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/Reassociate.h"
24 #include "llvm/ADT/APFloat.h"
25 #include "llvm/ADT/APInt.h"
26 #include "llvm/ADT/DenseMap.h"
27 #include "llvm/ADT/PostOrderIterator.h"
28 #include "llvm/ADT/SetVector.h"
29 #include "llvm/ADT/SmallPtrSet.h"
30 #include "llvm/ADT/SmallSet.h"
31 #include "llvm/ADT/SmallVector.h"
32 #include "llvm/ADT/Statistic.h"
33 #include "llvm/Analysis/GlobalsModRef.h"
34 #include "llvm/Transforms/Utils/Local.h"
35 #include "llvm/Analysis/ValueTracking.h"
36 #include "llvm/IR/Argument.h"
37 #include "llvm/IR/BasicBlock.h"
38 #include "llvm/IR/CFG.h"
39 #include "llvm/IR/Constant.h"
40 #include "llvm/IR/Constants.h"
41 #include "llvm/IR/Function.h"
42 #include "llvm/IR/IRBuilder.h"
43 #include "llvm/IR/InstrTypes.h"
44 #include "llvm/IR/Instruction.h"
45 #include "llvm/IR/Instructions.h"
46 #include "llvm/IR/IntrinsicInst.h"
47 #include "llvm/IR/Operator.h"
48 #include "llvm/IR/PassManager.h"
49 #include "llvm/IR/PatternMatch.h"
50 #include "llvm/IR/Type.h"
51 #include "llvm/IR/User.h"
52 #include "llvm/IR/Value.h"
53 #include "llvm/IR/ValueHandle.h"
54 #include "llvm/Pass.h"
55 #include "llvm/Support/Casting.h"
56 #include "llvm/Support/Debug.h"
57 #include "llvm/Support/ErrorHandling.h"
58 #include "llvm/Support/raw_ostream.h"
59 #include "llvm/Transforms/Scalar.h"
65 using namespace reassociate;
66 using namespace PatternMatch;
68 #define DEBUG_TYPE "reassociate"
70 STATISTIC(NumChanged, "Number of insts reassociated");
71 STATISTIC(NumAnnihil, "Number of expr tree annihilated");
72 STATISTIC(NumFactor , "Number of multiplies factored");
75 /// Print out the expression identified in the Ops list.
76 static void PrintOps(Instruction *I, const SmallVectorImpl<ValueEntry> &Ops) {
77 Module *M = I->getModule();
78 dbgs() << Instruction::getOpcodeName(I->getOpcode()) << " "
79 << *Ops[0].Op->getType() << '\t';
80 for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
82 Ops[i].Op->printAsOperand(dbgs(), false, M);
83 dbgs() << ", #" << Ops[i].Rank << "] ";
88 /// Utility class representing a non-constant Xor-operand. We classify
89 /// non-constant Xor-Operands into two categories:
90 /// C1) The operand is in the form "X & C", where C is a constant and C != ~0
92 /// C2.1) The operand is in the form of "X | C", where C is a non-zero
94 /// C2.2) Any operand E which doesn't fall into C1 and C2.1, we view this
95 /// operand as "E | 0"
96 class llvm::reassociate::XorOpnd {
100 bool isInvalid() const { return SymbolicPart == nullptr; }
101 bool isOrExpr() const { return isOr; }
102 Value *getValue() const { return OrigVal; }
103 Value *getSymbolicPart() const { return SymbolicPart; }
104 unsigned getSymbolicRank() const { return SymbolicRank; }
105 const APInt &getConstPart() const { return ConstPart; }
107 void Invalidate() { SymbolicPart = OrigVal = nullptr; }
108 void setSymbolicRank(unsigned R) { SymbolicRank = R; }
114 unsigned SymbolicRank;
118 XorOpnd::XorOpnd(Value *V) {
119 assert(!isa<ConstantInt>(V) && "No ConstantInt");
121 Instruction *I = dyn_cast<Instruction>(V);
124 if (I && (I->getOpcode() == Instruction::Or ||
125 I->getOpcode() == Instruction::And)) {
126 Value *V0 = I->getOperand(0);
127 Value *V1 = I->getOperand(1);
129 if (match(V0, m_APInt(C)))
132 if (match(V1, m_APInt(C))) {
135 isOr = (I->getOpcode() == Instruction::Or);
140 // view the operand as "V | 0"
142 ConstPart = APInt::getNullValue(V->getType()->getScalarSizeInBits());
146 /// Return true if V is an instruction of the specified opcode and if it
147 /// only has one use.
148 static BinaryOperator *isReassociableOp(Value *V, unsigned Opcode) {
149 auto *I = dyn_cast<Instruction>(V);
150 if (I && I->hasOneUse() && I->getOpcode() == Opcode)
151 if (!isa<FPMathOperator>(I) || I->isFast())
152 return cast<BinaryOperator>(I);
156 static BinaryOperator *isReassociableOp(Value *V, unsigned Opcode1,
158 auto *I = dyn_cast<Instruction>(V);
159 if (I && I->hasOneUse() &&
160 (I->getOpcode() == Opcode1 || I->getOpcode() == Opcode2))
161 if (!isa<FPMathOperator>(I) || I->isFast())
162 return cast<BinaryOperator>(I);
166 void ReassociatePass::BuildRankMap(Function &F,
167 ReversePostOrderTraversal<Function*> &RPOT) {
170 // Assign distinct ranks to function arguments.
171 for (auto &Arg : F.args()) {
172 ValueRankMap[&Arg] = ++Rank;
173 LLVM_DEBUG(dbgs() << "Calculated Rank[" << Arg.getName() << "] = " << Rank
177 // Traverse basic blocks in ReversePostOrder
178 for (BasicBlock *BB : RPOT) {
179 unsigned BBRank = RankMap[BB] = ++Rank << 16;
181 // Walk the basic block, adding precomputed ranks for any instructions that
182 // we cannot move. This ensures that the ranks for these instructions are
183 // all different in the block.
184 for (Instruction &I : *BB)
185 if (mayBeMemoryDependent(I))
186 ValueRankMap[&I] = ++BBRank;
190 unsigned ReassociatePass::getRank(Value *V) {
191 Instruction *I = dyn_cast<Instruction>(V);
193 if (isa<Argument>(V)) return ValueRankMap[V]; // Function argument.
194 return 0; // Otherwise it's a global or constant, rank 0.
197 if (unsigned Rank = ValueRankMap[I])
198 return Rank; // Rank already known?
200 // If this is an expression, return the 1+MAX(rank(LHS), rank(RHS)) so that
201 // we can reassociate expressions for code motion! Since we do not recurse
202 // for PHI nodes, we cannot have infinite recursion here, because there
203 // cannot be loops in the value graph that do not go through PHI nodes.
204 unsigned Rank = 0, MaxRank = RankMap[I->getParent()];
205 for (unsigned i = 0, e = I->getNumOperands(); i != e && Rank != MaxRank; ++i)
206 Rank = std::max(Rank, getRank(I->getOperand(i)));
208 // If this is a 'not' or 'neg' instruction, do not count it for rank. This
209 // assures us that X and ~X will have the same rank.
210 if (!match(I, m_Not(m_Value())) && !match(I, m_Neg(m_Value())) &&
211 !match(I, m_FNeg(m_Value())))
214 LLVM_DEBUG(dbgs() << "Calculated Rank[" << V->getName() << "] = " << Rank
217 return ValueRankMap[I] = Rank;
220 // Canonicalize constants to RHS. Otherwise, sort the operands by rank.
221 void ReassociatePass::canonicalizeOperands(Instruction *I) {
222 assert(isa<BinaryOperator>(I) && "Expected binary operator.");
223 assert(I->isCommutative() && "Expected commutative operator.");
225 Value *LHS = I->getOperand(0);
226 Value *RHS = I->getOperand(1);
227 if (LHS == RHS || isa<Constant>(RHS))
229 if (isa<Constant>(LHS) || getRank(RHS) < getRank(LHS))
230 cast<BinaryOperator>(I)->swapOperands();
233 static BinaryOperator *CreateAdd(Value *S1, Value *S2, const Twine &Name,
234 Instruction *InsertBefore, Value *FlagsOp) {
235 if (S1->getType()->isIntOrIntVectorTy())
236 return BinaryOperator::CreateAdd(S1, S2, Name, InsertBefore);
238 BinaryOperator *Res =
239 BinaryOperator::CreateFAdd(S1, S2, Name, InsertBefore);
240 Res->setFastMathFlags(cast<FPMathOperator>(FlagsOp)->getFastMathFlags());
245 static BinaryOperator *CreateMul(Value *S1, Value *S2, const Twine &Name,
246 Instruction *InsertBefore, Value *FlagsOp) {
247 if (S1->getType()->isIntOrIntVectorTy())
248 return BinaryOperator::CreateMul(S1, S2, Name, InsertBefore);
250 BinaryOperator *Res =
251 BinaryOperator::CreateFMul(S1, S2, Name, InsertBefore);
252 Res->setFastMathFlags(cast<FPMathOperator>(FlagsOp)->getFastMathFlags());
257 static BinaryOperator *CreateNeg(Value *S1, const Twine &Name,
258 Instruction *InsertBefore, Value *FlagsOp) {
259 if (S1->getType()->isIntOrIntVectorTy())
260 return BinaryOperator::CreateNeg(S1, Name, InsertBefore);
262 BinaryOperator *Res = BinaryOperator::CreateFNeg(S1, Name, InsertBefore);
263 Res->setFastMathFlags(cast<FPMathOperator>(FlagsOp)->getFastMathFlags());
268 /// Replace 0-X with X*-1.
269 static BinaryOperator *LowerNegateToMultiply(Instruction *Neg) {
270 Type *Ty = Neg->getType();
271 Constant *NegOne = Ty->isIntOrIntVectorTy() ?
272 ConstantInt::getAllOnesValue(Ty) : ConstantFP::get(Ty, -1.0);
274 BinaryOperator *Res = CreateMul(Neg->getOperand(1), NegOne, "", Neg, Neg);
275 Neg->setOperand(1, Constant::getNullValue(Ty)); // Drop use of op.
277 Neg->replaceAllUsesWith(Res);
278 Res->setDebugLoc(Neg->getDebugLoc());
282 /// Returns k such that lambda(2^Bitwidth) = 2^k, where lambda is the Carmichael
283 /// function. This means that x^(2^k) === 1 mod 2^Bitwidth for
284 /// every odd x, i.e. x^(2^k) = 1 for every odd x in Bitwidth-bit arithmetic.
285 /// Note that 0 <= k < Bitwidth, and if Bitwidth > 3 then x^(2^k) = 0 for every
286 /// even x in Bitwidth-bit arithmetic.
287 static unsigned CarmichaelShift(unsigned Bitwidth) {
293 /// Add the extra weight 'RHS' to the existing weight 'LHS',
294 /// reducing the combined weight using any special properties of the operation.
295 /// The existing weight LHS represents the computation X op X op ... op X where
296 /// X occurs LHS times. The combined weight represents X op X op ... op X with
297 /// X occurring LHS + RHS times. If op is "Xor" for example then the combined
298 /// operation is equivalent to X if LHS + RHS is odd, or 0 if LHS + RHS is even;
299 /// the routine returns 1 in LHS in the first case, and 0 in LHS in the second.
300 static void IncorporateWeight(APInt &LHS, const APInt &RHS, unsigned Opcode) {
301 // If we were working with infinite precision arithmetic then the combined
302 // weight would be LHS + RHS. But we are using finite precision arithmetic,
303 // and the APInt sum LHS + RHS may not be correct if it wraps (it is correct
304 // for nilpotent operations and addition, but not for idempotent operations
305 // and multiplication), so it is important to correctly reduce the combined
306 // weight back into range if wrapping would be wrong.
308 // If RHS is zero then the weight didn't change.
