lib/Analysis/ScalarEvolutionExpander.cpp

   1 //===- ScalarEvolutionExpander.cpp - Scalar Evolution Analysis --*- C++ -*-===//
   2 //
   3 //                     The LLVM Compiler Infrastructure
   4 //
   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.
   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/LoopInfo.h"
  17 #include "llvm/Analysis/ScalarEvolutionExpander.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(Value *V, const Type *Ty) {
  23   // FIXME: keep track of the cast instruction.
  24   if (Constant *C = dyn_cast<Constant>(V))
  25     return ConstantExpr::getCast(C, Ty);
  26
  27   if (Argument *A = dyn_cast<Argument>(V)) {
  28     // Check to see if there is already a cast!
  29     for (Value::use_iterator UI = A->use_begin(), E = A->use_end();
  30          UI != E; ++UI) {
  31       if ((*UI)->getType() == Ty)
  32         if (CastInst *CI = dyn_cast<CastInst>(cast<Instruction>(*UI))) {
  33           // If the cast isn't in the first instruction of the function,
  34           // move it.
  35           if (BasicBlock::iterator(CI) !=
  36               A->getParent()->getEntryBlock().begin()) {
  37             CI->moveBefore(A->getParent()->getEntryBlock().begin());
  38           }
  39           return CI;
  40         }
  41     }
  42     return new CastInst(V, Ty, V->getName(),
  43                         A->getParent()->getEntryBlock().begin());
  44   }
  45
  46   Instruction *I = cast<Instruction>(V);
  47
  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();
  50        UI != E; ++UI) {
  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.
  59           CI->moveBefore(It);
  60         }
  61         return CI;
  62       }
  63   }
  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 new CastInst(V, Ty, V->getName(), IP);
  69 }
  70
  71 Value *SCEVExpander::visitMulExpr(SCEVMulExpr *S) {
  72   const Type *Ty = S->getType();
  73   int FirstOp = 0;  // Set if we should emit a subtract.
  74   if (SCEVConstant *SC = dyn_cast<SCEVConstant>(S->getOperand(0)))
  75     if (SC->getValue()->isAllOnesValue())
  76       FirstOp = 1;
  77
  78   int i = S->getNumOperands()-2;
  79   Value *V = expandInTy(S->getOperand(i+1), Ty);
  80
  81   // Emit a bunch of multiply instructions
  82   for (; i >= FirstOp; --i)
  83     V = BinaryOperator::createMul(V, expandInTy(S->getOperand(i), Ty),
  84                                   "tmp.", InsertPt);
  85   // -1 * ...  --->  0 - ...
  86   if (FirstOp == 1)
  87     V = BinaryOperator::createNeg(V, "tmp.", InsertPt);
  88   return V;
  89 }
  90
  91 Value *SCEVExpander::visitAddRecExpr(SCEVAddRecExpr *S) {
  92   const Type *Ty = S->getType();
  93   const Loop *L = S->getLoop();
  94   // We cannot yet do fp recurrences, e.g. the xform of {X,+,F} --> X+{0,+,F}
  95   assert(Ty->isIntegral() && "Cannot expand fp recurrences yet!");
  96
  97   // {X,+,F} --> X + {0,+,F}
  98   if (!isa<SCEVConstant>(S->getStart()) ||
  99       !cast<SCEVConstant>(S->getStart())->getValue()->isNullValue()) {
 100     Value *Start = expandInTy(S->getStart(), Ty);
 101     std::vector<SCEVHandle> NewOps(S->op_begin(), S->op_end());
 102     NewOps[0] = SCEVUnknown::getIntegerSCEV(0, Ty);
 103     Value *Rest = expandInTy(SCEVAddRecExpr::get(NewOps, L), Ty);
 104
 105     // FIXME: look for an existing add to use.
 106     return BinaryOperator::createAdd(Rest, Start, "tmp.", InsertPt);
 107   }
 108
 109   // {0,+,1} --> Insert a canonical induction variable into the loop!
 110   if (S->getNumOperands() == 2 &&
 111       S->getOperand(1) == SCEVUnknown::getIntegerSCEV(1, Ty)) {
 112     // Create and insert the PHI node for the induction variable in the
 113     // specified loop.
 114     BasicBlock *Header = L->getHeader();
 115     PHINode *PN = new PHINode(Ty, "indvar", Header->begin());
 116     PN->addIncoming(Constant::getNullValue(Ty), L->getLoopPreheader());
 117
 118     pred_iterator HPI = pred_begin(Header);
 119     assert(HPI != pred_end(Header) && "Loop with zero preds???");
 120     if (!L->contains(*HPI)) ++HPI;
 121     assert(HPI != pred_end(Header) && L->contains(*HPI) &&
 122            "No backedge in loop?");
 123
 124     // Insert a unit add instruction right before the terminator corresponding
 125     // to the back-edge.
 126     Constant *One = Ty->isFloatingPoint() ? (Constant*)ConstantFP::get(Ty, 1.0)
 127                                           : ConstantInt::get(Ty, 1);
 128     Instruction *Add = BinaryOperator::createAdd(PN, One, "indvar.next",
 129                                                  (*HPI)->getTerminator());
 130
 131     pred_iterator PI = pred_begin(Header);
 132     if (*PI == L->getLoopPreheader())
 133       ++PI;
 134     PN->addIncoming(Add, *PI);
 135     return PN;
 136   }
 137
 138   // Get the canonical induction variable I for this loop.
 139   Value *I = getOrInsertCanonicalInductionVariable(L, Ty);
 140
 141   // If this is a simple linear addrec, emit it now as a special case.
 142   if (S->getNumOperands() == 2) {   // {0,+,F} --> i*F
 143     Value *F = expandInTy(S->getOperand(1), Ty);
 144
 145     // IF the step is by one, just return the inserted IV.
 146     if (ConstantIntegral *CI = dyn_cast<ConstantIntegral>(F))
 147       if (CI->getRawValue() == 1)
 148         return I;
 149
 150     // If the insert point is directly inside of the loop, emit the multiply at
 151     // the insert point.  Otherwise, L is a loop that is a parent of the insert
 152     // point loop.  If we can, move the multiply to the outer most loop that it
 153     // is safe to be in.
 154     Instruction *MulInsertPt = InsertPt;
 155     Loop *InsertPtLoop = LI.getLoopFor(MulInsertPt->getParent());
 156     if (InsertPtLoop != L && InsertPtLoop &&
 157         L->contains(InsertPtLoop->getHeader())) {
 158       while (InsertPtLoop != L) {
 159         // If we cannot hoist the multiply out of this loop, don't.
 160         if (!InsertPtLoop->isLoopInvariant(F)) break;
 161
 162         // Otherwise, move the insert point to the preheader of the loop.
 163         MulInsertPt = InsertPtLoop->getLoopPreheader()->getTerminator();
 164         InsertPtLoop = InsertPtLoop->getParentLoop();
 165       }
 166     }
 167
 168     return BinaryOperator::createMul(I, F, "tmp.", MulInsertPt);
 169   }
 170
 171   // If this is a chain of recurrences, turn it into a closed form, using the
 172   // folders, then expandCodeFor the closed form.  This allows the folders to
 173   // simplify the expression without having to build a bunch of special code
 174   // into this folder.
 175   SCEVHandle IH = SCEVUnknown::get(I);   // Get I as a "symbolic" SCEV.
 176
 177   SCEVHandle V = S->evaluateAtIteration(IH);
 178   //std::cerr << "Evaluated: " << *this << "\n     to: " << *V << "\n";
 179
 180   return expandInTy(V, Ty);
 181 }