lib/Analysis/ScalarEvolutionExpander.cpp

   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"
  18 using namespace llvm;
  19
  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,
  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.
 105 Value *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.
 118 Value *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
 147 Value *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
 161 Value *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
 185 Value *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
 203 Value *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
 303 Value *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
 312 Value *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
 321 Value *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
 330 Value *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
 347 Value *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
 364 Value *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
 372 Value *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 }