309 if (RHS.isMinValue())
311 // If LHS is zero then the combined weight is RHS.
312 if (LHS.isMinValue()) {
316 // From this point on we know that neither LHS nor RHS is zero.
318 if (Instruction::isIdempotent(Opcode)) {
319 // Idempotent means X op X === X, so any non-zero weight is equivalent to a
320 // weight of 1. Keeping weights at zero or one also means that wrapping is
322 assert(LHS == 1 && RHS == 1 && "Weights not reduced!");
323 return; // Return a weight of 1.
325 if (Instruction::isNilpotent(Opcode)) {
326 // Nilpotent means X op X === 0, so reduce weights modulo 2.
327 assert(LHS == 1 && RHS == 1 && "Weights not reduced!");
328 LHS = 0; // 1 + 1 === 0 modulo 2.
331 if (Opcode == Instruction::Add || Opcode == Instruction::FAdd) {
332 // TODO: Reduce the weight by exploiting nsw/nuw?
337 assert((Opcode == Instruction::Mul || Opcode == Instruction::FMul) &&
338 "Unknown associative operation!");
339 unsigned Bitwidth = LHS.getBitWidth();
340 // If CM is the Carmichael number then a weight W satisfying W >= CM+Bitwidth
341 // can be replaced with W-CM. That's because x^W=x^(W-CM) for every Bitwidth
342 // bit number x, since either x is odd in which case x^CM = 1, or x is even in
343 // which case both x^W and x^(W - CM) are zero. By subtracting off multiples
344 // of CM like this weights can always be reduced to the range [0, CM+Bitwidth)
345 // which by a happy accident means that they can always be represented using
347 // TODO: Reduce the weight by exploiting nsw/nuw? (Could do much better than
348 // the Carmichael number).
350 /// CM - The value of Carmichael's lambda function.
351 APInt CM = APInt::getOneBitSet(Bitwidth, CarmichaelShift(Bitwidth));
352 // Any weight W >= Threshold can be replaced with W - CM.
353 APInt Threshold = CM + Bitwidth;
354 assert(LHS.ult(Threshold) && RHS.ult(Threshold) && "Weights not reduced!");
355 // For Bitwidth 4 or more the following sum does not overflow.
357 while (LHS.uge(Threshold))
360 // To avoid problems with overflow do everything the same as above but using
362 unsigned CM = 1U << CarmichaelShift(Bitwidth);
363 unsigned Threshold = CM + Bitwidth;
364 assert(LHS.getZExtValue() < Threshold && RHS.getZExtValue() < Threshold &&
365 "Weights not reduced!");
366 unsigned Total = LHS.getZExtValue() + RHS.getZExtValue();
367 while (Total >= Threshold)
373 using RepeatedValue = std::pair<Value*, APInt>;
375 /// Given an associative binary expression, return the leaf
376 /// nodes in Ops along with their weights (how many times the leaf occurs). The
377 /// original expression is the same as
378 /// (Ops[0].first op Ops[0].first op ... Ops[0].first) <- Ops[0].second times
380 /// (Ops[1].first op Ops[1].first op ... Ops[1].first) <- Ops[1].second times
384 /// (Ops[N].first op Ops[N].first op ... Ops[N].first) <- Ops[N].second times
386 /// Note that the values Ops[0].first, ..., Ops[N].first are all distinct.
388 /// This routine may modify the function, in which case it returns 'true'. The
389 /// changes it makes may well be destructive, changing the value computed by 'I'
390 /// to something completely different. Thus if the routine returns 'true' then
391 /// you MUST either replace I with a new expression computed from the Ops array,
392 /// or use RewriteExprTree to put the values back in.
394 /// A leaf node is either not a binary operation of the same kind as the root
395 /// node 'I' (i.e. is not a binary operator at all, or is, but with a different
396 /// opcode), or is the same kind of binary operator but has a use which either
397 /// does not belong to the expression, or does belong to the expression but is
398 /// a leaf node. Every leaf node has at least one use that is a non-leaf node
399 /// of the expression, while for non-leaf nodes (except for the root 'I') every
400 /// use is a non-leaf node of the expression.
403 /// expression graph node names
413 /// The leaf nodes are C, E, F and G. The Ops array will contain (maybe not in
414 /// that order) (C, 1), (E, 1), (F, 2), (G, 2).
416 /// The expression is maximal: if some instruction is a binary operator of the
417 /// same kind as 'I', and all of its uses are non-leaf nodes of the expression,
418 /// then the instruction also belongs to the expression, is not a leaf node of
419 /// it, and its operands also belong to the expression (but may be leaf nodes).
421 /// NOTE: This routine will set operands of non-leaf non-root nodes to undef in
422 /// order to ensure that every non-root node in the expression has *exactly one*
423 /// use by a non-leaf node of the expression. This destruction means that the
424 /// caller MUST either replace 'I' with a new expression or use something like
425 /// RewriteExprTree to put the values back in if the routine indicates that it
426 /// made a change by returning 'true'.
428 /// In the above example either the right operand of A or the left operand of B
429 /// will be replaced by undef. If it is B's operand then this gives:
433 /// + + | A, B - operand of B replaced with undef
439 /// Note that such undef operands can only be reached by passing through 'I'.
440 /// For example, if you visit operands recursively starting from a leaf node
441 /// then you will never see such an undef operand unless you get back to 'I',
442 /// which requires passing through a phi node.
444 /// Note that this routine may also mutate binary operators of the wrong type
445 /// that have all uses inside the expression (i.e. only used by non-leaf nodes
446 /// of the expression) if it can turn them into binary operators of the right
447 /// type and thus make the expression bigger.
448 static bool LinearizeExprTree(BinaryOperator *I,
449 SmallVectorImpl<RepeatedValue> &Ops) {
450 LLVM_DEBUG(dbgs() << "LINEARIZE: " << *I << '\n');
451 unsigned Bitwidth = I->getType()->getScalarType()->getPrimitiveSizeInBits();
452 unsigned Opcode = I->getOpcode();
453 assert(I->isAssociative() && I->isCommutative() &&
454 "Expected an associative and commutative operation!");
456 // Visit all operands of the expression, keeping track of their weight (the
457 // number of paths from the expression root to the operand, or if you like
458 // the number of times that operand occurs in the linearized expression).
459 // For example, if I = X + A, where X = A + B, then I, X and B have weight 1
460 // while A has weight two.
462 // Worklist of non-leaf nodes (their operands are in the expression too) along
463 // with their weights, representing a certain number of paths to the operator.
464 // If an operator occurs in the worklist multiple times then we found multiple
465 // ways to get to it.
466 SmallVector<std::pair<BinaryOperator*, APInt>, 8> Worklist; // (Op, Weight)
467 Worklist.push_back(std::make_pair(I, APInt(Bitwidth, 1)));
468 bool Changed = false;
470 // Leaves of the expression are values that either aren't the right kind of
471 // operation (eg: a constant, or a multiply in an add tree), or are, but have
472 // some uses that are not inside the expression. For example, in I = X + X,
473 // X = A + B, the value X has two uses (by I) that are in the expression. If
474 // X has any other uses, for example in a return instruction, then we consider
475 // X to be a leaf, and won't analyze it further. When we first visit a value,
476 // if it has more than one use then at first we conservatively consider it to
477 // be a leaf. Later, as the expression is explored, we may discover some more
478 // uses of the value from inside the expression. If all uses turn out to be
479 // from within the expression (and the value is a binary operator of the right
480 // kind) then the value is no longer considered to be a leaf, and its operands
483 // Leaves - Keeps track of the set of putative leaves as well as the number of
484 // paths to each leaf seen so far.
485 using LeafMap = DenseMap<Value *, APInt>;
486 LeafMap Leaves; // Leaf -> Total weight so far.
487 SmallVector<Value *, 8> LeafOrder; // Ensure deterministic leaf output order.
490 SmallPtrSet<Value *, 8> Visited; // For sanity checking the iteration scheme.
492 while (!Worklist.empty()) {
493 std::pair<BinaryOperator*, APInt> P = Worklist.pop_back_val();
494 I = P.first; // We examine the operands of this binary operator.
496 for (unsigned OpIdx = 0; OpIdx < 2; ++OpIdx) { // Visit operands.
497 Value *Op = I->getOperand(OpIdx);
498 APInt Weight = P.second; // Number of paths to this operand.
499 LLVM_DEBUG(dbgs() << "OPERAND: " << *Op << " (" << Weight << ")\n");
500 assert(!Op->use_empty() && "No uses, so how did we get to it?!");
502 // If this is a binary operation of the right kind with only one use then
503 // add its operands to the expression.
504 if (BinaryOperator *BO = isReassociableOp(Op, Opcode)) {
505 assert(Visited.insert(Op).second && "Not first visit!");
506 LLVM_DEBUG(dbgs() << "DIRECT ADD: " << *Op << " (" << Weight << ")\n");
507 Worklist.push_back(std::make_pair(BO, Weight));
511 // Appears to be a leaf. Is the operand already in the set of leaves?
512 LeafMap::iterator It = Leaves.find(Op);
513 if (It == Leaves.end()) {
514 // Not in the leaf map. Must be the first time we saw this operand.
515 assert(Visited.insert(Op).second && "Not first visit!");
516 if (!Op->hasOneUse()) {
517 // This value has uses not accounted for by the expression, so it is
518 // not safe to modify. Mark it as being a leaf.
520 << "ADD USES LEAF: " << *Op << " (" << Weight << ")\n");
521 LeafOrder.push_back(Op);
525 // No uses outside the expression, try morphing it.
527 // Already in the leaf map.
528 assert(It != Leaves.end() && Visited.count(Op) &&
529 "In leaf map but not visited!");
531 // Update the number of paths to the leaf.
532 IncorporateWeight(It->second, Weight, Opcode);
534 #if 0 // TODO: Re-enable once PR13021 is fixed.
535 // The leaf already has one use from inside the expression. As we want
536 // exactly one such use, drop this new use of the leaf.
537 assert(!Op->hasOneUse() && "Only one use, but we got here twice!");
538 I->setOperand(OpIdx, UndefValue::get(I->getType()));
541 // If the leaf is a binary operation of the right kind and we now see
542 // that its multiple original uses were in fact all by nodes belonging
543 // to the expression, then no longer consider it to be a leaf and add
544 // its operands to the expression.
545 if (BinaryOperator *BO = isReassociableOp(Op, Opcode)) {
546 LLVM_DEBUG(dbgs() << "UNLEAF: " << *Op << " (" << It->second << ")\n");
547 Worklist.push_back(std::make_pair(BO, It->second));
553 // If we still have uses that are not accounted for by the expression
554 // then it is not safe to modify the value.
555 if (!Op->hasOneUse())
558 // No uses outside the expression, try morphing it.
560 Leaves.erase(It); // Since the value may be morphed below.
563 // At this point we have a value which, first of all, is not a binary
564 // expression of the right kind, and secondly, is only used inside the
565 // expression. This means that it can safely be modified. See if we
566 // can usefully morph it into an expression of the right kind.
567 assert((!isa<Instruction>(Op) ||
568 cast<Instruction>(Op)->getOpcode() != Opcode
569 || (isa<FPMathOperator>(Op) &&
570 !cast<Instruction>(Op)->isFast())) &&
571 "Should have been handled above!");
572 assert(Op->hasOneUse() && "Has uses outside the expression tree!");
574 // If this is a multiply expression, turn any internal negations into
575 // multiplies by -1 so they can be reassociated.
