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llvm/lib/Transforms/Scalar/IndVarSimplify.cpp

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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. 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. Additionally, on targets
// where it is profitable, the loop could be transformed to count down to zero
// (the "do loop" optimization).
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "indvars"
#include "llvm/Transforms/Scalar.h"
#include "llvm/BasicBlock.h"
#include "llvm/Constants.h"
#include "llvm/Instructions.h"
#include "llvm/Type.h"
#include "llvm/Analysis/ScalarEvolutionExpander.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/LoopPass.h"
#include "llvm/Support/CFG.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/GetElementPtrTypeIterator.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/Statistic.h"
using namespace llvm;
STATISTIC(NumRemoved , "Number of aux indvars removed");
STATISTIC(NumPointer , "Number of pointer indvars promoted");
STATISTIC(NumInserted, "Number of canonical indvars added");
STATISTIC(NumReplaced, "Number of exit values replaced");
STATISTIC(NumLFTR , "Number of loop exit tests replaced");
namespace {
class VISIBILITY_HIDDEN IndVarSimplify : public LoopPass {
LoopInfo *LI;
ScalarEvolution *SE;
bool Changed;
public:
static char ID; // Pass identification, replacement for typeid
IndVarSimplify() : LoopPass(&ID) {}
bool runOnLoop(Loop *L, LPPassManager &LPM);
bool doInitialization(Loop *L, LPPassManager &LPM);
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequired<ScalarEvolution>();
AU.addRequiredID(LCSSAID);
AU.addRequiredID(LoopSimplifyID);
AU.addRequired<LoopInfo>();
AU.addPreservedID(LoopSimplifyID);
AU.addPreservedID(LCSSAID);
AU.setPreservesCFG();
}
private:
void EliminatePointerRecurrence(PHINode *PN, BasicBlock *Preheader,
SmallPtrSet<Instruction*, 16> &DeadInsts);
Instruction *LinearFunctionTestReplace(Loop *L, SCEV *IterationCount,
SCEVExpander &RW);
void RewriteLoopExitValues(Loop *L, SCEV *IterationCount);
void DeleteTriviallyDeadInstructions(SmallPtrSet<Instruction*, 16> &Insts);
void OptimizeCanonicalIVType(Loop *L);
void HandleFloatingPointIV(Loop *L, PHINode *PH,
SmallPtrSet<Instruction*, 16> &DeadInsts);
};
}
char IndVarSimplify::ID = 0;
static RegisterPass<IndVarSimplify>
X("indvars", "Canonicalize Induction Variables");
Pass *llvm::createIndVarSimplifyPass() {
return new IndVarSimplify();
}
/// 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 IndVarSimplify::
DeleteTriviallyDeadInstructions(SmallPtrSet<Instruction*, 16> &Insts) {
while (!Insts.empty()) {
Instruction *I = *Insts.begin();
Insts.erase(I);
if (isInstructionTriviallyDead(I)) {
for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
if (Instruction *U = dyn_cast<Instruction>(I->getOperand(i)))
Insts.insert(U);
SE->deleteValueFromRecords(I);
DOUT << "INDVARS: Deleting: " << *I;
I->eraseFromParent();
Changed = true;
}
}
}
/// EliminatePointerRecurrence - Check to see if this is a trivial GEP pointer
/// recurrence. If so, change it into an integer recurrence, permitting
/// analysis by the SCEV routines.
void IndVarSimplify::EliminatePointerRecurrence(PHINode *PN,
BasicBlock *Preheader,
SmallPtrSet<Instruction*, 16> &DeadInsts) {
assert(PN->getNumIncomingValues() == 2 && "Noncanonicalized loop!");
unsigned PreheaderIdx = PN->getBasicBlockIndex(Preheader);
unsigned BackedgeIdx = PreheaderIdx^1;
if (GetElementPtrInst *GEPI =
dyn_cast<GetElementPtrInst>(PN->getIncomingValue(BackedgeIdx)))
if (GEPI->getOperand(0) == PN) {
assert(GEPI->getNumOperands() == 2 && "GEP types must match!");
DOUT << "INDVARS: Eliminating pointer recurrence: " << *GEPI;
// Okay, we found a pointer recurrence. Transform this pointer
// recurrence into an integer recurrence. Compute the value that gets
// added to the pointer at every iteration.
Value *AddedVal = GEPI->getOperand(1);
// Insert a new integer PHI node into the top of the block.
