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 #include "llvm/Transforms/Scalar.h"
24 #include "llvm/ADT/DenseMap.h"
25 #include "llvm/ADT/PostOrderIterator.h"
26 #include "llvm/ADT/STLExtras.h"
27 #include "llvm/ADT/SetVector.h"
28 #include "llvm/ADT/Statistic.h"
29 #include "llvm/Analysis/GlobalsModRef.h"
30 #include "llvm/Analysis/ValueTracking.h"
31 #include "llvm/IR/CFG.h"
32 #include "llvm/IR/Constants.h"
33 #include "llvm/IR/DerivedTypes.h"
34 #include "llvm/IR/Function.h"
35 #include "llvm/IR/IRBuilder.h"
36 #include "llvm/IR/Instructions.h"
37 #include "llvm/IR/IntrinsicInst.h"
38 #include "llvm/IR/ValueHandle.h"
39 #include "llvm/Pass.h"
40 #include "llvm/Support/Debug.h"
41 #include "llvm/Support/raw_ostream.h"
42 #include "llvm/Transforms/Utils/Local.h"
46 #define DEBUG_TYPE "reassociate"
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 /// 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 Ops[i].Op->printAsOperand(dbgs(), 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 in descending order by their power.
88 struct PowerDescendingSorter {
89 bool operator()(const Factor &LHS, const Factor &RHS) {
90 return LHS.Power > RHS.Power;
94 /// \brief Compare factors for equal powers.
96 bool operator()(const Factor &LHS, const Factor &RHS) {
97 return LHS.Power == RHS.Power;
102 /// Utility class representing a non-constant Xor-operand. We classify
103 /// non-constant Xor-Operands into two categories:
104 /// C1) The operand is in the form "X & C", where C is a constant and C != ~0
106 /// C2.1) The operand is in the form of "X | C", where C is a non-zero
108 /// C2.2) Any operand E which doesn't fall into C1 and C2.1, we view this
109 /// operand as "E | 0"
114 bool isInvalid() const { return SymbolicPart == nullptr; }
115 bool isOrExpr() const { return isOr; }
116 Value *getValue() const { return OrigVal; }
117 Value *getSymbolicPart() const { return SymbolicPart; }
118 unsigned getSymbolicRank() const { return SymbolicRank; }
119 const APInt &getConstPart() const { return ConstPart; }
121 void Invalidate() { SymbolicPart = OrigVal = nullptr; }
122 void setSymbolicRank(unsigned R) { SymbolicRank = R; }
124 // Sort the XorOpnd-Pointer in ascending order of symbolic-value-rank.
125 // The purpose is twofold:
126 // 1) Cluster together the operands sharing the same symbolic-value.
127 // 2) Operand having smaller symbolic-value-rank is permuted earlier, which
128 // could potentially shorten crital path, and expose more loop-invariants.
129 // Note that values' rank are basically defined in RPO order (FIXME).
130 // So, if Rank(X) < Rank(Y) < Rank(Z), it means X is defined earlier
131 // than Y which is defined earlier than Z. Permute "x | 1", "Y & 2",
132 // "z" in the order of X-Y-Z is better than any other orders.
133 struct PtrSortFunctor {
134 bool operator()(XorOpnd * const &LHS, XorOpnd * const &RHS) {
135 return LHS->getSymbolicRank() < RHS->getSymbolicRank();
142 unsigned SymbolicRank;
148 class Reassociate : public FunctionPass {
149 DenseMap<BasicBlock*, unsigned> RankMap;
150 DenseMap<AssertingVH<Value>, unsigned> ValueRankMap;
151 SetVector<AssertingVH<Instruction> > RedoInsts;
154 static char ID; // Pass identification, replacement for typeid
155 Reassociate() : FunctionPass(ID) {
156 initializeReassociatePass(*PassRegistry::getPassRegistry());
159 bool runOnFunction(Function &F) override;
161 void getAnalysisUsage(AnalysisUsage &AU) const override {
162 AU.setPreservesCFG();
163 AU.addPreserved<GlobalsAAWrapperPass>();
166 void BuildRankMap(Function &F);
167 unsigned getRank(Value *V);
168 void canonicalizeOperands(Instruction *I);
169 void ReassociateExpression(BinaryOperator *I);
170 void RewriteExprTree(BinaryOperator *I, SmallVectorImpl<ValueEntry> &Ops);
171 Value *OptimizeExpression(BinaryOperator *I,
172 SmallVectorImpl<ValueEntry> &Ops);
173 Value *OptimizeAdd(Instruction *I, SmallVectorImpl<ValueEntry> &Ops);
174 Value *OptimizeXor(Instruction *I, SmallVectorImpl<ValueEntry> &Ops);
175 bool CombineXorOpnd(Instruction *I, XorOpnd *Opnd1, APInt &ConstOpnd,
177 bool CombineXorOpnd(Instruction *I, XorOpnd *Opnd1, XorOpnd *Opnd2,
178 APInt &ConstOpnd, Value *&Res);
179 bool collectMultiplyFactors(SmallVectorImpl<ValueEntry> &Ops,
180 SmallVectorImpl<Factor> &Factors);
181 Value *buildMinimalMultiplyDAG(IRBuilder<> &Builder,
182 SmallVectorImpl<Factor> &Factors);
183 Value *OptimizeMul(BinaryOperator *I, SmallVectorImpl<ValueEntry> &Ops);
184 Value *RemoveFactorFromExpression(Value *V, Value *Factor);
185 void EraseInst(Instruction *I);
186 void OptimizeInst(Instruction *I);
187 Instruction *canonicalizeNegConstExpr(Instruction *I);
191 XorOpnd::XorOpnd(Value *V) {
192 assert(!isa<ConstantInt>(V) && "No ConstantInt");
194 Instruction *I = dyn_cast<Instruction>(V);
197 if (I && (I->getOpcode() == Instruction::Or ||
198 I->getOpcode() == Instruction::And)) {
199 Value *V0 = I->getOperand(0);
200 Value *V1 = I->getOperand(1);
201 if (isa<ConstantInt>(V0))
204 if (ConstantInt *C = dyn_cast<ConstantInt>(V1)) {
205 ConstPart = C->getValue();
207 isOr = (I->getOpcode() == Instruction::Or);
212 // view the operand as "V | 0"
214 ConstPart = APInt::getNullValue(V->getType()->getIntegerBitWidth());
218 char Reassociate::ID = 0;
219 INITIALIZE_PASS(Reassociate, "reassociate",
220 "Reassociate expressions", false, false)
222 // Public interface to the Reassociate pass
223 FunctionPass *llvm::createReassociatePass() { return new Reassociate(); }
225 /// Return true if V is an instruction of the specified opcode and if it
226 /// only has one use.
227 static BinaryOperator *isReassociableOp(Value *V, unsigned Opcode) {
228 if (V->hasOneUse() && isa<Instruction>(V) &&
229 cast<Instruction>(V)->getOpcode() == Opcode &&
230 (!isa<FPMathOperator>(V) ||
231 cast<Instruction>(V)->hasUnsafeAlgebra()))
232 return cast<BinaryOperator>(V);
236 static BinaryOperator *isReassociableOp(Value *V, unsigned Opcode1,
238 if (V->hasOneUse() && isa<Instruction>(V) &&
239 (cast<Instruction>(V)->getOpcode() == Opcode1 ||
240 cast<Instruction>(V)->getOpcode() == Opcode2) &&
241 (!isa<FPMathOperator>(V) ||
242 cast<Instruction>(V)->hasUnsafeAlgebra()))
243 return cast<BinaryOperator>(V);
247 void Reassociate::BuildRankMap(Function &F) {
250 // Assign distinct ranks to function arguments.
251 for (Function::arg_iterator I = F.arg_begin(), E = F.arg_end(); I != E; ++I) {
252 ValueRankMap[&*I] = ++i;
253 DEBUG(dbgs() << "Calculated Rank[" << I->getName() << "] = " << i << "\n");
256 ReversePostOrderTraversal<Function*> RPOT(&F);
257 for (ReversePostOrderTraversal<Function*>::rpo_iterator I = RPOT.begin(),
258 E = RPOT.end(); I != E; ++I) {
260 unsigned BBRank = RankMap[BB] = ++i << 16;
262 // Walk the basic block, adding precomputed ranks for any instructions that
263 // we cannot move. This ensures that the ranks for these instructions are
264 // all different in the block.
265 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
266 if (mayBeMemoryDependent(*I))
267 ValueRankMap[&*I] = ++BBRank;
271 unsigned Reassociate::getRank(Value *V) {
272 Instruction *I = dyn_cast<Instruction>(V);
274 if (isa<Argument>(V)) return ValueRankMap[V]; // Function argument.
275 return 0; // Otherwise it's a global or constant, rank 0.
278 if (unsigned Rank = ValueRankMap[I])
279 return Rank; // Rank already known?
281 // If this is an expression, return the 1+MAX(rank(LHS), rank(RHS)) so that
282 // we can reassociate expressions for code motion! Since we do not recurse
283 // for PHI nodes, we cannot have infinite recursion here, because there
284 // cannot be loops in the value graph that do not go through PHI nodes.
285 unsigned Rank = 0, MaxRank = RankMap[I->getParent()];
286 for (unsigned i = 0, e = I->getNumOperands();
287 i != e && Rank != MaxRank; ++i)
288 Rank = std::max(Rank, getRank(I->getOperand(i)));
290 // If this is a not or neg instruction, do not count it for rank. This
291 // assures us that X and ~X will have the same rank.
292 if (!BinaryOperator::isNot(I) && !BinaryOperator::isNeg(I) &&
293 !BinaryOperator::isFNeg(I))
296 DEBUG(dbgs() << "Calculated Rank[" << V->getName() << "] = " << Rank << "\n");
298 return ValueRankMap[I] = Rank;
301 // Canonicalize constants to RHS. Otherwise, sort the operands by rank.
302 void Reassociate::canonicalizeOperands(Instruction *I) {
303 assert(isa<BinaryOperator>(I) && "Expected binary operator.");
304 assert(I->isCommutative() && "Expected commutative operator.");
306 Value *LHS = I->getOperand(0);
307 Value *RHS = I->getOperand(1);
308 unsigned LHSRank = getRank(LHS);
309 unsigned RHSRank = getRank(RHS);
311 if (isa<Constant>(RHS))
314 if (isa<Constant>(LHS) || RHSRank < LHSRank)
315 cast<BinaryOperator>(I)->swapOperands();
318 static BinaryOperator *CreateAdd(Value *S1, Value *S2, const Twine &Name,
319 Instruction *InsertBefore, Value *FlagsOp) {
320 if (S1->getType()->isIntOrIntVectorTy())
321 return BinaryOperator::CreateAdd(S1, S2, Name, InsertBefore);
323 BinaryOperator *Res =
324 BinaryOperator::CreateFAdd(S1, S2, Name, InsertBefore);
325 Res->setFastMathFlags(cast<FPMathOperator>(FlagsOp)->getFastMathFlags());
330 static BinaryOperator *CreateMul(Value *S1, Value *S2, const Twine &Name,
331 Instruction *InsertBefore, Value *FlagsOp) {
332 if (S1->getType()->isIntOrIntVectorTy())
333 return BinaryOperator::CreateMul(S1, S2, Name, InsertBefore);
335 BinaryOperator *Res =
336 BinaryOperator::CreateFMul(S1, S2, Name, InsertBefore);
337 Res->setFastMathFlags(cast<FPMathOperator>(FlagsOp)->getFastMathFlags());
342 static BinaryOperator *CreateNeg(Value *S1, const Twine &Name,
343 Instruction *InsertBefore, Value *FlagsOp) {
344 if (S1->getType()->isIntOrIntVectorTy())
345 return BinaryOperator::CreateNeg(S1, Name, InsertBefore);
347 BinaryOperator *Res = BinaryOperator::CreateFNeg(S1, Name, InsertBefore);
348 Res->setFastMathFlags(cast<FPMathOperator>(FlagsOp)->getFastMathFlags());
353 /// Replace 0-X with X*-1.
