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llvm-project/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/Target/TargetData.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/SetVector.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/Statistic.h"
using namespace llvm;
STATISTIC(NumRemoved , "Number of aux indvars removed");
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;
TargetData *TD;
ScalarEvolution *SE;
bool Changed;
public:
static char ID; // Pass identification, replacement for typeid
IndVarSimplify() : LoopPass(&ID) {}
virtual bool runOnLoop(Loop *L, LPPassManager &LPM);
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequired<ScalarEvolution>();
AU.addRequiredID(LCSSAID);
AU.addRequiredID(LoopSimplifyID);
AU.addRequired<LoopInfo>();
AU.addRequired<TargetData>();
AU.addPreserved<ScalarEvolution>();
AU.addPreservedID(LoopSimplifyID);
AU.addPreservedID(LCSSAID);
AU.setPreservesCFG();
}
private:
void RewriteNonIntegerIVs(Loop *L);
void LinearFunctionTestReplace(Loop *L, SCEVHandle BackedgeTakenCount,
Value *IndVar,
BasicBlock *ExitingBlock,
BranchInst *BI,
SCEVExpander &Rewriter);
void RewriteLoopExitValues(Loop *L, SCEV *BackedgeTakenCount);
void DeleteTriviallyDeadInstructions(SmallPtrSet<Instruction*, 16> &Insts);
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;
}
}
}
/// 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.
void IndVarSimplify::LinearFunctionTestReplace(Loop *L,
SCEVHandle BackedgeTakenCount,
Value *IndVar,
BasicBlock *ExitingBlock,
BranchInst *BI,
SCEVExpander &Rewriter) {
// 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;
SCEVHandle RHS = BackedgeTakenCount;
if (ExitingBlock == 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.
SCEVHandle Zero = SE->getIntegerSCEV(0, BackedgeTakenCount->getType());
SCEVHandle N =
SE->getAddExpr(BackedgeTakenCount,
SE->getIntegerSCEV(1, BackedgeTakenCount->getType()));
if ((isa<SCEVConstant>(N) && !N->isZero()) ||
SE->isLoopGuardedByCond(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->getIntegerSCEV(1, IndVar->getType()));
}
// 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 = L->getCanonicalInductionVariableIncrement();
} else {
// We have to use the preincremented value...
RHS = SE->getTruncateOrZeroExtend(BackedgeTakenCount,
IndVar->getType());
CmpIndVar = IndVar;
}
// Expand the code for the iteration count into the preheader of the loop.
BasicBlock *Preheader = L->getLoopPreheader();
Value *ExitCnt = Rewriter.expandCodeFor(RHS, IndVar->getType(),
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;
DOUT << "INDVARS: Rewriting loop exit condition to:\n"
<< " LHS:" << *CmpIndVar // includes a newline
<< " op:\t"
<< (Opcode == ICmpInst::ICMP_NE ? "!=" : "==") << "\n"
<< " RHS:\t" << *RHS << "\n";
Value *Cond = new ICmpInst(Opcode, CmpIndVar, ExitCnt, "exitcond", BI);
BI->setCondition(Cond);
++NumLFTR;
Changed = true;
}
/// 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 *BackedgeTakenCount) {
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, *TD);
// 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>(BackedgeTakenCount);
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()) &&
!isa<PointerType>(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, PN->getType(), 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);
}
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();
SmallPtrSet<Instruction*, 16> DeadInsts;
for (BasicBlock::iterator I = Header->begin(); isa<PHINode>(I); ++I) {
PHINode *PN = cast<PHINode>(I);
HandleFloatingPointIV(L, PN, DeadInsts);
}
// 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->forgetLoopBackedgeTakenCount(L);
if (!DeadInsts.empty())
DeleteTriviallyDeadInstructions(DeadInsts);
}
/// getEffectiveIndvarType - Determine the widest type that the
/// induction-variable PHINode Phi is cast to.
