3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This pass reassociates commutative expressions in an order that is designed
11 // to promote better constant propagation, GCSE, LICM, PRE, etc.
13 // For example: 4 + (x + 5) -> x + (4 + 5)
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.
21 //===----------------------------------------------------------------------===//
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"
48 STATISTIC(NumChanged, "Number of insts reassociated");
49 STATISTIC(NumAnnihil, "Number of expr tree annihilated");
50 STATISTIC(NumFactor , "Number of multiplies factored");
56 ValueEntry(unsigned R, Value *O) : Rank(R), Op(O) {}
58 inline bool operator<(const ValueEntry &LHS, const ValueEntry &RHS) {
59 return LHS.Rank > RHS.Rank; // Sort so that highest rank goes to start.
64 /// PrintOps - Print out the expression identified in the Ops list.
66 static void PrintOps(Instruction *I, const SmallVectorImpl<ValueEntry> &Ops) {
67 Module *M = I->getParent()->getParent()->getParent();
68 dbgs() << Instruction::getOpcodeName(I->getOpcode()) << " "
69 << *Ops[0].Op->getType() << '\t';
70 for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
72 WriteAsOperand(dbgs(), Ops[i].Op, false, M);
73 dbgs() << ", #" << Ops[i].Rank << "] ";
79 /// \brief Utility class representing a base and exponent pair which form one
80 /// factor of some product.
85 Factor(Value *Base, unsigned Power) : Base(Base), Power(Power) {}
87 /// \brief Sort factors by their Base.
89 bool operator()(const Factor &LHS, const Factor &RHS) {
90 return LHS.Base < RHS.Base;
94 /// \brief Compare factors for equal bases.
96 bool operator()(const Factor &LHS, const Factor &RHS) {
97 return LHS.Base == RHS.Base;
101 /// \brief Sort factors in descending order by their power.
102 struct PowerDescendingSorter {
103 bool operator()(const Factor &LHS, const Factor &RHS) {
104 return LHS.Power > RHS.Power;
108 /// \brief Compare factors for equal powers.
110 bool operator()(const Factor &LHS, const Factor &RHS) {
111 return LHS.Power == RHS.Power;
121 class isInstDeadFunc {
123 bool operator() (Instruction* I) {
124 return isInstructionTriviallyDead(I);
128 class RmInstCallBackFunc {
129 Reassociate *reassoc_;
131 RmInstCallBackFunc(Reassociate* ra): reassoc_(ra) {}
132 inline void operator() (Instruction*);
135 // The worklist has following traits:
136 // - it is pretty much a dequeue.
137 // - has "set" semantic, meaning all elements in the worklist are distinct.
138 // - efficient in-place element removal (by replacing the element with
143 typedef AssertingVH<Instruction> value_type;
144 typedef std::set<value_type> set_type;
145 typedef std::deque<value_type> deque_type;
146 // caller cannot modify element via iterator, hence constant.
147 typedef deque_type::const_iterator iterator;
148 typedef deque_type::const_iterator const_iterator;
149 typedef deque_type::size_type size_type;
154 return deque_.empty();
157 size_type size() const {
158 return deque_.size();
161 // return true iff X is in the worklist
162 bool found(const value_type &X) {
163 return set_.find(X) != set_.end();
167 return deque_.begin();
170 const_iterator begin() const {
171 return deque_.begin();
178 const_iterator end() const {
182 const value_type &back() const {
183 assert(!empty() && "worklist is empty");
184 return deque_.back();
187 // If element X is already in the worklist, do nothing but return false;
188 // otherwise, append X to the worklist and return true.
190 bool push_back(const value_type &X) {
191 bool result = set_.insert(X).second;
197 // insert() is the alias of push_back()
198 bool insert(const value_type &X) {
208 assert(!empty() && "worklist is empty");
213 value_type pop_back_val() {
214 value_type Ret = back();
219 const value_type &front() const {
220 assert(!empty() && "worklist is empty");
221 return deque_.front();
225 assert(!empty() && "worklist is empty");
230 value_type pop_front_val() {
231 value_type Ret = front();
236 // Remove an element from the worklist. Return true iff the element was
238 bool remove(const value_type& X);
240 template <typename pred, typename call_back_func>
241 int inplace_remove(pred p, call_back_func cb);
243 template <typename pred, typename call_back_func>
244 int inplace_rremove(pred p, call_back_func cb);
246 void append(RedoWorklist&);
253 class Reassociate : public FunctionPass {
254 friend class RmInstCallBackFunc;
256 DenseMap<BasicBlock*, unsigned> RankMap;
257 DenseMap<AssertingVH<Value>, unsigned> ValueRankMap;
258 RedoWorklist RedoInsts;
259 RedoWorklist TmpRedoInsts;
262 static char ID; // Pass identification, replacement for typeid
263 Reassociate() : FunctionPass(ID) {
264 initializeReassociatePass(*PassRegistry::getPassRegistry());
267 bool runOnFunction(Function &F);
269 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
270 AU.setPreservesCFG();
273 void BuildRankMap(Function &F);
274 unsigned getRank(Value *V);
275 void ReassociateExpression(BinaryOperator *I);
276 void RewriteExprTree(BinaryOperator *I, SmallVectorImpl<ValueEntry> &Ops);
277 Value *OptimizeExpression(BinaryOperator *I,
278 SmallVectorImpl<ValueEntry> &Ops);
279 Value *OptimizeAdd(Instruction *I, SmallVectorImpl<ValueEntry> &Ops);
280 bool collectMultiplyFactors(SmallVectorImpl<ValueEntry> &Ops,
281 SmallVectorImpl<Factor> &Factors);
282 Value *buildMinimalMultiplyDAG(IRBuilder<> &Builder,
283 SmallVectorImpl<Factor> &Factors);
284 void removeNegFromMulOps(SmallVectorImpl<ValueEntry> &Ops);
285 Value *OptimizeMul(BinaryOperator *I, SmallVectorImpl<ValueEntry> &Ops);
286 Value *RemoveFactorFromExpression(Value *V, Value *Factor);
287 void EraseInst(Instruction *I);
288 void EraseInstCallBack(Instruction *I);
289 void EraseAllDeadInst();
290 void OptimizeInst(Instruction *I);
294 char Reassociate::ID = 0;
295 INITIALIZE_PASS(Reassociate, "reassociate",
296 "Reassociate expressions", false, false)
298 // Public interface to the Reassociate pass
299 FunctionPass *llvm::createReassociatePass() { return new Reassociate(); }
301 /// isReassociableOp - Return true if V is an instruction of the specified
302 /// opcode and if it only has one use.
303 static BinaryOperator *isReassociableOp(Value *V, unsigned Opcode) {
304 if (V->hasOneUse() && isa<Instruction>(V) &&
305 cast<Instruction>(V)->getOpcode() == Opcode)
306 return cast<BinaryOperator>(V);
310 static bool isUnmovableInstruction(Instruction *I) {
311 if (I->getOpcode() == Instruction::PHI ||
312 I->getOpcode() == Instruction::LandingPad ||
313 I->getOpcode() == Instruction::Alloca ||
314 I->getOpcode() == Instruction::Load ||
315 I->getOpcode() == Instruction::Invoke ||
316 (I->getOpcode() == Instruction::Call &&
317 !isa<DbgInfoIntrinsic>(I)) ||
318 I->getOpcode() == Instruction::UDiv ||
319 I->getOpcode() == Instruction::SDiv ||
320 I->getOpcode() == Instruction::FDiv ||
321 I->getOpcode() == Instruction::URem ||
322 I->getOpcode() == Instruction::SRem ||
323 I->getOpcode() == Instruction::FRem)
328 inline void RmInstCallBackFunc::operator() (Instruction* I) {
329 reassoc_->EraseInstCallBack(I);
332 // Remove an item from the worklist. Return true iff the element was
334 bool RedoWorklist::remove(const value_type& X) {
336 deque_type::iterator I = std::find(deque_.begin(), deque_.end(), X);
337 assert(I != deque_.end() && "Can not find element");
344 // Forward go through each element e, calling p(e) to tell if e should be
345 // removed or not; if p(e) = true, then e will be replaced with NULL to
346 // indicate it is removed from the worklist, and functor cb will be
347 // called for further processing on e. The functors should not invalidate
348 // the iterator by inserting or deleteing element to and from the worklist.
350 // Returns the number of instruction being deleted.
351 template <typename pred, typename call_back_func>
352 int RedoWorklist::inplace_remove(pred p, call_back_func cb) {
354 for (typename deque_type::iterator iter = deque_.begin(),
355 iter_e = deque_.end(); iter != iter_e; iter++) {
356 value_type &element = *iter;
357 if (p(element) && set_.erase(element)) {
358 Instruction* t = element;
359 element.~value_type();
360 new (&element) value_type(NULL);
368 // inplace_rremove() is the same as inplace_remove() except that elements
369 // are visited in backward order.
