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llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
Dan Gohman 92329c7fbe Add Loop contains utility methods for testing whether a loop 
contains another loop, or an instruction. The loop form is
substantially more efficient on large loops than the typical
code it replaces.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@91654 91177308-0d34-0410-b5e6-96231b3b80d8
2009-12-18 01:24:09 +00:00

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//===- LoopStrengthReduce.cpp - Strength Reduce IVs in Loops --------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This transformation analyzes and transforms the induction variables (and
// computations derived from them) into forms suitable for efficient execution
// on the target.
//
// This pass performs a strength reduction on array references inside loops that
// have as one or more of their components the loop induction variable, it
// rewrites expressions to take advantage of scaled-index addressing modes
// available on the target, and it performs a variety of other optimizations
// related to loop induction variables.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "loop-reduce"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Constants.h"
#include "llvm/Instructions.h"
#include "llvm/IntrinsicInst.h"
#include "llvm/DerivedTypes.h"
#include "llvm/Analysis/IVUsers.h"
#include "llvm/Analysis/LoopPass.h"
#include "llvm/Analysis/ScalarEvolutionExpander.h"
#include "llvm/Transforms/Utils/AddrModeMatcher.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/ValueHandle.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetLowering.h"
#include <algorithm>
using namespace llvm;
STATISTIC(NumReduced , "Number of IV uses 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");
STATISTIC(NumImmSunk, "Number of common expr immediates sunk into uses");
STATISTIC(NumLoopCond, "Number of loop terminating conds optimized");
STATISTIC(NumCountZero, "Number of count iv optimized to count toward zero");
static cl::opt<bool> EnableFullLSRMode("enable-full-lsr",
cl::init(false),
cl::Hidden);
namespace {
struct BasedUser;
/// 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 IVExpr {
const SCEV *Stride;
const SCEV *Base;
PHINode *PHI;
IVExpr(const SCEV *const stride, const SCEV *const base, PHINode *phi)
: Stride(stride), Base(base), PHI(phi) {}
};
/// IVsOfOneStride - This structure keeps track of all IV expression inserted
/// during StrengthReduceStridedIVUsers for a particular stride of the IV.
struct IVsOfOneStride {
std::vector<IVExpr> IVs;
void addIV(const SCEV *const Stride, const SCEV *const Base, PHINode *PHI) {
IVs.push_back(IVExpr(Stride, Base, PHI));
}
};
class LoopStrengthReduce : public LoopPass {
IVUsers *IU;
ScalarEvolution *SE;
bool Changed;
/// IVsByStride - Keep track of all IVs that have been inserted for a
/// particular stride.
std::map<const SCEV *, IVsOfOneStride> IVsByStride;
/// DeadInsts - Keep track of instructions we may have made dead, so that
/// we can remove them after we are done working.
SmallVector<WeakVH, 16> 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("loops");
AU.addPreserved("domfrontier");
AU.addPreserved("domtree");
AU.addRequiredID(LoopSimplifyID);
AU.addRequired<ScalarEvolution>();
AU.addPreserved<ScalarEvolution>();
AU.addRequired<IVUsers>();
AU.addPreserved<IVUsers>();
}
private:
void OptimizeIndvars(Loop *L);
/// OptimizeLoopTermCond - Change loop terminating condition to use the
/// postinc iv when possible.
void OptimizeLoopTermCond(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);
/// OptimizeMax - Rewrite the loop's terminating condition
/// if it uses a max computation.
ICmpInst *OptimizeMax(Loop *L, ICmpInst *Cond,
IVStrideUse* &CondUse);
/// OptimizeLoopCountIV - If, after all sharing of IVs, the IV used for
/// deciding when to exit the loop is used only for that purpose, try to
/// rearrange things so it counts down to a test against zero.
bool OptimizeLoopCountIV(Loop *L);
bool OptimizeLoopCountIVOfStride(const SCEV* &Stride,
IVStrideUse* &CondUse, Loop *L);
/// StrengthReduceIVUsersOfStride - 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.
void StrengthReduceIVUsersOfStride(const SCEV *Stride,
IVUsersOfOneStride &Uses,
Loop *L);
void StrengthReduceIVUsers(Loop *L);
ICmpInst *ChangeCompareStride(Loop *L, ICmpInst *Cond,
IVStrideUse* &CondUse,
const SCEV* &CondStride,
bool PostPass = false);
bool FindIVUserForCond(ICmpInst *Cond, IVStrideUse *&CondUse,
const SCEV* &CondStride);
bool RequiresTypeConversion(const Type *Ty, const Type *NewTy);
const SCEV *CheckForIVReuse(bool, bool, bool, const SCEV *,
IVExpr&, const Type*,
const std::vector<BasedUser>& UsersToProcess);
bool ValidScale(bool, int64_t,
const std::vector<BasedUser>& UsersToProcess);
bool ValidOffset(bool, int64_t, int64_t,
const std::vector<BasedUser>& UsersToProcess);
const SCEV *CollectIVUsers(const SCEV *Stride,
IVUsersOfOneStride &Uses,
Loop *L,
bool &AllUsesAreAddresses,
bool &AllUsesAreOutsideLoop,
std::vector<BasedUser> &UsersToProcess);
bool StrideMightBeShared(const SCEV *Stride, Loop *L, bool CheckPreInc);
bool ShouldUseFullStrengthReductionMode(
const std::vector<BasedUser> &UsersToProcess,
const Loop *L,
bool AllUsesAreAddresses,
const SCEV *Stride);
void PrepareToStrengthReduceFully(
std::vector<BasedUser> &UsersToProcess,
const SCEV *Stride,
const SCEV *CommonExprs,
const Loop *L,
SCEVExpander &PreheaderRewriter);
void PrepareToStrengthReduceFromSmallerStride(
std::vector<BasedUser> &UsersToProcess,
Value *CommonBaseV,
const IVExpr &ReuseIV,
Instruction *PreInsertPt);
void PrepareToStrengthReduceWithNewPhi(
std::vector<BasedUser> &UsersToProcess,
const SCEV *Stride,
const SCEV *CommonExprs,
Value *CommonBaseV,
Instruction *IVIncInsertPt,
const Loop *L,
SCEVExpander &PreheaderRewriter);
void DeleteTriviallyDeadInstructions();
};
}
char LoopStrengthReduce::ID = 0;
static RegisterPass<LoopStrengthReduce>
X("loop-reduce", "Loop Strength Reduction");
Pass *llvm::createLoopStrengthReducePass(const TargetLowering *TLI) {
return new LoopStrengthReduce(TLI);
}
/// 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() {
while (!DeadInsts.empty()) {
Instruction *I = dyn_cast_or_null<Instruction>(DeadInsts.pop_back_val());
if (I == 0 || !isInstructionTriviallyDead(I))
continue;
for (User::op_iterator OI = I->op_begin(), E = I->op_end(); OI != E; ++OI)
if (Instruction *U = dyn_cast<Instruction>(*OI)) {
*OI = 0;
if (U->use_empty())
DeadInsts.push_back(U);
}
I->eraseFromParent();
Changed = true;
}
}
/// isAddressUse - 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;
}
/// getAccessType - Return the type of the memory being accessed.
static const Type *getAccessType(const Instruction *Inst) {
const Type *AccessTy = Inst->getType();
if (const StoreInst *SI = dyn_cast<StoreInst>(Inst))
AccessTy = SI->getOperand(0)->getType();
else if (const 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::x86_sse_storeu_ps:
case Intrinsic::x86_sse2_storeu_pd:
case Intrinsic::x86_sse2_storeu_dq:
case Intrinsic::x86_sse2_storel_dq:
AccessTy = II->getOperand(1)->getType();
break;
}
}
return AccessTy;
}
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.
const SCEV *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. This is also sometimes used for loop-variant values that
/// must be added inside the loop.
const SCEV *Imm;
/// Phi - The induction variable that performs the striding that
/// should be used for this user.
PHINode *Phi;
// 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)
: Base(IVSU.getOffset()), Inst(IVSU.getUser()),
OperandValToReplace(IVSU.getOperandValToReplace()),
Imm(se->getIntegerSCEV(0, Base->getType())),
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 SCEV *NewBase,
Instruction *InsertPt,
SCEVExpander &Rewriter, Loop *L, Pass *P,
SmallVectorImpl<WeakVH> &DeadInsts,
ScalarEvolution *SE);
Value *InsertCodeForBaseAtPosition(const SCEV *NewBase,
const Type *Ty,
SCEVExpander &Rewriter,
Instruction *IP,
ScalarEvolution *SE);
void dump() const;
};
}
void BasedUser::dump() const {
errs() << " Base=" << *Base;
errs() << " Imm=" << *Imm;
errs() << " Inst: " << *Inst;
}
Value *BasedUser::InsertCodeForBaseAtPosition(const SCEV *NewBase,
const Type *Ty,
SCEVExpander &Rewriter,
Instruction *IP,
ScalarEvolution *SE) {
Value *Base = Rewriter.expandCodeFor(NewBase, 0, IP);
// Wrap the base in a SCEVUnknown so that ScalarEvolution doesn't try to
// re-analyze it.
const SCEV *NewValSCEV = SE->getUnknown(Base);
// Always emit the immediate into the same block as the user.
NewValSCEV = SE->getAddExpr(NewValSCEV, Imm);
return Rewriter.expandCodeFor(NewValSCEV, Ty, 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 SCEV *NewBase,
Instruction *NewBasePt,
SCEVExpander &Rewriter, Loop *L, Pass *P,
SmallVectorImpl<WeakVH> &DeadInsts,
ScalarEvolution *SE) {
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 this is a use outside the loop (which means after, since it is based
// on a loop indvar) we use the post-incremented value, so that we don't
// artificially make the preinc value live out the bottom of the loop.
if (!isUseOfPostIncrementedValue && L->contains(Inst)) {
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,
OperandValToReplace->getType(),
Rewriter, InsertPt, SE);
// Replace the use of the operand Value with the new Phi we just created.
Inst->replaceUsesOfWith(OperandValToReplace, NewVal);
DEBUG(errs() << " Replacing with ");
DEBUG(WriteAsOperand(errs(), NewVal, /*PrintType=*/false));
DEBUG(errs() << ", which has value " << *NewBase << " plus IMM "
<< *Imm << "\n");
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 the original expression is outside the loop, put the replacement
// code in the same place as the original expression,
// which need not be an immediate predecessor of this PHI. This way we
// need only one copy of it even if it is referenced multiple times in
// the PHI. We don't do this when the original expression is inside the
// loop because multiple copies sometimes do useful sinking of code in
// that case(?).
