ScalarEvolutionExpander.cpp revision cf5ab820227dedd77fb91d0904b6dc3694a7c196 
1//===- ScalarEvolutionExpander.cpp - Scalar Evolution Analysis --*- C++ -*-===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// 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(Instruction::CastOps opcode, Value *V,
23                                    const Type *Ty) {
24  // Short-circuit unnecessary bitcasts.
25  if (opcode == Instruction::BitCast && V->getType() == Ty)
26    return V;
27
28  // Short-circuit unnecessary inttoptr<->ptrtoint casts.
29  if ((opcode == Instruction::PtrToInt || opcode == Instruction::IntToPtr) &&
30      SE.getTypeSizeInBits(Ty) == SE.getTypeSizeInBits(V->getType())) {
31    if (CastInst *CI = dyn_cast<CastInst>(V))
32      if ((CI->getOpcode() == Instruction::PtrToInt ||
33           CI->getOpcode() == Instruction::IntToPtr) &&
34          SE.getTypeSizeInBits(CI->getType()) ==
35          SE.getTypeSizeInBits(CI->getOperand(0)->getType()))
36        return CI->getOperand(0);
37    if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V))
38      if ((CE->getOpcode() == Instruction::PtrToInt ||
39           CE->getOpcode() == Instruction::IntToPtr) &&
40          SE.getTypeSizeInBits(CE->getType()) ==
41          SE.getTypeSizeInBits(CE->getOperand(0)->getType()))
42        return CE->getOperand(0);
43  }
44
45  // FIXME: keep track of the cast instruction.
46  if (Constant *C = dyn_cast<Constant>(V))
47    return ConstantExpr::getCast(opcode, C, Ty);
48
49  if (Argument *A = dyn_cast<Argument>(V)) {
50    // Check to see if there is already a cast!
51    for (Value::use_iterator UI = A->use_begin(), E = A->use_end();
52         UI != E; ++UI) {
53      if ((*UI)->getType() == Ty)
54        if (CastInst *CI = dyn_cast<CastInst>(cast<Instruction>(*UI)))
55          if (CI->getOpcode() == opcode) {
56            // If the cast isn't the first instruction of the function, move it.
57            if (BasicBlock::iterator(CI) !=
58                A->getParent()->getEntryBlock().begin()) {
59              // If the CastInst is the insert point, change the insert point.
60              if (CI == InsertPt) ++InsertPt;
61              // Splice the cast at the beginning of the entry block.
62              CI->moveBefore(A->getParent()->getEntryBlock().begin());
63            }
64            return CI;
65          }
66    }
67    Instruction *I = CastInst::Create(opcode, V, Ty, V->getName(),
68                                      A->getParent()->getEntryBlock().begin());
69    InsertedValues.insert(I);
70    return I;
71  }
72
73  Instruction *I = cast<Instruction>(V);
74
75  // Check to see if there is already a cast.  If there is, use it.
76  for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
77       UI != E; ++UI) {
78    if ((*UI)->getType() == Ty)
79      if (CastInst *CI = dyn_cast<CastInst>(cast<Instruction>(*UI)))
80        if (CI->getOpcode() == opcode) {
81          BasicBlock::iterator It = I; ++It;
82          if (isa<InvokeInst>(I))
83            It = cast<InvokeInst>(I)->getNormalDest()->begin();
84          while (isa<PHINode>(It)) ++It;
85          if (It != BasicBlock::iterator(CI)) {
86            // If the CastInst is the insert point, change the insert point.
87            if (CI == InsertPt) ++InsertPt;
88            // Splice the cast immediately after the operand in question.
89            CI->moveBefore(It);
90          }
91          return CI;
92        }
93  }
94  BasicBlock::iterator IP = I; ++IP;
95  if (InvokeInst *II = dyn_cast<InvokeInst>(I))
96    IP = II->getNormalDest()->begin();
97  while (isa<PHINode>(IP)) ++IP;
98  Instruction *CI = CastInst::Create(opcode, V, Ty, V->getName(), IP);
99  InsertedValues.insert(CI);
100  return CI;
101}
102
103/// InsertNoopCastOfTo - Insert a cast of V to the specified type,
104/// which must be possible with a noop cast.