576 if (BinaryOperator *BO = dyn_cast<BinaryOperator>(Op))
577 if ((Opcode == Instruction::Mul && match(BO, m_Neg(m_Value()))) ||
578 (Opcode == Instruction::FMul && match(BO, m_FNeg(m_Value())))) {
580 << "MORPH LEAF: " << *Op << " (" << Weight << ") TO ");
581 BO = LowerNegateToMultiply(BO);
582 LLVM_DEBUG(dbgs() << *BO << '\n');
583 Worklist.push_back(std::make_pair(BO, Weight));
588 // Failed to morph into an expression of the right type. This really is
590 LLVM_DEBUG(dbgs() << "ADD LEAF: " << *Op << " (" << Weight << ")\n");
591 assert(!isReassociableOp(Op, Opcode) && "Value was morphed?");
592 LeafOrder.push_back(Op);
597 // The leaves, repeated according to their weights, represent the linearized
598 // form of the expression.
599 for (unsigned i = 0, e = LeafOrder.size(); i != e; ++i) {
600 Value *V = LeafOrder[i];
601 LeafMap::iterator It = Leaves.find(V);
602 if (It == Leaves.end())
603 // Node initially thought to be a leaf wasn't.
605 assert(!isReassociableOp(V, Opcode) && "Shouldn't be a leaf!");
606 APInt Weight = It->second;
607 if (Weight.isMinValue())
608 // Leaf already output or weight reduction eliminated it.
610 // Ensure the leaf is only output once.
612 Ops.push_back(std::make_pair(V, Weight));
615 // For nilpotent operations or addition there may be no operands, for example
616 // because the expression was "X xor X" or consisted of 2^Bitwidth additions:
617 // in both cases the weight reduces to 0 causing the value to be skipped.
619 Constant *Identity = ConstantExpr::getBinOpIdentity(Opcode, I->getType());
620 assert(Identity && "Associative operation without identity!");
621 Ops.emplace_back(Identity, APInt(Bitwidth, 1));
627 /// Now that the operands for this expression tree are
628 /// linearized and optimized, emit them in-order.
629 void ReassociatePass::RewriteExprTree(BinaryOperator *I,
630 SmallVectorImpl<ValueEntry> &Ops) {
631 assert(Ops.size() > 1 && "Single values should be used directly!");
633 // Since our optimizations should never increase the number of operations, the
634 // new expression can usually be written reusing the existing binary operators
635 // from the original expression tree, without creating any new instructions,
636 // though the rewritten expression may have a completely different topology.
637 // We take care to not change anything if the new expression will be the same
638 // as the original. If more than trivial changes (like commuting operands)
639 // were made then we are obliged to clear out any optional subclass data like
642 /// NodesToRewrite - Nodes from the original expression available for writing
643 /// the new expression into.
644 SmallVector<BinaryOperator*, 8> NodesToRewrite;
645 unsigned Opcode = I->getOpcode();
646 BinaryOperator *Op = I;
648 /// NotRewritable - The operands being written will be the leaves of the new
649 /// expression and must not be used as inner nodes (via NodesToRewrite) by
650 /// mistake. Inner nodes are always reassociable, and usually leaves are not
651 /// (if they were they would have been incorporated into the expression and so
652 /// would not be leaves), so most of the time there is no danger of this. But
653 /// in rare cases a leaf may become reassociable if an optimization kills uses
654 /// of it, or it may momentarily become reassociable during rewriting (below)
655 /// due it being removed as an operand of one of its uses. Ensure that misuse
656 /// of leaf nodes as inner nodes cannot occur by remembering all of the future
657 /// leaves and refusing to reuse any of them as inner nodes.
658 SmallPtrSet<Value*, 8> NotRewritable;
659 for (unsigned i = 0, e = Ops.size(); i != e; ++i)
660 NotRewritable.insert(Ops[i].Op);
662 // ExpressionChanged - Non-null if the rewritten expression differs from the
663 // original in some non-trivial way, requiring the clearing of optional flags.
664 // Flags are cleared from the operator in ExpressionChanged up to I inclusive.
665 BinaryOperator *ExpressionChanged = nullptr;
666 for (unsigned i = 0; ; ++i) {
667 // The last operation (which comes earliest in the IR) is special as both
668 // operands will come from Ops, rather than just one with the other being
670 if (i+2 == Ops.size()) {
671 Value *NewLHS = Ops[i].Op;
672 Value *NewRHS = Ops[i+1].Op;
673 Value *OldLHS = Op->getOperand(0);
674 Value *OldRHS = Op->getOperand(1);
676 if (NewLHS == OldLHS && NewRHS == OldRHS)
677 // Nothing changed, leave it alone.
680 if (NewLHS == OldRHS && NewRHS == OldLHS) {
681 // The order of the operands was reversed. Swap them.
682 LLVM_DEBUG(dbgs() << "RA: " << *Op << '\n');
684 LLVM_DEBUG(dbgs() << "TO: " << *Op << '\n');
690 // The new operation differs non-trivially from the original. Overwrite
691 // the old operands with the new ones.
692 LLVM_DEBUG(dbgs() << "RA: " << *Op << '\n');
693 if (NewLHS != OldLHS) {
694 BinaryOperator *BO = isReassociableOp(OldLHS, Opcode);
695 if (BO && !NotRewritable.count(BO))
696 NodesToRewrite.push_back(BO);
697 Op->setOperand(0, NewLHS);
699 if (NewRHS != OldRHS) {
700 BinaryOperator *BO = isReassociableOp(OldRHS, Opcode);
701 if (BO && !NotRewritable.count(BO))
702 NodesToRewrite.push_back(BO);
703 Op->setOperand(1, NewRHS);
705 LLVM_DEBUG(dbgs() << "TO: " << *Op << '\n');
707 ExpressionChanged = Op;
714 // Not the last operation. The left-hand side will be a sub-expression
715 // while the right-hand side will be the current element of Ops.
716 Value *NewRHS = Ops[i].Op;
717 if (NewRHS != Op->getOperand(1)) {
718 LLVM_DEBUG(dbgs() << "RA: " << *Op << '\n');
719 if (NewRHS == Op->getOperand(0)) {
720 // The new right-hand side was already present as the left operand. If
721 // we are lucky then swapping the operands will sort out both of them.
724 // Overwrite with the new right-hand side.
725 BinaryOperator *BO = isReassociableOp(Op->getOperand(1), Opcode);
726 if (BO && !NotRewritable.count(BO))
727 NodesToRewrite.push_back(BO);
728 Op->setOperand(1, NewRHS);
729 ExpressionChanged = Op;
731 LLVM_DEBUG(dbgs() << "TO: " << *Op << '\n');
736 // Now deal with the left-hand side. If this is already an operation node
737 // from the original expression then just rewrite the rest of the expression
739 BinaryOperator *BO = isReassociableOp(Op->getOperand(0), Opcode);
740 if (BO && !NotRewritable.count(BO)) {
745 // Otherwise, grab a spare node from the original expression and use that as
746 // the left-hand side. If there are no nodes left then the optimizers made
747 // an expression with more nodes than the original! This usually means that
748 // they did something stupid but it might mean that the problem was just too
749 // hard (finding the mimimal number of multiplications needed to realize a
750 // multiplication expression is NP-complete). Whatever the reason, smart or
751 // stupid, create a new node if there are none left.
752 BinaryOperator *NewOp;
753 if (NodesToRewrite.empty()) {
754 Constant *Undef = UndefValue::get(I->getType());
755 NewOp = BinaryOperator::Create(Instruction::BinaryOps(Opcode),
756 Undef, Undef, "", I);
757 if (NewOp->getType()->isFPOrFPVectorTy())
758 NewOp->setFastMathFlags(I->getFastMathFlags());
760 NewOp = NodesToRewrite.pop_back_val();
763 LLVM_DEBUG(dbgs() << "RA: " << *Op << '\n');
764 Op->setOperand(0, NewOp);
765 LLVM_DEBUG(dbgs() << "TO: " << *Op << '\n');
766 ExpressionChanged = Op;
772 // If the expression changed non-trivially then clear out all subclass data
773 // starting from the operator specified in ExpressionChanged, and compactify
774 // the operators to just before the expression root to guarantee that the
775 // expression tree is dominated by all of Ops.
776 if (ExpressionChanged)
778 // Preserve FastMathFlags.
779 if (isa<FPMathOperator>(I)) {
780 FastMathFlags Flags = I->getFastMathFlags();
781 ExpressionChanged->clearSubclassOptionalData();
782 ExpressionChanged->setFastMathFlags(Flags);
784 ExpressionChanged->clearSubclassOptionalData();
786 if (ExpressionChanged == I)
789 // Discard any debug info related to the expressions that has changed (we
790 // can leave debug infor related to the root, since the result of the
791 // expression tree should be the same even after reassociation).
792 replaceDbgUsesWithUndef(ExpressionChanged);
794 ExpressionChanged->moveBefore(I);
795 ExpressionChanged = cast<BinaryOperator>(*ExpressionChanged->user_begin());
798 // Throw away any left over nodes from the original expression.
799 for (unsigned i = 0, e = NodesToRewrite.size(); i != e; ++i)
800 RedoInsts.insert(NodesToRewrite[i]);
803 /// Insert instructions before the instruction pointed to by BI,
804 /// that computes the negative version of the value specified. The negative
805 /// version of the value is returned, and BI is left pointing at the instruction
806 /// that should be processed next by the reassociation pass.
807 /// Also add intermediate instructions to the redo list that are modified while
808 /// pushing the negates through adds. These will be revisited to see if
809 /// additional opportunities have been exposed.
810 static Value *NegateValue(Value *V, Instruction *BI,
811 ReassociatePass::OrderedSet &ToRedo) {
812 if (auto *C = dyn_cast<Constant>(V))
813 return C->getType()->isFPOrFPVectorTy() ? ConstantExpr::getFNeg(C) :
814 ConstantExpr::getNeg(C);
816 // We are trying to expose opportunity for reassociation. One of the things
817 // that we want to do to achieve this is to push a negation as deep into an
818 // expression chain as possible, to expose the add instructions. In practice,
819 // this means that we turn this:
820 // X = -(A+12+C+D) into X = -A + -12 + -C + -D = -12 + -A + -C + -D
821 // so that later, a: Y = 12+X could get reassociated with the -12 to eliminate
822 // the constants. We assume that instcombine will clean up the mess later if
823 // we introduce tons of unnecessary negation instructions.
825 if (BinaryOperator *I =
826 isReassociableOp(V, Instruction::Add, Instruction::FAdd)) {
827 // Push the negates through the add.
828 I->setOperand(0, NegateValue(I->getOperand(0), BI, ToRedo));
829 I->setOperand(1, NegateValue(I->getOperand(1), BI, ToRedo));
830 if (I->getOpcode() == Instruction::Add) {
831 I->setHasNoUnsignedWrap(false);
832 I->setHasNoSignedWrap(false);
835 // We must move the add instruction here, because the neg instructions do
836 // not dominate the old add instruction in general. By moving it, we are
837 // assured that the neg instructions we just inserted dominate the
838 // instruction we are about to insert after them.
841 I->setName(I->getName()+".neg");
843 // Add the intermediate negates to the redo list as processing them later
844 // could expose more reassociating opportunities.
849 // Okay, we need to materialize a negated version of V with an instruction.
850 // Scan the use lists of V to see if we have one already.
851 for (User *U : V->users()) {
852 if (!match(U, m_Neg(m_Value())) && !match(U, m_FNeg(m_Value())))
855 // We found one! Now we have to make sure that the definition dominates
856 // this use. We do this by moving it to the entry block (if it is a
857 // non-instruction value) or right after the definition. These negates will
858 // be zapped by reassociate later, so we don't need much finesse here.
859 BinaryOperator *TheNeg = cast<BinaryOperator>(U);
861 // Verify that the negate is in this function, V might be a constant expr.