370 template <typename pred, typename call_back_func>
371 int RedoWorklist::inplace_rremove(pred p, call_back_func cb) {
373 for (typename deque_type::reverse_iterator iter = deque_.rbegin(),
374 iter_e = deque_.rend(); iter != iter_e; iter++) {
375 value_type &element = *iter;
376 if (p(element) && set_.erase(element)) {
377 Instruction* t = element;
378 element.~value_type();
379 new (&element) value_type(NULL);
387 void RedoWorklist::append(RedoWorklist& that) {
388 deque_type &that_deque = that.deque_;
390 while (!that_deque.empty()) {
391 push_back(that_deque.front());
392 that_deque.pop_front();
397 void Reassociate::BuildRankMap(Function &F) {
400 // Assign distinct ranks to function arguments
401 for (Function::arg_iterator I = F.arg_begin(), E = F.arg_end(); I != E; ++I)
402 ValueRankMap[&*I] = ++i;
404 ReversePostOrderTraversal<Function*> RPOT(&F);
405 for (ReversePostOrderTraversal<Function*>::rpo_iterator I = RPOT.begin(),
406 E = RPOT.end(); I != E; ++I) {
408 unsigned BBRank = RankMap[BB] = ++i << 16;
410 // Walk the basic block, adding precomputed ranks for any instructions that
411 // we cannot move. This ensures that the ranks for these instructions are
412 // all different in the block.
413 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
414 if (isUnmovableInstruction(I))
415 ValueRankMap[&*I] = ++BBRank;
419 unsigned Reassociate::getRank(Value *V) {
420 Instruction *I = dyn_cast<Instruction>(V);
422 if (isa<Argument>(V)) return ValueRankMap[V]; // Function argument.
423 return 0; // Otherwise it's a global or constant, rank 0.
426 if (unsigned Rank = ValueRankMap[I])
427 return Rank; // Rank already known?
429 // If this is an expression, return the 1+MAX(rank(LHS), rank(RHS)) so that
430 // we can reassociate expressions for code motion! Since we do not recurse
431 // for PHI nodes, we cannot have infinite recursion here, because there
432 // cannot be loops in the value graph that do not go through PHI nodes.
433 unsigned Rank = 0, MaxRank = RankMap[I->getParent()];
434 for (unsigned i = 0, e = I->getNumOperands();
435 i != e && Rank != MaxRank; ++i)
436 Rank = std::max(Rank, getRank(I->getOperand(i)));
438 // If this is a not or neg instruction, do not count it for rank. This
439 // assures us that X and ~X will have the same rank.
440 if (!I->getType()->isIntegerTy() ||
441 (!BinaryOperator::isNot(I) && !BinaryOperator::isNeg(I)))
444 //DEBUG(dbgs() << "Calculated Rank[" << V->getName() << "] = "
447 return ValueRankMap[I] = Rank;
450 /// LowerNegateToMultiply - Replace 0-X with X*-1.
452 static BinaryOperator *LowerNegateToMultiply(Instruction *Neg) {
453 Constant *Cst = Constant::getAllOnesValue(Neg->getType());
455 BinaryOperator *Res =
456 BinaryOperator::CreateMul(Neg->getOperand(1), Cst, "",Neg);
457 Neg->setOperand(1, Constant::getNullValue(Neg->getType())); // Drop use of op.
459 Neg->replaceAllUsesWith(Res);
460 Res->setDebugLoc(Neg->getDebugLoc());
464 /// CarmichaelShift - Returns k such that lambda(2^Bitwidth) = 2^k, where lambda
465 /// is the Carmichael function. This means that x^(2^k) === 1 mod 2^Bitwidth for
466 /// every odd x, i.e. x^(2^k) = 1 for every odd x in Bitwidth-bit arithmetic.
467 /// Note that 0 <= k < Bitwidth, and if Bitwidth > 3 then x^(2^k) = 0 for every
468 /// even x in Bitwidth-bit arithmetic.
469 static unsigned CarmichaelShift(unsigned Bitwidth) {
475 /// IncorporateWeight - Add the extra weight 'RHS' to the existing weight 'LHS',
476 /// reducing the combined weight using any special properties of the operation.
477 /// The existing weight LHS represents the computation X op X op ... op X where
478 /// X occurs LHS times. The combined weight represents X op X op ... op X with
479 /// X occurring LHS + RHS times. If op is "Xor" for example then the combined
480 /// operation is equivalent to X if LHS + RHS is odd, or 0 if LHS + RHS is even;
481 /// the routine returns 1 in LHS in the first case, and 0 in LHS in the second.
482 static void IncorporateWeight(APInt &LHS, const APInt &RHS, unsigned Opcode) {
483 // If we were working with infinite precision arithmetic then the combined
484 // weight would be LHS + RHS. But we are using finite precision arithmetic,
485 // and the APInt sum LHS + RHS may not be correct if it wraps (it is correct
486 // for nilpotent operations and addition, but not for idempotent operations
487 // and multiplication), so it is important to correctly reduce the combined
488 // weight back into range if wrapping would be wrong.
490 // If RHS is zero then the weight didn't change.
491 if (RHS.isMinValue())
493 // If LHS is zero then the combined weight is RHS.
494 if (LHS.isMinValue()) {
498 // From this point on we know that neither LHS nor RHS is zero.
500 if (Instruction::isIdempotent(Opcode)) {
501 // Idempotent means X op X === X, so any non-zero weight is equivalent to a
502 // weight of 1. Keeping weights at zero or one also means that wrapping is
504 assert(LHS == 1 && RHS == 1 && "Weights not reduced!");
505 return; // Return a weight of 1.
507 if (Instruction::isNilpotent(Opcode)) {
508 // Nilpotent means X op X === 0, so reduce weights modulo 2.
509 assert(LHS == 1 && RHS == 1 && "Weights not reduced!");
510 LHS = 0; // 1 + 1 === 0 modulo 2.
513 if (Opcode == Instruction::Add) {
514 // TODO: Reduce the weight by exploiting nsw/nuw?
519 assert(Opcode == Instruction::Mul && "Unknown associative operation!");
520 unsigned Bitwidth = LHS.getBitWidth();
521 // If CM is the Carmichael number then a weight W satisfying W >= CM+Bitwidth
522 // can be replaced with W-CM. That's because x^W=x^(W-CM) for every Bitwidth
523 // bit number x, since either x is odd in which case x^CM = 1, or x is even in
524 // which case both x^W and x^(W - CM) are zero. By subtracting off multiples
525 // of CM like this weights can always be reduced to the range [0, CM+Bitwidth)
526 // which by a happy accident means that they can always be represented using
528 // TODO: Reduce the weight by exploiting nsw/nuw? (Could do much better than
529 // the Carmichael number).
531 /// CM - The value of Carmichael's lambda function.
532 APInt CM = APInt::getOneBitSet(Bitwidth, CarmichaelShift(Bitwidth));
533 // Any weight W >= Threshold can be replaced with W - CM.
534 APInt Threshold = CM + Bitwidth;
535 assert(LHS.ult(Threshold) && RHS.ult(Threshold) && "Weights not reduced!");
536 // For Bitwidth 4 or more the following sum does not overflow.
538 while (LHS.uge(Threshold))
541 // To avoid problems with overflow do everything the same as above but using
543 unsigned CM = 1U << CarmichaelShift(Bitwidth);
544 unsigned Threshold = CM + Bitwidth;
545 assert(LHS.getZExtValue() < Threshold && RHS.getZExtValue() < Threshold &&
546 "Weights not reduced!");
547 unsigned Total = LHS.getZExtValue() + RHS.getZExtValue();
548 while (Total >= Threshold)
554 /// EvaluateRepeatedConstant - Compute C op C op ... op C where the constant C
555 /// is repeated Weight times.
556 static Constant *EvaluateRepeatedConstant(unsigned Opcode, Constant *C,
558 // For addition the result can be efficiently computed as the product of the
559 // constant and the weight.
560 if (Opcode == Instruction::Add)
561 return ConstantExpr::getMul(C, ConstantInt::get(C->getContext(), Weight));
563 // The weight might be huge, so compute by repeated squaring to ensure that
564 // compile time is proportional to the logarithm of the weight.
565 Constant *Result = 0;
566 Constant *Power = C; // Successively C, C op C, (C op C) op (C op C) etc.
567 // Visit the bits in Weight.
568 while (Weight != 0) {
569 // If the current bit in Weight is non-zero do Result = Result op Power.
571 Result = Result ? ConstantExpr::get(Opcode, Result, Power) : Power;
572 // Move on to the next bit if any more are non-zero.
573 Weight = Weight.lshr(1);
574 if (Weight.isMinValue())
577 Power = ConstantExpr::get(Opcode, Power, Power);
580 assert(Result && "Only positive weights supported!");
584 typedef std::pair<Value*, APInt> RepeatedValue;
586 /// LinearizeExprTree - Given an associative binary expression, return the leaf
587 /// nodes in Ops along with their weights (how many times the leaf occurs). The
588 /// original expression is the same as
589 /// (Ops[0].first op Ops[0].first op ... Ops[0].first) <- Ops[0].second times
591 /// (Ops[1].first op Ops[1].first op ... Ops[1].first) <- Ops[1].second times
595 /// (Ops[N].first op Ops[N].first op ... Ops[N].first) <- Ops[N].second times
597 /// Note that the values Ops[0].first, ..., Ops[N].first are all distinct, and
598 /// they are all non-constant except possibly for the last one, which if it is
599 /// constant will have weight one (Ops[N].second === 1).
601 /// This routine may modify the function, in which case it returns 'true'. The
602 /// changes it makes may well be destructive, changing the value computed by 'I'
603 /// to something completely different. Thus if the routine returns 'true' then
604 /// you MUST either replace I with a new expression computed from the Ops array,
605 /// or use RewriteExprTree to put the values back in.