Instruction *OldLoc = dyn_cast<Instruction>(OperandValToReplace);
BasicBlock *PHIPred = PN->getIncomingBlock(i);
if (L->contains(OldLoc)) {
// 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.
if (e != 1 && PHIPred->getTerminator()->getNumSuccessors() > 1 &&
!isa<IndirectBrInst>(PHIPred->getTerminator()) &&
(PN->getParent() != L->getHeader() || !L->contains(PHIPred))) {
// First step, split the critical edge.
BasicBlock *NewBB = 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))
NewBB->moveBefore(PN->getParent());
// Splitting the edge can reduce the number of PHI entries we have.
e = PN->getNumIncomingValues();
PHIPred = NewBB;
i = PN->getBasicBlockIndex(PHIPred);
}
}
Value *&Code = InsertedCode[PHIPred];
if (!Code) {
// Insert the code into the end of the predecessor block.
Instruction *InsertPt = (L->contains(OldLoc)) ?
PHIPred->getTerminator() :
OldLoc->getParent()->getTerminator();
Code = InsertCodeForBaseAtPosition(NewBase, PN->getType(),
Rewriter, InsertPt, SE);
DEBUG(errs() << " Changing PHI use to ");
DEBUG(WriteAsOperand(errs(), Code, /*PrintType=*/false));
DEBUG(errs() << ", which has value " << *NewBase << " plus IMM "
<< *Imm << "\n");
}
// 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.push_back(Inst);
}
/// fitsInAddressMode - Return true if V can be subsumed within an addressing
/// mode, and does not need to be put in a register first.
static bool fitsInAddressMode(const SCEV *V, const Type *AccessTy,
const TargetLowering *TLI, bool HasBaseReg) {
if (const SCEVConstant *SC = dyn_cast<SCEVConstant>(V)) {
int64_t VC = SC->getValue()->getSExtValue();
if (TLI) {
TargetLowering::AddrMode AM;
AM.BaseOffs = VC;
AM.HasBaseReg = HasBaseReg;
return TLI->isLegalAddressingMode(AM, AccessTy);
} else {
// Defaults to PPC. PPC allows a sign-extended 16-bit immediate field.
return (VC > -(1 << 16) && VC < (1 << 16)-1);
}
}
if (const SCEVUnknown *SU = dyn_cast<SCEVUnknown>(V))
if (GlobalValue *GV = dyn_cast<GlobalValue>(SU->getValue())) {
if (TLI) {
TargetLowering::AddrMode AM;
AM.BaseGV = GV;
AM.HasBaseReg = HasBaseReg;
return TLI->isLegalAddressingMode(AM, AccessTy);
} else {
// Default: assume global addresses are not legal.
}
}
return false;
}
/// MoveLoopVariantsToImmediateField - Move any subexpressions from Val that are
/// loop varying to the Imm operand.
static void MoveLoopVariantsToImmediateField(const SCEV *&Val, const SCEV *&Imm,
Loop *L, ScalarEvolution *SE) {
if (Val->isLoopInvariant(L)) return; // Nothing to do.
if (const SCEVAddExpr *SAE = dyn_cast<SCEVAddExpr>(Val)) {
SmallVector<const SCEV *, 4> 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 (const SCEVAddRecExpr *SARE = dyn_cast<SCEVAddRecExpr>(Val)) {
// Try to pull immediates out of the start value of nested addrec's.
const SCEV *Start = SARE->getStart();
MoveLoopVariantsToImmediateField(Start, Imm, L, SE);
SmallVector<const SCEV *, 4> 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,
const Type *AccessTy,
const SCEV *&Val, const SCEV *&Imm,
bool isAddress, Loop *L,
ScalarEvolution *SE) {
if (const SCEVAddExpr *SAE = dyn_cast<SCEVAddExpr>(Val)) {
SmallVector<const SCEV *, 4> NewOps;
NewOps.reserve(SAE->getNumOperands());
for (unsigned i = 0; i != SAE->getNumOperands(); ++i) {
const SCEV *NewOp = SAE->getOperand(i);
MoveImmediateValues(TLI, AccessTy, 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 (const SCEVAddRecExpr *SARE = dyn_cast<SCEVAddRecExpr>(Val)) {
// Try to pull immediates out of the start value of nested addrec's.
const SCEV *Start = SARE->getStart();
MoveImmediateValues(TLI, AccessTy, Start, Imm, isAddress, L, SE);
if (Start != SARE->getStart()) {
SmallVector<const SCEV *, 4> Ops(SARE->op_begin(), SARE->op_end());
Ops[0] = Start;
Val = SE->getAddRecExpr(Ops, SARE->getLoop());
}
return;
} else if (const SCEVMulExpr *SME = dyn_cast<SCEVMulExpr>(Val)) {
// Transform "8 * (4 + v)" -> "32 + 8*V" if "32" fits in the immed field.
if (isAddress &&
fitsInAddressMode(SME->getOperand(0), AccessTy, TLI, false) &&
SME->getNumOperands() == 2 && SME->isLoopInvariant(L)) {
const SCEV *SubImm = SE->getIntegerSCEV(0, Val->getType());
const SCEV *NewOp = SME->getOperand(1);
MoveImmediateValues(TLI, AccessTy, 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 (fitsInAddressMode(SubImm, AccessTy, TLI, false)) {
// 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 && fitsInAddressMode(Val, AccessTy, TLI, false)) ||
!Val->isLoopInvariant(L)) {
Imm = SE->getAddExpr(Imm, Val);
Val = SE->getIntegerSCEV(0, Val->getType());
return;
}
// Otherwise, no immediates to move.
}
static void MoveImmediateValues(const TargetLowering *TLI,
Instruction *User,
const SCEV *&Val, const SCEV *&Imm,
bool isAddress, Loop *L,
ScalarEvolution *SE) {
const Type *AccessTy = getAccessType(User);
MoveImmediateValues(TLI, AccessTy, Val, Imm, isAddress, L, SE);
}
/// 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(SmallVector<const SCEV *, 16> &SubExprs,
const SCEV *Expr,
ScalarEvolution *SE) {
if (const SCEVAddExpr *AE = dyn_cast<SCEVAddExpr>(Expr)) {
for (unsigned j = 0, e = AE->getNumOperands(); j != e; ++j)
SeparateSubExprs(SubExprs, AE->getOperand(j), SE);
} else if (const SCEVAddRecExpr *SARE = dyn_cast<SCEVAddRecExpr>(Expr)) {
const SCEV *Zero = SE->getIntegerSCEV(0, Expr->getType());
if (SARE->getOperand(0) == Zero) {
SubExprs.push_back(Expr);
} else {
// Compute the addrec with zero as its base.
SmallVector<const SCEV *, 4> 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);
}
}
// This is logically local to the following function, but C++ says we have
// to make it file scope.
struct SubExprUseData { unsigned Count; bool notAllUsesAreFree; };
/// RemoveCommonExpressionsFromUseBases - Look through all of the Bases of all
/// the Uses, removing any common subexpressions, except that if all such
/// subexpressions can be folded into an addressing mode for all uses inside
/// the loop (this case is referred to as "free" in comments herein) we do
/// not remove anything. This looks for things like (a+b+c) and
/// (a+c+d) and computes the common (a+c) subexpression. The common expression
/// is *removed* from the Bases and returned.
static const SCEV *
RemoveCommonExpressionsFromUseBases(std::vector<BasedUser> &Uses,
ScalarEvolution *SE, Loop *L,
const TargetLowering *TLI) {
unsigned NumUses = Uses.size();
// Only one use? This is a very common case, so we handle it specially and
// cheaply.
const SCEV *Zero = SE->getIntegerSCEV(0, Uses[0].Base->getType());
const SCEV *Result = Zero;
const SCEV *FreeResult = Zero;
if (NumUses == 1) {
// If the use is inside the loop, use its base, regardless of what it is:
// it is clearly shared across all the IV's. If the use is outside the loop
// (which means after it) we don't want to factor anything *into* the loop,
// so just use 0 as the base.
if (L->contains(Uses[0].Inst))
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.
// Also track whether all uses of each expression can be moved into an
// an addressing mode "for free"; such expressions are left within the loop.
// struct SubExprUseData { unsigned Count; bool notAllUsesAreFree; };
std::map<const SCEV *, SubExprUseData> SubExpressionUseData;
// UniqueSubExprs - Keep track of all of the subexpressions we see in the
// order we see them.
SmallVector<const SCEV *, 16> UniqueSubExprs;
SmallVector<const SCEV *, 16> SubExprs;
unsigned NumUsesInsideLoop = 0;
for (unsigned i = 0; i != NumUses; ++i) {
// If the user is outside the loop, just ignore it for base computation.
// Since the user is outside the loop, it must be *after* the loop (if it
// were before, it could not be based on the loop IV). We don't want users
// after the loop to affect base computation of values *inside* the loop,
// because we can always add their offsets to the result IV after the loop
// is done, ensuring we get good code inside the loop.
if (!L->contains(Uses[i].Inst))
continue;
NumUsesInsideLoop++;
// 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;
// If this use is as an address we may be able to put CSEs in the addressing
// mode rather than hoisting them.
bool isAddrUse = isAddressUse(Uses[i].Inst, Uses[i].OperandValToReplace);
// We may need the AccessTy below, but only when isAddrUse, so compute it
// only in that case.
const Type *AccessTy = 0;
if (isAddrUse)
AccessTy = getAccessType(Uses[i].Inst);
// Split the expression into subexprs.
SeparateSubExprs(SubExprs, Uses[i].Base, SE);
// Add one to SubExpressionUseData.Count for each subexpr present, and
// if the subexpr is not a valid immediate within an addressing mode use,
// set SubExpressionUseData.notAllUsesAreFree. We definitely want to
// hoist these out of the loop (if they are common to all uses).
for (unsigned j = 0, e = SubExprs.size(); j != e; ++j) {
if (++SubExpressionUseData[SubExprs[j]].Count == 1)
UniqueSubExprs.push_back(SubExprs[j]);
if (!isAddrUse || !fitsInAddressMode(SubExprs[j], AccessTy, TLI, false))
SubExpressionUseData[SubExprs[j]].notAllUsesAreFree = true;
}
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<const SCEV *, SubExprUseData>::iterator I =
SubExpressionUseData.find(UniqueSubExprs[i]);
assert(I != SubExpressionUseData.end() && "Entry not found?");
if (I->second.Count == NumUsesInsideLoop) { // Found CSE!
if (I->second.notAllUsesAreFree)
Result = SE->getAddExpr(Result, I->first);
else
FreeResult = SE->getAddExpr(FreeResult, I->first);
} else
// Remove non-cse's from SubExpressionUseData.