///
static const Type *getEffectiveIndvarType(const PHINode *Phi,
const TargetData *TD) {
const Type *Ty = Phi->getType();
for (Value::use_const_iterator UI = Phi->use_begin(), UE = Phi->use_end();
UI != UE; ++UI) {
const Type *CandidateType = NULL;
if (const ZExtInst *ZI = dyn_cast<ZExtInst>(UI))
CandidateType = ZI->getDestTy();
else if (const SExtInst *SI = dyn_cast<SExtInst>(UI))
CandidateType = SI->getDestTy();
if (CandidateType &&
TD->getTypeSizeInBits(CandidateType) > TD->getTypeSizeInBits(Ty))
Ty = CandidateType;
}
return Ty;
}
/// TestOrigIVForWrap - Analyze the original induction variable
/// that controls the loop's iteration to determine whether it
/// would ever undergo signed or unsigned overflow. Also, check
/// whether an induction variable in the same type that starts
/// at 0 would undergo signed overflow.
///
/// In addition to setting the NoSignedWrap and NoUnsignedWrap
/// variables to true when appropriate (they are not set to false here),
/// return the PHI for this induction variable. Also record the initial
/// and final values and the increment; these are not meaningful unless
/// either NoSignedWrap or NoUnsignedWrap is true, and are always meaningful
/// in that case, although the final value may be 0 indicating a nonconstant.
///
/// TODO: This duplicates a fair amount of ScalarEvolution logic.
/// Perhaps this can be merged with
/// ScalarEvolution::getBackedgeTakenCount
/// and/or ScalarEvolution::get{Sign,Zero}ExtendExpr.
///
static const PHINode *TestOrigIVForWrap(const Loop *L,
const BranchInst *BI,
const Instruction *OrigCond,
const TargetData *TD,
bool &NoSignedWrap,
bool &NoUnsignedWrap,
const ConstantInt* &InitialVal,
const ConstantInt* &IncrVal,
const ConstantInt* &LimitVal) {
// Verify that the loop is sane and find the exit condition.
const ICmpInst *Cmp = dyn_cast<ICmpInst>(OrigCond);
if (!Cmp) return 0;
const Value *CmpLHS = Cmp->getOperand(0);
const Value *CmpRHS = Cmp->getOperand(1);
const BasicBlock *TrueBB = BI->getSuccessor(0);
const BasicBlock *FalseBB = BI->getSuccessor(1);
ICmpInst::Predicate Pred = Cmp->getPredicate();
// Canonicalize a constant to the RHS.
if (isa<ConstantInt>(CmpLHS)) {
Pred = ICmpInst::getSwappedPredicate(Pred);
std::swap(CmpLHS, CmpRHS);
}
// Canonicalize SLE to SLT.
if (Pred == ICmpInst::ICMP_SLE)
if (const ConstantInt *CI = dyn_cast<ConstantInt>(CmpRHS))
if (!CI->getValue().isMaxSignedValue()) {
CmpRHS = ConstantInt::get(CI->getValue() + 1);
Pred = ICmpInst::ICMP_SLT;
}
// Canonicalize SGT to SGE.
if (Pred == ICmpInst::ICMP_SGT)
if (const ConstantInt *CI = dyn_cast<ConstantInt>(CmpRHS))
if (!CI->getValue().isMaxSignedValue()) {
CmpRHS = ConstantInt::get(CI->getValue() + 1);
Pred = ICmpInst::ICMP_SGE;
}
// Canonicalize SGE to SLT.
if (Pred == ICmpInst::ICMP_SGE) {
std::swap(TrueBB, FalseBB);
Pred = ICmpInst::ICMP_SLT;
}
// Canonicalize ULE to ULT.
if (Pred == ICmpInst::ICMP_ULE)
if (const ConstantInt *CI = dyn_cast<ConstantInt>(CmpRHS))
if (!CI->getValue().isMaxValue()) {
CmpRHS = ConstantInt::get(CI->getValue() + 1);
Pred = ICmpInst::ICMP_ULT;
}
// Canonicalize UGT to UGE.
