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...
13 // For example: 4 + (x + 5) -> x + (4 + 5)
15 // In the implementation of this algorithm, constants are assigned rank = 0,
16 // function arguments are rank = 1, and other values are assigned ranks
17 // corresponding to the reverse post order traversal of current function
18 // (starting at 2), which effectively gives values in deep loops higher rank
19 // than values not in loops.
21 //===----------------------------------------------------------------------===//
23 #define DEBUG_TYPE "reassociate"
24 #include "llvm/Transforms/Scalar.h"
25 #include "llvm/Constants.h"
26 #include "llvm/DerivedTypes.h"
27 #include "llvm/Function.h"
28 #include "llvm/Instructions.h"
29 #include "llvm/Pass.h"
30 #include "llvm/Assembly/Writer.h"
31 #include "llvm/Support/CFG.h"
32 #include "llvm/Support/Compiler.h"
33 #include "llvm/Support/Debug.h"
34 #include "llvm/ADT/PostOrderIterator.h"
35 #include "llvm/ADT/Statistic.h"
40 STATISTIC(NumLinear , "Number of insts linearized");
41 STATISTIC(NumChanged, "Number of insts reassociated");
42 STATISTIC(NumAnnihil, "Number of expr tree annihilated");
43 STATISTIC(NumFactor , "Number of multiplies factored");
46 struct VISIBILITY_HIDDEN ValueEntry {
49 ValueEntry(unsigned R, Value *O) : Rank(R), Op(O) {}
51 inline bool operator<(const ValueEntry &LHS, const ValueEntry &RHS) {
52 return LHS.Rank > RHS.Rank; // Sort so that highest rank goes to start.
57 /// PrintOps - Print out the expression identified in the Ops list.
59 static void PrintOps(Instruction *I, const std::vector<ValueEntry> &Ops) {
60 Module *M = I->getParent()->getParent()->getParent();
61 cerr << Instruction::getOpcodeName(I->getOpcode()) << " "
62 << *Ops[0].Op->getType();
63 for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
64 WriteAsOperand(*cerr.stream() << " ", Ops[i].Op, false, M);
65 cerr << "," << Ops[i].Rank;
71 class VISIBILITY_HIDDEN Reassociate : public FunctionPass {
72 std::map<BasicBlock*, unsigned> RankMap;
73 std::map<Value*, unsigned> ValueRankMap;
76 static char ID; // Pass identification, replacement for typeid
77 Reassociate() : FunctionPass(&ID) {}
79 bool runOnFunction(Function &F);
81 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
85 void BuildRankMap(Function &F);
86 unsigned getRank(Value *V);
87 void ReassociateExpression(BinaryOperator *I);
88 void RewriteExprTree(BinaryOperator *I, std::vector<ValueEntry> &Ops,
90 Value *OptimizeExpression(BinaryOperator *I, std::vector<ValueEntry> &Ops);
91 void LinearizeExprTree(BinaryOperator *I, std::vector<ValueEntry> &Ops);
92 void LinearizeExpr(BinaryOperator *I);
93 Value *RemoveFactorFromExpression(Value *V, Value *Factor);
94 void ReassociateBB(BasicBlock *BB);
96 void RemoveDeadBinaryOp(Value *V);
100 char Reassociate::ID = 0;
101 static RegisterPass<Reassociate> X("reassociate", "Reassociate expressions");
103 // Public interface to the Reassociate pass
104 FunctionPass *llvm::createReassociatePass() { return new Reassociate(); }
106 void Reassociate::RemoveDeadBinaryOp(Value *V) {
107 Instruction *Op = dyn_cast<Instruction>(V);
108 if (!Op || !isa<BinaryOperator>(Op) || !isa<CmpInst>(Op) || !Op->use_empty())
111 Value *LHS = Op->getOperand(0), *RHS = Op->getOperand(1);
112 RemoveDeadBinaryOp(LHS);
