| //===- ScalarEvolutionExpander.cpp - Scalar Evolution Analysis --*- C++ -*-===// |
| // |
| // 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 file contains the implementation of the scalar evolution expander, |
| // which is used to generate the code corresponding to a given scalar evolution |
| // expression. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #include "llvm/Analysis/ScalarEvolutionExpander.h" |
| #include "llvm/Analysis/LoopInfo.h" |
| using namespace llvm; |
| |
| /// InsertCastOfTo - Insert a cast of V to the specified type, doing what |
| /// we can to share the casts. |
| Value *SCEVExpander::InsertCastOfTo(Instruction::CastOps opcode, Value *V, |
| const Type *Ty) { |
| // FIXME: keep track of the cast instruction. |
| if (Constant *C = dyn_cast<Constant>(V)) |
| return ConstantExpr::getCast(opcode, C, Ty); |
| |
| if (Argument *A = dyn_cast<Argument>(V)) { |
| // Check to see if there is already a cast! |
| for (Value::use_iterator UI = A->use_begin(), E = A->use_end(); |
| UI != E; ++UI) { |
| if ((*UI)->getType() == Ty) |
| if (CastInst *CI = dyn_cast<CastInst>(cast<Instruction>(*UI))) { |
| // If the cast isn't the first instruction of the function, move it. |
| if (BasicBlock::iterator(CI) != |
| A->getParent()->getEntryBlock().begin()) { |
| CI->moveBefore(A->getParent()->getEntryBlock().begin()); |
| } |
| return CI; |
| } |
| } |
| return CastInst::create(opcode, V, Ty, V->getName(), |
| A->getParent()->getEntryBlock().begin()); |
| } |
| |
| Instruction *I = 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. |
| CI->moveBefore(It); |
| } |
| return CI; |
| } |
| } |
| BasicBlock::iterator IP = I; ++IP; |
| if (InvokeInst *II = dyn_cast<InvokeInst>(I)) |
| IP = II->getNormalDest()->begin(); |
| while (isa<PHINode>(IP)) ++IP; |
| return CastInst::create(opcode, V, Ty, V->getName(), IP); |
| } |
| |
| /// InsertBinop - Insert the specified binary operator, doing a small amount |
| /// of work to avoid inserting an obviously redundant operation. |
| Value *SCEVExpander::InsertBinop(Instruction::BinaryOps Opcode, Value *LHS, |
| Value *RHS, Instruction *&InsertPt) { |
| // Do a quick scan to see if we have this binop nearby. If so, reuse it. |
| unsigned ScanLimit = 6; |
| for (BasicBlock::iterator IP = InsertPt, E = InsertPt->getParent()->begin(); |
| ScanLimit; --IP, --ScanLimit) { |
| if (BinaryOperator *BinOp = dyn_cast<BinaryOperator>(IP)) |
| if (BinOp->getOpcode() == Opcode && BinOp->getOperand(0) == LHS && |
| BinOp->getOperand(1) == RHS) { |
| // If we found the instruction *at* the insert point, insert later |
| // instructions after it. |
| if (BinOp == InsertPt) |
| InsertPt = ++IP; |
| return BinOp; |
| } |
| if (IP == E) break; |
| } |
| |
| // If we don't have |
| return BinaryOperator::create(Opcode, LHS, RHS, "tmp.", InsertPt); |
| } |
| |
| 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 = InsertBinop(Instruction::Mul, V, expandInTy(S->getOperand(i), Ty), |
| InsertPt); |
| // -1 * ... ---> 0 - ... |
| if (FirstOp == 1) |
| V = InsertBinop(Instruction::Sub, Constant::getNullValue(V->getType()), V, |
| 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->isInteger() && "Cannot expand fp recurrences yet!"); |
| |
| // {X,+,F} --> X + {0,+,F} |
| if (!isa<SCEVConstant>(S->getStart()) || |
| !cast<SCEVConstant>(S->getStart())->getValue()->isZero()) { |
| 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 InsertBinop(Instruction::Add, Rest, Start, 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 = 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 this is a simple linear addrec, emit it now as a special case. |
| if (S->getNumOperands() == 2) { // {0,+,F} --> i*F |
| Value *F = expandInTy(S->getOperand(1), Ty); |
| |
| // IF the step is by one, just return the inserted IV. |
| if (ConstantInt *CI = dyn_cast<ConstantInt>(F)) |
| if (CI->getValue() == 1) |
| return I; |
| |
| // If the insert point is directly inside of the loop, emit the multiply at |
| // the insert point. Otherwise, L is a loop that is a parent of the insert |
| // point loop. If we can, move the multiply to the outer most loop that it |
| // is safe to be in. |
| Instruction *MulInsertPt = InsertPt; |
| Loop *InsertPtLoop = LI.getLoopFor(MulInsertPt->getParent()); |
| if (InsertPtLoop != L && InsertPtLoop && |
| L->contains(InsertPtLoop->getHeader())) { |
| while (InsertPtLoop != L) { |
| // If we cannot hoist the multiply out of this loop, don't. |
| if (!InsertPtLoop->isLoopInvariant(F)) break; |
| |
| // Otherwise, move the insert point to the preheader of the loop. |
| MulInsertPt = InsertPtLoop->getLoopPreheader()->getTerminator(); |
| InsertPtLoop = InsertPtLoop->getParentLoop(); |
| } |
| } |
| |
| return InsertBinop(Instruction::Mul, I, F, MulInsertPt); |
| } |
| |
| // 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); |
| //cerr << "Evaluated: " << *this << "\n to: " << *V << "\n"; |
| |
| return expandInTy(V, Ty); |
| } |