105Value *SCEVExpander::InsertNoopCastOfTo(Value *V, const Type *Ty) {
106  Instruction::CastOps Op = CastInst::getCastOpcode(V, false, Ty, false);
107  assert((Op == Instruction::BitCast ||
108          Op == Instruction::PtrToInt ||
109          Op == Instruction::IntToPtr) &&
110         "InsertNoopCastOfTo cannot perform non-noop casts!");
111  assert(SE.getTypeSizeInBits(V->getType()) == SE.getTypeSizeInBits(Ty) &&
112         "InsertNoopCastOfTo cannot change sizes!");
113  return InsertCastOfTo(Op, V, Ty);
114}
115
116/// InsertBinop - Insert the specified binary operator, doing a small amount
117/// of work to avoid inserting an obviously redundant operation.
118Value *SCEVExpander::InsertBinop(Instruction::BinaryOps Opcode, Value *LHS,
119                                 Value *RHS, BasicBlock::iterator InsertPt) {
120  // Fold a binop with constant operands.
121  if (Constant *CLHS = dyn_cast<Constant>(LHS))
122    if (Constant *CRHS = dyn_cast<Constant>(RHS))
123      return ConstantExpr::get(Opcode, CLHS, CRHS);
124
125  // Do a quick scan to see if we have this binop nearby.  If so, reuse it.
126  unsigned ScanLimit = 6;
127  BasicBlock::iterator BlockBegin = InsertPt->getParent()->begin();
128  if (InsertPt != BlockBegin) {
129    // Scanning starts from the last instruction before InsertPt.
130    BasicBlock::iterator IP = InsertPt;
131    --IP;
132    for (; ScanLimit; --IP, --ScanLimit) {
133      if (BinaryOperator *BinOp = dyn_cast<BinaryOperator>(IP))
134        if (BinOp->getOpcode() == Opcode && BinOp->getOperand(0) == LHS &&
135            BinOp->getOperand(1) == RHS)
136          return BinOp;
137      if (IP == BlockBegin) break;
138    }
139  }
140
141  // If we haven't found this binop, insert it.
142  Instruction *BO = BinaryOperator::Create(Opcode, LHS, RHS, "tmp", InsertPt);
143  InsertedValues.insert(BO);
144  return BO;
145}
146
147Value *SCEVExpander::visitAddExpr(const SCEVAddExpr *S) {
148  const Type *Ty = SE.getEffectiveSCEVType(S->getType());
149  Value *V = expand(S->getOperand(S->getNumOperands()-1));
150  V = InsertNoopCastOfTo(V, Ty);
151
152  // Emit a bunch of add instructions
153  for (int i = S->getNumOperands()-2; i >= 0; --i) {
154    Value *W = expand(S->getOperand(i));
155    W = InsertNoopCastOfTo(W, Ty);
156    V = InsertBinop(Instruction::Add, V, W, InsertPt);
157  }
158  return V;
159}
160
161Value *SCEVExpander::visitMulExpr(const SCEVMulExpr *S) {
162  const Type *Ty = SE.getEffectiveSCEVType(S->getType());
163  int FirstOp = 0;  // Set if we should emit a subtract.
164  if (const SCEVConstant *SC = dyn_cast<SCEVConstant>(S->getOperand(0)))
165    if (SC->getValue()->isAllOnesValue())
166      FirstOp = 1;
167
168  int i = S->getNumOperands()-2;
169  Value *V = expand(S->getOperand(i+1));
170  V = InsertNoopCastOfTo(V, Ty);
171
172  // Emit a bunch of multiply instructions
173  for (; i >= FirstOp; --i) {
174    Value *W = expand(S->getOperand(i));
175    W = InsertNoopCastOfTo(W, Ty);
176    V = InsertBinop(Instruction::Mul, V, W, InsertPt);
177  }
178
179  // -1 * ...  --->  0 - ...
