1 //===- Reassociate.cpp - Reassociate binary expressions -------------------===//
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/ADT/DenseMap.h"
26 #include "llvm/ADT/PostOrderIterator.h"
27 #include "llvm/ADT/STLExtras.h"
28 #include "llvm/ADT/SetVector.h"
29 #include "llvm/ADT/Statistic.h"
30 #include "llvm/Assembly/Writer.h"
31 #include "llvm/IR/Constants.h"
32 #include "llvm/IR/DerivedTypes.h"
33 #include "llvm/IR/Function.h"
34 #include "llvm/IR/IRBuilder.h"
35 #include "llvm/IR/Instructions.h"
36 #include "llvm/IR/IntrinsicInst.h"
37 #include "llvm/Pass.h"
38 #include "llvm/Support/CFG.h"
39 #include "llvm/Support/Debug.h"
40 #include "llvm/Support/ValueHandle.h"
41 #include "llvm/Support/raw_ostream.h"
42 #include "llvm/Transforms/Utils/Local.h"
46 STATISTIC(NumChanged, "Number of insts reassociated");
47 STATISTIC(NumAnnihil, "Number of expr tree annihilated");
48 STATISTIC(NumFactor , "Number of multiplies factored");
54 ValueEntry(unsigned R, Value *O) : Rank(R), Op(O) {}
56 inline bool operator<(const ValueEntry &LHS, const ValueEntry &RHS) {
57 return LHS.Rank > RHS.Rank; // Sort so that highest rank goes to start.
62 /// PrintOps - Print out the expression identified in the Ops list.
64 static 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) {
70 WriteAsOperand(dbgs(), Ops[i].Op, false, M);
71 dbgs() << ", #" << Ops[i].Rank << "] ";
77 /// \brief Utility class representing a base and exponent pair which form one
78 /// factor of some product.
83 Factor(Value *Base, unsigned Power) : Base(Base), Power(Power) {}
85 /// \brief Sort factors by their Base.
87 bool operator()(const Factor &LHS, const Factor &RHS) {
88 return LHS.Base < RHS.Base;
92 /// \brief Compare factors for equal bases.
94 bool operator()(const Factor &LHS, const Factor &RHS) {
95 return LHS.Base == RHS.Base;
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;
106 /// \brief Compare factors for equal powers.
108 bool operator()(const Factor &LHS, const Factor &RHS) {
109 return LHS.Power == RHS.Power;
114 /// Utility class representing a non-constant Xor-operand. We classify
115 /// non-constant Xor-Operands into two categories:
116 /// C1) The operand is in the form "X & C", where C is a constant and C != ~0
118 /// C2.1) The operand is in the form of "X | C", where C is a non-zero
120 /// C2.2) Any operand E which doesn't fall into C1 and C2.1, we view this
121 /// operand as "E | 0"
125 const XorOpnd &operator=(const XorOpnd &That);
127 bool isInvalid() const { return SymbolicPart == 0; }
128 bool isOrExpr() const { return isOr; }
129 Value *getValue() const { return OrigVal; }
130 Value *getSymbolicPart() const { return SymbolicPart; }
131 unsigned getSymbolicRank() const { return SymbolicRank; }
132 const APInt &getConstPart() const { return ConstPart; }
134 void Invalidate() { SymbolicPart = OrigVal = 0; }
135 void setSymbolicRank(unsigned R) { SymbolicRank = R; }
137 // Sort the XorOpnd-Pointer in ascending order of symbolic-value-rank.
138 // The purpose is twofold:
139 // 1) Cluster together the operands sharing the same symbolic-value.
140 // 2) Operand having smaller symbolic-value-rank is permuted earlier, which
141 // could potentially shorten crital path, and expose more loop-invariants.
142 // Note that values' rank are basically defined in RPO order (FIXME).
143 // So, if Rank(X) < Rank(Y) < Rank(Z), it means X is defined earlier
144 // than Y which is defined earlier than Z. Permute "x | 1", "Y & 2",
145 // "z" in the order of X-Y-Z is better than any other orders.
146 struct PtrSortFunctor {
147 bool operator()(XorOpnd * const &LHS, XorOpnd * const &RHS) {
148 return LHS->getSymbolicRank() < RHS->getSymbolicRank();
155 unsigned SymbolicRank;
161 class Reassociate : public FunctionPass {
162 DenseMap<BasicBlock*, unsigned> RankMap;
163 DenseMap<AssertingVH<Value>, unsigned> ValueRankMap;
164 SetVector<AssertingVH<Instruction> > RedoInsts;
167 static char ID; // Pass identification, replacement for typeid
168 Reassociate() : FunctionPass(ID) {
169 initializeReassociatePass(*PassRegistry::getPassRegistry());
172 bool runOnFunction(Function &F);
174 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
175 AU.setPreservesCFG();
178 void BuildRankMap(Function &F);
179 unsigned getRank(Value *V);
180 void ReassociateExpression(BinaryOperator *I);
181 void RewriteExprTree(BinaryOperator *I, SmallVectorImpl<ValueEntry> &Ops);
182 Value *OptimizeExpression(BinaryOperator *I,
183 SmallVectorImpl<ValueEntry> &Ops);
184 Value *OptimizeAdd(Instruction *I, SmallVectorImpl<ValueEntry> &Ops);
185 Value *OptimizeXor(Instruction *I, SmallVectorImpl<ValueEntry> &Ops);
186 bool CombineXorOpnd(Instruction *I, XorOpnd *Opnd1, APInt &ConstOpnd,
188 bool CombineXorOpnd(Instruction *I, XorOpnd *Opnd1, XorOpnd *Opnd2,
189 APInt &ConstOpnd, Value *&Res);
190 bool collectMultiplyFactors(SmallVectorImpl<ValueEntry> &Ops,
191 SmallVectorImpl<Factor> &Factors);
192 Value *buildMinimalMultiplyDAG(IRBuilder<> &Builder,
193 SmallVectorImpl<Factor> &Factors);
194 Value *OptimizeMul(BinaryOperator *I, SmallVectorImpl<ValueEntry> &Ops);
195 Value *RemoveFactorFromExpression(Value *V, Value *Factor);
196 void EraseInst(Instruction *I);
197 void OptimizeInst(Instruction *I);
201 XorOpnd::XorOpnd(Value *V) {
202 assert(!isa<ConstantInt>(V) && "No ConstantInt");
204 Instruction *I = dyn_cast<Instruction>(V);
207 if (I && (I->getOpcode() == Instruction::Or ||
208 I->getOpcode() == Instruction::And)) {
209 Value *V0 = I->getOperand(0);
210 Value *V1 = I->getOperand(1);
211 if (isa<ConstantInt>(V0))
214 if (ConstantInt *C = dyn_cast<ConstantInt>(V1)) {
215 ConstPart = C->getValue();
217 isOr = (I->getOpcode() == Instruction::Or);
222 // view the operand as "V | 0"
224 ConstPart = APInt::getNullValue(V->getType()->getIntegerBitWidth());
228 const XorOpnd &XorOpnd::operator=(const XorOpnd &That) {
229 OrigVal = That.OrigVal;
230 SymbolicPart = That.SymbolicPart;
231 ConstPart = That.ConstPart;
232 SymbolicRank = That.SymbolicRank;
237 char Reassociate::ID = 0;
238 INITIALIZE_PASS(Reassociate, "reassociate",
239 "Reassociate expressions", false, false)
241 // Public interface to the Reassociate pass
242 FunctionPass *llvm::createReassociatePass() { return new Reassociate(); }
244 /// isReassociableOp - Return true if V is an instruction of the specified
245 /// opcode and if it only has one use.
246 static BinaryOperator *isReassociableOp(Value *V, unsigned Opcode) {
247 if (V->hasOneUse() && isa<Instruction>(V) &&
248 cast<Instruction>(V)->getOpcode() == Opcode)
249 return cast<BinaryOperator>(V);
253 static bool isUnmovableInstruction(Instruction *I) {
254 if (I->getOpcode() == Instruction::PHI ||
255 I->getOpcode() == Instruction::LandingPad ||
256 I->getOpcode() == Instruction::Alloca ||
257 I->getOpcode() == Instruction::Load ||
258 I->getOpcode() == Instruction::Invoke ||
259 (I->getOpcode() == Instruction::Call &&
260 !isa<DbgInfoIntrinsic>(I)) ||
261 I->getOpcode() == Instruction::UDiv ||
262 I->getOpcode() == Instruction::SDiv ||
263 I->getOpcode() == Instruction::FDiv ||
264 I->getOpcode() == Instruction::URem ||
265 I->getOpcode() == Instruction::SRem ||
266 I->getOpcode() == Instruction::FRem)
271 void Reassociate::BuildRankMap(Function &F) {
274 // Assign distinct ranks to function arguments
275 for (Function::arg_iterator I = F.arg_begin(), E = F.arg_end(); I != E; ++I)
276 ValueRankMap[&*I] = ++i;
278 ReversePostOrderTraversal<Function*> RPOT(&F);
279 for (ReversePostOrderTraversal<Function*>::rpo_iterator I = RPOT.begin(),
280 E = RPOT.end(); I != E; ++I) {
282 unsigned BBRank = RankMap[BB] = ++i << 16;
284 // Walk the basic block, adding precomputed ranks for any instructions that
285 // we cannot move. This ensures that the ranks for these instructions are
286 // all different in the block.
287 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
288 if (isUnmovableInstruction(I))
289 ValueRankMap[&*I] = ++BBRank;
293 unsigned Reassociate::getRank(Value *V) {
294 Instruction *I = dyn_cast<Instruction>(V);
296 if (isa<Argument>(V)) return ValueRankMap[V]; // Function argument.
297 return 0; // Otherwise it's a global or constant, rank 0.
300 if (unsigned Rank = ValueRankMap[I])
301 return Rank; // Rank already known?
