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llvm-6502/lib/Transforms/Scalar/IndVarSimplify.cpp
Andrew Trick fcdc9a44e5 indvars: incremental fixes for -disable-iv-rewrite and testcases. 
Use a proper worklist for use-def traversal without holding onto an
iterator. Now that we process all IV uses, we need complete logic for
resusing existing derived IV defs. See HoistStep.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@132103 91177308-0d34-0410-b5e6-96231b3b80d8
2011-05-26 00:46:11 +00:00

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//===- IndVarSimplify.cpp - Induction Variable Elimination ----------------===//
//
// 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 simpler forms suitable for subsequent
// analysis and transformation.
//
// This transformation makes the following changes to each loop with an
// identifiable induction variable:
// 1. All loops are transformed to have a SINGLE canonical induction variable
// which starts at zero and steps by one.
// 2. The canonical induction variable is guaranteed to be the first PHI node
// in the loop header block.
// 3. The canonical induction variable is guaranteed to be in a wide enough
// type so that IV expressions need not be (directly) zero-extended or
// sign-extended.
// 4. Any pointer arithmetic recurrences are raised to use array subscripts.
//
// If the trip count of a loop is computable, this pass also makes the following
// changes:
// 1. The exit condition for the loop is canonicalized to compare the
// induction value against the exit value. This turns loops like:
// 'for (i = 7; i*i < 1000; ++i)' into 'for (i = 0; i != 25; ++i)'
// 2. Any use outside of the loop of an expression derived from the indvar
// is changed to compute the derived value outside of the loop, eliminating
// the dependence on the exit value of the induction variable. If the only
// purpose of the loop is to compute the exit value of some derived
// expression, this transformation will make the loop dead.
//
// This transformation should be followed by strength reduction after all of the
// desired loop transformations have been performed.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "indvars"
#include "llvm/Transforms/Scalar.h"
#include "llvm/BasicBlock.h"
#include "llvm/Constants.h"
#include "llvm/Instructions.h"
#include "llvm/IntrinsicInst.h"
#include "llvm/LLVMContext.h"
#include "llvm/Type.h"
#include "llvm/Analysis/Dominators.h"
#include "llvm/Analysis/IVUsers.h"
#include "llvm/Analysis/ScalarEvolutionExpander.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/LoopPass.h"
#include "llvm/Support/CFG.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include "llvm/Target/TargetData.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/STLExtras.h"
using namespace llvm;
STATISTIC(NumRemoved , "Number of aux indvars removed");
STATISTIC(NumWidened , "Number of indvars widened");
STATISTIC(NumInserted, "Number of canonical indvars added");
STATISTIC(NumReplaced, "Number of exit values replaced");
STATISTIC(NumLFTR , "Number of loop exit tests replaced");
STATISTIC(NumElimExt , "Number of IV sign/zero extends eliminated");
STATISTIC(NumElimRem , "Number of IV remainder operations eliminated");
STATISTIC(NumElimCmp , "Number of IV comparisons eliminated");
// DisableIVRewrite mode currently affects IVUsers, so is defined in libAnalysis
// and referenced here.
namespace llvm {
extern bool DisableIVRewrite;
}
namespace {
class IndVarSimplify : public LoopPass {
IVUsers *IU;
LoopInfo *LI;
ScalarEvolution *SE;
DominatorTree *DT;
TargetData *TD;
SmallVector<WeakVH, 16> DeadInsts;
bool Changed;
public:
static char ID; // Pass identification, replacement for typeid
IndVarSimplify() : LoopPass(ID), IU(0), LI(0), SE(0), DT(0), TD(0) {
initializeIndVarSimplifyPass(*PassRegistry::getPassRegistry());
}
virtual bool runOnLoop(Loop *L, LPPassManager &LPM);
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequired<DominatorTree>();
AU.addRequired<LoopInfo>();
AU.addRequired<ScalarEvolution>();
AU.addRequiredID(LoopSimplifyID);
AU.addRequiredID(LCSSAID);
AU.addRequired<IVUsers>();
AU.addPreserved<ScalarEvolution>();
AU.addPreservedID(LoopSimplifyID);
AU.addPreservedID(LCSSAID);
AU.addPreserved<IVUsers>();
AU.setPreservesCFG();
}
private:
bool isValidRewrite(Value *FromVal, Value *ToVal);
void SimplifyIVUsers(SCEVExpander &Rewriter);
void EliminateIVComparison(ICmpInst *ICmp, Value *IVOperand);
void EliminateIVRemainder(BinaryOperator *Rem,
Value *IVOperand,
bool IsSigned,
PHINode *IVPhi);
void RewriteNonIntegerIVs(Loop *L);
ICmpInst *LinearFunctionTestReplace(Loop *L, const SCEV *BackedgeTakenCount,
PHINode *IndVar,
SCEVExpander &Rewriter);
void RewriteLoopExitValues(Loop *L, SCEVExpander &Rewriter);
void RewriteIVExpressions(Loop *L, SCEVExpander &Rewriter);
void SinkUnusedInvariants(Loop *L);
void HandleFloatingPointIV(Loop *L, PHINode *PH);
};
}
char IndVarSimplify::ID = 0;
INITIALIZE_PASS_BEGIN(IndVarSimplify, "indvars",
"Induction Variable Simplification", false, false)
INITIALIZE_PASS_DEPENDENCY(DominatorTree)
INITIALIZE_PASS_DEPENDENCY(LoopInfo)
INITIALIZE_PASS_DEPENDENCY(ScalarEvolution)
INITIALIZE_PASS_DEPENDENCY(LoopSimplify)
INITIALIZE_PASS_DEPENDENCY(LCSSA)
INITIALIZE_PASS_DEPENDENCY(IVUsers)
INITIALIZE_PASS_END(IndVarSimplify, "indvars",
"Induction Variable Simplification", false, false)
Pass *llvm::createIndVarSimplifyPass() {
return new IndVarSimplify();
}
/// isValidRewrite - Return true if the SCEV expansion generated by the
/// rewriter can replace the original value. SCEV guarantees that it
/// produces the same value, but the way it is produced may be illegal IR.
/// Ideally, this function will only be called for verification.
bool IndVarSimplify::isValidRewrite(Value *FromVal, Value *ToVal) {
// If an SCEV expression subsumed multiple pointers, its expansion could
// reassociate the GEP changing the base pointer. This is illegal because the
// final address produced by a GEP chain must be inbounds relative to its
// underlying object. Otherwise basic alias analysis, among other things,
// could fail in a dangerous way. Ultimately, SCEV will be improved to avoid
// producing an expression involving multiple pointers. Until then, we must
// bail out here.
//
// Retrieve the pointer operand of the GEP. Don't use GetUnderlyingObject
// because it understands lcssa phis while SCEV does not.
Value *FromPtr = FromVal;
Value *ToPtr = ToVal;
if (GEPOperator *GEP = dyn_cast<GEPOperator>(FromVal)) {
FromPtr = GEP->getPointerOperand();
}
if (GEPOperator *GEP = dyn_cast<GEPOperator>(ToVal)) {
ToPtr = GEP->getPointerOperand();
}
if (FromPtr != FromVal || ToPtr != ToVal) {
// Quickly check the common case
if (FromPtr == ToPtr)
return true;
// SCEV may have rewritten an expression that produces the GEP's pointer
// operand. That's ok as long as the pointer operand has the same base
// pointer. Unlike GetUnderlyingObject(), getPointerBase() will find the
// base of a recurrence. This handles the case in which SCEV expansion
// converts a pointer type recurrence into a nonrecurrent pointer base
// indexed by an integer recurrence.
const SCEV *FromBase = SE->getPointerBase(SE->getSCEV(FromPtr));
const SCEV *ToBase = SE->getPointerBase(SE->getSCEV(ToPtr));
if (FromBase == ToBase)
return true;
DEBUG(dbgs() << "INDVARS: GEP rewrite bail out "
<< *FromBase << " != " << *ToBase << "\n");
return false;
}
return true;
}
/// canExpandBackedgeTakenCount - Return true if this loop's backedge taken
/// count expression can be safely and cheaply expanded into an instruction
/// sequence that can be used by LinearFunctionTestReplace.
static bool canExpandBackedgeTakenCount(Loop *L, ScalarEvolution *SE) {
const SCEV *BackedgeTakenCount = SE->getBackedgeTakenCount(L);
if (isa<SCEVCouldNotCompute>(BackedgeTakenCount) ||
BackedgeTakenCount->isZero())
return false;
if (!L->getExitingBlock())
return false;
// Can't rewrite non-branch yet.
