forked from OSchip/llvm-project
2104 lines
83 KiB
C++
2104 lines
83 KiB
C++
//===- LoopStrengthReduce.cpp - Strength Reduce GEPs in Loops -------------===//
|
|
//
|
|
// The LLVM Compiler Infrastructure
|
|
//
|
|
// This file 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
|
|
// have as one or more of their components the loop induction variable. This is
|
|
// accomplished by creating a new Value to hold the initial value of the array
|
|
// access for the first iteration, and then creating a new GEP instruction in
|
|
// the loop to increment the value by the appropriate amount.
|
|
//
|
|
//===----------------------------------------------------------------------===//
|
|
|
|
#define DEBUG_TYPE "loop-reduce"
|
|
#include "llvm/Transforms/Scalar.h"
|
|
#include "llvm/Constants.h"
|
|
#include "llvm/Instructions.h"
|
|
#include "llvm/IntrinsicInst.h"
|
|
#include "llvm/Type.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/SetVector.h"
|
|
#include "llvm/ADT/SmallPtrSet.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");
|
|
STATISTIC(NumEliminated, "Number of strides eliminated");
|
|
STATISTIC(NumShadow, "Number of Shadow IVs optimized");
|
|
|
|
namespace {
|
|
|
|
struct BasedUser;
|
|
|
|
/// 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
|
|
/// 'OperandValToReplace' 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(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;
|
|
|
|
void addIV(const SCEVHandle &Stride, const SCEVHandle &Base, PHINode *PHI,
|
|
Value *IncV) {
|
|
IVs.push_back(IVExpr(Stride, Base, PHI, IncV));
|
|
}
|
|
};
|
|
|
|
class VISIBILITY_HIDDEN LoopStrengthReduce : public LoopPass {
|
|
LoopInfo *LI;
|
|
DominatorTree *DT;
|
|
ScalarEvolution *SE;
|
|
const TargetData *TD;
|
|
const Type *UIntPtrTy;
|
|
bool Changed;
|
|
|
|
/// 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.
|
|
SmallVector<SCEVHandle, 16> 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.
|
|
DenseMap<Value*, Value*> CastedPointers;
|
|
|
|
/// DeadInsts - Keep track of instructions we may have made dead, so that
|
|
/// we can remove them after we are done working.
|
|
SetVector<Instruction*> DeadInsts;
|
|
|
|
/// TLI - Keep a pointer of a TargetLowering to consult for determining
|
|
/// transformation profitability.
|
|
const TargetLowering *TLI;
|
|
|
|
public:
|
|
static char ID; // Pass ID, replacement for typeid
|
|
explicit LoopStrengthReduce(const TargetLowering *tli = NULL) :
|
|
LoopPass(&ID), TLI(tli) {
|
|
}
|
|
|
|
bool runOnLoop(Loop *L, LPPassManager &LPM);
|
|
|
|
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
|
|
// 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<DominanceFrontier>();
|
|
AU.addPreserved<DominatorTree>();
|
|
|
|
AU.addRequiredID(LoopSimplifyID);
|
|
AU.addRequired<LoopInfo>();
|
|
AU.addRequired<DominatorTree>();
|
|
AU.addRequired<TargetData>();
|
|
AU.addRequired<ScalarEvolution>();
|
|
AU.addPreserved<ScalarEvolution>();
|
|
}
|
|
|
|
/// getCastedVersionOf - Return the specified value casted to uintptr_t.
|
|
///
|
|
Value *getCastedVersionOf(Instruction::CastOps opcode, Value *V);
|
|
private:
|
|
bool AddUsersIfInteresting(Instruction *I, Loop *L,
|
|
SmallPtrSet<Instruction*,16> &Processed);
|
|
SCEVHandle GetExpressionSCEV(Instruction *E);
|
|
ICmpInst *ChangeCompareStride(Loop *L, ICmpInst *Cond,
|
|
IVStrideUse* &CondUse,
|
|
const SCEVHandle* &CondStride);
|
|
void OptimizeIndvars(Loop *L);
|
|
|
|
/// OptimizeShadowIV - If IV is used in a int-to-float cast
|
|
/// inside the loop then try to eliminate the cast opeation.
|
|
void OptimizeShadowIV(Loop *L);
|
|
|
|
/// OptimizeSMax - Rewrite the loop's terminating condition
|
|
/// if it uses an smax computation.
|
|
ICmpInst *OptimizeSMax(Loop *L, ICmpInst *Cond,
|
|
IVStrideUse* &CondUse);
|
|
|
|
bool FindIVUserForCond(ICmpInst *Cond, IVStrideUse *&CondUse,
|
|
const SCEVHandle *&CondStride);
|
|
bool RequiresTypeConversion(const Type *Ty, const Type *NewTy);
|
|
unsigned CheckForIVReuse(bool, bool, const SCEVHandle&,
|
|
IVExpr&, const Type*,
|
|
const std::vector<BasedUser>& UsersToProcess);
|
|
bool ValidStride(bool, int64_t,
|
|
const std::vector<BasedUser>& UsersToProcess);
|
|
SCEVHandle CollectIVUsers(const SCEVHandle &Stride,
|
|
IVUsersOfOneStride &Uses,
|
|
Loop *L,
|
|
bool &AllUsesAreAddresses,
|
|
std::vector<BasedUser> &UsersToProcess);
|
|
void StrengthReduceStridedIVUsers(const SCEVHandle &Stride,
|
|
IVUsersOfOneStride &Uses,
|
|
Loop *L, bool isOnlyStride);
|
|
void DeleteTriviallyDeadInstructions(SetVector<Instruction*> &Insts);
|
|
};
|
|
}
|
|
|
|
char LoopStrengthReduce::ID = 0;
|
|
static RegisterPass<LoopStrengthReduce>
|
|
X("loop-reduce", "Loop Strength Reduction");
|
|
|
|
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.
|
|
void LoopStrengthReduce::
|
|
DeleteTriviallyDeadInstructions(SetVector<Instruction*> &Insts) {
|
|
while (!Insts.empty()) {
|
|
Instruction *I = Insts.back();
|
|
Insts.pop_back();
|
|
|
|
if (PHINode *PN = dyn_cast<PHINode>(I)) {
|
|
// If all incoming values to the Phi are the same, we can replace the Phi
|
|
// with that value.
|
|
if (Value *PNV = PN->hasConstantValue()) {
|
|
if (Instruction *U = dyn_cast<Instruction>(PNV))
|
|
Insts.insert(U);
|
|
SE->deleteValueFromRecords(PN);
|
|
PN->replaceAllUsesWith(PNV);
|
|
PN->eraseFromParent();
|
|
Changed = true;
|
|
continue;
|
|
}
|
|
}
|
|
|
|
if (isInstructionTriviallyDead(I)) {
|
|
for (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i)
|
|
if (Instruction *U = dyn_cast<Instruction>(*i))
|
|
Insts.insert(U);
|
|
SE->deleteValueFromRecords(I);
|
|
I->eraseFromParent();
|
|
Changed = true;
|
|
}
|
|
}
|
|
}
|
|
|
|
|
|
/// GetExpressionSCEV - Compute and return the SCEV for the specified
|
|
/// instruction.