303 // If this is an expression, return the 1+MAX(rank(LHS), rank(RHS)) so that
304 // we can reassociate expressions for code motion! Since we do not recurse
305 // for PHI nodes, we cannot have infinite recursion here, because there
306 // cannot be loops in the value graph that do not go through PHI nodes.
307 unsigned Rank = 0, MaxRank = RankMap[I->getParent()];
308 for (unsigned i = 0, e = I->getNumOperands();
309 i != e && Rank != MaxRank; ++i)
310 Rank = std::max(Rank, getRank(I->getOperand(i)));
312 // If this is a not or neg instruction, do not count it for rank. This
313 // assures us that X and ~X will have the same rank.
314 if (!I->getType()->isIntegerTy() ||
315 (!BinaryOperator::isNot(I) && !BinaryOperator::isNeg(I)))
318 //DEBUG(dbgs() << "Calculated Rank[" << V->getName() << "] = "
321 return ValueRankMap[I] = Rank;
324 /// LowerNegateToMultiply - Replace 0-X with X*-1.
326 static BinaryOperator *LowerNegateToMultiply(Instruction *Neg) {
327 Constant *Cst = Constant::getAllOnesValue(Neg->getType());
329 BinaryOperator *Res =
330 BinaryOperator::CreateMul(Neg->getOperand(1), Cst, "",Neg);
331 Neg->setOperand(1, Constant::getNullValue(Neg->getType())); // Drop use of op.
333 Neg->replaceAllUsesWith(Res);
334 Res->setDebugLoc(Neg->getDebugLoc());
338 /// CarmichaelShift - Returns k such that lambda(2^Bitwidth) = 2^k, where lambda
339 /// is the Carmichael function. This means that x^(2^k) === 1 mod 2^Bitwidth for
340 /// every odd x, i.e. x^(2^k) = 1 for every odd x in Bitwidth-bit arithmetic.
341 /// Note that 0 <= k < Bitwidth, and if Bitwidth > 3 then x^(2^k) = 0 for every
342 /// even x in Bitwidth-bit arithmetic.
343 static unsigned CarmichaelShift(unsigned Bitwidth) {
349 /// IncorporateWeight - Add the extra weight 'RHS' to the existing weight 'LHS',
350 /// reducing the combined weight using any special properties of the operation.
351 /// The existing weight LHS represents the computation X op X op ... op X where
352 /// X occurs LHS times. The combined weight represents X op X op ... op X with
353 /// X occurring LHS + RHS times. If op is "Xor" for example then the combined
354 /// operation is equivalent to X if LHS + RHS is odd, or 0 if LHS + RHS is even;
355 /// the routine returns 1 in LHS in the first case, and 0 in LHS in the second.
356 static void IncorporateWeight(APInt &LHS, const APInt &RHS, unsigned Opcode) {
357 // If we were working with infinite precision arithmetic then the combined
358 // weight would be LHS + RHS. But we are using finite precision arithmetic,
359 // and the APInt sum LHS + RHS may not be correct if it wraps (it is correct
360 // for nilpotent operations and addition, but not for idempotent operations
361 // and multiplication), so it is important to correctly reduce the combined
362 // weight back into range if wrapping would be wrong.
364 // If RHS is zero then the weight didn't change.
365 if (RHS.isMinValue())
367 // If LHS is zero then the combined weight is RHS.
368 if (LHS.isMinValue()) {
372 // From this point on we know that neither LHS nor RHS is zero.
374 if (Instruction::isIdempotent(Opcode)) {
375 // Idempotent means X op X === X, so any non-zero weight is equivalent to a
376 // weight of 1. Keeping weights at zero or one also means that wrapping is
378 assert(LHS == 1 && RHS == 1 && "Weights not reduced!");
379 return; // Return a weight of 1.
381 if (Instruction::isNilpotent(Opcode)) {
382 // Nilpotent means X op X === 0, so reduce weights modulo 2.
383 assert(LHS == 1 && RHS == 1 && "Weights not reduced!");
384 LHS = 0; // 1 + 1 === 0 modulo 2.
387 if (Opcode == Instruction::Add) {
388 // TODO: Reduce the weight by exploiting nsw/nuw?
393 assert(Opcode == Instruction::Mul && "Unknown associative operation!");
394 unsigned Bitwidth = LHS.getBitWidth();
395 // If CM is the Carmichael number then a weight W satisfying W >= CM+Bitwidth
396 // can be replaced with W-CM. That's because x^W=x^(W-CM) for every Bitwidth
397 // bit number x, since either x is odd in which case x^CM = 1, or x is even in
398 // which case both x^W and x^(W - CM) are zero. By subtracting off multiples
399 // of CM like this weights can always be reduced to the range [0, CM+Bitwidth)
400 // which by a happy accident means that they can always be represented using
402 // TODO: Reduce the weight by exploiting nsw/nuw? (Could do much better than
403 // the Carmichael number).
405 /// CM - The value of Carmichael's lambda function.
406 APInt CM = APInt::getOneBitSet(Bitwidth, CarmichaelShift(Bitwidth));
407 // Any weight W >= Threshold can be replaced with W - CM.
408 APInt Threshold = CM + Bitwidth;
409 assert(LHS.ult(Threshold) && RHS.ult(Threshold) && "Weights not reduced!");
410 // For Bitwidth 4 or more the following sum does not overflow.
412 while (LHS.uge(Threshold))
415 // To avoid problems with overflow do everything the same as above but using
417 unsigned CM = 1U << CarmichaelShift(Bitwidth);
418 unsigned Threshold = CM + Bitwidth;
419 assert(LHS.getZExtValue() < Threshold && RHS.getZExtValue() < Threshold &&
420 "Weights not reduced!");
421 unsigned Total = LHS.getZExtValue() + RHS.getZExtValue();
422 while (Total >= Threshold)
428 typedef std::pair<Value*, APInt> RepeatedValue;
430 /// LinearizeExprTree - Given an associative binary expression, return the leaf
431 /// nodes in Ops along with their weights (how many times the leaf occurs). The
432 /// original expression is the same as
433 /// (Ops[0].first op Ops[0].first op ... Ops[0].first) <- Ops[0].second times
435 /// (Ops[1].first op Ops[1].first op ... Ops[1].first) <- Ops[1].second times
439 /// (Ops[N].first op Ops[N].first op ... Ops[N].first) <- Ops[N].second times
441 /// Note that the values Ops[0].first, ..., Ops[N].first are all distinct.
443 /// This routine may modify the function, in which case it returns 'true'. The
444 /// changes it makes may well be destructive, changing the value computed by 'I'
445 /// to something completely different. Thus if the routine returns 'true' then
446 /// you MUST either replace I with a new expression computed from the Ops array,
447 /// or use RewriteExprTree to put the values back in.
449 /// A leaf node is either not a binary operation of the same kind as the root
450 /// node 'I' (i.e. is not a binary operator at all, or is, but with a different
451 /// opcode), or is the same kind of binary operator but has a use which either
452 /// does not belong to the expression, or does belong to the expression but is
453 /// a leaf node. Every leaf node has at least one use that is a non-leaf node
454 /// of the expression, while for non-leaf nodes (except for the root 'I') every
455 /// use is a non-leaf node of the expression.
458 /// expression graph node names
468 /// The leaf nodes are C, E, F and G. The Ops array will contain (maybe not in
469 /// that order) (C, 1), (E, 1), (F, 2), (G, 2).
471 /// The expression is maximal: if some instruction is a binary operator of the
472 /// same kind as 'I', and all of its uses are non-leaf nodes of the expression,
473 /// then the instruction also belongs to the expression, is not a leaf node of
474 /// it, and its operands also belong to the expression (but may be leaf nodes).
476 /// NOTE: This routine will set operands of non-leaf non-root nodes to undef in
477 /// order to ensure that every non-root node in the expression has *exactly one*
478 /// use by a non-leaf node of the expression. This destruction means that the
479 /// caller MUST either replace 'I' with a new expression or use something like
480 /// RewriteExprTree to put the values back in if the routine indicates that it
481 /// made a change by returning 'true'.
483 /// In the above example either the right operand of A or the left operand of B
484 /// will be replaced by undef. If it is B's operand then this gives:
488 /// + + | A, B - operand of B replaced with undef
494 /// Note that such undef operands can only be reached by passing through 'I'.
495 /// For example, if you visit operands recursively starting from a leaf node
496 /// then you will never see such an undef operand unless you get back to 'I',
497 /// which requires passing through a phi node.
499 /// Note that this routine may also mutate binary operators of the wrong type
500 /// that have all uses inside the expression (i.e. only used by non-leaf nodes
501 /// of the expression) if it can turn them into binary operators of the right
502 /// type and thus make the expression bigger.
504 static bool LinearizeExprTree(BinaryOperator *I,
505 SmallVectorImpl<RepeatedValue> &Ops) {
506 DEBUG(dbgs() << "LINEARIZE: " << *I << '\n');
507 unsigned Bitwidth = I->getType()->getScalarType()->getPrimitiveSizeInBits();
508 unsigned Opcode = I->getOpcode();
509 assert(Instruction::isAssociative(Opcode) &&
510 Instruction::isCommutative(Opcode) &&
511 "Expected an associative and commutative operation!");
513 // Visit all operands of the expression, keeping track of their weight (the
514 // number of paths from the expression root to the operand, or if you like
515 // the number of times that operand occurs in the linearized expression).
516 // For example, if I = X + A, where X = A + B, then I, X and B have weight 1
517 // while A has weight two.
519 // Worklist of non-leaf nodes (their operands are in the expression too) along
520 // with their weights, representing a certain number of paths to the operator.
521 // If an operator occurs in the worklist multiple times then we found multiple
522 // ways to get to it.