354 static BinaryOperator *LowerNegateToMultiply(Instruction *Neg) {
355 Type *Ty = Neg->getType();
356 Constant *NegOne = Ty->isIntOrIntVectorTy() ?
357 ConstantInt::getAllOnesValue(Ty) : ConstantFP::get(Ty, -1.0);
359 BinaryOperator *Res = CreateMul(Neg->getOperand(1), NegOne, "", Neg, Neg);
360 Neg->setOperand(1, Constant::getNullValue(Ty)); // Drop use of op.
362 Neg->replaceAllUsesWith(Res);
363 Res->setDebugLoc(Neg->getDebugLoc());
367 /// Returns k such that lambda(2^Bitwidth) = 2^k, where lambda is the Carmichael
368 /// function. This means that x^(2^k) === 1 mod 2^Bitwidth for
369 /// every odd x, i.e. x^(2^k) = 1 for every odd x in Bitwidth-bit arithmetic.
370 /// Note that 0 <= k < Bitwidth, and if Bitwidth > 3 then x^(2^k) = 0 for every
371 /// even x in Bitwidth-bit arithmetic.
372 static unsigned CarmichaelShift(unsigned Bitwidth) {
378 /// Add the extra weight 'RHS' to the existing weight 'LHS',
379 /// reducing the combined weight using any special properties of the operation.
380 /// The existing weight LHS represents the computation X op X op ... op X where
381 /// X occurs LHS times. The combined weight represents X op X op ... op X with
382 /// X occurring LHS + RHS times. If op is "Xor" for example then the combined
383 /// operation is equivalent to X if LHS + RHS is odd, or 0 if LHS + RHS is even;
384 /// the routine returns 1 in LHS in the first case, and 0 in LHS in the second.
385 static void IncorporateWeight(APInt &LHS, const APInt &RHS, unsigned Opcode) {
386 // If we were working with infinite precision arithmetic then the combined
387 // weight would be LHS + RHS. But we are using finite precision arithmetic,
388 // and the APInt sum LHS + RHS may not be correct if it wraps (it is correct
389 // for nilpotent operations and addition, but not for idempotent operations
390 // and multiplication), so it is important to correctly reduce the combined
391 // weight back into range if wrapping would be wrong.
393 // If RHS is zero then the weight didn't change.
394 if (RHS.isMinValue())
396 // If LHS is zero then the combined weight is RHS.
397 if (LHS.isMinValue()) {
401 // From this point on we know that neither LHS nor RHS is zero.
403 if (Instruction::isIdempotent(Opcode)) {
404 // Idempotent means X op X === X, so any non-zero weight is equivalent to a
405 // weight of 1. Keeping weights at zero or one also means that wrapping is
407 assert(LHS == 1 && RHS == 1 && "Weights not reduced!");
408 return; // Return a weight of 1.
410 if (Instruction::isNilpotent(Opcode)) {
411 // Nilpotent means X op X === 0, so reduce weights modulo 2.
412 assert(LHS == 1 && RHS == 1 && "Weights not reduced!");
413 LHS = 0; // 1 + 1 === 0 modulo 2.
416 if (Opcode == Instruction::Add || Opcode == Instruction::FAdd) {
417 // TODO: Reduce the weight by exploiting nsw/nuw?
422 assert((Opcode == Instruction::Mul || Opcode == Instruction::FMul) &&
423 "Unknown associative operation!");
424 unsigned Bitwidth = LHS.getBitWidth();
425 // If CM is the Carmichael number then a weight W satisfying W >= CM+Bitwidth
426 // can be replaced with W-CM. That's because x^W=x^(W-CM) for every Bitwidth
427 // bit number x, since either x is odd in which case x^CM = 1, or x is even in
428 // which case both x^W and x^(W - CM) are zero. By subtracting off multiples
429 // of CM like this weights can always be reduced to the range [0, CM+Bitwidth)
430 // which by a happy accident means that they can always be represented using
432 // TODO: Reduce the weight by exploiting nsw/nuw? (Could do much better than
433 // the Carmichael number).
435 /// CM - The value of Carmichael's lambda function.
436 APInt CM = APInt::getOneBitSet(Bitwidth, CarmichaelShift(Bitwidth));
437 // Any weight W >= Threshold can be replaced with W - CM.
438 APInt Threshold = CM + Bitwidth;
439 assert(LHS.ult(Threshold) && RHS.ult(Threshold) && "Weights not reduced!");
440 // For Bitwidth 4 or more the following sum does not overflow.
442 while (LHS.uge(Threshold))
445 // To avoid problems with overflow do everything the same as above but using
447 unsigned CM = 1U << CarmichaelShift(Bitwidth);
448 unsigned Threshold = CM + Bitwidth;
449 assert(LHS.getZExtValue() < Threshold && RHS.getZExtValue() < Threshold &&
450 "Weights not reduced!");
451 unsigned Total = LHS.getZExtValue() + RHS.getZExtValue();
452 while (Total >= Threshold)
458 typedef std::pair<Value*, APInt> RepeatedValue;
460 /// Given an associative binary expression, return the leaf
461 /// nodes in Ops along with their weights (how many times the leaf occurs). The
462 /// original expression is the same as
463 /// (Ops[0].first op Ops[0].first op ... Ops[0].first) <- Ops[0].second times
465 /// (Ops[1].first op Ops[1].first op ... Ops[1].first) <- Ops[1].second times
469 /// (Ops[N].first op Ops[N].first op ... Ops[N].first) <- Ops[N].second times
471 /// Note that the values Ops[0].first, ..., Ops[N].first are all distinct.
473 /// This routine may modify the function, in which case it returns 'true'. The
474 /// changes it makes may well be destructive, changing the value computed by 'I'
475 /// to something completely different. Thus if the routine returns 'true' then
476 /// you MUST either replace I with a new expression computed from the Ops array,
477 /// or use RewriteExprTree to put the values back in.
479 /// A leaf node is either not a binary operation of the same kind as the root
480 /// node 'I' (i.e. is not a binary operator at all, or is, but with a different
481 /// opcode), or is the same kind of binary operator but has a use which either
482 /// does not belong to the expression, or does belong to the expression but is
483 /// a leaf node. Every leaf node has at least one use that is a non-leaf node
484 /// of the expression, while for non-leaf nodes (except for the root 'I') every
485 /// use is a non-leaf node of the expression.
488 /// expression graph node names
498 /// The leaf nodes are C, E, F and G. The Ops array will contain (maybe not in
499 /// that order) (C, 1), (E, 1), (F, 2), (G, 2).
501 /// The expression is maximal: if some instruction is a binary operator of the
502 /// same kind as 'I', and all of its uses are non-leaf nodes of the expression,
503 /// then the instruction also belongs to the expression, is not a leaf node of
504 /// it, and its operands also belong to the expression (but may be leaf nodes).
506 /// NOTE: This routine will set operands of non-leaf non-root nodes to undef in
507 /// order to ensure that every non-root node in the expression has *exactly one*
508 /// use by a non-leaf node of the expression. This destruction means that the
509 /// caller MUST either replace 'I' with a new expression or use something like
510 /// RewriteExprTree to put the values back in if the routine indicates that it
511 /// made a change by returning 'true'.
513 /// In the above example either the right operand of A or the left operand of B
514 /// will be replaced by undef. If it is B's operand then this gives:
518 /// + + | A, B - operand of B replaced with undef
524 /// Note that such undef operands can only be reached by passing through 'I'.
525 /// For example, if you visit operands recursively starting from a leaf node
526 /// then you will never see such an undef operand unless you get back to 'I',
527 /// which requires passing through a phi node.
529 /// Note that this routine may also mutate binary operators of the wrong type
530 /// that have all uses inside the expression (i.e. only used by non-leaf nodes
531 /// of the expression) if it can turn them into binary operators of the right
532 /// type and thus make the expression bigger.
534 static bool LinearizeExprTree(BinaryOperator *I,
535 SmallVectorImpl<RepeatedValue> &Ops) {
536 DEBUG(dbgs() << "LINEARIZE: " << *I << '\n');
537 unsigned Bitwidth = I->getType()->getScalarType()->getPrimitiveSizeInBits();
538 unsigned Opcode = I->getOpcode();
539 assert(I->isAssociative() && I->isCommutative() &&
540 "Expected an associative and commutative operation!");
542 // Visit all operands of the expression, keeping track of their weight (the
543 // number of paths from the expression root to the operand, or if you like
544 // the number of times that operand occurs in the linearized expression).
545 // For example, if I = X + A, where X = A + B, then I, X and B have weight 1
546 // while A has weight two.
548 // Worklist of non-leaf nodes (their operands are in the expression too) along
549 // with their weights, representing a certain number of paths to the operator.
550 // If an operator occurs in the worklist multiple times then we found multiple
551 // ways to get to it.
552 SmallVector<std::pair<BinaryOperator*, APInt>, 8> Worklist; // (Op, Weight)
553 Worklist.push_back(std::make_pair(I, APInt(Bitwidth, 1)));
554 bool Changed = false;
556 // Leaves of the expression are values that either aren't the right kind of
557 // operation (eg: a constant, or a multiply in an add tree), or are, but have
558 // some uses that are not inside the expression. For example, in I = X + X,
559 // X = A + B, the value X has two uses (by I) that are in the expression. If
560 // X has any other uses, for example in a return instruction, then we consider
561 // X to be a leaf, and won't analyze it further. When we first visit a value,
562 // if it has more than one use then at first we conservatively consider it to
563 // be a leaf. Later, as the expression is explored, we may discover some more
564 // uses of the value from inside the expression. If all uses turn out to be
565 // from within the expression (and the value is a binary operator of the right
566 // kind) then the value is no longer considered to be a leaf, and its operands
569 // Leaves - Keeps track of the set of putative leaves as well as the number of
570 // paths to each leaf seen so far.