|
|
SCEVHandle LoopStrengthReduce::GetExpressionSCEV(Instruction *Exp) {
|
|
// 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)));
|
|
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 the loop. 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 = SE->getUnknown(
|
|
getCastedVersionOf(Instruction::PtrToInt, GEP->getOperand(0)));
|
|
|
|
gep_type_iterator GTI = gep_type_begin(GEP);
|
|
|
|
for (User::op_iterator i = GEP->op_begin() + 1, e = GEP->op_end();
|
|
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>(*i)->getZExtValue();
|
|
uint64_t Offset = SL->getElementOffset(Idx);
|
|
GEPVal = SE->getAddExpr(GEPVal,
|
|
SE->getIntegerSCEV(Offset, UIntPtrTy));
|
|
} else {
|
|
unsigned GEPOpiBits =
|
|
(*i)->getType()->getPrimitiveSizeInBits();
|
|
unsigned IntPtrBits = UIntPtrTy->getPrimitiveSizeInBits();
|
|
Instruction::CastOps opcode = (GEPOpiBits < IntPtrBits ?
|
|
Instruction::SExt : (GEPOpiBits > IntPtrBits ? Instruction::Trunc :
|
|
Instruction::BitCast));
|
|
Value *OpVal = getCastedVersionOf(opcode, *i);
|
|
SCEVHandle Idx = SE->getSCEV(OpVal);
|
|
|
|
uint64_t TypeSize = TD->getABITypeSize(GTI.getIndexedType());
|
|
if (TypeSize != 1)
|
|
Idx = SE->getMulExpr(Idx,
|
|
SE->getConstant(ConstantInt::get(UIntPtrTy,
|
|
TypeSize)));
|
|
GEPVal = SE->getAddExpr(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,
|
|
ScalarEvolution *SE) {
|
|
SCEVHandle TheAddRec = Start; // Initialize to zero.
|
|
|
|
// 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 = SE->getAddExpr(AddRec, TheAddRec);
|
|
else
|
|
return false; // Nested IV of some sort?
|
|
} else {
|
|
Start = SE->getAddExpr(Start, AE->getOperand(i));
|
|
}
|
|
|
|
} else if (isa<SCEVAddRecExpr>(SH)) {
|
|
TheAddRec = SH;
|
|
} else {
|
|
return false; // not analyzable.
|
|
}
|
|
|
|
SCEVAddRecExpr *AddRec = dyn_cast<SCEVAddRecExpr>(TheAddRec);
|
|
if (!AddRec || AddRec->getLoop() != L) return false;
|
|
|
|
// FIXME: Generalize to non-affine IV's.
|
|
if (!AddRec->isAffine()) return false;
|
|
|
|
Start = SE->getAddExpr(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, DominatorTree *DT, Pass *P,
|
|
SetVector<Instruction*> &DeadInsts){
|
|
// 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 (DT->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 (!DT->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, false);
|
|
// Splitting the critical edge can reduce the number of entries in this
|
|
// PHI.
|
|
e = PN->getNumIncomingValues();
|
|
if (--NumUses == 0) break;
|
|
}
|
|
|
|
// PHI node might have become a constant value after SplitCriticalEdge.
|
|
DeadInsts.insert(User);
|
|
|
|
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,
|
|
SmallPtrSet<Instruction*,16> &Processed) {
|
|
if (!I->getType()->isInteger() && !isa<PointerType>(I->getType()))
|
|
return false; // Void and FP expressions cannot be reduced.
|
|
if (!Processed.insert(I))
|
|
return true; // Instruction already handled.
|
|
|
|
// Get the symbolic expression for this instruction.
|
|
SCEVHandle ISE = GetExpressionSCEV(I);
|
|
if (isa<SCEVCouldNotCompute>(ISE)) return false;
|
|
|
|
// Get the start and stride for this expression.
|
|
SCEVHandle Start = SE->getIntegerSCEV(0, ISE->getType());
|
|
SCEVHandle Stride = Start;
|
|
if (!getSCEVStartAndStride(ISE, L, Start, Stride, SE))
|
|
return false; // Non-reducible symbolic expression, bail out.
|
|
|
|
std::vector<Instruction *> IUsers;
|
|
// Collect all I uses now because IVUseShouldUsePostIncValue may
|
|
// invalidate use_iterator.
|
|
for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI != E; ++UI)
|
|
IUsers.push_back(cast<Instruction>(*UI));
|
|
|
|
for (unsigned iused_index = 0, iused_size = IUsers.size();
|
|
iused_index != iused_size; ++iused_index) {
|
|
|
|
Instruction *User = IUsers[iused_index];
|
|
|
|
// 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, DT, this, DeadInsts)) {
|
|
// The value used will be incremented by the stride more than we are
|
|
// expecting, so subtract this off.
|
|
SCEVHandle NewStart = SE->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;
|
|
}
|
|
|
|
namespace {
|
|
/// BasedUser - For a particular base value, keep information about how we've
|
|
/// partitioned the expression so far.
|
|
struct BasedUser {
|
|
/// SE - The current ScalarEvolution object.
|
|
ScalarEvolution *SE;
|
|
|
|
/// 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;
|
|
|
|
/// 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, ScalarEvolution *se)
|
|
: SE(se), Base(IVSU.Offset), Inst(IVSU.User),
|
|
OperandValToReplace(IVSU.OperandValToReplace),
|
|
Imm(SE->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,
|
|
Instruction *InsertPt,
|
|
SCEVExpander &Rewriter, Loop *L, Pass *P,
|
|
SetVector<Instruction*> &DeadInsts);
|
|
|
|
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 (Imm->isZero())
|
|
return Rewriter.expandCodeFor(NewBase, BaseInsertPt);
|
|
|
|
Value *Base = Rewriter.expandCodeFor(NewBase, BaseInsertPt);
|
|
|
|
// If we are inserting the base and imm values in the same block, make sure to
|
|
// adjust the IP position if insertion reused a result.
|
|
if (IP == BaseInsertPt)
|
|
IP = Rewriter.getInsertionPoint();
|
|
|
|
// Always emit the immediate (if non-zero) into the same block as the user.
|
|
SCEVHandle NewValSCEV = SE->getAddExpr(SE->getUnknown(Base), Imm);
|
|
return Rewriter.expandCodeFor(NewValSCEV, IP);
|
|
|
|
}
|
|
|
|
|
|
// 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. NewBasePt is the last instruction which contributes to the
|
|
// value of NewBase in the case that it's a diffferent instruction from
|
|
// the PHI that NewBase is computed from, or null otherwise.
|
|
//
|
|
void BasedUser::RewriteInstructionToUseNewBase(const SCEVHandle &NewBase,
|
|
Instruction *NewBasePt,
|
|
SCEVExpander &Rewriter, Loop *L, Pass *P,
|
|
SetVector<Instruction*> &DeadInsts) {
|
|
if (!isa<PHINode>(Inst)) {
|
|
// By default, insert code at the user instruction.
|
|
BasicBlock::iterator InsertPt = Inst;
|
|
|
|
// However, if the Operand is itself an instruction, the (potentially
|
|
// complex) inserted code may be shared by many users. Because of this, we
|
|
// want to emit code for the computation of the operand right before its old
|
|
// computation. This is usually safe, because we obviously used to use the
|
|
// computation when it was computed in its current block. However, in some
|
|
// cases (e.g. use of a post-incremented induction variable) the NewBase
|
|
// value will be pinned to live somewhere after the original computation.