523 SmallVector<std::pair<BinaryOperator*, APInt>, 8> Worklist; // (Op, Weight)
524 Worklist.push_back(std::make_pair(I, APInt(Bitwidth, 1)));
525 bool MadeChange = false;
527 // Leaves of the expression are values that either aren't the right kind of
528 // operation (eg: a constant, or a multiply in an add tree), or are, but have
529 // some uses that are not inside the expression. For example, in I = X + X,
530 // X = A + B, the value X has two uses (by I) that are in the expression. If
531 // X has any other uses, for example in a return instruction, then we consider
532 // X to be a leaf, and won't analyze it further. When we first visit a value,
533 // if it has more than one use then at first we conservatively consider it to
534 // be a leaf. Later, as the expression is explored, we may discover some more
535 // uses of the value from inside the expression. If all uses turn out to be
536 // from within the expression (and the value is a binary operator of the right
537 // kind) then the value is no longer considered to be a leaf, and its operands
540 // Leaves - Keeps track of the set of putative leaves as well as the number of
541 // paths to each leaf seen so far.
542 typedef DenseMap<Value*, APInt> LeafMap;
543 LeafMap Leaves; // Leaf -> Total weight so far.
544 SmallVector<Value*, 8> LeafOrder; // Ensure deterministic leaf output order.
547 SmallPtrSet<Value*, 8> Visited; // For sanity checking the iteration scheme.
549 while (!Worklist.empty()) {
550 std::pair<BinaryOperator*, APInt> P = Worklist.pop_back_val();
551 I = P.first; // We examine the operands of this binary operator.
553 for (unsigned OpIdx = 0; OpIdx < 2; ++OpIdx) { // Visit operands.
554 Value *Op = I->getOperand(OpIdx);
555 APInt Weight = P.second; // Number of paths to this operand.
556 DEBUG(dbgs() << "OPERAND: " << *Op << " (" << Weight << ")\n");
557 assert(!Op->use_empty() && "No uses, so how did we get to it?!");
559 // If this is a binary operation of the right kind with only one use then
560 // add its operands to the expression.
561 if (BinaryOperator *BO = isReassociableOp(Op, Opcode)) {
562 assert(Visited.insert(Op) && "Not first visit!");
563 DEBUG(dbgs() << "DIRECT ADD: " << *Op << " (" << Weight << ")\n");
564 Worklist.push_back(std::make_pair(BO, Weight));
568 // Appears to be a leaf. Is the operand already in the set of leaves?
569 LeafMap::iterator It = Leaves.find(Op);
570 if (It == Leaves.end()) {
571 // Not in the leaf map. Must be the first time we saw this operand.
572 assert(Visited.insert(Op) && "Not first visit!");
573 if (!Op->hasOneUse()) {
574 // This value has uses not accounted for by the expression, so it is
575 // not safe to modify. Mark it as being a leaf.
576 DEBUG(dbgs() << "ADD USES LEAF: " << *Op << " (" << Weight << ")\n");
577 LeafOrder.push_back(Op);
581 // No uses outside the expression, try morphing it.
582 } else if (It != Leaves.end()) {
583 // Already in the leaf map.
584 assert(Visited.count(Op) && "In leaf map but not visited!");
586 // Update the number of paths to the leaf.
587 IncorporateWeight(It->second, Weight, Opcode);
589 #if 0 // TODO: Re-enable once PR13021 is fixed.
590 // The leaf already has one use from inside the expression. As we want
591 // exactly one such use, drop this new use of the leaf.
592 assert(!Op->hasOneUse() && "Only one use, but we got here twice!");
593 I->setOperand(OpIdx, UndefValue::get(I->getType()));
596 // If the leaf is a binary operation of the right kind and we now see
597 // that its multiple original uses were in fact all by nodes belonging
598 // to the expression, then no longer consider it to be a leaf and add
599 // its operands to the expression.
600 if (BinaryOperator *BO = isReassociableOp(Op, Opcode)) {
601 DEBUG(dbgs() << "UNLEAF: " << *Op << " (" << It->second << ")\n");
602 Worklist.push_back(std::make_pair(BO, It->second));
608 // If we still have uses that are not accounted for by the expression
609 // then it is not safe to modify the value.
610 if (!Op->hasOneUse())
613 // No uses outside the expression, try morphing it.
615 Leaves.erase(It); // Since the value may be morphed below.
618 // At this point we have a value which, first of all, is not a binary
619 // expression of the right kind, and secondly, is only used inside the
620 // expression. This means that it can safely be modified. See if we
621 // can usefully morph it into an expression of the right kind.
622 assert((!isa<Instruction>(Op) ||
623 cast<Instruction>(Op)->getOpcode() != Opcode) &&
624 "Should have been handled above!");
625 assert(Op->hasOneUse() && "Has uses outside the expression tree!");
627 // If this is a multiply expression, turn any internal negations into
628 // multiplies by -1 so they can be reassociated.
629 BinaryOperator *BO = dyn_cast<BinaryOperator>(Op);
630 if (Opcode == Instruction::Mul && BO && BinaryOperator::isNeg(BO)) {
631 DEBUG(dbgs() << "MORPH LEAF: " << *Op << " (" << Weight << ") TO ");
632 BO = LowerNegateToMultiply(BO);
633 DEBUG(dbgs() << *BO << 'n');
634 Worklist.push_back(std::make_pair(BO, Weight));
639 // Failed to morph into an expression of the right type. This really is
641 DEBUG(dbgs() << "ADD LEAF: " << *Op << " (" << Weight << ")\n");
642 assert(!isReassociableOp(Op, Opcode) && "Value was morphed?");
643 LeafOrder.push_back(Op);
648 // The leaves, repeated according to their weights, represent the linearized
649 // form of the expression.
650 for (unsigned i = 0, e = LeafOrder.size(); i != e; ++i) {
651 Value *V = LeafOrder[i];
652 LeafMap::iterator It = Leaves.find(V);
653 if (It == Leaves.end())
654 // Node initially thought to be a leaf wasn't.
656 assert(!isReassociableOp(V, Opcode) && "Shouldn't be a leaf!");
657 APInt Weight = It->second;
658 if (Weight.isMinValue())
659 // Leaf already output or weight reduction eliminated it.
661 // Ensure the leaf is only output once.
663 Ops.push_back(std::make_pair(V, Weight));
666 // For nilpotent operations or addition there may be no operands, for example
667 // because the expression was "X xor X" or consisted of 2^Bitwidth additions:
668 // in both cases the weight reduces to 0 causing the value to be skipped.
670 Constant *Identity = ConstantExpr::getBinOpIdentity(Opcode, I->getType());
671 assert(Identity && "Associative operation without identity!");
672 Ops.push_back(std::make_pair(Identity, APInt(Bitwidth, 1)));
678 // RewriteExprTree - Now that the operands for this expression tree are
679 // linearized and optimized, emit them in-order.
680 void Reassociate::RewriteExprTree(BinaryOperator *I,
681 SmallVectorImpl<ValueEntry> &Ops) {
682 assert(Ops.size() > 1 && "Single values should be used directly!");
684 // Since our optimizations should never increase the number of operations, the
685 // new expression can usually be written reusing the existing binary operators
686 // from the original expression tree, without creating any new instructions,
687 // though the rewritten expression may have a completely different topology.
688 // We take care to not change anything if the new expression will be the same
689 // as the original. If more than trivial changes (like commuting operands)
690 // were made then we are obliged to clear out any optional subclass data like
693 /// NodesToRewrite - Nodes from the original expression available for writing
694 /// the new expression into.
695 SmallVector<BinaryOperator*, 8> NodesToRewrite;
696 unsigned Opcode = I->getOpcode();
697 BinaryOperator *Op = I;
699 /// NotRewritable - The operands being written will be the leaves of the new
700 /// expression and must not be used as inner nodes (via NodesToRewrite) by
701 /// mistake. Inner nodes are always reassociable, and usually leaves are not
702 /// (if they were they would have been incorporated into the expression and so
703 /// would not be leaves), so most of the time there is no danger of this. But
704 /// in rare cases a leaf may become reassociable if an optimization kills uses
705 /// of it, or it may momentarily become reassociable during rewriting (below)
706 /// due it being removed as an operand of one of its uses. Ensure that misuse
707 /// of leaf nodes as inner nodes cannot occur by remembering all of the future
708 /// leaves and refusing to reuse any of them as inner nodes.
709 SmallPtrSet<Value*, 8> NotRewritable;
710 for (unsigned i = 0, e = Ops.size(); i != e; ++i)
711 NotRewritable.insert(Ops[i].Op);
713 // ExpressionChanged - Non-null if the rewritten expression differs from the
714 // original in some non-trivial way, requiring the clearing of optional flags.
715 // Flags are cleared from the operator in ExpressionChanged up to I inclusive.
716 BinaryOperator *ExpressionChanged = 0;
717 for (unsigned i = 0; ; ++i) {
718 // The last operation (which comes earliest in the IR) is special as both
719 // operands will come from Ops, rather than just one with the other being
721 if (i+2 == Ops.size()) {
722 Value *NewLHS = Ops[i].Op;
723 Value *NewRHS = Ops[i+1].Op;
724 Value *OldLHS = Op->getOperand(0);
725 Value *OldRHS = Op->getOperand(1);
727 if (NewLHS == OldLHS && NewRHS == OldRHS)
728 // Nothing changed, leave it alone.
731 if (NewLHS == OldRHS && NewRHS == OldLHS) {
732 // The order of the operands was reversed. Swap them.
733 DEBUG(dbgs() << "RA: " << *Op << '\n');
735 DEBUG(dbgs() << "TO: " << *Op << '\n');
741 // The new operation differs non-trivially from the original. Overwrite
742 // the old operands with the new ones.