if (Pred == ICmpInst::ICMP_UGT)
if (const ConstantInt *CI = dyn_cast<ConstantInt>(CmpRHS))
if (!CI->getValue().isMaxValue()) {
CmpRHS = ConstantInt::get(CI->getValue() + 1);
Pred = ICmpInst::ICMP_UGE;
}
// Canonicalize UGE to ULT.
if (Pred == ICmpInst::ICMP_UGE) {
std::swap(TrueBB, FalseBB);
Pred = ICmpInst::ICMP_ULT;
}
// For now, analyze only LT loops for signed overflow.
if (Pred != ICmpInst::ICMP_SLT && Pred != ICmpInst::ICMP_ULT)
return 0;
bool isSigned = Pred == ICmpInst::ICMP_SLT;
// Get the increment instruction. Look past casts if we will
// be able to prove that the original induction variable doesn't
// undergo signed or unsigned overflow, respectively.
const Value *IncrInst = CmpLHS;
if (isSigned) {
if (const SExtInst *SI = dyn_cast<SExtInst>(CmpLHS)) {
if (!isa<ConstantInt>(CmpRHS) ||
!cast<ConstantInt>(CmpRHS)->getValue()
.isSignedIntN(TD->getTypeSizeInBits(IncrInst->getType())))
return 0;
IncrInst = SI->getOperand(0);
}
} else {
if (const ZExtInst *ZI = dyn_cast<ZExtInst>(CmpLHS)) {
if (!isa<ConstantInt>(CmpRHS) ||
!cast<ConstantInt>(CmpRHS)->getValue()
.isIntN(TD->getTypeSizeInBits(IncrInst->getType())))
return 0;
IncrInst = ZI->getOperand(0);
}
}
// For now, only analyze induction variables that have simple increments.
const BinaryOperator *IncrOp = dyn_cast<BinaryOperator>(IncrInst);
if (!IncrOp || IncrOp->getOpcode() != Instruction::Add)
return 0;
IncrVal = dyn_cast<ConstantInt>(IncrOp->getOperand(1));
if (!IncrVal)
return 0;
// Make sure the PHI looks like a normal IV.
const PHINode *PN = dyn_cast<PHINode>(IncrOp->getOperand(0));
if (!PN || PN->getNumIncomingValues() != 2)
return 0;
unsigned IncomingEdge = L->contains(PN->getIncomingBlock(0));
unsigned BackEdge = !IncomingEdge;
if (!L->contains(PN->getIncomingBlock(BackEdge)) ||
PN->getIncomingValue(BackEdge) != IncrOp)
return 0;
if (!L->contains(TrueBB))
return 0;
// For now, only analyze loops with a constant start value, so that
// we can easily determine if the start value is not a maximum value
// which would wrap on the first iteration.
InitialVal = dyn_cast<ConstantInt>(PN->getIncomingValue(IncomingEdge));
if (!InitialVal)
return 0;
// The upper limit need not be a constant; we'll check later.
LimitVal = dyn_cast<ConstantInt>(CmpRHS);
// We detect the impossibility of wrapping in two cases, both of
// which require starting with a non-max value:
// - The IV counts up by one, and the loop iterates only while it remains
// less than a limiting value (any) in the same type.