PHINode *NewPhi = PHINode::Create(AddedVal->getType(),
PN->getName()+".rec", PN);
NewPhi->addIncoming(Constant::getNullValue(NewPhi->getType()), Preheader);
// Create the new add instruction.
Value *NewAdd = BinaryOperator::CreateAdd(NewPhi, AddedVal,
GEPI->getName()+".rec", GEPI);
NewPhi->addIncoming(NewAdd, PN->getIncomingBlock(BackedgeIdx));
// Update the existing GEP to use the recurrence.
GEPI->setOperand(0, PN->getIncomingValue(PreheaderIdx));
// Update the GEP to use the new recurrence we just inserted.
GEPI->setOperand(1, NewAdd);
// If the incoming value is a constant expr GEP, try peeling out the array
// 0 index if possible to make things simpler.
if (ConstantExpr *CE = dyn_cast<ConstantExpr>(GEPI->getOperand(0)))
if (CE->getOpcode() == Instruction::GetElementPtr) {
unsigned NumOps = CE->getNumOperands();
assert(NumOps > 1 && "CE folding didn't work!");
if (CE->getOperand(NumOps-1)->isNullValue()) {
// Check to make sure the last index really is an array index.
gep_type_iterator GTI = gep_type_begin(CE);
for (unsigned i = 1, e = CE->getNumOperands()-1;
i != e; ++i, ++GTI)
/*empty*/;
if (isa<SequentialType>(*GTI)) {
// Pull the last index out of the constant expr GEP.
SmallVector<Value*, 8> CEIdxs(CE->op_begin()+1, CE->op_end()-1);
Constant *NCE = ConstantExpr::getGetElementPtr(CE->getOperand(0),
&CEIdxs[0],
CEIdxs.size());
Value *Idx[2];
Idx[0] = Constant::getNullValue(Type::Int32Ty);
Idx[1] = NewAdd;
GetElementPtrInst *NGEPI = GetElementPtrInst::Create(
NCE, Idx, Idx + 2,
GEPI->getName(), GEPI);
SE->deleteValueFromRecords(GEPI);
GEPI->replaceAllUsesWith(NGEPI);
GEPI->eraseFromParent();
GEPI = NGEPI;
}
}
}
// Finally, if there are any other users of the PHI node, we must
// insert a new GEP instruction that uses the pre-incremented version
// of the induction amount.
if (!PN->use_empty()) {
BasicBlock::iterator InsertPos = PN; ++InsertPos;
while (isa<PHINode>(InsertPos)) ++InsertPos;
Value *PreInc =
GetElementPtrInst::Create(PN->getIncomingValue(PreheaderIdx),
NewPhi, "", InsertPos);
PreInc->takeName(PN);
PN->replaceAllUsesWith(PreInc);
}
// Delete the old PHI for sure, and the GEP if its otherwise unused.
DeadInsts.insert(PN);
++NumPointer;
Changed = true;
}
}
/// 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.
///
/// This method returns a "potentially dead" instruction whose computation chain
/// should be deleted when convenient.
Instruction *IndVarSimplify::LinearFunctionTestReplace(Loop *L,
SCEV *IterationCount,
SCEVExpander &RW) {
// Find the exit block for the loop. We can currently only handle loops with
// a single exit.
SmallVector<BasicBlock*, 8> ExitBlocks;
L->getExitBlocks(ExitBlocks);
if (ExitBlocks.size() != 1) return 0;
BasicBlock *ExitBlock = ExitBlocks[0];
// Make sure there is only one predecessor block in the loop.
BasicBlock *ExitingBlock = 0;
for (pred_iterator PI = pred_begin(ExitBlock), PE = pred_end(ExitBlock);
PI != PE; ++PI)
if (L->contains(*PI)) {
if (ExitingBlock == 0)
ExitingBlock = *PI;
else
return 0; // Multiple exits from loop to this block.
}
assert(ExitingBlock && "Loop info is broken");
if (!isa<BranchInst>(ExitingBlock->getTerminator()))
return 0; // Can't rewrite non-branch yet
BranchInst *BI = cast<BranchInst>(ExitingBlock->getTerminator());
assert(BI->isConditional() && "Must be conditional to be part of loop!");
Instruction *PotentiallyDeadInst = dyn_cast<Instruction>(BI->getCondition());
// 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.
