Reassociate.cpp revision 243830
1//===- Reassociate.cpp - Reassociate binary expressions -------------------===//
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 pass reassociates commutative expressions in an order that is designed
11// to promote better constant propagation, GCSE, LICM, PRE, etc.
12//
13// For example: 4 + (x + 5) -> x + (4 + 5)
14//
15// In the implementation of this algorithm, constants are assigned rank = 0,
16// function arguments are rank = 1, and other values are assigned ranks
17// corresponding to the reverse post order traversal of current function
18// (starting at 2), which effectively gives values in deep loops higher rank
19// than values not in loops.
20//
21//===----------------------------------------------------------------------===//
22
23#define DEBUG_TYPE "reassociate"
24#include "llvm/Transforms/Scalar.h"
25#include "llvm/Transforms/Utils/Local.h"
26#include "llvm/Constants.h"
27#include "llvm/DerivedTypes.h"
28#include "llvm/Function.h"
29#include "llvm/IRBuilder.h"
30#include "llvm/Instructions.h"
31#include "llvm/IntrinsicInst.h"
32#include "llvm/Pass.h"
33#include "llvm/ADT/DenseMap.h"
34#include "llvm/ADT/PostOrderIterator.h"
35#include "llvm/ADT/STLExtras.h"
36#include "llvm/ADT/SetVector.h"
37#include "llvm/ADT/Statistic.h"
38#include "llvm/Assembly/Writer.h"
39#include "llvm/Support/CFG.h"
40#include "llvm/Support/Debug.h"
41#include "llvm/Support/ValueHandle.h"
42#include "llvm/Support/raw_ostream.h"
43#include <algorithm>
44using namespace llvm;
45
46STATISTIC(NumChanged, "Number of insts reassociated");
47STATISTIC(NumAnnihil, "Number of expr tree annihilated");
48STATISTIC(NumFactor , "Number of multiplies factored");
49
50namespace {
51  struct ValueEntry {
52    unsigned Rank;
53    Value *Op;
54    ValueEntry(unsigned R, Value *O) : Rank(R), Op(O) {}
55  };
56  inline bool operator<(const ValueEntry &LHS, const ValueEntry &RHS) {
57    return LHS.Rank > RHS.Rank;   // Sort so that highest rank goes to start.
58  }
59}
60
61#ifndef NDEBUG
62/// PrintOps - Print out the expression identified in the Ops list.
63///
64static void PrintOps(Instruction *I, const SmallVectorImpl<ValueEntry> &Ops) {
65  Module *M = I->getParent()->getParent()->getParent();
66  dbgs() << Instruction::getOpcodeName(I->getOpcode()) << " "
67       << *Ops[0].Op->getType() << '\t';
68  for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
69    dbgs() << "[ ";
70    WriteAsOperand(dbgs(), Ops[i].Op, false, M);
71    dbgs() << ", #" << Ops[i].Rank << "] ";
72  }
73}
74#endif
75
76namespace {
77  /// \brief Utility class representing a base and exponent pair which form one
78  /// factor of some product.
79  struct Factor {
80    Value *Base;
81    unsigned Power;
82
83    Factor(Value *Base, unsigned Power) : Base(Base), Power(Power) {}
84
85    /// \brief Sort factors by their Base.
86    struct BaseSorter {
87      bool operator()(const Factor &LHS, const Factor &RHS) {
88        return LHS.Base < RHS.Base;
89      }
90    };
91
92    /// \brief Compare factors for equal bases.
93    struct BaseEqual {
94      bool operator()(const Factor &LHS, const Factor &RHS) {
95        return LHS.Base == RHS.Base;
96      }
97    };
98
99    /// \brief Sort factors in descending order by their power.
100    struct PowerDescendingSorter {
101      bool operator()(const Factor &LHS, const Factor &RHS) {
102        return LHS.Power > RHS.Power;
103      }
104    };
105
106    /// \brief Compare factors for equal powers.
107    struct PowerEqual {
108      bool operator()(const Factor &LHS, const Factor &RHS) {
109        return LHS.Power == RHS.Power;
110      }
111    };
112  };
113}
114
115namespace {
116  class Reassociate : public FunctionPass {
117    DenseMap<BasicBlock*, unsigned> RankMap;
118    DenseMap<AssertingVH<Value>, unsigned> ValueRankMap;
119    SetVector<AssertingVH<Instruction> > RedoInsts;
120    bool MadeChange;
121  public:
122    static char ID; // Pass identification, replacement for typeid
123    Reassociate() : FunctionPass(ID) {
124      initializeReassociatePass(*PassRegistry::getPassRegistry());
125    }
126
127    bool runOnFunction(Function &F);
128
129    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
130      AU.setPreservesCFG();
131    }
132  private:
133    void BuildRankMap(Function &F);
134    unsigned getRank(Value *V);
135    void ReassociateExpression(BinaryOperator *I);
136    void RewriteExprTree(BinaryOperator *I, SmallVectorImpl<ValueEntry> &Ops);
137    Value *OptimizeExpression(BinaryOperator *I,
138                              SmallVectorImpl<ValueEntry> &Ops);
139    Value *OptimizeAdd(Instruction *I, SmallVectorImpl<ValueEntry> &Ops);
140    bool collectMultiplyFactors(SmallVectorImpl<ValueEntry> &Ops,
141                                SmallVectorImpl<Factor> &Factors);
142    Value *buildMinimalMultiplyDAG(IRBuilder<> &Builder,
143                                   SmallVectorImpl<Factor> &Factors);
144    Value *OptimizeMul(BinaryOperator *I, SmallVectorImpl<ValueEntry> &Ops);
145    Value *RemoveFactorFromExpression(Value *V, Value *Factor);
146    void EraseInst(Instruction *I);
147    void OptimizeInst(Instruction *I);
148  };
149}
150
151char Reassociate::ID = 0;
152INITIALIZE_PASS(Reassociate, "reassociate",
153                "Reassociate expressions", false, false)
154
155// Public interface to the Reassociate pass
156FunctionPass *llvm::createReassociatePass() { return new Reassociate(); }
157
158/// isReassociableOp - Return true if V is an instruction of the specified
159/// opcode and if it only has one use.
160static BinaryOperator *isReassociableOp(Value *V, unsigned Opcode) {
161  if (V->hasOneUse() && isa<Instruction>(V) &&
162      cast<Instruction>(V)->getOpcode() == Opcode)
163    return cast<BinaryOperator>(V);
164  return 0;
165}
166
167static bool isUnmovableInstruction(Instruction *I) {
168  if (I->getOpcode() == Instruction::PHI ||
169      I->getOpcode() == Instruction::LandingPad ||
170      I->getOpcode() == Instruction::Alloca ||
171      I->getOpcode() == Instruction::Load ||
172      I->getOpcode() == Instruction::Invoke ||
173      (I->getOpcode() == Instruction::Call &&
174       !isa<DbgInfoIntrinsic>(I)) ||
175      I->getOpcode() == Instruction::UDiv ||
176      I->getOpcode() == Instruction::SDiv ||
177      I->getOpcode() == Instruction::FDiv ||
178      I->getOpcode() == Instruction::URem ||
179      I->getOpcode() == Instruction::SRem ||
180      I->getOpcode() == Instruction::FRem)
181    return true;
182  return false;
183}
184
185void Reassociate::BuildRankMap(Function &F) {
186  unsigned i = 2;
187
188  // Assign distinct ranks to function arguments
189  for (Function::arg_iterator I = F.arg_begin(), E = F.arg_end(); I != E; ++I)
190    ValueRankMap[&*I] = ++i;
191
192  ReversePostOrderTraversal<Function*> RPOT(&F);
193  for (ReversePostOrderTraversal<Function*>::rpo_iterator I = RPOT.begin(),
194         E = RPOT.end(); I != E; ++I) {
195    BasicBlock *BB = *I;
196    unsigned BBRank = RankMap[BB] = ++i << 16;
197
198    // Walk the basic block, adding precomputed ranks for any instructions that
199    // we cannot move.  This ensures that the ranks for these instructions are
200    // all different in the block.
201    for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
202      if (isUnmovableInstruction(I))
203        ValueRankMap[&*I] = ++BBRank;
204  }
205}
206
207unsigned Reassociate::getRank(Value *V) {
208  Instruction *I = dyn_cast<Instruction>(V);
209  if (I == 0) {
210    if (isa<Argument>(V)) return ValueRankMap[V];   // Function argument.
211    return 0;  // Otherwise it's a global or constant, rank 0.
212  }
213
214  if (unsigned Rank = ValueRankMap[I])
215    return Rank;    // Rank already known?
216
217  // If this is an expression, return the 1+MAX(rank(LHS), rank(RHS)) so that
218  // we can reassociate expressions for code motion!  Since we do not recurse
219  // for PHI nodes, we cannot have infinite recursion here, because there
220  // cannot be loops in the value graph that do not go through PHI nodes.
221  unsigned Rank = 0, MaxRank = RankMap[I->getParent()];
222  for (unsigned i = 0, e = I->getNumOperands();
223       i != e && Rank != MaxRank; ++i)
224    Rank = std::max(Rank, getRank(I->getOperand(i)));
225
226  // If this is a not or neg instruction, do not count it for rank.  This
227  // assures us that X and ~X will have the same rank.
228  if (!I->getType()->isIntegerTy() ||
229      (!BinaryOperator::isNot(I) && !BinaryOperator::isNeg(I)))
230    ++Rank;
231
232  //DEBUG(dbgs() << "Calculated Rank[" << V->getName() << "] = "
233  //     << Rank << "\n");
234
235  return ValueRankMap[I] = Rank;
236}
237
238/// LowerNegateToMultiply - Replace 0-X with X*-1.