862 if (TheNeg->getParent()->getParent() != BI->getParent()->getParent())
865 BasicBlock::iterator InsertPt;
866 if (Instruction *InstInput = dyn_cast<Instruction>(V)) {
867 if (InvokeInst *II = dyn_cast<InvokeInst>(InstInput)) {
868 InsertPt = II->getNormalDest()->begin();
870 InsertPt = ++InstInput->getIterator();
872 while (isa<PHINode>(InsertPt)) ++InsertPt;
874 InsertPt = TheNeg->getParent()->getParent()->getEntryBlock().begin();
876 TheNeg->moveBefore(&*InsertPt);
877 if (TheNeg->getOpcode() == Instruction::Sub) {
878 TheNeg->setHasNoUnsignedWrap(false);
879 TheNeg->setHasNoSignedWrap(false);
881 TheNeg->andIRFlags(BI);
883 ToRedo.insert(TheNeg);
887 // Insert a 'neg' instruction that subtracts the value from zero to get the
889 BinaryOperator *NewNeg = CreateNeg(V, V->getName() + ".neg", BI, BI);
890 ToRedo.insert(NewNeg);
894 /// Return true if we should break up this subtract of X-Y into (X + -Y).
895 static bool ShouldBreakUpSubtract(Instruction *Sub) {
896 // If this is a negation, we can't split it up!
897 if (match(Sub, m_Neg(m_Value())) || match(Sub, m_FNeg(m_Value())))
900 // Don't breakup X - undef.
901 if (isa<UndefValue>(Sub->getOperand(1)))
904 // Don't bother to break this up unless either the LHS is an associable add or
905 // subtract or if this is only used by one.
906 Value *V0 = Sub->getOperand(0);
907 if (isReassociableOp(V0, Instruction::Add, Instruction::FAdd) ||
908 isReassociableOp(V0, Instruction::Sub, Instruction::FSub))
910 Value *V1 = Sub->getOperand(1);
911 if (isReassociableOp(V1, Instruction::Add, Instruction::FAdd) ||
912 isReassociableOp(V1, Instruction::Sub, Instruction::FSub))
914 Value *VB = Sub->user_back();
915 if (Sub->hasOneUse() &&
916 (isReassociableOp(VB, Instruction::Add, Instruction::FAdd) ||
917 isReassociableOp(VB, Instruction::Sub, Instruction::FSub)))
923 /// If we have (X-Y), and if either X is an add, or if this is only used by an
924 /// add, transform this into (X+(0-Y)) to promote better reassociation.
925 static BinaryOperator *BreakUpSubtract(Instruction *Sub,
926 ReassociatePass::OrderedSet &ToRedo) {
927 // Convert a subtract into an add and a neg instruction. This allows sub
928 // instructions to be commuted with other add instructions.
930 // Calculate the negative value of Operand 1 of the sub instruction,
931 // and set it as the RHS of the add instruction we just made.
932 Value *NegVal = NegateValue(Sub->getOperand(1), Sub, ToRedo);
933 BinaryOperator *New = CreateAdd(Sub->getOperand(0), NegVal, "", Sub, Sub);
934 Sub->setOperand(0, Constant::getNullValue(Sub->getType())); // Drop use of op.
935 Sub->setOperand(1, Constant::getNullValue(Sub->getType())); // Drop use of op.
938 // Everyone now refers to the add instruction.
939 Sub->replaceAllUsesWith(New);
940 New->setDebugLoc(Sub->getDebugLoc());
942 LLVM_DEBUG(dbgs() << "Negated: " << *New << '\n');
946 /// If this is a shift of a reassociable multiply or is used by one, change
947 /// this into a multiply by a constant to assist with further reassociation.
948 static BinaryOperator *ConvertShiftToMul(Instruction *Shl) {
949 Constant *MulCst = ConstantInt::get(Shl->getType(), 1);
950 MulCst = ConstantExpr::getShl(MulCst, cast<Constant>(Shl->getOperand(1)));
952 BinaryOperator *Mul =
953 BinaryOperator::CreateMul(Shl->getOperand(0), MulCst, "", Shl);
954 Shl->setOperand(0, UndefValue::get(Shl->getType())); // Drop use of op.
957 // Everyone now refers to the mul instruction.
958 Shl->replaceAllUsesWith(Mul);
959 Mul->setDebugLoc(Shl->getDebugLoc());
961 // We can safely preserve the nuw flag in all cases. It's also safe to turn a
962 // nuw nsw shl into a nuw nsw mul. However, nsw in isolation requires special
964 bool NSW = cast<BinaryOperator>(Shl)->hasNoSignedWrap();
965 bool NUW = cast<BinaryOperator>(Shl)->hasNoUnsignedWrap();
967 Mul->setHasNoSignedWrap(true);
968 Mul->setHasNoUnsignedWrap(NUW);
972 /// Scan backwards and forwards among values with the same rank as element i
973 /// to see if X exists. If X does not exist, return i. This is useful when
974 /// scanning for 'x' when we see '-x' because they both get the same rank.
975 static unsigned FindInOperandList(const SmallVectorImpl<ValueEntry> &Ops,
976 unsigned i, Value *X) {
977 unsigned XRank = Ops[i].Rank;
978 unsigned e = Ops.size();
979 for (unsigned j = i+1; j != e && Ops[j].Rank == XRank; ++j) {
982 if (Instruction *I1 = dyn_cast<Instruction>(Ops[j].Op))
983 if (Instruction *I2 = dyn_cast<Instruction>(X))
984 if (I1->isIdenticalTo(I2))
988 for (unsigned j = i-1; j != ~0U && Ops[j].Rank == XRank; --j) {
991 if (Instruction *I1 = dyn_cast<Instruction>(Ops[j].Op))
992 if (Instruction *I2 = dyn_cast<Instruction>(X))
993 if (I1->isIdenticalTo(I2))
999 /// Emit a tree of add instructions, summing Ops together
1000 /// and returning the result. Insert the tree before I.
1001 static Value *EmitAddTreeOfValues(Instruction *I,
1002 SmallVectorImpl<WeakTrackingVH> &Ops) {
1003 if (Ops.size() == 1) return Ops.back();
1005 Value *V1 = Ops.back();
1007 Value *V2 = EmitAddTreeOfValues(I, Ops);
1008 return CreateAdd(V2, V1, "reass.add", I, I);
1011 /// If V is an expression tree that is a multiplication sequence,
1012 /// and if this sequence contains a multiply by Factor,
1013 /// remove Factor from the tree and return the new tree.
1014 Value *ReassociatePass::RemoveFactorFromExpression(Value *V, Value *Factor) {
1015 BinaryOperator *BO = isReassociableOp(V, Instruction::Mul, Instruction::FMul);
1019 SmallVector<RepeatedValue, 8> Tree;
1020 MadeChange |= LinearizeExprTree(BO, Tree);
1021 SmallVector<ValueEntry, 8> Factors;
1022 Factors.reserve(Tree.size());
1023 for (unsigned i = 0, e = Tree.size(); i != e; ++i) {
1024 RepeatedValue E = Tree[i];
1025 Factors.append(E.second.getZExtValue(),
1026 ValueEntry(getRank(E.first), E.first));
1029 bool FoundFactor = false;
1030 bool NeedsNegate = false;
1031 for (unsigned i = 0, e = Factors.size(); i != e; ++i) {
1032 if (Factors[i].Op == Factor) {
1034 Factors.erase(Factors.begin()+i);
1038 // If this is a negative version of this factor, remove it.
1039 if (ConstantInt *FC1 = dyn_cast<ConstantInt>(Factor)) {
1040 if (ConstantInt *FC2 = dyn_cast<ConstantInt>(Factors[i].Op))
1041 if (FC1->getValue() == -FC2->getValue()) {
1042 FoundFactor = NeedsNegate = true;
1043 Factors.erase(Factors.begin()+i);
1046 } else if (ConstantFP *FC1 = dyn_cast<ConstantFP>(Factor)) {
1047 if (ConstantFP *FC2 = dyn_cast<ConstantFP>(Factors[i].Op)) {
1048 const APFloat &F1 = FC1->getValueAPF();
1049 APFloat F2(FC2->getValueAPF());
1051 if (F1.compare(F2) == APFloat::cmpEqual) {
1052 FoundFactor = NeedsNegate = true;
1053 Factors.erase(Factors.begin() + i);
1061 // Make sure to restore the operands to the expression tree.
1062 RewriteExprTree(BO, Factors);
1066 BasicBlock::iterator InsertPt = ++BO->getIterator();
1068 // If this was just a single multiply, remove the multiply and return the only
1069 // remaining operand.
1070 if (Factors.size() == 1) {
1071 RedoInsts.insert(BO);
1074 RewriteExprTree(BO, Factors);
1079 V = CreateNeg(V, "neg", &*InsertPt, BO);
1084 /// If V is a single-use multiply, recursively add its operands as factors,
1085 /// otherwise add V to the list of factors.
1087 /// Ops is the top-level list of add operands we're trying to factor.
1088 static void FindSingleUseMultiplyFactors(Value *V,
1089 SmallVectorImpl<Value*> &Factors) {
1090 BinaryOperator *BO = isReassociableOp(V, Instruction::Mul, Instruction::FMul);
1092 Factors.push_back(V);
1096 // Otherwise, add the LHS and RHS to the list of factors.
1097 FindSingleUseMultiplyFactors(BO->getOperand(1), Factors);
1098 FindSingleUseMultiplyFactors(BO->getOperand(0), Factors);
1101 /// Optimize a series of operands to an 'and', 'or', or 'xor' instruction.
1102 /// This optimizes based on identities. If it can be reduced to a single Value,
1103 /// it is returned, otherwise the Ops list is mutated as necessary.
1104 static Value *OptimizeAndOrXor(unsigned Opcode,
1105 SmallVectorImpl<ValueEntry> &Ops) {
1106 // Scan the operand lists looking for X and ~X pairs, along with X,X pairs.
1107 // If we find any, we can simplify the expression. X&~X == 0, X|~X == -1.
1108 for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
1109 // First, check for X and ~X in the operand list.
1110 assert(i < Ops.size());
1112 if (match(Ops[i].Op, m_Not(m_Value(X)))) { // Cannot occur for ^.
1113 unsigned FoundX = FindInOperandList(Ops, i, X);
1115 if (Opcode == Instruction::And) // ...&X&~X = 0
1116 return Constant::getNullValue(X->getType());
1118 if (Opcode == Instruction::Or) // ...|X|~X = -1
1119 return Constant::getAllOnesValue(X->getType());
1123 // Next, check for duplicate pairs of values, which we assume are next to
1124 // each other, due to our sorting criteria.
1125 assert(i < Ops.size());
1126 if (i+1 != Ops.size() && Ops[i+1].Op == Ops[i].Op) {
1127 if (Opcode == Instruction::And || Opcode == Instruction::Or) {
1128 // Drop duplicate values for And and Or.
1129 Ops.erase(Ops.begin()+i);
1135 // Drop pairs of values for Xor.
1136 assert(Opcode == Instruction::Xor);
1138 return Constant::getNullValue(Ops[0].Op->getType());
1141 Ops.erase(Ops.begin()+i, Ops.begin()+i+2);
1149 /// Helper function of CombineXorOpnd(). It creates a bitwise-and
1150 /// instruction with the given two operands, and return the resulting
1151 /// instruction. There are two special cases: 1) if the constant operand is 0,
1152 /// it will return NULL. 2) if the constant is ~0, the symbolic operand will
1154 static Value *createAndInstr(Instruction *InsertBefore, Value *Opnd,
1155 const APInt &ConstOpnd) {
1156 if (ConstOpnd.isNullValue())
1159 if (ConstOpnd.isAllOnesValue())
1162 Instruction *I = BinaryOperator::CreateAnd(
1163 Opnd, ConstantInt::get(Opnd->getType(), ConstOpnd), "and.ra",
1165 I->setDebugLoc(InsertBefore->getDebugLoc());
1169 // Helper function of OptimizeXor(). It tries to simplify "Opnd1 ^ ConstOpnd"
1170 // into "R ^ C", where C would be 0, and R is a symbolic value.
1172 // If it was successful, true is returned, and the "R" and "C" is returned
1173 // via "Res" and "ConstOpnd", respectively; otherwise, false is returned,
1174 // and both "Res" and "ConstOpnd" remain unchanged.