BasicBlock *Header = L->getHeader();
pred_iterator HPI = pred_begin(Header);
assert(HPI != pred_end(Header) && "Loop with zero preds???");
if (!L->contains(*HPI)) ++HPI;
assert(HPI != pred_end(Header) && L->contains(*HPI) &&
"No backedge in loop?");
SCEVHandle TripCount = IterationCount;
Value *IndVar;
if (*HPI == ExitingBlock) {
// The IterationCount expression contains the number of times that the
// backedge actually branches to the loop header. This is one less than the
// number of times the loop executes, so add one to it.
ConstantInt *OneC = ConstantInt::get(IterationCount->getType(), 1);
TripCount = SE->getAddExpr(IterationCount, SE->getConstant(OneC));
IndVar = L->getCanonicalInductionVariableIncrement();
} else {
// We have to use the preincremented value...
IndVar = L->getCanonicalInductionVariable();
}
DOUT << "INDVARS: LFTR: TripCount = " << *TripCount
<< " IndVar = " << *IndVar << "\n";
// Expand the code for the iteration count into the preheader of the loop.
BasicBlock *Preheader = L->getLoopPreheader();
Value *ExitCnt = RW.expandCodeFor(TripCount, Preheader->getTerminator());
// 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;
Value *Cond = new ICmpInst(Opcode, IndVar, ExitCnt, "exitcond", BI);
BI->setCondition(Cond);
++NumLFTR;
Changed = true;
return PotentiallyDeadInst;
}
/// 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.
void IndVarSimplify::RewriteLoopExitValues(Loop *L, SCEV *IterationCount) {
BasicBlock *Preheader = L->getLoopPreheader();
// Scan all of the instructions in the loop, looking at those that have
// extra-loop users and which are recurrences.
SCEVExpander Rewriter(*SE, *LI);
// We insert the code into the preheader of the loop if the loop contains
// multiple exit blocks, or in the exit block if there is exactly one.
BasicBlock *BlockToInsertInto;
SmallVector<BasicBlock*, 8> ExitBlocks;
L->getUniqueExitBlocks(ExitBlocks);
if (ExitBlocks.size() == 1)
BlockToInsertInto = ExitBlocks[0];
else
BlockToInsertInto = Preheader;
BasicBlock::iterator InsertPt = BlockToInsertInto->getFirstNonPHI();
bool HasConstantItCount = isa<SCEVConstant>(IterationCount);
SmallPtrSet<Instruction*, 16> InstructionsToDelete;
std::map<Instruction*, Value*> ExitValues;
// 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++))) {
// 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) ||
// SCEV only supports integer expressions for now.
!isa<IntegerType>(InVal->getType()))
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->getParent()))
continue;
// We require that this value either have a computable evolution or that
// the loop have a constant iteration count. In the case where the loop
// has a constant iteration count, we can sometimes force evaluation of
// the exit value through brute force.
SCEVHandle SH = SE->getSCEV(Inst);
if (!SH->hasComputableLoopEvolution(L) && !HasConstantItCount)
continue; // Cannot get exit evolution for the loop value.
// 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.
SCEVHandle ExitValue = SE->getSCEVAtScope(Inst, L->getParentLoop());
if (isa<SCEVCouldNotCompute>(ExitValue) ||
!ExitValue->isLoopInvariant(L))
continue;
Changed = true;
++NumReplaced;
// See if we already computed the exit value for the instruction, if so,
// just reuse it.
Value *&ExitVal = ExitValues[Inst];
if (!ExitVal)
ExitVal = Rewriter.expandCodeFor(ExitValue, InsertPt);
DOUT << "INDVARS: RLEV: AfterLoopVal = " << *ExitVal
<< " LoopVal = " << *Inst << "\n";
PN->setIncomingValue(i, ExitVal);
// If this instruction is dead now, schedule it to be removed.
if (Inst->use_empty())
InstructionsToDelete.insert(Inst);
// See if this is a single-entry LCSSA PHI node. If so, we can (and
// have to) remove
// the PHI entirely. This is safe, because the NewVal won't be variant
// in the loop, so we don't need an LCSSA phi node anymore.
if (NumPreds == 1) {
SE->deleteValueFromRecords(PN);
PN->replaceAllUsesWith(ExitVal);
PN->eraseFromParent();
break;
}
}
}
}
DeleteTriviallyDeadInstructions(InstructionsToDelete);
}
bool IndVarSimplify::doInitialization(Loop *L, LPPassManager &LPM) {
Changed = false;
// First step. Check to see if there are any trivial GEP pointer recurrences.
