ScalarEvolutionExpander.cpp revision 42a75517250017a52afb03a0ade03cbd49559fe5 
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/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  // FIXME: keep track of the cast instruction.
25  if (Constant *C = dyn_cast<Constant>(V))
26    return ConstantExpr::getCast(opcode, C, Ty);
27
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();
31         UI != E; ++UI) {
32      if ((*UI)->getType() == Ty)
33        if (CastInst *CI = dyn_cast<CastInst>(cast<Instruction>(*UI))) {
34          // If the cast isn't the first instruction of the function, 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 CastInst::create(opcode, 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 CastInst::create(opcode, V, Ty, V->getName(), IP);
69}
70
71Value *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
91Value *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->isInteger() && "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 (ConstantInt *CI = dyn_cast<ConstantInt>(F))
147      if (CI->getZExtValue() == 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  //cerr << "Evaluated: " << *this << "\n     to: " << *V << "\n";
179
180  return expandInTy(V, Ty);
181}
182