ScalarEvolutionExpander.cpp revision e81561909d128c6e2d8033cb5465a49b2596b26a
1//===- ScalarEvolutionExpander.cpp - Scalar Evolution Analysis --*- C++ -*-===// 2// 3// The LLVM Compiler Infrastructure 4// 5// This file was developed by the LLVM research group and is distributed under 6// the University of Illinois Open Source License. See LICENSE.TXT for details. 7// 8//===----------------------------------------------------------------------===// 9// 10// This file contains the implementation of the scalar evolution expander, 11// which is used to generate the code corresponding to a given scalar evolution 12// expression. 13// 14//===----------------------------------------------------------------------===// 15 16#include "llvm/Analysis/ScalarEvolutionExpander.h" 17#include "llvm/Analysis/LoopInfo.h" 18using namespace llvm; 19 20/// InsertCastOfTo - Insert a cast of V to the specified type, doing what 21/// we can to share the casts. 22Value *SCEVExpander::InsertCastOfTo(Value *V, const Type *Ty) { 23 // FIXME: keep track of the cast instruction. 24 if (Constant *C = dyn_cast<Constant>(V)) 25 return ConstantExpr::getCast(C, Ty); 26 27 if (Argument *A = dyn_cast<Argument>(V)) { 28 // Check to see if there is already a cast! 29 for (Value::use_iterator UI = A->use_begin(), E = A->use_end(); 30 UI != E; ++UI) { 31 if ((*UI)->getType() == Ty) 32 if (CastInst *CI = dyn_cast<CastInst>(cast<Instruction>(*UI))) { 33 // If the cast isn't the first instruction of the function, move it. 34 if (BasicBlock::iterator(CI) != 35 A->getParent()->getEntryBlock().begin()) { 36 CI->moveBefore(A->getParent()->getEntryBlock().begin()); 37 } 38 return CI; 39 } 40 } 41 return CastInst::createInferredCast( 42 V, Ty, V->getName(), A->getParent()->getEntryBlock().begin()); 43 } 44 45 Instruction *I = cast<Instruction>(V); 46 47 // Check to see if there is already a cast. If there is, use it. 48 for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); 49 UI != E; ++UI) { 50 if ((*UI)->getType() == Ty) 51 if (CastInst *CI = dyn_cast<CastInst>(cast<Instruction>(*UI))) { 52 BasicBlock::iterator It = I; ++It; 53 if (isa<InvokeInst>(I)) 54 It = cast<InvokeInst>(I)->getNormalDest()->begin(); 55 while (isa<PHINode>(It)) ++It; 56 if (It != BasicBlock::iterator(CI)) { 57 // Splice the cast immediately after the operand in question. 58 CI->moveBefore(It); 59 } 60 return CI; 61 } 62 } 63 BasicBlock::iterator IP = I; ++IP; 64 if (InvokeInst *II = dyn_cast<InvokeInst>(I)) 65 IP = II->getNormalDest()->begin(); 66 while (isa<PHINode>(IP)) ++IP; 67 return CastInst::createInferredCast(V, Ty, V->getName(), IP); 68} 69 70Value *SCEVExpander::visitMulExpr(SCEVMulExpr *S) { 71 const Type *Ty = S->getType(); 72 int FirstOp = 0; // Set if we should emit a subtract. 73 if (SCEVConstant *SC = dyn_cast<SCEVConstant>(S->getOperand(0))) 74 if (SC->getValue()->isAllOnesValue()) 75 FirstOp = 1; 76 77 int i = S->getNumOperands()-2; 78 Value *V = expandInTy(S->getOperand(i+1), Ty); 79 80 // Emit a bunch of multiply instructions 81 for (; i >= FirstOp; --i) 82 V = BinaryOperator::createMul(V, expandInTy(S->getOperand(i), Ty), 83 "tmp.", InsertPt); 84 // -1 * ... ---> 0 - ... 