607 /// A leaf node is either not a binary operation of the same kind as the root
608 /// node 'I' (i.e. is not a binary operator at all, or is, but with a different
609 /// opcode), or is the same kind of binary operator but has a use which either
610 /// does not belong to the expression, or does belong to the expression but is
611 /// a leaf node. Every leaf node has at least one use that is a non-leaf node
612 /// of the expression, while for non-leaf nodes (except for the root 'I') every
613 /// use is a non-leaf node of the expression.
616 /// expression graph node names
626 /// The leaf nodes are C, E, F and G. The Ops array will contain (maybe not in
627 /// that order) (C, 1), (E, 1), (F, 2), (G, 2).
629 /// The expression is maximal: if some instruction is a binary operator of the
630 /// same kind as 'I', and all of its uses are non-leaf nodes of the expression,
631 /// then the instruction also belongs to the expression, is not a leaf node of
632 /// it, and its operands also belong to the expression (but may be leaf nodes).
634 /// NOTE: This routine will set operands of non-leaf non-root nodes to undef in
635 /// order to ensure that every non-root node in the expression has *exactly one*
636 /// use by a non-leaf node of the expression. This destruction means that the
637 /// caller MUST either replace 'I' with a new expression or use something like
638 /// RewriteExprTree to put the values back in if the routine indicates that it
639 /// made a change by returning 'true'.
641 /// In the above example either the right operand of A or the left operand of B
642 /// will be replaced by undef. If it is B's operand then this gives:
646 /// + + | A, B - operand of B replaced with undef
652 /// Note that such undef operands can only be reached by passing through 'I'.
653 /// For example, if you visit operands recursively starting from a leaf node
654 /// then you will never see such an undef operand unless you get back to 'I',
655 /// which requires passing through a phi node.
657 /// Note that this routine may also mutate binary operators of the wrong type
658 /// that have all uses inside the expression (i.e. only used by non-leaf nodes
659 /// of the expression) if it can turn them into binary operators of the right
660 /// type and thus make the expression bigger.
662 static bool LinearizeExprTree(BinaryOperator *I,
663 SmallVectorImpl<RepeatedValue> &Ops) {
664 DEBUG(dbgs() << "LINEARIZE: " << *I << '\n');
665 unsigned Bitwidth = I->getType()->getScalarType()->getPrimitiveSizeInBits();
666 unsigned Opcode = I->getOpcode();
667 assert(Instruction::isAssociative(Opcode) &&
668 Instruction::isCommutative(Opcode) &&
669 "Expected an associative and commutative operation!");
670 // If we see an absorbing element then the entire expression must be equal to
671 // it. For example, if this is a multiplication expression and zero occurs as
672 // an operand somewhere in it then the result of the expression must be zero.
673 Constant *Absorber = ConstantExpr::getBinOpAbsorber(Opcode, I->getType());
675 // Visit all operands of the expression, keeping track of their weight (the
676 // number of paths from the expression root to the operand, or if you like
677 // the number of times that operand occurs in the linearized expression).
678 // For example, if I = X + A, where X = A + B, then I, X and B have weight 1
679 // while A has weight two.
681 // Worklist of non-leaf nodes (their operands are in the expression too) along
682 // with their weights, representing a certain number of paths to the operator.
683 // If an operator occurs in the worklist multiple times then we found multiple
684 // ways to get to it.
685 SmallVector<std::pair<BinaryOperator*, APInt>, 8> Worklist; // (Op, Weight)
686 Worklist.push_back(std::make_pair(I, APInt(Bitwidth, 1)));
687 bool MadeChange = false;
689 // Leaves of the expression are values that either aren't the right kind of
690 // operation (eg: a constant, or a multiply in an add tree), or are, but have
691 // some uses that are not inside the expression. For example, in I = X + X,
692 // X = A + B, the value X has two uses (by I) that are in the expression. If
693 // X has any other uses, for example in a return instruction, then we consider
694 // X to be a leaf, and won't analyze it further. When we first visit a value,
695 // if it has more than one use then at first we conservatively consider it to
696 // be a leaf. Later, as the expression is explored, we may discover some more
697 // uses of the value from inside the expression. If all uses turn out to be
698 // from within the expression (and the value is a binary operator of the right
699 // kind) then the value is no longer considered to be a leaf, and its operands
702 // Leaves - Keeps track of the set of putative leaves as well as the number of
703 // paths to each leaf seen so far.
704 typedef DenseMap<Value*, APInt> LeafMap;
705 LeafMap Leaves; // Leaf -> Total weight so far.
706 SmallVector<Value*, 8> LeafOrder; // Ensure deterministic leaf output order.
709 SmallPtrSet<Value*, 8> Visited; // For sanity checking the iteration scheme.
711 while (!Worklist.empty()) {
712 std::pair<BinaryOperator*, APInt> P = Worklist.pop_back_val();
713 I = P.first; // We examine the operands of this binary operator.
715 for (unsigned OpIdx = 0; OpIdx < 2; ++OpIdx) { // Visit operands.
716 Value *Op = I->getOperand(OpIdx);
717 APInt Weight = P.second; // Number of paths to this operand.
718 DEBUG(dbgs() << "OPERAND: " << *Op << " (" << Weight << ")\n");
719 assert(!Op->use_empty() && "No uses, so how did we get to it?!");
721 // If the expression contains an absorbing element then there is no need
722 // to analyze it further: it must evaluate to the absorbing element.
723 if (Op == Absorber && !Weight.isMinValue()) {
724 Ops.push_back(std::make_pair(Absorber, APInt(Bitwidth, 1)));
728 // If this is a binary operation of the right kind with only one use then
729 // add its operands to the expression.
730 if (BinaryOperator *BO = isReassociableOp(Op, Opcode)) {
731 assert(Visited.insert(Op) && "Not first visit!");
732 DEBUG(dbgs() << "DIRECT ADD: " << *Op << " (" << Weight << ")\n");
733 Worklist.push_back(std::make_pair(BO, Weight));
737 // Appears to be a leaf. Is the operand already in the set of leaves?
738 LeafMap::iterator It = Leaves.find(Op);
739 if (It == Leaves.end()) {
740 // Not in the leaf map. Must be the first time we saw this operand.
741 assert(Visited.insert(Op) && "Not first visit!");
742 if (!Op->hasOneUse()) {
743 // This value has uses not accounted for by the expression, so it is
744 // not safe to modify. Mark it as being a leaf.
745 DEBUG(dbgs() << "ADD USES LEAF: " << *Op << " (" << Weight << ")\n");
746 LeafOrder.push_back(Op);
750 // No uses outside the expression, try morphing it.
751 } else if (It != Leaves.end()) {
752 // Already in the leaf map.
753 assert(Visited.count(Op) && "In leaf map but not visited!");
755 // Update the number of paths to the leaf.
756 IncorporateWeight(It->second, Weight, Opcode);
758 #if 0 // TODO: Re-enable once PR13021 is fixed.
759 // The leaf already has one use from inside the expression. As we want
760 // exactly one such use, drop this new use of the leaf.
761 assert(!Op->hasOneUse() && "Only one use, but we got here twice!");
762 I->setOperand(OpIdx, UndefValue::get(I->getType()));
765 // If the leaf is a binary operation of the right kind and we now see
766 // that its multiple original uses were in fact all by nodes belonging
767 // to the expression, then no longer consider it to be a leaf and add
768 // its operands to the expression.
769 if (BinaryOperator *BO = isReassociableOp(Op, Opcode)) {
770 DEBUG(dbgs() << "UNLEAF: " << *Op << " (" << It->second << ")\n");
771 Worklist.push_back(std::make_pair(BO, It->second));
777 // If we still have uses that are not accounted for by the expression
778 // then it is not safe to modify the value.
779 if (!Op->hasOneUse())
782 // No uses outside the expression, try morphing it.
784 Leaves.erase(It); // Since the value may be morphed below.
787 // At this point we have a value which, first of all, is not a binary
788 // expression of the right kind, and secondly, is only used inside the
789 // expression. This means that it can safely be modified. See if we
790 // can usefully morph it into an expression of the right kind.
791 assert((!isa<Instruction>(Op) ||
792 cast<Instruction>(Op)->getOpcode() != Opcode) &&
793 "Should have been handled above!");
794 assert(Op->hasOneUse() && "Has uses outside the expression tree!");
796 // If this is a multiply expression, turn any internal negations into
797 // multiplies by -1 so they can be reassociated.
798 BinaryOperator *BO = dyn_cast<BinaryOperator>(Op);
799 if (Opcode == Instruction::Mul && BO && BinaryOperator::isNeg(BO)) {
800 DEBUG(dbgs() << "MORPH LEAF: " << *Op << " (" << Weight << ") TO ");
801 BO = LowerNegateToMultiply(BO);
802 DEBUG(dbgs() << *BO << 'n');
803 Worklist.push_back(std::make_pair(BO, Weight));
808 // Failed to morph into an expression of the right type. This really is
810 DEBUG(dbgs() << "ADD LEAF: " << *Op << " (" << Weight << ")\n");
811 assert(!isReassociableOp(Op, Opcode) && "Value was morphed?");
812 LeafOrder.push_back(Op);
817 // The leaves, repeated according to their weights, represent the linearized
818 // form of the expression.