743 DEBUG(dbgs() << "RA: " << *Op << '\n');
744 if (NewLHS != OldLHS) {
745 BinaryOperator *BO = isReassociableOp(OldLHS, Opcode);
746 if (BO && !NotRewritable.count(BO))
747 NodesToRewrite.push_back(BO);
748 Op->setOperand(0, NewLHS);
750 if (NewRHS != OldRHS) {
751 BinaryOperator *BO = isReassociableOp(OldRHS, Opcode);
752 if (BO && !NotRewritable.count(BO))
753 NodesToRewrite.push_back(BO);
754 Op->setOperand(1, NewRHS);
756 DEBUG(dbgs() << "TO: " << *Op << '\n');
758 ExpressionChanged = Op;
765 // Not the last operation. The left-hand side will be a sub-expression
766 // while the right-hand side will be the current element of Ops.
767 Value *NewRHS = Ops[i].Op;
768 if (NewRHS != Op->getOperand(1)) {
769 DEBUG(dbgs() << "RA: " << *Op << '\n');
770 if (NewRHS == Op->getOperand(0)) {
771 // The new right-hand side was already present as the left operand. If
772 // we are lucky then swapping the operands will sort out both of them.
775 // Overwrite with the new right-hand side.
776 BinaryOperator *BO = isReassociableOp(Op->getOperand(1), Opcode);
777 if (BO && !NotRewritable.count(BO))
778 NodesToRewrite.push_back(BO);
779 Op->setOperand(1, NewRHS);
780 ExpressionChanged = Op;
782 DEBUG(dbgs() << "TO: " << *Op << '\n');
787 // Now deal with the left-hand side. If this is already an operation node
788 // from the original expression then just rewrite the rest of the expression
790 BinaryOperator *BO = isReassociableOp(Op->getOperand(0), Opcode);
791 if (BO && !NotRewritable.count(BO)) {
796 // Otherwise, grab a spare node from the original expression and use that as
797 // the left-hand side. If there are no nodes left then the optimizers made
798 // an expression with more nodes than the original! This usually means that
799 // they did something stupid but it might mean that the problem was just too
800 // hard (finding the mimimal number of multiplications needed to realize a
801 // multiplication expression is NP-complete). Whatever the reason, smart or
802 // stupid, create a new node if there are none left.
803 BinaryOperator *NewOp;
804 if (NodesToRewrite.empty()) {
805 Constant *Undef = UndefValue::get(I->getType());
806 NewOp = BinaryOperator::Create(Instruction::BinaryOps(Opcode),
807 Undef, Undef, "", I);
809 NewOp = NodesToRewrite.pop_back_val();
812 DEBUG(dbgs() << "RA: " << *Op << '\n');
813 Op->setOperand(0, NewOp);
814 DEBUG(dbgs() << "TO: " << *Op << '\n');
815 ExpressionChanged = Op;
821 // If the expression changed non-trivially then clear out all subclass data
822 // starting from the operator specified in ExpressionChanged, and compactify
823 // the operators to just before the expression root to guarantee that the
824 // expression tree is dominated by all of Ops.
825 if (ExpressionChanged)
827 ExpressionChanged->clearSubclassOptionalData();
828 if (ExpressionChanged == I)
830 ExpressionChanged->moveBefore(I);
831 ExpressionChanged = cast<BinaryOperator>(*ExpressionChanged->use_begin());
834 // Throw away any left over nodes from the original expression.
835 for (unsigned i = 0, e = NodesToRewrite.size(); i != e; ++i)
836 RedoInsts.insert(NodesToRewrite[i]);
839 /// NegateValue - Insert instructions before the instruction pointed to by BI,
840 /// that computes the negative version of the value specified. The negative
841 /// version of the value is returned, and BI is left pointing at the instruction
842 /// that should be processed next by the reassociation pass.
843 static Value *NegateValue(Value *V, Instruction *BI) {
844 if (Constant *C = dyn_cast<Constant>(V))
845 return ConstantExpr::getNeg(C);
847 // We are trying to expose opportunity for reassociation. One of the things
848 // that we want to do to achieve this is to push a negation as deep into an
849 // expression chain as possible, to expose the add instructions. In practice,
850 // this means that we turn this:
851 // X = -(A+12+C+D) into X = -A + -12 + -C + -D = -12 + -A + -C + -D
852 // so that later, a: Y = 12+X could get reassociated with the -12 to eliminate
853 // the constants. We assume that instcombine will clean up the mess later if
854 // we introduce tons of unnecessary negation instructions.
856 if (BinaryOperator *I = isReassociableOp(V, Instruction::Add)) {
857 // Push the negates through the add.
858 I->setOperand(0, NegateValue(I->getOperand(0), BI));
859 I->setOperand(1, NegateValue(I->getOperand(1), BI));
861 // We must move the add instruction here, because the neg instructions do
862 // not dominate the old add instruction in general. By moving it, we are
863 // assured that the neg instructions we just inserted dominate the
864 // instruction we are about to insert after them.
867 I->setName(I->getName()+".neg");
871 // Okay, we need to materialize a negated version of V with an instruction.
872 // Scan the use lists of V to see if we have one already.
873 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E;++UI){
875 if (!BinaryOperator::isNeg(U)) continue;
877 // We found one! Now we have to make sure that the definition dominates
878 // this use. We do this by moving it to the entry block (if it is a
879 // non-instruction value) or right after the definition. These negates will
880 // be zapped by reassociate later, so we don't need much finesse here.
881 BinaryOperator *TheNeg = cast<BinaryOperator>(U);
883 // Verify that the negate is in this function, V might be a constant expr.
884 if (TheNeg->getParent()->getParent() != BI->getParent()->getParent())
887 BasicBlock::iterator InsertPt;
888 if (Instruction *InstInput = dyn_cast<Instruction>(V)) {
889 if (InvokeInst *II = dyn_cast<InvokeInst>(InstInput)) {
890 InsertPt = II->getNormalDest()->begin();
892 InsertPt = InstInput;
895 while (isa<PHINode>(InsertPt)) ++InsertPt;
897 InsertPt = TheNeg->getParent()->getParent()->getEntryBlock().begin();
899 TheNeg->moveBefore(InsertPt);
903 // Insert a 'neg' instruction that subtracts the value from zero to get the
905 return BinaryOperator::CreateNeg(V, V->getName() + ".neg", BI);
908 /// ShouldBreakUpSubtract - Return true if we should break up this subtract of
909 /// X-Y into (X + -Y).
910 static bool ShouldBreakUpSubtract(Instruction *Sub) {
911 // If this is a negation, we can't split it up!
912 if (BinaryOperator::isNeg(Sub))
915 // Don't bother to break this up unless either the LHS is an associable add or
916 // subtract or if this is only used by one.
917 if (isReassociableOp(Sub->getOperand(0), Instruction::Add) ||
918 isReassociableOp(Sub->getOperand(0), Instruction::Sub))
920 if (isReassociableOp(Sub->getOperand(1), Instruction::Add) ||
921 isReassociableOp(Sub->getOperand(1), Instruction::Sub))
923 if (Sub->hasOneUse() &&
924 (isReassociableOp(Sub->use_back(), Instruction::Add) ||
925 isReassociableOp(Sub->use_back(), Instruction::Sub)))
931 /// BreakUpSubtract - If we have (X-Y), and if either X is an add, or if this is
932 /// only used by an add, transform this into (X+(0-Y)) to promote better
934 static BinaryOperator *BreakUpSubtract(Instruction *Sub) {
935 // Convert a subtract into an add and a neg instruction. This allows sub
936 // instructions to be commuted with other add instructions.
938 // Calculate the negative value of Operand 1 of the sub instruction,
939 // and set it as the RHS of the add instruction we just made.
941 Value *NegVal = NegateValue(Sub->getOperand(1), Sub);
942 BinaryOperator *New =
943 BinaryOperator::CreateAdd(Sub->getOperand(0), NegVal, "", Sub);
944 Sub->setOperand(0, Constant::getNullValue(Sub->getType())); // Drop use of op.
945 Sub->setOperand(1, Constant::getNullValue(Sub->getType())); // Drop use of op.
948 // Everyone now refers to the add instruction.
949 Sub->replaceAllUsesWith(New);
950 New->setDebugLoc(Sub->getDebugLoc());
952 DEBUG(dbgs() << "Negated: " << *New << '\n');
956 /// ConvertShiftToMul - If this is a shift of a reassociable multiply or is used
957 /// by one, change this into a multiply by a constant to assist with further
959 static BinaryOperator *ConvertShiftToMul(Instruction *Shl) {
960 Constant *MulCst = ConstantInt::get(Shl->getType(), 1);
961 MulCst = ConstantExpr::getShl(MulCst, cast<Constant>(Shl->getOperand(1)));
963 BinaryOperator *Mul =
964 BinaryOperator::CreateMul(Shl->getOperand(0), MulCst, "", Shl);
965 Shl->setOperand(0, UndefValue::get(Shl->getType())); // Drop use of op.
967 Shl->replaceAllUsesWith(Mul);
968 Mul->setDebugLoc(Shl->getDebugLoc());
972 /// FindInOperandList - Scan backwards and forwards among values with the same
973 /// rank as element i to see if X exists. If X does not exist, return i. This
974 /// is useful when scanning for 'x' when we see '-x' because they both get the
976 static unsigned FindInOperandList(SmallVectorImpl<ValueEntry> &Ops, unsigned i,
978 unsigned XRank = Ops[i].Rank;
979 unsigned e = Ops.size();
980 for (unsigned j = i+1; j != e && Ops[j].Rank == XRank; ++j)
984 for (unsigned j = i-1; j != ~0U && Ops[j].Rank == XRank; --j)
990 /// EmitAddTreeOfValues - Emit a tree of add instructions, summing Ops together
991 /// and returning the result. Insert the tree before I.
