldUsePostIncValue(Instruction *User, Instruction *IV,
+ Loop *L, ETForest *EF, Pass *P) {
+ // If the user is in the loop, use the preinc value.
+ if (L->contains(User->getParent())) return false;
+
+ BasicBlock *LatchBlock = L->getLoopLatch();
+
+ // Ok, the user is outside of the loop. If it is dominated by the latch
+ // block, use the post-inc value.
+ if (EF->dominates(LatchBlock, User->getParent()))
+ return true;
+
+ // There is one case we have to be careful of: PHI nodes. These little guys
+ // can live in blocks that do not dominate the latch block, but (since their
+ // uses occur in the predecessor block, not the block the PHI lives in) should
+ // still use the post-inc value. Check for this case now.
+ PHINode *PN = dyn_cast<PHINode>(User);
+ if (!PN) return false; // not a phi, not dominated by latch block.
+
+ // Look at all of the uses of IV by the PHI node. If any use corresponds to
+ // a block that is not dominated by the latch block, give up and use the
+ // preincremented value.
+ unsigned NumUses = 0;
+ for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
+ if (PN->getIncomingValue(i) == IV) {
+ ++NumUses;
+ if (!EF->dominates(LatchBlock, PN->getIncomingBlock(i)))
+ return false;
+ }
+
+ // Okay, all uses of IV by PN are in predecessor blocks that really are
+ // dominated by the latch block. Split the critical edges and use the
+ // post-incremented value.
+ for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
+ if (PN->getIncomingValue(i) == IV) {
+ SplitCriticalEdge(PN->getIncomingBlock(i), PN->getParent(), P,
+ true);
+ // Splitting the critical edge can reduce the number of entries in this
+ // PHI.
+ e = PN->getNumIncomingValues();
+ if (--NumUses == 0) break;
+ }
+
+ return true;
+}
+
+
+
+/// AddUsersIfInteresting - Inspect the specified instruction. If it is a
+/// reducible SCEV, recursively add its users to the IVUsesByStride set and
+/// return true. Otherwise, return false.
+bool LoopStrengthReduce::AddUsersIfInteresting(Instruction *I, Loop *L,
+ std::set<Instruction*> &Processed) {
+ if (!I->getType()->isInteger() && !isa<PointerType>(I->getType()))
+ return false; // Void and FP expressions cannot be reduced.
+ if (!Processed.insert(I).second)
+ return true; // Instruction already handled.
+
+ // Get the symbolic expression for this instruction.
+ SCEVHandle ISE = GetExpressionSCEV(I, L);
+ if (isa<SCEVCouldNotCompute>(ISE)) return false;
+
+ // Get the start and stride for this expression.
+ SCEVHandle Start = SCEVUnknown::getIntegerSCEV(0, ISE->getType());
+ SCEVHandle Stride = Start;
+ if (!getSCEVStartAndStride(ISE, L, Start, Stride))
+ return false; // Non-reducible symbolic expression, bail out.
+
+ for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI != E;) {
+ Instruction *User = cast<Instruction>(*UI);
+
+ // Increment iterator now because IVUseShouldUsePostIncValue may remove
+ // User from the list of I users.
+ ++UI;
+
+ // Do not infinitely recurse on PHI nodes.
+ if (isa<PHINode>(User) && Processed.count(User))
+ continue;
+
+ // If this is an instruction defined in a nested loop, or outside this loop,
+ // don't recurse into it.
+ bool AddUserToIVUsers = false;
+ if (LI->getLoopFor(User->getParent()) != L) {
+ DOUT << "FOUND USER in other loop: " << *User
+ << " OF SCEV: " << *ISE << "\n";
+ AddUserToIVUsers = true;
+ } else if (!AddUsersIfInteresting(User, L, Processed)) {
+ DOUT << "FOUND USER: " << *User
+ << " OF SCEV: " << *ISE << "\n";
+ AddUserToIVUsers = true;
+ }
+
+ if (AddUserToIVUsers) {
+ IVUsersOfOneStride &StrideUses = IVUsesByStride[Stride];
+ if (StrideUses.Users.empty()) // First occurance of this stride?
+ StrideOrder.push_back(Stride);
+
+ // Okay, we found a user that we cannot reduce. Analyze the instruction
+ // and decide what to do with it. If we are a use inside of the loop, use
+ // the value before incrementation, otherwise use it after incrementation.
+ if (IVUseShouldUsePostIncValue(User, I, L, EF, this)) {
+ // The value used will be incremented by the stride more than we are
+ // expecting, so subtract this off.
+ SCEVHandle NewStart = SCEV::getMinusSCEV(Start, Stride);
+ StrideUses.addUser(NewStart, User, I);
+ StrideUses.Users.back().isUseOfPostIncrementedValue = true;
+ DOUT << " USING POSTINC SCEV, START=" << *NewStart<< "\n";
+ } else {
+ StrideUses.addUser(Start, User, I);
+ }
}
+ }
+ return true;
+}
- // The next step of the strength reduction is to create a PHI that will
- // choose between the initial GEP we created and inserted into the
- // preheader, and the incremented GEP that we will create below and insert
- // into the loop body.
- NewPHI = new PHINode(PreGEP->getType(),
- GEPI->getName()+".str", InsertBefore);
- NewPHI->addIncoming(PreGEP, Preheader);
+namespace {
+ /// BasedUser - For a particular base value, keep information about how we've
+ /// partitioned the expression so far.
+ struct BasedUser {
+ /// Base - The Base value for the PHI node that needs to be inserted for
+ /// this use. As the use is processed, information gets moved from this
+ /// field to the Imm field (below). BasedUser values are sorted by this
+ /// field.
+ SCEVHandle Base;
- // Now, create the GEP instruction to increment by one the value selected
- // by the PHI instruction we just created above, and add it as the second
- // incoming Value/BasicBlock pair to the PHINode. It is inserted before
- // the increment of the canonical induction variable.
- Instruction *IncrInst =
- const_cast<Instruction*>(L->getCanonicalInductionVariableIncrement());
- GetElementPtrInst *StrGEP = new GetElementPtrInst(NewPHI, inc_op_vector,
- GEPI->getName()+".inc",
- IncrInst);
- pred_iterator PI = pred_begin(Header);
- if (*PI == Preheader)
- ++PI;
- NewPHI->addIncoming(StrGEP, *PI);
- Cache->CachedPHINode = NewPHI;
+ /// Inst - The instruction using the induction variable.
+ Instruction *Inst;
+
+ /// OperandValToReplace - The operand value of Inst to replace with the
+ /// EmittedBase.
+ Value *OperandValToReplace;
+
+ /// Imm - The immediate value that should be added to the base immediately
+ /// before Inst, because it will be folded into the imm field of the
+ /// instruction.