819 Constant *Cst = 0; // Accumulate constants here.
820 for (unsigned i = 0, e = LeafOrder.size(); i != e; ++i) {
821 Value *V = LeafOrder[i];
822 LeafMap::iterator It = Leaves.find(V);
823 if (It == Leaves.end())
824 // Node initially thought to be a leaf wasn't.
826 assert(!isReassociableOp(V, Opcode) && "Shouldn't be a leaf!");
827 APInt Weight = It->second;
828 if (Weight.isMinValue())
829 // Leaf already output or weight reduction eliminated it.
831 // Ensure the leaf is only output once.
833 // Glob all constants together into Cst.
834 if (Constant *C = dyn_cast<Constant>(V)) {
835 C = EvaluateRepeatedConstant(Opcode, C, Weight);
836 Cst = Cst ? ConstantExpr::get(Opcode, Cst, C) : C;
840 Ops.push_back(std::make_pair(V, Weight));
843 // Add any constants back into Ops, all globbed together and reduced to having
844 // weight 1 for the convenience of users.
845 Constant *Identity = ConstantExpr::getBinOpIdentity(Opcode, I->getType());
846 if (Cst && Cst != Identity) {
847 // If combining multiple constants resulted in the absorber then the entire
848 // expression must evaluate to the absorber.
851 Ops.push_back(std::make_pair(Cst, APInt(Bitwidth, 1)));
854 // For nilpotent operations or addition there may be no operands, for example
855 // because the expression was "X xor X" or consisted of 2^Bitwidth additions:
856 // in both cases the weight reduces to 0 causing the value to be skipped.
858 assert(Identity && "Associative operation without identity!");
859 Ops.push_back(std::make_pair(Identity, APInt(Bitwidth, 1)));
865 // RewriteExprTree - Now that the operands for this expression tree are
866 // linearized and optimized, emit them in-order.
867 void Reassociate::RewriteExprTree(BinaryOperator *I,
868 SmallVectorImpl<ValueEntry> &Ops) {
869 assert(Ops.size() > 1 && "Single values should be used directly!");
871 // Since our optimizations never increase the number of operations, the new
872 // expression can always be written by reusing the existing binary operators
873 // from the original expression tree, without creating any new instructions,
874 // though the rewritten expression may have a completely different topology.
875 // We take care to not change anything if the new expression will be the same
876 // as the original. If more than trivial changes (like commuting operands)
877 // were made then we are obliged to clear out any optional subclass data like
880 /// NodesToRewrite - Nodes from the original expression available for writing
881 /// the new expression into.
882 SmallVector<BinaryOperator*, 8> NodesToRewrite;
883 unsigned Opcode = I->getOpcode();
884 BinaryOperator *Op = I;
886 // ExpressionChanged - Non-null if the rewritten expression differs from the
887 // original in some non-trivial way, requiring the clearing of optional flags.
888 // Flags are cleared from the operator in ExpressionChanged up to I inclusive.
889 BinaryOperator *ExpressionChanged = 0;
890 for (unsigned i = 0; ; ++i) {
891 // The last operation (which comes earliest in the IR) is special as both
892 // operands will come from Ops, rather than just one with the other being
894 if (i+2 == Ops.size()) {
895 Value *NewLHS = Ops[i].Op;
896 Value *NewRHS = Ops[i+1].Op;
897 Value *OldLHS = Op->getOperand(0);
898 Value *OldRHS = Op->getOperand(1);
900 if (NewLHS == OldLHS && NewRHS == OldRHS)
901 // Nothing changed, leave it alone.
904 if (NewLHS == OldRHS && NewRHS == OldLHS) {
905 // The order of the operands was reversed. Swap them.
906 DEBUG(dbgs() << "RA: " << *Op << '\n');
908 DEBUG(dbgs() << "TO: " << *Op << '\n');
914 // The new operation differs non-trivially from the original. Overwrite
915 // the old operands with the new ones.
916 DEBUG(dbgs() << "RA: " << *Op << '\n');
917 if (NewLHS != OldLHS) {
918 if (BinaryOperator *BO = isReassociableOp(OldLHS, Opcode))
919 NodesToRewrite.push_back(BO);
920 Op->setOperand(0, NewLHS);
922 if (NewRHS != OldRHS) {
923 if (BinaryOperator *BO = isReassociableOp(OldRHS, Opcode))
924 NodesToRewrite.push_back(BO);
925 Op->setOperand(1, NewRHS);
927 DEBUG(dbgs() << "TO: " << *Op << '\n');
929 ExpressionChanged = Op;
936 // Not the last operation. The left-hand side will be a sub-expression
937 // while the right-hand side will be the current element of Ops.
938 Value *NewRHS = Ops[i].Op;
939 if (NewRHS != Op->getOperand(1)) {
940 DEBUG(dbgs() << "RA: " << *Op << '\n');
941 if (NewRHS == Op->getOperand(0)) {
942 // The new right-hand side was already present as the left operand. If
943 // we are lucky then swapping the operands will sort out both of them.
946 // Overwrite with the new right-hand side.
947 if (BinaryOperator *BO = isReassociableOp(Op->getOperand(1), Opcode))
948 NodesToRewrite.push_back(BO);
949 Op->setOperand(1, NewRHS);
950 ExpressionChanged = Op;
952 DEBUG(dbgs() << "TO: " << *Op << '\n');
957 // Now deal with the left-hand side. If this is already an operation node
958 // from the original expression then just rewrite the rest of the expression
960 if (BinaryOperator *BO = isReassociableOp(Op->getOperand(0), Opcode)) {
965 // Otherwise, grab a spare node from the original expression and use that as
966 // the left-hand side. If there are no nodes left then the optimizers made
967 // an expression with more nodes than the original! This usually means that
968 // they did something stupid but it might mean that the problem was just too
969 // hard (finding the mimimal number of multiplications needed to realize a
970 // multiplication expression is NP-complete). Whatever the reason, smart or
971 // stupid, create a new node if there are none left.
972 BinaryOperator *NewOp;
973 if (NodesToRewrite.empty()) {
974 Constant *Undef = UndefValue::get(I->getType());
975 NewOp = BinaryOperator::Create(Instruction::BinaryOps(Opcode),
976 Undef, Undef, "", I);
978 NewOp = NodesToRewrite.pop_back_val();
981 DEBUG(dbgs() << "RA: " << *Op << '\n');
982 Op->setOperand(0, NewOp);
983 DEBUG(dbgs() << "TO: " << *Op << '\n');
984 ExpressionChanged = Op;
990 // If the expression changed non-trivially then clear out all subclass data
991 // starting from the operator specified in ExpressionChanged, and compactify
992 // the operators to just before the expression root to guarantee that the
993 // expression tree is dominated by all of Ops.
994 if (ExpressionChanged)
996 ExpressionChanged->clearSubclassOptionalData();
997 if (ExpressionChanged == I)
999 ExpressionChanged->moveBefore(I);
1000 ExpressionChanged = cast<BinaryOperator>(*ExpressionChanged->use_begin());
1003 // Throw away any left over nodes from the original expression.
1004 for (unsigned i = 0, e = NodesToRewrite.size(); i != e; ++i)
1005 RedoInsts.insert(NodesToRewrite[i]);
1008 /// NegateValue - Insert instructions before the instruction pointed to by BI,
1009 /// that computes the negative version of the value specified. The negative
1010 /// version of the value is returned, and BI is left pointing at the instruction
1011 /// that should be processed next by the reassociation pass.
1012 static Value *NegateValue(Value *V, Instruction *BI) {
1013 if (Constant *C = dyn_cast<Constant>(V))
1014 return ConstantExpr::getNeg(C);
1016 // We are trying to expose opportunity for reassociation. One of the things
1017 // that we want to do to achieve this is to push a negation as deep into an
1018 // expression chain as possible, to expose the add instructions. In practice,
1019 // this means that we turn this:
1020 // X = -(A+12+C+D) into X = -A + -12 + -C + -D = -12 + -A + -C + -D
1021 // so that later, a: Y = 12+X could get reassociated with the -12 to eliminate
1022 // the constants. We assume that instcombine will clean up the mess later if
1023 // we introduce tons of unnecessary negation instructions.
1025 if (BinaryOperator *I = isReassociableOp(V, Instruction::Add)) {
1026 // Push the negates through the add.
1027 I->setOperand(0, NegateValue(I->getOperand(0), BI));
1028 I->setOperand(1, NegateValue(I->getOperand(1), BI));
1030 // We must move the add instruction here, because the neg instructions do
1031 // not dominate the old add instruction in general. By moving it, we are
1032 // assured that the neg instructions we just inserted dominate the
1033 // instruction we are about to insert after them.
1036 I->setName(I->getName()+".neg");
1040 // Okay, we need to materialize a negated version of V with an instruction.
1041 // Scan the use lists of V to see if we have one already.
1042 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E;++UI){
1044 if (!BinaryOperator::isNeg(U)) continue;
1046 // We found one! Now we have to make sure that the definition dominates
1047 // this use. We do this by moving it to the entry block (if it is a
1048 // non-instruction value) or right after the definition. These negates will
1049 // be zapped by reassociate later, so we don't need much finesse here.