|
|
// In this case, we have to back off.
|
|
if (!isUseOfPostIncrementedValue) {
|
|
if (NewBasePt && isa<PHINode>(OperandValToReplace)) {
|
|
InsertPt = NewBasePt;
|
|
++InsertPt;
|
|
} else if (Instruction *OpInst
|
|
= dyn_cast<Instruction>(OperandValToReplace)) {
|
|
InsertPt = OpInst;
|
|
while (isa<PHINode>(InsertPt)) ++InsertPt;
|
|
}
|
|
}
|
|
Value *NewVal = InsertCodeForBaseAtPosition(NewBase, Rewriter, InsertPt, L);
|
|
// Adjust the type back to match the Inst. Note that we can't use InsertPt
|
|
// here because the SCEVExpander may have inserted the instructions after
|
|
// that point, in its efforts to avoid inserting redundant expressions.
|
|
if (isa<PointerType>(OperandValToReplace->getType())) {
|
|
NewVal = SCEVExpander::InsertCastOfTo(Instruction::IntToPtr,
|
|
NewVal,
|
|
OperandValToReplace->getType());
|
|
}
|
|
// Replace the use of the operand Value with the new Phi we just created.
|
|
Inst->replaceUsesOfWith(OperandValToReplace, NewVal);
|
|
DOUT << " CHANGED: IMM =" << *Imm;
|
|
DOUT << " \tNEWBASE =" << *NewBase;
|
|
DOUT << " \tInst = " << *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).
|
|
DenseMap<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, false);
|
|
|
|
// 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);
|
|
|
|
// Adjust the type back to match the PHI. Note that we can't use
|
|
// InsertPt here because the SCEVExpander may have inserted its
|
|
// instructions after that point, in its efforts to avoid inserting
|
|
// redundant expressions.
|
|
if (isa<PointerType>(PN->getType())) {
|
|
Code = SCEVExpander::InsertCastOfTo(Instruction::IntToPtr,
|
|
Code,
|
|
PN->getType());
|
|
}
|
|
}
|
|
|
|
// Replace the use of the operand Value with the new Phi we just created.
|
|
PN->setIncomingValue(i, Code);
|
|
Rewriter.clear();
|
|
}
|
|
}
|
|
|
|
// PHI node might have become a constant value after SplitCriticalEdge.
|
|
DeadInsts.insert(Inst);
|
|
|
|
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) {
|
|
TargetLowering::AddrMode AM;
|
|
AM.BaseOffs = VC;
|
|
return TLI->isLegalAddressingMode(AM, 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 (TLI && CE->getOpcode() == Instruction::PtrToInt) {
|
|
Constant *Op0 = CE->getOperand(0);
|
|
if (GlobalValue *GV = dyn_cast<GlobalValue>(Op0)) {
|
|
TargetLowering::AddrMode AM;
|
|
AM.BaseGV = GV;
|
|
return TLI->isLegalAddressingMode(AM, UseTy);
|
|
}
|
|
}
|
|
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, ScalarEvolution *SE) {
|
|
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 = SE->getAddExpr(Imm, SAE->getOperand(i));
|
|
} else {
|
|
NewOps.push_back(SAE->getOperand(i));
|
|
}
|
|
|
|
if (NewOps.empty())
|
|
Val = SE->getIntegerSCEV(0, Val->getType());
|
|
else
|
|
Val = SE->getAddExpr(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, SE);
|
|
|
|
std::vector<SCEVHandle> Ops(SARE->op_begin(), SARE->op_end());
|
|
Ops[0] = Start;
|
|
Val = SE->getAddRecExpr(Ops, SARE->getLoop());
|
|
} else {
|
|
// Otherwise, all of Val is variant, move the whole thing over.
|
|
Imm = SE->getAddExpr(Imm, Val);
|
|
Val = SE->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,
|
|
ScalarEvolution *SE) {
|
|
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, SE);
|
|
|
|
if (!NewOp->isLoopInvariant(L)) {
|
|
// If this is a loop-variant expression, it must stay in the immediate
|
|
// field of the expression.
|
|
Imm = SE->getAddExpr(Imm, NewOp);
|
|
} else {
|
|
NewOps.push_back(NewOp);
|
|
}
|
|
}
|
|
|
|
if (NewOps.empty())
|
|
Val = SE->getIntegerSCEV(0, Val->getType());
|
|
else
|
|
Val = SE->getAddExpr(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, SE);
|
|
|
|
if (Start != SARE->getStart()) {
|
|
std::vector<SCEVHandle> Ops(SARE->op_begin(), SARE->op_end());
|
|
Ops[0] = Start;
|
|
Val = SE->getAddRecExpr(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 = SE->getIntegerSCEV(0, Val->getType());
|
|
SCEVHandle NewOp = SME->getOperand(1);
|
|
MoveImmediateValues(TLI, User, NewOp, SubImm, isAddress, L, SE);
|
|
|
|
// 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 = SE->getMulExpr(SubImm, SME->getOperand(0));
|
|
if (isTargetConstant(SubImm, UseTy, TLI)) {
|
|
// Accumulate the immediate.
|
|
Imm = SE->getAddExpr(Imm, SubImm);
|
|
|
|
// Update what is left of 'Val'.
|
|
Val = SE->getMulExpr(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 = SE->getAddExpr(Imm, Val);
|
|
Val = SE->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,
|
|
ScalarEvolution *SE) {
|
|
if (SCEVAddExpr *AE = dyn_cast<SCEVAddExpr>(Expr)) {
|
|
for (unsigned j = 0, e = AE->getNumOperands(); j != e; ++j)
|
|
SeparateSubExprs(SubExprs, AE->getOperand(j), SE);
|
|
} else if (SCEVAddRecExpr *SARE = dyn_cast<SCEVAddRecExpr>(Expr)) {
|
|
SCEVHandle Zero = SE->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(SE->getAddRecExpr(Ops, SARE->getLoop()));
|
|
|
|
|
|
SeparateSubExprs(SubExprs, SARE->getOperand(0), SE);
|
|
}
|
|
} else if (!Expr->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,
|
|
ScalarEvolution *SE) {
|
|
unsigned NumUses = Uses.size();
|
|
|
|
// Only one use? Use its base, regardless of what it is!
|
|
SCEVHandle Zero = SE->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, SE);
|
|
// 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 = SE->getAddExpr(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;
|
|
|
|
// 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, SE);
|
|
|
|
// 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 = SE->getAddExpr(SubExprs);
|
|
SubExprs.clear();
|
|
}
|
|
|
|
return Result;
|
|
}
|
|
|
|
/// ValidStride - Check whether the given Scale is valid for all loads and
|
|
/// stores in UsersToProcess.