// If there are, change them into integer recurrences, permitting analysis by
// the SCEV routines.
//
BasicBlock *Header = L->getHeader();
BasicBlock *Preheader = L->getLoopPreheader();
SE = &LPM.getAnalysis<ScalarEvolution>();
SmallPtrSet<Instruction*, 16> DeadInsts;
for (BasicBlock::iterator I = Header->begin(); isa<PHINode>(I); ++I) {
PHINode *PN = cast<PHINode>(I);
if (isa<PointerType>(PN->getType()))
EliminatePointerRecurrence(PN, Preheader, DeadInsts);
else
HandleFloatingPointIV(L, PN, DeadInsts);
}
if (!DeadInsts.empty())
DeleteTriviallyDeadInstructions(DeadInsts);
return Changed;
}
bool IndVarSimplify::runOnLoop(Loop *L, LPPassManager &LPM) {
LI = &getAnalysis<LoopInfo>();
SE = &getAnalysis<ScalarEvolution>();
Changed = false;
BasicBlock *Header = L->getHeader();
SmallPtrSet<Instruction*, 16> DeadInsts;
// Verify the input to the pass in already in LCSSA form.
assert(L->isLCSSAForm());
// 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.
//
SCEVHandle IterationCount = SE->getIterationCount(L);
if (!isa<SCEVCouldNotCompute>(IterationCount))
RewriteLoopExitValues(L, IterationCount);
// Next, analyze all of the induction variables in the loop, canonicalizing
// auxillary induction variables.
std::vector<std::pair<PHINode*, SCEVHandle> > IndVars;
for (BasicBlock::iterator I = Header->begin(); isa<PHINode>(I); ++I) {
PHINode *PN = cast<PHINode>(I);
if (PN->getType()->isInteger()) { // FIXME: when we have fast-math, enable!
SCEVHandle SCEV = SE->getSCEV(PN);
if (SCEV->hasComputableLoopEvolution(L))
// 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.
if (SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(SCEV))
if (AR->isAffine())
IndVars.push_back(std::make_pair(PN, SCEV));
}
}
// If there are no induction variables in the loop, there is nothing more to
// do.
if (IndVars.empty()) {
// Actually, if we know how many times the loop iterates, lets insert a
// canonical induction variable to help subsequent passes.
if (!isa<SCEVCouldNotCompute>(IterationCount)) {
SCEVExpander Rewriter(*SE, *LI);
Rewriter.getOrInsertCanonicalInductionVariable(L,
IterationCount->getType());
if (Instruction *I = LinearFunctionTestReplace(L, IterationCount,
Rewriter)) {
SmallPtrSet<Instruction*, 16> InstructionsToDelete;
InstructionsToDelete.insert(I);
DeleteTriviallyDeadInstructions(InstructionsToDelete);
}
}
return Changed;
}
// Compute the type of the largest recurrence expression.
//
const Type *LargestType = IndVars[0].first->getType();
bool DifferingSizes = false;
for (unsigned i = 1, e = IndVars.size(); i != e; ++i) {
const Type *Ty = IndVars[i].first->getType();
DifferingSizes |=
Ty->getPrimitiveSizeInBits() != LargestType->getPrimitiveSizeInBits();
if (Ty->getPrimitiveSizeInBits() > LargestType->getPrimitiveSizeInBits())
LargestType = Ty;
}
// Create a rewriter object which we'll use to transform the code with.
SCEVExpander Rewriter(*SE, *LI);
// Now that we know the largest of of the induction variables in this loop,
// insert a canonical induction variable of the largest size.
Value *IndVar = Rewriter.getOrInsertCanonicalInductionVariable(L,LargestType);
++NumInserted;
Changed = true;
DOUT << "INDVARS: New CanIV: " << *IndVar;
if (!isa<SCEVCouldNotCompute>(IterationCount)) {
IterationCount = SE->getTruncateOrZeroExtend(IterationCount, LargestType);
if (Instruction *DI = LinearFunctionTestReplace(L, IterationCount,Rewriter))
DeadInsts.insert(DI);
}
// Now that we have a canonical induction variable, we can rewrite any
// recurrences in terms of the induction variable. Start with the auxillary
// induction variables, and recursively rewrite any of their uses.
