//===- IndVarSimplify.cpp - Induction Variable Elimination ----------------===//
+//
+// The LLVM Compiler Infrastructure
//
-// InductionVariableSimplify - Transform induction variables in a program
-// to all use a single cannonical induction variable per loop.
+// 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/Analysis/InductionVariable.h"
-#include "llvm/Analysis/LoopInfo.h"
-#include "llvm/iPHINode.h"
-#include "llvm/iOther.h"
-#include "llvm/Type.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 "Support/STLExtras.h"
-#include "Support/Statistic.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 {
- Statistic<> NumRemoved ("indvars", "Number of aux indvars removed");
- Statistic<> NumInserted("indvars", "Number of cannonical indvars added");
-}
+ /// 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;
-// InsertCast - Cast Val to Ty, setting a useful name on the cast if Val has a
-// name...
-//
-static Instruction *InsertCast(Value *Val, const Type *Ty,
- Instruction *InsertBefore) {
- return new CastInst(Val, Ty, Val->getName()+"-casted", InsertBefore);
-}
+ Instruction *InsertPt;
-static bool TransformLoop(LoopInfo *Loops, Loop *Loop) {
- // Transform all subloops before this loop...
- bool Changed = reduce_apply_bool(Loop->getSubLoops().begin(),
- Loop->getSubLoops().end(),
- std::bind1st(std::ptr_fun(TransformLoop), Loops));
- // Get the header node for this loop. All of the phi nodes that could be
- // induction variables must live in this basic block.
- //
- BasicBlock *Header = Loop->getBlocks().front();
-
- // Loop over all of the PHI nodes in the basic block, calculating the
- // induction variables that they represent... stuffing the induction variable
- // info into a vector...
- //
- std::vector<InductionVariable> IndVars; // Induction variables for block
- BasicBlock::iterator AfterPHIIt = Header->begin();
- for (; PHINode *PN = dyn_cast<PHINode>(&*AfterPHIIt); ++AfterPHIIt)
- IndVars.push_back(InductionVariable(PN, Loops));
- // AfterPHIIt now points to first nonphi instruction...
-
- // If there are no phi nodes in this basic block, there can't be indvars...
- if (IndVars.empty()) return Changed;
-
- // Loop over the induction variables, looking for a cannonical induction
- // variable, and checking to make sure they are not all unknown induction
- // variables.
- //
- bool FoundIndVars = false;
- InductionVariable *Cannonical = 0;
- for (unsigned i = 0; i < IndVars.size(); ++i) {
- if (IndVars[i].InductionType == InductionVariable::Cannonical &&
- !isa<PointerType>(IndVars[i].Phi->getType()))
- Cannonical = &IndVars[i];
- if (IndVars[i].InductionType != InductionVariable::Unknown)
- FoundIndVars = true;
- }
+ friend struct SCEVVisitor<SCEVExpander, Value*>;
+ public:
+ SCEVExpander(ScalarEvolution &se, LoopInfo &li) : SE(se), LI(li) {}
- // No induction variables, bail early... don't add a cannonnical indvar
- if (!FoundIndVars) return Changed;
-
- // Okay, we want to convert other induction variables to use a cannonical
- // indvar. If we don't have one, add one now...
- if (!Cannonical) {
- // Create the PHI node for the new induction variable, and insert the phi
- // node at the end of the other phi nodes...
- PHINode *PN = new PHINode(Type::UIntTy, "cann-indvar", AfterPHIIt);
+ /// 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);
+ }
- // Create the increment instruction to add one to the counter...
- Instruction *Add = BinaryOperator::create(Instruction::Add, PN,
- ConstantUInt::get(Type::UIntTy,1),
- "add1-indvar", AfterPHIIt);
+ /// 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);
+ }
- // Figure out which block is incoming and which is the backedge for the loop
- BasicBlock *Incoming, *BackEdgeBlock;
- pred_iterator PI = pred_begin(Header);
- assert(PI != pred_end(Header) && "Loop headers should have 2 preds!");
- if (Loop->contains(*PI)) { // First pred is back edge...
- BackEdgeBlock = *PI++;
- Incoming = *PI++;
- } else {
- Incoming = *PI++;
- BackEdgeBlock = *PI++;
- }
- assert(PI == pred_end(Header) && "Loop headers should have 2 preds!");
-
- // Add incoming values for the PHI node...
- PN->addIncoming(Constant::getNullValue(Type::UIntTy), Incoming);
- PN->addIncoming(Add, BackEdgeBlock);
-
- // Analyze the new induction variable...
- IndVars.push_back(InductionVariable(PN, Loops));
- assert(IndVars.back().InductionType == InductionVariable::Cannonical &&
- "Just inserted cannonical indvar that is not cannonical!");
- Cannonical = &IndVars.back();
- ++NumInserted;
- Changed = true;
- }
+ /// 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);
+ }
- DEBUG(std::cerr << "Induction variables:\n");
+ 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;
- // Get the current loop iteration count, which is always the value of the
- // cannonical phi node...