239///
240static BinaryOperator *LowerNegateToMultiply(Instruction *Neg) {
241  Constant *Cst = Constant::getAllOnesValue(Neg->getType());
242
243  BinaryOperator *Res =
244    BinaryOperator::CreateMul(Neg->getOperand(1), Cst, "",Neg);
245  Neg->setOperand(1, Constant::getNullValue(Neg->getType())); // Drop use of op.
246  Res->takeName(Neg);
247  Neg->replaceAllUsesWith(Res);
248  Res->setDebugLoc(Neg->getDebugLoc());
249  return Res;
250}
251
252/// CarmichaelShift - Returns k such that lambda(2^Bitwidth) = 2^k, where lambda
253/// is the Carmichael function. This means that x^(2^k) === 1 mod 2^Bitwidth for
254/// every odd x, i.e. x^(2^k) = 1 for every odd x in Bitwidth-bit arithmetic.
255/// Note that 0 <= k < Bitwidth, and if Bitwidth > 3 then x^(2^k) = 0 for every
256/// even x in Bitwidth-bit arithmetic.
257static unsigned CarmichaelShift(unsigned Bitwidth) {
258  if (Bitwidth < 3)
259    return Bitwidth - 1;
260  return Bitwidth - 2;
261}
262
263/// IncorporateWeight - Add the extra weight 'RHS' to the existing weight 'LHS',
264/// reducing the combined weight using any special properties of the operation.
265/// The existing weight LHS represents the computation X op X op ... op X where
266/// X occurs LHS times.  The combined weight represents  X op X op ... op X with
267/// X occurring LHS + RHS times.  If op is "Xor" for example then the combined
268/// operation is equivalent to X if LHS + RHS is odd, or 0 if LHS + RHS is even;
269/// the routine returns 1 in LHS in the first case, and 0 in LHS in the second.
270static void IncorporateWeight(APInt &LHS, const APInt &RHS, unsigned Opcode) {
271  // If we were working with infinite precision arithmetic then the combined
272  // weight would be LHS + RHS.  But we are using finite precision arithmetic,
273  // and the APInt sum LHS + RHS may not be correct if it wraps (it is correct
274  // for nilpotent operations and addition, but not for idempotent operations
275  // and multiplication), so it is important to correctly reduce the combined
276  // weight back into range if wrapping would be wrong.
277
278  // If RHS is zero then the weight didn't change.
279  if (RHS.isMinValue())
280    return;
281  // If LHS is zero then the combined weight is RHS.
282  if (LHS.isMinValue()) {
283    LHS = RHS;
284    return;
285  }
286  // From this point on we know that neither LHS nor RHS is zero.
287
288  if (Instruction::isIdempotent(Opcode)) {
289    // Idempotent means X op X === X, so any non-zero weight is equivalent to a
290    // weight of 1.  Keeping weights at zero or one also means that wrapping is
291    // not a problem.
292    assert(LHS == 1 && RHS == 1 && "Weights not reduced!");
293    return; // Return a weight of 1.
294  }
295  if (Instruction::isNilpotent(Opcode)) {
296    // Nilpotent means X op X === 0, so reduce weights modulo 2.
297    assert(LHS == 1 && RHS == 1 && "Weights not reduced!");
298    LHS = 0; // 1 + 1 === 0 modulo 2.
299    return;
300  }
301  if (Opcode == Instruction::Add) {
302    // TODO: Reduce the weight by exploiting nsw/nuw?
303    LHS += RHS;
304    return;
305  }
306
307  assert(Opcode == Instruction::Mul && "Unknown associative operation!");
308  unsigned Bitwidth = LHS.getBitWidth();
309  // If CM is the Carmichael number then a weight W satisfying W >= CM+Bitwidth
310  // can be replaced with W-CM.  That's because x^W=x^(W-CM) for every Bitwidth
311  // bit number x, since either x is odd in which case x^CM = 1, or x is even in
312  // which case both x^W and x^(W - CM) are zero.  By subtracting off multiples
313  // of CM like this weights can always be reduced to the range [0, CM+Bitwidth)
314  // which by a happy accident means that they can always be represented using
315  // Bitwidth bits.
316  // TODO: Reduce the weight by exploiting nsw/nuw?  (Could do much better than
317  // the Carmichael number).
318  if (Bitwidth > 3) {
319    /// CM - The value of Carmichael's lambda function.
320    APInt CM = APInt::getOneBitSet(Bitwidth, CarmichaelShift(Bitwidth));
321    // Any weight W >= Threshold can be replaced with W - CM.
322    APInt Threshold = CM + Bitwidth;
323    assert(LHS.ult(Threshold) && RHS.ult(Threshold) && "Weights not reduced!");
324    // For Bitwidth 4 or more the following sum does not overflow.
325    LHS += RHS;
326    while (LHS.uge(Threshold))
327      LHS -= CM;
328  } else {
329    // To avoid problems with overflow do everything the same as above but using
330    // a larger type.
331    unsigned CM = 1U << CarmichaelShift(Bitwidth);
332    unsigned Threshold = CM + Bitwidth;
333    assert(LHS.getZExtValue() < Threshold && RHS.getZExtValue() < Threshold &&
334           "Weights not reduced!");
335    unsigned Total = LHS.getZExtValue() + RHS.getZExtValue();
336    while (Total >= Threshold)
337      Total -= CM;
338    LHS = Total;
339  }
340}
341
342typedef std::pair<Value*, APInt> RepeatedValue;
343
344/// LinearizeExprTree - Given an associative binary expression, return the leaf
345/// nodes in Ops along with their weights (how many times the leaf occurs).  The
346/// original expression is the same as
347///   (Ops[0].first op Ops[0].first op ... Ops[0].first)  <- Ops[0].second times
348/// op
349///   (Ops[1].first op Ops[1].first op ... Ops[1].first)  <- Ops[1].second times
350/// op
351///   ...
352/// op
353///   (Ops[N].first op Ops[N].first op ... Ops[N].first)  <- Ops[N].second times
354///
355/// Note that the values Ops[0].first, ..., Ops[N].first are all distinct.
356///
357/// This routine may modify the function, in which case it returns 'true'.  The
358/// changes it makes may well be destructive, changing the value computed by 'I'
359/// to something completely different.  Thus if the routine returns 'true' then
360/// you MUST either replace I with a new expression computed from the Ops array,
361/// or use RewriteExprTree to put the values back in.
362///
363/// A leaf node is either not a binary operation of the same kind as the root
364/// node 'I' (i.e. is not a binary operator at all, or is, but with a different
365/// opcode), or is the same kind of binary operator but has a use which either
366/// does not belong to the expression, or does belong to the expression but is
367/// a leaf node.  Every leaf node has at least one use that is a non-leaf node
368/// of the expression, while for non-leaf nodes (except for the root 'I') every
369/// use is a non-leaf node of the expression.
370///
371/// For example:
372///           expression graph        node names
373///
374///                     +        |        I
375///                    / \       |
376///                   +   +      |      A,  B
377///                  / \ / \     |
378///                 *   +   *    |    C,  D,  E
379///                / \ / \ / \   |
380///                   +   *      |      F,  G
381///
382/// The leaf nodes are C, E, F and G.  The Ops array will contain (maybe not in
383/// that order) (C, 1), (E, 1), (F, 2), (G, 2).
384///
385/// The expression is maximal: if some instruction is a binary operator of the
386/// same kind as 'I', and all of its uses are non-leaf nodes of the expression,
387/// then the instruction also belongs to the expression, is not a leaf node of
388/// it, and its operands also belong to the expression (but may be leaf nodes).
389///
390/// NOTE: This routine will set operands of non-leaf non-root nodes to undef in
391/// order to ensure that every non-root node in the expression has *exactly one*
392/// use by a non-leaf node of the expression.  This destruction means that the
393/// caller MUST either replace 'I' with a new expression or use something like
394/// RewriteExprTree to put the values back in if the routine indicates that it
395/// made a change by returning 'true'.
396///
397/// In the above example either the right operand of A or the left operand of B
398/// will be replaced by undef.  If it is B's operand then this gives:
399///
400///                     +        |        I
401///                    / \       |
402///                   +   +      |      A,  B - operand of B replaced with undef
403///                  / \   \     |
404///                 *   +   *    |    C,  D,  E
405///                / \ / \ / \   |
406///                   +   *      |      F,  G
407///
408/// Note that such undef operands can only be reached by passing through 'I'.
409/// For example, if you visit operands recursively starting from a leaf node
410/// then you will never see such an undef operand unless you get back to 'I',
411/// which requires passing through a phi node.
412///
413/// Note that this routine may also mutate binary operators of the wrong type
414/// that have all uses inside the expression (i.e. only used by non-leaf nodes
415/// of the expression) if it can turn them into binary operators of the right
416/// type and thus make the expression bigger.
417
418static bool LinearizeExprTree(BinaryOperator *I,
419                              SmallVectorImpl<RepeatedValue> &Ops) {
420  DEBUG(dbgs() << "LINEARIZE: " << *I << '\n');
421  unsigned Bitwidth = I->getType()->getScalarType()->getPrimitiveSizeInBits();
422  unsigned Opcode = I->getOpcode();
423  assert(Instruction::isAssociative(Opcode) &&
424         Instruction::isCommutative(Opcode) &&
425         "Expected an associative and commutative operation!");
426  // If we see an absorbing element then the entire expression must be equal to
427  // it.  For example, if this is a multiplication expression and zero occurs as
428  // an operand somewhere in it then the result of the expression must be zero.