SubExpressionUseData.erase(I);
}
if (FreeResult != Zero) {
// We have some subexpressions that can be subsumed into addressing
// modes in every use inside the loop. However, it's possible that
// there are so many of them that the combined FreeResult cannot
// be subsumed, or that the target cannot handle both a FreeResult
// and a Result in the same instruction (for example because it would
// require too many registers). Check this.
for (unsigned i=0; i<NumUses; ++i) {
if (!L->contains(Uses[i].Inst))
continue;
// We know this is an addressing mode use; if there are any uses that
// are not, FreeResult would be Zero.
const Type *AccessTy = getAccessType(Uses[i].Inst);
if (!fitsInAddressMode(FreeResult, AccessTy, TLI, Result!=Zero)) {
// FIXME: could split up FreeResult into pieces here, some hoisted
// and some not. There is no obvious advantage to this.
Result = SE->getAddExpr(Result, FreeResult);
FreeResult = Zero;
break;
}
}
}
// If we found no CSE's, return now.
if (Result == Zero) return Result;
// If we still have a FreeResult, remove its subexpressions from
// SubExpressionUseData. This means they will remain in the use Bases.
if (FreeResult != Zero) {
SeparateSubExprs(SubExprs, FreeResult, SE);
for (unsigned j = 0, e = SubExprs.size(); j != e; ++j) {
std::map<const SCEV *, SubExprUseData>::iterator I =
SubExpressionUseData.find(SubExprs[j]);
SubExpressionUseData.erase(I);
}
SubExprs.clear();
}
// Otherwise, remove all of the CSE's we found from each of the base values.
for (unsigned i = 0; i != NumUses; ++i) {
// Uses outside the loop don't necessarily include the common base, but
// the final IV value coming into those uses does. Instead of trying to
// remove the pieces of the common base, which might not be there,
// subtract off the base to compensate for this.
if (!L->contains(Uses[i].Inst)) {
Uses[i].Base = SE->getMinusSCEV(Uses[i].Base, Result);
continue;
}
// 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 (SubExpressionUseData.count(SubExprs[j])) {
SubExprs.erase(SubExprs.begin()+j);
--j; --e;
}
// Finally, add the non-shared expressions together.
if (SubExprs.empty())
Uses[i].Base = Zero;
else
Uses[i].Base = SE->getAddExpr(SubExprs);
SubExprs.clear();
}
return Result;
}
/// ValidScale - Check whether the given Scale is valid for all loads and
/// stores in UsersToProcess.
///
bool LoopStrengthReduce::ValidScale(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::getVoidTy(UsersToProcess[i].Inst->getContext());
if (isAddressUse(UsersToProcess[i].Inst,
UsersToProcess[i].OperandValToReplace))
AccessTy = getAccessType(UsersToProcess[i].Inst);
else if (isa<PHINode>(UsersToProcess[i].Inst))
continue;
TargetLowering::AddrMode AM;
if (const 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;
}
/// ValidOffset - Check whether the given Offset is valid for all loads and
/// stores in UsersToProcess.
///
bool LoopStrengthReduce::ValidOffset(bool HasBaseReg,
int64_t Offset,
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::getVoidTy(UsersToProcess[i].Inst->getContext());
if (isAddressUse(UsersToProcess[i].Inst,
UsersToProcess[i].OperandValToReplace))
AccessTy = getAccessType(UsersToProcess[i].Inst);
else if (isa<PHINode>(UsersToProcess[i].Inst))
continue;
TargetLowering::AddrMode AM;
if (const SCEVConstant *SC = dyn_cast<SCEVConstant>(UsersToProcess[i].Imm))
AM.BaseOffs = SC->getValue()->getSExtValue();
AM.BaseOffs = (uint64_t)AM.BaseOffs + (uint64_t)Offset;
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 Ty1 to Ty2 is not
/// a nop.
bool LoopStrengthReduce::RequiresTypeConversion(const Type *Ty1,
const Type *Ty2) {
if (Ty1 == Ty2)
return false;
Ty1 = SE->getEffectiveSCEVType(Ty1);
Ty2 = SE->getEffectiveSCEVType(Ty2);
if (Ty1 == Ty2)
return false;
if (Ty1->canLosslesslyBitCastTo(Ty2))
return false;
if (TLI && TLI->isTruncateFree(Ty1, Ty2))
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 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. Factors can be negative on same targets, e.g. ARM.
///
/// If all uses are outside the loop, we don't require that all multiplies
/// be folded into the addressing mode, nor even that the factor be constant;
/// a multiply (executed once) outside the loop is better than another IV
/// within. Well, usually.
const SCEV *LoopStrengthReduce::CheckForIVReuse(bool HasBaseReg,
bool AllUsesAreAddresses,
bool AllUsesAreOutsideLoop,
const SCEV *Stride,
IVExpr &IV, const Type *Ty,
const std::vector<BasedUser>& UsersToProcess) {
if (const SCEVConstant *SC = dyn_cast<SCEVConstant>(Stride)) {
int64_t SInt = SC->getValue()->getSExtValue();
for (unsigned NewStride = 0, e = IU->StrideOrder.size();
NewStride != e; ++NewStride) {
std::map<const SCEV *, IVsOfOneStride>::iterator SI =
IVsByStride.find(IU->StrideOrder[NewStride]);
if (SI == IVsByStride.end() || !isa<SCEVConstant>(SI->first))
continue;
// The other stride has no uses, don't reuse it.
std::map<const SCEV *, IVUsersOfOneStride *>::iterator UI =
IU->IVUsesByStride.find(IU->StrideOrder[NewStride]);
if (UI->second->Users.empty())
continue;
int64_t SSInt = cast<SCEVConstant>(SI->first)->getValue()->getSExtValue();
if (SI->first != Stride &&
(unsigned(abs64(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 &&
ValidScale(HasBaseReg, Scale, UsersToProcess))) {
// Prefer to reuse an IV with a base of zero.
for (std::vector<IVExpr>::iterator II = SI->second.IVs.begin(),
IE = SI->second.IVs.end(); II != IE; ++II)
// Only reuse previous IV if it would not require a type conversion
// and if the base difference can be folded.
if (II->Base->isZero() &&
!RequiresTypeConversion(II->Base->getType(), Ty)) {
IV = *II;
return SE->getIntegerSCEV(Scale, Stride->getType());
}
// Otherwise, settle for an IV with a foldable base.
if (AllUsesAreAddresses)
for (std::vector<IVExpr>::iterator II = SI->second.IVs.begin(),
IE = SI->second.IVs.end(); II != IE; ++II)
// Only reuse previous IV if it would not require a type conversion
// and if the base difference can be folded.
if (SE->getEffectiveSCEVType(II->Base->getType()) ==
SE->getEffectiveSCEVType(Ty) &&
isa<SCEVConstant>(II->Base)) {
int64_t Base =
cast<SCEVConstant>(II->Base)->getValue()->getSExtValue();
if (Base > INT32_MIN && Base <= INT32_MAX &&
ValidOffset(HasBaseReg, -Base * Scale,
Scale, UsersToProcess)) {
IV = *II;
return SE->getIntegerSCEV(Scale, Stride->getType());
}
}
}
}
} else if (AllUsesAreOutsideLoop) {
// Accept nonconstant strides here; it is really really right to substitute
// an existing IV if we can.
for (unsigned NewStride = 0, e = IU->StrideOrder.size();
NewStride != e; ++NewStride) {
std::map<const SCEV *, IVsOfOneStride>::iterator SI =
IVsByStride.find(IU->StrideOrder[NewStride]);
if (SI == IVsByStride.end() || !isa<SCEVConstant>(SI->first))
continue;
int64_t SSInt = cast<SCEVConstant>(SI->first)->getValue()->getSExtValue();
if (SI->first != Stride && SSInt != 1)
continue;
for (std::vector<IVExpr>::iterator II = SI->second.IVs.begin(),
IE = SI->second.IVs.end(); II != IE; ++II)
// Accept nonzero base here.
// Only reuse previous IV if it would not require a type conversion.
if (!RequiresTypeConversion(II->Base->getType(), Ty)) {
IV = *II;
return Stride;
}
}
// Special case, old IV is -1*x and this one is x. Can treat this one as
// -1*old.
for (unsigned NewStride = 0, e = IU->StrideOrder.size();
NewStride != e; ++NewStride) {
std::map<const SCEV *, IVsOfOneStride>::iterator SI =
IVsByStride.find(IU->StrideOrder[NewStride]);
if (SI == IVsByStride.end())
continue;
if (const SCEVMulExpr *ME = dyn_cast<SCEVMulExpr>(SI->first))
if (const SCEVConstant *SC = dyn_cast<SCEVConstant>(ME->getOperand(0)))
if (Stride == ME->getOperand(1) &&
SC->getValue()->getSExtValue() == -1LL)
for (std::vector<IVExpr>::iterator II = SI->second.IVs.begin(),
IE = SI->second.IVs.end(); II != IE; ++II)
// Accept nonzero base here.
// Only reuse previous IV if it would not require type conversion.
if (!RequiresTypeConversion(II->Base->getType(), Ty)) {
IV = *II;
return SE->getIntegerSCEV(-1LL, Stride->getType());
}
}
}
return SE->getIntegerSCEV(0, Stride->getType());
}
/// 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 SCEV *Expr) {
const SCEVMulExpr *Mul = dyn_cast<SCEVMulExpr>(Expr);
if (!Mul) return false;
// If there is a constant factor, it will be first.
const 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();
}
/// 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.
const SCEV *LoopStrengthReduce::CollectIVUsers(const SCEV *Stride,
IVUsersOfOneStride &Uses,
Loop *L,
bool &AllUsesAreAddresses,
bool &AllUsesAreOutsideLoop,
std::vector<BasedUser> &UsersToProcess) {
// FIXME: Generalize to non-affine IV's.
if (!Stride->isLoopInvariant(L))
return SE->getIntegerSCEV(0, Stride->getType());
UsersToProcess.reserve(Uses.Users.size());
for (ilist<IVStrideUse>::iterator I = Uses.Users.begin(),
E = Uses.Users.end(); I != E; ++I) {
UsersToProcess.push_back(BasedUser(*I, SE));
// Move any loop variant 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.