1175 bool ReassociatePass::CombineXorOpnd(Instruction *I, XorOpnd *Opnd1,
1176 APInt &ConstOpnd, Value *&Res) {
1177 // Xor-Rule 1: (x | c1) ^ c2 = (x | c1) ^ (c1 ^ c1) ^ c2
1178 // = ((x | c1) ^ c1) ^ (c1 ^ c2)
1179 // = (x & ~c1) ^ (c1 ^ c2)
1180 // It is useful only when c1 == c2.
1181 if (!Opnd1->isOrExpr() || Opnd1->getConstPart().isNullValue())
1184 if (!Opnd1->getValue()->hasOneUse())
1187 const APInt &C1 = Opnd1->getConstPart();
1188 if (C1 != ConstOpnd)
1191 Value *X = Opnd1->getSymbolicPart();
1192 Res = createAndInstr(I, X, ~C1);
1193 // ConstOpnd was C2, now C1 ^ C2.
1196 if (Instruction *T = dyn_cast<Instruction>(Opnd1->getValue()))
1197 RedoInsts.insert(T);
1201 // Helper function of OptimizeXor(). It tries to simplify
1202 // "Opnd1 ^ Opnd2 ^ ConstOpnd" into "R ^ C", where C would be 0, and R is a
1205 // If it was successful, true is returned, and the "R" and "C" is returned
1206 // via "Res" and "ConstOpnd", respectively (If the entire expression is
1207 // evaluated to a constant, the Res is set to NULL); otherwise, false is
1208 // returned, and both "Res" and "ConstOpnd" remain unchanged.
1209 bool ReassociatePass::CombineXorOpnd(Instruction *I, XorOpnd *Opnd1,
1210 XorOpnd *Opnd2, APInt &ConstOpnd,
1212 Value *X = Opnd1->getSymbolicPart();
1213 if (X != Opnd2->getSymbolicPart())
1216 // This many instruction become dead.(At least "Opnd1 ^ Opnd2" will die.)
1217 int DeadInstNum = 1;
1218 if (Opnd1->getValue()->hasOneUse())
1220 if (Opnd2->getValue()->hasOneUse())
1224 // (x | c1) ^ (x & c2)
1225 // = (x|c1) ^ (x&c2) ^ (c1 ^ c1) = ((x|c1) ^ c1) ^ (x & c2) ^ c1
1226 // = (x & ~c1) ^ (x & c2) ^ c1 // Xor-Rule 1
1227 // = (x & c3) ^ c1, where c3 = ~c1 ^ c2 // Xor-rule 3
1229 if (Opnd1->isOrExpr() != Opnd2->isOrExpr()) {
1230 if (Opnd2->isOrExpr())
1231 std::swap(Opnd1, Opnd2);
1233 const APInt &C1 = Opnd1->getConstPart();
1234 const APInt &C2 = Opnd2->getConstPart();
1235 APInt C3((~C1) ^ C2);
1237 // Do not increase code size!
1238 if (!C3.isNullValue() && !C3.isAllOnesValue()) {
1239 int NewInstNum = ConstOpnd.getBoolValue() ? 1 : 2;
1240 if (NewInstNum > DeadInstNum)
1244 Res = createAndInstr(I, X, C3);
1246 } else if (Opnd1->isOrExpr()) {
1247 // Xor-Rule 3: (x | c1) ^ (x | c2) = (x & c3) ^ c3 where c3 = c1 ^ c2
1249 const APInt &C1 = Opnd1->getConstPart();
1250 const APInt &C2 = Opnd2->getConstPart();
1253 // Do not increase code size
1254 if (!C3.isNullValue() && !C3.isAllOnesValue()) {
1255 int NewInstNum = ConstOpnd.getBoolValue() ? 1 : 2;
1256 if (NewInstNum > DeadInstNum)
1260 Res = createAndInstr(I, X, C3);
1263 // Xor-Rule 4: (x & c1) ^ (x & c2) = (x & (c1^c2))
1265 const APInt &C1 = Opnd1->getConstPart();
1266 const APInt &C2 = Opnd2->getConstPart();
1268 Res = createAndInstr(I, X, C3);
1271 // Put the original operands in the Redo list; hope they will be deleted
1273 if (Instruction *T = dyn_cast<Instruction>(Opnd1->getValue()))
1274 RedoInsts.insert(T);
1275 if (Instruction *T = dyn_cast<Instruction>(Opnd2->getValue()))
1276 RedoInsts.insert(T);
1281 /// Optimize a series of operands to an 'xor' instruction. If it can be reduced
1282 /// to a single Value, it is returned, otherwise the Ops list is mutated as
1284 Value *ReassociatePass::OptimizeXor(Instruction *I,
1285 SmallVectorImpl<ValueEntry> &Ops) {
1286 if (Value *V = OptimizeAndOrXor(Instruction::Xor, Ops))
1289 if (Ops.size() == 1)
1292 SmallVector<XorOpnd, 8> Opnds;
1293 SmallVector<XorOpnd*, 8> OpndPtrs;
1294 Type *Ty = Ops[0].Op->getType();
1295 APInt ConstOpnd(Ty->getScalarSizeInBits(), 0);
1297 // Step 1: Convert ValueEntry to XorOpnd
1298 for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
1299 Value *V = Ops[i].Op;
1301 // TODO: Support non-splat vectors.
1302 if (match(V, m_APInt(C))) {
1306 O.setSymbolicRank(getRank(O.getSymbolicPart()));
1311 // NOTE: From this point on, do *NOT* add/delete element to/from "Opnds".
1312 // It would otherwise invalidate the "Opnds"'s iterator, and hence invalidate
1313 // the "OpndPtrs" as well. For the similar reason, do not fuse this loop
1314 // with the previous loop --- the iterator of the "Opnds" may be invalidated
1315 // when new elements are added to the vector.
1316 for (unsigned i = 0, e = Opnds.size(); i != e; ++i)
1317 OpndPtrs.push_back(&Opnds[i]);
1319 // Step 2: Sort the Xor-Operands in a way such that the operands containing
1320 // the same symbolic value cluster together. For instance, the input operand
1321 // sequence ("x | 123", "y & 456", "x & 789") will be sorted into:
1322 // ("x | 123", "x & 789", "y & 456").
1324 // The purpose is twofold:
1325 // 1) Cluster together the operands sharing the same symbolic-value.
1326 // 2) Operand having smaller symbolic-value-rank is permuted earlier, which
1327 // could potentially shorten crital path, and expose more loop-invariants.
1328 // Note that values' rank are basically defined in RPO order (FIXME).
1329 // So, if Rank(X) < Rank(Y) < Rank(Z), it means X is defined earlier
1330 // than Y which is defined earlier than Z. Permute "x | 1", "Y & 2",
1331 // "z" in the order of X-Y-Z is better than any other orders.
1332 std::stable_sort(OpndPtrs.begin(), OpndPtrs.end(),
1333 [](XorOpnd *LHS, XorOpnd *RHS) {
1334 return LHS->getSymbolicRank() < RHS->getSymbolicRank();
1337 // Step 3: Combine adjacent operands
1338 XorOpnd *PrevOpnd = nullptr;
1339 bool Changed = false;
1340 for (unsigned i = 0, e = Opnds.size(); i < e; i++) {
1341 XorOpnd *CurrOpnd = OpndPtrs[i];
1342 // The combined value
1345 // Step 3.1: Try simplifying "CurrOpnd ^ ConstOpnd"
1346 if (!ConstOpnd.isNullValue() &&
1347 CombineXorOpnd(I, CurrOpnd, ConstOpnd, CV)) {
1350 *CurrOpnd = XorOpnd(CV);
1352 CurrOpnd->Invalidate();
1357 if (!PrevOpnd || CurrOpnd->getSymbolicPart() != PrevOpnd->getSymbolicPart()) {
1358 PrevOpnd = CurrOpnd;
1362 // step 3.2: When previous and current operands share the same symbolic
1363 // value, try to simplify "PrevOpnd ^ CurrOpnd ^ ConstOpnd"
1364 if (CombineXorOpnd(I, CurrOpnd, PrevOpnd, ConstOpnd, CV)) {
1365 // Remove previous operand
1366 PrevOpnd->Invalidate();
1368 *CurrOpnd = XorOpnd(CV);
1369 PrevOpnd = CurrOpnd;
1371 CurrOpnd->Invalidate();
1378 // Step 4: Reassemble the Ops
1381 for (unsigned int i = 0, e = Opnds.size(); i < e; i++) {
1382 XorOpnd &O = Opnds[i];
1385 ValueEntry VE(getRank(O.getValue()), O.getValue());
1388 if (!ConstOpnd.isNullValue()) {
1389 Value *C = ConstantInt::get(Ty, ConstOpnd);
1390 ValueEntry VE(getRank(C), C);
1393 unsigned Sz = Ops.size();
1395 return Ops.back().Op;
1397 assert(ConstOpnd.isNullValue());
1398 return ConstantInt::get(Ty, ConstOpnd);
1405 /// Optimize a series of operands to an 'add' instruction. This
1406 /// optimizes based on identities. If it can be reduced to a single Value, it
1407 /// is returned, otherwise the Ops list is mutated as necessary.
1408 Value *ReassociatePass::OptimizeAdd(Instruction *I,
1409 SmallVectorImpl<ValueEntry> &Ops) {
1410 // Scan the operand lists looking for X and -X pairs. If we find any, we
1411 // can simplify expressions like X+-X == 0 and X+~X ==-1. While we're at it,
1413 // duplicates. We want to canonicalize Y+Y+Y+Z -> 3*Y+Z.
1415 for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
1416 Value *TheOp = Ops[i].Op;
1417 // Check to see if we've seen this operand before. If so, we factor all
1418 // instances of the operand together. Due to our sorting criteria, we know
1419 // that these need to be next to each other in the vector.
1420 if (i+1 != Ops.size() && Ops[i+1].Op == TheOp) {
1421 // Rescan the list, remove all instances of this operand from the expr.
1422 unsigned NumFound = 0;
1424 Ops.erase(Ops.begin()+i);
1426 } while (i != Ops.size() && Ops[i].Op == TheOp);
1428 LLVM_DEBUG(dbgs() << "\nFACTORING [" << NumFound << "]: " << *TheOp
1432 // Insert a new multiply.
1433 Type *Ty = TheOp->getType();
1434 Constant *C = Ty->isIntOrIntVectorTy() ?
1435 ConstantInt::get(Ty, NumFound) : ConstantFP::get(Ty, NumFound);
1436 Instruction *Mul = CreateMul(TheOp, C, "factor", I, I);
1438 // Now that we have inserted a multiply, optimize it. This allows us to
1439 // handle cases that require multiple factoring steps, such as this:
1440 // (X*2) + (X*2) + (X*2) -> (X*2)*3 -> X*6
1441 RedoInsts.insert(Mul);
1443 // If every add operand was a duplicate, return the multiply.
1447 // Otherwise, we had some input that didn't have the dupe, such as
1448 // "A + A + B" -> "A*2 + B". Add the new multiply to the list of
1449 // things being added by this operation.
1450 Ops.insert(Ops.begin(), ValueEntry(getRank(Mul), Mul));
1457 // Check for X and -X or X and ~X in the operand list.
1459 if (!match(TheOp, m_Neg(m_Value(X))) && !match(TheOp, m_Not(m_Value(X))) &&
1460 !match(TheOp, m_FNeg(m_Value(X))))
1463 unsigned FoundX = FindInOperandList(Ops, i, X);
1467 // Remove X and -X from the operand list.
1468 if (Ops.size() == 2 &&
1469 (match(TheOp, m_Neg(m_Value())) || match(TheOp, m_FNeg(m_Value()))))
1470 return Constant::getNullValue(X->getType());
1472 // Remove X and ~X from the operand list.