|
|
///
|
|
bool LoopStrengthReduce::ValidStride(bool HasBaseReg,
|
|
int64_t Scale,
|
|
const std::vector<BasedUser>& UsersToProcess) {
|
|
if (!TLI)
|
|
return true;
|
|
|
|
for (unsigned i=0, e = UsersToProcess.size(); i!=e; ++i) {
|
|
// 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();
|
|
else if (isa<PHINode>(UsersToProcess[i].Inst))
|
|
continue;
|
|
|
|
TargetLowering::AddrMode AM;
|
|
if (SCEVConstant *SC = dyn_cast<SCEVConstant>(UsersToProcess[i].Imm))
|
|
AM.BaseOffs = SC->getValue()->getSExtValue();
|
|
AM.HasBaseReg = HasBaseReg || !UsersToProcess[i].Base->isZero();
|
|
AM.Scale = Scale;
|
|
|
|
// If load[imm+r*scale] is illegal, bail out.
|
|
if (!TLI->isLegalAddressingMode(AM, AccessTy))
|
|
return false;
|
|
}
|
|
return true;
|
|
}
|
|
|
|
/// RequiresTypeConversion - Returns true if converting Ty to NewTy is not
|
|
/// a nop.
|
|
bool LoopStrengthReduce::RequiresTypeConversion(const Type *Ty1,
|
|
const Type *Ty2) {
|
|
if (Ty1 == Ty2)
|
|
return false;
|
|
if (TLI && TLI->isTruncateFree(Ty1, Ty2))
|
|
return false;
|
|
return (!Ty1->canLosslesslyBitCastTo(Ty2) &&
|
|
!(isa<PointerType>(Ty2) &&
|
|
Ty1->canLosslesslyBitCastTo(UIntPtrTy)) &&
|
|
!(isa<PointerType>(Ty1) &&
|
|
Ty2->canLosslesslyBitCastTo(UIntPtrTy)));
|
|
}
|
|
|
|
/// 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 and optional base reg. 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(bool HasBaseReg,
|
|
bool AllUsesAreAddresses,
|
|
const SCEVHandle &Stride,
|
|
IVExpr &IV, const Type *Ty,
|
|
const std::vector<BasedUser>& UsersToProcess) {
|
|
if (SCEVConstant *SC = dyn_cast<SCEVConstant>(Stride)) {
|
|
int64_t SInt = SC->getValue()->getSExtValue();
|
|
for (unsigned NewStride = 0, e = StrideOrder.size(); NewStride != e;
|
|
++NewStride) {
|
|
std::map<SCEVHandle, IVsOfOneStride>::iterator SI =
|
|
IVsByStride.find(StrideOrder[NewStride]);
|
|
if (SI == IVsByStride.end())
|
|
continue;
|
|
int64_t SSInt = cast<SCEVConstant>(SI->first)->getValue()->getSExtValue();
|
|
if (SI->first != Stride &&
|
|
(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 the scale is 1, then we don't need to worry about folding
|
|
// multiplications.
|
|
if (Scale == 1 ||
|
|
(AllUsesAreAddresses &&
|
|
ValidStride(HasBaseReg, 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 (II->Base->isZero() &&
|
|
!RequiresTypeConversion(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;
|
|
}
|
|
|
|
/// isNonConstantNegative - Return true if the specified scev is negated, but
|
|
/// not a constant.
|
|
static bool isNonConstantNegative(const SCEVHandle &Expr) {
|
|
SCEVMulExpr *Mul = dyn_cast<SCEVMulExpr>(Expr);
|
|
if (!Mul) return false;
|
|
|
|
// If there is a constant factor, it will be first.
|
|
SCEVConstant *SC = dyn_cast<SCEVConstant>(Mul->getOperand(0));
|
|
if (!SC) return false;
|
|
|
|
// Return true if the value is negative, this matches things like (-42 * V).
|
|
return SC->getValue()->getValue().isNegative();
|
|
}
|
|
|
|
/// isAddress - Returns true if the specified instruction is using the
|
|
/// specified value as an address.
|
|
static bool isAddressUse(Instruction *Inst, Value *OperandVal) {
|
|
bool isAddress = isa<LoadInst>(Inst);
|
|
if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
|
|
if (SI->getOperand(1) == OperandVal)
|
|
isAddress = true;
|
|
} else if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(Inst)) {
|
|
// Addressing modes can also be folded into prefetches and a variety
|
|
// of intrinsics.
|
|
switch (II->getIntrinsicID()) {
|
|
default: break;
|
|
case Intrinsic::prefetch:
|
|
case Intrinsic::x86_sse2_loadu_dq:
|
|
case Intrinsic::x86_sse2_loadu_pd:
|
|
case Intrinsic::x86_sse_loadu_ps:
|
|
case Intrinsic::x86_sse_storeu_ps:
|
|
case Intrinsic::x86_sse2_storeu_pd:
|
|
case Intrinsic::x86_sse2_storeu_dq:
|
|
case Intrinsic::x86_sse2_storel_dq:
|
|
if (II->getOperand(1) == OperandVal)
|
|
isAddress = true;
|
|
break;
|
|
}
|
|
}
|
|
return isAddress;
|
|
}
|
|
|
|
// CollectIVUsers - 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 accesses, as 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.
|
|
SCEVHandle LoopStrengthReduce::CollectIVUsers(const SCEVHandle &Stride,
|
|
IVUsersOfOneStride &Uses,
|
|
Loop *L,
|
|
bool &AllUsesAreAddresses,
|
|
std::vector<BasedUser> &UsersToProcess) {
|
|
UsersToProcess.reserve(Uses.Users.size());
|
|
for (unsigned i = 0, e = Uses.Users.size(); i != e; ++i) {
|
|
UsersToProcess.push_back(BasedUser(Uses.Users[i], SE));
|
|
|
|
// 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, SE);
|
|
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, SE);
|
|
|
|
// 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.
|
|
unsigned NumPHI = 0;
|
|
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 = SE->getAddExpr(UsersToProcess[i].Imm,
|
|
UsersToProcess[i].Base);
|
|
UsersToProcess[i].Base =
|
|
SE->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 isPHI = false;
|
|
bool isAddress = isAddressUse(UsersToProcess[i].Inst,
|
|
UsersToProcess[i].OperandValToReplace);
|
|
if (isa<PHINode>(UsersToProcess[i].Inst)) {
|
|
isPHI = true;
|
|
++NumPHI;
|
|
}
|
|
|
|
// If this use isn't an address, then not all uses are addresses.
|
|
if (!isAddress && !isPHI)
|
|
AllUsesAreAddresses = false;
|
|
|
|
MoveImmediateValues(TLI, UsersToProcess[i].Inst, UsersToProcess[i].Base,
|
|
UsersToProcess[i].Imm, isAddress, L, SE);
|
|
}
|
|
}
|
|
|
|
// If one of the use if a PHI node and all other uses are addresses, still
|
|
// allow iv reuse. Essentially we are trading one constant multiplication
|
|
// for one fewer iv.
|
|
if (NumPHI > 1)
|
|
AllUsesAreAddresses = false;
|
|
|
|
return CommonExprs;
|
|
}
|
|
|
|
/// 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) {
|
|
// If all the users are moved to another stride, then there is nothing to do.
|
|
if (Uses.Users.empty())
|
|
return;
|
|
|
|
// Keep track if every use in UsersToProcess is an address. If they all are,
|
|
// we may be able to rewrite the entire collection of them in terms of a
|
|
// smaller-stride IV.
