1 //===- ScalarEvolutionExpander.cpp - Scalar Evolution Analysis --*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
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.
8 //===----------------------------------------------------------------------===//
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
14 //===----------------------------------------------------------------------===//
16 #include "llvm/Analysis/ScalarEvolutionExpander.h"
17 #include "llvm/Analysis/LoopInfo.h"
20 /// InsertCastOfTo - Insert a cast of V to the specified type, doing what
21 /// we can to share the casts.
22 Value *SCEVExpander::InsertCastOfTo(Instruction::CastOps opcode, Value *V,
24 // FIXME: keep track of the cast instruction.
25 if (Constant *C = dyn_cast<Constant>(V))
26 return ConstantExpr::getCast(opcode, C, Ty);
28 if (Argument *A = dyn_cast<Argument>(V)) {
29 // Check to see if there is already a cast!
30 for (Value::use_iterator UI = A->use_begin(), E = A->use_end();
32 if ((*UI)->getType() == Ty)
33 if (CastInst *CI = dyn_cast<CastInst>(cast<Instruction>(*UI))) {
34 // If the cast isn't the first instruction of the function, move it.
35 if (BasicBlock::iterator(CI) !=
36 A->getParent()->getEntryBlock().begin()) {
37 CI->moveBefore(A->getParent()->getEntryBlock().begin());
42 return CastInst::create(opcode, V, Ty, V->getName(),
43 A->getParent()->getEntryBlock().begin());
46 Instruction *I = cast<Instruction>(V);
48 // Check to see if there is already a cast. If there is, use it.
49 for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
51 if ((*UI)->getType() == Ty)
52 if (CastInst *CI = dyn_cast<CastInst>(cast<Instruction>(*UI))) {
53 BasicBlock::iterator It = I; ++It;
54 if (isa<InvokeInst>(I))
55 It = cast<InvokeInst>(I)->getNormalDest()->begin();
56 while (isa<PHINode>(It)) ++It;
57 if (It != BasicBlock::iterator(CI)) {
58 // Splice the cast immediately after the operand in question.
64 BasicBlock::iterator IP = I; ++IP;
65 if (InvokeInst *II = dyn_cast<InvokeInst>(I))
66 IP = II->getNormalDest()->begin();
67 while (isa<PHINode>(IP)) ++IP;
68 return CastInst::create(opcode, V, Ty, V->getName(), IP);
71 /// InsertBinop - Insert the specified binary operator, doing a small amount
72 /// of work to avoid inserting an obviously redundant operation.
73 Value *SCEVExpander::InsertBinop(Instruction::BinaryOps Opcode, Value *LHS,
74 Value *RHS, Instruction *&InsertPt) {
75 // Do a quick scan to see if we have this binop nearby. If so, reuse it.
76 unsigned ScanLimit = 6;
77 for (BasicBlock::iterator IP = InsertPt, E = InsertPt->getParent()->begin();
78 ScanLimit; --IP, --ScanLimit) {
79 if (BinaryOperator *BinOp = dyn_cast<BinaryOperator>(IP))
80 if (BinOp->getOpcode() == Opcode && BinOp->getOperand(0) == LHS &&
81 BinOp->getOperand(1) == RHS) {
82 // If we found the instruction *at* the insert point, insert later
83 // instructions after it.
84 if (BinOp == InsertPt)
92 return BinaryOperator::create(Opcode, LHS, RHS, "tmp.", InsertPt);
95 Value *SCEVExpander::visitMulExpr(SCEVMulExpr *S) {
96 int FirstOp = 0; // Set if we should emit a subtract.
97 if (SCEVConstant *SC = dyn_cast<SCEVConstant>(S->getOperand(0)))
98 if (SC->getValue()->isAllOnesValue())
101 int i = S->getNumOperands()-2;
102 Value *V = expand(S->getOperand(i+1));
104 // Emit a bunch of multiply instructions
105 for (; i >= FirstOp; --i)
106 V = InsertBinop(Instruction::Mul, V, expand(S->getOperand(i)),
108 // -1 * ... ---> 0 - ...