1473 if (Ops.size() == 2 && match(TheOp, m_Not(m_Value())))
1474 return Constant::getAllOnesValue(X->getType());
1476 Ops.erase(Ops.begin()+i);
1480 --i; // Need to back up an extra one.
1481 Ops.erase(Ops.begin()+FoundX);
1483 --i; // Revisit element.
1484 e -= 2; // Removed two elements.
1486 // if X and ~X we append -1 to the operand list.
1487 if (match(TheOp, m_Not(m_Value()))) {
1488 Value *V = Constant::getAllOnesValue(X->getType());
1489 Ops.insert(Ops.end(), ValueEntry(getRank(V), V));
1494 // Scan the operand list, checking to see if there are any common factors
1495 // between operands. Consider something like A*A+A*B*C+D. We would like to
1496 // reassociate this to A*(A+B*C)+D, which reduces the number of multiplies.
1497 // To efficiently find this, we count the number of times a factor occurs
1498 // for any ADD operands that are MULs.
1499 DenseMap<Value*, unsigned> FactorOccurrences;
1501 // Keep track of each multiply we see, to avoid triggering on (X*4)+(X*4)
1502 // where they are actually the same multiply.
1503 unsigned MaxOcc = 0;
1504 Value *MaxOccVal = nullptr;
1505 for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
1506 BinaryOperator *BOp =
1507 isReassociableOp(Ops[i].Op, Instruction::Mul, Instruction::FMul);
1511 // Compute all of the factors of this added value.
1512 SmallVector<Value*, 8> Factors;
1513 FindSingleUseMultiplyFactors(BOp, Factors);
1514 assert(Factors.size() > 1 && "Bad linearize!");
1516 // Add one to FactorOccurrences for each unique factor in this op.
1517 SmallPtrSet<Value*, 8> Duplicates;
1518 for (unsigned i = 0, e = Factors.size(); i != e; ++i) {
1519 Value *Factor = Factors[i];
1520 if (!Duplicates.insert(Factor).second)
1523 unsigned Occ = ++FactorOccurrences[Factor];
1529 // If Factor is a negative constant, add the negated value as a factor
1530 // because we can percolate the negate out. Watch for minint, which
1531 // cannot be positivified.
1532 if (ConstantInt *CI = dyn_cast<ConstantInt>(Factor)) {
1533 if (CI->isNegative() && !CI->isMinValue(true)) {
1534 Factor = ConstantInt::get(CI->getContext(), -CI->getValue());
1535 if (!Duplicates.insert(Factor).second)
1537 unsigned Occ = ++FactorOccurrences[Factor];
1543 } else if (ConstantFP *CF = dyn_cast<ConstantFP>(Factor)) {
1544 if (CF->isNegative()) {
1545 APFloat F(CF->getValueAPF());
1547 Factor = ConstantFP::get(CF->getContext(), F);
1548 if (!Duplicates.insert(Factor).second)
1550 unsigned Occ = ++FactorOccurrences[Factor];
1560 // If any factor occurred more than one time, we can pull it out.
1562 LLVM_DEBUG(dbgs() << "\nFACTORING [" << MaxOcc << "]: " << *MaxOccVal
1566 // Create a new instruction that uses the MaxOccVal twice. If we don't do
1567 // this, we could otherwise run into situations where removing a factor
1568 // from an expression will drop a use of maxocc, and this can cause
1569 // RemoveFactorFromExpression on successive values to behave differently.
1570 Instruction *DummyInst =
1571 I->getType()->isIntOrIntVectorTy()
1572 ? BinaryOperator::CreateAdd(MaxOccVal, MaxOccVal)
1573 : BinaryOperator::CreateFAdd(MaxOccVal, MaxOccVal);
1575 SmallVector<WeakTrackingVH, 4> NewMulOps;
1576 for (unsigned i = 0; i != Ops.size(); ++i) {
1577 // Only try to remove factors from expressions we're allowed to.
1578 BinaryOperator *BOp =
1579 isReassociableOp(Ops[i].Op, Instruction::Mul, Instruction::FMul);
1583 if (Value *V = RemoveFactorFromExpression(Ops[i].Op, MaxOccVal)) {
1584 // The factorized operand may occur several times. Convert them all in
1586 for (unsigned j = Ops.size(); j != i;) {
1588 if (Ops[j].Op == Ops[i].Op) {
1589 NewMulOps.push_back(V);
1590 Ops.erase(Ops.begin()+j);
1597 // No need for extra uses anymore.
1598 DummyInst->deleteValue();
1600 unsigned NumAddedValues = NewMulOps.size();
1601 Value *V = EmitAddTreeOfValues(I, NewMulOps);
1603 // Now that we have inserted the add tree, optimize it. This allows us to
1604 // handle cases that require multiple factoring steps, such as this:
1605 // A*A*B + A*A*C --> A*(A*B+A*C) --> A*(A*(B+C))
1606 assert(NumAddedValues > 1 && "Each occurrence should contribute a value");
1607 (void)NumAddedValues;
1608 if (Instruction *VI = dyn_cast<Instruction>(V))
1609 RedoInsts.insert(VI);
1611 // Create the multiply.
1612 Instruction *V2 = CreateMul(V, MaxOccVal, "reass.mul", I, I);
1614 // Rerun associate on the multiply in case the inner expression turned into
1615 // a multiply. We want to make sure that we keep things in canonical form.
1616 RedoInsts.insert(V2);
1618 // If every add operand included the factor (e.g. "A*B + A*C"), then the
1619 // entire result expression is just the multiply "A*(B+C)".
1623 // Otherwise, we had some input that didn't have the factor, such as
1624 // "A*B + A*C + D" -> "A*(B+C) + D". Add the new multiply to the list of
1625 // things being added by this operation.
1626 Ops.insert(Ops.begin(), ValueEntry(getRank(V2), V2));
1632 /// Build up a vector of value/power pairs factoring a product.
1634 /// Given a series of multiplication operands, build a vector of factors and
1635 /// the powers each is raised to when forming the final product. Sort them in
1636 /// the order of descending power.
1638 /// (x*x) -> [(x, 2)]
1639 /// ((x*x)*x) -> [(x, 3)]
1640 /// ((((x*y)*x)*y)*x) -> [(x, 3), (y, 2)]
1642 /// \returns Whether any factors have a power greater than one.
1643 static bool collectMultiplyFactors(SmallVectorImpl<ValueEntry> &Ops,
1644 SmallVectorImpl<Factor> &Factors) {
1645 // FIXME: Have Ops be (ValueEntry, Multiplicity) pairs, simplifying this.
1646 // Compute the sum of powers of simplifiable factors.
1647 unsigned FactorPowerSum = 0;
1648 for (unsigned Idx = 1, Size = Ops.size(); Idx < Size; ++Idx) {
1649 Value *Op = Ops[Idx-1].Op;
1651 // Count the number of occurrences of this value.
1653 for (; Idx < Size && Ops[Idx].Op == Op; ++Idx)
1655 // Track for simplification all factors which occur 2 or more times.
1657 FactorPowerSum += Count;
1660 // We can only simplify factors if the sum of the powers of our simplifiable
1661 // factors is 4 or higher. When that is the case, we will *always* have
1662 // a simplification. This is an important invariant to prevent cyclicly
1663 // trying to simplify already minimal formations.
1664 if (FactorPowerSum < 4)
1667 // Now gather the simplifiable factors, removing them from Ops.
1669 for (unsigned Idx = 1; Idx < Ops.size(); ++Idx) {
1670 Value *Op = Ops[Idx-1].Op;
1672 // Count the number of occurrences of this value.
1674 for (; Idx < Ops.size() && Ops[Idx].Op == Op; ++Idx)
1678 // Move an even number of occurrences to Factors.
1681 FactorPowerSum += Count;
1682 Factors.push_back(Factor(Op, Count));
1683 Ops.erase(Ops.begin()+Idx, Ops.begin()+Idx+Count);
1686 // None of the adjustments above should have reduced the sum of factor powers
1687 // below our mininum of '4'.
1688 assert(FactorPowerSum >= 4);
1690 std::stable_sort(Factors.begin(), Factors.end(),
1691 [](const Factor &LHS, const Factor &RHS) {
1692 return LHS.Power > RHS.Power;
1697 /// Build a tree of multiplies, computing the product of Ops.
1698 static Value *buildMultiplyTree(IRBuilder<> &Builder,
1699 SmallVectorImpl<Value*> &Ops) {
1700 if (Ops.size() == 1)
1703 Value *LHS = Ops.pop_back_val();
1705 if (LHS->getType()->isIntOrIntVectorTy())
1706 LHS = Builder.CreateMul(LHS, Ops.pop_back_val());
1708 LHS = Builder.CreateFMul(LHS, Ops.pop_back_val());
1709 } while (!Ops.empty());
1714 /// Build a minimal multiplication DAG for (a^x)*(b^y)*(c^z)*...
1716 /// Given a vector of values raised to various powers, where no two values are
1717 /// equal and the powers are sorted in decreasing order, compute the minimal
1718 /// DAG of multiplies to compute the final product, and return that product
1721 ReassociatePass::buildMinimalMultiplyDAG(IRBuilder<> &Builder,
1722 SmallVectorImpl<Factor> &Factors) {
1723 assert(Factors[0].Power);
1724 SmallVector<Value *, 4> OuterProduct;
1725 for (unsigned LastIdx = 0, Idx = 1, Size = Factors.size();
1726 Idx < Size && Factors[Idx].Power > 0; ++Idx) {
1727 if (Factors[Idx].Power != Factors[LastIdx].Power) {
1732 // We want to multiply across all the factors with the same power so that
1733 // we can raise them to that power as a single entity. Build a mini tree
1735 SmallVector<Value *, 4> InnerProduct;
1736 InnerProduct.push_back(Factors[LastIdx].Base);
1738 InnerProduct.push_back(Factors[Idx].Base);
1740 } while (Idx < Size && Factors[Idx].Power == Factors[LastIdx].Power);
1742 // Reset the base value of the first factor to the new expression tree.
1743 // We'll remove all the factors with the same power in a second pass.
1744 Value *M = Factors[LastIdx].Base = buildMultiplyTree(Builder, InnerProduct);
1745 if (Instruction *MI = dyn_cast<Instruction>(M))
1746 RedoInsts.insert(MI);
1750 // Unique factors with equal powers -- we've folded them into the first one's
1752 Factors.erase(std::unique(Factors.begin(), Factors.end(),
1753 [](const Factor &LHS, const Factor &RHS) {
1754 return LHS.Power == RHS.Power;
1758 // Iteratively collect the base of each factor with an add power into the
1759 // outer product, and halve each power in preparation for squaring the
1761 for (unsigned Idx = 0, Size = Factors.size(); Idx != Size; ++Idx) {
1762 if (Factors[Idx].Power & 1)
1763 OuterProduct.push_back(Factors[Idx].Base);
1764 Factors[Idx].Power >>= 1;
1766 if (Factors[0].Power) {
1767 Value *SquareRoot = buildMinimalMultiplyDAG(Builder, Factors);
1768 OuterProduct.push_back(SquareRoot);
1769 OuterProduct.push_back(SquareRoot);
1771 if (OuterProduct.size() == 1)
1772 return OuterProduct.front();
1774 Value *V = buildMultiplyTree(Builder, OuterProduct);
1778 Value *ReassociatePass::OptimizeMul(BinaryOperator *I,
1779 SmallVectorImpl<ValueEntry> &Ops) {
1780 // We can only optimize the multiplies when there is a chain of more than
1781 // three, such that a balanced tree might require fewer total multiplies.
1785 // Try to turn linear trees of multiplies without other uses of the
1786 // intermediate stages into minimal multiply DAGs with perfect sub-expression
1788 SmallVector<Factor, 4> Factors;
1789 if (!collectMultiplyFactors(Ops, Factors))
1790 return nullptr; // All distinct factors, so nothing left for us to do.