571 typedef DenseMap<Value*, APInt> LeafMap;
572 LeafMap Leaves; // Leaf -> Total weight so far.
573 SmallVector<Value*, 8> LeafOrder; // Ensure deterministic leaf output order.
576 SmallPtrSet<Value*, 8> Visited; // For sanity checking the iteration scheme.
578 while (!Worklist.empty()) {
579 std::pair<BinaryOperator*, APInt> P = Worklist.pop_back_val();
580 I = P.first; // We examine the operands of this binary operator.
582 for (unsigned OpIdx = 0; OpIdx < 2; ++OpIdx) { // Visit operands.
583 Value *Op = I->getOperand(OpIdx);
584 APInt Weight = P.second; // Number of paths to this operand.
585 DEBUG(dbgs() << "OPERAND: " << *Op << " (" << Weight << ")\n");
586 assert(!Op->use_empty() && "No uses, so how did we get to it?!");
588 // If this is a binary operation of the right kind with only one use then
589 // add its operands to the expression.
590 if (BinaryOperator *BO = isReassociableOp(Op, Opcode)) {
591 assert(Visited.insert(Op).second && "Not first visit!");
592 DEBUG(dbgs() << "DIRECT ADD: " << *Op << " (" << Weight << ")\n");
593 Worklist.push_back(std::make_pair(BO, Weight));
597 // Appears to be a leaf. Is the operand already in the set of leaves?
598 LeafMap::iterator It = Leaves.find(Op);
599 if (It == Leaves.end()) {
600 // Not in the leaf map. Must be the first time we saw this operand.
601 assert(Visited.insert(Op).second && "Not first visit!");
602 if (!Op->hasOneUse()) {
603 // This value has uses not accounted for by the expression, so it is
604 // not safe to modify. Mark it as being a leaf.
605 DEBUG(dbgs() << "ADD USES LEAF: " << *Op << " (" << Weight << ")\n");
606 LeafOrder.push_back(Op);
610 // No uses outside the expression, try morphing it.
611 } else if (It != Leaves.end()) {
612 // Already in the leaf map.
613 assert(Visited.count(Op) && "In leaf map but not visited!");
615 // Update the number of paths to the leaf.
616 IncorporateWeight(It->second, Weight, Opcode);
618 #if 0 // TODO: Re-enable once PR13021 is fixed.
619 // The leaf already has one use from inside the expression. As we want
620 // exactly one such use, drop this new use of the leaf.
621 assert(!Op->hasOneUse() && "Only one use, but we got here twice!");
622 I->setOperand(OpIdx, UndefValue::get(I->getType()));
625 // If the leaf is a binary operation of the right kind and we now see
626 // that its multiple original uses were in fact all by nodes belonging
627 // to the expression, then no longer consider it to be a leaf and add
628 // its operands to the expression.
629 if (BinaryOperator *BO = isReassociableOp(Op, Opcode)) {
630 DEBUG(dbgs() << "UNLEAF: " << *Op << " (" << It->second << ")\n");
631 Worklist.push_back(std::make_pair(BO, It->second));
637 // If we still have uses that are not accounted for by the expression
638 // then it is not safe to modify the value.
639 if (!Op->hasOneUse())
642 // No uses outside the expression, try morphing it.
644 Leaves.erase(It); // Since the value may be morphed below.
647 // At this point we have a value which, first of all, is not a binary
648 // expression of the right kind, and secondly, is only used inside the
649 // expression. This means that it can safely be modified. See if we
650 // can usefully morph it into an expression of the right kind.
651 assert((!isa<Instruction>(Op) ||
652 cast<Instruction>(Op)->getOpcode() != Opcode
653 || (isa<FPMathOperator>(Op) &&
654 !cast<Instruction>(Op)->hasUnsafeAlgebra())) &&
655 "Should have been handled above!");
656 assert(Op->hasOneUse() && "Has uses outside the expression tree!");
658 // If this is a multiply expression, turn any internal negations into
659 // multiplies by -1 so they can be reassociated.
660 if (BinaryOperator *BO = dyn_cast<BinaryOperator>(Op))
661 if ((Opcode == Instruction::Mul && BinaryOperator::isNeg(BO)) ||
662 (Opcode == Instruction::FMul && BinaryOperator::isFNeg(BO))) {
663 DEBUG(dbgs() << "MORPH LEAF: " << *Op << " (" << Weight << ") TO ");
664 BO = LowerNegateToMultiply(BO);
665 DEBUG(dbgs() << *BO << '\n');
666 Worklist.push_back(std::make_pair(BO, Weight));
671 // Failed to morph into an expression of the right type. This really is
673 DEBUG(dbgs() << "ADD LEAF: " << *Op << " (" << Weight << ")\n");
674 assert(!isReassociableOp(Op, Opcode) && "Value was morphed?");
675 LeafOrder.push_back(Op);
680 // The leaves, repeated according to their weights, represent the linearized
681 // form of the expression.
682 for (unsigned i = 0, e = LeafOrder.size(); i != e; ++i) {
683 Value *V = LeafOrder[i];
684 LeafMap::iterator It = Leaves.find(V);
685 if (It == Leaves.end())
686 // Node initially thought to be a leaf wasn't.
688 assert(!isReassociableOp(V, Opcode) && "Shouldn't be a leaf!");
689 APInt Weight = It->second;
690 if (Weight.isMinValue())
691 // Leaf already output or weight reduction eliminated it.
693 // Ensure the leaf is only output once.
695 Ops.push_back(std::make_pair(V, Weight));
698 // For nilpotent operations or addition there may be no operands, for example
699 // because the expression was "X xor X" or consisted of 2^Bitwidth additions:
700 // in both cases the weight reduces to 0 causing the value to be skipped.
702 Constant *Identity = ConstantExpr::getBinOpIdentity(Opcode, I->getType());
703 assert(Identity && "Associative operation without identity!");
704 Ops.emplace_back(Identity, APInt(Bitwidth, 1));
710 /// Now that the operands for this expression tree are
711 /// linearized and optimized, emit them in-order.
712 void Reassociate::RewriteExprTree(BinaryOperator *I,
713 SmallVectorImpl<ValueEntry> &Ops) {
714 assert(Ops.size() > 1 && "Single values should be used directly!");
716 // Since our optimizations should never increase the number of operations, the
717 // new expression can usually be written reusing the existing binary operators
718 // from the original expression tree, without creating any new instructions,
719 // though the rewritten expression may have a completely different topology.
720 // We take care to not change anything if the new expression will be the same
721 // as the original. If more than trivial changes (like commuting operands)
722 // were made then we are obliged to clear out any optional subclass data like
725 /// NodesToRewrite - Nodes from the original expression available for writing
726 /// the new expression into.
727 SmallVector<BinaryOperator*, 8> NodesToRewrite;
728 unsigned Opcode = I->getOpcode();
729 BinaryOperator *Op = I;
731 /// NotRewritable - The operands being written will be the leaves of the new
732 /// expression and must not be used as inner nodes (via NodesToRewrite) by
733 /// mistake. Inner nodes are always reassociable, and usually leaves are not
734 /// (if they were they would have been incorporated into the expression and so
735 /// would not be leaves), so most of the time there is no danger of this. But
736 /// in rare cases a leaf may become reassociable if an optimization kills uses
737 /// of it, or it may momentarily become reassociable during rewriting (below)
738 /// due it being removed as an operand of one of its uses. Ensure that misuse
739 /// of leaf nodes as inner nodes cannot occur by remembering all of the future
740 /// leaves and refusing to reuse any of them as inner nodes.
741 SmallPtrSet<Value*, 8> NotRewritable;
742 for (unsigned i = 0, e = Ops.size(); i != e; ++i)
743 NotRewritable.insert(Ops[i].Op);
745 // ExpressionChanged - Non-null if the rewritten expression differs from the
746 // original in some non-trivial way, requiring the clearing of optional flags.
747 // Flags are cleared from the operator in ExpressionChanged up to I inclusive.
748 BinaryOperator *ExpressionChanged = nullptr;
749 for (unsigned i = 0; ; ++i) {
750 // The last operation (which comes earliest in the IR) is special as both
751 // operands will come from Ops, rather than just one with the other being
753 if (i+2 == Ops.size()) {
754 Value *NewLHS = Ops[i].Op;
755 Value *NewRHS = Ops[i+1].Op;
756 Value *OldLHS = Op->getOperand(0);
757 Value *OldRHS = Op->getOperand(1);
759 if (NewLHS == OldLHS && NewRHS == OldRHS)
760 // Nothing changed, leave it alone.
763 if (NewLHS == OldRHS && NewRHS == OldLHS) {
764 // The order of the operands was reversed. Swap them.
765 DEBUG(dbgs() << "RA: " << *Op << '\n');
767 DEBUG(dbgs() << "TO: " << *Op << '\n');
773 // The new operation differs non-trivially from the original. Overwrite
774 // the old operands with the new ones.
775 DEBUG(dbgs() << "RA: " << *Op << '\n');
776 if (NewLHS != OldLHS) {
777 BinaryOperator *BO = isReassociableOp(OldLHS, Opcode);
778 if (BO && !NotRewritable.count(BO))
779 NodesToRewrite.push_back(BO);
780 Op->setOperand(0, NewLHS);
782 if (NewRHS != OldRHS) {
783 BinaryOperator *BO = isReassociableOp(OldRHS, Opcode);
784 if (BO && !NotRewritable.count(BO))
785 NodesToRewrite.push_back(BO);
786 Op->setOperand(1, NewRHS);
788 DEBUG(dbgs() << "TO: " << *Op << '\n');
790 ExpressionChanged = Op;
797 // Not the last operation. The left-hand side will be a sub-expression
798 // while the right-hand side will be the current element of Ops.
799 Value *NewRHS = Ops[i].Op;
800 if (NewRHS != Op->getOperand(1)) {
801 DEBUG(dbgs() << "RA: " << *Op << '\n');
802 if (NewRHS == Op->getOperand(0)) {
803 // The new right-hand side was already present as the left operand. If
804 // we are lucky then swapping the operands will sort out both of them.
807 // Overwrite with the new right-hand side.
808 BinaryOperator *BO = isReassociableOp(Op->getOperand(1), Opcode);
809 if (BO && !NotRewritable.count(BO))
810 NodesToRewrite.push_back(BO);
811 Op->setOperand(1, NewRHS);
812 ExpressionChanged = Op;
814 DEBUG(dbgs() << "TO: " << *Op << '\n');
819 // Now deal with the left-hand side. If this is already an operation node
820 // from the original expression then just rewrite the rest of the expression
822 BinaryOperator *BO = isReassociableOp(Op->getOperand(0), Opcode);
823 if (BO && !NotRewritable.count(BO)) {
828 // Otherwise, grab a spare node from the original expression and use that as
829 // the left-hand side. If there are no nodes left then the optimizers made
830 // an expression with more nodes than the original! This usually means that
831 // they did something stupid but it might mean that the problem was just too
832 // hard (finding the mimimal number of multiplications needed to realize a
833 // multiplication expression is NP-complete). Whatever the reason, smart or
834 // stupid, create a new node if there are none left.
