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llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
Chris Lattner 8a7980b5ea Fix the second bug attached to PR504. 
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@20181 91177308-0d34-0410-b5e6-96231b3b80d8
2005-02-14 20:11:45 +00:00

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//===- IndVarSimplify.cpp - Induction Variable Elimination ----------------===//
//
// The LLVM Compiler Infrastructure
//
// This file was developed by the LLVM research group and 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 make 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).
//
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/Scalar.h"
#include "llvm/BasicBlock.h"
#include "llvm/Constants.h"
#include "llvm/Instructions.h"
#include "llvm/Type.h"
#include "llvm/Analysis/ScalarEvolutionExpressions.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Support/CFG.h"
#include "llvm/Support/GetElementPtrTypeIterator.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/ADT/Statistic.h"
using namespace llvm;
namespace {
/// SCEVExpander - This class uses information about analyze scalars to
/// rewrite expressions in canonical form.
///
/// Clients should create an instance of this class when rewriting is needed,
/// and destroying it when finished to allow the release of the associated
/// memory.
struct SCEVExpander : public SCEVVisitor<SCEVExpander, Value*> {
ScalarEvolution &SE;
LoopInfo &LI;
std::map<SCEVHandle, Value*> InsertedExpressions;
std::set<Instruction*> InsertedInstructions;
Instruction *InsertPt;
friend struct SCEVVisitor<SCEVExpander, Value*>;
public:
SCEVExpander(ScalarEvolution &se, LoopInfo &li) : SE(se), LI(li) {}
/// isInsertedInstruction - Return true if the specified instruction was
/// inserted by the code rewriter. If so, the client should not modify the
/// instruction.
bool isInsertedInstruction(Instruction *I) const {
return InsertedInstructions.count(I);
}
/// getOrInsertCanonicalInductionVariable - This method returns the
/// canonical induction variable of the specified type for the specified
/// loop (inserting one if there is none). A canonical induction variable
/// starts at zero and steps by one on each iteration.
Value *getOrInsertCanonicalInductionVariable(const Loop *L, const Type *Ty){
assert((Ty->isInteger() || Ty->isFloatingPoint()) &&
"Can only insert integer or floating point induction variables!");
SCEVHandle H = SCEVAddRecExpr::get(SCEVUnknown::getIntegerSCEV(0, Ty),
SCEVUnknown::getIntegerSCEV(1, Ty), L);
return expand(H);
}
/// addInsertedValue - Remember the specified instruction as being the
/// canonical form for the specified SCEV.
void addInsertedValue(Instruction *I, SCEV *S) {
InsertedExpressions[S] = (Value*)I;
InsertedInstructions.insert(I);
}
/// expandCodeFor - Insert code to directly compute the specified SCEV
/// expression into the program. The inserted code is inserted into the
/// specified block.
///
/// If a particular value sign is required, a type may be specified for the
/// result.
Value *expandCodeFor(SCEVHandle SH, Instruction *IP, const Type *Ty = 0) {
// Expand the code for this SCEV.
this->InsertPt = IP;
return expandInTy(SH, Ty);
}
protected:
Value *expand(SCEV *S) {
// Check to see if we already expanded this.
std::map<SCEVHandle, Value*>::iterator I = InsertedExpressions.find(S);
if (I != InsertedExpressions.end())
return I->second;
Value *V = visit(S);
InsertedExpressions[S] = V;
return V;
}
Value *expandInTy(SCEV *S, const Type *Ty) {
Value *V = expand(S);
if (Ty && V->getType() != Ty) {
// FIXME: keep track of the cast instruction.
if (Constant *C = dyn_cast<Constant>(V))
return ConstantExpr::getCast(C, Ty);
else if (Instruction *I = dyn_cast<Instruction>(V)) {
// Check to see if there is already a cast. If there is, use it.
for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
UI != E; ++UI) {
if ((*UI)->getType() == Ty)
if (CastInst *CI = dyn_cast<CastInst>(cast<Instruction>(*UI))) {
BasicBlock::iterator It = I; ++It;
if (isa<InvokeInst>(I))
It = cast<InvokeInst>(I)->getNormalDest()->begin();
while (isa<PHINode>(It)) ++It;
if (It != BasicBlock::iterator(CI)) {
// Splice the cast immediately after the operand in question.