180  if (FirstOp == 1)
181    V = InsertBinop(Instruction::Sub, Constant::getNullValue(Ty), V, InsertPt);
182  return V;
183}
184
185Value *SCEVExpander::visitUDivExpr(const SCEVUDivExpr *S) {
186  const Type *Ty = SE.getEffectiveSCEVType(S->getType());
187
188  Value *LHS = expand(S->getLHS());
189  LHS = InsertNoopCastOfTo(LHS, Ty);
190  if (const SCEVConstant *SC = dyn_cast<SCEVConstant>(S->getRHS())) {
191    const APInt &RHS = SC->getValue()->getValue();
192    if (RHS.isPowerOf2())
193      return InsertBinop(Instruction::LShr, LHS,
194                         ConstantInt::get(Ty, RHS.logBase2()),
195                         InsertPt);
196  }
197
198  Value *RHS = expand(S->getRHS());
199  RHS = InsertNoopCastOfTo(RHS, Ty);
200  return InsertBinop(Instruction::UDiv, LHS, RHS, InsertPt);
201}
202
203Value *SCEVExpander::visitAddRecExpr(const SCEVAddRecExpr *S) {
204  const Type *Ty = SE.getEffectiveSCEVType(S->getType());
205  const Loop *L = S->getLoop();
206
207  // {X,+,F} --> X + {0,+,F}
208  if (!S->getStart()->isZero()) {
209    Value *Start = expand(S->getStart());
210    Start = InsertNoopCastOfTo(Start, Ty);
211    std::vector<SCEVHandle> NewOps(S->op_begin(), S->op_end());
212    NewOps[0] = SE.getIntegerSCEV(0, Ty);
213    Value *Rest = expand(SE.getAddRecExpr(NewOps, L));
214    Rest = InsertNoopCastOfTo(Rest, Ty);
215
216    // FIXME: look for an existing add to use.
217    return InsertBinop(Instruction::Add, Rest, Start, InsertPt);
218  }
219
220  // {0,+,1} --> Insert a canonical induction variable into the loop!
221  if (S->isAffine() &&
222      S->getOperand(1) == SE.getIntegerSCEV(1, Ty)) {
223    // Create and insert the PHI node for the induction variable in the
224    // specified loop.
225    BasicBlock *Header = L->getHeader();
226    PHINode *PN = PHINode::Create(Ty, "indvar", Header->begin());
227    InsertedValues.insert(PN);
228    PN->addIncoming(Constant::getNullValue(Ty), L->getLoopPreheader());
229
230    pred_iterator HPI = pred_begin(Header);
231    assert(HPI != pred_end(Header) && "Loop with zero preds???");
232    if (!L->contains(*HPI)) ++HPI;
233    assert(HPI != pred_end(Header) && L->contains(*HPI) &&
234           "No backedge in loop?");
235
236    // Insert a unit add instruction right before the terminator corresponding
237    // to the back-edge.
238    Constant *One = ConstantInt::get(Ty, 1);
239    Instruction *Add = BinaryOperator::CreateAdd(PN, One, "indvar.next",
240                                                 (*HPI)->getTerminator());
241    InsertedValues.insert(Add);
242
243    pred_iterator PI = pred_begin(Header);
244    if (*PI == L->getLoopPreheader())
245      ++PI;
246    PN->addIncoming(Add, *PI);
247    return PN;
248  }
249
250  // Get the canonical induction variable I for this loop.
251  Value *I = getOrInsertCanonicalInductionVariable(L, Ty);
252
253  // If this is a simple linear addrec, emit it now as a special case.
254  if (S->isAffine()) {   // {0,+,F} --> i*F
255    Value *F = expand(S->getOperand(1));
256    F = InsertNoopCastOfTo(F, Ty);
257
258    // IF the step is by one, just return the inserted IV.
259    if (ConstantInt *CI = dyn_cast<ConstantInt>(F))
260      if (CI->getValue() == 1)
261        return I;
262
263    // If the insert point is directly inside of the loop, emit the multiply at
264    // the insert point.  Otherwise, L is a loop that is a parent of the insert
265    // point loop.  If we can, move the multiply to the outer most loop that it
266    // is safe to be in.
267    BasicBlock::iterator MulInsertPt = getInsertionPoint();
268    Loop *InsertPtLoop = LI.getLoopFor(MulInsertPt->getParent());
269    if (InsertPtLoop != L && InsertPtLoop &&
270        L->contains(InsertPtLoop->getHeader())) {
271      do {
272        // If we cannot hoist the multiply out of this loop, don't.
273        if (!InsertPtLoop->isLoopInvariant(F)) break;
274
275        BasicBlock *InsertPtLoopPH = InsertPtLoop->getLoopPreheader();
276
277        // If this loop hasn't got a preheader, we aren't able to hoist the
278        // multiply.
279        if (!InsertPtLoopPH)
280          break;
281
282        // Otherwise, move the insert point to the preheader.
283        MulInsertPt = InsertPtLoopPH->getTerminator();
284        InsertPtLoop = InsertPtLoop->getParentLoop();
285      } while (InsertPtLoop != L);
286    }
287
288    return InsertBinop(Instruction::Mul, I, F, MulInsertPt);
289  }
290
291  // If this is a chain of recurrences, turn it into a closed form, using the
292  // folders, then expandCodeFor the closed form.  This allows the folders to
293  // simplify the expression without having to build a bunch of special code
294  // into this folder.