835 BinaryOperator *NewOp;
836 if (NodesToRewrite.empty()) {
837 Constant *Undef = UndefValue::get(I->getType());
838 NewOp = BinaryOperator::Create(Instruction::BinaryOps(Opcode),
839 Undef, Undef, "", I);
840 if (NewOp->getType()->isFPOrFPVectorTy())
841 NewOp->setFastMathFlags(I->getFastMathFlags());
843 NewOp = NodesToRewrite.pop_back_val();
846 DEBUG(dbgs() << "RA: " << *Op << '\n');
847 Op->setOperand(0, NewOp);
848 DEBUG(dbgs() << "TO: " << *Op << '\n');
849 ExpressionChanged = Op;
855 // If the expression changed non-trivially then clear out all subclass data
856 // starting from the operator specified in ExpressionChanged, and compactify
857 // the operators to just before the expression root to guarantee that the
858 // expression tree is dominated by all of Ops.
859 if (ExpressionChanged)
861 // Preserve FastMathFlags.
862 if (isa<FPMathOperator>(I)) {
863 FastMathFlags Flags = I->getFastMathFlags();
864 ExpressionChanged->clearSubclassOptionalData();
865 ExpressionChanged->setFastMathFlags(Flags);
867 ExpressionChanged->clearSubclassOptionalData();
869 if (ExpressionChanged == I)
871 ExpressionChanged->moveBefore(I);
872 ExpressionChanged = cast<BinaryOperator>(*ExpressionChanged->user_begin());
875 // Throw away any left over nodes from the original expression.
876 for (unsigned i = 0, e = NodesToRewrite.size(); i != e; ++i)
877 RedoInsts.insert(NodesToRewrite[i]);
880 /// Insert instructions before the instruction pointed to by BI,
881 /// that computes the negative version of the value specified. The negative
882 /// version of the value is returned, and BI is left pointing at the instruction
883 /// that should be processed next by the reassociation pass.
884 static Value *NegateValue(Value *V, Instruction *BI) {
885 if (Constant *C = dyn_cast<Constant>(V)) {
886 if (C->getType()->isFPOrFPVectorTy()) {
887 return ConstantExpr::getFNeg(C);
889 return ConstantExpr::getNeg(C);
893 // We are trying to expose opportunity for reassociation. One of the things
894 // that we want to do to achieve this is to push a negation as deep into an
895 // expression chain as possible, to expose the add instructions. In practice,
896 // this means that we turn this:
897 // X = -(A+12+C+D) into X = -A + -12 + -C + -D = -12 + -A + -C + -D
898 // so that later, a: Y = 12+X could get reassociated with the -12 to eliminate
899 // the constants. We assume that instcombine will clean up the mess later if
900 // we introduce tons of unnecessary negation instructions.
902 if (BinaryOperator *I =
903 isReassociableOp(V, Instruction::Add, Instruction::FAdd)) {
904 // Push the negates through the add.
905 I->setOperand(0, NegateValue(I->getOperand(0), BI));
906 I->setOperand(1, NegateValue(I->getOperand(1), BI));
907 if (I->getOpcode() == Instruction::Add) {
908 I->setHasNoUnsignedWrap(false);
909 I->setHasNoSignedWrap(false);
912 // We must move the add instruction here, because the neg instructions do
913 // not dominate the old add instruction in general. By moving it, we are
914 // assured that the neg instructions we just inserted dominate the
915 // instruction we are about to insert after them.
918 I->setName(I->getName()+".neg");
922 // Okay, we need to materialize a negated version of V with an instruction.
923 // Scan the use lists of V to see if we have one already.
924 for (User *U : V->users()) {
925 if (!BinaryOperator::isNeg(U) && !BinaryOperator::isFNeg(U))
928 // We found one! Now we have to make sure that the definition dominates
929 // this use. We do this by moving it to the entry block (if it is a
930 // non-instruction value) or right after the definition. These negates will
931 // be zapped by reassociate later, so we don't need much finesse here.
932 BinaryOperator *TheNeg = cast<BinaryOperator>(U);
934 // Verify that the negate is in this function, V might be a constant expr.
935 if (TheNeg->getParent()->getParent() != BI->getParent()->getParent())
938 BasicBlock::iterator InsertPt;
939 if (Instruction *InstInput = dyn_cast<Instruction>(V)) {
940 if (InvokeInst *II = dyn_cast<InvokeInst>(InstInput)) {
941 InsertPt = II->getNormalDest()->begin();
942 } else if (auto *CPI = dyn_cast<CatchPadInst>(InstInput)) {
943 InsertPt = CPI->getNormalDest()->begin();
945 InsertPt = ++InstInput->getIterator();
947 while (isa<PHINode>(InsertPt)) ++InsertPt;
949 InsertPt = TheNeg->getParent()->getParent()->getEntryBlock().begin();
951 TheNeg->moveBefore(&*InsertPt);
952 if (TheNeg->getOpcode() == Instruction::Sub) {
953 TheNeg->setHasNoUnsignedWrap(false);
954 TheNeg->setHasNoSignedWrap(false);
956 TheNeg->andIRFlags(BI);
961 // Insert a 'neg' instruction that subtracts the value from zero to get the
963 return CreateNeg(V, V->getName() + ".neg", BI, BI);
966 /// Return true if we should break up this subtract of X-Y into (X + -Y).
967 static bool ShouldBreakUpSubtract(Instruction *Sub) {
968 // If this is a negation, we can't split it up!
969 if (BinaryOperator::isNeg(Sub) || BinaryOperator::isFNeg(Sub))
972 // Don't breakup X - undef.
973 if (isa<UndefValue>(Sub->getOperand(1)))
976 // Don't bother to break this up unless either the LHS is an associable add or
977 // subtract or if this is only used by one.
978 Value *V0 = Sub->getOperand(0);
979 if (isReassociableOp(V0, Instruction::Add, Instruction::FAdd) ||
980 isReassociableOp(V0, Instruction::Sub, Instruction::FSub))
982 Value *V1 = Sub->getOperand(1);
983 if (isReassociableOp(V1, Instruction::Add, Instruction::FAdd) ||
984 isReassociableOp(V1, Instruction::Sub, Instruction::FSub))
986 Value *VB = Sub->user_back();
987 if (Sub->hasOneUse() &&
988 (isReassociableOp(VB, Instruction::Add, Instruction::FAdd) ||
989 isReassociableOp(VB, Instruction::Sub, Instruction::FSub)))
995 /// If we have (X-Y), and if either X is an add, or if this is only used by an
996 /// add, transform this into (X+(0-Y)) to promote better reassociation.
997 static BinaryOperator *BreakUpSubtract(Instruction *Sub) {
998 // Convert a subtract into an add and a neg instruction. This allows sub
999 // instructions to be commuted with other add instructions.
1001 // Calculate the negative value of Operand 1 of the sub instruction,
1002 // and set it as the RHS of the add instruction we just made.
1004 Value *NegVal = NegateValue(Sub->getOperand(1), Sub);
1005 BinaryOperator *New = CreateAdd(Sub->getOperand(0), NegVal, "", Sub, Sub);
1006 Sub->setOperand(0, Constant::getNullValue(Sub->getType())); // Drop use of op.
1007 Sub->setOperand(1, Constant::getNullValue(Sub->getType())); // Drop use of op.
1010 // Everyone now refers to the add instruction.
1011 Sub->replaceAllUsesWith(New);
1012 New->setDebugLoc(Sub->getDebugLoc());
1014 DEBUG(dbgs() << "Negated: " << *New << '\n');
1018 /// If this is a shift of a reassociable multiply or is used by one, change
1019 /// this into a multiply by a constant to assist with further reassociation.
1020 static BinaryOperator *ConvertShiftToMul(Instruction *Shl) {
1021 Constant *MulCst = ConstantInt::get(Shl->getType(), 1);
1022 MulCst = ConstantExpr::getShl(MulCst, cast<Constant>(Shl->getOperand(1)));
1024 BinaryOperator *Mul =
1025 BinaryOperator::CreateMul(Shl->getOperand(0), MulCst, "", Shl);
1026 Shl->setOperand(0, UndefValue::get(Shl->getType())); // Drop use of op.
1029 // Everyone now refers to the mul instruction.
1030 Shl->replaceAllUsesWith(Mul);
1031 Mul->setDebugLoc(Shl->getDebugLoc());
1033 // We can safely preserve the nuw flag in all cases. It's also safe to turn a
1034 // nuw nsw shl into a nuw nsw mul. However, nsw in isolation requires special
1036 bool NSW = cast<BinaryOperator>(Shl)->hasNoSignedWrap();
1037 bool NUW = cast<BinaryOperator>(Shl)->hasNoUnsignedWrap();
1039 Mul->setHasNoSignedWrap(true);
1040 Mul->setHasNoUnsignedWrap(NUW);
1044 /// Scan backwards and forwards among values with the same rank as element i
1045 /// to see if X exists. If X does not exist, return i. This is useful when
1046 /// scanning for 'x' when we see '-x' because they both get the same rank.
1047 static unsigned FindInOperandList(SmallVectorImpl<ValueEntry> &Ops, unsigned i,
1049 unsigned XRank = Ops[i].Rank;
1050 unsigned e = Ops.size();
1051 for (unsigned j = i+1; j != e && Ops[j].Rank == XRank; ++j) {
1054 if (Instruction *I1 = dyn_cast<Instruction>(Ops[j].Op))
1055 if (Instruction *I2 = dyn_cast<Instruction>(X))
1056 if (I1->isIdenticalTo(I2))
1060 for (unsigned j = i-1; j != ~0U && Ops[j].Rank == XRank; --j) {
1063 if (Instruction *I1 = dyn_cast<Instruction>(Ops[j].Op))
1064 if (Instruction *I2 = dyn_cast<Instruction>(X))
1065 if (I1->isIdenticalTo(I2))
1071 /// Emit a tree of add instructions, summing Ops together
1072 /// and returning the result. Insert the tree before I.
1073 static Value *EmitAddTreeOfValues(Instruction *I,
1074 SmallVectorImpl<WeakVH> &Ops){
1075 if (Ops.size() == 1) return Ops.back();
1077 Value *V1 = Ops.back();
1079 Value *V2 = EmitAddTreeOfValues(I, Ops);
1080 return CreateAdd(V2, V1, "tmp", I, I);
1083 /// If V is an expression tree that is a multiplication sequence,
1084 /// and if this sequence contains a multiply by Factor,
1085 /// remove Factor from the tree and return the new tree.