992 static Value *EmitAddTreeOfValues(Instruction *I,
993 SmallVectorImpl<WeakVH> &Ops){
994 if (Ops.size() == 1) return Ops.back();
996 Value *V1 = Ops.back();
998 Value *V2 = EmitAddTreeOfValues(I, Ops);
999 return BinaryOperator::CreateAdd(V2, V1, "tmp", I);
1002 /// RemoveFactorFromExpression - If V is an expression tree that is a
1003 /// multiplication sequence, and if this sequence contains a multiply by Factor,
1004 /// remove Factor from the tree and return the new tree.
1005 Value *Reassociate::RemoveFactorFromExpression(Value *V, Value *Factor) {
1006 BinaryOperator *BO = isReassociableOp(V, Instruction::Mul);
1009 SmallVector<RepeatedValue, 8> Tree;
1010 MadeChange |= LinearizeExprTree(BO, Tree);
1011 SmallVector<ValueEntry, 8> Factors;
1012 Factors.reserve(Tree.size());
1013 for (unsigned i = 0, e = Tree.size(); i != e; ++i) {
1014 RepeatedValue E = Tree[i];
1015 Factors.append(E.second.getZExtValue(),
1016 ValueEntry(getRank(E.first), E.first));
1019 bool FoundFactor = false;
1020 bool NeedsNegate = false;
1021 for (unsigned i = 0, e = Factors.size(); i != e; ++i) {
1022 if (Factors[i].Op == Factor) {
1024 Factors.erase(Factors.begin()+i);
1028 // If this is a negative version of this factor, remove it.
1029 if (ConstantInt *FC1 = dyn_cast<ConstantInt>(Factor))
1030 if (ConstantInt *FC2 = dyn_cast<ConstantInt>(Factors[i].Op))
1031 if (FC1->getValue() == -FC2->getValue()) {
1032 FoundFactor = NeedsNegate = true;
1033 Factors.erase(Factors.begin()+i);
1039 // Make sure to restore the operands to the expression tree.
1040 RewriteExprTree(BO, Factors);
1044 BasicBlock::iterator InsertPt = BO; ++InsertPt;
1046 // If this was just a single multiply, remove the multiply and return the only
1047 // remaining operand.
1048 if (Factors.size() == 1) {
1049 RedoInsts.insert(BO);
1052 RewriteExprTree(BO, Factors);
1057 V = BinaryOperator::CreateNeg(V, "neg", InsertPt);
1062 /// FindSingleUseMultiplyFactors - If V is a single-use multiply, recursively
1063 /// add its operands as factors, otherwise add V to the list of factors.
1065 /// Ops is the top-level list of add operands we're trying to factor.
1066 static void FindSingleUseMultiplyFactors(Value *V,
1067 SmallVectorImpl<Value*> &Factors,
1068 const SmallVectorImpl<ValueEntry> &Ops) {
1069 BinaryOperator *BO = isReassociableOp(V, Instruction::Mul);
1071 Factors.push_back(V);
1075 // Otherwise, add the LHS and RHS to the list of factors.
1076 FindSingleUseMultiplyFactors(BO->getOperand(1), Factors, Ops);
1077 FindSingleUseMultiplyFactors(BO->getOperand(0), Factors, Ops);
1080 /// OptimizeAndOrXor - Optimize a series of operands to an 'and', 'or', or 'xor'
1081 /// instruction. This optimizes based on identities. If it can be reduced to
1082 /// a single Value, it is returned, otherwise the Ops list is mutated as
1084 static Value *OptimizeAndOrXor(unsigned Opcode,
1085 SmallVectorImpl<ValueEntry> &Ops) {
1086 // Scan the operand lists looking for X and ~X pairs, along with X,X pairs.
1087 // If we find any, we can simplify the expression. X&~X == 0, X|~X == -1.
1088 for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
1089 // First, check for X and ~X in the operand list.
1090 assert(i < Ops.size());
1091 if (BinaryOperator::isNot(Ops[i].Op)) { // Cannot occur for ^.
1092 Value *X = BinaryOperator::getNotArgument(Ops[i].Op);
1093 unsigned FoundX = FindInOperandList(Ops, i, X);
1095 if (Opcode == Instruction::And) // ...&X&~X = 0
1096 return Constant::getNullValue(X->getType());
1098 if (Opcode == Instruction::Or) // ...|X|~X = -1
1099 return Constant::getAllOnesValue(X->getType());
1103 // Next, check for duplicate pairs of values, which we assume are next to
1104 // each other, due to our sorting criteria.
1105 assert(i < Ops.size());
1106 if (i+1 != Ops.size() && Ops[i+1].Op == Ops[i].Op) {
1107 if (Opcode == Instruction::And || Opcode == Instruction::Or) {
1108 // Drop duplicate values for And and Or.
1109 Ops.erase(Ops.begin()+i);
1115 // Drop pairs of values for Xor.
1116 assert(Opcode == Instruction::Xor);
1118 return Constant::getNullValue(Ops[0].Op->getType());
1121 Ops.erase(Ops.begin()+i, Ops.begin()+i+2);
1129 /// Helper funciton of CombineXorOpnd(). It creates a bitwise-and
1130 /// instruction with the given two operands, and return the resulting
1131 /// instruction. There are two special cases: 1) if the constant operand is 0,
1132 /// it will return NULL. 2) if the constant is ~0, the symbolic operand will
1134 static Value *createAndInstr(Instruction *InsertBefore, Value *Opnd,
1135 const APInt &ConstOpnd) {
1136 if (ConstOpnd != 0) {
1137 if (!ConstOpnd.isAllOnesValue()) {
1138 LLVMContext &Ctx = Opnd->getType()->getContext();
1140 I = BinaryOperator::CreateAnd(Opnd, ConstantInt::get(Ctx, ConstOpnd),
1141 "and.ra", InsertBefore);
1142 I->setDebugLoc(InsertBefore->getDebugLoc());
1150 // Helper function of OptimizeXor(). It tries to simplify "Opnd1 ^ ConstOpnd"
1151 // into "R ^ C", where C would be 0, and R is a symbolic value.
1153 // If it was successful, true is returned, and the "R" and "C" is returned
1154 // via "Res" and "ConstOpnd", respectively; otherwise, false is returned,
1155 // and both "Res" and "ConstOpnd" remain unchanged.
1157 bool Reassociate::CombineXorOpnd(Instruction *I, XorOpnd *Opnd1,
1158 APInt &ConstOpnd, Value *&Res) {
1159 // Xor-Rule 1: (x | c1) ^ c2 = (x | c1) ^ (c1 ^ c1) ^ c2
1160 // = ((x | c1) ^ c1) ^ (c1 ^ c2)
1161 // = (x & ~c1) ^ (c1 ^ c2)
1162 // It is useful only when c1 == c2.
1163 if (Opnd1->isOrExpr() && Opnd1->getConstPart() != 0) {
1164 if (!Opnd1->getValue()->hasOneUse())
1167 const APInt &C1 = Opnd1->getConstPart();
1168 if (C1 != ConstOpnd)
1171 Value *X = Opnd1->getSymbolicPart();
1172 Res = createAndInstr(I, X, ~C1);
1173 // ConstOpnd was C2, now C1 ^ C2.
1176 if (Instruction *T = dyn_cast<Instruction>(Opnd1->getValue()))
1177 RedoInsts.insert(T);
1184 // Helper function of OptimizeXor(). It tries to simplify
1185 // "Opnd1 ^ Opnd2 ^ ConstOpnd" into "R ^ C", where C would be 0, and R is a
1188 // If it was successful, true is returned, and the "R" and "C" is returned
1189 // via "Res" and "ConstOpnd", respectively (If the entire expression is
1190 // evaluated to a constant, the Res is set to NULL); otherwise, false is
1191 // returned, and both "Res" and "ConstOpnd" remain unchanged.
1192 bool Reassociate::CombineXorOpnd(Instruction *I, XorOpnd *Opnd1, XorOpnd *Opnd2,
1193 APInt &ConstOpnd, Value *&Res) {
1194 Value *X = Opnd1->getSymbolicPart();
1195 if (X != Opnd2->getSymbolicPart())
1198 // This many instruction become dead.(At least "Opnd1 ^ Opnd2" will die.)
1199 int DeadInstNum = 1;
1200 if (Opnd1->getValue()->hasOneUse())
1202 if (Opnd2->getValue()->hasOneUse())
1206 // (x | c1) ^ (x & c2)
1207 // = (x|c1) ^ (x&c2) ^ (c1 ^ c1) = ((x|c1) ^ c1) ^ (x & c2) ^ c1
1208 // = (x & ~c1) ^ (x & c2) ^ c1 // Xor-Rule 1
1209 // = (x & c3) ^ c1, where c3 = ~c1 ^ c2 // Xor-rule 3
1211 if (Opnd1->isOrExpr() != Opnd2->isOrExpr()) {
1212 if (Opnd2->isOrExpr())
1213 std::swap(Opnd1, Opnd2);
1215 const APInt &C1 = Opnd1->getConstPart();
1216 const APInt &C2 = Opnd2->getConstPart();
1217 APInt C3((~C1) ^ C2);
1219 // Do not increase code size!