// - The IV counts up by a positive increment other than 1, and the
// constant limiting value + the increment is less than the max value
// (computed as max-increment to avoid overflow)
if (isSigned && !InitialVal->getValue().isMaxSignedValue()) {
if (IncrVal->equalsInt(1))
NoSignedWrap = true; // LimitVal need not be constant
else if (LimitVal) {
uint64_t numBits = LimitVal->getValue().getBitWidth();
if (IncrVal->getValue().sgt(APInt::getNullValue(numBits)) &&
(APInt::getSignedMaxValue(numBits) - IncrVal->getValue())
.sgt(LimitVal->getValue()))
NoSignedWrap = true;
}
} else if (!isSigned && !InitialVal->getValue().isMaxValue()) {
if (IncrVal->equalsInt(1))
NoUnsignedWrap = true; // LimitVal need not be constant
else if (LimitVal) {
uint64_t numBits = LimitVal->getValue().getBitWidth();
if (IncrVal->getValue().ugt(APInt::getNullValue(numBits)) &&
(APInt::getMaxValue(numBits) - IncrVal->getValue())
.ugt(LimitVal->getValue()))
NoUnsignedWrap = true;
}
}
return PN;
}
static Value *getSignExtendedTruncVar(const SCEVAddRecExpr *AR,
ScalarEvolution *SE,
const Type *LargestType, Loop *L,
const Type *myType,
SCEVExpander &Rewriter,
BasicBlock::iterator InsertPt) {
SCEVHandle ExtendedStart =
SE->getSignExtendExpr(AR->getStart(), LargestType);
SCEVHandle ExtendedStep =
SE->getSignExtendExpr(AR->getStepRecurrence(*SE), LargestType);
SCEVHandle ExtendedAddRec =
SE->getAddRecExpr(ExtendedStart, ExtendedStep, L);
if (LargestType != myType)
ExtendedAddRec = SE->getTruncateExpr(ExtendedAddRec, myType);
return Rewriter.expandCodeFor(ExtendedAddRec, myType, InsertPt);
}
static Value *getZeroExtendedTruncVar(const SCEVAddRecExpr *AR,
ScalarEvolution *SE,
const Type *LargestType, Loop *L,
const Type *myType,
SCEVExpander &Rewriter,
BasicBlock::iterator InsertPt) {
SCEVHandle ExtendedStart =
SE->getZeroExtendExpr(AR->getStart(), LargestType);
SCEVHandle ExtendedStep =
SE->getZeroExtendExpr(AR->getStepRecurrence(*SE), LargestType);
SCEVHandle ExtendedAddRec =
SE->getAddRecExpr(ExtendedStart, ExtendedStep, L);
if (LargestType != myType)
ExtendedAddRec = SE->getTruncateExpr(ExtendedAddRec, myType);
return Rewriter.expandCodeFor(ExtendedAddRec, myType, InsertPt);
}
/// allUsesAreSameTyped - See whether all Uses of I are instructions
/// with the same Opcode and the same type.
static bool allUsesAreSameTyped(unsigned int Opcode, Instruction *I) {
const Type* firstType = NULL;
for (Value::use_iterator UI = I->use_begin(), UE = I->use_end();
UI != UE; ++UI) {
Instruction *II = dyn_cast<Instruction>(*UI);
if (!II || II->getOpcode() != Opcode)
return false;
if (!firstType)
firstType = II->getType();
else if (firstType != II->getType())
return false;
}
return true;
}
bool IndVarSimplify::runOnLoop(Loop *L, LPPassManager &LPM) {
LI = &getAnalysis<LoopInfo>();
TD = &getAnalysis<TargetData>();
SE = &getAnalysis<ScalarEvolution>();
Changed = false;
// If there are any floating-point recurrences, attempt to
// transform them to use integer recurrences.
RewriteNonIntegerIVs(L);
BasicBlock *Header = L->getHeader();
BasicBlock *ExitingBlock = L->getExitingBlock();
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 BackedgeTakenCount = SE->getBackedgeTakenCount(L);
if (!isa<SCEVCouldNotCompute>(BackedgeTakenCount))
RewriteLoopExitValues(L, BackedgeTakenCount);
// 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() || isa<PointerType>(PN->getType())) {
SCEVHandle SCEV = SE->getSCEV(PN);
// 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->getLoop() == L && AR->isAffine())
IndVars.push_back(std::make_pair(PN, SCEV));
}
}
// Compute the type of the largest recurrence expression, and collect
// the set of the types of the other recurrence expressions.