429  Constant *Absorber = ConstantExpr::getBinOpAbsorber(Opcode, I->getType());
430
431  // Visit all operands of the expression, keeping track of their weight (the
432  // number of paths from the expression root to the operand, or if you like
433  // the number of times that operand occurs in the linearized expression).
434  // For example, if I = X + A, where X = A + B, then I, X and B have weight 1
435  // while A has weight two.
436
437  // Worklist of non-leaf nodes (their operands are in the expression too) along
438  // with their weights, representing a certain number of paths to the operator.
439  // If an operator occurs in the worklist multiple times then we found multiple
440  // ways to get to it.
441  SmallVector<std::pair<BinaryOperator*, APInt>, 8> Worklist; // (Op, Weight)
442  Worklist.push_back(std::make_pair(I, APInt(Bitwidth, 1)));
443  bool MadeChange = false;
444
445  // Leaves of the expression are values that either aren't the right kind of
446  // operation (eg: a constant, or a multiply in an add tree), or are, but have
447  // some uses that are not inside the expression.  For example, in I = X + X,
448  // X = A + B, the value X has two uses (by I) that are in the expression.  If
449  // X has any other uses, for example in a return instruction, then we consider
450  // X to be a leaf, and won't analyze it further.  When we first visit a value,
451  // if it has more than one use then at first we conservatively consider it to
452  // be a leaf.  Later, as the expression is explored, we may discover some more
453  // uses of the value from inside the expression.  If all uses turn out to be
454  // from within the expression (and the value is a binary operator of the right
455  // kind) then the value is no longer considered to be a leaf, and its operands
456  // are explored.
457
458  // Leaves - Keeps track of the set of putative leaves as well as the number of
459  // paths to each leaf seen so far.
460  typedef DenseMap<Value*, APInt> LeafMap;
461  LeafMap Leaves; // Leaf -> Total weight so far.
462  SmallVector<Value*, 8> LeafOrder; // Ensure deterministic leaf output order.
463
464#ifndef NDEBUG
465  SmallPtrSet<Value*, 8> Visited; // For sanity checking the iteration scheme.
466#endif
467  while (!Worklist.empty()) {
468    std::pair<BinaryOperator*, APInt> P = Worklist.pop_back_val();
469    I = P.first; // We examine the operands of this binary operator.
470
471    for (unsigned OpIdx = 0; OpIdx < 2; ++OpIdx) { // Visit operands.
472      Value *Op = I->getOperand(OpIdx);
473      APInt Weight = P.second; // Number of paths to this operand.
474      DEBUG(dbgs() << "OPERAND: " << *Op << " (" << Weight << ")\n");
475      assert(!Op->use_empty() && "No uses, so how did we get to it?!");
476
477      // If the expression contains an absorbing element then there is no need
478      // to analyze it further: it must evaluate to the absorbing element.
479      if (Op == Absorber && !Weight.isMinValue()) {
480        Ops.push_back(std::make_pair(Absorber, APInt(Bitwidth, 1)));
481        return MadeChange;
482      }
483
484      // If this is a binary operation of the right kind with only one use then
485      // add its operands to the expression.
486      if (BinaryOperator *BO = isReassociableOp(Op, Opcode)) {
487        assert(Visited.insert(Op) && "Not first visit!");
488        DEBUG(dbgs() << "DIRECT ADD: " << *Op << " (" << Weight << ")\n");
489        Worklist.push_back(std::make_pair(BO, Weight));
490        continue;
491      }
492
493      // Appears to be a leaf.  Is the operand already in the set of leaves?
494      LeafMap::iterator It = Leaves.find(Op);
495      if (It == Leaves.end()) {
496        // Not in the leaf map.  Must be the first time we saw this operand.
497        assert(Visited.insert(Op) && "Not first visit!");
498        if (!Op->hasOneUse()) {
499          // This value has uses not accounted for by the expression, so it is
500          // not safe to modify.  Mark it as being a leaf.
501          DEBUG(dbgs() << "ADD USES LEAF: " << *Op << " (" << Weight << ")\n");
502          LeafOrder.push_back(Op);
503          Leaves[Op] = Weight;
504          continue;
505        }
506        // No uses outside the expression, try morphing it.
507      } else if (It != Leaves.end()) {
508        // Already in the leaf map.
509        assert(Visited.count(Op) && "In leaf map but not visited!");
510
511        // Update the number of paths to the leaf.
512        IncorporateWeight(It->second, Weight, Opcode);
513
514#if 0   // TODO: Re-enable once PR13021 is fixed.
515        // The leaf already has one use from inside the expression.  As we want
516        // exactly one such use, drop this new use of the leaf.
517        assert(!Op->hasOneUse() && "Only one use, but we got here twice!");
518        I->setOperand(OpIdx, UndefValue::get(I->getType()));
519        MadeChange = true;
520
521        // If the leaf is a binary operation of the right kind and we now see
522        // that its multiple original uses were in fact all by nodes belonging
523        // to the expression, then no longer consider it to be a leaf and add
524        // its operands to the expression.
525        if (BinaryOperator *BO = isReassociableOp(Op, Opcode)) {
526          DEBUG(dbgs() << "UNLEAF: " << *Op << " (" << It->second << ")\n");
527          Worklist.push_back(std::make_pair(BO, It->second));
528          Leaves.erase(It);
529          continue;
530        }
531#endif
532
533        // If we still have uses that are not accounted for by the expression
534        // then it is not safe to modify the value.
535        if (!Op->hasOneUse())
536          continue;
537
538        // No uses outside the expression, try morphing it.
539        Weight = It->second;
540        Leaves.erase(It); // Since the value may be morphed below.
541      }
542
543      // At this point we have a value which, first of all, is not a binary
544      // expression of the right kind, and secondly, is only used inside the
545      // expression.  This means that it can safely be modified.  See if we
546      // can usefully morph it into an expression of the right kind.
547      assert((!isa<Instruction>(Op) ||
548              cast<Instruction>(Op)->getOpcode() != Opcode) &&
549             "Should have been handled above!");
550      assert(Op->hasOneUse() && "Has uses outside the expression tree!");
551
552      // If this is a multiply expression, turn any internal negations into
553      // multiplies by -1 so they can be reassociated.
554      BinaryOperator *BO = dyn_cast<BinaryOperator>(Op);
555      if (Opcode == Instruction::Mul && BO && BinaryOperator::isNeg(BO)) {
556        DEBUG(dbgs() << "MORPH LEAF: " << *Op << " (" << Weight << ") TO ");
557        BO = LowerNegateToMultiply(BO);
558        DEBUG(dbgs() << *BO << 'n');
559        Worklist.push_back(std::make_pair(BO, Weight));
560        MadeChange = true;
561        continue;
562      }
563
564      // Failed to morph into an expression of the right type.  This really is
565      // a leaf.
566      DEBUG(dbgs() << "ADD LEAF: " << *Op << " (" << Weight << ")\n");
567      assert(!isReassociableOp(Op, Opcode) && "Value was morphed?");
568      LeafOrder.push_back(Op);
569      Leaves[Op] = Weight;
570    }
571  }
572
573  // The leaves, repeated according to their weights, represent the linearized
574  // form of the expression.
575  for (unsigned i = 0, e = LeafOrder.size(); i != e; ++i) {
576    Value *V = LeafOrder[i];
577    LeafMap::iterator It = Leaves.find(V);
578    if (It == Leaves.end())
579      // Node initially thought to be a leaf wasn't.
580      continue;
581    assert(!isReassociableOp(V, Opcode) && "Shouldn't be a leaf!");
582    APInt Weight = It->second;
583    if (Weight.isMinValue())
584      // Leaf already output or weight reduction eliminated it.
585      continue;
586    // Ensure the leaf is only output once.
587    It->second = 0;
588    Ops.push_back(std::make_pair(V, Weight));
589  }
590
591  // For nilpotent operations or addition there may be no operands, for example
592  // because the expression was "X xor X" or consisted of 2^Bitwidth additions:
593  // in both cases the weight reduces to 0 causing the value to be skipped.
594  if (Ops.empty()) {
595    Constant *Identity = ConstantExpr::getBinOpIdentity(Opcode, I->getType());
596    assert(Identity && "Associative operation without identity!");
597    Ops.push_back(std::make_pair(Identity, APInt(Bitwidth, 1)));
598  }
599
600  return MadeChange;
601}
602
603// RewriteExprTree - Now that the operands for this expression tree are
604// linearized and optimized, emit them in-order.
605void Reassociate::RewriteExprTree(BinaryOperator *I,
606                                  SmallVectorImpl<ValueEntry> &Ops) {
607  assert(Ops.size() > 1 && "Single values should be used directly!");
608
609  // Since our optimizations should never increase the number of operations, the
610  // new expression can usually be written reusing the existing binary operators
611  // from the original expression tree, without creating any new instructions,
612  // though the rewritten expression may have a completely different topology.
613  // We take care to not change anything if the new expression will be the same
614  // as the original.  If more than trivial changes (like commuting operands)
615  // were made then we are obliged to clear out any optional subclass data like
616  // nsw flags.
617
618  /// NodesToRewrite - Nodes from the original expression available for writing
619  /// the new expression into.