1220 if (C3 != 0 && !C3.isAllOnesValue()) {
1221 int NewInstNum = ConstOpnd != 0 ? 1 : 2;
1222 if (NewInstNum > DeadInstNum)
1226 Res = createAndInstr(I, X, C3);
1229 } else if (Opnd1->isOrExpr()) {
1230 // Xor-Rule 3: (x | c1) ^ (x | c2) = (x & c3) ^ c3 where c3 = c1 ^ c2
1232 const APInt &C1 = Opnd1->getConstPart();
1233 const APInt &C2 = Opnd2->getConstPart();
1236 // Do not increase code size
1237 if (C3 != 0 && !C3.isAllOnesValue()) {
1238 int NewInstNum = ConstOpnd != 0 ? 1 : 2;
1239 if (NewInstNum > DeadInstNum)
1243 Res = createAndInstr(I, X, C3);
1246 // Xor-Rule 4: (x & c1) ^ (x & c2) = (x & (c1^c2))
1248 const APInt &C1 = Opnd1->getConstPart();
1249 const APInt &C2 = Opnd2->getConstPart();
1251 Res = createAndInstr(I, X, C3);
1254 // Put the original operands in the Redo list; hope they will be deleted
1256 if (Instruction *T = dyn_cast<Instruction>(Opnd1->getValue()))
1257 RedoInsts.insert(T);
1258 if (Instruction *T = dyn_cast<Instruction>(Opnd2->getValue()))
1259 RedoInsts.insert(T);
1264 /// Optimize a series of operands to an 'xor' instruction. If it can be reduced
1265 /// to a single Value, it is returned, otherwise the Ops list is mutated as
1267 Value *Reassociate::OptimizeXor(Instruction *I,
1268 SmallVectorImpl<ValueEntry> &Ops) {
1269 if (Value *V = OptimizeAndOrXor(Instruction::Xor, Ops))
1272 if (Ops.size() == 1)
1275 SmallVector<XorOpnd, 8> Opnds;
1276 SmallVector<XorOpnd*, 8> OpndPtrs;
1277 Type *Ty = Ops[0].Op->getType();
1278 APInt ConstOpnd(Ty->getIntegerBitWidth(), 0);
1280 // Step 1: Convert ValueEntry to XorOpnd
1281 for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
1282 Value *V = Ops[i].Op;
1283 if (!isa<ConstantInt>(V)) {
1285 O.setSymbolicRank(getRank(O.getSymbolicPart()));
1288 ConstOpnd ^= cast<ConstantInt>(V)->getValue();
1291 // NOTE: From this point on, do *NOT* add/delete element to/from "Opnds".
1292 // It would otherwise invalidate the "Opnds"'s iterator, and hence invalidate
1293 // the "OpndPtrs" as well. For the similar reason, do not fuse this loop
1294 // with the previous loop --- the iterator of the "Opnds" may be invalidated
1295 // when new elements are added to the vector.
1296 for (unsigned i = 0, e = Opnds.size(); i != e; ++i)
1297 OpndPtrs.push_back(&Opnds[i]);
1299 // Step 2: Sort the Xor-Operands in a way such that the operands containing
1300 // the same symbolic value cluster together. For instance, the input operand
1301 // sequence ("x | 123", "y & 456", "x & 789") will be sorted into:
1302 // ("x | 123", "x & 789", "y & 456").
1303 std::sort(OpndPtrs.begin(), OpndPtrs.end(), XorOpnd::PtrSortFunctor());
1305 // Step 3: Combine adjacent operands
1306 XorOpnd *PrevOpnd = 0;
1307 bool Changed = false;
1308 for (unsigned i = 0, e = Opnds.size(); i < e; i++) {
1309 XorOpnd *CurrOpnd = OpndPtrs[i];
1310 // The combined value
1313 // Step 3.1: Try simplifying "CurrOpnd ^ ConstOpnd"
1314 if (ConstOpnd != 0 && CombineXorOpnd(I, CurrOpnd, ConstOpnd, CV)) {
1317 *CurrOpnd = XorOpnd(CV);
1319 CurrOpnd->Invalidate();
1324 if (!PrevOpnd || CurrOpnd->getSymbolicPart() != PrevOpnd->getSymbolicPart()) {
1325 PrevOpnd = CurrOpnd;
1329 // step 3.2: When previous and current operands share the same symbolic
1330 // value, try to simplify "PrevOpnd ^ CurrOpnd ^ ConstOpnd"
1332 if (CombineXorOpnd(I, CurrOpnd, PrevOpnd, ConstOpnd, CV)) {
1333 // Remove previous operand
1334 PrevOpnd->Invalidate();
1336 *CurrOpnd = XorOpnd(CV);
1337 PrevOpnd = CurrOpnd;
1339 CurrOpnd->Invalidate();
1346 // Step 4: Reassemble the Ops
1349 for (unsigned int i = 0, e = Opnds.size(); i < e; i++) {
1350 XorOpnd &O = Opnds[i];
1353 ValueEntry VE(getRank(O.getValue()), O.getValue());
1356 if (ConstOpnd != 0) {
1357 Value *C = ConstantInt::get(Ty->getContext(), ConstOpnd);
1358 ValueEntry VE(getRank(C), C);
1361 int Sz = Ops.size();
1363 return Ops.back().Op;
1365 assert(ConstOpnd == 0);
1366 return ConstantInt::get(Ty->getContext(), ConstOpnd);
1373 /// OptimizeAdd - Optimize a series of operands to an 'add' instruction. This
1374 /// optimizes based on identities. If it can be reduced to a single Value, it
1375 /// is returned, otherwise the Ops list is mutated as necessary.
1376 Value *Reassociate::OptimizeAdd(Instruction *I,
1377 SmallVectorImpl<ValueEntry> &Ops) {
1378 // Scan the operand lists looking for X and -X pairs. If we find any, we
1379 // can simplify the expression. X+-X == 0. While we're at it, scan for any
1380 // duplicates. We want to canonicalize Y+Y+Y+Z -> 3*Y+Z.
1382 // TODO: We could handle "X + ~X" -> "-1" if we wanted, since "-X = ~X+1".
1384 for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
1385 Value *TheOp = Ops[i].Op;
1386 // Check to see if we've seen this operand before. If so, we factor all
1387 // instances of the operand together. Due to our sorting criteria, we know
1388 // that these need to be next to each other in the vector.
1389 if (i+1 != Ops.size() && Ops[i+1].Op == TheOp) {
1390 // Rescan the list, remove all instances of this operand from the expr.
1391 unsigned NumFound = 0;
1393 Ops.erase(Ops.begin()+i);
1395 } while (i != Ops.size() && Ops[i].Op == TheOp);
1397 DEBUG(errs() << "\nFACTORING [" << NumFound << "]: " << *TheOp << '\n');
1400 // Insert a new multiply.
1401 Value *Mul = ConstantInt::get(cast<IntegerType>(I->getType()), NumFound);
1402 Mul = BinaryOperator::CreateMul(TheOp, Mul, "factor", I);
1404 // Now that we have inserted a multiply, optimize it. This allows us to
1405 // handle cases that require multiple factoring steps, such as this:
1406 // (X*2) + (X*2) + (X*2) -> (X*2)*3 -> X*6
1407 RedoInsts.insert(cast<Instruction>(Mul));
1409 // If every add operand was a duplicate, return the multiply.
1413 // Otherwise, we had some input that didn't have the dupe, such as
1414 // "A + A + B" -> "A*2 + B". Add the new multiply to the list of
1415 // things being added by this operation.
1416 Ops.insert(Ops.begin(), ValueEntry(getRank(Mul), Mul));
1423 // Check for X and -X in the operand list.
1424 if (!BinaryOperator::isNeg(TheOp))
1427 Value *X = BinaryOperator::getNegArgument(TheOp);
1428 unsigned FoundX = FindInOperandList(Ops, i, X);
1432 // Remove X and -X from the operand list.
1433 if (Ops.size() == 2)
1434 return Constant::getNullValue(X->getType());
1436 Ops.erase(Ops.begin()+i);
1440 --i; // Need to back up an extra one.
1441 Ops.erase(Ops.begin()+FoundX);
1443 --i; // Revisit element.
1444 e -= 2; // Removed two elements.
1447 // Scan the operand list, checking to see if there are any common factors
1448 // between operands. Consider something like A*A+A*B*C+D. We would like to
1449 // reassociate this to A*(A+B*C)+D, which reduces the number of multiplies.
1450 // To efficiently find this, we count the number of times a factor occurs
1451 // for any ADD operands that are MULs.
1452 DenseMap<Value*, unsigned> FactorOccurrences;
1454 // Keep track of each multiply we see, to avoid triggering on (X*4)+(X*4)
1455 // where they are actually the same multiply.
1456 unsigned MaxOcc = 0;
1457 Value *MaxOccVal = 0;
1458 for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
1459 BinaryOperator *BOp = isReassociableOp(Ops[i].Op, Instruction::Mul);
1463 // Compute all of the factors of this added value.
1464 SmallVector<Value*, 8> Factors;
1465 FindSingleUseMultiplyFactors(BOp, Factors, Ops);
1466 assert(Factors.size() > 1 && "Bad linearize!");
1468 // Add one to FactorOccurrences for each unique factor in this op.
1469 SmallPtrSet<Value*, 8> Duplicates;
1470 for (unsigned i = 0, e = Factors.size(); i != e; ++i) {
1471 Value *Factor = Factors[i];
1472 if (!Duplicates.insert(Factor)) continue;
1474 unsigned Occ = ++FactorOccurrences[Factor];
1475 if (Occ > MaxOcc) { MaxOcc = Occ; MaxOccVal = Factor; }
1477 // If Factor is a negative constant, add the negated value as a factor
1478 // because we can percolate the negate out. Watch for minint, which
1479 // cannot be positivified.
1480 if (ConstantInt *CI = dyn_cast<ConstantInt>(Factor))
1481 if (CI->isNegative() && !CI->isMinValue(true)) {
1482 Factor = ConstantInt::get(CI->getContext(), -CI->getValue());
1483 assert(!Duplicates.count(Factor) &&
1484 "Shouldn't have two constant factors, missed a canonicalize");
1486 unsigned Occ = ++FactorOccurrences[Factor];
1487 if (Occ > MaxOcc) { MaxOcc = Occ; MaxOccVal = Factor; }
1492 // If any factor occurred more than one time, we can pull it out.