BranchInst *BI = dyn_cast<BranchInst>(L->getExitingBlock()->getTerminator());
if (!BI)
return false;
// Special case: If the backedge-taken count is a UDiv, it's very likely a
// UDiv that ScalarEvolution produced in order to compute a precise
// expression, rather than a UDiv from the user's code. If we can't find a
// UDiv in the code with some simple searching, assume the former and forego
// rewriting the loop.
if (isa<SCEVUDivExpr>(BackedgeTakenCount)) {
ICmpInst *OrigCond = dyn_cast<ICmpInst>(BI->getCondition());
if (!OrigCond) return false;
const SCEV *R = SE->getSCEV(OrigCond->getOperand(1));
R = SE->getMinusSCEV(R, SE->getConstant(R->getType(), 1));
if (R != BackedgeTakenCount) {
const SCEV *L = SE->getSCEV(OrigCond->getOperand(0));
L = SE->getMinusSCEV(L, SE->getConstant(L->getType(), 1));
if (L != BackedgeTakenCount)
return false;
}
}
return true;
}
/// getBackedgeIVType - Get the widest type used by the loop test after peeking
/// through Truncs.
///
/// TODO: Unnecessary once LinearFunctionTestReplace is removed.
static const Type *getBackedgeIVType(Loop *L) {
if (!L->getExitingBlock())
return 0;
// Can't rewrite non-branch yet.
BranchInst *BI = dyn_cast<BranchInst>(L->getExitingBlock()->getTerminator());
if (!BI)
return 0;
ICmpInst *Cond = dyn_cast<ICmpInst>(BI->getCondition());
if (!Cond)
return 0;
const Type *Ty = 0;
for(User::op_iterator OI = Cond->op_begin(), OE = Cond->op_end();
OI != OE; ++OI) {
assert((!Ty || Ty == (*OI)->getType()) && "bad icmp operand types");
TruncInst *Trunc = dyn_cast<TruncInst>(*OI);
if (!Trunc)
continue;
return Trunc->getSrcTy();
}
return Ty;
}
/// LinearFunctionTestReplace - This method rewrites the exit condition of the
/// loop to be a canonical != comparison against the incremented loop induction
/// variable. This pass is able to rewrite the exit tests of any loop where the
/// SCEV analysis can determine a loop-invariant trip count of the loop, which
/// is actually a much broader range than just linear tests.
ICmpInst *IndVarSimplify::
LinearFunctionTestReplace(Loop *L,
const SCEV *BackedgeTakenCount,
PHINode *IndVar,
SCEVExpander &Rewriter) {
assert(canExpandBackedgeTakenCount(L, SE) && "precondition");
BranchInst *BI = cast<BranchInst>(L->getExitingBlock()->getTerminator());
// If the exiting block is not the same as the backedge block, we must compare
// against the preincremented value, otherwise we prefer to compare against
// the post-incremented value.
Value *CmpIndVar;
const SCEV *RHS = BackedgeTakenCount;
if (L->getExitingBlock() == L->getLoopLatch()) {
// Add one to the "backedge-taken" count to get the trip count.
// If this addition may overflow, we have to be more pessimistic and
// cast the induction variable before doing the add.
const SCEV *Zero = SE->getConstant(BackedgeTakenCount->getType(), 0);
const SCEV *N =
SE->getAddExpr(BackedgeTakenCount,
SE->getConstant(BackedgeTakenCount->getType(), 1));
if ((isa<SCEVConstant>(N) && !N->isZero()) ||
SE->isLoopEntryGuardedByCond(L, ICmpInst::ICMP_NE, N, Zero)) {
// No overflow. Cast the sum.
RHS = SE->getTruncateOrZeroExtend(N, IndVar->getType());
} else {
// Potential overflow. Cast before doing the add.
RHS = SE->getTruncateOrZeroExtend(BackedgeTakenCount,
IndVar->getType());
RHS = SE->getAddExpr(RHS,
SE->getConstant(IndVar->getType(), 1));
}
// The BackedgeTaken expression contains the number of times that the
// backedge branches to the loop header. This is one less than the
// number of times the loop executes, so use the incremented indvar.
CmpIndVar = IndVar->getIncomingValueForBlock(L->getExitingBlock());
} else {
// We have to use the preincremented value...
RHS = SE->getTruncateOrZeroExtend(BackedgeTakenCount,
IndVar->getType());
CmpIndVar = IndVar;
}
// Expand the code for the iteration count.
assert(SE->isLoopInvariant(RHS, L) &&
"Computed iteration count is not loop invariant!");
Value *ExitCnt = Rewriter.expandCodeFor(RHS, IndVar->getType(), BI);
// Insert a new icmp_ne or icmp_eq instruction before the branch.
ICmpInst::Predicate Opcode;
if (L->contains(BI->getSuccessor(0)))
Opcode = ICmpInst::ICMP_NE;
else
Opcode = ICmpInst::ICMP_EQ;
DEBUG(dbgs() << "INDVARS: Rewriting loop exit condition to:\n"
<< " LHS:" << *CmpIndVar << '\n'
<< " op:\t"
<< (Opcode == ICmpInst::ICMP_NE ? "!=" : "==") << "\n"
<< " RHS:\t" << *RHS << "\n");
ICmpInst *Cond = new ICmpInst(BI, Opcode, CmpIndVar, ExitCnt, "exitcond");
Value *OrigCond = BI->getCondition();
// It's tempting to use replaceAllUsesWith here to fully replace the old
// comparison, but that's not immediately safe, since users of the old
// comparison may not be dominated by the new comparison. Instead, just
// update the branch to use the new comparison; in the common case this
// will make old comparison dead.
BI->setCondition(Cond);
DeadInsts.push_back(OrigCond);
++NumLFTR;
Changed = true;
return Cond;
}
/// RewriteLoopExitValues - Check to see if this loop has a computable
/// loop-invariant execution count. If so, this means that we can compute the
/// final value of any expressions that are recurrent in the loop, and
/// substitute the exit values from the loop into any instructions outside of
/// the loop that use the final values of the current expressions.
///
/// This is mostly redundant with the regular IndVarSimplify activities that
/// happen later, except that it's more powerful in some cases, because it's
/// able to brute-force evaluate arbitrary instructions as long as they have
/// constant operands at the beginning of the loop.
void IndVarSimplify::RewriteLoopExitValues(Loop *L, SCEVExpander &Rewriter) {
// Verify the input to the pass in already in LCSSA form.
assert(L->isLCSSAForm(*DT));
SmallVector<BasicBlock*, 8> ExitBlocks;
L->getUniqueExitBlocks(ExitBlocks);
// Find all values that are computed inside the loop, but used outside of it.
// Because of LCSSA, these values will only occur in LCSSA PHI Nodes. Scan
// the exit blocks of the loop to find them.
for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) {
BasicBlock *ExitBB = ExitBlocks[i];
// If there are no PHI nodes in this exit block, then no values defined
// inside the loop are used on this path, skip it.
PHINode *PN = dyn_cast<PHINode>(ExitBB->begin());
if (!PN) continue;
unsigned NumPreds = PN->getNumIncomingValues();
// Iterate over all of the PHI nodes.