|
|
bool AllUsesAreAddresses = true;
|
|
|
|
// 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;
|
|
SCEVHandle CommonExprs = CollectIVUsers(Stride, Uses, L, AllUsesAreAddresses,
|
|
UsersToProcess);
|
|
|
|
// If we managed to find some expressions in common, we'll need to carry
|
|
// their value in a register and add it in for each use. This will take up
|
|
// a register operand, which potentially restricts what stride values are
|
|
// valid.
|
|
bool HaveCommonExprs = !CommonExprs->isZero();
|
|
|
|
// If all uses are addresses, check if it is possible to reuse an IV with a
|
|
// stride that is a factor of this stride. And that the multiple is a number
|
|
// that can be encoded in the scale field of the target addressing mode. And
|
|
// that we will have a valid instruction after this substition, including the
|
|
// immediate field, if any.
|
|
PHINode *NewPHI = NULL;
|
|
Value *IncV = NULL;
|
|
IVExpr ReuseIV(SE->getIntegerSCEV(0, Type::Int32Ty),
|
|
SE->getIntegerSCEV(0, Type::Int32Ty),
|
|
0, 0);
|
|
unsigned RewriteFactor = 0;
|
|
RewriteFactor = CheckForIVReuse(HaveCommonExprs, AllUsesAreAddresses,
|
|
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 << ": ";
|
|
|
|
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);
|
|
|
|
if (RewriteFactor == 0) {
|
|
// Create a new Phi for this base, and stick it in the loop header.
|
|
NewPHI = PHINode::Create(ReplacedTy, "iv.", PhiInsertBefore);
|
|
++NumInserted;
|
|
|
|
// Add common base to the new Phi node.
|
|
NewPHI->addIncoming(CommonBaseV, Preheader);
|
|
|
|
// If the stride is negative, insert a sub instead of an add for the
|
|
// increment.
|
|
bool isNegative = isNonConstantNegative(Stride);
|
|
SCEVHandle IncAmount = Stride;
|
|
if (isNegative)
|
|
IncAmount = SE->getNegativeSCEV(Stride);
|
|
|
|
// Insert the stride into the preheader.
|
|
Value *StrideV = PreheaderRewriter.expandCodeFor(IncAmount, PreInsertPt);
|
|
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 = SE->getUnknown(StrideV);
|
|
if (isNegative)
|
|
IncExp = SE->getNegativeSCEV(IncExp);
|
|
IncExp = SE->getAddExpr(SE->getUnknown(NewPHI), IncExp);
|
|
|
|
IncV = Rewriter.expandCodeFor(IncExp, LatchBlock->getTerminator());
|
|
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);
|
|
|
|
DOUT << " IV=%" << NewPHI->getNameStr() << " INC=%" << IncV->getNameStr();
|
|
} else {
|
|
Constant *C = dyn_cast<Constant>(CommonBaseV);
|
|
if (!C ||
|
|
(!C->isNullValue() &&
|
|
!isTargetConstant(SE->getUnknown(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);
|
|
}
|
|
DOUT << "\n";
|
|
|
|
// 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);
|
|
|
|
// 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 consequtive 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;
|
|
|
|
// Emit the code for Base into the preheader.
|
|
Value *BaseV = PreheaderRewriter.expandCodeFor(Base, PreInsertPt);
|
|
|
|
DOUT << " INSERTING code for BASE = " << *Base << ":";
|
|
if (BaseV->hasName())
|
|
DOUT << " Result value name = %" << BaseV->getNameStr();
|
|
DOUT << "\n";
|
|
|
|
// 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 = SE->getUnknown(RewriteOp);
|
|
|
|
// If we had to insert new instrutions for RewriteOp, we have to
|
|
// consider that they may not have been able to end up immediately
|
|
// next to RewriteOp, because non-PHI instructions may never precede
|
|
// PHI instructions in a block. In this case, remember where the last
|
|
// instruction was inserted so that if we're replacing a different
|
|
// PHI node, we can use the later point to expand the final
|
|
// RewriteExpr.
|
|
Instruction *NewBasePt = dyn_cast<Instruction>(RewriteOp);
|
|
if (RewriteOp == NewPHI) NewBasePt = 0;
|
|
|
|
// 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 = SE->getMulExpr(SE->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 = SE->getAddExpr(RewriteExpr,
|
|
SE->getUnknown(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 = SE->getAddExpr(RewriteExpr, SE->getUnknown(BaseV));
|
|
|
|
User.RewriteInstructionToUseNewBase(RewriteExpr, NewBasePt,
|
|
Rewriter, L, this,
|
|
DeadInsts);
|
|
|
|
// 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.
|
|
}
|
|
|
|
/// FindIVUserForCond - If Cond has an operand that is an expression of an IV,
|
|
/// set the IV user and stride information and return true, otherwise return
|
|
/// false.
|
|
bool LoopStrengthReduce::FindIVUserForCond(ICmpInst *Cond, IVStrideUse *&CondUse,
|
|
const SCEVHandle *&CondStride) {
|
|
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) {
|
|
// 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.
|
|
CondUse = &*UI;
|
|
CondStride = &SI->first;
|
|
return true;
|
|
}
|
|
}
|
|
return false;
|
|
}
|
|
|
|
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);
|
|
}
|
|
};
|
|
}
|
|
|
|
/// ChangeCompareStride - If a loop termination compare instruction is the
|
|
/// only use of its stride, and the compaison is against a constant value,
|
|
/// try eliminate the stride by moving the compare instruction to another
|
|
/// stride and change its constant operand accordingly. e.g.
|
|
///
|
|
/// loop:
|
|
/// ...
|
|
/// v1 = v1 + 3
|
|
/// v2 = v2 + 1
|
|
/// if (v2 < 10) goto loop
|
|
/// =>
|
|
/// loop:
|
|
/// ...
|
|
/// v1 = v1 + 3
|
|
/// if (v1 < 30) goto loop
|
|
ICmpInst *LoopStrengthReduce::ChangeCompareStride(Loop *L, ICmpInst *Cond,
|
|
IVStrideUse* &CondUse,
|
|
const SCEVHandle* &CondStride) {
|
|
if (StrideOrder.size() < 2 ||
|
|
IVUsesByStride[*CondStride].Users.size() != 1)
|
|
return Cond;
|
|
const SCEVConstant *SC = dyn_cast<SCEVConstant>(*CondStride);
|
|
if (!SC) return Cond;
|
|
ConstantInt *C = dyn_cast<ConstantInt>(Cond->getOperand(1));
|
|
if (!C) return Cond;
|
|
|
|
ICmpInst::Predicate Predicate = Cond->getPredicate();
|
|
int64_t CmpSSInt = SC->getValue()->getSExtValue();
|
|
int64_t CmpVal = C->getValue().getSExtValue();
|
|
unsigned BitWidth = C->getValue().getBitWidth();
|
|
uint64_t SignBit = 1ULL << (BitWidth-1);
|
|
const Type *CmpTy = C->getType();
|
|
const Type *NewCmpTy = NULL;
|
|
unsigned TyBits = CmpTy->getPrimitiveSizeInBits();
|
|
unsigned NewTyBits = 0;
|
|
int64_t NewCmpVal = CmpVal;
|
|
SCEVHandle *NewStride = NULL;
|
|
Value *NewIncV = NULL;
|
|
int64_t Scale = 1;
|
|
|
|
// Check stride constant and the comparision constant signs to detect
|
|
// overflow.