1086 Value *Reassociate::RemoveFactorFromExpression(Value *V, Value *Factor) {
1087 BinaryOperator *BO = isReassociableOp(V, Instruction::Mul, Instruction::FMul);
1091 SmallVector<RepeatedValue, 8> Tree;
1092 MadeChange |= LinearizeExprTree(BO, Tree);
1093 SmallVector<ValueEntry, 8> Factors;
1094 Factors.reserve(Tree.size());
1095 for (unsigned i = 0, e = Tree.size(); i != e; ++i) {
1096 RepeatedValue E = Tree[i];
1097 Factors.append(E.second.getZExtValue(),
1098 ValueEntry(getRank(E.first), E.first));
1101 bool FoundFactor = false;
1102 bool NeedsNegate = false;
1103 for (unsigned i = 0, e = Factors.size(); i != e; ++i) {
1104 if (Factors[i].Op == Factor) {
1106 Factors.erase(Factors.begin()+i);
1110 // If this is a negative version of this factor, remove it.
1111 if (ConstantInt *FC1 = dyn_cast<ConstantInt>(Factor)) {
1112 if (ConstantInt *FC2 = dyn_cast<ConstantInt>(Factors[i].Op))
1113 if (FC1->getValue() == -FC2->getValue()) {
1114 FoundFactor = NeedsNegate = true;
1115 Factors.erase(Factors.begin()+i);
1118 } else if (ConstantFP *FC1 = dyn_cast<ConstantFP>(Factor)) {
1119 if (ConstantFP *FC2 = dyn_cast<ConstantFP>(Factors[i].Op)) {
1120 APFloat F1(FC1->getValueAPF());
1121 APFloat F2(FC2->getValueAPF());
1123 if (F1.compare(F2) == APFloat::cmpEqual) {
1124 FoundFactor = NeedsNegate = true;
1125 Factors.erase(Factors.begin() + i);
1133 // Make sure to restore the operands to the expression tree.
1134 RewriteExprTree(BO, Factors);
1138 BasicBlock::iterator InsertPt = ++BO->getIterator();
1140 // If this was just a single multiply, remove the multiply and return the only
1141 // remaining operand.
1142 if (Factors.size() == 1) {
1143 RedoInsts.insert(BO);
1146 RewriteExprTree(BO, Factors);
1151 V = CreateNeg(V, "neg", &*InsertPt, BO);
1156 /// If V is a single-use multiply, recursively add its operands as factors,
1157 /// otherwise add V to the list of factors.
1159 /// Ops is the top-level list of add operands we're trying to factor.
1160 static void FindSingleUseMultiplyFactors(Value *V,
1161 SmallVectorImpl<Value*> &Factors,
1162 const SmallVectorImpl<ValueEntry> &Ops) {
1163 BinaryOperator *BO = isReassociableOp(V, Instruction::Mul, Instruction::FMul);
1165 Factors.push_back(V);
1169 // Otherwise, add the LHS and RHS to the list of factors.
1170 FindSingleUseMultiplyFactors(BO->getOperand(1), Factors, Ops);
1171 FindSingleUseMultiplyFactors(BO->getOperand(0), Factors, Ops);
1174 /// Optimize a series of operands to an 'and', 'or', or 'xor' instruction.
1175 /// This optimizes based on identities. If it can be reduced to a single Value,
1176 /// it is returned, otherwise the Ops list is mutated as necessary.
1177 static Value *OptimizeAndOrXor(unsigned Opcode,
1178 SmallVectorImpl<ValueEntry> &Ops) {
1179 // Scan the operand lists looking for X and ~X pairs, along with X,X pairs.
1180 // If we find any, we can simplify the expression. X&~X == 0, X|~X == -1.
1181 for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
1182 // First, check for X and ~X in the operand list.
1183 assert(i < Ops.size());
1184 if (BinaryOperator::isNot(Ops[i].Op)) { // Cannot occur for ^.
1185 Value *X = BinaryOperator::getNotArgument(Ops[i].Op);
1186 unsigned FoundX = FindInOperandList(Ops, i, X);
1188 if (Opcode == Instruction::And) // ...&X&~X = 0
1189 return Constant::getNullValue(X->getType());
1191 if (Opcode == Instruction::Or) // ...|X|~X = -1
1192 return Constant::getAllOnesValue(X->getType());
1196 // Next, check for duplicate pairs of values, which we assume are next to
1197 // each other, due to our sorting criteria.
1198 assert(i < Ops.size());
1199 if (i+1 != Ops.size() && Ops[i+1].Op == Ops[i].Op) {
1200 if (Opcode == Instruction::And || Opcode == Instruction::Or) {
1201 // Drop duplicate values for And and Or.
1202 Ops.erase(Ops.begin()+i);
1208 // Drop pairs of values for Xor.
1209 assert(Opcode == Instruction::Xor);
1211 return Constant::getNullValue(Ops[0].Op->getType());
1214 Ops.erase(Ops.begin()+i, Ops.begin()+i+2);
1222 /// Helper funciton of CombineXorOpnd(). It creates a bitwise-and
1223 /// instruction with the given two operands, and return the resulting
1224 /// instruction. There are two special cases: 1) if the constant operand is 0,
1225 /// it will return NULL. 2) if the constant is ~0, the symbolic operand will
1227 static Value *createAndInstr(Instruction *InsertBefore, Value *Opnd,
1228 const APInt &ConstOpnd) {
1229 if (ConstOpnd != 0) {
1230 if (!ConstOpnd.isAllOnesValue()) {
1231 LLVMContext &Ctx = Opnd->getType()->getContext();
1233 I = BinaryOperator::CreateAnd(Opnd, ConstantInt::get(Ctx, ConstOpnd),
1234 "and.ra", InsertBefore);
1235 I->setDebugLoc(InsertBefore->getDebugLoc());
1243 // Helper function of OptimizeXor(). It tries to simplify "Opnd1 ^ ConstOpnd"
1244 // into "R ^ C", where C would be 0, and R is a symbolic value.
1246 // If it was successful, true is returned, and the "R" and "C" is returned
1247 // via "Res" and "ConstOpnd", respectively; otherwise, false is returned,
1248 // and both "Res" and "ConstOpnd" remain unchanged.
1250 bool Reassociate::CombineXorOpnd(Instruction *I, XorOpnd *Opnd1,
1251 APInt &ConstOpnd, Value *&Res) {
1252 // Xor-Rule 1: (x | c1) ^ c2 = (x | c1) ^ (c1 ^ c1) ^ c2
1253 // = ((x | c1) ^ c1) ^ (c1 ^ c2)
1254 // = (x & ~c1) ^ (c1 ^ c2)
1255 // It is useful only when c1 == c2.
1256 if (Opnd1->isOrExpr() && Opnd1->getConstPart() != 0) {
1257 if (!Opnd1->getValue()->hasOneUse())
1260 const APInt &C1 = Opnd1->getConstPart();
1261 if (C1 != ConstOpnd)
1264 Value *X = Opnd1->getSymbolicPart();
1265 Res = createAndInstr(I, X, ~C1);
1266 // ConstOpnd was C2, now C1 ^ C2.
1269 if (Instruction *T = dyn_cast<Instruction>(Opnd1->getValue()))
1270 RedoInsts.insert(T);
1277 // Helper function of OptimizeXor(). It tries to simplify
1278 // "Opnd1 ^ Opnd2 ^ ConstOpnd" into "R ^ C", where C would be 0, and R is a
1281 // If it was successful, true is returned, and the "R" and "C" is returned
1282 // via "Res" and "ConstOpnd", respectively (If the entire expression is
1283 // evaluated to a constant, the Res is set to NULL); otherwise, false is
1284 // returned, and both "Res" and "ConstOpnd" remain unchanged.
1285 bool Reassociate::CombineXorOpnd(Instruction *I, XorOpnd *Opnd1, XorOpnd *Opnd2,
1286 APInt &ConstOpnd, Value *&Res) {
1287 Value *X = Opnd1->getSymbolicPart();
1288 if (X != Opnd2->getSymbolicPart())
1291 // This many instruction become dead.(At least "Opnd1 ^ Opnd2" will die.)
1292 int DeadInstNum = 1;
1293 if (Opnd1->getValue()->hasOneUse())
1295 if (Opnd2->getValue()->hasOneUse())
1299 // (x | c1) ^ (x & c2)
1300 // = (x|c1) ^ (x&c2) ^ (c1 ^ c1) = ((x|c1) ^ c1) ^ (x & c2) ^ c1
1301 // = (x & ~c1) ^ (x & c2) ^ c1 // Xor-Rule 1
1302 // = (x & c3) ^ c1, where c3 = ~c1 ^ c2 // Xor-rule 3
1304 if (Opnd1->isOrExpr() != Opnd2->isOrExpr()) {
1305 if (Opnd2->isOrExpr())
1306 std::swap(Opnd1, Opnd2);
1308 const APInt &C1 = Opnd1->getConstPart();
1309 const APInt &C2 = Opnd2->getConstPart();
1310 APInt C3((~C1) ^ C2);
1312 // Do not increase code size!
1313 if (C3 != 0 && !C3.isAllOnesValue()) {
1314 int NewInstNum = ConstOpnd != 0 ? 1 : 2;
1315 if (NewInstNum > DeadInstNum)
1319 Res = createAndInstr(I, X, C3);
1322 } else if (Opnd1->isOrExpr()) {
1323 // Xor-Rule 3: (x | c1) ^ (x | c2) = (x & c3) ^ c3 where c3 = c1 ^ c2
1325 const APInt &C1 = Opnd1->getConstPart();
1326 const APInt &C2 = Opnd2->getConstPart();
1329 // Do not increase code size
1330 if (C3 != 0 && !C3.isAllOnesValue()) {
1331 int NewInstNum = ConstOpnd != 0 ? 1 : 2;
1332 if (NewInstNum > DeadInstNum)
1336 Res = createAndInstr(I, X, C3);
1339 // Xor-Rule 4: (x & c1) ^ (x & c2) = (x & (c1^c2))
1341 const APInt &C1 = Opnd1->getConstPart();
1342 const APInt &C2 = Opnd2->getConstPart();
1344 Res = createAndInstr(I, X, C3);
1347 // Put the original operands in the Redo list; hope they will be deleted
1349 if (Instruction *T = dyn_cast<Instruction>(Opnd1->getValue()))
1350 RedoInsts.insert(T);
1351 if (Instruction *T = dyn_cast<Instruction>(Opnd2->getValue()))
1352 RedoInsts.insert(T);
1357 /// Optimize a series of operands to an 'xor' instruction. If it can be reduced
1358 /// to a single Value, it is returned, otherwise the Ops list is mutated as
1360 Value *Reassociate::OptimizeXor(Instruction *I,
1361 SmallVectorImpl<ValueEntry> &Ops) {
1362 if (Value *V = OptimizeAndOrXor(Instruction::Xor, Ops))
1365 if (Ops.size() == 1)
1368 SmallVector<XorOpnd, 8> Opnds;
1369 SmallVector<XorOpnd*, 8> OpndPtrs;
1370 Type *Ty = Ops[0].Op->getType();
1371 APInt ConstOpnd(Ty->getIntegerBitWidth(), 0);
1373 // Step 1: Convert ValueEntry to XorOpnd
1374 for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
1375 Value *V = Ops[i].Op;
1376 if (!isa<ConstantInt>(V)) {
1378 O.setSymbolicRank(getRank(O.getSymbolicPart()));
1381 ConstOpnd ^= cast<ConstantInt>(V)->getValue();
1384 // NOTE: From this point on, do *NOT* add/delete element to/from "Opnds".