620  SmallVector<BinaryOperator*, 8> NodesToRewrite;
621  unsigned Opcode = I->getOpcode();
622  BinaryOperator *Op = I;
623
624  /// NotRewritable - The operands being written will be the leaves of the new
625  /// expression and must not be used as inner nodes (via NodesToRewrite) by
626  /// mistake.  Inner nodes are always reassociable, and usually leaves are not
627  /// (if they were they would have been incorporated into the expression and so
628  /// would not be leaves), so most of the time there is no danger of this.  But
629  /// in rare cases a leaf may become reassociable if an optimization kills uses
630  /// of it, or it may momentarily become reassociable during rewriting (below)
631  /// due it being removed as an operand of one of its uses.  Ensure that misuse
632  /// of leaf nodes as inner nodes cannot occur by remembering all of the future
633  /// leaves and refusing to reuse any of them as inner nodes.
634  SmallPtrSet<Value*, 8> NotRewritable;
635  for (unsigned i = 0, e = Ops.size(); i != e; ++i)
636    NotRewritable.insert(Ops[i].Op);
637
638  // ExpressionChanged - Non-null if the rewritten expression differs from the
639  // original in some non-trivial way, requiring the clearing of optional flags.
640  // Flags are cleared from the operator in ExpressionChanged up to I inclusive.
641  BinaryOperator *ExpressionChanged = 0;
642  for (unsigned i = 0; ; ++i) {
643    // The last operation (which comes earliest in the IR) is special as both
644    // operands will come from Ops, rather than just one with the other being
645    // a subexpression.
646    if (i+2 == Ops.size()) {
647      Value *NewLHS = Ops[i].Op;
648      Value *NewRHS = Ops[i+1].Op;
649      Value *OldLHS = Op->getOperand(0);
650      Value *OldRHS = Op->getOperand(1);
651
652      if (NewLHS == OldLHS && NewRHS == OldRHS)
653        // Nothing changed, leave it alone.
654        break;
655
656      if (NewLHS == OldRHS && NewRHS == OldLHS) {
657        // The order of the operands was reversed.  Swap them.
658        DEBUG(dbgs() << "RA: " << *Op << '\n');
659        Op->swapOperands();
660        DEBUG(dbgs() << "TO: " << *Op << '\n');
661        MadeChange = true;
662        ++NumChanged;
663        break;
664      }
665
666      // The new operation differs non-trivially from the original. Overwrite
667      // the old operands with the new ones.
668      DEBUG(dbgs() << "RA: " << *Op << '\n');
669      if (NewLHS != OldLHS) {
670        BinaryOperator *BO = isReassociableOp(OldLHS, Opcode);
671        if (BO && !NotRewritable.count(BO))
672          NodesToRewrite.push_back(BO);
673        Op->setOperand(0, NewLHS);
674      }
675      if (NewRHS != OldRHS) {
676        BinaryOperator *BO = isReassociableOp(OldRHS, Opcode);
677        if (BO && !NotRewritable.count(BO))
678          NodesToRewrite.push_back(BO);
679        Op->setOperand(1, NewRHS);
680      }
681      DEBUG(dbgs() << "TO: " << *Op << '\n');
682
683      ExpressionChanged = Op;
684      MadeChange = true;
685      ++NumChanged;
686
687      break;
688    }
689
690    // Not the last operation.  The left-hand side will be a sub-expression
691    // while the right-hand side will be the current element of Ops.
692    Value *NewRHS = Ops[i].Op;
693    if (NewRHS != Op->getOperand(1)) {
694      DEBUG(dbgs() << "RA: " << *Op << '\n');
695      if (NewRHS == Op->getOperand(0)) {
696        // The new right-hand side was already present as the left operand.  If
697        // we are lucky then swapping the operands will sort out both of them.
698        Op->swapOperands();
699      } else {
700        // Overwrite with the new right-hand side.
701        BinaryOperator *BO = isReassociableOp(Op->getOperand(1), Opcode);
702        if (BO && !NotRewritable.count(BO))
703          NodesToRewrite.push_back(BO);
704        Op->setOperand(1, NewRHS);
705        ExpressionChanged = Op;
706      }
707      DEBUG(dbgs() << "TO: " << *Op << '\n');
708      MadeChange = true;
709      ++NumChanged;
710    }
711
712    // Now deal with the left-hand side.  If this is already an operation node
713    // from the original expression then just rewrite the rest of the expression
714    // into it.
715    BinaryOperator *BO = isReassociableOp(Op->getOperand(0), Opcode);
716    if (BO && !NotRewritable.count(BO)) {
717      Op = BO;
718      continue;
719    }
720
721    // Otherwise, grab a spare node from the original expression and use that as
722    // the left-hand side.  If there are no nodes left then the optimizers made
723    // an expression with more nodes than the original!  This usually means that
724    // they did something stupid but it might mean that the problem was just too
725    // hard (finding the mimimal number of multiplications needed to realize a
726    // multiplication expression is NP-complete).  Whatever the reason, smart or
727    // stupid, create a new node if there are none left.
728    BinaryOperator *NewOp;
729    if (NodesToRewrite.empty()) {
730      Constant *Undef = UndefValue::get(I->getType());
731      NewOp = BinaryOperator::Create(Instruction::BinaryOps(Opcode),
732                                     Undef, Undef, "", I);
733    } else {
734      NewOp = NodesToRewrite.pop_back_val();
735    }
736
737    DEBUG(dbgs() << "RA: " << *Op << '\n');
738    Op->setOperand(0, NewOp);
739    DEBUG(dbgs() << "TO: " << *Op << '\n');
740    ExpressionChanged = Op;
741    MadeChange = true;
742    ++NumChanged;
743    Op = NewOp;
744  }
745
746  // If the expression changed non-trivially then clear out all subclass data
747  // starting from the operator specified in ExpressionChanged, and compactify
748  // the operators to just before the expression root to guarantee that the
749  // expression tree is dominated by all of Ops.
750  if (ExpressionChanged)
751    do {
752      ExpressionChanged->clearSubclassOptionalData();
753      if (ExpressionChanged == I)
754        break;
755      ExpressionChanged->moveBefore(I);
756      ExpressionChanged = cast<BinaryOperator>(*ExpressionChanged->use_begin());
757    } while (1);
758
759  // Throw away any left over nodes from the original expression.
760  for (unsigned i = 0, e = NodesToRewrite.size(); i != e; ++i)
761    RedoInsts.insert(NodesToRewrite[i]);
762}
763
764/// NegateValue - Insert instructions before the instruction pointed to by BI,
765/// that computes the negative version of the value specified.  The negative
766/// version of the value is returned, and BI is left pointing at the instruction
767/// that should be processed next by the reassociation pass.
768static Value *NegateValue(Value *V, Instruction *BI) {
769  if (Constant *C = dyn_cast<Constant>(V))
770    return ConstantExpr::getNeg(C);
771
772  // We are trying to expose opportunity for reassociation.  One of the things
773  // that we want to do to achieve this is to push a negation as deep into an
774  // expression chain as possible, to expose the add instructions.  In practice,
775  // this means that we turn this:
776  //   X = -(A+12+C+D)   into    X = -A + -12 + -C + -D = -12 + -A + -C + -D
777  // so that later, a: Y = 12+X could get reassociated with the -12 to eliminate
778  // the constants.  We assume that instcombine will clean up the mess later if
779  // we introduce tons of unnecessary negation instructions.
780  //
781  if (BinaryOperator *I = isReassociableOp(V, Instruction::Add)) {
782    // Push the negates through the add.
783    I->setOperand(0, NegateValue(I->getOperand(0), BI));
784    I->setOperand(1, NegateValue(I->getOperand(1), BI));
785
786    // We must move the add instruction here, because the neg instructions do
787    // not dominate the old add instruction in general.  By moving it, we are
788    // assured that the neg instructions we just inserted dominate the
789    // instruction we are about to insert after them.
790    //
791    I->moveBefore(BI);
792    I->setName(I->getName()+".neg");
793    return I;
794  }
795
796  // Okay, we need to materialize a negated version of V with an instruction.
797  // Scan the use lists of V to see if we have one already.
798  for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E;++UI){
799    User *U = *UI;
800    if (!BinaryOperator::isNeg(U)) continue;
801
802    // We found one!  Now we have to make sure that the definition dominates
803    // this use.  We do this by moving it to the entry block (if it is a
804    // non-instruction value) or right after the definition.  These negates will
805    // be zapped by reassociate later, so we don't need much finesse here.
806    BinaryOperator *TheNeg = cast<BinaryOperator>(U);
807
808    // Verify that the negate is in this function, V might be a constant expr.
809    if (TheNeg->getParent()->getParent() != BI->getParent()->getParent())
810      continue;
811
812    BasicBlock::iterator InsertPt;
813    if (Instruction *InstInput = dyn_cast<Instruction>(V)) {
814      if (InvokeInst *II = dyn_cast<InvokeInst>(InstInput)) {
815        InsertPt = II->getNormalDest()->begin();
816      } else {
817        InsertPt = InstInput;
818        ++InsertPt;
819      }
820      while (isa<PHINode>(InsertPt)) ++InsertPt;
821    } else {
822      InsertPt = TheNeg->getParent()->getParent()->getEntryBlock().begin();
823    }
824    TheNeg->moveBefore(InsertPt);
825    return TheNeg;
826  }
827
828  // Insert a 'neg' instruction that subtracts the value from zero to get the
829  // negation.
830  return BinaryOperator::CreateNeg(V, V->getName() + ".neg", BI);
831}
832
833/// ShouldBreakUpSubtract - Return true if we should break up this subtract of
834/// X-Y into (X + -Y).
835static bool ShouldBreakUpSubtract(Instruction *Sub) {
836  // If this is a negation, we can't split it up!