110 V = InsertBinop(Instruction::Sub, Constant::getNullValue(V->getType()), V,
115 Value *SCEVExpander::visitAddRecExpr(SCEVAddRecExpr *S) {
116 const Type *Ty = S->getType();
117 const Loop *L = S->getLoop();
118 // We cannot yet do fp recurrences, e.g. the xform of {X,+,F} --> X+{0,+,F}
119 assert(Ty->isInteger() && "Cannot expand fp recurrences yet!");
121 // {X,+,F} --> X + {0,+,F}
122 if (!isa<SCEVConstant>(S->getStart()) ||
123 !cast<SCEVConstant>(S->getStart())->getValue()->isZero()) {
124 Value *Start = expand(S->getStart());
125 std::vector<SCEVHandle> NewOps(S->op_begin(), S->op_end());
126 NewOps[0] = SCEVUnknown::getIntegerSCEV(0, Ty);
127 Value *Rest = expand(SCEVAddRecExpr::get(NewOps, L));
129 // FIXME: look for an existing add to use.
130 return InsertBinop(Instruction::Add, Rest, Start, InsertPt);
133 // {0,+,1} --> Insert a canonical induction variable into the loop!
134 if (S->getNumOperands() == 2 &&
135 S->getOperand(1) == SCEVUnknown::getIntegerSCEV(1, Ty)) {
136 // Create and insert the PHI node for the induction variable in the
138 BasicBlock *Header = L->getHeader();
139 PHINode *PN = new PHINode(Ty, "indvar", Header->begin());
140 PN->addIncoming(Constant::getNullValue(Ty), L->getLoopPreheader());
142 pred_iterator HPI = pred_begin(Header);
143 assert(HPI != pred_end(Header) && "Loop with zero preds???");
144 if (!L->contains(*HPI)) ++HPI;
145 assert(HPI != pred_end(Header) && L->contains(*HPI) &&
146 "No backedge in loop?");
148 // Insert a unit add instruction right before the terminator corresponding
150 Constant *One = ConstantInt::get(Ty, 1);
151 Instruction *Add = BinaryOperator::createAdd(PN, One, "indvar.next",
152 (*HPI)->getTerminator());
154 pred_iterator PI = pred_begin(Header);
155 if (*PI == L->getLoopPreheader())
157 PN->addIncoming(Add, *PI);
161 // Get the canonical induction variable I for this loop.
162 Value *I = getOrInsertCanonicalInductionVariable(L, Ty);
164 // If this is a simple linear addrec, emit it now as a special case.
165 if (S->getNumOperands() == 2) { // {0,+,F} --> i*F
166 Value *F = expand(S->getOperand(1));
168 // IF the step is by one, just return the inserted IV.
169 if (ConstantInt *CI = dyn_cast<ConstantInt>(F))
170 if (CI->getValue() == 1)
173 // If the insert point is directly inside of the loop, emit the multiply at
174 // the insert point. Otherwise, L is a loop that is a parent of the insert
175 // point loop. If we can, move the multiply to the outer most loop that it
177 Instruction *MulInsertPt = InsertPt;
178 Loop *InsertPtLoop = LI.getLoopFor(MulInsertPt->getParent());
179 if (InsertPtLoop != L && InsertPtLoop &&
180 L->contains(InsertPtLoop->getHeader())) {
181 while (InsertPtLoop != L) {
182 // If we cannot hoist the multiply out of this loop, don't.
183 if (!InsertPtLoop->isLoopInvariant(F)) break;
185 // Otherwise, move the insert point to the preheader of the loop.
186 MulInsertPt = InsertPtLoop->getLoopPreheader()->getTerminator();
187 InsertPtLoop = InsertPtLoop->getParentLoop();
191 return InsertBinop(Instruction::Mul, I, F, MulInsertPt);
194 // If this is a chain of recurrences, turn it into a closed form, using the
195 // folders, then expandCodeFor the closed form. This allows the folders to
196 // simplify the expression without having to build a bunch of special code
198 SCEVHandle IH = SCEVUnknown::get(I); // Get I as a "symbolic" SCEV.
200 SCEVHandle V = S->evaluateAtIteration(IH);
201 //cerr << "Evaluated: " << *this << "\n to: " << *V << "\n";