+ SCEVHandle Imm;
+
+ /// EmittedBase - The actual value* to use for the base value of this
+ /// operation. This is null if we should just use zero so far.
+ Value *EmittedBase;
+
+ // isUseOfPostIncrementedValue - True if this should use the
+ // post-incremented version of this IV, not the preincremented version.
+ // This can only be set in special cases, such as the terminating setcc
+ // instruction for a loop and uses outside the loop that are dominated by
+ // the loop.
+ bool isUseOfPostIncrementedValue;
+
+ BasedUser(IVStrideUse &IVSU)
+ : Base(IVSU.Offset), Inst(IVSU.User),
+ OperandValToReplace(IVSU.OperandValToReplace),
+ Imm(SCEVUnknown::getIntegerSCEV(0, Base->getType())), EmittedBase(0),
+ isUseOfPostIncrementedValue(IVSU.isUseOfPostIncrementedValue) {}
+
+ // Once we rewrite the code to insert the new IVs we want, update the
+ // operands of Inst to use the new expression 'NewBase', with 'Imm' added
+ // to it.
+ void RewriteInstructionToUseNewBase(const SCEVHandle &NewBase,
+ SCEVExpander &Rewriter, Loop *L,
+ Pass *P);
+
+ Value *InsertCodeForBaseAtPosition(const SCEVHandle &NewBase,
+ SCEVExpander &Rewriter,
+ Instruction *IP, Loop *L);
+ void dump() const;
+ };
+}
+
+void BasedUser::dump() const {
+ cerr << " Base=" << *Base;
+ cerr << " Imm=" << *Imm;
+ if (EmittedBase)
+ cerr << " EB=" << *EmittedBase;
+
+ cerr << " Inst: " << *Inst;
+}
+
+Value *BasedUser::InsertCodeForBaseAtPosition(const SCEVHandle &NewBase,
+ SCEVExpander &Rewriter,
+ Instruction *IP, Loop *L) {
+ // Figure out where we *really* want to insert this code. In particular, if
+ // the user is inside of a loop that is nested inside of L, we really don't
+ // want to insert this expression before the user, we'd rather pull it out as
+ // many loops as possible.
+ LoopInfo &LI = Rewriter.getLoopInfo();
+ Instruction *BaseInsertPt = IP;
+
+ // Figure out the most-nested loop that IP is in.
+ Loop *InsertLoop = LI.getLoopFor(IP->getParent());
+
+ // If InsertLoop is not L, and InsertLoop is nested inside of L, figure out
+ // the preheader of the outer-most loop where NewBase is not loop invariant.
+ while (InsertLoop && NewBase->isLoopInvariant(InsertLoop)) {
+ BaseInsertPt = InsertLoop->getLoopPreheader()->getTerminator();
+ InsertLoop = InsertLoop->getParentLoop();
+ }
+
+ // If there is no immediate value, skip the next part.
+ if (SCEVConstant *SC = dyn_cast<SCEVConstant>(Imm))
+ if (SC->getValue()->isZero())
+ return Rewriter.expandCodeFor(NewBase, BaseInsertPt,
+ OperandValToReplace->getType());
+
+ Value *Base = Rewriter.expandCodeFor(NewBase, BaseInsertPt);
+
+ // Always emit the immediate (if non-zero) into the same block as the user.
+ SCEVHandle NewValSCEV = SCEVAddExpr::get(SCEVUnknown::get(Base), Imm);
+ return Rewriter.expandCodeFor(NewValSCEV, IP,
+ OperandValToReplace->getType());
+}
+
+
+// Once we rewrite the code to insert the new IVs we want, update the
+// operands of Inst to use the new expression 'NewBase', with 'Imm' added
+// to it.
+void BasedUser::RewriteInstructionToUseNewBase(const SCEVHandle &NewBase,
+ SCEVExpander &Rewriter,
+ Loop *L, Pass *P) {
+ if (!isa<PHINode>(Inst)) {
+ Value *NewVal = InsertCodeForBaseAtPosition(NewBase, Rewriter, Inst, L);
+ // Replace the use of the operand Value with the new Phi we just created.
+ Inst->replaceUsesOfWith(OperandValToReplace, NewVal);
+ DOUT << " CHANGED: IMM =" << *Imm << " Inst = " << *Inst;
+ return;
+ }
+
+ // PHI nodes are more complex. We have to insert one copy of the NewBase+Imm
+ // expression into each operand block that uses it. Note that PHI nodes can
+ // have multiple entries for the same predecessor. We use a map to make sure
+ // that a PHI node only has a single Value* for each predecessor (which also
+ // prevents us from inserting duplicate code in some blocks).
+ std::map<BasicBlock*, Value*> InsertedCode;
+ PHINode *PN = cast<PHINode>(Inst);
+ for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
+ if (PN->getIncomingValue(i) == OperandValToReplace) {
+ // If this is a critical edge, split the edge so that we do not insert the
+ // code on all predecessor/successor paths. We do this unless this is the
+ // canonical backedge for this loop, as this can make some inserted code
+ // be in an illegal position.
+ BasicBlock *PHIPred = PN->getIncomingBlock(i);
+ if (e != 1 && PHIPred->getTerminator()->getNumSuccessors() > 1 &&
+ (PN->getParent() != L->getHeader() || !L->contains(PHIPred))) {
+
+ // First step, split the critical edge.
+ SplitCriticalEdge(PHIPred, PN->getParent(), P, true);
+
+ // Next step: move the basic block. In particular, if the PHI node
+ // is outside of the loop, and PredTI is in the loop, we want to
+ // move the block to be immediately before the PHI block, not
+ // immediately after PredTI.
+ if (L->contains(PHIPred) && !L->contains(PN->getParent())) {
+ BasicBlock *NewBB = PN->getIncomingBlock(i);
+ NewBB->moveBefore(PN->getParent());
+ }
+
+ // Splitting the edge can reduce the number of PHI entries we have.
+ e = PN->getNumIncomingValues();
+ }
+
+ Value *&Code = InsertedCode[PN->getIncomingBlock(i)];
+ if (!Code) {
+ // Insert the code into the end of the predecessor block.
+ Instruction *InsertPt = PN->getIncomingBlock(i)->getTerminator();
+ Code = InsertCodeForBaseAtPosition(NewBase, Rewriter, InsertPt, L);
+ }
+
+ // Replace the use of the operand Value with the new Phi we just created.
+ PN->setIncomingValue(i, Code);
+ Rewriter.clear();
+ }
+ }
+ DOUT << " CHANGED: IMM =" << *Imm << " Inst = " << *Inst;
+}
+
+
+/// isTargetConstant - Return true if the following can be referenced by the
+/// immediate field of a target instruction.