- //
- PHINode *IterCount = Cannonical->Phi;
+ Value *V = visit(S);
+ InsertedExpressions[S] = V;
+ return V;
+ }
- // Loop through and replace all of the auxillary induction variables with
- // references to the primary induction variable...
- //
- for (unsigned i = 0; i < IndVars.size(); ++i) {
- InductionVariable *IV = &IndVars[i];
+ 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;
+ while (isa<PHINode>(It)) ++It;
+ if (It != BasicBlock::iterator(CI)) {
+ // Splice the cast immediately after the operand in question.
+ BasicBlock::InstListType &InstList =
+ I->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;
+ }
- DEBUG(IV->print(std::cerr));
+ Value *visitConstant(SCEVConstant *S) {
+ return S->getValue();
+ }
- // Don't do math with pointers...
- const Type *IVTy = IV->Phi->getType();
- if (isa<PointerType>(IVTy)) IVTy = Type::ULongTy;
+ Value *visitTruncateExpr(SCEVTruncateExpr *S) {
+ Value *V = expand(S->getOperand());
+ return new CastInst(V, S->getType(), "tmp.", InsertPt);
+ }
- // Don't modify the cannonical indvar or unrecognized indvars...
- if (IV != Cannonical && IV->InductionType != InductionVariable::Unknown) {
- Instruction *Val = IterCount;
- if (!isa<ConstantInt>(IV->Step) || // If the step != 1
- !cast<ConstantInt>(IV->Step)->equalsInt(1)) {
+ Value *visitZeroExtendExpr(SCEVZeroExtendExpr *S) {
+ Value *V = expandInTy(S->getOperand(),S->getType()->getUnsignedVersion());
+ return new CastInst(V, S->getType(), "tmp.", InsertPt);
+ }
- // If the types are not compatible, insert a cast now...
- if (Val->getType() != IVTy)
- Val = InsertCast(Val, IVTy, AfterPHIIt);
- if (IV->Step->getType() != IVTy)
- IV->Step = InsertCast(IV->Step, IVTy, AfterPHIIt);
+ Value *visitAddExpr(SCEVAddExpr *S) {
+ const Type *Ty = S->getType();
+ Value *V = expandInTy(S->getOperand(S->getNumOperands()-1), Ty);
- Val = BinaryOperator::create(Instruction::Mul, Val, IV->Step,
- IV->Phi->getName()+"-scale", AfterPHIIt);
- }
+ // 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;
+ }
- // If the start != 0
- if (IV->Start != Constant::getNullValue(IV->Start->getType())) {
- // If the types are not compatible, insert a cast now...
- if (Val->getType() != IVTy)
- Val = InsertCast(Val, IVTy, AfterPHIIt);
- if (IV->Start->getType() != IVTy)
- IV->Start = InsertCast(IV->Start, IVTy, AfterPHIIt);
-
- // Insert the instruction after the phi nodes...
- Val = BinaryOperator::create(Instruction::Add, Val, IV->Start,
- IV->Phi->getName()+"-offset", AfterPHIIt);
- }
+ Value *visitMulExpr(SCEVMulExpr *S);
- // If the PHI node has a different type than val is, insert a cast now...
- if (Val->getType() != IV->Phi->getType())
- Val = InsertCast(Val, IV->Phi->getType(), AfterPHIIt);
-
- // Replace all uses of the old PHI node with the new computed value...
- IV->Phi->replaceAllUsesWith(Val);
+ 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);
+ }
- // Move the PHI name to it's new equivalent value...
- std::string OldName = IV->Phi->getName();
- IV->Phi->setName("");
- Val->setName(OldName);
+ Value *visitAddRecExpr(SCEVAddRecExpr *S);
- // Delete the old, now unused, phi node...
- Header->getInstList().erase(IV->Phi);
- Changed = true;
- ++NumRemoved;
+ 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);
}
- return Changed;
+ // 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 {
- struct InductionVariableSimplify : public FunctionPass {
+ 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 &) {
- LoopInfo &LI = getAnalysis<LoopInfo>();
+ LI = &getAnalysis<LoopInfo>();
+ SE = &getAnalysis<ScalarEvolution>();
+ Changed = false;
// Induction Variables live in the header nodes of loops
- return reduce_apply_bool(LI.getTopLevelLoops().begin(),
- LI.getTopLevelLoops().end(),
- std::bind1st(std::ptr_fun(TransformLoop), &LI));
+ 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<InductionVariableSimplify> X("indvars",
- "Cannonicalize Induction Variables");
+ 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;
+ }
+ }
}
-Pass *createIndVarSimplifyPass() {
- return new InductionVariableSimplify();
+
+/// 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);
}
projects / oota-llvm.git / blobdiff