1050 BinaryOperator *TheNeg = cast<BinaryOperator>(U);
1052 // Verify that the negate is in this function, V might be a constant expr.
1053 if (TheNeg->getParent()->getParent() != BI->getParent()->getParent())
1056 BasicBlock::iterator InsertPt;
1057 if (Instruction *InstInput = dyn_cast<Instruction>(V)) {
1058 if (InvokeInst *II = dyn_cast<InvokeInst>(InstInput)) {
1059 InsertPt = II->getNormalDest()->begin();
1061 InsertPt = InstInput;
1064 while (isa<PHINode>(InsertPt)) ++InsertPt;
1066 InsertPt = TheNeg->getParent()->getParent()->getEntryBlock().begin();
1068 TheNeg->moveBefore(InsertPt);
1072 // Insert a 'neg' instruction that subtracts the value from zero to get the
1074 return BinaryOperator::CreateNeg(V, V->getName() + ".neg", BI);
1077 /// ShouldBreakUpSubtract - Return true if we should break up this subtract of
1078 /// X-Y into (X + -Y).
1079 static bool ShouldBreakUpSubtract(Instruction *Sub) {
1080 // If this is a negation, we can't split it up!
1081 if (BinaryOperator::isNeg(Sub))
1084 // Don't bother to break this up unless either the LHS is an associable add or
1085 // subtract or if this is only used by one.
1086 if (isReassociableOp(Sub->getOperand(0), Instruction::Add) ||
1087 isReassociableOp(Sub->getOperand(0), Instruction::Sub))
1089 if (isReassociableOp(Sub->getOperand(1), Instruction::Add) ||
1090 isReassociableOp(Sub->getOperand(1), Instruction::Sub))
1092 if (Sub->hasOneUse() &&
1093 (isReassociableOp(Sub->use_back(), Instruction::Add) ||
1094 isReassociableOp(Sub->use_back(), Instruction::Sub)))
1100 /// BreakUpSubtract - If we have (X-Y), and if either X is an add, or if this is
1101 /// only used by an add, transform this into (X+(0-Y)) to promote better
1103 static BinaryOperator *BreakUpSubtract(Instruction *Sub) {
1104 // Convert a subtract into an add and a neg instruction. This allows sub
1105 // instructions to be commuted with other add instructions.
1107 // Calculate the negative value of Operand 1 of the sub instruction,
1108 // and set it as the RHS of the add instruction we just made.
1110 Value *NegVal = NegateValue(Sub->getOperand(1), Sub);
1111 BinaryOperator *New =
1112 BinaryOperator::CreateAdd(Sub->getOperand(0), NegVal, "", Sub);
1113 Sub->setOperand(0, Constant::getNullValue(Sub->getType())); // Drop use of op.
1114 Sub->setOperand(1, Constant::getNullValue(Sub->getType())); // Drop use of op.
1117 // Everyone now refers to the add instruction.
1118 Sub->replaceAllUsesWith(New);
1119 New->setDebugLoc(Sub->getDebugLoc());
1121 DEBUG(dbgs() << "Negated: " << *New << '\n');
1125 /// ConvertShiftToMul - If this is a shift of a reassociable multiply or is used
1126 /// by one, change this into a multiply by a constant to assist with further
1128 static BinaryOperator *ConvertShiftToMul(Instruction *Shl) {
1129 Constant *MulCst = ConstantInt::get(Shl->getType(), 1);
1130 MulCst = ConstantExpr::getShl(MulCst, cast<Constant>(Shl->getOperand(1)));
1132 BinaryOperator *Mul =
1133 BinaryOperator::CreateMul(Shl->getOperand(0), MulCst, "", Shl);
1134 Shl->setOperand(0, UndefValue::get(Shl->getType())); // Drop use of op.
1136 Shl->replaceAllUsesWith(Mul);
1137 Mul->setDebugLoc(Shl->getDebugLoc());
1141 /// FindInOperandList - Scan backwards and forwards among values with the same
1142 /// rank as element i to see if X exists. If X does not exist, return i. This
1143 /// is useful when scanning for 'x' when we see '-x' because they both get the
1145 static unsigned FindInOperandList(SmallVectorImpl<ValueEntry> &Ops, unsigned i,
1147 unsigned XRank = Ops[i].Rank;
1148 unsigned e = Ops.size();
1149 for (unsigned j = i+1; j != e && Ops[j].Rank == XRank; ++j)
1153 for (unsigned j = i-1; j != ~0U && Ops[j].Rank == XRank; --j)
1159 /// EmitAddTreeOfValues - Emit a tree of add instructions, summing Ops together
1160 /// and returning the result. Insert the tree before I.
1161 static Value *EmitAddTreeOfValues(Instruction *I,
1162 SmallVectorImpl<WeakVH> &Ops){
1163 if (Ops.size() == 1) return Ops.back();
1165 Value *V1 = Ops.back();
1167 Value *V2 = EmitAddTreeOfValues(I, Ops);
1168 return BinaryOperator::CreateAdd(V2, V1, "tmp", I);
1171 /// RemoveFactorFromExpression - If V is an expression tree that is a
1172 /// multiplication sequence, and if this sequence contains a multiply by Factor,
1173 /// remove Factor from the tree and return the new tree.
1174 Value *Reassociate::RemoveFactorFromExpression(Value *V, Value *Factor) {
1175 BinaryOperator *BO = isReassociableOp(V, Instruction::Mul);
1178 SmallVector<RepeatedValue, 8> Tree;
1179 MadeChange |= LinearizeExprTree(BO, Tree);
1180 SmallVector<ValueEntry, 8> Factors;
1181 Factors.reserve(Tree.size());
1182 for (unsigned i = 0, e = Tree.size(); i != e; ++i) {
1183 RepeatedValue E = Tree[i];
1184 Factors.append(E.second.getZExtValue(),
1185 ValueEntry(getRank(E.first), E.first));
1188 bool FoundFactor = false;
1189 bool NeedsNegate = false;
1190 for (unsigned i = 0, e = Factors.size(); i != e; ++i) {
1191 if (Factors[i].Op == Factor) {
1193 Factors.erase(Factors.begin()+i);
1197 // If this is a negative version of this factor, remove it.
1198 if (ConstantInt *FC1 = dyn_cast<ConstantInt>(Factor))
1199 if (ConstantInt *FC2 = dyn_cast<ConstantInt>(Factors[i].Op))
1200 if (FC1->getValue() == -FC2->getValue()) {
1201 FoundFactor = NeedsNegate = true;
1202 Factors.erase(Factors.begin()+i);
1208 // Make sure to restore the operands to the expression tree.
1209 RewriteExprTree(BO, Factors);
1213 BasicBlock::iterator InsertPt = BO; ++InsertPt;
1215 // If this was just a single multiply, remove the multiply and return the only
1216 // remaining operand.
1217 if (Factors.size() == 1) {
1218 RedoInsts.insert(BO);
1221 RewriteExprTree(BO, Factors);
1226 V = BinaryOperator::CreateNeg(V, "neg", InsertPt);
1231 /// FindSingleUseMultiplyFactors - If V is a single-use multiply, recursively
1232 /// add its operands as factors, otherwise add V to the list of factors.
1234 /// Ops is the top-level list of add operands we're trying to factor.
1235 static void FindSingleUseMultiplyFactors(Value *V,
1236 SmallVectorImpl<Value*> &Factors,
1237 const SmallVectorImpl<ValueEntry> &Ops) {
1238 BinaryOperator *BO = isReassociableOp(V, Instruction::Mul);
1240 Factors.push_back(V);
1244 // Otherwise, add the LHS and RHS to the list of factors.
1245 FindSingleUseMultiplyFactors(BO->getOperand(1), Factors, Ops);
1246 FindSingleUseMultiplyFactors(BO->getOperand(0), Factors, Ops);
1249 /// OptimizeAndOrXor - Optimize a series of operands to an 'and', 'or', or 'xor'
1250 /// instruction. This optimizes based on identities. If it can be reduced to
1251 /// a single Value, it is returned, otherwise the Ops list is mutated as
1253 static Value *OptimizeAndOrXor(unsigned Opcode,
1254 SmallVectorImpl<ValueEntry> &Ops) {
1255 // Scan the operand lists looking for X and ~X pairs, along with X,X pairs.
1256 // If we find any, we can simplify the expression. X&~X == 0, X|~X == -1.
1257 for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
1258 // First, check for X and ~X in the operand list.
1259 assert(i < Ops.size());
1260 if (BinaryOperator::isNot(Ops[i].Op)) { // Cannot occur for ^.
1261 Value *X = BinaryOperator::getNotArgument(Ops[i].Op);
1262 unsigned FoundX = FindInOperandList(Ops, i, X);
1264 if (Opcode == Instruction::And) // ...&X&~X = 0
1265 return Constant::getNullValue(X->getType());
1267 if (Opcode == Instruction::Or) // ...|X|~X = -1
1268 return Constant::getAllOnesValue(X->getType());
1272 // Next, check for duplicate pairs of values, which we assume are next to
1273 // each other, due to our sorting criteria.
1274 assert(i < Ops.size());
1275 if (i+1 != Ops.size() && Ops[i+1].Op == Ops[i].Op) {
1276 if (Opcode == Instruction::And || Opcode == Instruction::Or) {
1277 // Drop duplicate values for And and Or.