|
|
if ((CmpVal & SignBit) != (CmpSSInt & SignBit))
|
|
return Cond;
|
|
|
|
// Look for a suitable stride / iv as replacement.
|
|
std::stable_sort(StrideOrder.begin(), StrideOrder.end(), StrideCompare());
|
|
for (unsigned i = 0, e = StrideOrder.size(); i != e; ++i) {
|
|
std::map<SCEVHandle, IVUsersOfOneStride>::iterator SI =
|
|
IVUsesByStride.find(StrideOrder[i]);
|
|
if (!isa<SCEVConstant>(SI->first))
|
|
continue;
|
|
int64_t SSInt = cast<SCEVConstant>(SI->first)->getValue()->getSExtValue();
|
|
if (abs(SSInt) <= abs(CmpSSInt) || (SSInt % CmpSSInt) != 0)
|
|
continue;
|
|
|
|
Scale = SSInt / CmpSSInt;
|
|
NewCmpVal = CmpVal * Scale;
|
|
APInt Mul = APInt(BitWidth, NewCmpVal);
|
|
// Check for overflow.
|
|
if (Mul.getSExtValue() != NewCmpVal) {
|
|
NewCmpVal = CmpVal;
|
|
continue;
|
|
}
|
|
|
|
// Watch out for overflow.
|
|
if (ICmpInst::isSignedPredicate(Predicate) &&
|
|
(CmpVal & SignBit) != (NewCmpVal & SignBit))
|
|
NewCmpVal = CmpVal;
|
|
|
|
if (NewCmpVal != CmpVal) {
|
|
// Pick the best iv to use trying to avoid a cast.
|
|
NewIncV = NULL;
|
|
for (std::vector<IVStrideUse>::iterator UI = SI->second.Users.begin(),
|
|
E = SI->second.Users.end(); UI != E; ++UI) {
|
|
NewIncV = UI->OperandValToReplace;
|
|
if (NewIncV->getType() == CmpTy)
|
|
break;
|
|
}
|
|
if (!NewIncV) {
|
|
NewCmpVal = CmpVal;
|
|
continue;
|
|
}
|
|
|
|
NewCmpTy = NewIncV->getType();
|
|
NewTyBits = isa<PointerType>(NewCmpTy)
|
|
? UIntPtrTy->getPrimitiveSizeInBits()
|
|
: NewCmpTy->getPrimitiveSizeInBits();
|
|
if (RequiresTypeConversion(NewCmpTy, CmpTy)) {
|
|
// Check if it is possible to rewrite it using
|
|
// an iv / stride of a smaller integer type.
|
|
bool TruncOk = false;
|
|
if (NewCmpTy->isInteger()) {
|
|
unsigned Bits = NewTyBits;
|
|
if (ICmpInst::isSignedPredicate(Predicate))
|
|
--Bits;
|
|
uint64_t Mask = (1ULL << Bits) - 1;
|
|
if (((uint64_t)NewCmpVal & Mask) == (uint64_t)NewCmpVal)
|
|
TruncOk = true;
|
|
}
|
|
if (!TruncOk) {
|
|
NewCmpVal = CmpVal;
|
|
continue;
|
|
}
|
|
}
|
|
|
|
// Don't rewrite if use offset is non-constant and the new type is
|
|
// of a different type.
|
|
// FIXME: too conservative?
|
|
if (NewTyBits != TyBits && !isa<SCEVConstant>(CondUse->Offset)) {
|
|
NewCmpVal = CmpVal;
|
|
continue;
|
|
}
|
|
|
|
bool AllUsesAreAddresses = true;
|
|
std::vector<BasedUser> UsersToProcess;
|
|
SCEVHandle CommonExprs = CollectIVUsers(SI->first, SI->second, L,
|
|
AllUsesAreAddresses,
|
|
UsersToProcess);
|
|
// Avoid rewriting the compare instruction with an iv of new stride
|
|
// if it's likely the new stride uses will be rewritten using the
|
|
if (AllUsesAreAddresses &&
|
|
ValidStride(!CommonExprs->isZero(), Scale, UsersToProcess)) {
|
|
NewCmpVal = CmpVal;
|
|
continue;
|
|
}
|
|
|
|
// If scale is negative, use swapped predicate unless it's testing
|
|
// for equality.
|
|
if (Scale < 0 && !Cond->isEquality())
|
|
Predicate = ICmpInst::getSwappedPredicate(Predicate);
|
|
|
|
NewStride = &StrideOrder[i];
|
|
break;
|
|
}
|
|
}
|
|
|
|
// Forgo this transformation if it the increment happens to be
|
|
// unfortunately positioned after the condition, and the condition
|
|
// has multiple uses which prevent it from being moved immediately
|
|
// before the branch. See
|
|
// test/Transforms/LoopStrengthReduce/change-compare-stride-trickiness-*.ll
|
|
// for an example of this situation.
|
|
if (!Cond->hasOneUse()) {
|
|
for (BasicBlock::iterator I = Cond, E = Cond->getParent()->end();
|
|
I != E; ++I)
|
|
if (I == NewIncV)
|
|
return Cond;
|
|
}
|
|
|
|
if (NewCmpVal != CmpVal) {
|
|
// Create a new compare instruction using new stride / iv.
|
|
ICmpInst *OldCond = Cond;
|
|
Value *RHS;
|
|
if (!isa<PointerType>(NewCmpTy))
|
|
RHS = ConstantInt::get(NewCmpTy, NewCmpVal);
|
|
else {
|
|
RHS = ConstantInt::get(UIntPtrTy, NewCmpVal);
|
|
RHS = SCEVExpander::InsertCastOfTo(Instruction::IntToPtr, RHS, NewCmpTy);
|
|
}
|
|
// Insert new compare instruction.
|
|
Cond = new ICmpInst(Predicate, NewIncV, RHS,
|
|
L->getHeader()->getName() + ".termcond",
|
|
OldCond);
|
|
|
|
// Remove the old compare instruction. The old indvar is probably dead too.
|
|
DeadInsts.insert(cast<Instruction>(CondUse->OperandValToReplace));
|
|
SE->deleteValueFromRecords(OldCond);
|
|
OldCond->replaceAllUsesWith(Cond);
|
|
OldCond->eraseFromParent();
|
|
|
|
IVUsesByStride[*CondStride].Users.pop_back();
|
|
SCEVHandle NewOffset = TyBits == NewTyBits
|
|
? SE->getMulExpr(CondUse->Offset,
|
|
SE->getConstant(ConstantInt::get(CmpTy, Scale)))
|
|
: SE->getConstant(ConstantInt::get(NewCmpTy,
|
|
cast<SCEVConstant>(CondUse->Offset)->getValue()->getSExtValue()*Scale));
|
|
IVUsesByStride[*NewStride].addUser(NewOffset, Cond, NewIncV);
|
|
CondUse = &IVUsesByStride[*NewStride].Users.back();
|
|
CondStride = NewStride;
|
|
++NumEliminated;
|
|
}
|
|
|
|
return Cond;
|
|
}
|
|
|
|
/// OptimizeSMax - Rewrite the loop's terminating condition if it uses
|
|
/// an smax computation.