BasicBlock::iterator BBI = ExitBB->begin();
while ((PN = dyn_cast<PHINode>(BBI++))) {
if (PN->use_empty())
continue; // dead use, don't replace it
// SCEV only supports integer expressions for now.
if (!PN->getType()->isIntegerTy() && !PN->getType()->isPointerTy())
continue;
// It's necessary to tell ScalarEvolution about this explicitly so that
// it can walk the def-use list and forget all SCEVs, as it may not be
// watching the PHI itself. Once the new exit value is in place, there
// may not be a def-use connection between the loop and every instruction
// which got a SCEVAddRecExpr for that loop.
SE->forgetValue(PN);
// Iterate over all of the values in all the PHI nodes.
for (unsigned i = 0; i != NumPreds; ++i) {
// If the value being merged in is not integer or is not defined
// in the loop, skip it.
Value *InVal = PN->getIncomingValue(i);
if (!isa<Instruction>(InVal))
continue;
// If this pred is for a subloop, not L itself, skip it.
if (LI->getLoopFor(PN->getIncomingBlock(i)) != L)
continue; // The Block is in a subloop, skip it.
// Check that InVal is defined in the loop.
Instruction *Inst = cast<Instruction>(InVal);
if (!L->contains(Inst))
continue;
// Okay, this instruction has a user outside of the current loop
// and varies predictably *inside* the loop. Evaluate the value it
// contains when the loop exits, if possible.
const SCEV *ExitValue = SE->getSCEVAtScope(Inst, L->getParentLoop());
if (!SE->isLoopInvariant(ExitValue, L))
continue;
Value *ExitVal = Rewriter.expandCodeFor(ExitValue, PN->getType(), Inst);
DEBUG(dbgs() << "INDVARS: RLEV: AfterLoopVal = " << *ExitVal << '\n'
<< " LoopVal = " << *Inst << "\n");
if (!isValidRewrite(Inst, ExitVal)) {
DeadInsts.push_back(ExitVal);
continue;
}
Changed = true;
++NumReplaced;
PN->setIncomingValue(i, ExitVal);
// If this instruction is dead now, delete it.
RecursivelyDeleteTriviallyDeadInstructions(Inst);
if (NumPreds == 1) {
// Completely replace a single-pred PHI. This is safe, because the
// NewVal won't be variant in the loop, so we don't need an LCSSA phi
// node anymore.
PN->replaceAllUsesWith(ExitVal);
RecursivelyDeleteTriviallyDeadInstructions(PN);
}
}
if (NumPreds != 1) {
// Clone the PHI and delete the original one. This lets IVUsers and
// any other maps purge the original user from their records.
PHINode *NewPN = cast<PHINode>(PN->clone());
NewPN->takeName(PN);
NewPN->insertBefore(PN);
PN->replaceAllUsesWith(NewPN);
PN->eraseFromParent();
}
}
}
// The insertion point instruction may have been deleted; clear it out
// so that the rewriter doesn't trip over it later.
Rewriter.clearInsertPoint();
}
void IndVarSimplify::RewriteNonIntegerIVs(Loop *L) {
// First step. Check to see if there are any floating-point recurrences.
// If there are, change them into integer recurrences, permitting analysis by
// the SCEV routines.
//
BasicBlock *Header = L->getHeader();
SmallVector<WeakVH, 8> PHIs;
for (BasicBlock::iterator I = Header->begin();
PHINode *PN = dyn_cast<PHINode>(I); ++I)
PHIs.push_back(PN);
for (unsigned i = 0, e = PHIs.size(); i != e; ++i)
if (PHINode *PN = dyn_cast_or_null<PHINode>(&*PHIs[i]))
HandleFloatingPointIV(L, PN);
// If the loop previously had floating-point IV, ScalarEvolution
// may not have been able to compute a trip count. Now that we've done some
// re-writing, the trip count may be computable.
if (Changed)
SE->forgetLoop(L);
}
namespace {
// Collect information about induction variables that are used by sign/zero
// extend operations. This information is recorded by CollectExtend and
// provides the input to WidenIV.
struct WideIVInfo {
const Type *WidestNativeType; // Widest integer type created [sz]ext
bool IsSigned; // Was an sext user seen before a zext?
WideIVInfo() : WidestNativeType(0), IsSigned(false) {}
};
typedef std::map<PHINode *, WideIVInfo> WideIVMap;
}
/// CollectExtend - Update information about the induction variable that is
/// extended by this sign or zero extend operation. This is used to determine
/// the final width of the IV before actually widening it.
static void CollectExtend(CastInst *Cast, PHINode *Phi, bool IsSigned,
WideIVMap &IVMap, ScalarEvolution *SE,
const TargetData *TD) {
const Type *Ty = Cast->getType();
uint64_t Width = SE->getTypeSizeInBits(Ty);
if (TD && !TD->isLegalInteger(Width))
return;
WideIVInfo &IVInfo = IVMap[Phi];
if (!IVInfo.WidestNativeType) {
IVInfo.WidestNativeType = SE->getEffectiveSCEVType(Ty);
IVInfo.IsSigned = IsSigned;
return;
}
// We extend the IV to satisfy the sign of its first user, arbitrarily.
if (IVInfo.IsSigned != IsSigned)
return;
if (Width > SE->getTypeSizeInBits(IVInfo.WidestNativeType))
IVInfo.WidestNativeType = SE->getEffectiveSCEVType(Ty);
}
namespace {
/// WidenIV - The goal of this transform is to remove sign and zero extends
/// without creating any new induction variables. To do this, it creates a new
/// phi of the wider type and redirects all users, either removing extends or
/// inserting truncs whenever we stop propagating the type.
///
class WidenIV {
PHINode *OrigPhi;
const Type *WideType;
bool IsSigned;
IVUsers *IU;
LoopInfo *LI;
Loop *L;
ScalarEvolution *SE;
DominatorTree *DT;
SmallVectorImpl<WeakVH> &DeadInsts;
PHINode *WidePhi;
Instruction *WideInc;
const SCEV *WideIncExpr;
SmallPtrSet<Instruction*,16> Processed;
public:
WidenIV(PHINode *PN, const WideIVInfo &IVInfo, IVUsers *IUsers,
LoopInfo *LInfo, ScalarEvolution *SEv, DominatorTree *DTree,
SmallVectorImpl<WeakVH> &DI) :
OrigPhi(PN),
WideType(IVInfo.WidestNativeType),
IsSigned(IVInfo.IsSigned),
IU(IUsers),
LI(LInfo),
L(LI->getLoopFor(OrigPhi->getParent())),
SE(SEv),
DT(DTree),
DeadInsts(DI),
WidePhi(0),
WideInc(0),
WideIncExpr(0) {
assert(L->getHeader() == OrigPhi->getParent() && "Phi must be an IV");
}
bool CreateWideIV(SCEVExpander &Rewriter);
protected:
Instruction *CloneIVUser(Instruction *NarrowUse,
Instruction *NarrowDef,
Instruction *WideDef);
const SCEVAddRecExpr *GetWideRecurrence(Instruction *NarrowUse);
Instruction *WidenIVUse(Instruction *NarrowUse,
Instruction *NarrowDef,
Instruction *WideDef);
};
} // anonymous namespace
/// SimplifyIVUsers - Iteratively perform simplification on IVUsers within this
/// loop. IVUsers is treated as a worklist. Each successive simplification may
/// push more users which may themselves be candidates for simplification.