+static bool isTargetConstant(const SCEVHandle &V, const Type *UseTy,
+ const TargetLowering *TLI) {
+ if (SCEVConstant *SC = dyn_cast<SCEVConstant>(V)) {
+ int64_t VC = SC->getValue()->getSExtValue();
+ if (TLI)
+ return TLI->isLegalAddressImmediate(VC, UseTy);
+ else
+ // Defaults to PPC. PPC allows a sign-extended 16-bit immediate field.
+ return (VC > -(1 << 16) && VC < (1 << 16)-1);
+ }
+
+ if (SCEVUnknown *SU = dyn_cast<SCEVUnknown>(V))
+ if (ConstantExpr *CE = dyn_cast<ConstantExpr>(SU->getValue()))
+ if (CE->getOpcode() == Instruction::PtrToInt) {
+ Constant *Op0 = CE->getOperand(0);
+ if (isa<GlobalValue>(Op0) && TLI &&
+ TLI->isLegalAddressImmediate(cast<GlobalValue>(Op0)))
+ return true;
+ }
+ return false;
+}
+
+/// MoveLoopVariantsToImediateField - Move any subexpressions from Val that are
+/// loop varying to the Imm operand.
+static void MoveLoopVariantsToImediateField(SCEVHandle &Val, SCEVHandle &Imm,
+ Loop *L) {
+ if (Val->isLoopInvariant(L)) return; // Nothing to do.
+
+ if (SCEVAddExpr *SAE = dyn_cast<SCEVAddExpr>(Val)) {
+ std::vector<SCEVHandle> NewOps;
+ NewOps.reserve(SAE->getNumOperands());
+
+ for (unsigned i = 0; i != SAE->getNumOperands(); ++i)
+ if (!SAE->getOperand(i)->isLoopInvariant(L)) {
+ // If this is a loop-variant expression, it must stay in the immediate
+ // field of the expression.
+ Imm = SCEVAddExpr::get(Imm, SAE->getOperand(i));
+ } else {
+ NewOps.push_back(SAE->getOperand(i));
+ }
+
+ if (NewOps.empty())
+ Val = SCEVUnknown::getIntegerSCEV(0, Val->getType());
+ else
+ Val = SCEVAddExpr::get(NewOps);
+ } else if (SCEVAddRecExpr *SARE = dyn_cast<SCEVAddRecExpr>(Val)) {
+ // Try to pull immediates out of the start value of nested addrec's.
+ SCEVHandle Start = SARE->getStart();
+ MoveLoopVariantsToImediateField(Start, Imm, L);
+
+ std::vector<SCEVHandle> Ops(SARE->op_begin(), SARE->op_end());
+ Ops[0] = Start;
+ Val = SCEVAddRecExpr::get(Ops, SARE->getLoop());
} else {
- // Reuse previously created pointer, as it is identical to the one we were
- // about to create.
- NewPHI = Cache->CachedPHINode;
+ // Otherwise, all of Val is variant, move the whole thing over.
+ Imm = SCEVAddExpr::get(Imm, Val);
+ Val = SCEVUnknown::getIntegerSCEV(0, Val->getType());
}
+}
+
+
+/// MoveImmediateValues - Look at Val, and pull out any additions of constants
+/// that can fit into the immediate field of instructions in the target.
+/// Accumulate these immediate values into the Imm value.
+static void MoveImmediateValues(const TargetLowering *TLI,
+ Instruction *User,
+ SCEVHandle &Val, SCEVHandle &Imm,
+ bool isAddress, Loop *L) {
+ const Type *UseTy = User->getType();
+ if (StoreInst *SI = dyn_cast<StoreInst>(User))
+ UseTy = SI->getOperand(0)->getType();
+
+ if (SCEVAddExpr *SAE = dyn_cast<SCEVAddExpr>(Val)) {
+ std::vector<SCEVHandle> NewOps;
+ NewOps.reserve(SAE->getNumOperands());
+
+ for (unsigned i = 0; i != SAE->getNumOperands(); ++i) {
+ SCEVHandle NewOp = SAE->getOperand(i);
+ MoveImmediateValues(TLI, User, NewOp, Imm, isAddress, L);
+
+ if (!NewOp->isLoopInvariant(L)) {
+ // If this is a loop-variant expression, it must stay in the immediate
+ // field of the expression.
+ Imm = SCEVAddExpr::get(Imm, NewOp);
+ } else {
+ NewOps.push_back(NewOp);
+ }
+ }
+
+ if (NewOps.empty())
+ Val = SCEVUnknown::getIntegerSCEV(0, Val->getType());
+ else
+ Val = SCEVAddExpr::get(NewOps);
+ return;
+ } else if (SCEVAddRecExpr *SARE = dyn_cast<SCEVAddRecExpr>(Val)) {
+ // Try to pull immediates out of the start value of nested addrec's.
+ SCEVHandle Start = SARE->getStart();
+ MoveImmediateValues(TLI, User, Start, Imm, isAddress, L);
+
+ if (Start != SARE->getStart()) {
+ std::vector<SCEVHandle> Ops(SARE->op_begin(), SARE->op_end());
+ Ops[0] = Start;
+ Val = SCEVAddRecExpr::get(Ops, SARE->getLoop());
+ }
+ return;
+ } else if (SCEVMulExpr *SME = dyn_cast<SCEVMulExpr>(Val)) {
+ // Transform "8 * (4 + v)" -> "32 + 8*V" if "32" fits in the immed field.
+ if (isAddress && isTargetConstant(SME->getOperand(0), UseTy, TLI) &&
+ SME->getNumOperands() == 2 && SME->isLoopInvariant(L)) {
+
+ SCEVHandle SubImm = SCEVUnknown::getIntegerSCEV(0, Val->getType());
+ SCEVHandle NewOp = SME->getOperand(1);
+ MoveImmediateValues(TLI, User, NewOp, SubImm, isAddress, L);
+
+ // If we extracted something out of the subexpressions, see if we can
+ // simplify this!
+ if (NewOp != SME->getOperand(1)) {
+ // Scale SubImm up by "8". If the result is a target constant, we are
+ // good.
+ SubImm = SCEVMulExpr::get(SubImm, SME->getOperand(0));
+ if (isTargetConstant(SubImm, UseTy, TLI)) {
+ // Accumulate the immediate.
+ Imm = SCEVAddExpr::get(Imm, SubImm);
+
+ // Update what is left of 'Val'.
+ Val = SCEVMulExpr::get(SME->getOperand(0), NewOp);
+ return;
+ }
+ }
+ }
+ }
+
+ // Loop-variant expressions must stay in the immediate field of the
+ // expression.
+ if ((isAddress && isTargetConstant(Val, UseTy, TLI)) ||
+ !Val->isLoopInvariant(L)) {
+ Imm = SCEVAddExpr::get(Imm, Val);
+ Val = SCEVUnknown::getIntegerSCEV(0, Val->getType());
+ return;
+ }
+
+ // Otherwise, no immediates to move.