BasicBlock::InstListType &InstList =
It->getParent()->getInstList();
InstList.splice(It, CI->getParent()->getInstList(), CI);
}
return CI;
}
}
BasicBlock::iterator IP = I; ++IP;
if (InvokeInst *II = dyn_cast<InvokeInst>(I))
IP = II->getNormalDest()->begin();
while (isa<PHINode>(IP)) ++IP;
return new CastInst(V, Ty, V->getName(), IP);
} else {
// FIXME: check to see if there is already a cast!
return new CastInst(V, Ty, V->getName(), InsertPt);
}
}
return V;
}
Value *visitConstant(SCEVConstant *S) {
return S->getValue();
}
Value *visitTruncateExpr(SCEVTruncateExpr *S) {
Value *V = expand(S->getOperand());
return new CastInst(V, S->getType(), "tmp.", InsertPt);
}
Value *visitZeroExtendExpr(SCEVZeroExtendExpr *S) {
Value *V = expandInTy(S->getOperand(),S->getType()->getUnsignedVersion());
return new CastInst(V, S->getType(), "tmp.", InsertPt);
}
Value *visitAddExpr(SCEVAddExpr *S) {
const Type *Ty = S->getType();
Value *V = expandInTy(S->getOperand(S->getNumOperands()-1), Ty);
// Emit a bunch of add instructions
for (int i = S->getNumOperands()-2; i >= 0; --i)
V = BinaryOperator::createAdd(V, expandInTy(S->getOperand(i), Ty),
"tmp.", InsertPt);
return V;
}
Value *visitMulExpr(SCEVMulExpr *S);
Value *visitUDivExpr(SCEVUDivExpr *S) {
const Type *Ty = S->getType();
Value *LHS = expandInTy(S->getLHS(), Ty);
Value *RHS = expandInTy(S->getRHS(), Ty);
return BinaryOperator::createDiv(LHS, RHS, "tmp.", InsertPt);
}
Value *visitAddRecExpr(SCEVAddRecExpr *S);
Value *visitUnknown(SCEVUnknown *S) {
return S->getValue();
}
};
}
Value *SCEVExpander::visitMulExpr(SCEVMulExpr *S) {
const Type *Ty = S->getType();
int FirstOp = 0; // Set if we should emit a subtract.
if (SCEVConstant *SC = dyn_cast<SCEVConstant>(S->getOperand(0)))
if (SC->getValue()->isAllOnesValue())
FirstOp = 1;
int i = S->getNumOperands()-2;
Value *V = expandInTy(S->getOperand(i+1), Ty);
// Emit a bunch of multiply instructions
for (; i >= FirstOp; --i)
V = BinaryOperator::createMul(V, expandInTy(S->getOperand(i), Ty),
"tmp.", InsertPt);
// -1 * ... ---> 0 - ...
if (FirstOp == 1)
V = BinaryOperator::createNeg(V, "tmp.", InsertPt);
return V;
}
Value *SCEVExpander::visitAddRecExpr(SCEVAddRecExpr *S) {
const Type *Ty = S->getType();
const Loop *L = S->getLoop();
// We cannot yet do fp recurrences, e.g. the xform of {X,+,F} --> X+{0,+,F}
assert(Ty->isIntegral() && "Cannot expand fp recurrences yet!");
// {X,+,F} --> X + {0,+,F}
if (!isa<SCEVConstant>(S->getStart()) ||
!cast<SCEVConstant>(S->getStart())->getValue()->isNullValue()) {
Value *Start = expandInTy(S->getStart(), Ty);
std::vector<SCEVHandle> NewOps(S->op_begin(), S->op_end());
NewOps[0] = SCEVUnknown::getIntegerSCEV(0, Ty);
Value *Rest = expandInTy(SCEVAddRecExpr::get(NewOps, L), Ty);
// FIXME: look for an existing add to use.
return BinaryOperator::createAdd(Rest, Start, "tmp.", InsertPt);
}
// {0,+,1} --> Insert a canonical induction variable into the loop!
if (S->getNumOperands() == 2 &&
S->getOperand(1) == SCEVUnknown::getIntegerSCEV(1, Ty)) {
// Create and insert the PHI node for the induction variable in the
// specified loop.