1278 Ops.erase(Ops.begin()+i);
1284 // Drop pairs of values for Xor.
1285 assert(Opcode == Instruction::Xor);
1287 return Constant::getNullValue(Ops[0].Op->getType());
1290 Ops.erase(Ops.begin()+i, Ops.begin()+i+2);
1298 /// OptimizeAdd - Optimize a series of operands to an 'add' instruction. This
1299 /// optimizes based on identities. If it can be reduced to a single Value, it
1300 /// is returned, otherwise the Ops list is mutated as necessary.
1301 Value *Reassociate::OptimizeAdd(Instruction *I,
1302 SmallVectorImpl<ValueEntry> &Ops) {
1303 // Scan the operand lists looking for X and -X pairs. If we find any, we
1304 // can simplify the expression. X+-X == 0. While we're at it, scan for any
1305 // duplicates. We want to canonicalize Y+Y+Y+Z -> 3*Y+Z.
1307 // TODO: We could handle "X + ~X" -> "-1" if we wanted, since "-X = ~X+1".
1309 for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
1310 Value *TheOp = Ops[i].Op;
1311 // Check to see if we've seen this operand before. If so, we factor all
1312 // instances of the operand together. Due to our sorting criteria, we know
1313 // that these need to be next to each other in the vector.
1314 if (i+1 != Ops.size() && Ops[i+1].Op == TheOp) {
1315 // Rescan the list, remove all instances of this operand from the expr.
1316 unsigned NumFound = 0;
1318 Ops.erase(Ops.begin()+i);
1320 } while (i != Ops.size() && Ops[i].Op == TheOp);
1322 DEBUG(errs() << "\nFACTORING [" << NumFound << "]: " << *TheOp << '\n');
1325 // Insert a new multiply.
1326 Value *Mul = ConstantInt::get(cast<IntegerType>(I->getType()), NumFound);
1327 Mul = BinaryOperator::CreateMul(TheOp, Mul, "factor", I);
1329 // Now that we have inserted a multiply, optimize it. This allows us to
1330 // handle cases that require multiple factoring steps, such as this:
1331 // (X*2) + (X*2) + (X*2) -> (X*2)*3 -> X*6
1332 RedoInsts.insert(cast<Instruction>(Mul));
1334 // If every add operand was a duplicate, return the multiply.
1338 // Otherwise, we had some input that didn't have the dupe, such as
1339 // "A + A + B" -> "A*2 + B". Add the new multiply to the list of
1340 // things being added by this operation.
1341 Ops.insert(Ops.begin(), ValueEntry(getRank(Mul), Mul));
1348 // Check for X and -X in the operand list.
1349 if (!BinaryOperator::isNeg(TheOp))
1352 Value *X = BinaryOperator::getNegArgument(TheOp);
1353 unsigned FoundX = FindInOperandList(Ops, i, X);
1357 // Remove X and -X from the operand list.
1358 if (Ops.size() == 2)
1359 return Constant::getNullValue(X->getType());
1361 Ops.erase(Ops.begin()+i);
1365 --i; // Need to back up an extra one.
1366 Ops.erase(Ops.begin()+FoundX);
1368 --i; // Revisit element.
1369 e -= 2; // Removed two elements.
1372 // Scan the operand list, checking to see if there are any common factors
1373 // between operands. Consider something like A*A+A*B*C+D. We would like to
1374 // reassociate this to A*(A+B*C)+D, which reduces the number of multiplies.
1375 // To efficiently find this, we count the number of times a factor occurs
1376 // for any ADD operands that are MULs.
1377 DenseMap<Value*, unsigned> FactorOccurrences;
1379 // Keep track of each multiply we see, to avoid triggering on (X*4)+(X*4)
1380 // where they are actually the same multiply.
1381 unsigned MaxOcc = 0;
1382 Value *MaxOccVal = 0;
1383 for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
1384 BinaryOperator *BOp = isReassociableOp(Ops[i].Op, Instruction::Mul);
1388 // Compute all of the factors of this added value.
1389 SmallVector<Value*, 8> Factors;
1390 FindSingleUseMultiplyFactors(BOp, Factors, Ops);
1391 assert(Factors.size() > 1 && "Bad linearize!");
1393 // Add one to FactorOccurrences for each unique factor in this op.
1394 SmallPtrSet<Value*, 8> Duplicates;
1395 for (unsigned i = 0, e = Factors.size(); i != e; ++i) {
1396 Value *Factor = Factors[i];
1397 if (!Duplicates.insert(Factor)) continue;
1399 unsigned Occ = ++FactorOccurrences[Factor];
1400 if (Occ > MaxOcc) { MaxOcc = Occ; MaxOccVal = Factor; }
1402 // If Factor is a negative constant, add the negated value as a factor
1403 // because we can percolate the negate out. Watch for minint, which
1404 // cannot be positivified.
1405 if (ConstantInt *CI = dyn_cast<ConstantInt>(Factor))
1406 if (CI->isNegative() && !CI->isMinValue(true)) {
1407 Factor = ConstantInt::get(CI->getContext(), -CI->getValue());
1408 assert(!Duplicates.count(Factor) &&
1409 "Shouldn't have two constant factors, missed a canonicalize");
1411 unsigned Occ = ++FactorOccurrences[Factor];
1412 if (Occ > MaxOcc) { MaxOcc = Occ; MaxOccVal = Factor; }
1417 // If any factor occurred more than one time, we can pull it out.
1419 DEBUG(errs() << "\nFACTORING [" << MaxOcc << "]: " << *MaxOccVal << '\n');
1422 // Create a new instruction that uses the MaxOccVal twice. If we don't do
1423 // this, we could otherwise run into situations where removing a factor
1424 // from an expression will drop a use of maxocc, and this can cause
1425 // RemoveFactorFromExpression on successive values to behave differently.
1426 Instruction *DummyInst = BinaryOperator::CreateAdd(MaxOccVal, MaxOccVal);
1427 SmallVector<WeakVH, 4> NewMulOps;
1428 for (unsigned i = 0; i != Ops.size(); ++i) {
1429 // Only try to remove factors from expressions we're allowed to.
1430 BinaryOperator *BOp = isReassociableOp(Ops[i].Op, Instruction::Mul);
1434 if (Value *V = RemoveFactorFromExpression(Ops[i].Op, MaxOccVal)) {
1435 // The factorized operand may occur several times. Convert them all in
1437 for (unsigned j = Ops.size(); j != i;) {
1439 if (Ops[j].Op == Ops[i].Op) {
1440 NewMulOps.push_back(V);
1441 Ops.erase(Ops.begin()+j);
1448 // No need for extra uses anymore.
1451 unsigned NumAddedValues = NewMulOps.size();
1452 Value *V = EmitAddTreeOfValues(I, NewMulOps);
1454 // Now that we have inserted the add tree, optimize it. This allows us to
1455 // handle cases that require multiple factoring steps, such as this:
1456 // A*A*B + A*A*C --> A*(A*B+A*C) --> A*(A*(B+C))
1457 assert(NumAddedValues > 1 && "Each occurrence should contribute a value");
1458 (void)NumAddedValues;
1459 if (Instruction *VI = dyn_cast<Instruction>(V))
1460 RedoInsts.insert(VI);
1462 // Create the multiply.
1463 Instruction *V2 = BinaryOperator::CreateMul(V, MaxOccVal, "tmp", I);
1465 // Rerun associate on the multiply in case the inner expression turned into
1466 // a multiply. We want to make sure that we keep things in canonical form.
1467 RedoInsts.insert(V2);
1469 // If every add operand included the factor (e.g. "A*B + A*C"), then the
1470 // entire result expression is just the multiply "A*(B+C)".
1474 // Otherwise, we had some input that didn't have the factor, such as
1475 // "A*B + A*C + D" -> "A*(B+C) + D". Add the new multiply to the list of
1476 // things being added by this operation.
1477 Ops.insert(Ops.begin(), ValueEntry(getRank(V2), V2));
1484 /// \brief Predicate tests whether a ValueEntry's op is in a map.
1485 struct IsValueInMap {
1486 const DenseMap<Value *, unsigned> ⤅
1488 IsValueInMap(const DenseMap<Value *, unsigned> &Map) : Map(Map) {}
1490 bool operator()(const ValueEntry &Entry) {
1491 return Map.find(Entry.Op) != Map.end();
1496 /// \brief Build up a vector of value/power pairs factoring a product.
1498 /// Given a series of multiplication operands, build a vector of factors and
1499 /// the powers each is raised to when forming the final product. Sort them in
1500 /// the order of descending power.
1502 /// (x*x) -> [(x, 2)]
1503 /// ((x*x)*x) -> [(x, 3)]
1504 /// ((((x*y)*x)*y)*x) -> [(x, 3), (y, 2)]
1506 /// \returns Whether any factors have a power greater than one.
1507 bool Reassociate::collectMultiplyFactors(SmallVectorImpl<ValueEntry> &Ops,
1508 SmallVectorImpl<Factor> &Factors) {
1509 // FIXME: Have Ops be (ValueEntry, Multiplicity) pairs, simplifying this.
1510 // Compute the sum of powers of simplifiable factors.
1511 unsigned FactorPowerSum = 0;
1512 for (unsigned Idx = 1, Size = Ops.size(); Idx < Size; ++Idx) {
1513 Value *Op = Ops[Idx-1].Op;
1515 // Count the number of occurrences of this value.