///
void IndVarSimplify::SimplifyIVUsers(SCEVExpander &Rewriter) {
WideIVMap IVMap;
// Each round of simplification involves a round of eliminating operations
// followed by a round of widening IVs. A single IVUsers worklist is used
// across all rounds. The inner loop advances the user. If widening exposes
// more uses, then another pass through the outer loop is triggered.
for (IVUsers::iterator I = IU->begin(), E = IU->end(); I != E;) {
for(; I != E; ++I) {
Instruction *UseInst = I->getUser();
Value *IVOperand = I->getOperandValToReplace();
if (DisableIVRewrite) {
if (CastInst *Cast = dyn_cast<CastInst>(UseInst)) {
bool IsSigned = Cast->getOpcode() == Instruction::SExt;
if (IsSigned || Cast->getOpcode() == Instruction::ZExt) {
CollectExtend(Cast, I->getPhi(), IsSigned, IVMap, SE, TD);
continue;
}
}
}
if (ICmpInst *ICmp = dyn_cast<ICmpInst>(UseInst)) {
EliminateIVComparison(ICmp, IVOperand);
continue;
}
if (BinaryOperator *Rem = dyn_cast<BinaryOperator>(UseInst)) {
bool IsSigned = Rem->getOpcode() == Instruction::SRem;
if (IsSigned || Rem->getOpcode() == Instruction::URem) {
EliminateIVRemainder(Rem, IVOperand, IsSigned, I->getPhi());
continue;
}
}
}
for (WideIVMap::const_iterator I = IVMap.begin(), E = IVMap.end();
I != E; ++I) {
WidenIV Widener(I->first, I->second, IU, LI, SE, DT, DeadInsts);
if (Widener.CreateWideIV(Rewriter))
Changed = true;
}
}
}
static Value *getExtend( Value *NarrowOper, const Type *WideType,
bool IsSigned, IRBuilder<> &Builder) {
return IsSigned ? Builder.CreateSExt(NarrowOper, WideType) :
Builder.CreateZExt(NarrowOper, WideType);
}
/// CloneIVUser - Instantiate a wide operation to replace a narrow
/// operation. This only needs to handle operations that can evaluation to
/// SCEVAddRec. It can safely return 0 for any operation we decide not to clone.
Instruction *WidenIV::CloneIVUser(Instruction *NarrowUse,
Instruction *NarrowDef,
Instruction *WideDef) {
unsigned Opcode = NarrowUse->getOpcode();
switch (Opcode) {
default:
return 0;
case Instruction::Add:
case Instruction::Mul:
case Instruction::UDiv:
case Instruction::Sub:
case Instruction::And:
case Instruction::Or:
case Instruction::Xor:
case Instruction::Shl:
case Instruction::LShr:
case Instruction::AShr:
DEBUG(dbgs() << "Cloning IVUser: " << *NarrowUse << "\n");
IRBuilder<> Builder(NarrowUse);
// Replace NarrowDef operands with WideDef. Otherwise, we don't know
// anything about the narrow operand yet so must insert a [sz]ext. It is
// probably loop invariant and will be folded or hoisted. If it actually
// comes from a widened IV, it should be removed during a future call to
// WidenIVUse.
Value *LHS = (NarrowUse->getOperand(0) == NarrowDef) ? WideDef :
getExtend(NarrowUse->getOperand(0), WideType, IsSigned, Builder);
Value *RHS = (NarrowUse->getOperand(1) == NarrowDef) ? WideDef :
getExtend(NarrowUse->getOperand(1), WideType, IsSigned, Builder);
BinaryOperator *NarrowBO = cast<BinaryOperator>(NarrowUse);
BinaryOperator *WideBO = BinaryOperator::Create(NarrowBO->getOpcode(),
LHS, RHS,
NarrowBO->getName());
Builder.Insert(WideBO);
if (NarrowBO->hasNoUnsignedWrap()) WideBO->setHasNoUnsignedWrap();
if (NarrowBO->hasNoSignedWrap()) WideBO->setHasNoSignedWrap();
return WideBO;
}
llvm_unreachable(0);
}
// GetWideRecurrence - Is this instruction potentially interesting from IVUsers'
// perspective after widening it's type? In other words, can the extend be
// safely hoisted out of the loop with SCEV reducing the value to a recurrence
// on the same loop. If so, return the sign or zero extended
// recurrence. Otherwise return NULL.
const SCEVAddRecExpr *WidenIV::GetWideRecurrence(Instruction *NarrowUse) {
if (!SE->isSCEVable(NarrowUse->getType()))
return 0;
const SCEV *NarrowExpr = SE->getSCEV(NarrowUse);
const SCEV *WideExpr = IsSigned ?
SE->getSignExtendExpr(NarrowExpr, WideType) :
SE->getZeroExtendExpr(NarrowExpr, WideType);
const SCEVAddRecExpr *AddRec = dyn_cast<SCEVAddRecExpr>(WideExpr);
if (!AddRec || AddRec->getLoop() != L)
return 0;
return AddRec;
}
/// HoistStep - Attempt to hoist an IV increment above a potential use.
///
/// To successfully hoist, two criteria must be met:
/// - IncV operands dominate InsertPos and
/// - InsertPos dominates IncV
///
/// Meeting the second condition means that we don't need to check all of IncV's
/// existing uses (it's moving up in the domtree).
///
/// This does not yet recursively hoist the operands, although that would
/// not be difficult.
static bool HoistStep(Instruction *IncV, Instruction *InsertPos,
const DominatorTree *DT)
{
if (DT->dominates(IncV, InsertPos))
return true;
if (!DT->dominates(InsertPos->getParent(), IncV->getParent()))
return false;
if (IncV->mayHaveSideEffects())
return false;
// Attempt to hoist IncV
for (User::op_iterator OI = IncV->op_begin(), OE = IncV->op_end();
OI != OE; ++OI) {
Instruction *OInst = dyn_cast<Instruction>(OI);
if (OInst && !DT->dominates(OInst, InsertPos))
return false;
}
IncV->moveBefore(InsertPos);
return true;
}
/// WidenIVUse - Determine whether an individual user of the narrow IV can be
/// widened. If so, return the wide clone of the user.
Instruction *WidenIV::WidenIVUse(Instruction *NarrowUse,
Instruction *NarrowDef,
Instruction *WideDef) {
// To be consistent with IVUsers, stop traversing the def-use chain at
// inner-loop phis or post-loop phis.
if (isa<PHINode>(NarrowUse) && LI->getLoopFor(NarrowUse->getParent()) != L)
return 0;
// Handle data flow merges and bizarre phi cycles.
if (!Processed.insert(NarrowUse))
return 0;
// Our raison d'etre! Eliminate sign and zero extension.
if (IsSigned ? isa<SExtInst>(NarrowUse) : isa<ZExtInst>(NarrowUse)) {
Value *NewDef = WideDef;
if (NarrowUse->getType() != WideType) {
unsigned CastWidth = SE->getTypeSizeInBits(NarrowUse->getType());
unsigned IVWidth = SE->getTypeSizeInBits(WideType);
if (CastWidth < IVWidth) {
// The cast isn't as wide as the IV, so insert a Trunc.
IRBuilder<> Builder(NarrowUse);
NewDef = Builder.CreateTrunc(WideDef, NarrowUse->getType());
}
else {
// A wider extend was hidden behind a narrower one. This may induce
// another round of IV widening in which the intermediate IV becomes
// dead. It should be very rare.
DEBUG(dbgs() << "INDVARS: New IV " << *WidePhi
<< " not wide enough to subsume " << *NarrowUse << "\n");
NarrowUse->replaceUsesOfWith(NarrowDef, WideDef);
NewDef = NarrowUse;
}
}
if (NewDef != NarrowUse) {
DEBUG(dbgs() << "INDVARS: eliminating " << *NarrowUse
<< " replaced by " << *WideDef << "\n");
++NumElimExt;
NarrowUse->replaceAllUsesWith(NewDef);
DeadInsts.push_back(NarrowUse);
}
// Now that the extend is gone, expose it's uses to IVUsers for potential
// further simplification within SimplifyIVUsers.
IU->AddUsersIfInteresting(WideDef, WidePhi);
// No further widening is needed. The deceased [sz]ext had done it for us.
return 0;
}
const SCEVAddRecExpr *WideAddRec = GetWideRecurrence(NarrowUse);
if (!WideAddRec) {
// This user does not evaluate to a recurence after widening, so don't
// follow it. Instead insert a Trunc to kill off the original use,
// eventually isolating the original narrow IV so it can be removed.