MoveLoopVariantsToImmediateField(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.
const SCEV *CommonExprs =
RemoveCommonExpressionsFromUseBases(UsersToProcess, SE, L, TLI);
// 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;
bool HasAddress = false;
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)) {
UsersToProcess[i].Imm = SE->getAddExpr(UsersToProcess[i].Imm,
UsersToProcess[i].Base);
UsersToProcess[i].Base =
SE->getIntegerSCEV(0, UsersToProcess[i].Base->getType());
} else {
// Not all uses are outside the loop.
AllUsesAreOutsideLoop = false;
// 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 (isAddress)
HasAddress = true;
// 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 is 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;
// There are no in-loop address uses.
if (AllUsesAreAddresses && (!HasAddress && !AllUsesAreOutsideLoop))
AllUsesAreAddresses = false;
return CommonExprs;
}
/// ShouldUseFullStrengthReductionMode - Test whether full strength-reduction
/// is valid and profitable for the given set of users of a stride. In
/// full strength-reduction mode, all addresses at the current stride are
/// strength-reduced all the way down to pointer arithmetic.
///
bool LoopStrengthReduce::ShouldUseFullStrengthReductionMode(
const std::vector<BasedUser> &UsersToProcess,
const Loop *L,
bool AllUsesAreAddresses,
const SCEV *Stride) {
if (!EnableFullLSRMode)
return false;
// The heuristics below aim to avoid increasing register pressure, but
// fully strength-reducing all the addresses increases the number of
// add instructions, so don't do this when optimizing for size.
// TODO: If the loop is large, the savings due to simpler addresses
// may oughtweight the costs of the extra increment instructions.
if (L->getHeader()->getParent()->hasFnAttr(Attribute::OptimizeForSize))
return false;
// TODO: For now, don't do full strength reduction if there could
// potentially be greater-stride multiples of the current stride
// which could reuse the current stride IV.
if (IU->StrideOrder.back() != Stride)
return false;
// Iterate through the uses to find conditions that automatically rule out
// full-lsr mode.
for (unsigned i = 0, e = UsersToProcess.size(); i != e; ) {
const SCEV *Base = UsersToProcess[i].Base;
const SCEV *Imm = UsersToProcess[i].Imm;
// If any users have a loop-variant component, they can't be fully
// strength-reduced.
if (Imm && !Imm->isLoopInvariant(L))
return false;
// If there are to users with the same base and the difference between
// the two Imm values can't be folded into the address, full
// strength reduction would increase register pressure.
do {
const SCEV *CurImm = UsersToProcess[i].Imm;
if ((CurImm || Imm) && CurImm != Imm) {
if (!CurImm) CurImm = SE->getIntegerSCEV(0, Stride->getType());
if (!Imm) Imm = SE->getIntegerSCEV(0, Stride->getType());
const Instruction *Inst = UsersToProcess[i].Inst;
const Type *AccessTy = getAccessType(Inst);
const SCEV *Diff = SE->getMinusSCEV(UsersToProcess[i].Imm, Imm);
if (!Diff->isZero() &&
(!AllUsesAreAddresses ||
!fitsInAddressMode(Diff, AccessTy, TLI, /*HasBaseReg=*/true)))
return false;
}
} while (++i != e && Base == UsersToProcess[i].Base);
}
// If there's exactly one user in this stride, fully strength-reducing it
// won't increase register pressure. If it's starting from a non-zero base,
// it'll be simpler this way.
if (UsersToProcess.size() == 1 && !UsersToProcess[0].Base->isZero())
return true;
// Otherwise, if there are any users in this stride that don't require
// a register for their base, full strength-reduction will increase
// register pressure.
for (unsigned i = 0, e = UsersToProcess.size(); i != e; ++i)
if (UsersToProcess[i].Base->isZero())
return false;
// Otherwise, go for it.
return true;
}
/// InsertAffinePhi Create and insert a PHI node for an induction variable
/// with the specified start and step values in the specified loop.
///
/// If NegateStride is true, the stride should be negated by using a
/// subtract instead of an add.
///
/// Return the created phi node.
///
static PHINode *InsertAffinePhi(const SCEV *Start, const SCEV *Step,
Instruction *IVIncInsertPt,
const Loop *L,
SCEVExpander &Rewriter) {
assert(Start->isLoopInvariant(L) && "New PHI start is not loop invariant!");
assert(Step->isLoopInvariant(L) && "New PHI stride is not loop invariant!");
BasicBlock *Header = L->getHeader();
BasicBlock *Preheader = L->getLoopPreheader();
BasicBlock *LatchBlock = L->getLoopLatch();
const Type *Ty = Start->getType();
Ty = Rewriter.SE.getEffectiveSCEVType(Ty);
PHINode *PN = PHINode::Create(Ty, "lsr.iv", Header->begin());
PN->addIncoming(Rewriter.expandCodeFor(Start, Ty, Preheader->getTerminator()),
Preheader);
// If the stride is negative, insert a sub instead of an add for the
// increment.
bool isNegative = isNonConstantNegative(Step);
const SCEV *IncAmount = Step;
if (isNegative)
IncAmount = Rewriter.SE.getNegativeSCEV(Step);
// Insert an add instruction right before the terminator corresponding
// to the back-edge or just before the only use. The location is determined
// by the caller and passed in as IVIncInsertPt.
Value *StepV = Rewriter.expandCodeFor(IncAmount, Ty,
Preheader->getTerminator());
Instruction *IncV;
if (isNegative) {
IncV = BinaryOperator::CreateSub(PN, StepV, "lsr.iv.next",
IVIncInsertPt);
} else {
IncV = BinaryOperator::CreateAdd(PN, StepV, "lsr.iv.next",
IVIncInsertPt);
}
if (!isa<ConstantInt>(StepV)) ++NumVariable;
PN->addIncoming(IncV, LatchBlock);
++NumInserted;
return PN;
}
static void SortUsersToProcess(std::vector<BasedUser> &UsersToProcess) {
// 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
// const SCEV *'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.
const SCEV *Base = UsersToProcess[i].Base;
// Compact everything with this base to be consecutive with this one.
for (unsigned j = i+1; j != e; ++j) {
if (UsersToProcess[j].Base == Base) {
std::swap(UsersToProcess[i+1], UsersToProcess[j]);
++i;
}
}
}
}
/// PrepareToStrengthReduceFully - Prepare to fully strength-reduce
/// UsersToProcess, meaning lowering addresses all the way down to direct
/// pointer arithmetic.
///
void
LoopStrengthReduce::PrepareToStrengthReduceFully(
std::vector<BasedUser> &UsersToProcess,
const SCEV *Stride,
const SCEV *CommonExprs,
const Loop *L,
SCEVExpander &PreheaderRewriter) {
DEBUG(errs() << " Fully reducing all users\n");
// Rewrite the UsersToProcess records, creating a separate PHI for each
// unique Base value.
Instruction *IVIncInsertPt = L->getLoopLatch()->getTerminator();
for (unsigned i = 0, e = UsersToProcess.size(); i != e; ) {
// TODO: The uses are grouped by base, but not sorted. We arbitrarily
// pick the first Imm value here to start with, and adjust it for the
// other uses.
const SCEV *Imm = UsersToProcess[i].Imm;
const SCEV *Base = UsersToProcess[i].Base;
const SCEV *Start = SE->getAddExpr(CommonExprs, Base, Imm);
PHINode *Phi = InsertAffinePhi(Start, Stride, IVIncInsertPt, L,
PreheaderRewriter);
// Loop over all the users with the same base.
do {
UsersToProcess[i].Base = SE->getIntegerSCEV(0, Stride->getType());
UsersToProcess[i].Imm = SE->getMinusSCEV(UsersToProcess[i].Imm, Imm);
UsersToProcess[i].Phi = Phi;
assert(UsersToProcess[i].Imm->isLoopInvariant(L) &&
"ShouldUseFullStrengthReductionMode should reject this!");
} while (++i != e && Base == UsersToProcess[i].Base);
}
}
/// FindIVIncInsertPt - Return the location to insert the increment instruction.
/// If the only use if a use of postinc value, (must be the loop termination
/// condition), then insert it just before the use.
static Instruction *FindIVIncInsertPt(std::vector<BasedUser> &UsersToProcess,
const Loop *L) {
if (UsersToProcess.size() == 1 &&
UsersToProcess[0].isUseOfPostIncrementedValue &&
L->contains(UsersToProcess[0].Inst))
return UsersToProcess[0].Inst;
return L->getLoopLatch()->getTerminator();
}
/// PrepareToStrengthReduceWithNewPhi - Insert a new induction variable for the
/// given users to share.
///
void
LoopStrengthReduce::PrepareToStrengthReduceWithNewPhi(
std::vector<BasedUser> &UsersToProcess,
const SCEV *Stride,
const SCEV *CommonExprs,
Value *CommonBaseV,
Instruction *IVIncInsertPt,
const Loop *L,
SCEVExpander &PreheaderRewriter) {
DEBUG(errs() << " Inserting new PHI:\n");
PHINode *Phi = InsertAffinePhi(SE->getUnknown(CommonBaseV),
Stride, IVIncInsertPt, L,
PreheaderRewriter);
// Remember this in case a later stride is multiple of this.
IVsByStride[Stride].addIV(Stride, CommonExprs, Phi);
// All the users will share this new IV.
for (unsigned i = 0, e = UsersToProcess.size(); i != e; ++i)
UsersToProcess[i].Phi = Phi;
DEBUG(errs() << " IV=");
DEBUG(WriteAsOperand(errs(), Phi, /*PrintType=*/false));
DEBUG(errs() << "\n");
}
/// PrepareToStrengthReduceFromSmallerStride - Prepare for the given users to
/// reuse an induction variable with a stride that is a factor of the current
/// induction variable.