1517 for (; Idx < Size && Ops[Idx].Op == Op; ++Idx)
1519 // Track for simplification all factors which occur 2 or more times.
1521 FactorPowerSum += Count;
1524 // We can only simplify factors if the sum of the powers of our simplifiable
1525 // factors is 4 or higher. When that is the case, we will *always* have
1526 // a simplification. This is an important invariant to prevent cyclicly
1527 // trying to simplify already minimal formations.
1528 if (FactorPowerSum < 4)
1531 // Now gather the simplifiable factors, removing them from Ops.
1533 for (unsigned Idx = 1; Idx < Ops.size(); ++Idx) {
1534 Value *Op = Ops[Idx-1].Op;
1536 // Count the number of occurrences of this value.
1538 for (; Idx < Ops.size() && Ops[Idx].Op == Op; ++Idx)
1542 // Move an even number of occurrences to Factors.
1545 FactorPowerSum += Count;
1546 Factors.push_back(Factor(Op, Count));
1547 Ops.erase(Ops.begin()+Idx, Ops.begin()+Idx+Count);
1550 // None of the adjustments above should have reduced the sum of factor powers
1551 // below our mininum of '4'.
1552 assert(FactorPowerSum >= 4);
1554 std::sort(Factors.begin(), Factors.end(), Factor::PowerDescendingSorter());
1558 /// \brief Build a tree of multiplies, computing the product of Ops.
1559 static Value *buildMultiplyTree(IRBuilder<> &Builder,
1560 SmallVectorImpl<Value*> &Ops) {
1561 if (Ops.size() == 1)
1564 Value *LHS = Ops.pop_back_val();
1566 LHS = Builder.CreateMul(LHS, Ops.pop_back_val());
1567 } while (!Ops.empty());
1572 /// \brief Build a minimal multiplication DAG for (a^x)*(b^y)*(c^z)*...
1574 /// Given a vector of values raised to various powers, where no two values are
1575 /// equal and the powers are sorted in decreasing order, compute the minimal
1576 /// DAG of multiplies to compute the final product, and return that product
1578 Value *Reassociate::buildMinimalMultiplyDAG(IRBuilder<> &Builder,
1579 SmallVectorImpl<Factor> &Factors) {
1580 assert(Factors[0].Power);
1581 SmallVector<Value *, 4> OuterProduct;
1582 for (unsigned LastIdx = 0, Idx = 1, Size = Factors.size();
1583 Idx < Size && Factors[Idx].Power > 0; ++Idx) {
1584 if (Factors[Idx].Power != Factors[LastIdx].Power) {
1589 // We want to multiply across all the factors with the same power so that
1590 // we can raise them to that power as a single entity. Build a mini tree
1592 SmallVector<Value *, 4> InnerProduct;
1593 InnerProduct.push_back(Factors[LastIdx].Base);
1595 InnerProduct.push_back(Factors[Idx].Base);
1597 } while (Idx < Size && Factors[Idx].Power == Factors[LastIdx].Power);
1599 // Reset the base value of the first factor to the new expression tree.
1600 // We'll remove all the factors with the same power in a second pass.
1601 Value *M = Factors[LastIdx].Base = buildMultiplyTree(Builder, InnerProduct);
1602 if (Instruction *MI = dyn_cast<Instruction>(M))
1603 RedoInsts.insert(MI);
1607 // Unique factors with equal powers -- we've folded them into the first one's
1609 Factors.erase(std::unique(Factors.begin(), Factors.end(),
1610 Factor::PowerEqual()),
1613 // Iteratively collect the base of each factor with an add power into the
1614 // outer product, and halve each power in preparation for squaring the
1616 for (unsigned Idx = 0, Size = Factors.size(); Idx != Size; ++Idx) {
1617 if (Factors[Idx].Power & 1)
1618 OuterProduct.push_back(Factors[Idx].Base);
1619 Factors[Idx].Power >>= 1;
1621 if (Factors[0].Power) {
1622 Value *SquareRoot = buildMinimalMultiplyDAG(Builder, Factors);
1623 OuterProduct.push_back(SquareRoot);
1624 OuterProduct.push_back(SquareRoot);
1626 if (OuterProduct.size() == 1)
1627 return OuterProduct.front();
1629 Value *V = buildMultiplyTree(Builder, OuterProduct);
1633 // Multiply Ops may have some negation operators. This situation arises
1634 // when the negation operators have multiple uses, and LinearizeExprTree() has
1635 // to treat them as leaf operands. Before multiplication optimization begins,
1636 // get rid of the negations wherever possible.
1637 void Reassociate::removeNegFromMulOps(SmallVectorImpl<ValueEntry> &Ops) {
1638 int32_t NegIdx = -1;
1640 // loop over all elements except the last one
1641 for (int32_t Idx = 0, IdxEnd = Ops.size() - 1; Idx < IdxEnd; Idx++) {
1642 ValueEntry &VE = Ops[Idx];
1643 if (!BinaryOperator::isNeg(VE.Op))
1651 // Find a pair of negation operators, say -X and -Y, change them to
1652 // X and Y respectively.
1653 ValueEntry &VEX = Ops[NegIdx];
1654 Value *OpX = cast<BinaryOperator>(VEX.Op)->getOperand(1);
1656 VEX.Rank = getRank(OpX);
1658 Value *OpY = cast<BinaryOperator>(VE.Op)->getOperand(1);
1660 VE.Rank = getRank(OpY);
1665 // We have visited odd number of negation operators so far.
1666 // Check if the last element is negation as well.
1667 ValueEntry &Last = Ops.back();
1668 Value *LastOp = Last.Op;
1669 if (!isa<ConstantInt>(LastOp) && !BinaryOperator::isNeg(LastOp))
1672 ValueEntry& PrevNeg = Ops[NegIdx];
1673 Value *Op = cast<BinaryOperator>(PrevNeg.Op)->getOperand(1);
1675 PrevNeg.Rank = getRank(Op);
1677 if (isa<ConstantInt>(LastOp))
1678 Last.Op = ConstantExpr::getNeg(cast<Constant>(LastOp));
1680 LastOp = cast<BinaryOperator>(PrevNeg.Op)->getOperand(1);
1682 Last.Rank = getRank(LastOp);
1687 Value *Reassociate::OptimizeMul(BinaryOperator *I,
1688 SmallVectorImpl<ValueEntry> &Ops) {
1690 // Simplify the operands: (-x)*(-y) -> x*y, and (-x)*c -> x*(-c)
1691 removeNegFromMulOps(Ops);
1693 // We can only optimize the multiplies when there is a chain of more than
1694 // three, such that a balanced tree might require fewer total multiplies.
1698 // Try to turn linear trees of multiplies without other uses of the
1699 // intermediate stages into minimal multiply DAGs with perfect sub-expression
1701 SmallVector<Factor, 4> Factors;
1702 if (!collectMultiplyFactors(Ops, Factors))
1703 return 0; // All distinct factors, so nothing left for us to do.
1705 IRBuilder<> Builder(I);
1706 Value *V = buildMinimalMultiplyDAG(Builder, Factors);
1710 ValueEntry NewEntry = ValueEntry(getRank(V), V);
1711 Ops.insert(std::lower_bound(Ops.begin(), Ops.end(), NewEntry), NewEntry);
1715 Value *Reassociate::OptimizeExpression(BinaryOperator *I,
1716 SmallVectorImpl<ValueEntry> &Ops) {
1717 // Now that we have the linearized expression tree, try to optimize it.
1718 // Start by folding any constants that we found.
1719 if (Ops.size() == 1) return Ops[0].Op;
1721 unsigned Opcode = I->getOpcode();
1723 // Handle destructive annihilation due to identities between elements in the
1724 // argument list here.
1725 unsigned NumOps = Ops.size();
1728 case Instruction::And:
1729 case Instruction::Or:
1730 case Instruction::Xor:
1731 if (Value *Result = OptimizeAndOrXor(Opcode, Ops))
1735 case Instruction::Add:
1736 if (Value *Result = OptimizeAdd(I, Ops))
1740 case Instruction::Mul:
1741 if (Value *Result = OptimizeMul(I, Ops))
1746 if (Ops.size() != NumOps)
1747 return OptimizeExpression(I, Ops);
1751 // EraseInstCallBack is a helper function of EraseInst which will be called to
1752 // delete an individual instruction, and it is also a callback funciton when
1753 // EraseAllDeadInst is called to delete all dead instruciton in the Redo
1754 // worklist (RedoInsts).
1756 void Reassociate::EraseInstCallBack(Instruction *I) {
1757 DEBUG(dbgs() << "Erase instruction :" << *I << "\n");
1758 assert(isInstructionTriviallyDead(I) && "Trivially dead instructions only!");
1759 SmallVector<Value*, 8> Ops(I->op_begin(), I->op_end());
1760 // Erase the dead instruction.
1761 ValueRankMap.erase(I);
1762 I->eraseFromParent();
1763 // Optimize its operands.
1764 SmallPtrSet<Instruction *, 8> Visited; // Detect self-referential nodes.
1765 for (unsigned i = 0, e = Ops.size(); i != e; ++i)
1766 if (Instruction *Op = dyn_cast<Instruction>(Ops[i])) {
1767 // If this is a node in an expression tree, climb to the expression root
1768 // and add that since that's where optimization actually happens.