IRBuilder<> Builder(NarrowUse);
Value *Trunc = Builder.CreateTrunc(WideDef, NarrowDef->getType());
NarrowUse->replaceUsesOfWith(NarrowDef, Trunc);
return 0;
}
// Reuse the IV increment that SCEVExpander created as long as it dominates
// NarrowUse.
Instruction *WideUse = 0;
if (WideAddRec == WideIncExpr && HoistStep(WideInc, NarrowUse, DT)) {
WideUse = WideInc;
}
else {
WideUse = CloneIVUser(NarrowUse, NarrowDef, WideDef);
if (!WideUse)
return 0;
}
// GetWideRecurrence ensured that the narrow expression could be extended
// outside the loop without overflow. This suggests that the wide use
// evaluates to the same expression as the extended narrow use, but doesn't
// absolutely guarantee it. Hence the following failsafe check. In rare cases
// where it fails, we simple throw away the newly created wide use.
if (WideAddRec != SE->getSCEV(WideUse)) {
DEBUG(dbgs() << "Wide use expression mismatch: " << *WideUse
<< ": " << *SE->getSCEV(WideUse) << " != " << *WideAddRec << "\n");
DeadInsts.push_back(WideUse);
return 0;
}
// Returning WideUse pushes it on the worklist.
return WideUse;
}
/// CreateWideIV - Process a single induction variable. First use the
/// SCEVExpander to create a wide induction variable that evaluates to the same
/// recurrence as the original narrow IV. Then use a worklist to forward
/// traverse the narrow IV's def-use chain. After WidenIVUse as processed all
/// interesting IV users, the narrow IV will be isolated for removal by
/// DeleteDeadPHIs.
///
/// It would be simpler to delete uses as they are processed, but we must avoid
/// invalidating SCEV expressions.
///
bool WidenIV::CreateWideIV(SCEVExpander &Rewriter) {
// Is this phi an induction variable?
const SCEVAddRecExpr *AddRec = dyn_cast<SCEVAddRecExpr>(SE->getSCEV(OrigPhi));
if (!AddRec)
return false;
// Widen the induction variable expression.
const SCEV *WideIVExpr = IsSigned ?
SE->getSignExtendExpr(AddRec, WideType) :
SE->getZeroExtendExpr(AddRec, WideType);
assert(SE->getEffectiveSCEVType(WideIVExpr->getType()) == WideType &&
"Expect the new IV expression to preserve its type");
// Can the IV be extended outside the loop without overflow?
AddRec = dyn_cast<SCEVAddRecExpr>(WideIVExpr);
if (!AddRec || AddRec->getLoop() != L)
return false;
// An AddRec must have loop-invariant operands. Since this AddRec it
// materialized by a loop header phi, the expression cannot have any post-loop
// operands, so they must dominate the loop header.
assert(SE->properlyDominates(AddRec->getStart(), L->getHeader()) &&
SE->properlyDominates(AddRec->getStepRecurrence(*SE), L->getHeader())
&& "Loop header phi recurrence inputs do not dominate the loop");
// The rewriter provides a value for the desired IV expression. This may
// either find an existing phi or materialize a new one. Either way, we
// expect a well-formed cyclic phi-with-increments. i.e. any operand not part
// of the phi-SCC dominates the loop entry.
Instruction *InsertPt = L->getHeader()->begin();
WidePhi = cast<PHINode>(Rewriter.expandCodeFor(AddRec, WideType, InsertPt));
// Remembering the WideIV increment generated by SCEVExpander allows
// WidenIVUse to reuse it when widening the narrow IV's increment. We don't
// employ a general reuse mechanism because the call above is the only call to
// SCEVExpander. Henceforth, we produce 1-to-1 narrow to wide uses.
if (BasicBlock *LatchBlock = L->getLoopLatch()) {
WideInc =
cast<Instruction>(WidePhi->getIncomingValueForBlock(LatchBlock));
WideIncExpr = SE->getSCEV(WideInc);
}
DEBUG(dbgs() << "Wide IV: " << *WidePhi << "\n");
++NumWidened;
// Traverse the def-use chain using a worklist starting at the original IV.
assert(Processed.empty() && "expect initial state" );
// Each worklist entry has a Narrow def-use link and Wide def.
SmallVector<std::pair<Use *, Instruction *>, 8> NarrowIVUsers;
for (Value::use_iterator UI = OrigPhi->use_begin(),
UE = OrigPhi->use_end(); UI != UE; ++UI) {
NarrowIVUsers.push_back(std::make_pair(&UI.getUse(), WidePhi));
}
while (!NarrowIVUsers.empty()) {
Use *NarrowDefUse;
Instruction *WideDef;
tie(NarrowDefUse, WideDef) = NarrowIVUsers.pop_back_val();
// Process a def-use edge. This may replace the use, so don't hold a
// use_iterator across it.
Instruction *NarrowDef = cast<Instruction>(NarrowDefUse->get());
Instruction *NarrowUse = cast<Instruction>(NarrowDefUse->getUser());
Instruction *WideUse = WidenIVUse(NarrowUse, NarrowDef, WideDef);
// Follow all def-use edges from the previous narrow use.
if (WideUse) {
for (Value::use_iterator UI = NarrowUse->use_begin(),
UE = NarrowUse->use_end(); UI != UE; ++UI) {
NarrowIVUsers.push_back(std::make_pair(&UI.getUse(), WideUse));
}
}
// WidenIVUse may have removed the def-use edge.
if (NarrowDef->use_empty())
DeadInsts.push_back(NarrowDef);
}
return true;
}
void IndVarSimplify::EliminateIVComparison(ICmpInst *ICmp, Value *IVOperand) {
unsigned IVOperIdx = 0;
ICmpInst::Predicate Pred = ICmp->getPredicate();
if (IVOperand != ICmp->getOperand(0)) {
// Swapped
assert(IVOperand == ICmp->getOperand(1) && "Can't find IVOperand");
IVOperIdx = 1;
Pred = ICmpInst::getSwappedPredicate(Pred);
}
// Get the SCEVs for the ICmp operands.
const SCEV *S = SE->getSCEV(ICmp->getOperand(IVOperIdx));
const SCEV *X = SE->getSCEV(ICmp->getOperand(1 - IVOperIdx));
// Simplify unnecessary loops away.
const Loop *ICmpLoop = LI->getLoopFor(ICmp->getParent());
S = SE->getSCEVAtScope(S, ICmpLoop);
X = SE->getSCEVAtScope(X, ICmpLoop);
// If the condition is always true or always false, replace it with
// a constant value.
if (SE->isKnownPredicate(Pred, S, X))
ICmp->replaceAllUsesWith(ConstantInt::getTrue(ICmp->getContext()));
else if (SE->isKnownPredicate(ICmpInst::getInversePredicate(Pred), S, X))
ICmp->replaceAllUsesWith(ConstantInt::getFalse(ICmp->getContext()));
else
return;
DEBUG(dbgs() << "INDVARS: Eliminated comparison: " << *ICmp << '\n');
++NumElimCmp;
Changed = true;
DeadInsts.push_back(ICmp);
}
void IndVarSimplify::EliminateIVRemainder(BinaryOperator *Rem,
Value *IVOperand,
bool IsSigned,
PHINode *IVPhi) {
// We're only interested in the case where we know something about
// the numerator.
if (IVOperand != Rem->getOperand(0))
return;
// Get the SCEVs for the ICmp operands.
const SCEV *S = SE->getSCEV(Rem->getOperand(0));
const SCEV *X = SE->getSCEV(Rem->getOperand(1));
// Simplify unnecessary loops away.
const Loop *ICmpLoop = LI->getLoopFor(Rem->getParent());
S = SE->getSCEVAtScope(S, ICmpLoop);
X = SE->getSCEVAtScope(X, ICmpLoop);
// i % n --> i if i is in [0,n).
if ((!IsSigned || SE->isKnownNonNegative(S)) &&
SE->isKnownPredicate(IsSigned ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
S, X))
Rem->replaceAllUsesWith(Rem->getOperand(0));
else {
// (i+1) % n --> (i+1)==n?0:(i+1) if i is in [0,n).
const SCEV *LessOne =
SE->getMinusSCEV(S, SE->getConstant(S->getType(), 1));
if (IsSigned && !SE->isKnownNonNegative(LessOne))
return;
if (!SE->isKnownPredicate(IsSigned ?
ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
LessOne, X))
return;
ICmpInst *ICmp = new ICmpInst(Rem, ICmpInst::ICMP_EQ,
Rem->getOperand(0), Rem->getOperand(1),
"tmp");
SelectInst *Sel =
SelectInst::Create(ICmp,
ConstantInt::get(Rem->getType(), 0),
Rem->getOperand(0), "tmp", Rem);
Rem->replaceAllUsesWith(Sel);
}
// Inform IVUsers about the new users.
if (Instruction *I = dyn_cast<Instruction>(Rem->getOperand(0)))
IU->AddUsersIfInteresting(I, IVPhi);
DEBUG(dbgs() << "INDVARS: Simplified rem: " << *Rem << '\n');
++NumElimRem;
Changed = true;
DeadInsts.push_back(Rem);
}
bool IndVarSimplify::runOnLoop(Loop *L, LPPassManager &LPM) {
// If LoopSimplify form is not available, stay out of trouble. Some notes:
// - LSR currently only supports LoopSimplify-form loops. Indvars'
// canonicalization can be a pessimization without LSR to "clean up"
// afterwards.
// - We depend on having a preheader; in particular,
// Loop::getCanonicalInductionVariable only supports loops with preheaders,
// and we're in trouble if we can't find the induction variable even when
// we've manually inserted one.
if (!L->isLoopSimplifyForm())
return false;
IU = &getAnalysis<IVUsers>();
LI = &getAnalysis<LoopInfo>();
SE = &getAnalysis<ScalarEvolution>();
DT = &getAnalysis<DominatorTree>();
TD = getAnalysisIfAvailable<TargetData>();
DeadInsts.clear();
Changed = false;
// If there are any floating-point recurrences, attempt to
// transform them to use integer recurrences.
RewriteNonIntegerIVs(L);
const SCEV *BackedgeTakenCount = SE->getBackedgeTakenCount(L);
// Create a rewriter object which we'll use to transform the code with.
SCEVExpander Rewriter(*SE);
if (DisableIVRewrite)
Rewriter.disableCanonicalMode();
// Check to see if this loop has a computable loop-invariant execution count.
// If so, this means that we can compute the final value of any expressions
// that are recurrent in the loop, and substitute the exit values from the
// loop into any instructions outside of the loop that use the final values of
// the current expressions.
//
if (!isa<SCEVCouldNotCompute>(BackedgeTakenCount))
RewriteLoopExitValues(L, Rewriter);
// Eliminate redundant IV users.
SimplifyIVUsers(Rewriter);
// Compute the type of the largest recurrence expression, and decide whether
// a canonical induction variable should be inserted.
const Type *LargestType = 0;
bool NeedCannIV = false;
bool ExpandBECount = canExpandBackedgeTakenCount(L, SE);
if (ExpandBECount) {
// If we have a known trip count and a single exit block, we'll be
// rewriting the loop exit test condition below, which requires a
// canonical induction variable.
NeedCannIV = true;
const Type *Ty = BackedgeTakenCount->getType();
if (DisableIVRewrite) {
// In this mode, SimplifyIVUsers may have already widened the IV used by
// the backedge test and inserted a Trunc on the compare's operand. Get
// the wider type to avoid creating a redundant narrow IV only used by the
// loop test.
LargestType = getBackedgeIVType(L);
}
if (!LargestType ||
SE->getTypeSizeInBits(Ty) >
SE->getTypeSizeInBits(LargestType))
LargestType = SE->getEffectiveSCEVType(Ty);
}
if (!DisableIVRewrite) {
for (IVUsers::const_iterator I = IU->begin(), E = IU->end(); I != E; ++I) {
NeedCannIV = true;
const Type *Ty =
SE->getEffectiveSCEVType(I->getOperandValToReplace()->getType());
if (!LargestType ||
SE->getTypeSizeInBits(Ty) >
SE->getTypeSizeInBits(LargestType))
LargestType = Ty;
}
}
// Now that we know the largest of the induction variable expressions
// in this loop, insert a canonical induction variable of the largest size.
PHINode *IndVar = 0;
if (NeedCannIV) {
// Check to see if the loop already has any canonical-looking induction
// variables. If any are present and wider than the planned canonical
// induction variable, temporarily remove them, so that the Rewriter
// doesn't attempt to reuse them.
SmallVector<PHINode *, 2> OldCannIVs;
while (PHINode *OldCannIV = L->getCanonicalInductionVariable()) {
if (SE->getTypeSizeInBits(OldCannIV->getType()) >
SE->getTypeSizeInBits(LargestType))
OldCannIV->removeFromParent();
else
break;
OldCannIVs.push_back(OldCannIV);
}
IndVar = Rewriter.getOrInsertCanonicalInductionVariable(L, LargestType);
++NumInserted;
Changed = true;
DEBUG(dbgs() << "INDVARS: New CanIV: " << *IndVar << '\n');
// Now that the official induction variable is established, reinsert
// any old canonical-looking variables after it so that the IR remains
// consistent. They will be deleted as part of the dead-PHI deletion at
// the end of the pass.
while (!OldCannIVs.empty()) {
PHINode *OldCannIV = OldCannIVs.pop_back_val();
OldCannIV->insertBefore(L->getHeader()->getFirstNonPHI());
}
}
// If we have a trip count expression, rewrite the loop's exit condition
// using it. We can currently only handle loops with a single exit.
ICmpInst *NewICmp = 0;
if (ExpandBECount) {
assert(canExpandBackedgeTakenCount(L, SE) &&
"canonical IV disrupted BackedgeTaken expansion");
assert(NeedCannIV &&
"LinearFunctionTestReplace requires a canonical induction variable");
NewICmp = LinearFunctionTestReplace(L, BackedgeTakenCount, IndVar,
Rewriter);
}
// Rewrite IV-derived expressions.
if (!DisableIVRewrite)
RewriteIVExpressions(L, Rewriter);
// Clear the rewriter cache, because values that are in the rewriter's cache
// can be deleted in the loop below, causing the AssertingVH in the cache to
// trigger.
Rewriter.clear();
// Now that we're done iterating through lists, clean up any instructions
// which are now dead.
while (!DeadInsts.empty())
if (Instruction *Inst =
dyn_cast_or_null<Instruction>(&*DeadInsts.pop_back_val()))
RecursivelyDeleteTriviallyDeadInstructions(Inst);
// The Rewriter may not be used from this point on.
// Loop-invariant instructions in the preheader that aren't used in the
// loop may be sunk below the loop to reduce register pressure.
SinkUnusedInvariants(L);
// For completeness, inform IVUsers of the IV use in the newly-created
// loop exit test instruction.
if (NewICmp)
IU->AddUsersIfInteresting(cast<Instruction>(NewICmp->getOperand(0)),
IndVar);
// Clean up dead instructions.