1792 IRBuilder<> Builder(I);
1793 // The reassociate transformation for FP operations is performed only
1794 // if unsafe algebra is permitted by FastMathFlags. Propagate those flags
1795 // to the newly generated operations.
1796 if (auto FPI = dyn_cast<FPMathOperator>(I))
1797 Builder.setFastMathFlags(FPI->getFastMathFlags());
1799 Value *V = buildMinimalMultiplyDAG(Builder, Factors);
1803 ValueEntry NewEntry = ValueEntry(getRank(V), V);
1804 Ops.insert(std::lower_bound(Ops.begin(), Ops.end(), NewEntry), NewEntry);
1808 Value *ReassociatePass::OptimizeExpression(BinaryOperator *I,
1809 SmallVectorImpl<ValueEntry> &Ops) {
1810 // Now that we have the linearized expression tree, try to optimize it.
1811 // Start by folding any constants that we found.
1812 Constant *Cst = nullptr;
1813 unsigned Opcode = I->getOpcode();
1814 while (!Ops.empty() && isa<Constant>(Ops.back().Op)) {
1815 Constant *C = cast<Constant>(Ops.pop_back_val().Op);
1816 Cst = Cst ? ConstantExpr::get(Opcode, C, Cst) : C;
1818 // If there was nothing but constants then we are done.
1822 // Put the combined constant back at the end of the operand list, except if
1823 // there is no point. For example, an add of 0 gets dropped here, while a
1824 // multiplication by zero turns the whole expression into zero.
1825 if (Cst && Cst != ConstantExpr::getBinOpIdentity(Opcode, I->getType())) {
1826 if (Cst == ConstantExpr::getBinOpAbsorber(Opcode, I->getType()))
1828 Ops.push_back(ValueEntry(0, Cst));
1831 if (Ops.size() == 1) return Ops[0].Op;
1833 // Handle destructive annihilation due to identities between elements in the
1834 // argument list here.
1835 unsigned NumOps = Ops.size();
1838 case Instruction::And:
1839 case Instruction::Or:
1840 if (Value *Result = OptimizeAndOrXor(Opcode, Ops))
1844 case Instruction::Xor:
1845 if (Value *Result = OptimizeXor(I, Ops))
1849 case Instruction::Add:
1850 case Instruction::FAdd:
1851 if (Value *Result = OptimizeAdd(I, Ops))
1855 case Instruction::Mul:
1856 case Instruction::FMul:
1857 if (Value *Result = OptimizeMul(I, Ops))
1862 if (Ops.size() != NumOps)
1863 return OptimizeExpression(I, Ops);
1867 // Remove dead instructions and if any operands are trivially dead add them to
1868 // Insts so they will be removed as well.
1869 void ReassociatePass::RecursivelyEraseDeadInsts(Instruction *I,
1870 OrderedSet &Insts) {
1871 assert(isInstructionTriviallyDead(I) && "Trivially dead instructions only!");
1872 SmallVector<Value *, 4> Ops(I->op_begin(), I->op_end());
1873 ValueRankMap.erase(I);
1875 RedoInsts.remove(I);
1876 I->eraseFromParent();
1878 if (Instruction *OpInst = dyn_cast<Instruction>(Op))
1879 if (OpInst->use_empty())
1880 Insts.insert(OpInst);
1883 /// Zap the given instruction, adding interesting operands to the work list.
1884 void ReassociatePass::EraseInst(Instruction *I) {
1885 assert(isInstructionTriviallyDead(I) && "Trivially dead instructions only!");
1886 LLVM_DEBUG(dbgs() << "Erasing dead inst: "; I->dump());
1888 SmallVector<Value*, 8> Ops(I->op_begin(), I->op_end());
1889 // Erase the dead instruction.
1890 ValueRankMap.erase(I);
1891 RedoInsts.remove(I);
1892 I->eraseFromParent();
1893 // Optimize its operands.
1894 SmallPtrSet<Instruction *, 8> Visited; // Detect self-referential nodes.
1895 for (unsigned i = 0, e = Ops.size(); i != e; ++i)
1896 if (Instruction *Op = dyn_cast<Instruction>(Ops[i])) {
1897 // If this is a node in an expression tree, climb to the expression root
1898 // and add that since that's where optimization actually happens.
1899 unsigned Opcode = Op->getOpcode();
1900 while (Op->hasOneUse() && Op->user_back()->getOpcode() == Opcode &&
1901 Visited.insert(Op).second)
1902 Op = Op->user_back();
1904 // The instruction we're going to push may be coming from a
1905 // dead block, and Reassociate skips the processing of unreachable
1906 // blocks because it's a waste of time and also because it can
1907 // lead to infinite loop due to LLVM's non-standard definition
1909 if (ValueRankMap.find(Op) != ValueRankMap.end())
1910 RedoInsts.insert(Op);
1916 // Canonicalize expressions of the following form:
1917 // x + (-Constant * y) -> x - (Constant * y)
1918 // x - (-Constant * y) -> x + (Constant * y)
1919 Instruction *ReassociatePass::canonicalizeNegConstExpr(Instruction *I) {
1920 if (!I->hasOneUse() || I->getType()->isVectorTy())
1923 // Must be a fmul or fdiv instruction.
1924 unsigned Opcode = I->getOpcode();
1925 if (Opcode != Instruction::FMul && Opcode != Instruction::FDiv)
1928 auto *C0 = dyn_cast<ConstantFP>(I->getOperand(0));
1929 auto *C1 = dyn_cast<ConstantFP>(I->getOperand(1));
1931 // Both operands are constant, let it get constant folded away.
1935 ConstantFP *CF = C0 ? C0 : C1;
1937 // Must have one constant operand.
1941 // Must be a negative ConstantFP.
1942 if (!CF->isNegative())
1945 // User must be a binary operator with one or more uses.
1946 Instruction *User = I->user_back();
1947 if (!isa<BinaryOperator>(User) || User->use_empty())
1950 unsigned UserOpcode = User->getOpcode();
1951 if (UserOpcode != Instruction::FAdd && UserOpcode != Instruction::FSub)
1954 // Subtraction is not commutative. Explicitly, the following transform is
1955 // not valid: (-Constant * y) - x -> x + (Constant * y)
1956 if (!User->isCommutative() && User->getOperand(1) != I)
1959 // Don't canonicalize x + (-Constant * y) -> x - (Constant * y), if the
1960 // resulting subtract will be broken up later. This can get us into an
1961 // infinite loop during reassociation.
1962 if (UserOpcode == Instruction::FAdd && ShouldBreakUpSubtract(User))
1965 // Change the sign of the constant.
1966 APFloat Val = CF->getValueAPF();
1968 I->setOperand(C0 ? 0 : 1, ConstantFP::get(CF->getContext(), Val));
1970 // Canonicalize I to RHS to simplify the next bit of logic. E.g.,
1971 // ((-Const*y) + x) -> (x + (-Const*y)).
1972 if (User->getOperand(0) == I && User->isCommutative())
1973 cast<BinaryOperator>(User)->swapOperands();
1975 Value *Op0 = User->getOperand(0);
1976 Value *Op1 = User->getOperand(1);
1978 switch (UserOpcode) {
1980 llvm_unreachable("Unexpected Opcode!");
1981 case Instruction::FAdd:
1982 NI = BinaryOperator::CreateFSub(Op0, Op1);
1983 NI->setFastMathFlags(cast<FPMathOperator>(User)->getFastMathFlags());
1985 case Instruction::FSub:
1986 NI = BinaryOperator::CreateFAdd(Op0, Op1);
1987 NI->setFastMathFlags(cast<FPMathOperator>(User)->getFastMathFlags());
1991 NI->insertBefore(User);
1992 NI->setName(User->getName());
1993 User->replaceAllUsesWith(NI);
1994 NI->setDebugLoc(I->getDebugLoc());
1995 RedoInsts.insert(I);
2000 /// Inspect and optimize the given instruction. Note that erasing
2001 /// instructions is not allowed.
2002 void ReassociatePass::OptimizeInst(Instruction *I) {
2003 // Only consider operations that we understand.
2004 if (!isa<BinaryOperator>(I))
2007 if (I->getOpcode() == Instruction::Shl && isa<ConstantInt>(I->getOperand(1)))
2008 // If an operand of this shift is a reassociable multiply, or if the shift
2009 // is used by a reassociable multiply or add, turn into a multiply.
2010 if (isReassociableOp(I->getOperand(0), Instruction::Mul) ||
2012 (isReassociableOp(I->user_back(), Instruction::Mul) ||
2013 isReassociableOp(I->user_back(), Instruction::Add)))) {
2014 Instruction *NI = ConvertShiftToMul(I);
2015 RedoInsts.insert(I);
2020 // Canonicalize negative constants out of expressions.
2021 if (Instruction *Res = canonicalizeNegConstExpr(I))
2024 // Commute binary operators, to canonicalize the order of their operands.
2025 // This can potentially expose more CSE opportunities, and makes writing other
2026 // transformations simpler.
2027 if (I->isCommutative())
2028 canonicalizeOperands(I);
2030 // Don't optimize floating-point instructions unless they are 'fast'.
2031 if (I->getType()->isFPOrFPVectorTy() && !I->isFast())
2034 // Do not reassociate boolean (i1) expressions. We want to preserve the
2035 // original order of evaluation for short-circuited comparisons that
2036 // SimplifyCFG has folded to AND/OR expressions. If the expression
2037 // is not further optimized, it is likely to be transformed back to a
2038 // short-circuited form for code gen, and the source order may have been
2039 // optimized for the most likely conditions.
2040 if (I->getType()->isIntegerTy(1))
2043 // If this is a subtract instruction which is not already in negate form,
2044 // see if we can convert it to X+-Y.
2045 if (I->getOpcode() == Instruction::Sub) {
2046 if (ShouldBreakUpSubtract(I)) {
2047 Instruction *NI = BreakUpSubtract(I, RedoInsts);
2048 RedoInsts.insert(I);
2051 } else if (match(I, m_Neg(m_Value()))) {
2052 // Otherwise, this is a negation. See if the operand is a multiply tree
2053 // and if this is not an inner node of a multiply tree.
2054 if (isReassociableOp(I->getOperand(1), Instruction::Mul) &&
2056 !isReassociableOp(I->user_back(), Instruction::Mul))) {
2057 Instruction *NI = LowerNegateToMultiply(I);
2058 // If the negate was simplified, revisit the users to see if we can
2059 // reassociate further.
2060 for (User *U : NI->users()) {
2061 if (BinaryOperator *Tmp = dyn_cast<BinaryOperator>(U))
2062 RedoInsts.insert(Tmp);
2064 RedoInsts.insert(I);
2069 } else if (I->getOpcode() == Instruction::FSub) {
2070 if (ShouldBreakUpSubtract(I)) {
2071 Instruction *NI = BreakUpSubtract(I, RedoInsts);
2072 RedoInsts.insert(I);
2075 } else if (match(I, m_FNeg(m_Value()))) {
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::FMul) &&
2080 !isReassociableOp(I->user_back(), Instruction::FMul))) {
2081 // If the negate was simplified, revisit the users to see if we can
2082 // reassociate further.
2083 Instruction *NI = LowerNegateToMultiply(I);
2084 for (User *U : NI->users()) {
2085 if (BinaryOperator *Tmp = dyn_cast<BinaryOperator>(U))
2086 RedoInsts.insert(Tmp);
2088 RedoInsts.insert(I);
2095 // If this instruction is an associative binary operator, process it.
2096 if (!I->isAssociative()) return;
2097 BinaryOperator *BO = cast<BinaryOperator>(I);
2099 // If this is an interior node of a reassociable tree, ignore it until we
2100 // get to the root of the tree, to avoid N^2 analysis.
2101 unsigned Opcode = BO->getOpcode();
2102 if (BO->hasOneUse() && BO->user_back()->getOpcode() == Opcode) {
2103 // During the initial run we will get to the root of the tree.