1769 unsigned Opcode = Op->getOpcode();
1770 while (Op->hasOneUse() && Op->use_back()->getOpcode() == Opcode &&
1772 Op = Op->use_back();
1774 // The caller may be itearating the RedoInsts. Inserting a new element to
1775 // RedoInsts will invaidate the iterator. Instead, we temporally place the
1776 // new candidate to TmpRedoInsts. It is up to caller to combine
1777 // TmpRedoInsts and RedoInsts together.
1779 if (!RedoInsts.found(Op))
1780 TmpRedoInsts.insert(Op);
1784 /// EraseInst - Zap the given instruction, adding interesting operands to the
1786 void Reassociate::EraseInst(Instruction *I) {
1787 RedoInsts.remove(I);
1789 // Since EraseInstCallBack() put new reassociation candidates to TmpRedoInsts
1790 // we need to copy the candidates back to RedoInsts.
1791 TmpRedoInsts.clear();
1792 EraseInstCallBack(I);
1793 RedoInsts.append(TmpRedoInsts);
1796 /// EraseAllDeadInst - Remove all dead instructions from the worklist.
1797 void Reassociate::EraseAllDeadInst() {
1798 TmpRedoInsts.clear();
1799 RedoInsts.inplace_rremove(isInstDeadFunc(), RmInstCallBackFunc(this));
1800 RedoInsts.append(TmpRedoInsts);
1803 /// OptimizeInst - Inspect and optimize the given instruction. Note that erasing
1804 /// instructions is not allowed.
1805 void Reassociate::OptimizeInst(Instruction *I) {
1806 // Only consider operations that we understand.
1807 if (!isa<BinaryOperator>(I))
1810 DEBUG(dbgs() << "\n>Opt Instruction: " << *I << '\n');
1812 if (I->getOpcode() == Instruction::Shl &&
1813 isa<ConstantInt>(I->getOperand(1)))
1814 // If an operand of this shift is a reassociable multiply, or if the shift
1815 // is used by a reassociable multiply or add, turn into a multiply.
1816 if (isReassociableOp(I->getOperand(0), Instruction::Mul) ||
1818 (isReassociableOp(I->use_back(), Instruction::Mul) ||
1819 isReassociableOp(I->use_back(), Instruction::Add)))) {
1820 Instruction *NI = ConvertShiftToMul(I);
1821 RedoInsts.insert(I);
1826 // Floating point binary operators are not associative, but we can still
1827 // commute (some) of them, to canonicalize the order of their operands.
1828 // This can potentially expose more CSE opportunities, and makes writing
1829 // other transformations simpler.
1830 if ((I->getType()->isFloatingPointTy() || I->getType()->isVectorTy())) {
1831 // FAdd and FMul can be commuted.
1832 if (I->getOpcode() != Instruction::FMul &&
1833 I->getOpcode() != Instruction::FAdd)
1836 Value *LHS = I->getOperand(0);
1837 Value *RHS = I->getOperand(1);
1838 unsigned LHSRank = getRank(LHS);
1839 unsigned RHSRank = getRank(RHS);
1841 // Sort the operands by rank.
1842 if (RHSRank < LHSRank) {
1843 I->setOperand(0, RHS);
1844 I->setOperand(1, LHS);
1850 // Do not reassociate boolean (i1) expressions. We want to preserve the
1851 // original order of evaluation for short-circuited comparisons that
1852 // SimplifyCFG has folded to AND/OR expressions. If the expression
1853 // is not further optimized, it is likely to be transformed back to a
1854 // short-circuited form for code gen, and the source order may have been
1855 // optimized for the most likely conditions.
1856 if (I->getType()->isIntegerTy(1))
1859 // If this is a subtract instruction which is not already in negate form,
1860 // see if we can convert it to X+-Y.
1861 if (I->getOpcode() == Instruction::Sub) {
1862 if (ShouldBreakUpSubtract(I)) {
1863 Instruction *NI = BreakUpSubtract(I);
1864 RedoInsts.insert(I);
1867 } else if (BinaryOperator::isNeg(I)) {
1868 // Otherwise, this is a negation. See if the operand is a multiply tree
1869 // and if this is not an inner node of a multiply tree.
1870 if (isReassociableOp(I->getOperand(1), Instruction::Mul) &&
1872 !isReassociableOp(I->use_back(), Instruction::Mul))) {
1873 Instruction *NI = LowerNegateToMultiply(I);
1874 RedoInsts.insert(I);
1881 // If this instruction is an associative binary operator, process it.
1882 if (!I->isAssociative()) return;
1883 BinaryOperator *BO = cast<BinaryOperator>(I);
1885 // If this is an interior node of a reassociable tree, ignore it until we
1886 // get to the root of the tree, to avoid N^2 analysis.
1887 unsigned Opcode = BO->getOpcode();
1888 if (BO->hasOneUse() && BO->use_back()->getOpcode() == Opcode)
1891 // If this is an add tree that is used by a sub instruction, ignore it
1892 // until we process the subtract.
1893 if (BO->hasOneUse() && BO->getOpcode() == Instruction::Add &&
1894 cast<Instruction>(BO->use_back())->getOpcode() == Instruction::Sub)
1897 ReassociateExpression(BO);
1900 void Reassociate::ReassociateExpression(BinaryOperator *I) {
1902 // First, walk the expression tree, linearizing the tree, collecting the
1903 // operand information.
1904 SmallVector<RepeatedValue, 8> Tree;
1905 MadeChange |= LinearizeExprTree(I, Tree);
1906 SmallVector<ValueEntry, 8> Ops;
1907 Ops.reserve(Tree.size());
1908 for (unsigned i = 0, e = Tree.size(); i != e; ++i) {
1909 RepeatedValue E = Tree[i];
1910 Ops.append(E.second.getZExtValue(),
1911 ValueEntry(getRank(E.first), E.first));
1914 DEBUG(dbgs() << "RAIn:\t"; PrintOps(I, Ops); dbgs() << '\n');
1916 // Now that we have linearized the tree to a list and have gathered all of
1917 // the operands and their ranks, sort the operands by their rank. Use a
1918 // stable_sort so that values with equal ranks will have their relative
1919 // positions maintained (and so the compiler is deterministic). Note that
1920 // this sorts so that the highest ranking values end up at the beginning of
1922 std::stable_sort(Ops.begin(), Ops.end());
1924 // OptimizeExpression - Now that we have the expression tree in a convenient
1925 // sorted form, optimize it globally if possible.
1926 if (Value *V = OptimizeExpression(I, Ops)) {
1928 // Self-referential expression in unreachable code.
1930 // This expression tree simplified to something that isn't a tree,
1932 DEBUG(dbgs() << "Reassoc to scalar: " << *V << '\n');
1933 I->replaceAllUsesWith(V);
1934 if (Instruction *VI = dyn_cast<Instruction>(V))
1935 VI->setDebugLoc(I->getDebugLoc());
1936 RedoInsts.insert(I);
1941 // We want to sink immediates as deeply as possible except in the case where
1942 // this is a multiply tree used only by an add, and the immediate is a -1.
1943 // In this case we reassociate to put the negation on the outside so that we
1944 // can fold the negation into the add: (-X)*Y + Z -> Z-X*Y
1945 if (I->getOpcode() == Instruction::Mul && I->hasOneUse() &&
1946 cast<Instruction>(I->use_back())->getOpcode() == Instruction::Add &&
1947 isa<ConstantInt>(Ops.back().Op) &&
1948 cast<ConstantInt>(Ops.back().Op)->isAllOnesValue()) {
1949 ValueEntry Tmp = Ops.pop_back_val();
1950 Ops.insert(Ops.begin(), Tmp);
1953 DEBUG(dbgs() << "RAOut:\t"; PrintOps(I, Ops); dbgs() << '\n');
1955 if (Ops.size() == 1) {
1957 // Self-referential expression in unreachable code.
1960 // This expression tree simplified to something that isn't a tree,
1962 I->replaceAllUsesWith(Ops[0].Op);
1963 if (Instruction *OI = dyn_cast<Instruction>(Ops[0].Op))
1964 OI->setDebugLoc(I->getDebugLoc());
1965 RedoInsts.insert(I);
1969 // Now that we ordered and optimized the expressions, splat them back into
1970 // the expression tree, removing any unneeded nodes.
1971 RewriteExprTree(I, Ops);
1974 bool Reassociate::runOnFunction(Function &F) {
1975 // Calculate the rank map for F
1979 for (Function::iterator BI = F.begin(), BE = F.end(); BI != BE; ++BI) {
1980 // Optimize every instruction in the basic block.
1981 for (BasicBlock::iterator II = BI->begin(), IE = BI->end(); II != IE; )
1982 if (isInstructionTriviallyDead(II)) {
1986 assert(II->getParent() == BI && "Moved to a different block!");
1990 DEBUG(dbgs() << "Process instructions in worklist\n");
1993 // If this produced extra instructions to optimize, handle them now.
1994 while (!RedoInsts.empty()) {
1995 Instruction *I = RedoInsts.pop_front_val();
1998 if (isInstructionTriviallyDead(I))
2005 // We are done with the rank map.
2007 ValueRankMap.clear();