|
|
///
|
|
/// This is a narrow solution to a specific, but acute, problem. For loops
|
|
/// like this:
|
|
///
|
|
/// i = 0;
|
|
/// do {
|
|
/// p[i] = 0.0;
|
|
/// } while (++i < n);
|
|
///
|
|
/// where the comparison is signed, the trip count isn't just 'n', because
|
|
/// 'n' could be negative. And unfortunately this can come up even for loops
|
|
/// where the user didn't use a C do-while loop. For example, seemingly
|
|
/// well-behaved top-test loops will commonly be lowered like this:
|
|
//
|
|
/// if (n > 0) {
|
|
/// i = 0;
|
|
/// do {
|
|
/// p[i] = 0.0;
|
|
/// } while (++i < n);
|
|
/// }
|
|
///
|
|
/// and then it's possible for subsequent optimization to obscure the if
|
|
/// test in such a way that indvars can't find it.
|
|
///
|
|
/// When indvars can't find the if test in loops like this, it creates a
|
|
/// signed-max expression, which allows it to give the loop a canonical
|
|
/// induction variable:
|
|
///
|
|
/// i = 0;
|
|
/// smax = n < 1 ? 1 : n;
|
|
/// do {
|
|
/// p[i] = 0.0;
|
|
/// } while (++i != smax);
|
|
///
|
|
/// Canonical induction variables are necessary because the loop passes
|
|
/// are designed around them. The most obvious example of this is the
|
|
/// LoopInfo analysis, which doesn't remember trip count values. It
|
|
/// expects to be able to rediscover the trip count each time it is
|
|
/// needed, and it does this using a simple analyis that only succeeds if
|
|
/// the loop has a canonical induction variable.
|
|
///
|
|
/// However, when it comes time to generate code, the maximum operation
|
|
/// can be quite costly, especially if it's inside of an outer loop.
|
|
///
|
|
/// This function solves this problem by detecting this type of loop and
|
|
/// rewriting their conditions from ICMP_NE back to ICMP_SLT, and deleting
|
|
/// the instructions for the maximum computation.
|
|
///
|
|
ICmpInst *LoopStrengthReduce::OptimizeSMax(Loop *L, ICmpInst *Cond,
|
|
IVStrideUse* &CondUse) {
|
|
// Check that the loop matches the pattern we're looking for.
|
|
if (Cond->getPredicate() != CmpInst::ICMP_EQ &&
|
|
Cond->getPredicate() != CmpInst::ICMP_NE)
|
|
return Cond;
|
|
|
|
SelectInst *Sel = dyn_cast<SelectInst>(Cond->getOperand(1));
|
|
if (!Sel || !Sel->hasOneUse()) return Cond;
|
|
|
|
SCEVHandle IterationCount = SE->getIterationCount(L);
|
|
if (isa<SCEVCouldNotCompute>(IterationCount))
|
|
return Cond;
|
|
SCEVHandle One = SE->getIntegerSCEV(1, IterationCount->getType());
|
|
|
|
// Adjust for an annoying getIterationCount quirk.
|
|
IterationCount = SE->getAddExpr(IterationCount, One);
|
|
|
|
// Check for a max calculation that matches the pattern.
|
|
SCEVSMaxExpr *SMax = dyn_cast<SCEVSMaxExpr>(IterationCount);
|
|
if (!SMax || SMax != SE->getSCEV(Sel)) return Cond;
|
|
|
|
SCEVHandle SMaxLHS = SMax->getOperand(0);
|
|
SCEVHandle SMaxRHS = SMax->getOperand(1);
|
|
if (!SMaxLHS || SMaxLHS != One) return Cond;
|
|
|
|
// Check the relevant induction variable for conformance to
|
|
// the pattern.
|
|
SCEVHandle IV = SE->getSCEV(Cond->getOperand(0));
|
|
SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(IV);
|
|
if (!AR || !AR->isAffine() ||
|
|
AR->getStart() != One ||
|
|
AR->getStepRecurrence(*SE) != One)
|
|
return Cond;
|
|
|
|
// Check the right operand of the select, and remember it, as it will
|
|
// be used in the new comparison instruction.
|
|
Value *NewRHS = 0;
|
|
if (SE->getSCEV(Sel->getOperand(1)) == SMaxRHS)
|
|
NewRHS = Sel->getOperand(1);
|
|
else if (SE->getSCEV(Sel->getOperand(2)) == SMaxRHS)
|
|
NewRHS = Sel->getOperand(2);
|
|
if (!NewRHS) return Cond;
|
|
|
|
// Ok, everything looks ok to change the condition into an SLT or SGE and
|
|
// delete the max calculation.
|
|
ICmpInst *NewCond =
|
|
new ICmpInst(Cond->getPredicate() == CmpInst::ICMP_NE ?
|
|
CmpInst::ICMP_SLT :
|
|
CmpInst::ICMP_SGE,
|
|
Cond->getOperand(0), NewRHS, "scmp", Cond);
|
|
|
|
// Delete the max calculation instructions.
|
|
SE->deleteValueFromRecords(Cond);
|
|
Cond->replaceAllUsesWith(NewCond);
|
|
Cond->eraseFromParent();
|
|
Instruction *Cmp = cast<Instruction>(Sel->getOperand(0));
|
|
SE->deleteValueFromRecords(Sel);
|
|
Sel->eraseFromParent();
|
|
if (Cmp->use_empty()) {
|
|
SE->deleteValueFromRecords(Cmp);
|
|
Cmp->eraseFromParent();
|
|
}
|
|
CondUse->User = NewCond;
|
|
return NewCond;
|
|
}
|
|
|
|
/// OptimizeShadowIV - If IV is used in a int-to-float cast
|
|
/// inside the loop then try to eliminate the cast opeation.
|
|
void LoopStrengthReduce::OptimizeShadowIV(Loop *L) {
|
|
|
|
SCEVHandle IterationCount = SE->getIterationCount(L);
|
|
if (isa<SCEVCouldNotCompute>(IterationCount))
|
|
return;
|
|
|
|
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!");
|
|
if (!isa<SCEVConstant>(SI->first))
|
|
continue;
|
|
|
|
for (std::vector<IVStrideUse>::iterator UI = SI->second.Users.begin(),
|
|
E = SI->second.Users.end(); UI != E; /* empty */) {
|
|
std::vector<IVStrideUse>::iterator CandidateUI = UI;
|
|
++UI;
|
|
Instruction *ShadowUse = CandidateUI->User;
|
|
const Type *DestTy = NULL;
|
|
|
|
/* If shadow use is a int->float cast then insert a second IV
|
|
to eliminate this cast.