BasicBlock::iterator InsertPt = Header->getFirstNonPHI();
// If there were induction variables of other sizes, cast the primary
// induction variable to the right size for them, avoiding the need for the
// code evaluation methods to insert induction variables of different sizes.
if (DifferingSizes) {
SmallVector<unsigned,4> InsertedSizes;
InsertedSizes.push_back(LargestType->getPrimitiveSizeInBits());
for (unsigned i = 0, e = IndVars.size(); i != e; ++i) {
unsigned ithSize = IndVars[i].first->getType()->getPrimitiveSizeInBits();
if (std::find(InsertedSizes.begin(), InsertedSizes.end(), ithSize)
== InsertedSizes.end()) {
PHINode *PN = IndVars[i].first;
InsertedSizes.push_back(ithSize);
Instruction *New = new TruncInst(IndVar, PN->getType(), "indvar",
InsertPt);
Rewriter.addInsertedValue(New, SE->getSCEV(New));
DOUT << "INDVARS: Made trunc IV for " << *PN
<< " NewVal = " << *New << "\n";
}
}
}
// Rewrite all induction variables in terms of the canonical induction
// variable.
while (!IndVars.empty()) {
PHINode *PN = IndVars.back().first;
Value *NewVal = Rewriter.expandCodeFor(IndVars.back().second, InsertPt);
DOUT << "INDVARS: Rewrote IV '" << *IndVars.back().second << "' " << *PN
<< " into = " << *NewVal << "\n";
NewVal->takeName(PN);
// Replace the old PHI Node with the inserted computation.
PN->replaceAllUsesWith(NewVal);
DeadInsts.insert(PN);
IndVars.pop_back();
++NumRemoved;
Changed = true;
}
#if 0
// Now replace all derived expressions in the loop body with simpler
// expressions.
for (LoopInfo::block_iterator I = L->block_begin(), E = L->block_end();
I != E; ++I) {
BasicBlock *BB = *I;
if (LI->getLoopFor(BB) == L) { // Not in a subloop...
for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
if (I->getType()->isInteger() && // Is an integer instruction
!I->use_empty() &&
!Rewriter.isInsertedInstruction(I)) {
SCEVHandle SH = SE->getSCEV(I);
Value *V = Rewriter.expandCodeFor(SH, I, I->getType());
if (V != I) {
if (isa<Instruction>(V))
V->takeName(I);
I->replaceAllUsesWith(V);
DeadInsts.insert(I);
++NumRemoved;
Changed = true;
}
}
}
}
#endif
DeleteTriviallyDeadInstructions(DeadInsts);
OptimizeCanonicalIVType(L);
assert(L->isLCSSAForm());
return Changed;
}
/// OptimizeCanonicalIVType - If loop induction variable is always
/// sign or zero extended then extend the type of the induction
/// variable.
void IndVarSimplify::OptimizeCanonicalIVType(Loop *L) {
PHINode *PH = L->getCanonicalInductionVariable();
if (!PH) return;
// Check loop iteration count.
SCEVHandle IC = SE->getIterationCount(L);
if (isa<SCEVCouldNotCompute>(IC)) return;
SCEVConstant *IterationCount = dyn_cast<SCEVConstant>(IC);
if (!IterationCount) return;
unsigned IncomingEdge = L->contains(PH->getIncomingBlock(0));
unsigned BackEdge = IncomingEdge^1;
// Check IV uses. If all IV uses are either SEXT or ZEXT (except
// IV increment instruction) then this IV is suitable for this
// transformation.
bool isSEXT = false;
BinaryOperator *Incr = NULL;
const Type *NewType = NULL;
for(Value::use_iterator UI = PH->use_begin(), UE = PH->use_end();
UI != UE; ++UI) {
const Type *CandidateType = NULL;
if (ZExtInst *ZI = dyn_cast<ZExtInst>(UI))
CandidateType = ZI->getDestTy();
else if (SExtInst *SI = dyn_cast<SExtInst>(UI)) {
CandidateType = SI->getDestTy();
isSEXT = true;
}
else if ((Incr = dyn_cast<BinaryOperator>(UI))) {
// Validate IV increment instruction.
if (PH->getIncomingValue(BackEdge) == Incr)
continue;
}
if (!CandidateType) {
NewType = NULL;
break;
}
if (!NewType)
NewType = CandidateType;
else if (NewType != CandidateType) {
NewType = NULL;
break;
}
}
// IV uses are not suitable then avoid this transformation.
if (!NewType || !Incr)
return;
// IV increment instruction has two uses, one is loop exit condition
// and second is the IV (phi node) itself.