///
void
LoopStrengthReduce::PrepareToStrengthReduceFromSmallerStride(
std::vector<BasedUser> &UsersToProcess,
Value *CommonBaseV,
const IVExpr &ReuseIV,
Instruction *PreInsertPt) {
DEBUG(errs() << " Rewriting in terms of existing IV of STRIDE "
<< *ReuseIV.Stride << " and BASE " << *ReuseIV.Base << "\n");
// All the users will share the reused IV.
for (unsigned i = 0, e = UsersToProcess.size(); i != e; ++i)
UsersToProcess[i].Phi = ReuseIV.PHI;
Constant *C = dyn_cast<Constant>(CommonBaseV);
if (C &&
(!C->isNullValue() &&
!fitsInAddressMode(SE->getUnknown(CommonBaseV), CommonBaseV->getType(),
TLI, false)))
// 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);
}
static bool IsImmFoldedIntoAddrMode(GlobalValue *GV, int64_t Offset,
const Type *AccessTy,
std::vector<BasedUser> &UsersToProcess,
const TargetLowering *TLI) {
SmallVector<Instruction*, 16> AddrModeInsts;
for (unsigned i = 0, e = UsersToProcess.size(); i != e; ++i) {
if (UsersToProcess[i].isUseOfPostIncrementedValue)
continue;
ExtAddrMode AddrMode =
AddressingModeMatcher::Match(UsersToProcess[i].OperandValToReplace,
AccessTy, UsersToProcess[i].Inst,
AddrModeInsts, *TLI);
if (GV && GV != AddrMode.BaseGV)
return false;
if (Offset && !AddrMode.BaseOffs)
// FIXME: How to accurate check it's immediate offset is folded.
return false;
AddrModeInsts.clear();
}
return true;
}
/// StrengthReduceIVUsersOfStride - 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.
void
LoopStrengthReduce::StrengthReduceIVUsersOfStride(const SCEV *Stride,
IVUsersOfOneStride &Uses,
Loop *L) {
// 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;
// Keep track if every use of a single stride is outside the loop. If so,
// we want to be more aggressive about reusing a smaller-stride IV; a
// multiply outside the loop is better than another IV inside. Well, usually.
bool AllUsesAreOutsideLoop = 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;
const SCEV *CommonExprs = CollectIVUsers(Stride, Uses, L, AllUsesAreAddresses,
AllUsesAreOutsideLoop,
UsersToProcess);
// Sort the UsersToProcess array so that users with common bases are
// next to each other.
SortUsersToProcess(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();
const Type *ReplacedTy = CommonExprs->getType();
// If all uses are addresses, consider sinking the immediate part of the
// common expression back into uses if they can fit in the immediate fields.
if (TLI && HaveCommonExprs && AllUsesAreAddresses) {
const SCEV *NewCommon = CommonExprs;
const SCEV *Imm = SE->getIntegerSCEV(0, ReplacedTy);
MoveImmediateValues(TLI, Type::getVoidTy(
L->getLoopPreheader()->getContext()),
NewCommon, Imm, true, L, SE);
if (!Imm->isZero()) {
bool DoSink = true;
// If the immediate part of the common expression is a GV, check if it's
// possible to fold it into the target addressing mode.
GlobalValue *GV = 0;
if (const SCEVUnknown *SU = dyn_cast<SCEVUnknown>(Imm))
GV = dyn_cast<GlobalValue>(SU->getValue());
int64_t Offset = 0;
if (const SCEVConstant *SC = dyn_cast<SCEVConstant>(Imm))
Offset = SC->getValue()->getSExtValue();
if (GV || Offset)
// Pass VoidTy as the AccessTy to be conservative, because
// there could be multiple access types among all the uses.
DoSink = IsImmFoldedIntoAddrMode(GV, Offset,
Type::getVoidTy(L->getLoopPreheader()->getContext()),
UsersToProcess, TLI);
if (DoSink) {
DEBUG(errs() << " Sinking " << *Imm << " back down into uses\n");
for (unsigned i = 0, e = UsersToProcess.size(); i != e; ++i)
UsersToProcess[i].Imm = SE->getAddExpr(UsersToProcess[i].Imm, Imm);
CommonExprs = NewCommon;
HaveCommonExprs = !CommonExprs->isZero();
++NumImmSunk;
}
}
}
// Now that we know what we need to do, insert the PHI node itself.
//
DEBUG(errs() << "LSR: Examining IVs of TYPE " << *ReplacedTy << " of STRIDE "
<< *Stride << ":\n"
<< " Common base: " << *CommonExprs << "\n");
SCEVExpander Rewriter(*SE);
SCEVExpander PreheaderRewriter(*SE);
BasicBlock *Preheader = L->getLoopPreheader();
Instruction *PreInsertPt = Preheader->getTerminator();
BasicBlock *LatchBlock = L->getLoopLatch();
Instruction *IVIncInsertPt = LatchBlock->getTerminator();
Value *CommonBaseV = Constant::getNullValue(ReplacedTy);
const SCEV *RewriteFactor = SE->getIntegerSCEV(0, ReplacedTy);
IVExpr ReuseIV(SE->getIntegerSCEV(0,
Type::getInt32Ty(Preheader->getContext())),
SE->getIntegerSCEV(0,
Type::getInt32Ty(Preheader->getContext())),
0);
// Choose a strength-reduction strategy and prepare for it by creating
// the necessary PHIs and adjusting the bookkeeping.
if (ShouldUseFullStrengthReductionMode(UsersToProcess, L,
AllUsesAreAddresses, Stride)) {
PrepareToStrengthReduceFully(UsersToProcess, Stride, CommonExprs, L,
PreheaderRewriter);
} else {
// Emit the initial base value into the loop preheader.
CommonBaseV = PreheaderRewriter.expandCodeFor(CommonExprs, ReplacedTy,
PreInsertPt);
// If all uses are addresses, check if it is possible to reuse an IV. The
// new IV must have a stride that is a multiple of the old stride; the
// multiple must be a number that can be encoded in the scale field of the
// target addressing mode; and we must have a valid instruction after this
// substitution, including the immediate field, if any.
RewriteFactor = CheckForIVReuse(HaveCommonExprs, AllUsesAreAddresses,
AllUsesAreOutsideLoop,
Stride, ReuseIV, ReplacedTy,
UsersToProcess);
if (!RewriteFactor->isZero())
PrepareToStrengthReduceFromSmallerStride(UsersToProcess, CommonBaseV,
ReuseIV, PreInsertPt);
else {
IVIncInsertPt = FindIVIncInsertPt(UsersToProcess, L);
PrepareToStrengthReduceWithNewPhi(UsersToProcess, Stride, CommonExprs,
CommonBaseV, IVIncInsertPt,
L, PreheaderRewriter);
}
}
// Process all the users now, replacing their strided uses with
// strength-reduced forms. This outer loop handles all bases, the inner
// loop handles all users of a particular base.
while (!UsersToProcess.empty()) {
const SCEV *Base = UsersToProcess.back().Base;
Instruction *Inst = UsersToProcess.back().Inst;
// Emit the code for Base into the preheader.
Value *BaseV = 0;
if (!Base->isZero()) {
BaseV = PreheaderRewriter.expandCodeFor(Base, 0, PreInsertPt);
DEBUG(errs() << " INSERTING code for BASE = " << *Base << ":");
if (BaseV->hasName())
DEBUG(errs() << " Result value name = %" << BaseV->getName());
DEBUG(errs() << "\n");
// If BaseV is a non-zero constant, 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 (!fitsInAddressMode(Base, getAccessType(Inst), TLI, false) &&
isa<Constant>(BaseV)) {
// 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();
DEBUG(errs() << " Examining ");
if (User.isUseOfPostIncrementedValue)
DEBUG(errs() << "postinc");
else
DEBUG(errs() << "preinc");
DEBUG(errs() << " use ");
DEBUG(WriteAsOperand(errs(), UsersToProcess.back().OperandValToReplace,
/*PrintType=*/false));
DEBUG(errs() << " in Inst: " << *User.Inst);
// 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 = User.Phi;
if (User.isUseOfPostIncrementedValue) {
RewriteOp = User.Phi->getIncomingValueForBlock(LatchBlock);
// 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. In case it's the
// only use of the iv, the increment instruction is already before the
// use.
if (L->contains(User.Inst) && User.Inst != IVIncInsertPt)
User.Inst->moveBefore(IVIncInsertPt);
}
const SCEV *RewriteExpr = SE->getUnknown(RewriteOp);
if (SE->getEffectiveSCEVType(RewriteOp->getType()) !=
SE->getEffectiveSCEVType(ReplacedTy)) {
assert(SE->getTypeSizeInBits(RewriteOp->getType()) >
SE->getTypeSizeInBits(ReplacedTy) &&
"Unexpected widening cast!");
RewriteExpr = SE->getTruncateExpr(RewriteExpr, ReplacedTy);
}
// If we had to insert new instructions 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 == User.Phi) 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 to take advantage of the addressing mode scale component.
if (!RewriteFactor->isZero()) {
// If we're reusing an IV with a nonzero base (currently this happens
// only when all reuses are outside the loop) subtract that base here.
// The base has been used to initialize the PHI node but we don't want
// it here.
if (!ReuseIV.Base->isZero()) {
const SCEV *typedBase = ReuseIV.Base;
if (SE->getEffectiveSCEVType(RewriteExpr->getType()) !=
SE->getEffectiveSCEVType(ReuseIV.Base->getType())) {
// It's possible the original IV is a larger type than the new IV,
// in which case we have to truncate the Base. We checked in
// RequiresTypeConversion that this is valid.
assert(SE->getTypeSizeInBits(RewriteExpr->getType()) <
SE->getTypeSizeInBits(ReuseIV.Base->getType()) &&
"Unexpected lengthening conversion!");
typedBase = SE->getTruncateExpr(ReuseIV.Base,
RewriteExpr->getType());
}
RewriteExpr = SE->getMinusSCEV(RewriteExpr, typedBase);
}
// Multiply old variable, with base removed, by new scale factor.
RewriteExpr = SE->getMulExpr(RewriteFactor,
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.
// When this use is outside the loop, we earlier subtracted the
// common base, and are adding it back here. Use the same expression
// as before, rather than CommonBaseV, so DAGCombiner will zap it.
if (!CommonExprs->isZero()) {
if (L->contains(User.Inst))
RewriteExpr = SE->getAddExpr(RewriteExpr,
SE->getUnknown(CommonBaseV));
else
RewriteExpr = SE->getAddExpr(RewriteExpr, CommonExprs);
}
}
// Now that we know what we need to do, insert code before User for the
// immediate and any loop-variant expressions.
if (BaseV)
// Add BaseV to the PHI value if needed.
RewriteExpr = SE->getAddExpr(RewriteExpr, SE->getUnknown(BaseV));
User.RewriteInstructionToUseNewBase(RewriteExpr, NewBasePt,
Rewriter, L, this,
DeadInsts, SE);
// Mark old value we replaced as possibly dead, so that it is eliminated
// if we just replaced the last use of that value.