295  SCEVHandle IH = SE.getUnknown(I);   // Get I as a "symbolic" SCEV.
296
297  SCEVHandle V = S->evaluateAtIteration(IH, SE);
298  //cerr << "Evaluated: " << *this << "\n     to: " << *V << "\n";
299
300  return expand(V);
301}
302
303Value *SCEVExpander::visitTruncateExpr(const SCEVTruncateExpr *S) {
304  const Type *Ty = SE.getEffectiveSCEVType(S->getType());
305  Value *V = expand(S->getOperand());
306  V = InsertNoopCastOfTo(V, SE.getEffectiveSCEVType(V->getType()));
307  Instruction *I = new TruncInst(V, Ty, "tmp.", InsertPt);
308  InsertedValues.insert(I);
309  return I;
310}
311
312Value *SCEVExpander::visitZeroExtendExpr(const SCEVZeroExtendExpr *S) {
313  const Type *Ty = SE.getEffectiveSCEVType(S->getType());
314  Value *V = expand(S->getOperand());
315  V = InsertNoopCastOfTo(V, SE.getEffectiveSCEVType(V->getType()));
316  Instruction *I = new ZExtInst(V, Ty, "tmp.", InsertPt);
317  InsertedValues.insert(I);
318  return I;
319}
320
321Value *SCEVExpander::visitSignExtendExpr(const SCEVSignExtendExpr *S) {
322  const Type *Ty = SE.getEffectiveSCEVType(S->getType());
323  Value *V = expand(S->getOperand());
324  V = InsertNoopCastOfTo(V, SE.getEffectiveSCEVType(V->getType()));
325  Instruction *I = new SExtInst(V, Ty, "tmp.", InsertPt);
326  InsertedValues.insert(I);
327  return I;
328}
329
330Value *SCEVExpander::visitSMaxExpr(const SCEVSMaxExpr *S) {
331  const Type *Ty = SE.getEffectiveSCEVType(S->getType());
332  Value *LHS = expand(S->getOperand(0));
333  LHS = InsertNoopCastOfTo(LHS, Ty);
334  for (unsigned i = 1; i < S->getNumOperands(); ++i) {
335    Value *RHS = expand(S->getOperand(i));
336    RHS = InsertNoopCastOfTo(RHS, Ty);
337    Instruction *ICmp =
338      new ICmpInst(ICmpInst::ICMP_SGT, LHS, RHS, "tmp", InsertPt);
339    InsertedValues.insert(ICmp);
340    Instruction *Sel = SelectInst::Create(ICmp, LHS, RHS, "smax", InsertPt);
341    InsertedValues.insert(Sel);
342    LHS = Sel;
343  }
344  return LHS;
345}
346
347Value *SCEVExpander::visitUMaxExpr(const SCEVUMaxExpr *S) {
348  const Type *Ty = SE.getEffectiveSCEVType(S->getType());
349  Value *LHS = expand(S->getOperand(0));
350  LHS = InsertNoopCastOfTo(LHS, Ty);
351  for (unsigned i = 1; i < S->getNumOperands(); ++i) {
352    Value *RHS = expand(S->getOperand(i));
353    RHS = InsertNoopCastOfTo(RHS, Ty);
354    Instruction *ICmp =
355      new ICmpInst(ICmpInst::ICMP_UGT, LHS, RHS, "tmp", InsertPt);
356    InsertedValues.insert(ICmp);
357    Instruction *Sel = SelectInst::Create(ICmp, LHS, RHS, "umax", InsertPt);
358    InsertedValues.insert(Sel);
359    LHS = Sel;
360  }
361  return LHS;
362}
363
364Value *SCEVExpander::expandCodeFor(SCEVHandle SH, const Type *Ty) {
365  // Expand the code for this SCEV.
366  assert(SE.getTypeSizeInBits(Ty) == SE.getTypeSizeInBits(SH->getType()) &&
367         "non-trivial casts should be done with the SCEVs directly!");
368  Value *V = expand(SH);
369  return InsertNoopCastOfTo(V, Ty);
370}
371
372Value *SCEVExpander::expand(const SCEV *S) {
373  // Check to see if we already expanded this.
374  std::map<SCEVHandle, Value*>::iterator I = InsertedExpressions.find(S);
375  if (I != InsertedExpressions.end())
376    return I->second;
377
378  Value *V = visit(S);
379  InsertedExpressions[S] = V;
380  return V;
381}
382