837  if (BinaryOperator::isNeg(Sub))
838    return false;
839
840  // Don't bother to break this up unless either the LHS is an associable add or
841  // subtract or if this is only used by one.
842  if (isReassociableOp(Sub->getOperand(0), Instruction::Add) ||
843      isReassociableOp(Sub->getOperand(0), Instruction::Sub))
844    return true;
845  if (isReassociableOp(Sub->getOperand(1), Instruction::Add) ||
846      isReassociableOp(Sub->getOperand(1), Instruction::Sub))
847    return true;
848  if (Sub->hasOneUse() &&
849      (isReassociableOp(Sub->use_back(), Instruction::Add) ||
850       isReassociableOp(Sub->use_back(), Instruction::Sub)))
851    return true;
852
853  return false;
854}
855
856/// BreakUpSubtract - If we have (X-Y), and if either X is an add, or if this is
857/// only used by an add, transform this into (X+(0-Y)) to promote better
858/// reassociation.
859static BinaryOperator *BreakUpSubtract(Instruction *Sub) {
860  // Convert a subtract into an add and a neg instruction. This allows sub
861  // instructions to be commuted with other add instructions.
862  //
863  // Calculate the negative value of Operand 1 of the sub instruction,
864  // and set it as the RHS of the add instruction we just made.
865  //
866  Value *NegVal = NegateValue(Sub->getOperand(1), Sub);
867  BinaryOperator *New =
868    BinaryOperator::CreateAdd(Sub->getOperand(0), NegVal, "", Sub);
869  Sub->setOperand(0, Constant::getNullValue(Sub->getType())); // Drop use of op.
870  Sub->setOperand(1, Constant::getNullValue(Sub->getType())); // Drop use of op.
871  New->takeName(Sub);
872
873  // Everyone now refers to the add instruction.
874  Sub->replaceAllUsesWith(New);
875  New->setDebugLoc(Sub->getDebugLoc());
876
877  DEBUG(dbgs() << "Negated: " << *New << '\n');
878  return New;
879}
880
881/// ConvertShiftToMul - If this is a shift of a reassociable multiply or is used
882/// by one, change this into a multiply by a constant to assist with further
883/// reassociation.
884static BinaryOperator *ConvertShiftToMul(Instruction *Shl) {
885  Constant *MulCst = ConstantInt::get(Shl->getType(), 1);
886  MulCst = ConstantExpr::getShl(MulCst, cast<Constant>(Shl->getOperand(1)));
887
888  BinaryOperator *Mul =
889    BinaryOperator::CreateMul(Shl->getOperand(0), MulCst, "", Shl);
890  Shl->setOperand(0, UndefValue::get(Shl->getType())); // Drop use of op.
891  Mul->takeName(Shl);
892  Shl->replaceAllUsesWith(Mul);
893  Mul->setDebugLoc(Shl->getDebugLoc());
894  return Mul;
895}
896
897/// FindInOperandList - Scan backwards and forwards among values with the same
898/// rank as element i to see if X exists.  If X does not exist, return i.  This
899/// is useful when scanning for 'x' when we see '-x' because they both get the
900/// same rank.
901static unsigned FindInOperandList(SmallVectorImpl<ValueEntry> &Ops, unsigned i,
902                                  Value *X) {
903  unsigned XRank = Ops[i].Rank;
904  unsigned e = Ops.size();
905  for (unsigned j = i+1; j != e && Ops[j].Rank == XRank; ++j)
906    if (Ops[j].Op == X)
907      return j;
908  // Scan backwards.
909  for (unsigned j = i-1; j != ~0U && Ops[j].Rank == XRank; --j)
910    if (Ops[j].Op == X)
911      return j;
912  return i;
913}
914
915/// EmitAddTreeOfValues - Emit a tree of add instructions, summing Ops together
916/// and returning the result.  Insert the tree before I.
917static Value *EmitAddTreeOfValues(Instruction *I,
918                                  SmallVectorImpl<WeakVH> &Ops){
919  if (Ops.size() == 1) return Ops.back();
920
921  Value *V1 = Ops.back();
922  Ops.pop_back();
923  Value *V2 = EmitAddTreeOfValues(I, Ops);
924  return BinaryOperator::CreateAdd(V2, V1, "tmp", I);
925}
926
927/// RemoveFactorFromExpression - If V is an expression tree that is a
928/// multiplication sequence, and if this sequence contains a multiply by Factor,
929/// remove Factor from the tree and return the new tree.
930Value *Reassociate::RemoveFactorFromExpression(Value *V, Value *Factor) {
931  BinaryOperator *BO = isReassociableOp(V, Instruction::Mul);
932  if (!BO) return 0;
933
934  SmallVector<RepeatedValue, 8> Tree;
935  MadeChange |= LinearizeExprTree(BO, Tree);
936  SmallVector<ValueEntry, 8> Factors;
937  Factors.reserve(Tree.size());
938  for (unsigned i = 0, e = Tree.size(); i != e; ++i) {
939    RepeatedValue E = Tree[i];
940    Factors.append(E.second.getZExtValue(),
941                   ValueEntry(getRank(E.first), E.first));
942  }
943
944  bool FoundFactor = false;
945  bool NeedsNegate = false;
946  for (unsigned i = 0, e = Factors.size(); i != e; ++i) {
947    if (Factors[i].Op == Factor) {
948      FoundFactor = true;
949      Factors.erase(Factors.begin()+i);
950      break;
951    }
952
953    // If this is a negative version of this factor, remove it.
954    if (ConstantInt *FC1 = dyn_cast<ConstantInt>(Factor))
955      if (ConstantInt *FC2 = dyn_cast<ConstantInt>(Factors[i].Op))
956        if (FC1->getValue() == -FC2->getValue()) {
957          FoundFactor = NeedsNegate = true;
958          Factors.erase(Factors.begin()+i);
959          break;
960        }
961  }
962
963  if (!FoundFactor) {
964    // Make sure to restore the operands to the expression tree.
965    RewriteExprTree(BO, Factors);
966    return 0;
967  }
968
969  BasicBlock::iterator InsertPt = BO; ++InsertPt;
970
971  // If this was just a single multiply, remove the multiply and return the only
972  // remaining operand.
973  if (Factors.size() == 1) {
974    RedoInsts.insert(BO);
975    V = Factors[0].Op;
976  } else {
977    RewriteExprTree(BO, Factors);
978    V = BO;
979  }
980
981  if (NeedsNegate)
982    V = BinaryOperator::CreateNeg(V, "neg", InsertPt);
983
984  return V;
985}
986
987/// FindSingleUseMultiplyFactors - If V is a single-use multiply, recursively
988/// add its operands as factors, otherwise add V to the list of factors.
989///
990/// Ops is the top-level list of add operands we're trying to factor.
991static void FindSingleUseMultiplyFactors(Value *V,
992                                         SmallVectorImpl<Value*> &Factors,
993                                       const SmallVectorImpl<ValueEntry> &Ops) {
994  BinaryOperator *BO = isReassociableOp(V, Instruction::Mul);
995  if (!BO) {
996    Factors.push_back(V);
997    return;
998  }
999
1000  // Otherwise, add the LHS and RHS to the list of factors.
1001  FindSingleUseMultiplyFactors(BO->getOperand(1), Factors, Ops);
1002  FindSingleUseMultiplyFactors(BO->getOperand(0), Factors, Ops);
1003}
1004
1005/// OptimizeAndOrXor - Optimize a series of operands to an 'and', 'or', or 'xor'
1006/// instruction.  This optimizes based on identities.  If it can be reduced to
1007/// a single Value, it is returned, otherwise the Ops list is mutated as
1008/// necessary.
1009static Value *OptimizeAndOrXor(unsigned Opcode,
1010                               SmallVectorImpl<ValueEntry> &Ops) {
1011  // Scan the operand lists looking for X and ~X pairs, along with X,X pairs.
1012  // If we find any, we can simplify the expression. X&~X == 0, X|~X == -1.
1013  for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
1014    // First, check for X and ~X in the operand list.
1015    assert(i < Ops.size());
1016    if (BinaryOperator::isNot(Ops[i].Op)) {    // Cannot occur for ^.
1017      Value *X = BinaryOperator::getNotArgument(Ops[i].Op);
1018      unsigned FoundX = FindInOperandList(Ops, i, X);
1019      if (FoundX != i) {
1020        if (Opcode == Instruction::And)   // ...&X&~X = 0
1021          return Constant::getNullValue(X->getType());
1022
1023        if (Opcode == Instruction::Or)    // ...|X|~X = -1
1024          return Constant::getAllOnesValue(X->getType());
1025      }
1026    }
1027
1028    // Next, check for duplicate pairs of values, which we assume are next to
1029    // each other, due to our sorting criteria.
1030    assert(i < Ops.size());
1031    if (i+1 != Ops.size() && Ops[i+1].Op == Ops[i].Op) {
1032      if (Opcode == Instruction::And || Opcode == Instruction::Or) {
1033        // Drop duplicate values for And and Or.
1034        Ops.erase(Ops.begin()+i);
1035        --i; --e;
1036        ++NumAnnihil;
1037        continue;
1038      }
1039
1040      // Drop pairs of values for Xor.
1041      assert(Opcode == Instruction::Xor);
1042      if (e == 2)
1043        return Constant::getNullValue(Ops[0].Op->getType());
1044
1045      // Y ^ X^X -> Y
1046      Ops.erase(Ops.begin()+i, Ops.begin()+i+2);
1047      i -= 1; e -= 2;
1048      ++NumAnnihil;
1049    }
1050  }
1051  return 0;
1052}
1053
1054/// OptimizeAdd - Optimize a series of operands to an 'add' instruction.  This
1055/// optimizes based on identities.  If it can be reduced to a single Value, it
1056/// is returned, otherwise the Ops list is mutated as necessary.