DeadInsts.push_back(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::StrengthReduceIVUsers(Loop *L) {
// Note: this processes each stride/type pair individually. All users
// passed into StrengthReduceIVUsersOfStride 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 = IU->StrideOrder.size(); Stride != e; ++Stride) {
std::map<const SCEV *, IVUsersOfOneStride *>::iterator SI =
IU->IVUsesByStride.find(IU->StrideOrder[Stride]);
assert(SI != IU->IVUsesByStride.end() && "Stride doesn't exist!");
// FIXME: Generalize to non-affine IV's.
if (!SI->first->isLoopInvariant(L))
continue;
StrengthReduceIVUsersOfStride(SI->first, *SI->second, L);
}
}
/// 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 SCEV* &CondStride) {
for (unsigned Stride = 0, e = IU->StrideOrder.size();
Stride != e && !CondUse; ++Stride) {
std::map<const SCEV *, IVUsersOfOneStride *>::iterator SI =
IU->IVUsesByStride.find(IU->StrideOrder[Stride]);
assert(SI != IU->IVUsesByStride.end() && "Stride doesn't exist!");
for (ilist<IVStrideUse>::iterator UI = SI->second->Users.begin(),
E = SI->second->Users.end(); UI != E; ++UI)
if (UI->getUser() == 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 {
const ScalarEvolution *SE;
explicit StrideCompare(const ScalarEvolution *se) : SE(se) {}
bool operator()(const SCEV *LHS, const SCEV *RHS) {
const SCEVConstant *LHSC = dyn_cast<SCEVConstant>(LHS);
const 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) {
if (LV != RV)
return LV > RV;
} else {
return ALV < ARV;
}
// If it's the same value but different type, sort by bit width so
// that we emit larger induction variables before smaller
// ones, letting the smaller be re-written in terms of larger ones.
return SE->getTypeSizeInBits(RHS->getType()) <
SE->getTypeSizeInBits(LHS->getType());
}
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 SCEV* &CondStride,
bool PostPass) {
// If there's only one stride in the loop, there's nothing to do here.
if (IU->StrideOrder.size() < 2)
return Cond;
// If there are other users of the condition's stride, don't bother
// trying to change the condition because the stride will still
// remain.
std::map<const SCEV *, IVUsersOfOneStride *>::iterator I =
IU->IVUsesByStride.find(CondStride);
if (I == IU->IVUsesByStride.end())
return Cond;
if (I->second->Users.size() > 1) {
for (ilist<IVStrideUse>::iterator II = I->second->Users.begin(),
EE = I->second->Users.end(); II != EE; ++II) {
if (II->getUser() == Cond)
continue;
if (!isInstructionTriviallyDead(II->getUser()))
return Cond;
}
}
// Only handle constant strides for now.
const SCEVConstant *SC = dyn_cast<SCEVConstant>(CondStride);
if (!SC) return Cond;
ICmpInst::Predicate Predicate = Cond->getPredicate();
int64_t CmpSSInt = SC->getValue()->getSExtValue();
unsigned BitWidth = SE->getTypeSizeInBits(CondStride->getType());
uint64_t SignBit = 1ULL << (BitWidth-1);
const Type *CmpTy = Cond->getOperand(0)->getType();
const Type *NewCmpTy = NULL;
unsigned TyBits = SE->getTypeSizeInBits(CmpTy);
unsigned NewTyBits = 0;
const SCEV *NewStride = NULL;
Value *NewCmpLHS = NULL;
Value *NewCmpRHS = NULL;
int64_t Scale = 1;
const SCEV *NewOffset = SE->getIntegerSCEV(0, CmpTy);
if (ConstantInt *C = dyn_cast<ConstantInt>(Cond->getOperand(1))) {
int64_t CmpVal = C->getValue().getSExtValue();
// Check the relevant induction variable for conformance to
// the pattern.
const SCEV *IV = SE->getSCEV(Cond->getOperand(0));
const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(IV);
if (!AR || !AR->isAffine())
return Cond;
const SCEVConstant *StartC = dyn_cast<SCEVConstant>(AR->getStart());
// Check stride constant and the comparision constant signs to detect
// overflow.
if (StartC) {
if ((StartC->getValue()->getSExtValue() < CmpVal && CmpSSInt < 0) ||
(StartC->getValue()->getSExtValue() > CmpVal && CmpSSInt > 0))
return Cond;
} else {
// More restrictive check for the other cases.
if ((CmpVal & SignBit) != (CmpSSInt & SignBit))
return Cond;
}
// Look for a suitable stride / iv as replacement.
for (unsigned i = 0, e = IU->StrideOrder.size(); i != e; ++i) {
std::map<const SCEV *, IVUsersOfOneStride *>::iterator SI =
IU->IVUsesByStride.find(IU->StrideOrder[i]);
if (!isa<SCEVConstant>(SI->first) || SI->second->Users.empty())
continue;
int64_t SSInt = cast<SCEVConstant>(SI->first)->getValue()->getSExtValue();
if (SSInt == CmpSSInt ||
abs64(SSInt) < abs64(CmpSSInt) ||
(SSInt % CmpSSInt) != 0)
continue;
Scale = SSInt / CmpSSInt;
int64_t NewCmpVal = CmpVal * Scale;
// If old icmp value fits in icmp immediate field, but the new one doesn't
// try something else.
if (TLI &&
TLI->isLegalICmpImmediate(CmpVal) &&
!TLI->isLegalICmpImmediate(NewCmpVal))
continue;
APInt Mul = APInt(BitWidth*2, CmpVal, true);
Mul = Mul * APInt(BitWidth*2, Scale, true);
// Check for overflow.
if (!Mul.isSignedIntN(BitWidth))
continue;
// Check for overflow in the stride's type too.
if (!Mul.isSignedIntN(SE->getTypeSizeInBits(SI->first->getType())))
continue;
// Watch out for overflow.
if (ICmpInst::isSigned(Predicate) &&
(CmpVal & SignBit) != (NewCmpVal & SignBit))
continue;
// Pick the best iv to use trying to avoid a cast.
NewCmpLHS = NULL;
for (ilist<IVStrideUse>::iterator UI = SI->second->Users.begin(),
E = SI->second->Users.end(); UI != E; ++UI) {
Value *Op = UI->getOperandValToReplace();
// If the IVStrideUse implies a cast, check for an actual cast which
// can be used to find the original IV expression.
if (SE->getEffectiveSCEVType(Op->getType()) !=
SE->getEffectiveSCEVType(SI->first->getType())) {
CastInst *CI = dyn_cast<CastInst>(Op);
// If it's not a simple cast, it's complicated.
if (!CI)
continue;
// If it's a cast from a type other than the stride type,
// it's complicated.
if (CI->getOperand(0)->getType() != SI->first->getType())
continue;
// Ok, we found the IV expression in the stride's type.
Op = CI->getOperand(0);
}
NewCmpLHS = Op;
if (NewCmpLHS->getType() == CmpTy)
break;
}
if (!NewCmpLHS)
continue;
NewCmpTy = NewCmpLHS->getType();
NewTyBits = SE->getTypeSizeInBits(NewCmpTy);
const Type *NewCmpIntTy = IntegerType::get(Cond->getContext(), NewTyBits);
if (RequiresTypeConversion(NewCmpTy, CmpTy)) {
// Check if it is possible to rewrite it using
// an iv / stride of a smaller integer type.
unsigned Bits = NewTyBits;
if (ICmpInst::isSigned(Predicate))
--Bits;
uint64_t Mask = (1ULL << Bits) - 1;
if (((uint64_t)NewCmpVal & Mask) != (uint64_t)NewCmpVal)
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->getOffset()))
continue;
if (!PostPass) {
bool AllUsesAreAddresses = true;
bool AllUsesAreOutsideLoop = true;
std::vector<BasedUser> UsersToProcess;
const SCEV *CommonExprs = CollectIVUsers(SI->first, *SI->second, L,
AllUsesAreAddresses,
AllUsesAreOutsideLoop,
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
// stride of the compare instruction.
if (AllUsesAreAddresses &&
ValidScale(!CommonExprs->isZero(), Scale, UsersToProcess))
continue;
}
// Avoid rewriting the compare instruction with an iv which has
// implicit extension or truncation built into it.
// TODO: This is over-conservative.
if (SE->getTypeSizeInBits(CondUse->getOffset()->getType()) != TyBits)
continue;
// If scale is negative, use swapped predicate unless it's testing
// for equality.
if (Scale < 0 && !Cond->isEquality())
Predicate = ICmpInst::getSwappedPredicate(Predicate);
NewStride = IU->StrideOrder[i];
if (!isa<PointerType>(NewCmpTy))
NewCmpRHS = ConstantInt::get(NewCmpTy, NewCmpVal);
else {
Constant *CI = ConstantInt::get(NewCmpIntTy, NewCmpVal);
NewCmpRHS = ConstantExpr::getIntToPtr(CI, NewCmpTy);
}
NewOffset = TyBits == NewTyBits
? SE->getMulExpr(CondUse->getOffset(),
SE->getConstant(CmpTy, Scale))
: SE->getConstant(NewCmpIntTy,
cast<SCEVConstant>(CondUse->getOffset())->getValue()
->getSExtValue()*Scale);
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 == NewCmpLHS)
return Cond;
}
if (NewCmpRHS) {
// Create a new compare instruction using new stride / iv.
ICmpInst *OldCond = Cond;
// Insert new compare instruction.
Cond = new ICmpInst(OldCond, Predicate, NewCmpLHS, NewCmpRHS,
L->getHeader()->getName() + ".termcond");
DEBUG(errs() << " Change compare stride in Inst " << *OldCond);
DEBUG(errs() << " to " << *Cond << '\n');
// Remove the old compare instruction. The old indvar is probably dead too.