const Type *LargestType = 0;
SmallSetVector<const Type *, 4> SizesToInsert;
if (!isa<SCEVCouldNotCompute>(BackedgeTakenCount)) {
LargestType = BackedgeTakenCount->getType();
if (isa<PointerType>(LargestType))
LargestType = TD->getIntPtrType();
SizesToInsert.insert(LargestType);
}
for (unsigned i = 0, e = IndVars.size(); i != e; ++i) {
const PHINode *PN = IndVars[i].first;
const Type *PNTy = PN->getType();
if (isa<PointerType>(PNTy)) PNTy = TD->getIntPtrType();
SizesToInsert.insert(PNTy);
const Type *EffTy = getEffectiveIndvarType(PN, TD);
if (isa<PointerType>(EffTy)) EffTy = TD->getIntPtrType();
SizesToInsert.insert(EffTy);
if (!LargestType ||
TD->getTypeSizeInBits(EffTy) >
TD->getTypeSizeInBits(LargestType))
LargestType = EffTy;
}
// Create a rewriter object which we'll use to transform the code with.
SCEVExpander Rewriter(*SE, *LI, *TD);
// 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 = 0;
if (!SizesToInsert.empty()) {
IndVar = Rewriter.getOrInsertCanonicalInductionVariable(L,LargestType);
++NumInserted;
Changed = true;
DOUT << "INDVARS: New CanIV: " << *IndVar;
}
// 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.
bool NoSignedWrap = false;
bool NoUnsignedWrap = false;
const ConstantInt* InitialVal, * IncrVal, * LimitVal;
const PHINode *OrigControllingPHI = 0;
if (!isa<SCEVCouldNotCompute>(BackedgeTakenCount) && ExitingBlock)
// Can't rewrite non-branch yet.
if (BranchInst *BI = dyn_cast<BranchInst>(ExitingBlock->getTerminator())) {
if (Instruction *OrigCond = dyn_cast<Instruction>(BI->getCondition())) {
// Determine if the OrigIV will ever undergo overflow.
OrigControllingPHI =
TestOrigIVForWrap(L, BI, OrigCond, TD,
NoSignedWrap, NoUnsignedWrap,
InitialVal, IncrVal, LimitVal);
// We'll be replacing the original condition, so it'll be dead.
DeadInsts.insert(OrigCond);
}
LinearFunctionTestReplace(L, BackedgeTakenCount, IndVar,
ExitingBlock, BI, Rewriter);
}
// 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.
for (unsigned i = 0, e = SizesToInsert.size(); i != e; ++i) {
const Type *Ty = SizesToInsert[i];
if (Ty != LargestType) {
Instruction *New = new TruncInst(IndVar, Ty, "indvar", InsertPt);
Rewriter.addInsertedValue(New, SE->getSCEV(New));
DOUT << "INDVARS: Made trunc IV for type " << *Ty << ": "
<< *New << "\n";
}
}
// Rewrite all induction variables in terms of the canonical induction
// variable.
while (!IndVars.empty()) {
PHINode *PN = IndVars.back().first;
SCEVAddRecExpr *AR = cast<SCEVAddRecExpr>(IndVars.back().second);
Value *NewVal = Rewriter.expandCodeFor(AR, PN->getType(), InsertPt);
DOUT << "INDVARS: Rewrote IV '" << *AR << "' " << *PN
<< " into = " << *NewVal << "\n";
NewVal->takeName(PN);
/// If the new canonical induction variable is wider than the original,
/// and the original has uses that are casts to wider types, see if the
/// truncate and extend can be omitted.
if (PN == OrigControllingPHI && PN->getType() != LargestType)
for (Value::use_iterator UI = PN->use_begin(), UE = PN->use_end();
UI != UE; ++UI) {
Instruction *UInst = dyn_cast<Instruction>(*UI);
if (UInst && isa<SExtInst>(UInst) && NoSignedWrap) {
Value *TruncIndVar = getSignExtendedTruncVar(AR, SE, LargestType, L,
UInst->getType(), Rewriter, InsertPt);
UInst->replaceAllUsesWith(TruncIndVar);
DeadInsts.insert(UInst);
}
// See if we can figure out sext(i+constant) doesn't wrap, so we can
// use a larger add. This is common in subscripting.