Changed |= DeleteDeadPHIs(L->getHeader());
// Check a post-condition.
assert(L->isLCSSAForm(*DT) && "Indvars did not leave the loop in lcssa form!");
return Changed;
}
// FIXME: It is an extremely bad idea to indvar substitute anything more
// complex than affine induction variables. Doing so will put expensive
// polynomial evaluations inside of the loop, and the str reduction pass
// currently can only reduce affine polynomials. For now just disable
// indvar subst on anything more complex than an affine addrec, unless
// it can be expanded to a trivial value.
static bool isSafe(const SCEV *S, const Loop *L, ScalarEvolution *SE) {
// Loop-invariant values are safe.
if (SE->isLoopInvariant(S, L)) return true;
// Affine addrecs are safe. Non-affine are not, because LSR doesn't know how
// to transform them into efficient code.
if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S))
return AR->isAffine();
// An add is safe it all its operands are safe.
if (const SCEVCommutativeExpr *Commutative = dyn_cast<SCEVCommutativeExpr>(S)) {
for (SCEVCommutativeExpr::op_iterator I = Commutative->op_begin(),
E = Commutative->op_end(); I != E; ++I)
if (!isSafe(*I, L, SE)) return false;
return true;
}
// A cast is safe if its operand is.
if (const SCEVCastExpr *C = dyn_cast<SCEVCastExpr>(S))
return isSafe(C->getOperand(), L, SE);
// A udiv is safe if its operands are.
if (const SCEVUDivExpr *UD = dyn_cast<SCEVUDivExpr>(S))
return isSafe(UD->getLHS(), L, SE) &&
isSafe(UD->getRHS(), L, SE);
// SCEVUnknown is always safe.
if (isa<SCEVUnknown>(S))
return true;
// Nothing else is safe.
return false;
}
void IndVarSimplify::RewriteIVExpressions(Loop *L, SCEVExpander &Rewriter) {
// Rewrite all induction variable expressions in terms of the canonical
// induction variable.
//
// If there were induction variables of other sizes or offsets, manually
// add the offsets to the primary induction variable and cast, avoiding
// the need for the code evaluation methods to insert induction variables
// of different sizes.
for (IVUsers::iterator UI = IU->begin(), E = IU->end(); UI != E; ++UI) {
Value *Op = UI->getOperandValToReplace();
const Type *UseTy = Op->getType();
Instruction *User = UI->getUser();
// Compute the final addrec to expand into code.
const SCEV *AR = IU->getReplacementExpr(*UI);
// Evaluate the expression out of the loop, if possible.
if (!L->contains(UI->getUser())) {
const SCEV *ExitVal = SE->getSCEVAtScope(AR, L->getParentLoop());
if (SE->isLoopInvariant(ExitVal, L))
AR = ExitVal;
}
// FIXME: It is an extremely bad idea to indvar substitute anything more
// complex than affine induction variables. Doing so will put expensive
// polynomial evaluations inside of the loop, and the str reduction pass
// currently can only reduce affine polynomials. For now just disable
// indvar subst on anything more complex than an affine addrec, unless
// it can be expanded to a trivial value.
if (!isSafe(AR, L, SE))
continue;
// Determine the insertion point for this user. By default, insert
// immediately before the user. The SCEVExpander class will automatically
// hoist loop invariants out of the loop. For PHI nodes, there may be
// multiple uses, so compute the nearest common dominator for the
// incoming blocks.
Instruction *InsertPt = User;
if (PHINode *PHI = dyn_cast<PHINode>(InsertPt))
for (unsigned i = 0, e = PHI->getNumIncomingValues(); i != e; ++i)
if (PHI->getIncomingValue(i) == Op) {
if (InsertPt == User)
InsertPt = PHI->getIncomingBlock(i)->getTerminator();
else
InsertPt =
DT->findNearestCommonDominator(InsertPt->getParent(),
PHI->getIncomingBlock(i))
->getTerminator();
}
// Now expand it into actual Instructions and patch it into place.
Value *NewVal = Rewriter.expandCodeFor(AR, UseTy, InsertPt);
DEBUG(dbgs() << "INDVARS: Rewrote IV '" << *AR << "' " << *Op << '\n'
<< " into = " << *NewVal << "\n");
if (!isValidRewrite(Op, NewVal)) {
DeadInsts.push_back(NewVal);
continue;
}
// Inform ScalarEvolution that this value is changing. The change doesn't
// affect its value, but it does potentially affect which use lists the
// value will be on after the replacement, which affects ScalarEvolution's
// ability to walk use lists and drop dangling pointers when a value is
// deleted.
SE->forgetValue(User);
// Patch the new value into place.
if (Op->hasName())
NewVal->takeName(Op);
User->replaceUsesOfWith(Op, NewVal);
UI->setOperandValToReplace(NewVal);
++NumRemoved;
Changed = true;
// The old value may be dead now.
DeadInsts.push_back(Op);
}
}
/// If there's a single exit block, sink any loop-invariant values that
/// were defined in the preheader but not used inside the loop into the
/// exit block to reduce register pressure in the loop.
void IndVarSimplify::SinkUnusedInvariants(Loop *L) {
BasicBlock *ExitBlock = L->getExitBlock();
if (!ExitBlock) return;
BasicBlock *Preheader = L->getLoopPreheader();
if (!Preheader) return;
Instruction *InsertPt = ExitBlock->getFirstNonPHI();
BasicBlock::iterator I = Preheader->getTerminator();
while (I != Preheader->begin()) {
--I;
// New instructions were inserted at the end of the preheader.
if (isa<PHINode>(I))
break;
// Don't move instructions which might have side effects, since the side
// effects need to complete before instructions inside the loop. Also don't
// move instructions which might read memory, since the loop may modify
// memory. Note that it's okay if the instruction might have undefined
// behavior: LoopSimplify guarantees that the preheader dominates the exit
// block.
if (I->mayHaveSideEffects() || I->mayReadFromMemory())
continue;
// Skip debug info intrinsics.
if (isa<DbgInfoIntrinsic>(I))
continue;
// Don't sink static AllocaInsts out of the entry block, which would
// turn them into dynamic allocas!
if (AllocaInst *AI = dyn_cast<AllocaInst>(I))
if (AI->isStaticAlloca())
continue;
// Determine if there is a use in or before the loop (direct or
// otherwise).
bool UsedInLoop = false;
for (Value::use_iterator UI = I->use_begin(), UE = I->use_end();
UI != UE; ++UI) {
User *U = *UI;
BasicBlock *UseBB = cast<Instruction>(U)->getParent();
if (PHINode *P = dyn_cast<PHINode>(U)) {
unsigned i =
PHINode::getIncomingValueNumForOperand(UI.getOperandNo());
UseBB = P->getIncomingBlock(i);
}
if (UseBB == Preheader || L->contains(UseBB)) {
UsedInLoop = true;
break;
}
}
// If there is, the def must remain in the preheader.
if (UsedInLoop)
continue;
// Otherwise, sink it to the exit block.
Instruction *ToMove = I;
bool Done = false;
if (I != Preheader->begin()) {
// Skip debug info intrinsics.
do {
--I;
} while (isa<DbgInfoIntrinsic>(I) && I != Preheader->begin());
if (isa<DbgInfoIntrinsic>(I) && I == Preheader->begin())
Done = true;
} else {
Done = true;
}
ToMove->moveBefore(InsertPt);
if (Done) break;
InsertPt = ToMove;
}
}
/// ConvertToSInt - Convert APF to an integer, if possible.
static bool ConvertToSInt(const APFloat &APF, int64_t &IntVal) {
bool isExact = false;
if (&APF.getSemantics() == &APFloat::PPCDoubleDouble)
return false;
// See if we can convert this to an int64_t
uint64_t UIntVal;
if (APF.convertToInteger(&UIntVal, 64, true, APFloat::rmTowardZero,
&isExact) != APFloat::opOK || !isExact)
return false;
IntVal = UIntVal;
return true;
}
/// HandleFloatingPointIV - If the loop has floating induction variable
/// then insert corresponding integer induction variable if possible.
/// For example,
/// for(double i = 0; i < 10000; ++i)
/// bar(i)
/// is converted into
/// for(int i = 0; i < 10000; ++i)
/// bar((double)i);
///
void IndVarSimplify::HandleFloatingPointIV(Loop *L, PHINode *PN) {
unsigned IncomingEdge = L->contains(PN->getIncomingBlock(0));
unsigned BackEdge = IncomingEdge^1;
// Check incoming value.
ConstantFP *InitValueVal =
dyn_cast<ConstantFP>(PN->getIncomingValue(IncomingEdge));
int64_t InitValue;
if (!InitValueVal || !ConvertToSInt(InitValueVal->getValueAPF(), InitValue))
return;
// Check IV increment. Reject this PN if increment operation is not
// an add or increment value can not be represented by an integer.
