1 //===- ScalarEvolutionExpander.cpp - Scalar Evolution Analysis --*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // 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 (CI->getOpcode() == opcode) {
35 // If the cast isn't the first instruction of the function, move it.
36 if (BasicBlock::iterator(CI) !=
37 A->getParent()->getEntryBlock().begin()) {
38 CI->moveBefore(A->getParent()->getEntryBlock().begin());
43 return CastInst::Create(opcode, V, Ty, V->getName(),
44 A->getParent()->getEntryBlock().begin());
47 Instruction *I = cast<Instruction>(V);
49 // Check to see if there is already a cast. If there is, use it.
50 for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
52 if ((*UI)->getType() == Ty)
53 if (CastInst *CI = dyn_cast<CastInst>(cast<Instruction>(*UI)))
54 if (CI->getOpcode() == opcode) {
55 BasicBlock::iterator It = I; ++It;
56 if (isa<InvokeInst>(I))
57 It = cast<InvokeInst>(I)->getNormalDest()->begin();
58 while (isa<PHINode>(It)) ++It;
59 if (It != BasicBlock::iterator(CI)) {
60 // Splice the cast immediately after the operand in question.
66 BasicBlock::iterator IP = I; ++IP;
67 if (InvokeInst *II = dyn_cast<InvokeInst>(I))
68 IP = II->getNormalDest()->begin();
69 while (isa<PHINode>(IP)) ++IP;
70 return CastInst::Create(opcode, V, Ty, V->getName(), IP);
73 /// InsertBinop - Insert the specified binary operator, doing a small amount
74 /// of work to avoid inserting an obviously redundant operation.
75 Value *SCEVExpander::InsertBinop(Instruction::BinaryOps Opcode, Value *LHS,
76 Value *RHS, Instruction *InsertPt) {
77 // Fold a binop with constant operands.
78 if (Constant *CLHS = dyn_cast<Constant>(LHS))
79 if (Constant *CRHS = dyn_cast<Constant>(RHS))
80 return ConstantExpr::get(Opcode, CLHS, CRHS);
82 // Do a quick scan to see if we have this binop nearby. If so, reuse it.
83 unsigned ScanLimit = 6;
84 BasicBlock::iterator BlockBegin = InsertPt->getParent()->begin();
85 if (InsertPt != BlockBegin) {
86 // Scanning starts from the last instruction before InsertPt.
87 BasicBlock::iterator IP = InsertPt;
89 for (; ScanLimit; --IP, --ScanLimit) {
90 if (BinaryOperator *BinOp = dyn_cast<BinaryOperator>(IP))
91 if (BinOp->getOpcode() == Opcode && BinOp->getOperand(0) == LHS &&
92 BinOp->getOperand(1) == RHS)
94 if (IP == BlockBegin) break;
98 // If we haven't found this binop, insert it.
99 return BinaryOperator::Create(Opcode, LHS, RHS, "tmp", InsertPt);
102 Value *SCEVExpander::visitAddExpr(SCEVAddExpr *S) {
103 Value *V = expand(S->getOperand(S->getNumOperands()-1));
105 // Emit a bunch of add instructions
106 for (int i = S->getNumOperands()-2; i >= 0; --i)
107 V = InsertBinop(Instruction::Add, V, expand(S->getOperand(i)),
112 Value *SCEVExpander::visitMulExpr(SCEVMulExpr *S) {
113 int FirstOp = 0; // Set if we should emit a subtract.
114 if (SCEVConstant *SC = dyn_cast<SCEVConstant>(S->getOperand(0)))
115 if (SC->getValue()->isAllOnesValue())
118 int i = S->getNumOperands()-2;
119 Value *V = expand(S->getOperand(i+1));
121 // Emit a bunch of multiply instructions
122 for (; i >= FirstOp; --i)
123 V = InsertBinop(Instruction::Mul, V, expand(S->getOperand(i)),
125 // -1 * ... ---> 0 - ...
127 V = InsertBinop(Instruction::Sub, Constant::getNullValue(V->getType()), V,
132 Value *SCEVExpander::visitUDivExpr(SCEVUDivExpr *S) {
133 Value *LHS = expand(S->getLHS());
134 if (SCEVConstant *SC = dyn_cast<SCEVConstant>(S->getRHS())) {
135 const APInt &RHS = SC->getValue()->getValue();
136 if (RHS.isPowerOf2())
137 return InsertBinop(Instruction::LShr, LHS,
138 ConstantInt::get(S->getType(), RHS.logBase2()),
142 Value *RHS = expand(S->getRHS());
143 return InsertBinop(Instruction::UDiv, LHS, RHS, InsertPt);
146 Value *SCEVExpander::visitSDivExpr(SCEVSDivExpr *S) {
147 // Do not fold sdiv into ashr, unless you know that LHS is positive. On
148 // negative values, it rounds the wrong way.
150 Value *LHS = expand(S->getLHS());
151 Value *RHS = expand(S->getRHS());
152 return InsertBinop(Instruction::SDiv, LHS, RHS, InsertPt);
155 Value *SCEVExpander::visitAddRecExpr(SCEVAddRecExpr *S) {
156 const Type *Ty = S->getType();
157 const Loop *L = S->getLoop();
158 // We cannot yet do fp recurrences, e.g. the xform of {X,+,F} --> X+{0,+,F}
159 assert(Ty->isInteger() && "Cannot expand fp recurrences yet!");
161 // {X,+,F} --> X + {0,+,F}
162 if (!S->getStart()->isZero()) {
163 Value *Start = expand(S->getStart());
164 std::vector<SCEVHandle> NewOps(S->op_begin(), S->op_end());
165 NewOps[0] = SE.getIntegerSCEV(0, Ty);
166 Value *Rest = expand(SE.getAddRecExpr(NewOps, L));
168 // FIXME: look for an existing add to use.