2104 // But if we get here while we are redoing instructions, there is no
2105 // guarantee that the root will be visited. So Redo later
2106 if (BO->user_back() != BO &&
2107 BO->getParent() == BO->user_back()->getParent())
2108 RedoInsts.insert(BO->user_back());
2112 // If this is an add tree that is used by a sub instruction, ignore it
2113 // until we process the subtract.
2114 if (BO->hasOneUse() && BO->getOpcode() == Instruction::Add &&
2115 cast<Instruction>(BO->user_back())->getOpcode() == Instruction::Sub)
2117 if (BO->hasOneUse() && BO->getOpcode() == Instruction::FAdd &&
2118 cast<Instruction>(BO->user_back())->getOpcode() == Instruction::FSub)
2121 ReassociateExpression(BO);
2124 void ReassociatePass::ReassociateExpression(BinaryOperator *I) {
2125 // First, walk the expression tree, linearizing the tree, collecting the
2126 // operand information.
2127 SmallVector<RepeatedValue, 8> Tree;
2128 MadeChange |= LinearizeExprTree(I, Tree);
2129 SmallVector<ValueEntry, 8> Ops;
2130 Ops.reserve(Tree.size());
2131 for (unsigned i = 0, e = Tree.size(); i != e; ++i) {
2132 RepeatedValue E = Tree[i];
2133 Ops.append(E.second.getZExtValue(),
2134 ValueEntry(getRank(E.first), E.first));
2137 LLVM_DEBUG(dbgs() << "RAIn:\t"; PrintOps(I, Ops); dbgs() << '\n');
2139 // Now that we have linearized the tree to a list and have gathered all of
2140 // the operands and their ranks, sort the operands by their rank. Use a
2141 // stable_sort so that values with equal ranks will have their relative
2142 // positions maintained (and so the compiler is deterministic). Note that
2143 // this sorts so that the highest ranking values end up at the beginning of
2145 std::stable_sort(Ops.begin(), Ops.end());
2147 // Now that we have the expression tree in a convenient
2148 // sorted form, optimize it globally if possible.
2149 if (Value *V = OptimizeExpression(I, Ops)) {
2151 // Self-referential expression in unreachable code.
2153 // This expression tree simplified to something that isn't a tree,
2155 LLVM_DEBUG(dbgs() << "Reassoc to scalar: " << *V << '\n');
2156 I->replaceAllUsesWith(V);
2157 if (Instruction *VI = dyn_cast<Instruction>(V))
2158 if (I->getDebugLoc())
2159 VI->setDebugLoc(I->getDebugLoc());
2160 RedoInsts.insert(I);
2165 // We want to sink immediates as deeply as possible except in the case where
2166 // this is a multiply tree used only by an add, and the immediate is a -1.
2167 // In this case we reassociate to put the negation on the outside so that we
2168 // can fold the negation into the add: (-X)*Y + Z -> Z-X*Y
2169 if (I->hasOneUse()) {
2170 if (I->getOpcode() == Instruction::Mul &&
2171 cast<Instruction>(I->user_back())->getOpcode() == Instruction::Add &&
2172 isa<ConstantInt>(Ops.back().Op) &&
2173 cast<ConstantInt>(Ops.back().Op)->isMinusOne()) {
2174 ValueEntry Tmp = Ops.pop_back_val();
2175 Ops.insert(Ops.begin(), Tmp);
2176 } else if (I->getOpcode() == Instruction::FMul &&
2177 cast<Instruction>(I->user_back())->getOpcode() ==
2178 Instruction::FAdd &&
2179 isa<ConstantFP>(Ops.back().Op) &&
2180 cast<ConstantFP>(Ops.back().Op)->isExactlyValue(-1.0)) {
2181 ValueEntry Tmp = Ops.pop_back_val();
2182 Ops.insert(Ops.begin(), Tmp);
2186 LLVM_DEBUG(dbgs() << "RAOut:\t"; PrintOps(I, Ops); dbgs() << '\n');
2188 if (Ops.size() == 1) {
2190 // Self-referential expression in unreachable code.
2193 // This expression tree simplified to something that isn't a tree,
2195 I->replaceAllUsesWith(Ops[0].Op);
2196 if (Instruction *OI = dyn_cast<Instruction>(Ops[0].Op))
2197 OI->setDebugLoc(I->getDebugLoc());
2198 RedoInsts.insert(I);
2202 if (Ops.size() > 2 && Ops.size() <= GlobalReassociateLimit) {
2203 // Find the pair with the highest count in the pairmap and move it to the
2204 // back of the list so that it can later be CSE'd.
2207 // if c*e is the most "popular" pair, we can express this as
2210 unsigned BestRank = 0;
2211 std::pair<unsigned, unsigned> BestPair;
2212 unsigned Idx = I->getOpcode() - Instruction::BinaryOpsBegin;
2213 for (unsigned i = 0; i < Ops.size() - 1; ++i)
2214 for (unsigned j = i + 1; j < Ops.size(); ++j) {
2216 Value *Op0 = Ops[i].Op;
2217 Value *Op1 = Ops[j].Op;
2218 if (std::less<Value *>()(Op1, Op0))
2219 std::swap(Op0, Op1);
2220 auto it = PairMap[Idx].find({Op0, Op1});
2221 if (it != PairMap[Idx].end())
2222 Score += it->second;
2224 unsigned MaxRank = std::max(Ops[i].Rank, Ops[j].Rank);
2225 if (Score > Max || (Score == Max && MaxRank < BestRank)) {
2232 auto Op0 = Ops[BestPair.first];
2233 auto Op1 = Ops[BestPair.second];
2234 Ops.erase(&Ops[BestPair.second]);
2235 Ops.erase(&Ops[BestPair.first]);
2240 // Now that we ordered and optimized the expressions, splat them back into
2241 // the expression tree, removing any unneeded nodes.
2242 RewriteExprTree(I, Ops);
2246 ReassociatePass::BuildPairMap(ReversePostOrderTraversal<Function *> &RPOT) {
2247 // Make a "pairmap" of how often each operand pair occurs.
2248 for (BasicBlock *BI : RPOT) {
2249 for (Instruction &I : *BI) {
2250 if (!I.isAssociative())
2253 // Ignore nodes that aren't at the root of trees.
2254 if (I.hasOneUse() && I.user_back()->getOpcode() == I.getOpcode())
2257 // Collect all operands in a single reassociable expression.
2258 // Since Reassociate has already been run once, we can assume things
2259 // are already canonical according to Reassociation's regime.
2260 SmallVector<Value *, 8> Worklist = { I.getOperand(0), I.getOperand(1) };
2261 SmallVector<Value *, 8> Ops;
2262 while (!Worklist.empty() && Ops.size() <= GlobalReassociateLimit) {
2263 Value *Op = Worklist.pop_back_val();
2264 Instruction *OpI = dyn_cast<Instruction>(Op);
2265 if (!OpI || OpI->getOpcode() != I.getOpcode() || !OpI->hasOneUse()) {
2269 // Be paranoid about self-referencing expressions in unreachable code.
2270 if (OpI->getOperand(0) != OpI)
2271 Worklist.push_back(OpI->getOperand(0));
2272 if (OpI->getOperand(1) != OpI)
2273 Worklist.push_back(OpI->getOperand(1));
2275 // Skip extremely long expressions.
2276 if (Ops.size() > GlobalReassociateLimit)
2279 // Add all pairwise combinations of operands to the pair map.
2280 unsigned BinaryIdx = I.getOpcode() - Instruction::BinaryOpsBegin;
2281 SmallSet<std::pair<Value *, Value*>, 32> Visited;
2282 for (unsigned i = 0; i < Ops.size() - 1; ++i) {
2283 for (unsigned j = i + 1; j < Ops.size(); ++j) {
2284 // Canonicalize operand orderings.
2285 Value *Op0 = Ops[i];
2286 Value *Op1 = Ops[j];
2287 if (std::less<Value *>()(Op1, Op0))
2288 std::swap(Op0, Op1);
2289 if (!Visited.insert({Op0, Op1}).second)
2291 auto res = PairMap[BinaryIdx].insert({{Op0, Op1}, 1});
2293 ++res.first->second;
2300 PreservedAnalyses ReassociatePass::run(Function &F, FunctionAnalysisManager &) {
2301 // Get the functions basic blocks in Reverse Post Order. This order is used by
2302 // BuildRankMap to pre calculate ranks correctly. It also excludes dead basic
2303 // blocks (it has been seen that the analysis in this pass could hang when
2304 // analysing dead basic blocks).
2305 ReversePostOrderTraversal<Function *> RPOT(&F);
2307 // Calculate the rank map for F.
2308 BuildRankMap(F, RPOT);
2310 // Build the pair map before running reassociate.
2311 // Technically this would be more accurate if we did it after one round
2312 // of reassociation, but in practice it doesn't seem to help much on
2313 // real-world code, so don't waste the compile time running reassociate
2315 // If a user wants, they could expicitly run reassociate twice in their
2316 // pass pipeline for further potential gains.
2317 // It might also be possible to update the pair map during runtime, but the
2318 // overhead of that may be large if there's many reassociable chains.
2323 // Traverse the same blocks that were analysed by BuildRankMap.
2324 for (BasicBlock *BI : RPOT) {
2325 assert(RankMap.count(&*BI) && "BB should be ranked.");
2326 // Optimize every instruction in the basic block.
2327 for (BasicBlock::iterator II = BI->begin(), IE = BI->end(); II != IE;)
2328 if (isInstructionTriviallyDead(&*II)) {
2332 assert(II->getParent() == &*BI && "Moved to a different block!");
2336 // Make a copy of all the instructions to be redone so we can remove dead
2338 OrderedSet ToRedo(RedoInsts);
2339 // Iterate over all instructions to be reevaluated and remove trivially dead
2340 // instructions. If any operand of the trivially dead instruction becomes
2341 // dead mark it for deletion as well. Continue this process until all
2342 // trivially dead instructions have been removed.
2343 while (!ToRedo.empty()) {
2344 Instruction *I = ToRedo.pop_back_val();
2345 if (isInstructionTriviallyDead(I)) {
2346 RecursivelyEraseDeadInsts(I, ToRedo);
2351 // Now that we have removed dead instructions, we can reoptimize the
2352 // remaining instructions.
2353 while (!RedoInsts.empty()) {
2354 Instruction *I = RedoInsts.front();
2355 RedoInsts.erase(RedoInsts.begin());
2356 if (isInstructionTriviallyDead(I))
2363 // We are done with the rank map and pair map.
2365 ValueRankMap.clear();
2366 for (auto &Entry : PairMap)
2370 PreservedAnalyses PA;
2371 PA.preserveSet<CFGAnalyses>();
2372 PA.preserve<GlobalsAA>();
2376 return PreservedAnalyses::all();
2381 class ReassociateLegacyPass : public FunctionPass {
2382 ReassociatePass Impl;
2385 static char ID; // Pass identification, replacement for typeid
2387 ReassociateLegacyPass() : FunctionPass(ID) {
2388 initializeReassociateLegacyPassPass(*PassRegistry::getPassRegistry());
2391 bool runOnFunction(Function &F) override {
2392 if (skipFunction(F))
2395 FunctionAnalysisManager DummyFAM;
2396 auto PA = Impl.run(F, DummyFAM);
2397 return !PA.areAllPreserved();
2400 void getAnalysisUsage(AnalysisUsage &AU) const override {
2401 AU.setPreservesCFG();
2402 AU.addPreserved<GlobalsAAWrapperPass>();
2406 } // end anonymous namespace
2408 char ReassociateLegacyPass::ID = 0;
2410 INITIALIZE_PASS(ReassociateLegacyPass, "reassociate",
2411 "Reassociate expressions", false, false)
2413 // Public interface to the Reassociate pass
2414 FunctionPass *llvm::createReassociatePass() {
2415 return new ReassociateLegacyPass();