+}
+
+
+/// SeparateSubExprs - Decompose Expr into all of the subexpressions that are
+/// added together. This is used to reassociate common addition subexprs
+/// together for maximal sharing when rewriting bases.
+static void SeparateSubExprs(std::vector<SCEVHandle> &SubExprs,
+ SCEVHandle Expr) {
+ if (SCEVAddExpr *AE = dyn_cast<SCEVAddExpr>(Expr)) {
+ for (unsigned j = 0, e = AE->getNumOperands(); j != e; ++j)
+ SeparateSubExprs(SubExprs, AE->getOperand(j));
+ } else if (SCEVAddRecExpr *SARE = dyn_cast<SCEVAddRecExpr>(Expr)) {
+ SCEVHandle Zero = SCEVUnknown::getIntegerSCEV(0, Expr->getType());
+ if (SARE->getOperand(0) == Zero) {
+ SubExprs.push_back(Expr);
+ } else {
+ // Compute the addrec with zero as its base.
+ std::vector<SCEVHandle> Ops(SARE->op_begin(), SARE->op_end());
+ Ops[0] = Zero; // Start with zero base.
+ SubExprs.push_back(SCEVAddRecExpr::get(Ops, SARE->getLoop()));
+
+
+ SeparateSubExprs(SubExprs, SARE->getOperand(0));
+ }
+ } else if (!isa<SCEVConstant>(Expr) ||
+ !cast<SCEVConstant>(Expr)->getValue()->isZero()) {
+ // Do not add zero.
+ SubExprs.push_back(Expr);
+ }
+}
+
+
+/// RemoveCommonExpressionsFromUseBases - Look through all of the uses in Bases,
+/// removing any common subexpressions from it. Anything truly common is
+/// removed, accumulated, and returned. This looks for things like (a+b+c) and
+/// (a+c+d) -> (a+c). The common expression is *removed* from the Bases.
+static SCEVHandle
+RemoveCommonExpressionsFromUseBases(std::vector<BasedUser> &Uses) {
+ unsigned NumUses = Uses.size();
+
+ // Only one use? Use its base, regardless of what it is!
+ SCEVHandle Zero = SCEVUnknown::getIntegerSCEV(0, Uses[0].Base->getType());
+ SCEVHandle Result = Zero;
+ if (NumUses == 1) {
+ std::swap(Result, Uses[0].Base);
+ return Result;
+ }
+
+ // To find common subexpressions, count how many of Uses use each expression.
+ // If any subexpressions are used Uses.size() times, they are common.
+ std::map<SCEVHandle, unsigned> SubExpressionUseCounts;
+
+ // UniqueSubExprs - Keep track of all of the subexpressions we see in the
+ // order we see them.
+ std::vector<SCEVHandle> UniqueSubExprs;
+
+ std::vector<SCEVHandle> SubExprs;
+ for (unsigned i = 0; i != NumUses; ++i) {
+ // If the base is zero (which is common), return zero now, there are no
+ // CSEs we can find.
+ if (Uses[i].Base == Zero) return Zero;
+
+ // Split the expression into subexprs.
+ SeparateSubExprs(SubExprs, Uses[i].Base);
+ // Add one to SubExpressionUseCounts for each subexpr present.
+ for (unsigned j = 0, e = SubExprs.size(); j != e; ++j)
+ if (++SubExpressionUseCounts[SubExprs[j]] == 1)
+ UniqueSubExprs.push_back(SubExprs[j]);
+ SubExprs.clear();
+ }
+
+ // Now that we know how many times each is used, build Result. Iterate over
+ // UniqueSubexprs so that we have a stable ordering.
+ for (unsigned i = 0, e = UniqueSubExprs.size(); i != e; ++i) {
+ std::map<SCEVHandle, unsigned>::iterator I =
+ SubExpressionUseCounts.find(UniqueSubExprs[i]);
+ assert(I != SubExpressionUseCounts.end() && "Entry not found?");
+ if (I->second == NumUses) { // Found CSE!
+ Result = SCEVAddExpr::get(Result, I->first);
+ } else {
+ // Remove non-cse's from SubExpressionUseCounts.
+ SubExpressionUseCounts.erase(I);
+ }
+ }
+
+ // If we found no CSE's, return now.
+ if (Result == Zero) return Result;
- if (GEPI->getNumOperands() - 1 == indvar) {
- // If there were no operands following the induction variable, replace all
- // uses of the old GEP instruction with the new PHI.
- GEPI->replaceAllUsesWith(NewPHI);
+ // Otherwise, remove all of the CSE's we found from each of the base values.
+ for (unsigned i = 0; i != NumUses; ++i) {
+ // Split the expression into subexprs.
+ SeparateSubExprs(SubExprs, Uses[i].Base);
+
+ // Remove any common subexpressions.
+ for (unsigned j = 0, e = SubExprs.size(); j != e; ++j)
+ if (SubExpressionUseCounts.count(SubExprs[j])) {
+ SubExprs.erase(SubExprs.begin()+j);
+ --j; --e;
+ }
+
+ // Finally, the non-shared expressions together.
+ if (SubExprs.empty())
+ Uses[i].Base = Zero;
+ else
+ Uses[i].Base = SCEVAddExpr::get(SubExprs);
+ SubExprs.clear();
+ }
+
+ return Result;
+}
+
+/// isZero - returns true if the scalar evolution expression is zero.
+///
+static bool isZero(SCEVHandle &V) {
+ if (SCEVConstant *SC = dyn_cast<SCEVConstant>(V))
+ return SC->getValue()->isZero();
+ return false;
+}
+
+/// ValidStride - Check whether the given Scale is valid for all loads and
+/// stores in UsersToProcess. Pulled into a function to avoid disturbing the
+/// sensibilities of those who dislike goto's.
+///
+bool LoopStrengthReduce::ValidStride(int64_t Scale,
+ const std::vector<BasedUser>& UsersToProcess) {
+ int64_t Imm;
+ for (unsigned i=0, e = UsersToProcess.size(); i!=e; ++i) {
+ if (SCEVConstant *SC = dyn_cast<SCEVConstant>(UsersToProcess[i].Imm))
+ Imm = SC->getValue()->getSExtValue();
+ else
+ Imm = 0;
+
+ // If this is a load or other access, pass the type of the access in.
+ const Type *AccessTy = Type::VoidTy;
+ if (StoreInst *SI = dyn_cast<StoreInst>(UsersToProcess[i].Inst))
+ AccessTy = SI->getOperand(0)->getType();
+ else if (LoadInst *LI = dyn_cast<LoadInst>(UsersToProcess[i].Inst))
+ AccessTy = LI->getType();
+
+ if (!TLI->isLegalAddressScaleAndImm(Scale, Imm, AccessTy))
+ return false;
+ }
+ return true;
+}
+
+/// CheckForIVReuse - Returns the multiple if the stride is the multiple
+/// of a previous stride and it is a legal value for the target addressing
+/// mode scale component. This allows the users of this stride to be rewritten
+/// as prev iv * factor. It returns 0 if no reuse is possible.