1385 // It would otherwise invalidate the "Opnds"'s iterator, and hence invalidate
1386 // the "OpndPtrs" as well. For the similar reason, do not fuse this loop
1387 // with the previous loop --- the iterator of the "Opnds" may be invalidated
1388 // when new elements are added to the vector.
1389 for (unsigned i = 0, e = Opnds.size(); i != e; ++i)
1390 OpndPtrs.push_back(&Opnds[i]);
1392 // Step 2: Sort the Xor-Operands in a way such that the operands containing
1393 // the same symbolic value cluster together. For instance, the input operand
1394 // sequence ("x | 123", "y & 456", "x & 789") will be sorted into:
1395 // ("x | 123", "x & 789", "y & 456").
1396 std::stable_sort(OpndPtrs.begin(), OpndPtrs.end(), XorOpnd::PtrSortFunctor());
1398 // Step 3: Combine adjacent operands
1399 XorOpnd *PrevOpnd = nullptr;
1400 bool Changed = false;
1401 for (unsigned i = 0, e = Opnds.size(); i < e; i++) {
1402 XorOpnd *CurrOpnd = OpndPtrs[i];
1403 // The combined value
1406 // Step 3.1: Try simplifying "CurrOpnd ^ ConstOpnd"
1407 if (ConstOpnd != 0 && CombineXorOpnd(I, CurrOpnd, ConstOpnd, CV)) {
1410 *CurrOpnd = XorOpnd(CV);
1412 CurrOpnd->Invalidate();
1417 if (!PrevOpnd || CurrOpnd->getSymbolicPart() != PrevOpnd->getSymbolicPart()) {
1418 PrevOpnd = CurrOpnd;
1422 // step 3.2: When previous and current operands share the same symbolic
1423 // value, try to simplify "PrevOpnd ^ CurrOpnd ^ ConstOpnd"
1425 if (CombineXorOpnd(I, CurrOpnd, PrevOpnd, ConstOpnd, CV)) {
1426 // Remove previous operand
1427 PrevOpnd->Invalidate();
1429 *CurrOpnd = XorOpnd(CV);
1430 PrevOpnd = CurrOpnd;
1432 CurrOpnd->Invalidate();
1439 // Step 4: Reassemble the Ops
1442 for (unsigned int i = 0, e = Opnds.size(); i < e; i++) {
1443 XorOpnd &O = Opnds[i];
1446 ValueEntry VE(getRank(O.getValue()), O.getValue());
1449 if (ConstOpnd != 0) {
1450 Value *C = ConstantInt::get(Ty->getContext(), ConstOpnd);
1451 ValueEntry VE(getRank(C), C);
1454 int Sz = Ops.size();
1456 return Ops.back().Op;
1458 assert(ConstOpnd == 0);
1459 return ConstantInt::get(Ty->getContext(), ConstOpnd);
1466 /// Optimize a series of operands to an 'add' instruction. This
1467 /// optimizes based on identities. If it can be reduced to a single Value, it
1468 /// is returned, otherwise the Ops list is mutated as necessary.
1469 Value *Reassociate::OptimizeAdd(Instruction *I,
1470 SmallVectorImpl<ValueEntry> &Ops) {
1471 // Scan the operand lists looking for X and -X pairs. If we find any, we
1472 // can simplify expressions like X+-X == 0 and X+~X ==-1. While we're at it,
1474 // duplicates. We want to canonicalize Y+Y+Y+Z -> 3*Y+Z.
1476 for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
1477 Value *TheOp = Ops[i].Op;
1478 // Check to see if we've seen this operand before. If so, we factor all
1479 // instances of the operand together. Due to our sorting criteria, we know
1480 // that these need to be next to each other in the vector.
1481 if (i+1 != Ops.size() && Ops[i+1].Op == TheOp) {
1482 // Rescan the list, remove all instances of this operand from the expr.
1483 unsigned NumFound = 0;
1485 Ops.erase(Ops.begin()+i);
1487 } while (i != Ops.size() && Ops[i].Op == TheOp);
1489 DEBUG(dbgs() << "\nFACTORING [" << NumFound << "]: " << *TheOp << '\n');
1492 // Insert a new multiply.
1493 Type *Ty = TheOp->getType();
1494 Constant *C = Ty->isIntOrIntVectorTy() ?
1495 ConstantInt::get(Ty, NumFound) : ConstantFP::get(Ty, NumFound);
1496 Instruction *Mul = CreateMul(TheOp, C, "factor", I, I);
1498 // Now that we have inserted a multiply, optimize it. This allows us to
1499 // handle cases that require multiple factoring steps, such as this:
1500 // (X*2) + (X*2) + (X*2) -> (X*2)*3 -> X*6
1501 RedoInsts.insert(Mul);
1503 // If every add operand was a duplicate, return the multiply.
1507 // Otherwise, we had some input that didn't have the dupe, such as
1508 // "A + A + B" -> "A*2 + B". Add the new multiply to the list of
1509 // things being added by this operation.
1510 Ops.insert(Ops.begin(), ValueEntry(getRank(Mul), Mul));
1517 // Check for X and -X or X and ~X in the operand list.
1518 if (!BinaryOperator::isNeg(TheOp) && !BinaryOperator::isFNeg(TheOp) &&
1519 !BinaryOperator::isNot(TheOp))
1523 if (BinaryOperator::isNeg(TheOp) || BinaryOperator::isFNeg(TheOp))
1524 X = BinaryOperator::getNegArgument(TheOp);
1525 else if (BinaryOperator::isNot(TheOp))
1526 X = BinaryOperator::getNotArgument(TheOp);
1528 unsigned FoundX = FindInOperandList(Ops, i, X);
1532 // Remove X and -X from the operand list.
1533 if (Ops.size() == 2 &&
1534 (BinaryOperator::isNeg(TheOp) || BinaryOperator::isFNeg(TheOp)))
1535 return Constant::getNullValue(X->getType());
1537 // Remove X and ~X from the operand list.
1538 if (Ops.size() == 2 && BinaryOperator::isNot(TheOp))
1539 return Constant::getAllOnesValue(X->getType());
1541 Ops.erase(Ops.begin()+i);
1545 --i; // Need to back up an extra one.
1546 Ops.erase(Ops.begin()+FoundX);
1548 --i; // Revisit element.
1549 e -= 2; // Removed two elements.
1551 // if X and ~X we append -1 to the operand list.
1552 if (BinaryOperator::isNot(TheOp)) {
1553 Value *V = Constant::getAllOnesValue(X->getType());
1554 Ops.insert(Ops.end(), ValueEntry(getRank(V), V));
1559 // Scan the operand list, checking to see if there are any common factors
1560 // between operands. Consider something like A*A+A*B*C+D. We would like to
1561 // reassociate this to A*(A+B*C)+D, which reduces the number of multiplies.
1562 // To efficiently find this, we count the number of times a factor occurs
1563 // for any ADD operands that are MULs.
1564 DenseMap<Value*, unsigned> FactorOccurrences;
1566 // Keep track of each multiply we see, to avoid triggering on (X*4)+(X*4)
1567 // where they are actually the same multiply.
1568 unsigned MaxOcc = 0;
1569 Value *MaxOccVal = nullptr;
1570 for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
1571 BinaryOperator *BOp =
1572 isReassociableOp(Ops[i].Op, Instruction::Mul, Instruction::FMul);
1576 // Compute all of the factors of this added value.
1577 SmallVector<Value*, 8> Factors;
1578 FindSingleUseMultiplyFactors(BOp, Factors, Ops);
1579 assert(Factors.size() > 1 && "Bad linearize!");
1581 // Add one to FactorOccurrences for each unique factor in this op.
1582 SmallPtrSet<Value*, 8> Duplicates;
1583 for (unsigned i = 0, e = Factors.size(); i != e; ++i) {
1584 Value *Factor = Factors[i];
1585 if (!Duplicates.insert(Factor).second)
1588 unsigned Occ = ++FactorOccurrences[Factor];
1594 // If Factor is a negative constant, add the negated value as a factor
1595 // because we can percolate the negate out. Watch for minint, which
1596 // cannot be positivified.
1597 if (ConstantInt *CI = dyn_cast<ConstantInt>(Factor)) {
1598 if (CI->isNegative() && !CI->isMinValue(true)) {
1599 Factor = ConstantInt::get(CI->getContext(), -CI->getValue());
1600 assert(!Duplicates.count(Factor) &&
1601 "Shouldn't have two constant factors, missed a canonicalize");
1602 unsigned Occ = ++FactorOccurrences[Factor];
1608 } else if (ConstantFP *CF = dyn_cast<ConstantFP>(Factor)) {
1609 if (CF->isNegative()) {
1610 APFloat F(CF->getValueAPF());
1612 Factor = ConstantFP::get(CF->getContext(), F);
1613 assert(!Duplicates.count(Factor) &&
1614 "Shouldn't have two constant factors, missed a canonicalize");
1615 unsigned Occ = ++FactorOccurrences[Factor];
1625 // If any factor occurred more than one time, we can pull it out.
1627 DEBUG(dbgs() << "\nFACTORING [" << MaxOcc << "]: " << *MaxOccVal << '\n');
1630 // Create a new instruction that uses the MaxOccVal twice. If we don't do
1631 // this, we could otherwise run into situations where removing a factor
1632 // from an expression will drop a use of maxocc, and this can cause
1633 // RemoveFactorFromExpression on successive values to behave differently.
1634 Instruction *DummyInst =
1635 I->getType()->isIntOrIntVectorTy()
1636 ? BinaryOperator::CreateAdd(MaxOccVal, MaxOccVal)
1637 : BinaryOperator::CreateFAdd(MaxOccVal, MaxOccVal);
1639 SmallVector<WeakVH, 4> NewMulOps;
1640 for (unsigned i = 0; i != Ops.size(); ++i) {
1641 // Only try to remove factors from expressions we're allowed to.
1642 BinaryOperator *BOp =
1643 isReassociableOp(Ops[i].Op, Instruction::Mul, Instruction::FMul);
1647 if (Value *V = RemoveFactorFromExpression(Ops[i].Op, MaxOccVal)) {
1648 // The factorized operand may occur several times. Convert them all in
1650 for (unsigned j = Ops.size(); j != i;) {
1652 if (Ops[j].Op == Ops[i].Op) {
1653 NewMulOps.push_back(V);
1654 Ops.erase(Ops.begin()+j);
1661 // No need for extra uses anymore.
1664 unsigned NumAddedValues = NewMulOps.size();
1665 Value *V = EmitAddTreeOfValues(I, NewMulOps);
1667 // Now that we have inserted the add tree, optimize it. This allows us to
1668 // handle cases that require multiple factoring steps, such as this:
1669 // A*A*B + A*A*C --> A*(A*B+A*C) --> A*(A*(B+C))
1670 assert(NumAddedValues > 1 && "Each occurrence should contribute a value");
1671 (void)NumAddedValues;
1672 if (Instruction *VI = dyn_cast<Instruction>(V))
1673 RedoInsts.insert(VI);
1675 // Create the multiply.
