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222 lines
8.4 KiB
C++
222 lines
8.4 KiB
C++
//===- ScalarEvolutionExpander.cpp - Scalar Evolution Analysis --*- C++ -*-===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file was developed by the LLVM research group and is distributed under
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// the University of Illinois Open Source License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file contains the implementation of the scalar evolution expander,
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// which is used to generate the code corresponding to a given scalar evolution
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// expression.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Analysis/ScalarEvolutionExpander.h"
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#include "llvm/Analysis/LoopInfo.h"
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using namespace llvm;
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/// InsertCastOfTo - Insert a cast of V to the specified type, doing what
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/// we can to share the casts.
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Value *SCEVExpander::InsertCastOfTo(Instruction::CastOps opcode, Value *V,
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const Type *Ty) {
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// FIXME: keep track of the cast instruction.
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if (Constant *C = dyn_cast<Constant>(V))
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return ConstantExpr::getCast(opcode, C, Ty);
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if (Argument *A = dyn_cast<Argument>(V)) {
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// Check to see if there is already a cast!
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for (Value::use_iterator UI = A->use_begin(), E = A->use_end();
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UI != E; ++UI) {
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if ((*UI)->getType() == Ty)
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if (CastInst *CI = dyn_cast<CastInst>(cast<Instruction>(*UI))) {
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// If the cast isn't the first instruction of the function, move it.
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if (BasicBlock::iterator(CI) !=
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A->getParent()->getEntryBlock().begin()) {
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CI->moveBefore(A->getParent()->getEntryBlock().begin());
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}
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return CI;
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}
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}
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return CastInst::create(opcode, V, Ty, V->getName(),
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A->getParent()->getEntryBlock().begin());
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}
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Instruction *I = cast<Instruction>(V);
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// Check to see if there is already a cast. If there is, use it.
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for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
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UI != E; ++UI) {
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if ((*UI)->getType() == Ty)
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if (CastInst *CI = dyn_cast<CastInst>(cast<Instruction>(*UI))) {
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BasicBlock::iterator It = I; ++It;
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if (isa<InvokeInst>(I))
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It = cast<InvokeInst>(I)->getNormalDest()->begin();
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while (isa<PHINode>(It)) ++It;
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if (It != BasicBlock::iterator(CI)) {
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// Splice the cast immediately after the operand in question.
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CI->moveBefore(It);
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}
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return CI;
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}
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}
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BasicBlock::iterator IP = I; ++IP;
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if (InvokeInst *II = dyn_cast<InvokeInst>(I))
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IP = II->getNormalDest()->begin();
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while (isa<PHINode>(IP)) ++IP;
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return CastInst::create(opcode, V, Ty, V->getName(), IP);
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}
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/// InsertBinop - Insert the specified binary operator, doing a small amount
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/// of work to avoid inserting an obviously redundant operation.
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Value *SCEVExpander::InsertBinop(Instruction::BinaryOps Opcode, Value *LHS,
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Value *RHS, Instruction *&InsertPt) {
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// Fold a binop with constant operands.
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if (Constant *CLHS = dyn_cast<Constant>(LHS))
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if (Constant *CRHS = dyn_cast<Constant>(RHS))
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return ConstantExpr::get(Opcode, CLHS, CRHS);
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// Do a quick scan to see if we have this binop nearby. If so, reuse it.
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unsigned ScanLimit = 6;
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for (BasicBlock::iterator IP = InsertPt, E = InsertPt->getParent()->begin();
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ScanLimit; --IP, --ScanLimit) {
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if (BinaryOperator *BinOp = dyn_cast<BinaryOperator>(IP))
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if (BinOp->getOpcode() == Opcode && BinOp->getOperand(0) == LHS &&
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BinOp->getOperand(1) == RHS) {
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// If we found the instruction *at* the insert point, insert later
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// instructions after it.
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if (BinOp == InsertPt)
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InsertPt = ++IP;
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return BinOp;
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}
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if (IP == E) break;
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}
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// If we don't have
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return BinaryOperator::create(Opcode, LHS, RHS, "tmp", InsertPt);
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}
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Value *SCEVExpander::visitMulExpr(SCEVMulExpr *S) {
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int FirstOp = 0; // Set if we should emit a subtract.
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if (SCEVConstant *SC = dyn_cast<SCEVConstant>(S->getOperand(0)))
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if (SC->getValue()->isAllOnesValue())
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FirstOp = 1;
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int i = S->getNumOperands()-2;
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Value *V = expand(S->getOperand(i+1));
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// Emit a bunch of multiply instructions
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for (; i >= FirstOp; --i)
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V = InsertBinop(Instruction::Mul, V, expand(S->getOperand(i)),
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InsertPt);
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// -1 * ... ---> 0 - ...