1057Value *Reassociate::OptimizeAdd(Instruction *I,
1058                                SmallVectorImpl<ValueEntry> &Ops) {
1059  // Scan the operand lists looking for X and -X pairs.  If we find any, we
1060  // can simplify the expression. X+-X == 0.  While we're at it, scan for any
1061  // duplicates.  We want to canonicalize Y+Y+Y+Z -> 3*Y+Z.
1062  //
1063  // TODO: We could handle "X + ~X" -> "-1" if we wanted, since "-X = ~X+1".
1064  //
1065  for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
1066    Value *TheOp = Ops[i].Op;
1067    // Check to see if we've seen this operand before.  If so, we factor all
1068    // instances of the operand together.  Due to our sorting criteria, we know
1069    // that these need to be next to each other in the vector.
1070    if (i+1 != Ops.size() && Ops[i+1].Op == TheOp) {
1071      // Rescan the list, remove all instances of this operand from the expr.
1072      unsigned NumFound = 0;
1073      do {
1074        Ops.erase(Ops.begin()+i);
1075        ++NumFound;
1076      } while (i != Ops.size() && Ops[i].Op == TheOp);
1077
1078      DEBUG(errs() << "\nFACTORING [" << NumFound << "]: " << *TheOp << '\n');
1079      ++NumFactor;
1080
1081      // Insert a new multiply.
1082      Value *Mul = ConstantInt::get(cast<IntegerType>(I->getType()), NumFound);
1083      Mul = BinaryOperator::CreateMul(TheOp, Mul, "factor", I);
1084
1085      // Now that we have inserted a multiply, optimize it. This allows us to
1086      // handle cases that require multiple factoring steps, such as this:
1087      // (X*2) + (X*2) + (X*2) -> (X*2)*3 -> X*6
1088      RedoInsts.insert(cast<Instruction>(Mul));
1089
1090      // If every add operand was a duplicate, return the multiply.
1091      if (Ops.empty())
1092        return Mul;
1093
1094      // Otherwise, we had some input that didn't have the dupe, such as
1095      // "A + A + B" -> "A*2 + B".  Add the new multiply to the list of
1096      // things being added by this operation.
1097      Ops.insert(Ops.begin(), ValueEntry(getRank(Mul), Mul));
1098
1099      --i;
1100      e = Ops.size();
1101      continue;
1102    }
1103
1104    // Check for X and -X in the operand list.
1105    if (!BinaryOperator::isNeg(TheOp))
1106      continue;
1107
1108    Value *X = BinaryOperator::getNegArgument(TheOp);
1109    unsigned FoundX = FindInOperandList(Ops, i, X);
1110    if (FoundX == i)
1111      continue;
1112
1113    // Remove X and -X from the operand list.
1114    if (Ops.size() == 2)
1115      return Constant::getNullValue(X->getType());
1116
1117    Ops.erase(Ops.begin()+i);
1118    if (i < FoundX)
1119      --FoundX;
1120    else
1121      --i;   // Need to back up an extra one.
1122    Ops.erase(Ops.begin()+FoundX);
1123    ++NumAnnihil;
1124    --i;     // Revisit element.
1125    e -= 2;  // Removed two elements.
1126  }
1127
1128  // Scan the operand list, checking to see if there are any common factors
1129  // between operands.  Consider something like A*A+A*B*C+D.  We would like to
1130  // reassociate this to A*(A+B*C)+D, which reduces the number of multiplies.
1131  // To efficiently find this, we count the number of times a factor occurs
1132  // for any ADD operands that are MULs.
1133  DenseMap<Value*, unsigned> FactorOccurrences;
1134
1135  // Keep track of each multiply we see, to avoid triggering on (X*4)+(X*4)
1136  // where they are actually the same multiply.
1137  unsigned MaxOcc = 0;
1138  Value *MaxOccVal = 0;
1139  for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
1140    BinaryOperator *BOp = isReassociableOp(Ops[i].Op, Instruction::Mul);
1141    if (!BOp)
1142      continue;
1143
1144    // Compute all of the factors of this added value.
1145    SmallVector<Value*, 8> Factors;
1146    FindSingleUseMultiplyFactors(BOp, Factors, Ops);
1147    assert(Factors.size() > 1 && "Bad linearize!");
1148
1149    // Add one to FactorOccurrences for each unique factor in this op.
1150    SmallPtrSet<Value*, 8> Duplicates;
1151    for (unsigned i = 0, e = Factors.size(); i != e; ++i) {
1152      Value *Factor = Factors[i];
1153      if (!Duplicates.insert(Factor)) continue;
1154
1155      unsigned Occ = ++FactorOccurrences[Factor];
1156      if (Occ > MaxOcc) { MaxOcc = Occ; MaxOccVal = Factor; }
1157
1158      // If Factor is a negative constant, add the negated value as a factor
1159      // because we can percolate the negate out.  Watch for minint, which
1160      // cannot be positivified.
1161      if (ConstantInt *CI = dyn_cast<ConstantInt>(Factor))
1162        if (CI->isNegative() && !CI->isMinValue(true)) {
1163          Factor = ConstantInt::get(CI->getContext(), -CI->getValue());
1164          assert(!Duplicates.count(Factor) &&
1165                 "Shouldn't have two constant factors, missed a canonicalize");
1166
1167          unsigned Occ = ++FactorOccurrences[Factor];
1168          if (Occ > MaxOcc) { MaxOcc = Occ; MaxOccVal = Factor; }
1169        }
1170    }
1171  }
1172
1173  // If any factor occurred more than one time, we can pull it out.
1174  if (MaxOcc > 1) {
1175    DEBUG(errs() << "\nFACTORING [" << MaxOcc << "]: " << *MaxOccVal << '\n');
1176    ++NumFactor;
1177
1178    // Create a new instruction that uses the MaxOccVal twice.  If we don't do
1179    // this, we could otherwise run into situations where removing a factor
1180    // from an expression will drop a use of maxocc, and this can cause
1181    // RemoveFactorFromExpression on successive values to behave differently.
1182    Instruction *DummyInst = BinaryOperator::CreateAdd(MaxOccVal, MaxOccVal);
1183    SmallVector<WeakVH, 4> NewMulOps;
1184    for (unsigned i = 0; i != Ops.size(); ++i) {
1185      // Only try to remove factors from expressions we're allowed to.
1186      BinaryOperator *BOp = isReassociableOp(Ops[i].Op, Instruction::Mul);
1187      if (!BOp)
1188        continue;
1189
1190      if (Value *V = RemoveFactorFromExpression(Ops[i].Op, MaxOccVal)) {
1191        // The factorized operand may occur several times.  Convert them all in
1192        // one fell swoop.
1193        for (unsigned j = Ops.size(); j != i;) {
1194          --j;
1195          if (Ops[j].Op == Ops[i].Op) {
1196            NewMulOps.push_back(V);
1197            Ops.erase(Ops.begin()+j);
1198          }
1199        }
1200        --i;
1201      }
1202    }
1203
1204    // No need for extra uses anymore.
1205    delete DummyInst;
1206
1207    unsigned NumAddedValues = NewMulOps.size();
1208    Value *V = EmitAddTreeOfValues(I, NewMulOps);
1209
1210    // Now that we have inserted the add tree, optimize it. This allows us to
1211    // handle cases that require multiple factoring steps, such as this:
1212    // A*A*B + A*A*C   -->   A*(A*B+A*C)   -->   A*(A*(B+C))
1213    assert(NumAddedValues > 1 && "Each occurrence should contribute a value");
1214    (void)NumAddedValues;
1215    if (Instruction *VI = dyn_cast<Instruction>(V))
1216      RedoInsts.insert(VI);
1217
1218    // Create the multiply.
1219    Instruction *V2 = BinaryOperator::CreateMul(V, MaxOccVal, "tmp", I);
1220
1221    // Rerun associate on the multiply in case the inner expression turned into
1222    // a multiply.  We want to make sure that we keep things in canonical form.
1223    RedoInsts.insert(V2);
1224
1225    // If every add operand included the factor (e.g. "A*B + A*C"), then the
1226    // entire result expression is just the multiply "A*(B+C)".
1227    if (Ops.empty())
1228      return V2;
1229
1230    // Otherwise, we had some input that didn't have the factor, such as
1231    // "A*B + A*C + D" -> "A*(B+C) + D".  Add the new multiply to the list of
1232    // things being added by this operation.
1233    Ops.insert(Ops.begin(), ValueEntry(getRank(V2), V2));
1234  }
1235
1236  return 0;
1237}
1238
1239namespace {
1240  /// \brief Predicate tests whether a ValueEntry's op is in a map.
1241  struct IsValueInMap {
1242    const DenseMap<Value *, unsigned> &Map;
1243
1244    IsValueInMap(const DenseMap<Value *, unsigned> &Map) : Map(Map) {}
1245
1246    bool operator()(const ValueEntry &Entry) {
1247      return Map.find(Entry.Op) != Map.end();
1248    }
1249  };
1250}
1251
1252/// \brief Build up a vector of value/power pairs factoring a product.
1253///
1254/// Given a series of multiplication operands, build a vector of factors and
1255/// the powers each is raised to when forming the final product. Sort them in
1256/// the order of descending power.