1676 Instruction *V2 = CreateMul(V, MaxOccVal, "tmp", I, I);
1678 // Rerun associate on the multiply in case the inner expression turned into
1679 // a multiply. We want to make sure that we keep things in canonical form.
1680 RedoInsts.insert(V2);
1682 // If every add operand included the factor (e.g. "A*B + A*C"), then the
1683 // entire result expression is just the multiply "A*(B+C)".
1687 // Otherwise, we had some input that didn't have the factor, such as
1688 // "A*B + A*C + D" -> "A*(B+C) + D". Add the new multiply to the list of
1689 // things being added by this operation.
1690 Ops.insert(Ops.begin(), ValueEntry(getRank(V2), V2));
1696 /// \brief Build up a vector of value/power pairs factoring a product.
1698 /// Given a series of multiplication operands, build a vector of factors and
1699 /// the powers each is raised to when forming the final product. Sort them in
1700 /// the order of descending power.
1702 /// (x*x) -> [(x, 2)]
1703 /// ((x*x)*x) -> [(x, 3)]
1704 /// ((((x*y)*x)*y)*x) -> [(x, 3), (y, 2)]
1706 /// \returns Whether any factors have a power greater than one.
1707 bool Reassociate::collectMultiplyFactors(SmallVectorImpl<ValueEntry> &Ops,
1708 SmallVectorImpl<Factor> &Factors) {
1709 // FIXME: Have Ops be (ValueEntry, Multiplicity) pairs, simplifying this.
1710 // Compute the sum of powers of simplifiable factors.
1711 unsigned FactorPowerSum = 0;
1712 for (unsigned Idx = 1, Size = Ops.size(); Idx < Size; ++Idx) {
1713 Value *Op = Ops[Idx-1].Op;
1715 // Count the number of occurrences of this value.
1717 for (; Idx < Size && Ops[Idx].Op == Op; ++Idx)
1719 // Track for simplification all factors which occur 2 or more times.
1721 FactorPowerSum += Count;
1724 // We can only simplify factors if the sum of the powers of our simplifiable
1725 // factors is 4 or higher. When that is the case, we will *always* have
1726 // a simplification. This is an important invariant to prevent cyclicly
1727 // trying to simplify already minimal formations.
1728 if (FactorPowerSum < 4)
1731 // Now gather the simplifiable factors, removing them from Ops.
1733 for (unsigned Idx = 1; Idx < Ops.size(); ++Idx) {
1734 Value *Op = Ops[Idx-1].Op;
1736 // Count the number of occurrences of this value.
1738 for (; Idx < Ops.size() && Ops[Idx].Op == Op; ++Idx)
1742 // Move an even number of occurrences to Factors.
1745 FactorPowerSum += Count;
1746 Factors.push_back(Factor(Op, Count));
1747 Ops.erase(Ops.begin()+Idx, Ops.begin()+Idx+Count);
1750 // None of the adjustments above should have reduced the sum of factor powers
1751 // below our mininum of '4'.
1752 assert(FactorPowerSum >= 4);
1754 std::stable_sort(Factors.begin(), Factors.end(), Factor::PowerDescendingSorter());
1758 /// \brief Build a tree of multiplies, computing the product of Ops.
1759 static Value *buildMultiplyTree(IRBuilder<> &Builder,
1760 SmallVectorImpl<Value*> &Ops) {
1761 if (Ops.size() == 1)
1764 Value *LHS = Ops.pop_back_val();
1766 if (LHS->getType()->isIntOrIntVectorTy())
1767 LHS = Builder.CreateMul(LHS, Ops.pop_back_val());
1769 LHS = Builder.CreateFMul(LHS, Ops.pop_back_val());
1770 } while (!Ops.empty());
1775 /// \brief Build a minimal multiplication DAG for (a^x)*(b^y)*(c^z)*...
1777 /// Given a vector of values raised to various powers, where no two values are
1778 /// equal and the powers are sorted in decreasing order, compute the minimal
1779 /// DAG of multiplies to compute the final product, and return that product
1781 Value *Reassociate::buildMinimalMultiplyDAG(IRBuilder<> &Builder,
1782 SmallVectorImpl<Factor> &Factors) {
1783 assert(Factors[0].Power);
1784 SmallVector<Value *, 4> OuterProduct;
1785 for (unsigned LastIdx = 0, Idx = 1, Size = Factors.size();
1786 Idx < Size && Factors[Idx].Power > 0; ++Idx) {
1787 if (Factors[Idx].Power != Factors[LastIdx].Power) {
1792 // We want to multiply across all the factors with the same power so that
1793 // we can raise them to that power as a single entity. Build a mini tree
1795 SmallVector<Value *, 4> InnerProduct;
1796 InnerProduct.push_back(Factors[LastIdx].Base);
1798 InnerProduct.push_back(Factors[Idx].Base);
1800 } while (Idx < Size && Factors[Idx].Power == Factors[LastIdx].Power);
1802 // Reset the base value of the first factor to the new expression tree.
1803 // We'll remove all the factors with the same power in a second pass.
1804 Value *M = Factors[LastIdx].Base = buildMultiplyTree(Builder, InnerProduct);
1805 if (Instruction *MI = dyn_cast<Instruction>(M))
1806 RedoInsts.insert(MI);
1810 // Unique factors with equal powers -- we've folded them into the first one's
1812 Factors.erase(std::unique(Factors.begin(), Factors.end(),
1813 Factor::PowerEqual()),
1816 // Iteratively collect the base of each factor with an add power into the
1817 // outer product, and halve each power in preparation for squaring the
1819 for (unsigned Idx = 0, Size = Factors.size(); Idx != Size; ++Idx) {
1820 if (Factors[Idx].Power & 1)
1821 OuterProduct.push_back(Factors[Idx].Base);
1822 Factors[Idx].Power >>= 1;
1824 if (Factors[0].Power) {
1825 Value *SquareRoot = buildMinimalMultiplyDAG(Builder, Factors);
1826 OuterProduct.push_back(SquareRoot);
1827 OuterProduct.push_back(SquareRoot);
1829 if (OuterProduct.size() == 1)
1830 return OuterProduct.front();
1832 Value *V = buildMultiplyTree(Builder, OuterProduct);
1836 Value *Reassociate::OptimizeMul(BinaryOperator *I,
1837 SmallVectorImpl<ValueEntry> &Ops) {
1838 // We can only optimize the multiplies when there is a chain of more than
1839 // three, such that a balanced tree might require fewer total multiplies.
1843 // Try to turn linear trees of multiplies without other uses of the
1844 // intermediate stages into minimal multiply DAGs with perfect sub-expression
1846 SmallVector<Factor, 4> Factors;
1847 if (!collectMultiplyFactors(Ops, Factors))
1848 return nullptr; // All distinct factors, so nothing left for us to do.
1850 IRBuilder<> Builder(I);
1851 Value *V = buildMinimalMultiplyDAG(Builder, Factors);
1855 ValueEntry NewEntry = ValueEntry(getRank(V), V);
1856 Ops.insert(std::lower_bound(Ops.begin(), Ops.end(), NewEntry), NewEntry);
1860 Value *Reassociate::OptimizeExpression(BinaryOperator *I,
1861 SmallVectorImpl<ValueEntry> &Ops) {
1862 // Now that we have the linearized expression tree, try to optimize it.
1863 // Start by folding any constants that we found.
1864 Constant *Cst = nullptr;
1865 unsigned Opcode = I->getOpcode();
1866 while (!Ops.empty() && isa<Constant>(Ops.back().Op)) {
1867 Constant *C = cast<Constant>(Ops.pop_back_val().Op);
1868 Cst = Cst ? ConstantExpr::get(Opcode, C, Cst) : C;
1870 // If there was nothing but constants then we are done.
1874 // Put the combined constant back at the end of the operand list, except if
1875 // there is no point. For example, an add of 0 gets dropped here, while a
1876 // multiplication by zero turns the whole expression into zero.
1877 if (Cst && Cst != ConstantExpr::getBinOpIdentity(Opcode, I->getType())) {
1878 if (Cst == ConstantExpr::getBinOpAbsorber(Opcode, I->getType()))
1880 Ops.push_back(ValueEntry(0, Cst));
1883 if (Ops.size() == 1) return Ops[0].Op;
1885 // Handle destructive annihilation due to identities between elements in the
1886 // argument list here.
1887 unsigned NumOps = Ops.size();
1890 case Instruction::And:
1891 case Instruction::Or:
1892 if (Value *Result = OptimizeAndOrXor(Opcode, Ops))
1896 case Instruction::Xor:
1897 if (Value *Result = OptimizeXor(I, Ops))
1901 case Instruction::Add:
1902 case Instruction::FAdd:
1903 if (Value *Result = OptimizeAdd(I, Ops))
1907 case Instruction::Mul:
1908 case Instruction::FMul:
1909 if (Value *Result = OptimizeMul(I, Ops))
1914 if (Ops.size() != NumOps)
1915 return OptimizeExpression(I, Ops);
1919 /// Zap the given instruction, adding interesting operands to the work list.
1920 void Reassociate::EraseInst(Instruction *I) {
1921 assert(isInstructionTriviallyDead(I) && "Trivially dead instructions only!");
1922 SmallVector<Value*, 8> Ops(I->op_begin(), I->op_end());
1923 // Erase the dead instruction.
1924 ValueRankMap.erase(I);
1925 RedoInsts.remove(I);
1926 I->eraseFromParent();
1927 // Optimize its operands.
1928 SmallPtrSet<Instruction *, 8> Visited; // Detect self-referential nodes.
1929 for (unsigned i = 0, e = Ops.size(); i != e; ++i)
1930 if (Instruction *Op = dyn_cast<Instruction>(Ops[i])) {
1931 // If this is a node in an expression tree, climb to the expression root
1932 // and add that since that's where optimization actually happens.
1933 unsigned Opcode = Op->getOpcode();
1934 while (Op->hasOneUse() && Op->user_back()->getOpcode() == Opcode &&
1935 Visited.insert(Op).second)
1936 Op = Op->user_back();
1937 RedoInsts.insert(Op);
1941 // Canonicalize expressions of the following form:
1942 // x + (-Constant * y) -> x - (Constant * y)
1943 // x - (-Constant * y) -> x + (Constant * y)
1944 Instruction *Reassociate::canonicalizeNegConstExpr(Instruction *I) {
1945 if (!I->hasOneUse() || I->getType()->isVectorTy())
1948 // Must be a fmul or fdiv instruction.
1949 unsigned Opcode = I->getOpcode();
1950 if (Opcode != Instruction::FMul && Opcode != Instruction::FDiv)
1953 auto *C0 = dyn_cast<ConstantFP>(I->getOperand(0));
1954 auto *C1 = dyn_cast<ConstantFP>(I->getOperand(1));
1956 // Both operands are constant, let it get constant folded away.