BasicBlock *Header = L->getHeader();
PHINode *PN = new PHINode(Ty, "indvar", Header->begin());
PN->addIncoming(Constant::getNullValue(Ty), L->getLoopPreheader());
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?");
// Insert a unit add instruction right before the terminator corresponding
// to the back-edge.
Constant *One = Ty->isFloatingPoint() ? (Constant*)ConstantFP::get(Ty, 1.0)
: ConstantInt::get(Ty, 1);
Instruction *Add = BinaryOperator::createAdd(PN, One, "indvar.next",
(*HPI)->getTerminator());
pred_iterator PI = pred_begin(Header);
if (*PI == L->getLoopPreheader())
++PI;
PN->addIncoming(Add, *PI);
return PN;
}
// Get the canonical induction variable I for this loop.
Value *I = getOrInsertCanonicalInductionVariable(L, Ty);
if (S->getNumOperands() == 2) { // {0,+,F} --> i*F
Value *F = expandInTy(S->getOperand(1), Ty);
return BinaryOperator::createMul(I, F, "tmp.", InsertPt);
}
// If this is a chain of recurrences, turn it into a closed form, using the
// folders, then expandCodeFor the closed form. This allows the folders to
// simplify the expression without having to build a bunch of special code
// into this folder.
SCEVHandle IH = SCEVUnknown::get(I); // Get I as a "symbolic" SCEV.
SCEVHandle V = S->evaluateAtIteration(IH);
//std::cerr << "Evaluated: " << *this << "\n to: " << *V << "\n";
return expandInTy(V, Ty);
}
namespace {
Statistic<> NumRemoved ("indvars", "Number of aux indvars removed");
Statistic<> NumPointer ("indvars", "Number of pointer indvars promoted");
Statistic<> NumInserted("indvars", "Number of canonical indvars added");
Statistic<> NumReplaced("indvars", "Number of exit values replaced");
Statistic<> NumLFTR ("indvars", "Number of loop exit tests replaced");
class IndVarSimplify : public FunctionPass {
LoopInfo *LI;
ScalarEvolution *SE;
bool Changed;
public:
virtual bool runOnFunction(Function &) {
LI = &getAnalysis<LoopInfo>();
SE = &getAnalysis<ScalarEvolution>();
Changed = false;
// Induction Variables live in the header nodes of loops
for (LoopInfo::iterator I = LI->begin(), E = LI->end(); I != E; ++I)
runOnLoop(*I);
return Changed;
}
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequiredID(LoopSimplifyID);
AU.addRequired<ScalarEvolution>();
AU.addRequired<LoopInfo>();
AU.addPreservedID(LoopSimplifyID);
AU.setPreservesCFG();
}
private:
void runOnLoop(Loop *L);
void EliminatePointerRecurrence(PHINode *PN, BasicBlock *Preheader,
std::set<Instruction*> &DeadInsts);
void LinearFunctionTestReplace(Loop *L, SCEV *IterationCount,
SCEVExpander &RW);
void RewriteLoopExitValues(Loop *L);
void DeleteTriviallyDeadInstructions(std::set<Instruction*> &Insts);
};
RegisterOpt<IndVarSimplify> X("indvars", "Canonicalize Induction Variables");
}
FunctionPass *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(std::set<Instruction*> &Insts) {
while (!Insts.empty()) {
Instruction *I = *Insts.begin();
Insts.erase(Insts.begin());
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->deleteInstructionFromRecords(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,
std::set<Instruction*> &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 mismatch!");
// 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 = new PHINode(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(GEPI);
for (unsigned i = 1, e = GEPI->getNumOperands()-1;
i != e; ++i, ++GTI)
/*empty*/;
if (isa<SequentialType>(*GTI)) {
// Pull the last index out of the constant expr GEP.