if (UInst && UInst->getOpcode()==Instruction::Add &&
allUsesAreSameTyped(Instruction::SExt, UInst) &&
isa<ConstantInt>(UInst->getOperand(1)) &&
NoSignedWrap && LimitVal) {
uint64_t oldBitSize = LimitVal->getValue().getBitWidth();
uint64_t newBitSize = LargestType->getPrimitiveSizeInBits();
ConstantInt* AddRHS = dyn_cast<ConstantInt>(UInst->getOperand(1));
if (((APInt::getSignedMaxValue(oldBitSize) - IncrVal->getValue()) -
AddRHS->getValue()).sgt(LimitVal->getValue())) {
// We've determined this is (i+constant) and it won't overflow.
if (isa<SExtInst>(UInst->use_begin())) {
SExtInst* oldSext = dyn_cast<SExtInst>(UInst->use_begin());
Value *TruncIndVar = getSignExtendedTruncVar(AR, SE, LargestType,
L, oldSext->getType(), Rewriter,
InsertPt);
APInt APcopy = APInt(AddRHS->getValue());
ConstantInt* newAddRHS =ConstantInt::get(APcopy.sext(newBitSize));
Value *NewAdd =
BinaryOperator::CreateAdd(TruncIndVar, newAddRHS,
UInst->getName()+".nosex", UInst);
for (Value::use_iterator UI2 = UInst->use_begin(),
UE2 = UInst->use_end(); UI2 != UE2; ++UI2) {
Instruction *II = dyn_cast<Instruction>(UI2);
II->replaceAllUsesWith(NewAdd);
DeadInsts.insert(II);
}
DeadInsts.insert(UInst);
}
}
}
// Try for sext(i | constant). This is safe as long as the
// high bit of the constant is not set.
if (UInst && UInst->getOpcode()==Instruction::Or &&
allUsesAreSameTyped(Instruction::SExt, UInst) && NoSignedWrap &&
isa<ConstantInt>(UInst->getOperand(1))) {
ConstantInt* RHS = dyn_cast<ConstantInt>(UInst->getOperand(1));
if (!RHS->getValue().isNegative()) {
uint64_t newBitSize = LargestType->getPrimitiveSizeInBits();
SExtInst* oldSext = dyn_cast<SExtInst>(UInst->use_begin());
Value *TruncIndVar = getSignExtendedTruncVar(AR, SE, LargestType,
L, oldSext->getType(), Rewriter,
InsertPt);
APInt APcopy = APInt(RHS->getValue());
ConstantInt* newRHS =ConstantInt::get(APcopy.sext(newBitSize));
Value *NewAdd =
BinaryOperator::CreateOr(TruncIndVar, newRHS,
UInst->getName()+".nosex", UInst);
for (Value::use_iterator UI2 = UInst->use_begin(),
UE2 = UInst->use_end(); UI2 != UE2; ++UI2) {
Instruction *II = dyn_cast<Instruction>(UI2);
II->replaceAllUsesWith(NewAdd);
DeadInsts.insert(II);
}
DeadInsts.insert(UInst);
}
}
// A zext of a signed variable known not to overflow is still safe.
if (UInst && isa<ZExtInst>(UInst) && (NoUnsignedWrap || NoSignedWrap)) {
Value *TruncIndVar = getZeroExtendedTruncVar(AR, SE, LargestType, L,
UInst->getType(), Rewriter, InsertPt);
UInst->replaceAllUsesWith(TruncIndVar);
DeadInsts.insert(UInst);
}
// If we have zext(i&constant), it's always safe to use the larger
// variable. This is not common but is a bottleneck in Openssl.