85 if (FirstOp == 1) 86 V = BinaryOperator::createNeg(V, "tmp.", InsertPt); 87 return V; 88} 89 90Value *SCEVExpander::visitAddRecExpr(SCEVAddRecExpr *S) { 91 const Type *Ty = S->getType(); 92 const Loop *L = S->getLoop(); 93 // We cannot yet do fp recurrences, e.g. the xform of {X,+,F} --> X+{0,+,F} 94 assert(Ty->isIntegral() && "Cannot expand fp recurrences yet!"); 95 96 // {X,+,F} --> X + {0,+,F} 97 if (!isa<SCEVConstant>(S->getStart()) || 98 !cast<SCEVConstant>(S->getStart())->getValue()->isNullValue()) { 99 Value *Start = expandInTy(S->getStart(), Ty); 100 std::vector<SCEVHandle> NewOps(S->op_begin(), S->op_end()); 101 NewOps[0] = SCEVUnknown::getIntegerSCEV(0, Ty); 102 Value *Rest = expandInTy(SCEVAddRecExpr::get(NewOps, L), Ty); 103 104 // FIXME: look for an existing add to use. 105 return BinaryOperator::createAdd(Rest, Start, "tmp.", InsertPt); 106 } 107 108 // {0,+,1} --> Insert a canonical induction variable into the loop! 109 if (S->getNumOperands() == 2 && 110 S->getOperand(1) == SCEVUnknown::getIntegerSCEV(1, Ty)) { 111 // Create and insert the PHI node for the induction variable in the 112 // specified loop. 113 BasicBlock *Header = L->getHeader(); 114 PHINode *PN = new PHINode(Ty, "indvar", Header->begin()); 115 PN->addIncoming(Constant::getNullValue(Ty), L->getLoopPreheader()); 116 117 pred_iterator HPI = pred_begin(Header); 118 assert(HPI != pred_end(Header) && "Loop with zero preds???"); 119 if (!L->contains(*HPI)) ++HPI; 120 assert(HPI != pred_end(Header) && L->contains(*HPI) && 121 "No backedge in loop?"); 122 123 // Insert a unit add instruction right before the terminator corresponding 124 // to the back-edge. 125 Constant *One = Ty->isFloatingPoint() ? (Constant*)ConstantFP::get(Ty, 1.0) 126 : ConstantInt::get(Ty, 1); 127 Instruction *Add = BinaryOperator::createAdd(PN, One, "indvar.next", 128 (*HPI)->getTerminator()); 129 130 pred_iterator PI = pred_begin(Header); 131 if (*PI == L->getLoopPreheader()) 132 ++PI; 133 PN->addIncoming(Add, *PI); 134 return PN; 135 } 136 137 // Get the canonical induction variable I for this loop. 138 Value *I = getOrInsertCanonicalInductionVariable(L, Ty); 139 140 // If this is a simple linear addrec, emit it now as a special case. 141 if (S->getNumOperands() == 2) { // {0,+,F} --> i*F 142 Value *F = expandInTy(S->getOperand(1), Ty); 143 144 // IF the step is by one, just return the inserted IV. 145 if (ConstantIntegral *CI = dyn_cast<ConstantIntegral>(F)) 146 if (CI->getZExtValue() == 1) 147 return I; 148 149 // If the insert point is directly inside of the loop, emit the multiply at 150 // the insert point. Otherwise, L is a loop that is a parent of the insert 151 // point loop. If we can, move the multiply to the outer most loop that it 152 // is safe to be in. 153 Instruction *MulInsertPt = InsertPt; 154 Loop *InsertPtLoop = LI.getLoopFor(MulInsertPt->getParent()); 155 if (InsertPtLoop != L && InsertPtLoop && 156 L->contains(InsertPtLoop->getHeader())) { 157 while (InsertPtLoop != L) { 158 // If we cannot hoist the multiply out of this loop, don't. 159 if (!InsertPtLoop->isLoopInvariant(F)) break; 160 161 // Otherwise, move the insert point to the preheader of the loop. 162 MulInsertPt = InsertPtLoop->getLoopPreheader()->getTerminator(); 163 InsertPtLoop = InsertPtLoop->getParentLoop(); 164 } 165 } 166 167 return BinaryOperator::createMul(I, F, "tmp.", MulInsertPt); 168 } 169 170 // If this is a chain of recurrences, turn it into a closed form, using the 171 // folders, then expandCodeFor the closed form. This allows the folders to 172 // simplify the expression without having to build a bunch of special code 173 // into this folder. 174 SCEVHandle IH = SCEVUnknown::get(I); // Get I as a "symbolic" SCEV. 175 176 SCEVHandle V = S->evaluateAtIteration(IH); 177 //cerr << "Evaluated: " << *this << "\n to: " << *V << "\n"; 178 179 return expandInTy(V, Ty); 180} 181