std::vector<Value*> CEIdxs(CE->op_begin()+1, CE->op_end()-1);
Constant *NCE = ConstantExpr::getGetElementPtr(CE->getOperand(0),
CEIdxs);
GetElementPtrInst *NGEPI =
new GetElementPtrInst(NCE, Constant::getNullValue(Type::IntTy),
NewAdd, GEPI->getName(), 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;
std::string Name = PN->getName(); PN->setName("");
Value *PreInc =
new GetElementPtrInst(PN->getIncomingValue(PreheaderIdx),
std::vector<Value*>(1, NewPhi), Name,
InsertPos);
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.
void 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.
std::vector<BasicBlock*> ExitBlocks;
L->getExitBlocks(ExitBlocks);
if (ExitBlocks.size() != 1) return;
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; // Multiple exits from loop to this block.
}
assert(ExitingBlock && "Loop info is broken");
if (!isa<BranchInst>(ExitingBlock->getTerminator()))
return; // Can't rewrite non-branch yet
BranchInst *BI = cast<BranchInst>(ExitingBlock->getTerminator());
assert(BI->isConditional() && "Must be conditional to be part of loop!");
std::set<Instruction*> InstructionsToDelete;
if (Instruction *Cond = dyn_cast<Instruction>(BI->getCondition()))
InstructionsToDelete.insert(Cond);
// 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.
Constant *OneC = ConstantInt::get(IterationCount->getType(), 1);
TripCount = SCEVAddExpr::get(IterationCount, SCEVUnknown::get(OneC));
IndVar = L->getCanonicalInductionVariableIncrement();
} else {
// We have to use the preincremented value...
IndVar = L->getCanonicalInductionVariable();
}
// Expand the code for the iteration count into the preheader of the loop.
BasicBlock *Preheader = L->getLoopPreheader();
Value *ExitCnt = RW.expandCodeFor(TripCount, Preheader->getTerminator(),
IndVar->getType());
// Insert a new setne or seteq instruction before the branch.
Instruction::BinaryOps Opcode;
if (L->contains(BI->getSuccessor(0)))
Opcode = Instruction::SetNE;
else
Opcode = Instruction::SetEQ;
Value *Cond = new SetCondInst(Opcode, IndVar, ExitCnt, "exitcond", BI);
BI->setCondition(Cond);
++NumLFTR;
Changed = true;
DeleteTriviallyDeadInstructions(InstructionsToDelete);
}
/// 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) {
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;
std::vector<BasicBlock*> ExitBlocks;
L->getExitBlocks(ExitBlocks);
if (ExitBlocks.size() == 1)
BlockToInsertInto = ExitBlocks[0];
else
BlockToInsertInto = Preheader;
BasicBlock::iterator InsertPt = BlockToInsertInto->begin();
while (isa<PHINode>(InsertPt)) ++InsertPt;
bool HasConstantItCount = isa<SCEVConstant>(SE->getIterationCount(L));
std::set<Instruction*> InstructionsToDelete;
for (unsigned i = 0, e = L->getBlocks().size(); i != e; ++i)
if (LI->getLoopFor(L->getBlocks()[i]) == L) { // Not in a subloop...
BasicBlock *BB = L->getBlocks()[i];
for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
if (I->getType()->isInteger()) { // Is an integer instruction
SCEVHandle SH = SE->getSCEV(I);
if (SH->hasComputableLoopEvolution(L) || // Varies predictably
HasConstantItCount) {
// Find out if this predictably varying value is actually used
// outside of the loop. "extra" as opposed to "intra".
std::vector<User*> ExtraLoopUsers;
for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
UI != E; ++UI)
if (!L->contains(cast<Instruction>(*UI)->getParent()))
ExtraLoopUsers.push_back(*UI);
if (!ExtraLoopUsers.empty()) {
// Okay, this instruction has a user outside of the current loop
// and varies predictably in this loop. Evaluate the value it
// contains when the loop exits, and insert code for it.
