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