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if (FirstOp == 1)
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V = InsertBinop(Instruction::Sub, Constant::getNullValue(V->getType()), V,
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InsertPt);
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return V;
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}
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Value *SCEVExpander::visitAddRecExpr(SCEVAddRecExpr *S) {
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const Type *Ty = S->getType();
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const Loop *L = S->getLoop();
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// We cannot yet do fp recurrences, e.g. the xform of {X,+,F} --> X+{0,+,F}
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assert(Ty->isInteger() && "Cannot expand fp recurrences yet!");
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// {X,+,F} --> X + {0,+,F}
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if (!isa<SCEVConstant>(S->getStart()) ||
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!cast<SCEVConstant>(S->getStart())->getValue()->isZero()) {
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Value *Start = expand(S->getStart());
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std::vector<SCEVHandle> NewOps(S->op_begin(), S->op_end());
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NewOps[0] = SCEVUnknown::getIntegerSCEV(0, Ty);
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Value *Rest = expand(SCEVAddRecExpr::get(NewOps, L));
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// FIXME: look for an existing add to use.
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return InsertBinop(Instruction::Add, Rest, Start, InsertPt);
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}
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// {0,+,1} --> Insert a canonical induction variable into the loop!
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if (S->getNumOperands() == 2 &&
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S->getOperand(1) == SCEVUnknown::getIntegerSCEV(1, Ty)) {
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// Create and insert the PHI node for the induction variable in the
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// specified loop.
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BasicBlock *Header = L->getHeader();
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PHINode *PN = new PHINode(Ty, "indvar", Header->begin());
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PN->addIncoming(Constant::getNullValue(Ty), L->getLoopPreheader());
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pred_iterator HPI = pred_begin(Header);
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assert(HPI != pred_end(Header) && "Loop with zero preds???");
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if (!L->contains(*HPI)) ++HPI;
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assert(HPI != pred_end(Header) && L->contains(*HPI) &&
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"No backedge in loop?");
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// Insert a unit add instruction right before the terminator corresponding
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// to the back-edge.
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Constant *One = ConstantInt::get(Ty, 1);
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Instruction *Add = BinaryOperator::createAdd(PN, One, "indvar.next",
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(*HPI)->getTerminator());
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pred_iterator PI = pred_begin(Header);
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if (*PI == L->getLoopPreheader())
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++PI;
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PN->addIncoming(Add, *PI);
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return PN;
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}
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// Get the canonical induction variable I for this loop.
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Value *I = getOrInsertCanonicalInductionVariable(L, Ty);
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// If this is a simple linear addrec, emit it now as a special case.
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if (S->getNumOperands() == 2) { // {0,+,F} --> i*F
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Value *F = expand(S->getOperand(1));
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// IF the step is by one, just return the inserted IV.
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if (ConstantInt *CI = dyn_cast<ConstantInt>(F))
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if (CI->getValue() == 1)
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return I;
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// If the insert point is directly inside of the loop, emit the multiply at
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// the insert point. Otherwise, L is a loop that is a parent of the insert
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// point loop. If we can, move the multiply to the outer most loop that it
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// is safe to be in.
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Instruction *MulInsertPt = InsertPt;
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Loop *InsertPtLoop = LI.getLoopFor(MulInsertPt->getParent());
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if (InsertPtLoop != L && InsertPtLoop &&
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L->contains(InsertPtLoop->getHeader())) {
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while (InsertPtLoop != L) {
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// If we cannot hoist the multiply out of this loop, don't.
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if (!InsertPtLoop->isLoopInvariant(F)) break;
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// Otherwise, move the insert point to the preheader of the loop.
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MulInsertPt = InsertPtLoop->getLoopPreheader()->getTerminator();
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InsertPtLoop = InsertPtLoop->getParentLoop();
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}
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}
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return InsertBinop(Instruction::Mul, I, F, MulInsertPt);
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}
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// If this is a chain of recurrences, turn it into a closed form, using the
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// folders, then expandCodeFor the closed form. This allows the folders to
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// simplify the expression without having to build a bunch of special code
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// into this folder.
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SCEVHandle IH = SCEVUnknown::get(I); // Get I as a "symbolic" SCEV.
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SCEVHandle V = S->evaluateAtIteration(IH);
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//cerr << "Evaluated: " << *this << "\n to: " << *V << "\n";
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return expand(V);
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}
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Value *SCEVExpander::expand(SCEV *S) {
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// Check to see if we already expanded this.
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std::map<SCEVHandle, Value*>::iterator I = InsertedExpressions.find(S);
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if (I != InsertedExpressions.end())
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return I->second;
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Value *V = visit(S);
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InsertedExpressions[S] = V;
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return V;
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}
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