+unsigned LoopStrengthReduce::CheckForIVReuse(const SCEVHandle &Stride,
+ IVExpr &IV, const Type *Ty,
+ const std::vector<BasedUser>& UsersToProcess) {
+ if (!TLI) return 0;
+
+ if (SCEVConstant *SC = dyn_cast<SCEVConstant>(Stride)) {
+ int64_t SInt = SC->getValue()->getSExtValue();
+ if (SInt == 1) return 0;
+
+ for (std::map<SCEVHandle, IVsOfOneStride>::iterator SI= IVsByStride.begin(),
+ SE = IVsByStride.end(); SI != SE; ++SI) {
+ int64_t SSInt = cast<SCEVConstant>(SI->first)->getValue()->getSExtValue();
+ if (SInt != -SSInt &&
+ (unsigned(abs(SInt)) < SSInt || (SInt % SSInt) != 0))
+ continue;
+ int64_t Scale = SInt / SSInt;
+ // Check that this stride is valid for all the types used for loads and
+ // stores; if it can be used for some and not others, we might as well use
+ // the original stride everywhere, since we have to create the IV for it
+ // anyway.
+ if (ValidStride(Scale, UsersToProcess))
+ for (std::vector<IVExpr>::iterator II = SI->second.IVs.begin(),
+ IE = SI->second.IVs.end(); II != IE; ++II)
+ // FIXME: Only handle base == 0 for now.
+ // Only reuse previous IV if it would not require a type conversion.
+ if (isZero(II->Base) && II->Base->getType() == Ty) {
+ IV = *II;
+ return Scale;
+ }
+ }
+ }
+ return 0;
+}
+
+/// PartitionByIsUseOfPostIncrementedValue - Simple boolean predicate that
+/// returns true if Val's isUseOfPostIncrementedValue is true.
+static bool PartitionByIsUseOfPostIncrementedValue(const BasedUser &Val) {
+ return Val.isUseOfPostIncrementedValue;
+}
+
+/// StrengthReduceStridedIVUsers - Strength reduce all of the users of a single
+/// stride of IV. All of the users may have different starting values, and this
+/// may not be the only stride (we know it is if isOnlyStride is true).
+void LoopStrengthReduce::StrengthReduceStridedIVUsers(const SCEVHandle &Stride,
+ IVUsersOfOneStride &Uses,
+ Loop *L,
+ bool isOnlyStride) {
+ // Transform our list of users and offsets to a bit more complex table. In
+ // this new vector, each 'BasedUser' contains 'Base' the base of the
+ // strided accessas well as the old information from Uses. We progressively
+ // move information from the Base field to the Imm field, until we eventually
+ // have the full access expression to rewrite the use.
+ std::vector<BasedUser> UsersToProcess;
+ UsersToProcess.reserve(Uses.Users.size());
+ for (unsigned i = 0, e = Uses.Users.size(); i != e; ++i) {
+ UsersToProcess.push_back(Uses.Users[i]);
+
+ // Move any loop invariant operands from the offset field to the immediate
+ // field of the use, so that we don't try to use something before it is
+ // computed.
+ MoveLoopVariantsToImediateField(UsersToProcess.back().Base,
+ UsersToProcess.back().Imm, L);
+ assert(UsersToProcess.back().Base->isLoopInvariant(L) &&
+ "Base value is not loop invariant!");
+ }
+
+ // We now have a whole bunch of uses of like-strided induction variables, but
+ // they might all have different bases. We want to emit one PHI node for this
+ // stride which we fold as many common expressions (between the IVs) into as
+ // possible. Start by identifying the common expressions in the base values
+ // for the strides (e.g. if we have "A+C+B" and "A+B+D" as our bases, find
+ // "A+B"), emit it to the preheader, then remove the expression from the
+ // UsersToProcess base values.
+ SCEVHandle CommonExprs =
+ RemoveCommonExpressionsFromUseBases(UsersToProcess);
+
+ // Next, figure out what we can represent in the immediate fields of
+ // instructions. If we can represent anything there, move it to the imm
+ // fields of the BasedUsers. We do this so that it increases the commonality
+ // of the remaining uses.
+ for (unsigned i = 0, e = UsersToProcess.size(); i != e; ++i) {
+ // If the user is not in the current loop, this means it is using the exit
+ // value of the IV. Do not put anything in the base, make sure it's all in
+ // the immediate field to allow as much factoring as possible.
+ if (!L->contains(UsersToProcess[i].Inst->getParent())) {
+ UsersToProcess[i].Imm = SCEVAddExpr::get(UsersToProcess[i].Imm,
+ UsersToProcess[i].Base);
+ UsersToProcess[i].Base =
+ SCEVUnknown::getIntegerSCEV(0, UsersToProcess[i].Base->getType());
+ } else {
+
+ // Addressing modes can be folded into loads and stores. Be careful that
+ // the store is through the expression, not of the expression though.
+ bool isAddress = isa<LoadInst>(UsersToProcess[i].Inst);
+ if (StoreInst *SI = dyn_cast<StoreInst>(UsersToProcess[i].Inst))
+ if (SI->getOperand(1) == UsersToProcess[i].OperandValToReplace)
+ isAddress = true;
+
+ MoveImmediateValues(TLI, UsersToProcess[i].Inst, UsersToProcess[i].Base,
+ UsersToProcess[i].Imm, isAddress, L);
+ }
+ }
+
+ // Check if it is possible to reuse a IV with stride that is factor of this
+ // stride. And the multiple is a number that can be encoded in the scale
+ // field of the target addressing mode. And we will have a valid
+ // instruction after this substition, including the immediate field, if any.
+ PHINode *NewPHI = NULL;
+ Value *IncV = NULL;
+ IVExpr ReuseIV;
+ unsigned RewriteFactor = CheckForIVReuse(Stride, ReuseIV,
+ CommonExprs->getType(),
+ UsersToProcess);
+ if (RewriteFactor != 0) {
+ DOUT << "BASED ON IV of STRIDE " << *ReuseIV.Stride
+ << " and BASE " << *ReuseIV.Base << " :\n";
+ NewPHI = ReuseIV.PHI;
+ IncV = ReuseIV.IncV;
+ }
+
+ const Type *ReplacedTy = CommonExprs->getType();
+
+ // Now that we know what we need to do, insert the PHI node itself.