1257///
1258///      (x*x)          -> [(x, 2)]
1259///     ((x*x)*x)       -> [(x, 3)]
1260///   ((((x*y)*x)*y)*x) -> [(x, 3), (y, 2)]
1261///
1262/// \returns Whether any factors have a power greater than one.
1263bool Reassociate::collectMultiplyFactors(SmallVectorImpl<ValueEntry> &Ops,
1264                                         SmallVectorImpl<Factor> &Factors) {
1265  // FIXME: Have Ops be (ValueEntry, Multiplicity) pairs, simplifying this.
1266  // Compute the sum of powers of simplifiable factors.
1267  unsigned FactorPowerSum = 0;
1268  for (unsigned Idx = 1, Size = Ops.size(); Idx < Size; ++Idx) {
1269    Value *Op = Ops[Idx-1].Op;
1270
1271    // Count the number of occurrences of this value.
1272    unsigned Count = 1;
1273    for (; Idx < Size && Ops[Idx].Op == Op; ++Idx)
1274      ++Count;
1275    // Track for simplification all factors which occur 2 or more times.
1276    if (Count > 1)
1277      FactorPowerSum += Count;
1278  }
1279
1280  // We can only simplify factors if the sum of the powers of our simplifiable
1281  // factors is 4 or higher. When that is the case, we will *always* have
1282  // a simplification. This is an important invariant to prevent cyclicly
1283  // trying to simplify already minimal formations.
1284  if (FactorPowerSum < 4)
1285    return false;
1286
1287  // Now gather the simplifiable factors, removing them from Ops.
1288  FactorPowerSum = 0;
1289  for (unsigned Idx = 1; Idx < Ops.size(); ++Idx) {
1290    Value *Op = Ops[Idx-1].Op;
1291
1292    // Count the number of occurrences of this value.
1293    unsigned Count = 1;
1294    for (; Idx < Ops.size() && Ops[Idx].Op == Op; ++Idx)
1295      ++Count;
1296    if (Count == 1)
1297      continue;
1298    // Move an even number of occurrences to Factors.
1299    Count &= ~1U;
1300    Idx -= Count;
1301    FactorPowerSum += Count;
1302    Factors.push_back(Factor(Op, Count));
1303    Ops.erase(Ops.begin()+Idx, Ops.begin()+Idx+Count);
1304  }
1305
1306  // None of the adjustments above should have reduced the sum of factor powers
1307  // below our mininum of '4'.
1308  assert(FactorPowerSum >= 4);
1309
1310  std::sort(Factors.begin(), Factors.end(), Factor::PowerDescendingSorter());
1311  return true;
1312}
1313
1314/// \brief Build a tree of multiplies, computing the product of Ops.
1315static Value *buildMultiplyTree(IRBuilder<> &Builder,
1316                                SmallVectorImpl<Value*> &Ops) {
1317  if (Ops.size() == 1)
1318    return Ops.back();
1319
1320  Value *LHS = Ops.pop_back_val();
1321  do {
1322    LHS = Builder.CreateMul(LHS, Ops.pop_back_val());
1323  } while (!Ops.empty());
1324
1325  return LHS;
1326}
1327
1328/// \brief Build a minimal multiplication DAG for (a^x)*(b^y)*(c^z)*...
1329///
1330/// Given a vector of values raised to various powers, where no two values are
1331/// equal and the powers are sorted in decreasing order, compute the minimal
1332/// DAG of multiplies to compute the final product, and return that product
1333/// value.
1334Value *Reassociate::buildMinimalMultiplyDAG(IRBuilder<> &Builder,
1335                                            SmallVectorImpl<Factor> &Factors) {
1336  assert(Factors[0].Power);
1337  SmallVector<Value *, 4> OuterProduct;
1338  for (unsigned LastIdx = 0, Idx = 1, Size = Factors.size();
1339       Idx < Size && Factors[Idx].Power > 0; ++Idx) {
1340    if (Factors[Idx].Power != Factors[LastIdx].Power) {
1341      LastIdx = Idx;
1342      continue;
1343    }
1344
1345    // We want to multiply across all the factors with the same power so that
1346    // we can raise them to that power as a single entity. Build a mini tree
1347    // for that.
1348    SmallVector<Value *, 4> InnerProduct;
1349    InnerProduct.push_back(Factors[LastIdx].Base);
1350    do {
1351      InnerProduct.push_back(Factors[Idx].Base);
1352      ++Idx;
1353    } while (Idx < Size && Factors[Idx].Power == Factors[LastIdx].Power);
1354
1355    // Reset the base value of the first factor to the new expression tree.
1356    // We'll remove all the factors with the same power in a second pass.
1357    Value *M = Factors[LastIdx].Base = buildMultiplyTree(Builder, InnerProduct);
1358    if (Instruction *MI = dyn_cast<Instruction>(M))
1359      RedoInsts.insert(MI);
1360
1361    LastIdx = Idx;
1362  }
1363  // Unique factors with equal powers -- we've folded them into the first one's
1364  // base.
1365  Factors.erase(std::unique(Factors.begin(), Factors.end(),
1366                            Factor::PowerEqual()),
1367                Factors.end());
1368
1369  // Iteratively collect the base of each factor with an add power into the
1370  // outer product, and halve each power in preparation for squaring the
1371  // expression.
1372  for (unsigned Idx = 0, Size = Factors.size(); Idx != Size; ++Idx) {
1373    if (Factors[Idx].Power & 1)
1374      OuterProduct.push_back(Factors[Idx].Base);
1375    Factors[Idx].Power >>= 1;
1376  }
1377  if (Factors[0].Power) {
1378    Value *SquareRoot = buildMinimalMultiplyDAG(Builder, Factors);
1379    OuterProduct.push_back(SquareRoot);
1380    OuterProduct.push_back(SquareRoot);
1381  }
1382  if (OuterProduct.size() == 1)
1383    return OuterProduct.front();
1384
1385  Value *V = buildMultiplyTree(Builder, OuterProduct);
1386  return V;
1387}
1388
1389Value *Reassociate::OptimizeMul(BinaryOperator *I,
1390                                SmallVectorImpl<ValueEntry> &Ops) {
1391  // We can only optimize the multiplies when there is a chain of more than
1392  // three, such that a balanced tree might require fewer total multiplies.
1393  if (Ops.size() < 4)
1394    return 0;
1395
1396  // Try to turn linear trees of multiplies without other uses of the
1397  // intermediate stages into minimal multiply DAGs with perfect sub-expression
1398  // re-use.
1399  SmallVector<Factor, 4> Factors;
1400  if (!collectMultiplyFactors(Ops, Factors))
1401    return 0; // All distinct factors, so nothing left for us to do.
1402
1403  IRBuilder<> Builder(I);
1404  Value *V = buildMinimalMultiplyDAG(Builder, Factors);
1405  if (Ops.empty())
1406    return V;
1407
1408  ValueEntry NewEntry = ValueEntry(getRank(V), V);
1409  Ops.insert(std::lower_bound(Ops.begin(), Ops.end(), NewEntry), NewEntry);
1410  return 0;
1411}
1412
1413Value *Reassociate::OptimizeExpression(BinaryOperator *I,
1414                                       SmallVectorImpl<ValueEntry> &Ops) {
1415  // Now that we have the linearized expression tree, try to optimize it.
1416  // Start by folding any constants that we found.
1417  Constant *Cst = 0;
1418  unsigned Opcode = I->getOpcode();
1419  while (!Ops.empty() && isa<Constant>(Ops.back().Op)) {
1420    Constant *C = cast<Constant>(Ops.pop_back_val().Op);
1421    Cst = Cst ? ConstantExpr::get(Opcode, C, Cst) : C;
1422  }
1423  // If there was nothing but constants then we are done.
1424  if (Ops.empty())
1425    return Cst;
1426
1427  // Put the combined constant back at the end of the operand list, except if
1428  // there is no point.  For example, an add of 0 gets dropped here, while a
1429  // multiplication by zero turns the whole expression into zero.
1430  if (Cst && Cst != ConstantExpr::getBinOpIdentity(Opcode, I->getType())) {
1431    if (Cst == ConstantExpr::getBinOpAbsorber(Opcode, I->getType()))
1432      return Cst;
1433    Ops.push_back(ValueEntry(0, Cst));
1434  }
1435
1436  if (Ops.size() == 1) return Ops[0].Op;
1437
1438  // Handle destructive annihilation due to identities between elements in the
1439  // argument list here.
1440  unsigned NumOps = Ops.size();
1441  switch (Opcode) {
1442  default: break;
1443  case Instruction::And:
1444  case Instruction::Or:
1445  case Instruction::Xor:
1446    if (Value *Result = OptimizeAndOrXor(Opcode, Ops))
1447      return Result;
1448    break;
1449
1450  case Instruction::Add:
1451    if (Value *Result = OptimizeAdd(I, Ops))
1452      return Result;
1453    break;
1454
1455  case Instruction::Mul:
1456    if (Value *Result = OptimizeMul(I, Ops))
1457      return Result;
1458    break;
1459  }
1460
1461  if (Ops.size() != NumOps)
1462    return OptimizeExpression(I, Ops);
1463  return 0;
1464}
1465
1466/// EraseInst - Zap the given instruction, adding interesting operands to the
1467/// work list.
1468void Reassociate::EraseInst(Instruction *I) {
1469  assert(isInstructionTriviallyDead(I) && "Trivially dead instructions only!");
1470  SmallVector<Value*, 8> Ops(I->op_begin(), I->op_end());
1471  // Erase the dead instruction.
1472  ValueRankMap.erase(I);
1473  RedoInsts.remove(I);
1474  I->eraseFromParent();
1475  // Optimize its operands.