BinaryOperator *Incr =
dyn_cast<BinaryOperator>(PN->getIncomingValue(BackEdge));
if (Incr == 0 || Incr->getOpcode() != Instruction::FAdd) return;
// If this is not an add of the PHI with a constantfp, or if the constant fp
// is not an integer, bail out.
ConstantFP *IncValueVal = dyn_cast<ConstantFP>(Incr->getOperand(1));
int64_t IncValue;
if (IncValueVal == 0 || Incr->getOperand(0) != PN ||
!ConvertToSInt(IncValueVal->getValueAPF(), IncValue))
return;
// Check Incr uses. One user is PN and the other user is an exit condition
// used by the conditional terminator.
Value::use_iterator IncrUse = Incr->use_begin();
Instruction *U1 = cast<Instruction>(*IncrUse++);
if (IncrUse == Incr->use_end()) return;
Instruction *U2 = cast<Instruction>(*IncrUse++);
if (IncrUse != Incr->use_end()) return;
// Find exit condition, which is an fcmp. If it doesn't exist, or if it isn't
// only used by a branch, we can't transform it.
FCmpInst *Compare = dyn_cast<FCmpInst>(U1);
if (!Compare)
Compare = dyn_cast<FCmpInst>(U2);
if (Compare == 0 || !Compare->hasOneUse() ||
!isa<BranchInst>(Compare->use_back()))
return;
BranchInst *TheBr = cast<BranchInst>(Compare->use_back());
// We need to verify that the branch actually controls the iteration count
// of the loop. If not, the new IV can overflow and no one will notice.
// The branch block must be in the loop and one of the successors must be out
// of the loop.
assert(TheBr->isConditional() && "Can't use fcmp if not conditional");
if (!L->contains(TheBr->getParent()) ||
(L->contains(TheBr->getSuccessor(0)) &&
L->contains(TheBr->getSuccessor(1))))
return;
// If it isn't a comparison with an integer-as-fp (the exit value), we can't
// transform it.
ConstantFP *ExitValueVal = dyn_cast<ConstantFP>(Compare->getOperand(1));
int64_t ExitValue;
if (ExitValueVal == 0 ||
!ConvertToSInt(ExitValueVal->getValueAPF(), ExitValue))
return;
// Find new predicate for integer comparison.
CmpInst::Predicate NewPred = CmpInst::BAD_ICMP_PREDICATE;
switch (Compare->getPredicate()) {
default: return; // Unknown comparison.
case CmpInst::FCMP_OEQ:
case CmpInst::FCMP_UEQ: NewPred = CmpInst::ICMP_EQ; break;
case CmpInst::FCMP_ONE:
case CmpInst::FCMP_UNE: NewPred = CmpInst::ICMP_NE; break;
case CmpInst::FCMP_OGT:
case CmpInst::FCMP_UGT: NewPred = CmpInst::ICMP_SGT; break;
case CmpInst::FCMP_OGE:
case CmpInst::FCMP_UGE: NewPred = CmpInst::ICMP_SGE; break;
case CmpInst::FCMP_OLT:
case CmpInst::FCMP_ULT: NewPred = CmpInst::ICMP_SLT; break;
case CmpInst::FCMP_OLE:
case CmpInst::FCMP_ULE: NewPred = CmpInst::ICMP_SLE; break;
}
// We convert the floating point induction variable to a signed i32 value if
// we can. This is only safe if the comparison will not overflow in a way
// that won't be trapped by the integer equivalent operations. Check for this
// now.
// TODO: We could use i64 if it is native and the range requires it.
// The start/stride/exit values must all fit in signed i32.
if (!isInt<32>(InitValue) || !isInt<32>(IncValue) || !isInt<32>(ExitValue))
return;
// If not actually striding (add x, 0.0), avoid touching the code.
if (IncValue == 0)
return;
// Positive and negative strides have different safety conditions.
if (IncValue > 0) {
// If we have a positive stride, we require the init to be less than the
// exit value and an equality or less than comparison.
if (InitValue >= ExitValue ||
NewPred == CmpInst::ICMP_SGT || NewPred == CmpInst::ICMP_SGE)
return;
uint32_t Range = uint32_t(ExitValue-InitValue);
if (NewPred == CmpInst::ICMP_SLE) {
// Normalize SLE -> SLT, check for infinite loop.
if (++Range == 0) return; // Range overflows.
}
unsigned Leftover = Range % uint32_t(IncValue);
// If this is an equality comparison, we require that the strided value
// exactly land on the exit value, otherwise the IV condition will wrap
// around and do things the fp IV wouldn't.
if ((NewPred == CmpInst::ICMP_EQ || NewPred == CmpInst::ICMP_NE) &&
Leftover != 0)
return;
// If the stride would wrap around the i32 before exiting, we can't
// transform the IV.
if (Leftover != 0 && int32_t(ExitValue+IncValue) < ExitValue)
return;
} else {
// If we have a negative stride, we require the init to be greater than the
// exit value and an equality or greater than comparison.
if (InitValue >= ExitValue ||
NewPred == CmpInst::ICMP_SLT || NewPred == CmpInst::ICMP_SLE)
return;
uint32_t Range = uint32_t(InitValue-ExitValue);
if (NewPred == CmpInst::ICMP_SGE) {
// Normalize SGE -> SGT, check for infinite loop.
if (++Range == 0) return; // Range overflows.
}
unsigned Leftover = Range % uint32_t(-IncValue);
// If this is an equality comparison, we require that the strided value
// exactly land on the exit value, otherwise the IV condition will wrap
// around and do things the fp IV wouldn't.
if ((NewPred == CmpInst::ICMP_EQ || NewPred == CmpInst::ICMP_NE) &&
Leftover != 0)
return;
// If the stride would wrap around the i32 before exiting, we can't
// transform the IV.
if (Leftover != 0 && int32_t(ExitValue+IncValue) > ExitValue)
return;
}
const IntegerType *Int32Ty = Type::getInt32Ty(PN->getContext());
// Insert new integer induction variable.
PHINode *NewPHI = PHINode::Create(Int32Ty, 2, PN->getName()+".int", PN);
NewPHI->addIncoming(ConstantInt::get(Int32Ty, InitValue),
PN->getIncomingBlock(IncomingEdge));
Value *NewAdd =
BinaryOperator::CreateAdd(NewPHI, ConstantInt::get(Int32Ty, IncValue),
Incr->getName()+".int", Incr);
NewPHI->addIncoming(NewAdd, PN->getIncomingBlock(BackEdge));
ICmpInst *NewCompare = new ICmpInst(TheBr, NewPred, NewAdd,
ConstantInt::get(Int32Ty, ExitValue),
Compare->getName());
// In the following deletions, PN may become dead and may be deleted.
// Use a WeakVH to observe whether this happens.
WeakVH WeakPH = PN;
// Delete the old floating point exit comparison. The branch starts using the
// new comparison.
NewCompare->takeName(Compare);
Compare->replaceAllUsesWith(NewCompare);
RecursivelyDeleteTriviallyDeadInstructions(Compare);
// Delete the old floating point increment.
Incr->replaceAllUsesWith(UndefValue::get(Incr->getType()));
RecursivelyDeleteTriviallyDeadInstructions(Incr);
// If the FP induction variable still has uses, this is because something else
// in the loop uses its value. In order to canonicalize the induction
// variable, we chose to eliminate the IV and rewrite it in terms of an
// int->fp cast.
//
// We give preference to sitofp over uitofp because it is faster on most
// platforms.
if (WeakPH) {
Value *Conv = new SIToFPInst(NewPHI, PN->getType(), "indvar.conv",
PN->getParent()->getFirstNonPHI());
PN->replaceAllUsesWith(Conv);
RecursivelyDeleteTriviallyDeadInstructions(PN);
}
// Add a new IVUsers entry for the newly-created integer PHI.
IU->AddUsersIfInteresting(NewPHI, NewPHI);
}
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