|
|
|
|
for (unsigned i = 0; i < n; ++i)
|
|
foo((double)i);
|
|
|
|
is transformed into
|
|
|
|
double d = 0.0;
|
|
for (unsigned i = 0; i < n; ++i, ++d)
|
|
foo(d);
|
|
*/
|
|
if (UIToFPInst *UCast = dyn_cast<UIToFPInst>(CandidateUI->User))
|
|
DestTy = UCast->getDestTy();
|
|
else if (SIToFPInst *SCast = dyn_cast<SIToFPInst>(CandidateUI->User))
|
|
DestTy = SCast->getDestTy();
|
|
if (!DestTy) continue;
|
|
|
|
if (TLI) {
|
|
/* If target does not support DestTy natively then do not apply
|
|
this transformation. */
|
|
MVT DVT = TLI->getValueType(DestTy);
|
|
if (!TLI->isTypeLegal(DVT)) continue;
|
|
}
|
|
|
|
PHINode *PH = dyn_cast<PHINode>(ShadowUse->getOperand(0));
|
|
if (!PH) continue;
|
|
if (PH->getNumIncomingValues() != 2) continue;
|
|
|
|
const Type *SrcTy = PH->getType();
|
|
int Mantissa = DestTy->getFPMantissaWidth();
|
|
if (Mantissa == -1) continue;
|
|
if ((int)TD->getTypeSizeInBits(SrcTy) > Mantissa)
|
|
continue;
|
|
|
|
unsigned Entry, Latch;
|
|
if (PH->getIncomingBlock(0) == L->getLoopPreheader()) {
|
|
Entry = 0;
|
|
Latch = 1;
|
|
} else {
|
|
Entry = 1;
|
|
Latch = 0;
|
|
}
|
|
|
|
ConstantInt *Init = dyn_cast<ConstantInt>(PH->getIncomingValue(Entry));
|
|
if (!Init) continue;
|
|
ConstantFP *NewInit = ConstantFP::get(DestTy, Init->getZExtValue());
|
|
|
|
BinaryOperator *Incr =
|
|
dyn_cast<BinaryOperator>(PH->getIncomingValue(Latch));
|
|
if (!Incr) continue;
|
|
if (Incr->getOpcode() != Instruction::Add
|
|
&& Incr->getOpcode() != Instruction::Sub)
|
|
continue;
|
|
|
|
/* Initialize new IV, double d = 0.0 in above example. */
|
|
ConstantInt *C = NULL;
|
|
if (Incr->getOperand(0) == PH)
|
|
C = dyn_cast<ConstantInt>(Incr->getOperand(1));
|
|
else if (Incr->getOperand(1) == PH)
|
|
C = dyn_cast<ConstantInt>(Incr->getOperand(0));
|
|
else
|
|
continue;
|
|
|
|
if (!C) continue;
|
|
|
|
/* Add new PHINode. */
|
|
PHINode *NewPH = PHINode::Create(DestTy, "IV.S.", PH);
|
|
|
|
/* create new increment. '++d' in above example. */
|
|
ConstantFP *CFP = ConstantFP::get(DestTy, C->getZExtValue());
|
|
BinaryOperator *NewIncr =
|
|
BinaryOperator::Create(Incr->getOpcode(),
|
|
NewPH, CFP, "IV.S.next.", Incr);
|
|
|
|
NewPH->addIncoming(NewInit, PH->getIncomingBlock(Entry));
|
|
NewPH->addIncoming(NewIncr, PH->getIncomingBlock(Latch));
|
|
|
|
/* Remove cast operation */
|
|
SE->deleteValueFromRecords(ShadowUse);
|
|
ShadowUse->replaceAllUsesWith(NewPH);
|
|
ShadowUse->eraseFromParent();
|
|
SI->second.Users.erase(CandidateUI);
|
|
NumShadow++;
|
|
break;
|
|
}
|
|
}
|
|
}
|
|
|
|
// 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.
|
|
|
|
OptimizeShadowIV(L);
|
|
|
|
// 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());
|
|
|
|
// Search IVUsesByStride to find Cond's IVUse if there is one.
|
|
IVStrideUse *CondUse = 0;
|
|
const SCEVHandle *CondStride = 0;
|
|
|
|
if (!FindIVUserForCond(Cond, CondUse, CondStride))
|
|
return; // setcc doesn't use the IV.
|
|
|
|
// If the trip count is computed in terms of an smax (due to ScalarEvolution
|
|
// being unable to find a sufficient guard, for example), change the loop
|
|
// comparison to use SLT instead of NE.
|
|
Cond = OptimizeSMax(L, Cond, CondUse);
|
|
|
|
// If possible, change stride and operands of the compare instruction to
|
|
// eliminate one stride.
|
|
Cond = ChangeCompareStride(L, Cond, CondUse, CondStride);
|
|
|
|
// 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 = SE->getMinusSCEV(CondUse->Offset, *CondStride);
|
|
CondUse->isUseOfPostIncrementedValue = true;
|
|
Changed = true;
|
|
}
|
|
|
|
bool LoopStrengthReduce::runOnLoop(Loop *L, LPPassManager &LPM) {
|
|
|
|
LI = &getAnalysis<LoopInfo>();
|
|
DT = &getAnalysis<DominatorTree>();
|
|
SE = &getAnalysis<ScalarEvolution>();
|
|
TD = &getAnalysis<TargetData>();
|
|
UIntPtrTy = TD->getIntPtrType();
|
|
Changed = false;
|
|
|
|
// 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.
|
|
SmallPtrSet<Instruction*,16> Processed; // Don't reprocess instructions.
|
|
for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ++I)
|
|
AddUsersIfInteresting(I, L, Processed);
|
|
|
|
if (!IVUsesByStride.empty()) {
|
|
// 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.
|
|
assert(IVsByStride.empty() && "Stale entries in IVsByStride?");
|
|
|
|
// 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, note 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);
|
|
}
|
|
}
|
|
|
|
// We're done analyzing this loop; release all the state we built up for it.
|
|
CastedPointers.clear();
|
|
IVUsesByStride.clear();
|
|
IVsByStride.clear();
|
|
StrideOrder.clear();
|
|
|
|
// Clean up after ourselves
|
|
if (!DeadInsts.empty()) {
|
|
DeleteTriviallyDeadInstructions(DeadInsts);
|
|
|
|
BasicBlock::iterator I = L->getHeader()->begin();
|
|
while (PHINode *PN = dyn_cast<PHINode>(I++)) {
|
|
// At this point, we know that we have killed one or more IV users.
|
|
// It is worth checking to see if the cann indvar is also
|
|
// dead, so that we can remove it as well.
|
|
//
|
|
// We can remove a PHI if it is on a cycle in the def-use graph
|
|
// where each node in the cycle has degree one, i.e. only one use,
|
|
// and is an instruction with no side effects.
|
|
//
|
|
// FIXME: this needs to eliminate an induction variable even if it's being
|
|
// compared against some value to decide loop termination.
|
|
if (PN->hasOneUse()) {
|
|
SmallPtrSet<PHINode *, 2> PHIs;
|
|
for (Instruction *J = dyn_cast<Instruction>(*PN->use_begin());
|
|
J && J->hasOneUse() && !J->mayWriteToMemory();
|
|
J = dyn_cast<Instruction>(*J->use_begin())) {
|
|
// If we find the original PHI, we've discovered a cycle.
|
|
if (J == PN) {
|
|
// Break the cycle and mark the PHI for deletion.
|
|
SE->deleteValueFromRecords(PN);
|
|
PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
|
|
DeadInsts.insert(PN);
|
|
Changed = true;
|
|
break;
|
|
}
|
|
// If we find a PHI more than once, we're on a cycle that
|
|
// won't prove fruitful.
|
|
if (isa<PHINode>(J) && !PHIs.insert(cast<PHINode>(J)))
|
|
break;
|
|
}
|
|
}
|
|
}
|
|
DeleteTriviallyDeadInstructions(DeadInsts);
|
|
}
|
|
return Changed;
|
|
}
|