ICmpInst *Exit = NULL;
for(Value::use_iterator II = Incr->use_begin(), IE = Incr->use_end();
II != IE; ++II) {
if (PH == *II) continue;
Exit = dyn_cast<ICmpInst>(*II);
break;
}
if (!Exit) return;
ConstantInt *EV = dyn_cast<ConstantInt>(Exit->getOperand(0));
if (!EV)
EV = dyn_cast<ConstantInt>(Exit->getOperand(1));
if (!EV) return;
// Check iteration count max value to avoid loops that wrap around IV.
APInt ICount = IterationCount->getValue()->getValue();
if (ICount.isNegative()) return;
uint32_t BW = PH->getType()->getPrimitiveSizeInBits();
APInt Max = (isSEXT ? APInt::getSignedMaxValue(BW) : APInt::getMaxValue(BW));
if (ICount.getZExtValue() > Max.getZExtValue()) return;
// Extend IV type.
SCEVExpander Rewriter(*SE, *LI);
Value *NewIV = Rewriter.getOrInsertCanonicalInductionVariable(L,NewType);
PHINode *NewPH = cast<PHINode>(NewIV);
Instruction *NewIncr = cast<Instruction>(NewPH->getIncomingValue(BackEdge));
// Replace all SEXT or ZEXT uses.
SmallVector<Instruction *, 4> PHUses;
for(Value::use_iterator UI = PH->use_begin(), UE = PH->use_end();
UI != UE; ++UI) {
Instruction *I = cast<Instruction>(UI);
PHUses.push_back(I);
}
while (!PHUses.empty()){
Instruction *Use = PHUses.back(); PHUses.pop_back();
if (Incr == Use) continue;
SE->deleteValueFromRecords(Use);
Use->replaceAllUsesWith(NewIV);
Use->eraseFromParent();
}
// Replace exit condition.
ConstantInt *NEV = ConstantInt::get(NewType, EV->getZExtValue());
Instruction *NE = new ICmpInst(Exit->getPredicate(),
NewIncr, NEV, "new.exit",
Exit->getParent()->getTerminator());
SE->deleteValueFromRecords(Exit);
Exit->replaceAllUsesWith(NE);
Exit->eraseFromParent();
// Remove old IV and increment instructions.
SE->deleteValueFromRecords(PH);
PH->removeIncomingValue((unsigned)0);
PH->removeIncomingValue((unsigned)0);
SE->deleteValueFromRecords(Incr);
Incr->eraseFromParent();
}
/// Return true if it is OK to use SIToFPInst for an inducation variable
/// with given inital and exit values.
static bool useSIToFPInst(ConstantFP &InitV, ConstantFP &ExitV,
uint64_t intIV, uint64_t intEV) {
if (InitV.getValueAPF().isNegative() || ExitV.getValueAPF().isNegative())
return true;
// If the iteration range can be handled by SIToFPInst then use it.
APInt Max = APInt::getSignedMaxValue(32);
if (Max.getZExtValue() > static_cast<uint64_t>(abs(intEV - intIV)))
return true;
return false;
}
/// convertToInt - Convert APF to an integer, if possible.
static bool convertToInt(const APFloat &APF, uint64_t *intVal) {
bool isExact = false;
if (&APF.getSemantics() == &APFloat::PPCDoubleDouble)
return false;
if (APF.convertToInteger(intVal, 32, APF.isNegative(),
APFloat::rmTowardZero, &isExact)
!= APFloat::opOK)
return false;
if (!isExact)
return false;
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 *PH,
SmallPtrSet<Instruction*, 16> &DeadInsts) {
unsigned IncomingEdge = L->contains(PH->getIncomingBlock(0));
unsigned BackEdge = IncomingEdge^1;
// Check incoming value.
ConstantFP *InitValue = dyn_cast<ConstantFP>(PH->getIncomingValue(IncomingEdge));
if (!InitValue) return;
uint64_t newInitValue = Type::Int32Ty->getPrimitiveSizeInBits();
if (!convertToInt(InitValue->getValueAPF(), &newInitValue))
return;
// Check IV increment. Reject this PH if increement operation is not
// an add or increment value can not be represented by an integer.