DeadInsts.push_back(CondUse->getOperandValToReplace());
OldCond->replaceAllUsesWith(Cond);
OldCond->eraseFromParent();
IU->IVUsesByStride[NewStride]->addUser(NewOffset, Cond, NewCmpLHS);
CondUse = &IU->IVUsesByStride[NewStride]->Users.back();
CondStride = NewStride;
++NumEliminated;
Changed = true;
}
return Cond;
}
/// OptimizeMax - Rewrite the loop's terminating condition if it uses
/// a max 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);
///
/// the trip count isn't just 'n', because 'n' might not be positive. 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
/// max expression, which allows it to give the loop a canonical
/// induction variable:
///
/// i = 0;
/// max = n < 1 ? 1 : n;
/// do {
/// p[i] = 0.0;
/// } while (++i != max);
///
/// 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::OptimizeMax(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;
const SCEV *BackedgeTakenCount = SE->getBackedgeTakenCount(L);
if (isa<SCEVCouldNotCompute>(BackedgeTakenCount))
return Cond;
const SCEV *One = SE->getIntegerSCEV(1, BackedgeTakenCount->getType());
// Add one to the backedge-taken count to get the trip count.
const SCEV *IterationCount = SE->getAddExpr(BackedgeTakenCount, One);
// Check for a max calculation that matches the pattern.
if (!isa<SCEVSMaxExpr>(IterationCount) && !isa<SCEVUMaxExpr>(IterationCount))
return Cond;
const SCEVNAryExpr *Max = cast<SCEVNAryExpr>(IterationCount);
if (Max != SE->getSCEV(Sel)) return Cond;
// To handle a max with more than two operands, this optimization would
// require additional checking and setup.
if (Max->getNumOperands() != 2)
return Cond;
const SCEV *MaxLHS = Max->getOperand(0);
const SCEV *MaxRHS = Max->getOperand(1);
if (!MaxLHS || MaxLHS != One) return Cond;
// Check the relevant induction variable for conformance to
// the pattern.
const SCEV *IV = SE->getSCEV(Cond->getOperand(0));
const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(IV);
if (!AR || !AR->isAffine() ||
AR->getStart() != One ||
AR->getStepRecurrence(*SE) != One)
return Cond;
assert(AR->getLoop() == L &&
"Loop condition operand is an addrec in a different loop!");
// 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)) == MaxRHS)
NewRHS = Sel->getOperand(1);
else if (SE->getSCEV(Sel->getOperand(2)) == MaxRHS)
NewRHS = Sel->getOperand(2);
if (!NewRHS) return Cond;
// Determine the new comparison opcode. It may be signed or unsigned,
// and the original comparison may be either equality or inequality.
CmpInst::Predicate Pred =
isa<SCEVSMaxExpr>(Max) ? CmpInst::ICMP_SLT : CmpInst::ICMP_ULT;
if (Cond->getPredicate() == CmpInst::ICMP_EQ)
Pred = CmpInst::getInversePredicate(Pred);
// Ok, everything looks ok to change the condition into an SLT or SGE and
// delete the max calculation.
ICmpInst *NewCond =
new ICmpInst(Cond, Pred, Cond->getOperand(0), NewRHS, "scmp");
// Delete the max calculation instructions.
Cond->replaceAllUsesWith(NewCond);
CondUse->setUser(NewCond);
Instruction *Cmp = cast<Instruction>(Sel->getOperand(0));
Cond->eraseFromParent();
Sel->eraseFromParent();
if (Cmp->use_empty())
Cmp->eraseFromParent();
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) {
const SCEV *BackedgeTakenCount = SE->getBackedgeTakenCount(L);
if (isa<SCEVCouldNotCompute>(BackedgeTakenCount))
return;
for (unsigned Stride = 0, e = IU->StrideOrder.size(); Stride != e;
++Stride) {
std::map<const SCEV *, IVUsersOfOneStride *>::iterator SI =
IU->IVUsesByStride.find(IU->StrideOrder[Stride]);
assert(SI != IU->IVUsesByStride.end() && "Stride doesn't exist!");
if (!isa<SCEVConstant>(SI->first))
continue;
for (ilist<IVStrideUse>::iterator UI = SI->second->Users.begin(),
E = SI->second->Users.end(); UI != E; /* empty */) {
ilist<IVStrideUse>::iterator CandidateUI = UI;
++UI;
Instruction *ShadowUse = CandidateUI->getUser();
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->getUser()))
DestTy = UCast->getDestTy();
else if (SIToFPInst *SCast = dyn_cast<SIToFPInst>(CandidateUI->getUser()))
DestTy = SCast->getDestTy();
if (!DestTy) continue;
if (TLI) {
// If target does not support DestTy natively then do not apply
// this transformation.
EVT 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)SE->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;
Constant *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;
// Ignore negative constants, as the code below doesn't handle them
// correctly. TODO: Remove this restriction.
if (!C->getValue().isStrictlyPositive()) continue;
/* Add new PHINode. */
PHINode *NewPH = PHINode::Create(DestTy, "IV.S.", PH);
/* create new increment. '++d' in above example. */
Constant *CFP = ConstantFP::get(DestTy, C->getZExtValue());
BinaryOperator *NewIncr =
BinaryOperator::Create(Incr->getOpcode() == Instruction::Add ?
Instruction::FAdd : Instruction::FSub,
NewPH, CFP, "IV.S.next.", Incr);
NewPH->addIncoming(NewInit, PH->getIncomingBlock(Entry));
NewPH->addIncoming(NewIncr, PH->getIncomingBlock(Latch));
/* Remove cast operation */
ShadowUse->replaceAllUsesWith(NewPH);
ShadowUse->eraseFromParent();
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);
}
bool LoopStrengthReduce::StrideMightBeShared(const SCEV* Stride, Loop *L,
bool CheckPreInc) {
int64_t SInt = cast<SCEVConstant>(Stride)->getValue()->getSExtValue();
for (unsigned i = 0, e = IU->StrideOrder.size(); i != e; ++i) {
std::map<const SCEV *, IVUsersOfOneStride *>::iterator SI =
IU->IVUsesByStride.find(IU->StrideOrder[i]);
const SCEV *Share = SI->first;
if (!isa<SCEVConstant>(SI->first) || Share == Stride)
continue;
int64_t SSInt = cast<SCEVConstant>(Share)->getValue()->getSExtValue();
if (SSInt == SInt)
return true; // This can definitely be reused.
if (unsigned(abs64(SSInt)) < SInt || (SSInt % SInt) != 0)
continue;
int64_t Scale = SSInt / SInt;
bool AllUsesAreAddresses = true;
bool AllUsesAreOutsideLoop = true;
std::vector<BasedUser> UsersToProcess;
const SCEV *CommonExprs = CollectIVUsers(SI->first, *SI->second, L,
AllUsesAreAddresses,
AllUsesAreOutsideLoop,
UsersToProcess);
if (AllUsesAreAddresses &&
ValidScale(!CommonExprs->isZero(), Scale, UsersToProcess)) {
if (!CheckPreInc)
return true;
// Any pre-inc iv use?
IVUsersOfOneStride &StrideUses = *IU->IVUsesByStride[Share];
for (ilist<IVStrideUse>::iterator I = StrideUses.Users.begin(),
E = StrideUses.Users.end(); I != E; ++I) {
if (!I->isUseOfPostIncrementedValue())
return true;
}
}
}
return false;
}
/// isUsedByExitBranch - Return true if icmp is used by a loop terminating
/// conditional branch or it's and / or with other conditions before being used
/// as the condition.
static bool isUsedByExitBranch(ICmpInst *Cond, Loop *L) {
BasicBlock *CondBB = Cond->getParent();
if (!L->isLoopExiting(CondBB))
return false;
BranchInst *TermBr = dyn_cast<BranchInst>(CondBB->getTerminator());
if (!TermBr || !TermBr->isConditional())
return false;
Value *User = *Cond->use_begin();
Instruction *UserInst = dyn_cast<Instruction>(User);
while (UserInst &&
(UserInst->getOpcode() == Instruction::And ||
UserInst->getOpcode() == Instruction::Or)) {
if (!UserInst->hasOneUse() || UserInst->getParent() != CondBB)
return false;
User = *User->use_begin();
UserInst = dyn_cast<Instruction>(User);
}
return User == TermBr;
}
static bool ShouldCountToZero(ICmpInst *Cond, IVStrideUse* &CondUse,
ScalarEvolution *SE, Loop *L,
const TargetLowering *TLI = 0) {
if (!L->contains(Cond))
return false;
if (!isa<SCEVConstant>(CondUse->getOffset()))
return false;
// Handle only tests for equality for the moment.
if (!Cond->isEquality() || !Cond->hasOneUse())
return false;
if (!isUsedByExitBranch(Cond, L))
return false;
Value *CondOp0 = Cond->getOperand(0);
const SCEV *IV = SE->getSCEV(CondOp0);
const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(IV);
if (!AR || !AR->isAffine())
return false;
const SCEVConstant *SC = dyn_cast<SCEVConstant>(AR->getStepRecurrence(*SE));
if (!SC || SC->getValue()->getSExtValue() < 0)
// If it's already counting down, don't do anything.
return false;
// If the RHS of the comparison is not an loop invariant, the rewrite
// cannot be done. Also bail out if it's already comparing against a zero.
// If we are checking this before cmp stride optimization, check if it's
// comparing against a already legal immediate.
Value *RHS = Cond->getOperand(1);
ConstantInt *RHSC = dyn_cast<ConstantInt>(RHS);
if (!L->isLoopInvariant(RHS) ||
(RHSC && RHSC->isZero()) ||
(RHSC && TLI && TLI->isLegalICmpImmediate(RHSC->getSExtValue())))
return false;
// Make sure the IV is only used for counting. Value may be preinc or
// postinc; 2 uses in either case.
if (!CondOp0->hasNUses(2))
return false;
return true;
}
/// OptimizeLoopTermCond - Change loop terminating condition to use the
/// postinc iv when possible.
void LoopStrengthReduce::OptimizeLoopTermCond(Loop *L) {
BasicBlock *LatchBlock = L->getLoopLatch();
bool LatchExit = L->isLoopExiting(LatchBlock);
SmallVector<BasicBlock*, 8> ExitingBlocks;
L->getExitingBlocks(ExitingBlocks);
for (unsigned i = 0, e = ExitingBlocks.size(); i != e; ++i) {
BasicBlock *ExitingBlock = ExitingBlocks[i];
// 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.
BranchInst *TermBr = dyn_cast<BranchInst>(ExitingBlock->getTerminator());
if (!TermBr)
continue;
// FIXME: Overly conservative, termination condition could be an 'or' etc..
if (TermBr->isUnconditional() || !isa<ICmpInst>(TermBr->getCondition()))
continue;
// Search IVUsesByStride to find Cond's IVUse if there is one.
IVStrideUse *CondUse = 0;
const SCEV *CondStride = 0;
ICmpInst *Cond = cast<ICmpInst>(TermBr->getCondition());
if (!FindIVUserForCond(Cond, CondUse, CondStride))
continue;
// If the latch block is exiting and it's not a single block loop, it's
// not safe to use postinc iv in other exiting blocks. FIXME: overly
// conservative? How about icmp stride optimization?
bool UsePostInc = !(e > 1 && LatchExit && ExitingBlock != LatchBlock);
if (UsePostInc && ExitingBlock != LatchBlock) {
if (!Cond->hasOneUse())
// See below, we don't want the condition to be cloned.