// (RHS doesn't have to be constant. There should be a better approach
// than bottom-up pattern matching for this...)
if (UInst && UInst->getOpcode()==Instruction::And &&
allUsesAreSameTyped(Instruction::ZExt, UInst) &&
isa<ConstantInt>(UInst->getOperand(1))) {
uint64_t newBitSize = LargestType->getPrimitiveSizeInBits();
ConstantInt* AndRHS = dyn_cast<ConstantInt>(UInst->getOperand(1));
ZExtInst* oldZext = dyn_cast<ZExtInst>(UInst->use_begin());
Value *TruncIndVar = getSignExtendedTruncVar(AR, SE, LargestType,
L, oldZext->getType(), Rewriter, InsertPt);
APInt APcopy = APInt(AndRHS->getValue());
ConstantInt* newAndRHS = ConstantInt::get(APcopy.zext(newBitSize));
Value *NewAnd =
BinaryOperator::CreateAnd(TruncIndVar, newAndRHS,
UInst->getName()+".nozex", UInst);
for (Value::use_iterator UI2 = UInst->use_begin(),
UE2 = UInst->use_end(); UI2 != UE2; ++UI2) {
Instruction *II = dyn_cast<Instruction>(UI2);
II->replaceAllUsesWith(NewAnd);
DeadInsts.insert(II);
}
DeadInsts.insert(UInst);
}
// If we have zext((i+constant)&constant), we can use the larger
// variable even if the add does overflow. This works whenever the
// constant being ANDed is the same size as i, which it presumably is.
// We don't need to restrict the expression being and'ed to i+const,
// but we have to promote everything in it, so it's convenient.
// zext((i | constant)&constant) is also valid and accepted here.
if (UInst && (UInst->getOpcode()==Instruction::Add ||
UInst->getOpcode()==Instruction::Or) &&
UInst->hasOneUse() &&
isa<ConstantInt>(UInst->getOperand(1))) {
uint64_t newBitSize = LargestType->getPrimitiveSizeInBits();
ConstantInt* AddRHS = dyn_cast<ConstantInt>(UInst->getOperand(1));
Instruction *UInst2 = dyn_cast<Instruction>(UInst->use_begin());
if (UInst2 && UInst2->getOpcode() == Instruction::And &&
allUsesAreSameTyped(Instruction::ZExt, UInst2) &&
isa<ConstantInt>(UInst2->getOperand(1))) {
ZExtInst* oldZext = dyn_cast<ZExtInst>(UInst2->use_begin());
Value *TruncIndVar = getSignExtendedTruncVar(AR, SE, LargestType,
L, oldZext->getType(), Rewriter, InsertPt);
ConstantInt* AndRHS = dyn_cast<ConstantInt>(UInst2->getOperand(1));
APInt APcopy = APInt(AddRHS->getValue());
ConstantInt* newAddRHS = ConstantInt::get(APcopy.zext(newBitSize));
Value *NewAdd = ((UInst->getOpcode()==Instruction::Add) ?
BinaryOperator::CreateAdd(TruncIndVar, newAddRHS,
UInst->getName()+".nozex", UInst2) :
BinaryOperator::CreateOr(TruncIndVar, newAddRHS,
UInst->getName()+".nozex", UInst2));
APInt APcopy2 = APInt(AndRHS->getValue());
ConstantInt* newAndRHS = ConstantInt::get(APcopy2.zext(newBitSize));
Value *NewAnd =
BinaryOperator::CreateAnd(NewAdd, newAndRHS,
UInst->getName()+".nozex", UInst2);
for (Value::use_iterator UI2 = UInst2->use_begin(),
UE2 = UInst2->use_end(); UI2 != UE2; ++UI2) {
Instruction *II = dyn_cast<Instruction>(UI2);
II->replaceAllUsesWith(NewAnd);
DeadInsts.insert(II);
}
DeadInsts.insert(UInst);
DeadInsts.insert(UInst2);
}
}
}
// Replace the old PHI Node with the inserted computation.
PN->replaceAllUsesWith(NewVal);
DeadInsts.insert(PN);
IndVars.pop_back();
++NumRemoved;
Changed = true;
}
DeleteTriviallyDeadInstructions(DeadInsts);
assert(L->isLCSSAForm());
return Changed;
}
/// 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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