169 return InsertBinop(Instruction::Add, Rest, Start, InsertPt);
172 // {0,+,1} --> Insert a canonical induction variable into the loop!
174 S->getOperand(1) == SE.getIntegerSCEV(1, Ty)) {
175 // Create and insert the PHI node for the induction variable in the
177 BasicBlock *Header = L->getHeader();
178 PHINode *PN = PHINode::Create(Ty, "indvar", Header->begin());
179 PN->addIncoming(Constant::getNullValue(Ty), L->getLoopPreheader());
181 pred_iterator HPI = pred_begin(Header);
182 assert(HPI != pred_end(Header) && "Loop with zero preds???");
183 if (!L->contains(*HPI)) ++HPI;
184 assert(HPI != pred_end(Header) && L->contains(*HPI) &&
185 "No backedge in loop?");
187 // Insert a unit add instruction right before the terminator corresponding
189 Constant *One = ConstantInt::get(Ty, 1);
190 Instruction *Add = BinaryOperator::CreateAdd(PN, One, "indvar.next",
191 (*HPI)->getTerminator());
193 pred_iterator PI = pred_begin(Header);
194 if (*PI == L->getLoopPreheader())
196 PN->addIncoming(Add, *PI);
200 // Get the canonical induction variable I for this loop.
201 Value *I = getOrInsertCanonicalInductionVariable(L, Ty);
203 // If this is a simple linear addrec, emit it now as a special case.
204 if (S->isAffine()) { // {0,+,F} --> i*F
205 Value *F = expand(S->getOperand(1));
207 // IF the step is by one, just return the inserted IV.
208 if (ConstantInt *CI = dyn_cast<ConstantInt>(F))
209 if (CI->getValue() == 1)
212 // If the insert point is directly inside of the loop, emit the multiply at
213 // the insert point. Otherwise, L is a loop that is a parent of the insert
214 // point loop. If we can, move the multiply to the outer most loop that it
216 Instruction *MulInsertPt = InsertPt;
217 Loop *InsertPtLoop = LI.getLoopFor(MulInsertPt->getParent());
218 if (InsertPtLoop != L && InsertPtLoop &&
219 L->contains(InsertPtLoop->getHeader())) {
221 // If we cannot hoist the multiply out of this loop, don't.
222 if (!InsertPtLoop->isLoopInvariant(F)) break;
224 BasicBlock *InsertPtLoopPH = InsertPtLoop->getLoopPreheader();
226 // If this loop hasn't got a preheader, we aren't able to hoist the
231 // Otherwise, move the insert point to the preheader.
232 MulInsertPt = InsertPtLoopPH->getTerminator();
233 InsertPtLoop = InsertPtLoop->getParentLoop();
234 } while (InsertPtLoop != L);
237 return InsertBinop(Instruction::Mul, I, F, MulInsertPt);
240 // If this is a chain of recurrences, turn it into a closed form, using the
241 // folders, then expandCodeFor the closed form. This allows the folders to
242 // simplify the expression without having to build a bunch of special code
244 SCEVHandle IH = SE.getUnknown(I); // Get I as a "symbolic" SCEV.
246 SCEVHandle V = S->evaluateAtIteration(IH, SE);
247 //cerr << "Evaluated: " << *this << "\n to: " << *V << "\n";
252 Value *SCEVExpander::visitTruncateExpr(SCEVTruncateExpr *S) {
253 Value *V = expand(S->getOperand());
254 return CastInst::CreateTruncOrBitCast(V, S->getType(), "tmp.", InsertPt);
257 Value *SCEVExpander::visitZeroExtendExpr(SCEVZeroExtendExpr *S) {
258 Value *V = expand(S->getOperand());
259 return CastInst::CreateZExtOrBitCast(V, S->getType(), "tmp.", InsertPt);
262 Value *SCEVExpander::visitSignExtendExpr(SCEVSignExtendExpr *S) {
263 Value *V = expand(S->getOperand());
264 return CastInst::CreateSExtOrBitCast(V, S->getType(), "tmp.", InsertPt);
267 Value *SCEVExpander::visitSMaxExpr(SCEVSMaxExpr *S) {
268 Value *LHS = expand(S->getOperand(0));
269 for (unsigned i = 1; i < S->getNumOperands(); ++i) {
270 Value *RHS = expand(S->getOperand(i));
271 Value *ICmp = new ICmpInst(ICmpInst::ICMP_SGT, LHS, RHS, "tmp", InsertPt);
272 LHS = SelectInst::Create(ICmp, LHS, RHS, "smax", InsertPt);
277 Value *SCEVExpander::visitUMaxExpr(SCEVUMaxExpr *S) {
278 Value *LHS = expand(S->getOperand(0));
279 for (unsigned i = 1; i < S->getNumOperands(); ++i) {
280 Value *RHS = expand(S->getOperand(i));
281 Value *ICmp = new ICmpInst(ICmpInst::ICMP_UGT, LHS, RHS, "tmp", InsertPt);
282 LHS = SelectInst::Create(ICmp, LHS, RHS, "umax", InsertPt);
287 Value *SCEVExpander::expandCodeFor(SCEVHandle SH, Instruction *IP) {
288 // Expand the code for this SCEV.
293 Value *SCEVExpander::expand(SCEV *S) {
294 // Check to see if we already expanded this.
295 std::map<SCEVHandle, Value*>::iterator I = InsertedExpressions.find(S);
296 if (I != InsertedExpressions.end())
300 InsertedExpressions[S] = V;