+ //
+ DOUT << "INSERTING IV of TYPE " << *ReplacedTy << " of STRIDE "
+ << *Stride << " and BASE " << *CommonExprs << " :\n";
+
+ SCEVExpander Rewriter(*SE, *LI);
+ SCEVExpander PreheaderRewriter(*SE, *LI);
+
+ BasicBlock *Preheader = L->getLoopPreheader();
+ Instruction *PreInsertPt = Preheader->getTerminator();
+ Instruction *PhiInsertBefore = L->getHeader()->begin();
+
+ BasicBlock *LatchBlock = L->getLoopLatch();
+
+
+ // Emit the initial base value into the loop preheader.
+ Value *CommonBaseV
+ = PreheaderRewriter.expandCodeFor(CommonExprs, PreInsertPt,
+ ReplacedTy);
+
+ if (RewriteFactor == 0) {
+ // Create a new Phi for this base, and stick it in the loop header.
+ NewPHI = new PHINode(ReplacedTy, "iv.", PhiInsertBefore);
+ ++NumInserted;
+
+ // Add common base to the new Phi node.
+ NewPHI->addIncoming(CommonBaseV, Preheader);
+
+ // Insert the stride into the preheader.
+ Value *StrideV = PreheaderRewriter.expandCodeFor(Stride, PreInsertPt,
+ ReplacedTy);
+ if (!isa<ConstantInt>(StrideV)) ++NumVariable;
+
+ // Emit the increment of the base value before the terminator of the loop
+ // latch block, and add it to the Phi node.
+ SCEVHandle IncExp = SCEVAddExpr::get(SCEVUnknown::get(NewPHI),
+ SCEVUnknown::get(StrideV));
+
+ IncV = Rewriter.expandCodeFor(IncExp, LatchBlock->getTerminator(),
+ ReplacedTy);
+ IncV->setName(NewPHI->getName()+".inc");
+ NewPHI->addIncoming(IncV, LatchBlock);
+
+ // Remember this in case a later stride is multiple of this.
+ IVsByStride[Stride].addIV(Stride, CommonExprs, NewPHI, IncV);
} else {
- // Create a new GEP instruction using the new PHI as the base. The
- // operands of the original GEP past the induction variable become
- // operands of this new GEP.
- std::vector<Value *> op_vector;
- const Type *Ty = CanonicalIndVar->getType();
- op_vector.push_back(Constant::getNullValue(Ty));
- for (unsigned op = indvar + 1; op < GEPI->getNumOperands(); op++)
- op_vector.push_back(GEPI->getOperand(op));
- GetElementPtrInst *newGEP = new GetElementPtrInst(NewPHI, op_vector,
- GEPI->getName() + ".lsr",
- GEPI);
- GEPI->replaceAllUsesWith(newGEP);
+ Constant *C = dyn_cast<Constant>(CommonBaseV);
+ if (!C ||
+ (!C->isNullValue() &&
+ !isTargetConstant(SCEVUnknown::get(CommonBaseV), ReplacedTy, TLI)))
+ // We want the common base emitted into the preheader! This is just
+ // using cast as a copy so BitCast (no-op cast) is appropriate
+ CommonBaseV = new BitCastInst(CommonBaseV, CommonBaseV->getType(),
+ "commonbase", PreInsertPt);
}
+
+ // We want to emit code for users inside the loop first. To do this, we
+ // rearrange BasedUser so that the entries at the end have
+ // isUseOfPostIncrementedValue = false, because we pop off the end of the
+ // vector (so we handle them first).
+ std::partition(UsersToProcess.begin(), UsersToProcess.end(),
+ PartitionByIsUseOfPostIncrementedValue);
- // The old GEP is now dead.
- DeadInsts.insert(GEPI);
- ++NumReduced;
+ // Sort this by base, so that things with the same base are handled
+ // together. By partitioning first and stable-sorting later, we are
+ // guaranteed that within each base we will pop off users from within the
+ // loop before users outside of the loop with a particular base.
+ //
+ // We would like to use stable_sort here, but we can't. The problem is that
+ // SCEVHandle's don't have a deterministic ordering w.r.t to each other, so
+ // we don't have anything to do a '<' comparison on. Because we think the
+ // number of uses is small, do a horrible bubble sort which just relies on
+ // ==.
+ for (unsigned i = 0, e = UsersToProcess.size(); i != e; ++i) {
+ // Get a base value.
+ SCEVHandle Base = UsersToProcess[i].Base;
+
+ // Compact everything with this base to be consequetive with this one.
+ for (unsigned j = i+1; j != e; ++j) {
+ if (UsersToProcess[j].Base == Base) {
+ std::swap(UsersToProcess[i+1], UsersToProcess[j]);
+ ++i;
+ }
+ }
+ }
+
+ // Process all the users now. This outer loop handles all bases, the inner
+ // loop handles all users of a particular base.
+ while (!UsersToProcess.empty()) {
+ SCEVHandle Base = UsersToProcess.back().Base;
+
+ DOUT << " INSERTING code for BASE = " << *Base << ":\n";
+
+ // Emit the code for Base into the preheader.
+ Value *BaseV = PreheaderRewriter.expandCodeFor(Base, PreInsertPt,
+ ReplacedTy);
+
+ // If BaseV is a constant other than 0, make sure that it gets inserted into
+ // the preheader, instead of being forward substituted into the uses. We do
+ // this by forcing a BitCast (noop cast) to be inserted into the preheader
+ // in this case.
+ if (Constant *C = dyn_cast<Constant>(BaseV)) {
+ if (!C->isNullValue() && !isTargetConstant(Base, ReplacedTy, TLI)) {
+ // We want this constant emitted into the preheader! This is just
+ // using cast as a copy so BitCast (no-op cast) is appropriate
+ BaseV = new BitCastInst(BaseV, BaseV->getType(), "preheaderinsert",
+ PreInsertPt);
+ }
+ }
+
+ // Emit the code to add the immediate offset to the Phi value, just before
+ // the instructions that we identified as using this stride and base.
+ do {
+ // FIXME: Use emitted users to emit other users.
+ BasedUser &User = UsersToProcess.back();
+
+ // If this instruction wants to use the post-incremented value, move it
+ // after the post-inc and use its value instead of the PHI.
+ Value *RewriteOp = NewPHI;
+ if (User.isUseOfPostIncrementedValue) {
+ RewriteOp = IncV;
+
+ // If this user is in the loop, make sure it is the last thing in the
+ // loop to ensure it is dominated by the increment.
+ if (L->contains(User.Inst->getParent()))
+ User.Inst->moveBefore(LatchBlock->getTerminator());
+ }
+ if (RewriteOp->getType() != ReplacedTy) {
+ Instruction::CastOps opcode = Instruction::Trunc;
+ if (ReplacedTy->getPrimitiveSizeInBits() ==
+ RewriteOp->getType()->getPrimitiveSizeInBits())
+ opcode = Instruction::BitCast;
+ RewriteOp = SCEVExpander::InsertCastOfTo(opcode, RewriteOp, ReplacedTy);
+ }
+
+ SCEVHandle RewriteExpr = SCEVUnknown::get(RewriteOp);
+
+ // Clear the SCEVExpander's expression map so that we are guaranteed
+ // to have the code emitted where we expect it.