1960 ConstantFP *CF = C0 ? C0 : C1;
1962 // Must have one constant operand.
1966 // Must be a negative ConstantFP.
1967 if (!CF->isNegative())
1970 // User must be a binary operator with one or more uses.
1971 Instruction *User = I->user_back();
1972 if (!isa<BinaryOperator>(User) || !User->hasNUsesOrMore(1))
1975 unsigned UserOpcode = User->getOpcode();
1976 if (UserOpcode != Instruction::FAdd && UserOpcode != Instruction::FSub)
1979 // Subtraction is not commutative. Explicitly, the following transform is
1980 // not valid: (-Constant * y) - x -> x + (Constant * y)
1981 if (!User->isCommutative() && User->getOperand(1) != I)
1984 // Change the sign of the constant.
1985 APFloat Val = CF->getValueAPF();
1987 I->setOperand(C0 ? 0 : 1, ConstantFP::get(CF->getContext(), Val));
1989 // Canonicalize I to RHS to simplify the next bit of logic. E.g.,
1990 // ((-Const*y) + x) -> (x + (-Const*y)).
1991 if (User->getOperand(0) == I && User->isCommutative())
1992 cast<BinaryOperator>(User)->swapOperands();
1994 Value *Op0 = User->getOperand(0);
1995 Value *Op1 = User->getOperand(1);
1997 switch (UserOpcode) {
1999 llvm_unreachable("Unexpected Opcode!");
2000 case Instruction::FAdd:
2001 NI = BinaryOperator::CreateFSub(Op0, Op1);
2002 NI->setFastMathFlags(cast<FPMathOperator>(User)->getFastMathFlags());
2004 case Instruction::FSub:
2005 NI = BinaryOperator::CreateFAdd(Op0, Op1);
2006 NI->setFastMathFlags(cast<FPMathOperator>(User)->getFastMathFlags());
2010 NI->insertBefore(User);
2011 NI->setName(User->getName());
2012 User->replaceAllUsesWith(NI);
2013 NI->setDebugLoc(I->getDebugLoc());
2014 RedoInsts.insert(I);
2019 /// Inspect and optimize the given instruction. Note that erasing
2020 /// instructions is not allowed.
2021 void Reassociate::OptimizeInst(Instruction *I) {
2022 // Only consider operations that we understand.
2023 if (!isa<BinaryOperator>(I))
2026 if (I->getOpcode() == Instruction::Shl && isa<ConstantInt>(I->getOperand(1)))
2027 // If an operand of this shift is a reassociable multiply, or if the shift
2028 // is used by a reassociable multiply or add, turn into a multiply.
2029 if (isReassociableOp(I->getOperand(0), Instruction::Mul) ||
2031 (isReassociableOp(I->user_back(), Instruction::Mul) ||
2032 isReassociableOp(I->user_back(), Instruction::Add)))) {
2033 Instruction *NI = ConvertShiftToMul(I);
2034 RedoInsts.insert(I);
2039 // Canonicalize negative constants out of expressions.
2040 if (Instruction *Res = canonicalizeNegConstExpr(I))
2043 // Commute binary operators, to canonicalize the order of their operands.
2044 // This can potentially expose more CSE opportunities, and makes writing other
2045 // transformations simpler.
2046 if (I->isCommutative())
2047 canonicalizeOperands(I);
2049 // TODO: We should optimize vector Xor instructions, but they are
2050 // currently unsupported.
2051 if (I->getType()->isVectorTy() && I->getOpcode() == Instruction::Xor)
2054 // Don't optimize floating point instructions that don't have unsafe algebra.
2055 if (I->getType()->isFloatingPointTy() && !I->hasUnsafeAlgebra())
2058 // Do not reassociate boolean (i1) expressions. We want to preserve the
2059 // original order of evaluation for short-circuited comparisons that
2060 // SimplifyCFG has folded to AND/OR expressions. If the expression
2061 // is not further optimized, it is likely to be transformed back to a
2062 // short-circuited form for code gen, and the source order may have been
2063 // optimized for the most likely conditions.
2064 if (I->getType()->isIntegerTy(1))
2067 // If this is a subtract instruction which is not already in negate form,
2068 // see if we can convert it to X+-Y.
2069 if (I->getOpcode() == Instruction::Sub) {
2070 if (ShouldBreakUpSubtract(I)) {
2071 Instruction *NI = BreakUpSubtract(I);
2072 RedoInsts.insert(I);
2075 } else if (BinaryOperator::isNeg(I)) {
2076 // Otherwise, this is a negation. See if the operand is a multiply tree
2077 // and if this is not an inner node of a multiply tree.
2078 if (isReassociableOp(I->getOperand(1), Instruction::Mul) &&
2080 !isReassociableOp(I->user_back(), Instruction::Mul))) {
2081 Instruction *NI = LowerNegateToMultiply(I);
2082 RedoInsts.insert(I);
2087 } else if (I->getOpcode() == Instruction::FSub) {
2088 if (ShouldBreakUpSubtract(I)) {
2089 Instruction *NI = BreakUpSubtract(I);
2090 RedoInsts.insert(I);
2093 } else if (BinaryOperator::isFNeg(I)) {
2094 // Otherwise, this is a negation. See if the operand is a multiply tree
2095 // and if this is not an inner node of a multiply tree.
2096 if (isReassociableOp(I->getOperand(1), Instruction::FMul) &&
2098 !isReassociableOp(I->user_back(), Instruction::FMul))) {
2099 Instruction *NI = LowerNegateToMultiply(I);
2100 RedoInsts.insert(I);
2107 // If this instruction is an associative binary operator, process it.
2108 if (!I->isAssociative()) return;
2109 BinaryOperator *BO = cast<BinaryOperator>(I);
2111 // If this is an interior node of a reassociable tree, ignore it until we
2112 // get to the root of the tree, to avoid N^2 analysis.
2113 unsigned Opcode = BO->getOpcode();
2114 if (BO->hasOneUse() && BO->user_back()->getOpcode() == Opcode)
2117 // If this is an add tree that is used by a sub instruction, ignore it
2118 // until we process the subtract.
2119 if (BO->hasOneUse() && BO->getOpcode() == Instruction::Add &&
2120 cast<Instruction>(BO->user_back())->getOpcode() == Instruction::Sub)
2122 if (BO->hasOneUse() && BO->getOpcode() == Instruction::FAdd &&
2123 cast<Instruction>(BO->user_back())->getOpcode() == Instruction::FSub)
2126 ReassociateExpression(BO);
2129 void Reassociate::ReassociateExpression(BinaryOperator *I) {
2130 // First, walk the expression tree, linearizing the tree, collecting the
2131 // operand information.
2132 SmallVector<RepeatedValue, 8> Tree;
2133 MadeChange |= LinearizeExprTree(I, Tree);
2134 SmallVector<ValueEntry, 8> Ops;
2135 Ops.reserve(Tree.size());
2136 for (unsigned i = 0, e = Tree.size(); i != e; ++i) {
2137 RepeatedValue E = Tree[i];
2138 Ops.append(E.second.getZExtValue(),
2139 ValueEntry(getRank(E.first), E.first));
2142 DEBUG(dbgs() << "RAIn:\t"; PrintOps(I, Ops); dbgs() << '\n');
2144 // Now that we have linearized the tree to a list and have gathered all of
2145 // the operands and their ranks, sort the operands by their rank. Use a
2146 // stable_sort so that values with equal ranks will have their relative
2147 // positions maintained (and so the compiler is deterministic). Note that
2148 // this sorts so that the highest ranking values end up at the beginning of
2150 std::stable_sort(Ops.begin(), Ops.end());
2152 // Now that we have the expression tree in a convenient
2153 // sorted form, optimize it globally if possible.
2154 if (Value *V = OptimizeExpression(I, Ops)) {
2156 // Self-referential expression in unreachable code.
2158 // This expression tree simplified to something that isn't a tree,
2160 DEBUG(dbgs() << "Reassoc to scalar: " << *V << '\n');
2161 I->replaceAllUsesWith(V);
2162 if (Instruction *VI = dyn_cast<Instruction>(V))
2163 VI->setDebugLoc(I->getDebugLoc());
2164 RedoInsts.insert(I);
2169 // We want to sink immediates as deeply as possible except in the case where
2170 // this is a multiply tree used only by an add, and the immediate is a -1.
2171 // In this case we reassociate to put the negation on the outside so that we
2172 // can fold the negation into the add: (-X)*Y + Z -> Z-X*Y
2173 if (I->hasOneUse()) {
2174 if (I->getOpcode() == Instruction::Mul &&
2175 cast<Instruction>(I->user_back())->getOpcode() == Instruction::Add &&
2176 isa<ConstantInt>(Ops.back().Op) &&
2177 cast<ConstantInt>(Ops.back().Op)->isAllOnesValue()) {
2178 ValueEntry Tmp = Ops.pop_back_val();
2179 Ops.insert(Ops.begin(), Tmp);
2180 } else if (I->getOpcode() == Instruction::FMul &&
2181 cast<Instruction>(I->user_back())->getOpcode() ==
2182 Instruction::FAdd &&
2183 isa<ConstantFP>(Ops.back().Op) &&
2184 cast<ConstantFP>(Ops.back().Op)->isExactlyValue(-1.0)) {
2185 ValueEntry Tmp = Ops.pop_back_val();
2186 Ops.insert(Ops.begin(), Tmp);
2190 DEBUG(dbgs() << "RAOut:\t"; PrintOps(I, Ops); dbgs() << '\n');
2192 if (Ops.size() == 1) {
2194 // Self-referential expression in unreachable code.
2197 // This expression tree simplified to something that isn't a tree,
2199 I->replaceAllUsesWith(Ops[0].Op);
2200 if (Instruction *OI = dyn_cast<Instruction>(Ops[0].Op))
2201 OI->setDebugLoc(I->getDebugLoc());
2202 RedoInsts.insert(I);
2206 // Now that we ordered and optimized the expressions, splat them back into
2207 // the expression tree, removing any unneeded nodes.
2208 RewriteExprTree(I, Ops);
2211 bool Reassociate::runOnFunction(Function &F) {
2212 if (skipOptnoneFunction(F))
2215 // Calculate the rank map for F
2219 for (Function::iterator BI = F.begin(), BE = F.end(); BI != BE; ++BI) {
2220 // Optimize every instruction in the basic block.
2221 for (BasicBlock::iterator II = BI->begin(), IE = BI->end(); II != IE; )
2222 if (isInstructionTriviallyDead(&*II)) {
2226 assert(II->getParent() == BI && "Moved to a different block!");
2230 // If this produced extra instructions to optimize, handle them now.
2231 while (!RedoInsts.empty()) {
2232 Instruction *I = RedoInsts.pop_back_val();
2233 if (isInstructionTriviallyDead(I))
2240 // We are done with the rank map.
2242 ValueRankMap.clear();