BinaryOperator *Incr =
dyn_cast<BinaryOperator>(PH->getIncomingValue(BackEdge));
if (!Incr) return;
if (Incr->getOpcode() != Instruction::Add) return;
ConstantFP *IncrValue = NULL;
unsigned IncrVIndex = 1;
if (Incr->getOperand(1) == PH)
IncrVIndex = 0;
IncrValue = dyn_cast<ConstantFP>(Incr->getOperand(IncrVIndex));
if (!IncrValue) return;
uint64_t newIncrValue = Type::Int32Ty->getPrimitiveSizeInBits();
if (!convertToInt(IncrValue->getValueAPF(), &newIncrValue))
return;
// Check Incr uses. One user is PH and the other users is 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.
FCmpInst *EC = dyn_cast<FCmpInst>(U1);
if (!EC)
EC = dyn_cast<FCmpInst>(U2);
if (!EC) return;
if (BranchInst *BI = dyn_cast<BranchInst>(EC->getParent()->getTerminator())) {
if (!BI->isConditional()) return;
if (BI->getCondition() != EC) return;
}
// Find exit value. If exit value can not be represented as an interger then
// do not handle this floating point PH.
ConstantFP *EV = NULL;
unsigned EVIndex = 1;
if (EC->getOperand(1) == Incr)
EVIndex = 0;
EV = dyn_cast<ConstantFP>(EC->getOperand(EVIndex));
if (!EV) return;
uint64_t intEV = Type::Int32Ty->getPrimitiveSizeInBits();
if (!convertToInt(EV->getValueAPF(), &intEV))
return;
// Find new predicate for integer comparison.
CmpInst::Predicate NewPred = CmpInst::BAD_ICMP_PREDICATE;
switch (EC->getPredicate()) {
case CmpInst::FCMP_OEQ:
case CmpInst::FCMP_UEQ:
NewPred = CmpInst::ICMP_EQ;
break;
case CmpInst::FCMP_OGT:
case CmpInst::FCMP_UGT:
NewPred = CmpInst::ICMP_UGT;
break;
case CmpInst::FCMP_OGE:
case CmpInst::FCMP_UGE:
NewPred = CmpInst::ICMP_UGE;
break;
case CmpInst::FCMP_OLT:
case CmpInst::FCMP_ULT:
NewPred = CmpInst::ICMP_ULT;
break;
case CmpInst::FCMP_OLE:
case CmpInst::FCMP_ULE:
NewPred = CmpInst::ICMP_ULE;
break;
default:
break;
}
if (NewPred == CmpInst::BAD_ICMP_PREDICATE) return;
// Insert new integer induction variable.
PHINode *NewPHI = PHINode::Create(Type::Int32Ty,
PH->getName()+".int", PH);
NewPHI->addIncoming(ConstantInt::get(Type::Int32Ty, newInitValue),
PH->getIncomingBlock(IncomingEdge));
Value *NewAdd = BinaryOperator::CreateAdd(NewPHI,
ConstantInt::get(Type::Int32Ty,
newIncrValue),
Incr->getName()+".int", Incr);
NewPHI->addIncoming(NewAdd, PH->getIncomingBlock(BackEdge));
ConstantInt *NewEV = ConstantInt::get(Type::Int32Ty, intEV);
Value *LHS = (EVIndex == 1 ? NewPHI->getIncomingValue(BackEdge) : NewEV);
Value *RHS = (EVIndex == 1 ? NewEV : NewPHI->getIncomingValue(BackEdge));
ICmpInst *NewEC = new ICmpInst(NewPred, LHS, RHS, EC->getNameStart(),
EC->getParent()->getTerminator());
// Delete old, floating point, exit comparision instruction.
EC->replaceAllUsesWith(NewEC);
DeadInsts.insert(EC);
// Delete old, floating point, increment instruction.
Incr->replaceAllUsesWith(UndefValue::get(Incr->getType()));
DeadInsts.insert(Incr);
// Replace floating induction variable. Give SIToFPInst preference over
// UIToFPInst because it is faster on platforms that are widely used.
if (useSIToFPInst(*InitValue, *EV, newInitValue, intEV)) {
SIToFPInst *Conv = new SIToFPInst(NewPHI, PH->getType(), "indvar.conv",
PH->getParent()->getFirstNonPHI());
PH->replaceAllUsesWith(Conv);
} else {
UIToFPInst *Conv = new UIToFPInst(NewPHI, PH->getType(), "indvar.conv",
PH->getParent()->getFirstNonPHI());
PH->replaceAllUsesWith(Conv);
}
DeadInsts.insert(PH);
}
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