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Diffstat (limited to 'lib/Analysis/ScalarEvolutionExpander.cpp')
| -rw-r--r-- | lib/Analysis/ScalarEvolutionExpander.cpp | 209 |
1 files changed, 209 insertions, 0 deletions
diff --git a/lib/Analysis/ScalarEvolutionExpander.cpp b/lib/Analysis/ScalarEvolutionExpander.cpp new file mode 100644 index 0000000..3e590d6 --- /dev/null +++ b/lib/Analysis/ScalarEvolutionExpander.cpp @@ -0,0 +1,209 @@ +//===- 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) { + // Fold a binop with constant operands. + if (Constant *CLHS = dyn_cast<Constant>(LHS)) + if (Constant *CRHS = dyn_cast<Constant>(RHS)) + return ConstantExpr::get(Opcode, CLHS, CRHS); + + // 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) { + 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 = expand(S->getOperand(i+1)); + + // Emit a bunch of multiply instructions + for (; i >= FirstOp; --i) + V = InsertBinop(Instruction::Mul, V, expand(S->getOperand(i)), + 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 = expand(S->getStart()); + std::vector<SCEVHandle> NewOps(S->op_begin(), S->op_end()); + NewOps[0] = SCEVUnknown::getIntegerSCEV(0, Ty); + Value *Rest = expand(SCEVAddRecExpr::get(NewOps, L)); + + // 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 = expand(S->getOperand(1)); + + // 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 expand(V); +} |