+ Rewriter.clear();
+
+ // If we are reusing the iv, then it must be multiplied by a constant
+ // factor take advantage of addressing mode scale component.
+ if (RewriteFactor != 0) {
+ RewriteExpr =
+ SCEVMulExpr::get(SCEVUnknown::getIntegerSCEV(RewriteFactor,
+ RewriteExpr->getType()),
+ RewriteExpr);
+
+ // The common base is emitted in the loop preheader. But since we
+ // are reusing an IV, it has not been used to initialize the PHI node.
+ // Add it to the expression used to rewrite the uses.
+ if (!isa<ConstantInt>(CommonBaseV) ||
+ !cast<ConstantInt>(CommonBaseV)->isZero())
+ RewriteExpr = SCEVAddExpr::get(RewriteExpr,
+ SCEVUnknown::get(CommonBaseV));
+ }
+
+ // Now that we know what we need to do, insert code before User for the
+ // immediate and any loop-variant expressions.
+ if (!isa<ConstantInt>(BaseV) || !cast<ConstantInt>(BaseV)->isZero())
+ // Add BaseV to the PHI value if needed.
+ RewriteExpr = SCEVAddExpr::get(RewriteExpr, SCEVUnknown::get(BaseV));
+
+ User.RewriteInstructionToUseNewBase(RewriteExpr, Rewriter, L, this);
+
+ // Mark old value we replaced as possibly dead, so that it is elminated
+ // if we just replaced the last use of that value.
+ DeadInsts.insert(cast<Instruction>(User.OperandValToReplace));
+
+ UsersToProcess.pop_back();
+ ++NumReduced;
+
+ // If there are any more users to process with the same base, process them
+ // now. We sorted by base above, so we just have to check the last elt.
+ } while (!UsersToProcess.empty() && UsersToProcess.back().Base == Base);
+ // TODO: Next, find out which base index is the most common, pull it out.
+ }
+
+ // IMPORTANT TODO: Figure out how to partition the IV's with this stride, but
+ // different starting values, into different PHIs.
}
-void LoopStrengthReduce::runOnLoop(Loop *L) {
- // First step, transform all loops nesting inside of this loop.
- for (LoopInfo::iterator I = L->begin(), E = L->end(); I != E; ++I)
- runOnLoop(*I);
+// OptimizeIndvars - Now that IVUsesByStride is set up with all of the indvar
+// uses in the loop, look to see if we can eliminate some, in favor of using
+// common indvars for the different uses.
+void LoopStrengthReduce::OptimizeIndvars(Loop *L) {
+ // TODO: implement optzns here.
- // Next, get the first PHINode since it is guaranteed to be the canonical
- // induction variable for the loop by the preceding IndVarSimplify pass.
- PHINode *PN = L->getCanonicalInductionVariable();
- if (0 == PN)
+ // Finally, get the terminating condition for the loop if possible. If we
+ // can, we want to change it to use a post-incremented version of its
+ // induction variable, to allow coalescing the live ranges for the IV into
+ // one register value.
+ PHINode *SomePHI = cast<PHINode>(L->getHeader()->begin());
+ BasicBlock *Preheader = L->getLoopPreheader();
+ BasicBlock *LatchBlock =
+ SomePHI->getIncomingBlock(SomePHI->getIncomingBlock(0) == Preheader);
+ BranchInst *TermBr = dyn_cast<BranchInst>(LatchBlock->getTerminator());
+ if (!TermBr || TermBr->isUnconditional() ||
+ !isa<ICmpInst>(TermBr->getCondition()))
return;
+ ICmpInst *Cond = cast<ICmpInst>(TermBr->getCondition());
- // FIXME: Need to use SCEV to detect GEP uses of the indvar, since indvars
- // pass creates code like this, which we can't currently detect:
- // %tmp.1 = sub uint 2000, %indvar
- // %tmp.8 = getelementptr int* %y, uint %tmp.1
-
- // Strength reduce all GEPs in the Loop. Insert secondary PHI nodes for the
- // strength reduced pointers we'll be creating after the canonical induction
- // variable's PHI.
- std::set<Instruction*> DeadInsts;
- GEPCache Cache;
- for (Value::use_iterator UI = PN->use_begin(), UE = PN->use_end();
- UI != UE; ++UI)
- if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(*UI))
- strengthReduceGEP(GEPI, L, &Cache, PN->getNext(), DeadInsts);
+ // Search IVUsesByStride to find Cond's IVUse if there is one.
+ IVStrideUse *CondUse = 0;
+ const SCEVHandle *CondStride = 0;
+
+ for (unsigned Stride = 0, e = StrideOrder.size(); Stride != e && !CondUse;
+ ++Stride) {
+ std::map<SCEVHandle, IVUsersOfOneStride>::iterator SI =
+ IVUsesByStride.find(StrideOrder[Stride]);
+ assert(SI != IVUsesByStride.end() && "Stride doesn't exist!");
+
+ for (std::vector<IVStrideUse>::iterator UI = SI->second.Users.begin(),
+ E = SI->second.Users.end(); UI != E; ++UI)
+ if (UI->User == Cond) {
+ CondUse = &*UI;
+ CondStride = &SI->first;
+ // NOTE: we could handle setcc instructions with multiple uses here, but
+ // InstCombine does it as well for simple uses, it's not clear that it
+ // occurs enough in real life to handle.
+ break;
+ }
+ }
+ if (!CondUse) return; // setcc doesn't use the IV.
+
+ // It's possible for the setcc instruction to be anywhere in the loop, and
+ // possible for it to have multiple users. If it is not immediately before
+ // the latch block branch, move it.
+ if (&*++BasicBlock::iterator(Cond) != (Instruction*)TermBr) {
+ if (Cond->hasOneUse()) { // Condition has a single use, just move it.
+ Cond->moveBefore(TermBr);
+ } else {
+ // Otherwise, clone the terminating condition and insert into the loopend.
+ Cond = cast<ICmpInst>(Cond->clone());
+ Cond->setName(L->getHeader()->getName() + ".termcond");
+ LatchBlock->getInstList().insert(TermBr, Cond);
+
+ // Clone the IVUse, as the old use still exists!
+ IVUsesByStride[*CondStride].addUser(CondUse->Offset, Cond,
+ CondUse->OperandValToReplace);
+ CondUse = &IVUsesByStride[*CondStride].Users.back();
+ }
+ }
+
+ // If we get to here, we know that we can transform the setcc instruction to
+ // use the post-incremented version of the IV, allowing us to coalesce the
+ // live ranges for the IV correctly.