UsePostInc = false;
else {
// If exiting block is the latch block, we know it's safe and profitable
// to transform the icmp to use post-inc iv. Otherwise do so only if it
// would not reuse another iv and its iv would be reused by other uses.
// We are optimizing for the case where the icmp is the only use of the
// iv.
IVUsersOfOneStride &StrideUses = *IU->IVUsesByStride[CondStride];
for (ilist<IVStrideUse>::iterator I = StrideUses.Users.begin(),
E = StrideUses.Users.end(); I != E; ++I) {
if (I->getUser() == Cond)
continue;
if (!I->isUseOfPostIncrementedValue()) {
UsePostInc = false;
break;
}
}
}
// If iv for the stride might be shared and any of the users use pre-inc
// iv might be used, then it's not safe to use post-inc iv.
if (UsePostInc &&
isa<SCEVConstant>(CondStride) &&
StrideMightBeShared(CondStride, L, true))
UsePostInc = false;
}
// If the trip count is computed in terms of a max (due to ScalarEvolution
// being unable to find a sufficient guard, for example), change the loop
// comparison to use SLT or ULT instead of NE.
Cond = OptimizeMax(L, Cond, CondUse);
// If possible, change stride and operands of the compare instruction to
// eliminate one stride. However, avoid rewriting the compare instruction
// with an iv of new stride if it's likely the new stride uses will be
// rewritten using the stride of the compare instruction.
if (ExitingBlock == LatchBlock && isa<SCEVConstant>(CondStride)) {
// If the condition stride is a constant and it's the only use, we might
// want to optimize it first by turning it to count toward zero.
if (!StrideMightBeShared(CondStride, L, false) &&
!ShouldCountToZero(Cond, CondUse, SE, L, TLI))
Cond = ChangeCompareStride(L, Cond, CondUse, CondStride);
}
if (!UsePostInc)
continue;
DEBUG(errs() << " Change loop exiting icmp to use postinc iv: "
<< *Cond << '\n');
// 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 exiting 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");
ExitingBlock->getInstList().insert(TermBr, Cond);
// Clone the IVUse, as the old use still exists!
IU->IVUsesByStride[CondStride]->addUser(CondUse->getOffset(), Cond,
CondUse->getOperandValToReplace());
CondUse = &IU->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->setOffset(SE->getMinusSCEV(CondUse->getOffset(), CondStride));
CondUse->setIsUseOfPostIncrementedValue(true);
Changed = true;
++NumLoopCond;
}
}
bool LoopStrengthReduce::OptimizeLoopCountIVOfStride(const SCEV* &Stride,
IVStrideUse* &CondUse,
Loop *L) {
// If the only use is an icmp of a loop exiting conditional branch, then
// attempt the optimization.
BasedUser User = BasedUser(*CondUse, SE);
assert(isa<ICmpInst>(User.Inst) && "Expecting an ICMPInst!");
ICmpInst *Cond = cast<ICmpInst>(User.Inst);
// Less strict check now that compare stride optimization is done.
if (!ShouldCountToZero(Cond, CondUse, SE, L))
return false;
Value *CondOp0 = Cond->getOperand(0);
PHINode *PHIExpr = dyn_cast<PHINode>(CondOp0);
Instruction *Incr;
if (!PHIExpr) {
// Value tested is postinc. Find the phi node.
Incr = dyn_cast<BinaryOperator>(CondOp0);
// FIXME: Just use User.OperandValToReplace here?
if (!Incr || Incr->getOpcode() != Instruction::Add)
return false;
PHIExpr = dyn_cast<PHINode>(Incr->getOperand(0));
if (!PHIExpr)
return false;
// 1 use for preinc value, the increment.
if (!PHIExpr->hasOneUse())
return false;
} else {
assert(isa<PHINode>(CondOp0) &&
"Unexpected loop exiting counting instruction sequence!");
PHIExpr = cast<PHINode>(CondOp0);
// Value tested is preinc. Find the increment.
// A CmpInst is not a BinaryOperator; we depend on this.
Instruction::use_iterator UI = PHIExpr->use_begin();
Incr = dyn_cast<BinaryOperator>(UI);
if (!Incr)
Incr = dyn_cast<BinaryOperator>(++UI);
// One use for postinc value, the phi. Unnecessarily conservative?
if (!Incr || !Incr->hasOneUse() || Incr->getOpcode() != Instruction::Add)
return false;
}
// Replace the increment with a decrement.
DEBUG(errs() << "LSR: Examining use ");
DEBUG(WriteAsOperand(errs(), CondOp0, /*PrintType=*/false));
DEBUG(errs() << " in Inst: " << *Cond << '\n');
BinaryOperator *Decr = BinaryOperator::Create(Instruction::Sub,
Incr->getOperand(0), Incr->getOperand(1), "tmp", Incr);
Incr->replaceAllUsesWith(Decr);
Incr->eraseFromParent();
// Substitute endval-startval for the original startval, and 0 for the
// original endval. Since we're only testing for equality this is OK even
// if the computation wraps around.
BasicBlock *Preheader = L->getLoopPreheader();
Instruction *PreInsertPt = Preheader->getTerminator();
unsigned InBlock = L->contains(PHIExpr->getIncomingBlock(0)) ? 1 : 0;
Value *StartVal = PHIExpr->getIncomingValue(InBlock);
Value *EndVal = Cond->getOperand(1);
DEBUG(errs() << " Optimize loop counting iv to count down ["
<< *EndVal << " .. " << *StartVal << "]\n");
// FIXME: check for case where both are constant.
Constant* Zero = ConstantInt::get(Cond->getOperand(1)->getType(), 0);
BinaryOperator *NewStartVal = BinaryOperator::Create(Instruction::Sub,
EndVal, StartVal, "tmp", PreInsertPt);
PHIExpr->setIncomingValue(InBlock, NewStartVal);
Cond->setOperand(1, Zero);
DEBUG(errs() << " New icmp: " << *Cond << "\n");
int64_t SInt = cast<SCEVConstant>(Stride)->getValue()->getSExtValue();
const SCEV *NewStride = 0;
bool Found = false;
for (unsigned i = 0, e = IU->StrideOrder.size(); i != e; ++i) {
const SCEV *OldStride = IU->StrideOrder[i];
if (const SCEVConstant *SC = dyn_cast<SCEVConstant>(OldStride))
if (SC->getValue()->getSExtValue() == -SInt) {
Found = true;
NewStride = OldStride;
break;
}
}
if (!Found)
NewStride = SE->getIntegerSCEV(-SInt, Stride->getType());
IU->AddUser(NewStride, CondUse->getOffset(), Cond, Cond->getOperand(0));
IU->IVUsesByStride[Stride]->removeUser(CondUse);
CondUse = &IU->IVUsesByStride[NewStride]->Users.back();
Stride = NewStride;
++NumCountZero;
return true;
}
/// OptimizeLoopCountIV - If, after all sharing of IVs, the IV used for deciding
/// when to exit the loop is used only for that purpose, try to rearrange things
/// so it counts down to a test against zero.
bool LoopStrengthReduce::OptimizeLoopCountIV(Loop *L) {
bool ThisChanged = false;
for (unsigned i = 0, e = IU->StrideOrder.size(); i != e; ++i) {
const SCEV *Stride = IU->StrideOrder[i];
std::map<const SCEV *, IVUsersOfOneStride *>::iterator SI =
IU->IVUsesByStride.find(Stride);
assert(SI != IU->IVUsesByStride.end() && "Stride doesn't exist!");
// FIXME: Generalize to non-affine IV's.
if (!SI->first->isLoopInvariant(L))
continue;
// If stride is a constant and it has an icmpinst use, check if we can
// optimize the loop to count down.
if (isa<SCEVConstant>(Stride) && SI->second->Users.size() == 1) {
Instruction *User = SI->second->Users.begin()->getUser();
if (!isa<ICmpInst>(User))
continue;
const SCEV *CondStride = Stride;
IVStrideUse *Use = &*SI->second->Users.begin();
if (!OptimizeLoopCountIVOfStride(CondStride, Use, L))
continue;
ThisChanged = true;
// Now check if it's possible to reuse this iv for other stride uses.
for (unsigned j = 0, ee = IU->StrideOrder.size(); j != ee; ++j) {
const SCEV *SStride = IU->StrideOrder[j];
if (SStride == CondStride)
continue;
std::map<const SCEV *, IVUsersOfOneStride *>::iterator SII =
IU->IVUsesByStride.find(SStride);
assert(SII != IU->IVUsesByStride.end() && "Stride doesn't exist!");
// FIXME: Generalize to non-affine IV's.
if (!SII->first->isLoopInvariant(L))
continue;
// FIXME: Rewrite other stride using CondStride.
}
}
}
Changed |= ThisChanged;
return ThisChanged;
}
bool LoopStrengthReduce::runOnLoop(Loop *L, LPPassManager &LPM) {
IU = &getAnalysis<IVUsers>();
SE = &getAnalysis<ScalarEvolution>();
Changed = false;
// If LoopSimplify form is not available, stay out of trouble.
if (!L->getLoopPreheader() || !L->getLoopLatch())
return false;
if (!IU->IVUsesByStride.empty()) {
DEBUG(errs() << "\nLSR on \"" << L->getHeader()->getParent()->getName()
<< "\" ";
L->dump());
// Sort the StrideOrder so we process larger strides first.
std::stable_sort(IU->StrideOrder.begin(), IU->StrideOrder.end(),
StrideCompare(SE));
// 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);
// Change loop terminating condition to use the postinc iv when possible
// and optimize loop terminating compare. FIXME: Move this after
// StrengthReduceIVUsersOfStride?
OptimizeLoopTermCond(L);
// FIXME: We can shrink overlarge IV's here. e.g. if the code has
// computation in i64 values and the target doesn't support i64, demote
// the computation to 32-bit 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.
// IVsByStride keeps IVs for one particular loop.
assert(IVsByStride.empty() && "Stale entries in IVsByStride?");
StrengthReduceIVUsers(L);
// After all sharing is done, see if we can adjust the loop to test against
// zero instead of counting up to a maximum. This is usually faster.
OptimizeLoopCountIV(L);
// We're done analyzing this loop; release all the state we built up for it.
IVsByStride.clear();
// Clean up after ourselves
DeleteTriviallyDeadInstructions();
}
// At this point, it is worth checking to see if any recurrence PHIs are also
// dead, so that we can remove them as well.
DeleteDeadPHIs(L->getHeader());
return Changed;
}
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