SCEVHandle ExitValue = SE->getSCEVAtScope(I, L->getParentLoop());
if (!isa<SCEVCouldNotCompute>(ExitValue)) {
Changed = true;
++NumReplaced;
Value *NewVal = Rewriter.expandCodeFor(ExitValue, InsertPt,
I->getType());
// Rewrite any users of the computed value outside of the loop
// with the newly computed value.
for (unsigned i = 0, e = ExtraLoopUsers.size(); i != e; ++i)
ExtraLoopUsers[i]->replaceUsesOfWith(I, NewVal);
// If this instruction is dead now, schedule it to be removed.
if (I->use_empty())
InstructionsToDelete.insert(I);
}
}
}
}
}
DeleteTriviallyDeadInstructions(InstructionsToDelete);
}
void IndVarSimplify::runOnLoop(Loop *L) {
// 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();
std::set<Instruction*> 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);
}
if (!DeadInsts.empty())
DeleteTriviallyDeadInstructions(DeadInsts);
// Next, transform all loops nesting inside of this loop.
for (LoopInfo::iterator I = L->begin(), E = L->end(); I != E; ++I)
runOnLoop(*I);
// 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);
// 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: Without a strength reduction pass, it is an extremely bad idea
// to indvar substitute anything more complex than a linear induction
// variable. Doing so will put expensive multiply instructions inside
// of the loop. For now just disable indvar subst on anything more
// complex than a linear addrec.
if (SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(SCEV))
if (AR->getNumOperands() == 2 && isa<SCEVConstant>(AR->getOperand(1)))
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());
LinearFunctionTestReplace(L, IterationCount, Rewriter);
}
return;
}
// 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->getPrimitiveSize() != LargestType->getPrimitiveSize();
if (Ty->getPrimitiveSize() > LargestType->getPrimitiveSize())
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.
LargestType = LargestType->getUnsignedVersion();
Value *IndVar = Rewriter.getOrInsertCanonicalInductionVariable(L,LargestType);
++NumInserted;
Changed = true;
if (!isa<SCEVCouldNotCompute>(IterationCount))
LinearFunctionTestReplace(L, IterationCount, 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->begin();
while (isa<PHINode>(InsertPt)) ++InsertPt;
// 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) {
bool InsertedSizes[17] = { false };
InsertedSizes[LargestType->getPrimitiveSize()] = true;
for (unsigned i = 0, e = IndVars.size(); i != e; ++i)
if (!InsertedSizes[IndVars[i].first->getType()->getPrimitiveSize()]) {
PHINode *PN = IndVars[i].first;
InsertedSizes[PN->getType()->getPrimitiveSize()] = true;
Instruction *New = new CastInst(IndVar,
PN->getType()->getUnsignedVersion(),
"indvar", InsertPt);
Rewriter.addInsertedValue(New, SE->getSCEV(New));
}
}
// 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.
std::map<unsigned, Value*> InsertedSizes;
while (!IndVars.empty()) {
PHINode *PN = IndVars.back().first;
Value *NewVal = Rewriter.expandCodeFor(IndVars.back().second, InsertPt,
PN->getType());
std::string Name = PN->getName();
PN->setName("");
NewVal->setName(Name);
// 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 (unsigned i = 0, e = L->getBlocks().size(); i != e; ++i)
if (LI->getLoopFor(L->getBlocks()[i]) == L) { // Not in a subloop...
BasicBlock *BB = L->getBlocks()[i];
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)) {
std::string Name = I->getName();
I->setName("");
V->setName(Name);
}
I->replaceAllUsesWith(V);
DeadInsts.insert(I);
++NumRemoved;
Changed = true;
}
}
}
#endif
DeleteTriviallyDeadInstructions(DeadInsts);
}
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