+ CondUse->Offset = SCEV::getMinusSCEV(CondUse->Offset, *CondStride);
+ CondUse->isUseOfPostIncrementedValue = true;
+}
+
+namespace {
+ // Constant strides come first which in turns are sorted by their absolute
+ // values. If absolute values are the same, then positive strides comes first.
+ // e.g.
+ // 4, -1, X, 1, 2 ==> 1, -1, 2, 4, X
+ struct StrideCompare {
+ bool operator()(const SCEVHandle &LHS, const SCEVHandle &RHS) {
+ SCEVConstant *LHSC = dyn_cast<SCEVConstant>(LHS);
+ SCEVConstant *RHSC = dyn_cast<SCEVConstant>(RHS);
+ if (LHSC && RHSC) {
+ int64_t LV = LHSC->getValue()->getSExtValue();
+ int64_t RV = RHSC->getValue()->getSExtValue();
+ uint64_t ALV = (LV < 0) ? -LV : LV;
+ uint64_t ARV = (RV < 0) ? -RV : RV;
+ if (ALV == ARV)
+ return LV > RV;
+ else
+ return ALV < ARV;
+ }
+ return (LHSC && !RHSC);
+ }
+ };
+}
+
+bool LoopStrengthReduce::runOnLoop(Loop *L, LPPassManager &LPM) {
+
+ LI = &getAnalysis<LoopInfo>();
+ EF = &getAnalysis<ETForest>();
+ SE = &getAnalysis<ScalarEvolution>();
+ TD = &getAnalysis<TargetData>();
+ UIntPtrTy = TD->getIntPtrType();
+
+ // Find all uses of induction variables in this loop, and catagorize
+ // them by stride. Start by finding all of the PHI nodes in the header for
+ // this loop. If they are induction variables, inspect their uses.
+ std::set<Instruction*> Processed; // Don't reprocess instructions.
+ for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ++I)
+ AddUsersIfInteresting(I, L, Processed);
+
+ // If we have nothing to do, return.
+ if (IVUsesByStride.empty()) return false;
+
+ // Optimize induction variables. Some indvar uses can be transformed to use
+ // strides that will be needed for other purposes. A common example of this
+ // is the exit test for the loop, which can often be rewritten to use the
+ // computation of some other indvar to decide when to terminate the loop.
+ OptimizeIndvars(L);
+
+
+ // FIXME: We can widen subreg IV's here for RISC targets. e.g. instead of
+ // doing computation in byte values, promote to 32-bit values if safe.
+
+ // FIXME: Attempt to reuse values across multiple IV's. In particular, we
+ // could have something like "for(i) { foo(i*8); bar(i*16) }", which should be
+ // codegened as "for (j = 0;; j+=8) { foo(j); bar(j+j); }" on X86/PPC. Need
+ // to be careful that IV's are all the same type. Only works for intptr_t
+ // indvars.
+
+ // If we only have one stride, we can more aggressively eliminate some things.
+ bool HasOneStride = IVUsesByStride.size() == 1;
+
+#ifndef NDEBUG
+ DOUT << "\nLSR on ";
+ DEBUG(L->dump());
+#endif
+
+ // IVsByStride keeps IVs for one particular loop.
+ IVsByStride.clear();
+
+ // Sort the StrideOrder so we process larger strides first.
+ std::stable_sort(StrideOrder.begin(), StrideOrder.end(), StrideCompare());
+
+ // Note: this processes each stride/type pair individually. All users passed
+ // into StrengthReduceStridedIVUsers have the same type AND stride. Also,
+ // node that we iterate over IVUsesByStride indirectly by using StrideOrder.
+ // This extra layer of indirection makes the ordering of strides deterministic
+ // - not dependent on map order.
+ for (unsigned Stride = 0, e = StrideOrder.size(); Stride != e; ++Stride) {
+ std::map<SCEVHandle, IVUsersOfOneStride>::iterator SI =
+ IVUsesByStride.find(StrideOrder[Stride]);
+ assert(SI != IVUsesByStride.end() && "Stride doesn't exist!");
+ StrengthReduceStridedIVUsers(SI->first, SI->second, L, HasOneStride);
+ }
// Clean up after ourselves
if (!DeadInsts.empty()) {
DeleteTriviallyDeadInstructions(DeadInsts);
- // At this point, we know that we have killed one or more GEP instructions.
- // It is worth checking to see if the cann indvar is also dead, so that we
- // can remove it as well. The requirements for the cann indvar to be
- // considered dead are:
- // 1. the cann indvar has one use
- // 2. the use is an add instruction
- // 3. the add has one use
- // 4. the add is used by the cann indvar
- // If all four cases above are true, then we can remove both the add and
- // the cann indvar.
- // FIXME: this needs to eliminate an induction variable even if it's being
- // compared against some value to decide loop termination.
- if (PN->hasOneUse()) {
- BinaryOperator *BO = dyn_cast<BinaryOperator>(*(PN->use_begin()));
- if (BO && BO->getOpcode() == Instruction::Add)
- if (BO->hasOneUse()) {
- if (PN == dyn_cast<PHINode>(*(BO->use_begin()))) {
+ BasicBlock::iterator I = L->getHeader()->begin();
+ PHINode *PN;
+ while ((PN = dyn_cast<PHINode>(I))) {
+ ++I; // Preincrement iterator to avoid invalidating it when deleting PN.
+
+ // At this point, we know that we have killed one or more GEP
+ // instructions. It is worth checking to see if the cann indvar is also
+ // dead, so that we can remove it as well. The requirements for the cann
+ // indvar to be considered dead are:
+ // 1. the cann indvar has one use
+ // 2. the use is an add instruction
+ // 3. the add has one use
+ // 4. the add is used by the cann indvar
+ // If all four cases above are true, then we can remove both the add and
+ // the cann indvar.
+ // FIXME: this needs to eliminate an induction variable even if it's being
+ // compared against some value to decide loop termination.
+ if (PN->hasOneUse()) {
+ Instruction *BO = dyn_cast<Instruction>(*PN->use_begin());
+ if (BO && (isa<BinaryOperator>(BO) || isa<CmpInst>(BO))) {
+ if (BO->hasOneUse() && PN == *(BO->use_begin())) {
DeadInsts.insert(BO);
// Break the cycle, then delete the PHI.
PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
+ SE->deleteInstructionFromRecords(PN);
PN->eraseFromParent();
- DeleteTriviallyDeadInstructions(DeadInsts);
}
}
+ }
}
+ DeleteTriviallyDeadInstructions(DeadInsts);
}
+
+ CastedPointers.clear();
+ IVUsesByStride.clear();
+ StrideOrder.clear();
+ return false;
}
projects / oota-llvm.git / blobdiff