1476  SmallPtrSet<Instruction *, 8> Visited; // Detect self-referential nodes.
1477  for (unsigned i = 0, e = Ops.size(); i != e; ++i)
1478    if (Instruction *Op = dyn_cast<Instruction>(Ops[i])) {
1479      // If this is a node in an expression tree, climb to the expression root
1480      // and add that since that's where optimization actually happens.
1481      unsigned Opcode = Op->getOpcode();
1482      while (Op->hasOneUse() && Op->use_back()->getOpcode() == Opcode &&
1483             Visited.insert(Op))
1484        Op = Op->use_back();
1485      RedoInsts.insert(Op);
1486    }
1487}
1488
1489/// OptimizeInst - Inspect and optimize the given instruction. Note that erasing
1490/// instructions is not allowed.
1491void Reassociate::OptimizeInst(Instruction *I) {
1492  // Only consider operations that we understand.
1493  if (!isa<BinaryOperator>(I))
1494    return;
1495
1496  if (I->getOpcode() == Instruction::Shl &&
1497      isa<ConstantInt>(I->getOperand(1)))
1498    // If an operand of this shift is a reassociable multiply, or if the shift
1499    // is used by a reassociable multiply or add, turn into a multiply.
1500    if (isReassociableOp(I->getOperand(0), Instruction::Mul) ||
1501        (I->hasOneUse() &&
1502         (isReassociableOp(I->use_back(), Instruction::Mul) ||
1503          isReassociableOp(I->use_back(), Instruction::Add)))) {
1504      Instruction *NI = ConvertShiftToMul(I);
1505      RedoInsts.insert(I);
1506      MadeChange = true;
1507      I = NI;
1508    }
1509
1510  // Floating point binary operators are not associative, but we can still
1511  // commute (some) of them, to canonicalize the order of their operands.
1512  // This can potentially expose more CSE opportunities, and makes writing
1513  // other transformations simpler.
1514  if ((I->getType()->isFloatingPointTy() || I->getType()->isVectorTy())) {
1515    // FAdd and FMul can be commuted.
1516    if (I->getOpcode() != Instruction::FMul &&
1517        I->getOpcode() != Instruction::FAdd)
1518      return;
1519
1520    Value *LHS = I->getOperand(0);
1521    Value *RHS = I->getOperand(1);
1522    unsigned LHSRank = getRank(LHS);
1523    unsigned RHSRank = getRank(RHS);
1524
1525    // Sort the operands by rank.
1526    if (RHSRank < LHSRank) {
1527      I->setOperand(0, RHS);
1528      I->setOperand(1, LHS);
1529    }
1530
1531    return;
1532  }
1533
1534  // Do not reassociate boolean (i1) expressions.  We want to preserve the
1535  // original order of evaluation for short-circuited comparisons that
1536  // SimplifyCFG has folded to AND/OR expressions.  If the expression
1537  // is not further optimized, it is likely to be transformed back to a
1538  // short-circuited form for code gen, and the source order may have been
1539  // optimized for the most likely conditions.
1540  if (I->getType()->isIntegerTy(1))
1541    return;
1542
1543  // If this is a subtract instruction which is not already in negate form,
1544  // see if we can convert it to X+-Y.
1545  if (I->getOpcode() == Instruction::Sub) {
1546    if (ShouldBreakUpSubtract(I)) {
1547      Instruction *NI = BreakUpSubtract(I);
1548      RedoInsts.insert(I);
1549      MadeChange = true;
1550      I = NI;
1551    } else if (BinaryOperator::isNeg(I)) {
1552      // Otherwise, this is a negation.  See if the operand is a multiply tree
1553      // and if this is not an inner node of a multiply tree.
1554      if (isReassociableOp(I->getOperand(1), Instruction::Mul) &&
1555          (!I->hasOneUse() ||
1556           !isReassociableOp(I->use_back(), Instruction::Mul))) {
1557        Instruction *NI = LowerNegateToMultiply(I);
1558        RedoInsts.insert(I);
1559        MadeChange = true;
1560        I = NI;
1561      }
1562    }
1563  }
1564
1565  // If this instruction is an associative binary operator, process it.
1566  if (!I->isAssociative()) return;
1567  BinaryOperator *BO = cast<BinaryOperator>(I);
1568
1569  // If this is an interior node of a reassociable tree, ignore it until we
1570  // get to the root of the tree, to avoid N^2 analysis.
1571  unsigned Opcode = BO->getOpcode();
1572  if (BO->hasOneUse() && BO->use_back()->getOpcode() == Opcode)
1573    return;
1574
1575  // If this is an add tree that is used by a sub instruction, ignore it
1576  // until we process the subtract.
1577  if (BO->hasOneUse() && BO->getOpcode() == Instruction::Add &&
1578      cast<Instruction>(BO->use_back())->getOpcode() == Instruction::Sub)
1579    return;
1580
1581  ReassociateExpression(BO);
1582}
1583
1584void Reassociate::ReassociateExpression(BinaryOperator *I) {
1585
1586  // First, walk the expression tree, linearizing the tree, collecting the
1587  // operand information.
1588  SmallVector<RepeatedValue, 8> Tree;
1589  MadeChange |= LinearizeExprTree(I, Tree);
1590  SmallVector<ValueEntry, 8> Ops;
1591  Ops.reserve(Tree.size());
1592  for (unsigned i = 0, e = Tree.size(); i != e; ++i) {
1593    RepeatedValue E = Tree[i];
1594    Ops.append(E.second.getZExtValue(),
1595               ValueEntry(getRank(E.first), E.first));
1596  }
1597
1598  DEBUG(dbgs() << "RAIn:\t"; PrintOps(I, Ops); dbgs() << '\n');
1599
1600  // Now that we have linearized the tree to a list and have gathered all of
1601  // the operands and their ranks, sort the operands by their rank.  Use a
1602  // stable_sort so that values with equal ranks will have their relative
1603  // positions maintained (and so the compiler is deterministic).  Note that
1604  // this sorts so that the highest ranking values end up at the beginning of
1605  // the vector.
1606  std::stable_sort(Ops.begin(), Ops.end());
1607
1608  // OptimizeExpression - Now that we have the expression tree in a convenient
1609  // sorted form, optimize it globally if possible.
1610  if (Value *V = OptimizeExpression(I, Ops)) {
1611    if (V == I)
1612      // Self-referential expression in unreachable code.
1613      return;
1614    // This expression tree simplified to something that isn't a tree,
1615    // eliminate it.
1616    DEBUG(dbgs() << "Reassoc to scalar: " << *V << '\n');
1617    I->replaceAllUsesWith(V);
1618    if (Instruction *VI = dyn_cast<Instruction>(V))
1619      VI->setDebugLoc(I->getDebugLoc());
1620    RedoInsts.insert(I);
1621    ++NumAnnihil;
1622    return;
1623  }
1624
1625  // We want to sink immediates as deeply as possible except in the case where
1626  // this is a multiply tree used only by an add, and the immediate is a -1.
1627  // In this case we reassociate to put the negation on the outside so that we
1628  // can fold the negation into the add: (-X)*Y + Z -> Z-X*Y
1629  if (I->getOpcode() == Instruction::Mul && I->hasOneUse() &&
1630      cast<Instruction>(I->use_back())->getOpcode() == Instruction::Add &&
1631      isa<ConstantInt>(Ops.back().Op) &&
1632      cast<ConstantInt>(Ops.back().Op)->isAllOnesValue()) {
1633    ValueEntry Tmp = Ops.pop_back_val();
1634    Ops.insert(Ops.begin(), Tmp);
1635  }
1636
1637  DEBUG(dbgs() << "RAOut:\t"; PrintOps(I, Ops); dbgs() << '\n');
1638
1639  if (Ops.size() == 1) {
1640    if (Ops[0].Op == I)
1641      // Self-referential expression in unreachable code.
1642      return;
1643
1644    // This expression tree simplified to something that isn't a tree,
1645    // eliminate it.
1646    I->replaceAllUsesWith(Ops[0].Op);
1647    if (Instruction *OI = dyn_cast<Instruction>(Ops[0].Op))
1648      OI->setDebugLoc(I->getDebugLoc());
1649    RedoInsts.insert(I);
1650    return;
1651  }
1652
1653  // Now that we ordered and optimized the expressions, splat them back into
1654  // the expression tree, removing any unneeded nodes.
1655  RewriteExprTree(I, Ops);
1656}
1657
1658bool Reassociate::runOnFunction(Function &F) {
1659  // Calculate the rank map for F
1660  BuildRankMap(F);
1661
1662  MadeChange = false;
1663  for (Function::iterator BI = F.begin(), BE = F.end(); BI != BE; ++BI) {
1664    // Optimize every instruction in the basic block.
1665    for (BasicBlock::iterator II = BI->begin(), IE = BI->end(); II != IE; )
1666      if (isInstructionTriviallyDead(II)) {
1667        EraseInst(II++);
1668      } else {
1669        OptimizeInst(II);
1670        assert(II->getParent() == BI && "Moved to a different block!");
1671        ++II;
1672      }
1673
1674    // If this produced extra instructions to optimize, handle them now.
1675    while (!RedoInsts.empty()) {
1676      Instruction *I = RedoInsts.pop_back_val();
1677      if (isInstructionTriviallyDead(I))
1678        EraseInst(I);
1679      else
1680        OptimizeInst(I);
1681    }
1682  }
1683
1684  // We are done with the rank map.
1685  RankMap.clear();
1686  ValueRankMap.clear();
1687
1688  return MadeChange;
1689}
1690