1494 DEBUG(errs() << "\nFACTORING [" << MaxOcc << "]: " << *MaxOccVal << '\n');
1497 // Create a new instruction that uses the MaxOccVal twice. If we don't do
1498 // this, we could otherwise run into situations where removing a factor
1499 // from an expression will drop a use of maxocc, and this can cause
1500 // RemoveFactorFromExpression on successive values to behave differently.
1501 Instruction *DummyInst = BinaryOperator::CreateAdd(MaxOccVal, MaxOccVal);
1502 SmallVector<WeakVH, 4> NewMulOps;
1503 for (unsigned i = 0; i != Ops.size(); ++i) {
1504 // Only try to remove factors from expressions we're allowed to.
1505 BinaryOperator *BOp = isReassociableOp(Ops[i].Op, Instruction::Mul);
1509 if (Value *V = RemoveFactorFromExpression(Ops[i].Op, MaxOccVal)) {
1510 // The factorized operand may occur several times. Convert them all in
1512 for (unsigned j = Ops.size(); j != i;) {
1514 if (Ops[j].Op == Ops[i].Op) {
1515 NewMulOps.push_back(V);
1516 Ops.erase(Ops.begin()+j);
1523 // No need for extra uses anymore.
1526 unsigned NumAddedValues = NewMulOps.size();
1527 Value *V = EmitAddTreeOfValues(I, NewMulOps);
1529 // Now that we have inserted the add tree, optimize it. This allows us to
1530 // handle cases that require multiple factoring steps, such as this:
1531 // A*A*B + A*A*C --> A*(A*B+A*C) --> A*(A*(B+C))
1532 assert(NumAddedValues > 1 && "Each occurrence should contribute a value");
1533 (void)NumAddedValues;
1534 if (Instruction *VI = dyn_cast<Instruction>(V))
1535 RedoInsts.insert(VI);
1537 // Create the multiply.
1538 Instruction *V2 = BinaryOperator::CreateMul(V, MaxOccVal, "tmp", I);
1540 // Rerun associate on the multiply in case the inner expression turned into
1541 // a multiply. We want to make sure that we keep things in canonical form.
1542 RedoInsts.insert(V2);
1544 // If every add operand included the factor (e.g. "A*B + A*C"), then the
1545 // entire result expression is just the multiply "A*(B+C)".
1549 // Otherwise, we had some input that didn't have the factor, such as
1550 // "A*B + A*C + D" -> "A*(B+C) + D". Add the new multiply to the list of
1551 // things being added by this operation.
1552 Ops.insert(Ops.begin(), ValueEntry(getRank(V2), V2));
1559 /// \brief Predicate tests whether a ValueEntry's op is in a map.
1560 struct IsValueInMap {
1561 const DenseMap<Value *, unsigned> ⤅
1563 IsValueInMap(const DenseMap<Value *, unsigned> &Map) : Map(Map) {}
1565 bool operator()(const ValueEntry &Entry) {
1566 return Map.find(Entry.Op) != Map.end();
1571 /// \brief Build up a vector of value/power pairs factoring a product.
1573 /// Given a series of multiplication operands, build a vector of factors and
1574 /// the powers each is raised to when forming the final product. Sort them in
1575 /// the order of descending power.
1577 /// (x*x) -> [(x, 2)]
1578 /// ((x*x)*x) -> [(x, 3)]
1579 /// ((((x*y)*x)*y)*x) -> [(x, 3), (y, 2)]
1581 /// \returns Whether any factors have a power greater than one.
1582 bool Reassociate::collectMultiplyFactors(SmallVectorImpl<ValueEntry> &Ops,
1583 SmallVectorImpl<Factor> &Factors) {
1584 // FIXME: Have Ops be (ValueEntry, Multiplicity) pairs, simplifying this.
1585 // Compute the sum of powers of simplifiable factors.
1586 unsigned FactorPowerSum = 0;
1587 for (unsigned Idx = 1, Size = Ops.size(); Idx < Size; ++Idx) {
1588 Value *Op = Ops[Idx-1].Op;
1590 // Count the number of occurrences of this value.
1592 for (; Idx < Size && Ops[Idx].Op == Op; ++Idx)
1594 // Track for simplification all factors which occur 2 or more times.
1596 FactorPowerSum += Count;
1599 // We can only simplify factors if the sum of the powers of our simplifiable
1600 // factors is 4 or higher. When that is the case, we will *always* have
1601 // a simplification. This is an important invariant to prevent cyclicly
1602 // trying to simplify already minimal formations.
1603 if (FactorPowerSum < 4)
1606 // Now gather the simplifiable factors, removing them from Ops.
1608 for (unsigned Idx = 1; Idx < Ops.size(); ++Idx) {
1609 Value *Op = Ops[Idx-1].Op;
1611 // Count the number of occurrences of this value.
1613 for (; Idx < Ops.size() && Ops[Idx].Op == Op; ++Idx)
1617 // Move an even number of occurrences to Factors.
1620 FactorPowerSum += Count;
1621 Factors.push_back(Factor(Op, Count));
1622 Ops.erase(Ops.begin()+Idx, Ops.begin()+Idx+Count);
1625 // None of the adjustments above should have reduced the sum of factor powers
1626 // below our mininum of '4'.
1627 assert(FactorPowerSum >= 4);
1629 std::sort(Factors.begin(), Factors.end(), Factor::PowerDescendingSorter());
1633 /// \brief Build a tree of multiplies, computing the product of Ops.
1634 static Value *buildMultiplyTree(IRBuilder<> &Builder,
1635 SmallVectorImpl<Value*> &Ops) {
1636 if (Ops.size() == 1)
1639 Value *LHS = Ops.pop_back_val();
1641 LHS = Builder.CreateMul(LHS, Ops.pop_back_val());
1642 } while (!Ops.empty());
1647 /// \brief Build a minimal multiplication DAG for (a^x)*(b^y)*(c^z)*...
1649 /// Given a vector of values raised to various powers, where no two values are
1650 /// equal and the powers are sorted in decreasing order, compute the minimal
1651 /// DAG of multiplies to compute the final product, and return that product
1653 Value *Reassociate::buildMinimalMultiplyDAG(IRBuilder<> &Builder,
1654 SmallVectorImpl<Factor> &Factors) {
1655 assert(Factors[0].Power);
1656 SmallVector<Value *, 4> OuterProduct;
1657 for (unsigned LastIdx = 0, Idx = 1, Size = Factors.size();
1658 Idx < Size && Factors[Idx].Power > 0; ++Idx) {
1659 if (Factors[Idx].Power != Factors[LastIdx].Power) {
1664 // We want to multiply across all the factors with the same power so that
1665 // we can raise them to that power as a single entity. Build a mini tree
1667 SmallVector<Value *, 4> InnerProduct;
1668 InnerProduct.push_back(Factors[LastIdx].Base);
1670 InnerProduct.push_back(Factors[Idx].Base);
1672 } while (Idx < Size && Factors[Idx].Power == Factors[LastIdx].Power);
1674 // Reset the base value of the first factor to the new expression tree.
1675 // We'll remove all the factors with the same power in a second pass.
1676 Value *M = Factors[LastIdx].Base = buildMultiplyTree(Builder, InnerProduct);
1677 if (Instruction *MI = dyn_cast<Instruction>(M))
1678 RedoInsts.insert(MI);
1682 // Unique factors with equal powers -- we've folded them into the first one's
1684 Factors.erase(std::unique(Factors.begin(), Factors.end(),
1685 Factor::PowerEqual()),
1688 // Iteratively collect the base of each factor with an add power into the
1689 // outer product, and halve each power in preparation for squaring the
1691 for (unsigned Idx = 0, Size = Factors.size(); Idx != Size; ++Idx) {
1692 if (Factors[Idx].Power & 1)
1693 OuterProduct.push_back(Factors[Idx].Base);
1694 Factors[Idx].Power >>= 1;
1696 if (Factors[0].Power) {
1697 Value *SquareRoot = buildMinimalMultiplyDAG(Builder, Factors);
1698 OuterProduct.push_back(SquareRoot);
1699 OuterProduct.push_back(SquareRoot);
1701 if (OuterProduct.size() == 1)
1702 return OuterProduct.front();
1704 Value *V = buildMultiplyTree(Builder, OuterProduct);
1708 Value *Reassociate::OptimizeMul(BinaryOperator *I,
1709 SmallVectorImpl<ValueEntry> &Ops) {
1710 // We can only optimize the multiplies when there is a chain of more than
1711 // three, such that a balanced tree might require fewer total multiplies.
1715 // Try to turn linear trees of multiplies without other uses of the
1716 // intermediate stages into minimal multiply DAGs with perfect sub-expression
1718 SmallVector<Factor, 4> Factors;
1719 if (!collectMultiplyFactors(Ops, Factors))
1720 return 0; // All distinct factors, so nothing left for us to do.
1722 IRBuilder<> Builder(I);
1723 Value *V = buildMinimalMultiplyDAG(Builder, Factors);
1727 ValueEntry NewEntry = ValueEntry(getRank(V), V);
1728 Ops.insert(std::lower_bound(Ops.begin(), Ops.end(), NewEntry), NewEntry);
1732 Value *Reassociate::OptimizeExpression(BinaryOperator *I,
1733 SmallVectorImpl<ValueEntry> &Ops) {
1734 // Now that we have the linearized expression tree, try to optimize it.
1735 // Start by folding any constants that we found.
1737 unsigned Opcode = I->getOpcode();
1738 while (!Ops.empty() && isa<Constant>(Ops.back().Op)) {
1739 Constant *C = cast<Constant>(Ops.pop_back_val().Op);
1740 Cst = Cst ? ConstantExpr::get(Opcode, C, Cst) : C;
1742 // If there was nothing but constants then we are done.
1746 // Put the combined constant back at the end of the operand list, except if
1747 // there is no point. For example, an add of 0 gets dropped here, while a
1748 // multiplication by zero turns the whole expression into zero.
1749 if (Cst && Cst != ConstantExpr::getBinOpIdentity(Opcode, I->getType())) {
1750 if (Cst == ConstantExpr::getBinOpAbsorber(Opcode, I->getType()))
1752 Ops.push_back(ValueEntry(0, Cst));
1755 if (Ops.size() == 1) return Ops[0].Op;
1757 // Handle destructive annihilation due to identities between elements in the
1758 // argument list here.
1759 unsigned NumOps = Ops.size();
1762 case Instruction::And:
1763 case Instruction::Or:
1764 if (Value *Result = OptimizeAndOrXor(Opcode, Ops))
1768 case Instruction::Xor:
1769 if (Value *Result = OptimizeXor(I, Ops))
1773 case Instruction::Add:
1774 if (Value *Result = OptimizeAdd(I, Ops))
1778 case Instruction::Mul:
1779 if (Value *Result = OptimizeMul(I, Ops))
1784 if (Ops.size() != NumOps)
1785 return OptimizeExpression(I, Ops);
1789 /// EraseInst - Zap the given instruction, adding interesting operands to the
1791 void Reassociate::EraseInst(Instruction *I) {
1792 assert(isInstructionTriviallyDead(I) && "Trivially dead instructions only!");
1793 SmallVector<Value*, 8> Ops(I->op_begin(), I->op_end());
1794 // Erase the dead instruction.
1795 ValueRankMap.erase(I);
1796 RedoInsts.remove(I);
1797 I->eraseFromParent();
1798 // Optimize its operands.
1799 SmallPtrSet<Instruction *, 8> Visited; // Detect self-referential nodes.
1800 for (unsigned i = 0, e = Ops.size(); i != e; ++i)
1801 if (Instruction *Op = dyn_cast<Instruction>(Ops[i])) {
1802 // If this is a node in an expression tree, climb to the expression root
1803 // and add that since that's where optimization actually happens.
1804 unsigned Opcode = Op->getOpcode();
1805 while (Op->hasOneUse() && Op->use_back()->getOpcode() == Opcode &&
1807 Op = Op->use_back();
1808 RedoInsts.insert(Op);
1812 /// OptimizeInst - Inspect and optimize the given instruction. Note that erasing
1813 /// instructions is not allowed.
1814 void Reassociate::OptimizeInst(Instruction *I) {
1815 // Only consider operations that we understand.
1816 if (!isa<BinaryOperator>(I))
1819 if (I->getOpcode() == Instruction::Shl &&
1820 isa<ConstantInt>(I->getOperand(1)))
1821 // If an operand of this shift is a reassociable multiply, or if the shift
1822 // is used by a reassociable multiply or add, turn into a multiply.
1823 if (isReassociableOp(I->getOperand(0), Instruction::Mul) ||
1825 (isReassociableOp(I->use_back(), Instruction::Mul) ||
1826 isReassociableOp(I->use_back(), Instruction::Add)))) {
1827 Instruction *NI = ConvertShiftToMul(I);
1828 RedoInsts.insert(I);
1833 // Floating point binary operators are not associative, but we can still
1834 // commute (some) of them, to canonicalize the order of their operands.
1835 // This can potentially expose more CSE opportunities, and makes writing
1836 // other transformations simpler.
1837 if ((I->getType()->isFloatingPointTy() || I->getType()->isVectorTy())) {
1838 // FAdd and FMul can be commuted.
1839 if (I->getOpcode() != Instruction::FMul &&
1840 I->getOpcode() != Instruction::FAdd)
1843 Value *LHS = I->getOperand(0);
1844 Value *RHS = I->getOperand(1);
1845 unsigned LHSRank = getRank(LHS);
1846 unsigned RHSRank = getRank(RHS);
1848 // Sort the operands by rank.
1849 if (RHSRank < LHSRank) {
1850 I->setOperand(0, RHS);
1851 I->setOperand(1, LHS);
1857 // Do not reassociate boolean (i1) expressions. We want to preserve the
1858 // original order of evaluation for short-circuited comparisons that
1859 // SimplifyCFG has folded to AND/OR expressions. If the expression
1860 // is not further optimized, it is likely to be transformed back to a
1861 // short-circuited form for code gen, and the source order may have been
1862 // optimized for the most likely conditions.
1863 if (I->getType()->isIntegerTy(1))
1866 // If this is a subtract instruction which is not already in negate form,
1867 // see if we can convert it to X+-Y.
1868 if (I->getOpcode() == Instruction::Sub) {
1869 if (ShouldBreakUpSubtract(I)) {
1870 Instruction *NI = BreakUpSubtract(I);
1871 RedoInsts.insert(I);
1874 } else if (BinaryOperator::isNeg(I)) {
1875 // Otherwise, this is a negation. See if the operand is a multiply tree
1876 // and if this is not an inner node of a multiply tree.
1877 if (isReassociableOp(I->getOperand(1), Instruction::Mul) &&
1879 !isReassociableOp(I->use_back(), Instruction::Mul))) {
1880 Instruction *NI = LowerNegateToMultiply(I);
1881 RedoInsts.insert(I);
1888 // If this instruction is an associative binary operator, process it.
1889 if (!I->isAssociative()) return;
1890 BinaryOperator *BO = cast<BinaryOperator>(I);
1892 // If this is an interior node of a reassociable tree, ignore it until we
1893 // get to the root of the tree, to avoid N^2 analysis.
1894 unsigned Opcode = BO->getOpcode();
1895 if (BO->hasOneUse() && BO->use_back()->getOpcode() == Opcode)
1898 // If this is an add tree that is used by a sub instruction, ignore it
1899 // until we process the subtract.
1900 if (BO->hasOneUse() && BO->getOpcode() == Instruction::Add &&
1901 cast<Instruction>(BO->use_back())->getOpcode() == Instruction::Sub)
1904 ReassociateExpression(BO);
1907 void Reassociate::ReassociateExpression(BinaryOperator *I) {
1909 // First, walk the expression tree, linearizing the tree, collecting the
1910 // operand information.
1911 SmallVector<RepeatedValue, 8> Tree;
1912 MadeChange |= LinearizeExprTree(I, Tree);
1913 SmallVector<ValueEntry, 8> Ops;
1914 Ops.reserve(Tree.size());
1915 for (unsigned i = 0, e = Tree.size(); i != e; ++i) {
1916 RepeatedValue E = Tree[i];
1917 Ops.append(E.second.getZExtValue(),
1918 ValueEntry(getRank(E.first), E.first));
1921 DEBUG(dbgs() << "RAIn:\t"; PrintOps(I, Ops); dbgs() << '\n');
1923 // Now that we have linearized the tree to a list and have gathered all of
1924 // the operands and their ranks, sort the operands by their rank. Use a
1925 // stable_sort so that values with equal ranks will have their relative
1926 // positions maintained (and so the compiler is deterministic). Note that
1927 // this sorts so that the highest ranking values end up at the beginning of
1929 std::stable_sort(Ops.begin(), Ops.end());
1931 // OptimizeExpression - Now that we have the expression tree in a convenient
1932 // sorted form, optimize it globally if possible.
1933 if (Value *V = OptimizeExpression(I, Ops)) {
1935 // Self-referential expression in unreachable code.
1937 // This expression tree simplified to something that isn't a tree,
1939 DEBUG(dbgs() << "Reassoc to scalar: " << *V << '\n');
1940 I->replaceAllUsesWith(V);
1941 if (Instruction *VI = dyn_cast<Instruction>(V))
1942 VI->setDebugLoc(I->getDebugLoc());
1943 RedoInsts.insert(I);
1948 // We want to sink immediates as deeply as possible except in the case where
1949 // this is a multiply tree used only by an add, and the immediate is a -1.
1950 // In this case we reassociate to put the negation on the outside so that we
1951 // can fold the negation into the add: (-X)*Y + Z -> Z-X*Y
1952 if (I->getOpcode() == Instruction::Mul && I->hasOneUse() &&
1953 cast<Instruction>(I->use_back())->getOpcode() == Instruction::Add &&
1954 isa<ConstantInt>(Ops.back().Op) &&
1955 cast<ConstantInt>(Ops.back().Op)->isAllOnesValue()) {
1956 ValueEntry Tmp = Ops.pop_back_val();
1957 Ops.insert(Ops.begin(), Tmp);
1960 DEBUG(dbgs() << "RAOut:\t"; PrintOps(I, Ops); dbgs() << '\n');
1962 if (Ops.size() == 1) {
1964 // Self-referential expression in unreachable code.
1967 // This expression tree simplified to something that isn't a tree,
1969 I->replaceAllUsesWith(Ops[0].Op);
1970 if (Instruction *OI = dyn_cast<Instruction>(Ops[0].Op))
1971 OI->setDebugLoc(I->getDebugLoc());
1972 RedoInsts.insert(I);
1976 // Now that we ordered and optimized the expressions, splat them back into
1977 // the expression tree, removing any unneeded nodes.
1978 RewriteExprTree(I, Ops);
1981 bool Reassociate::runOnFunction(Function &F) {
1982 // Calculate the rank map for F
1986 for (Function::iterator BI = F.begin(), BE = F.end(); BI != BE; ++BI) {
1987 // Optimize every instruction in the basic block.
1988 for (BasicBlock::iterator II = BI->begin(), IE = BI->end(); II != IE; )
1989 if (isInstructionTriviallyDead(II)) {
1993 assert(II->getParent() == BI && "Moved to a different block!");
1997 // If this produced extra instructions to optimize, handle them now.
1998 while (!RedoInsts.empty()) {
1999 Instruction *I = RedoInsts.pop_back_val();
2000 if (isInstructionTriviallyDead(I))
2007 // We are done with the rank map.
2009 ValueRankMap.clear();