113 RemoveDeadBinaryOp(RHS);
117 static bool isUnmovableInstruction(Instruction *I) {
118 if (I->getOpcode() == Instruction::PHI ||
119 I->getOpcode() == Instruction::Alloca ||
120 I->getOpcode() == Instruction::Load ||
121 I->getOpcode() == Instruction::Malloc ||
122 I->getOpcode() == Instruction::Invoke ||
123 I->getOpcode() == Instruction::Call ||
124 I->getOpcode() == Instruction::UDiv ||
125 I->getOpcode() == Instruction::SDiv ||
126 I->getOpcode() == Instruction::FDiv ||
127 I->getOpcode() == Instruction::URem ||
128 I->getOpcode() == Instruction::SRem ||
129 I->getOpcode() == Instruction::FRem)
134 void Reassociate::BuildRankMap(Function &F) {
137 // Assign distinct ranks to function arguments
138 for (Function::arg_iterator I = F.arg_begin(), E = F.arg_end(); I != E; ++I)
139 ValueRankMap[I] = ++i;
141 ReversePostOrderTraversal<Function*> RPOT(&F);
142 for (ReversePostOrderTraversal<Function*>::rpo_iterator I = RPOT.begin(),
143 E = RPOT.end(); I != E; ++I) {
145 unsigned BBRank = RankMap[BB] = ++i << 16;
147 // Walk the basic block, adding precomputed ranks for any instructions that
148 // we cannot move. This ensures that the ranks for these instructions are
149 // all different in the block.
150 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
151 if (isUnmovableInstruction(I))
152 ValueRankMap[I] = ++BBRank;
156 unsigned Reassociate::getRank(Value *V) {
157 if (isa<Argument>(V)) return ValueRankMap[V]; // Function argument...
159 Instruction *I = dyn_cast<Instruction>(V);
160 if (I == 0) return 0; // Otherwise it's a global or constant, rank 0.
162 unsigned &CachedRank = ValueRankMap[I];
163 if (CachedRank) return CachedRank; // Rank already known?
165 // If this is an expression, return the 1+MAX(rank(LHS), rank(RHS)) so that
166 // we can reassociate expressions for code motion! Since we do not recurse
167 // for PHI nodes, we cannot have infinite recursion here, because there
168 // cannot be loops in the value graph that do not go through PHI nodes.
169 unsigned Rank = 0, MaxRank = RankMap[I->getParent()];
170 for (unsigned i = 0, e = I->getNumOperands();
171 i != e && Rank != MaxRank; ++i)
172 Rank = std::max(Rank, getRank(I->getOperand(i)));
174 // If this is a not or neg instruction, do not count it for rank. This
175 // assures us that X and ~X will have the same rank.
176 if (!I->getType()->isInteger() ||
177 (!BinaryOperator::isNot(I) && !BinaryOperator::isNeg(I)))
180 //DOUT << "Calculated Rank[" << V->getName() << "] = "
183 return CachedRank = Rank;
186 /// isReassociableOp - Return true if V is an instruction of the specified
187 /// opcode and if it only has one use.
188 static BinaryOperator *isReassociableOp(Value *V, unsigned Opcode) {
189 if ((V->hasOneUse() || V->use_empty()) && isa<Instruction>(V) &&
190 cast<Instruction>(V)->getOpcode() == Opcode)
191 return cast<BinaryOperator>(V);
195 /// LowerNegateToMultiply - Replace 0-X with X*-1.
197 static Instruction *LowerNegateToMultiply(Instruction *Neg) {
198 Constant *Cst = ConstantInt::getAllOnesValue(Neg->getType());
200 Instruction *Res = BinaryOperator::CreateMul(Neg->getOperand(1), Cst, "",Neg);
202 Neg->replaceAllUsesWith(Res);
203 Neg->eraseFromParent();
207 // Given an expression of the form '(A+B)+(D+C)', turn it into '(((A+B)+C)+D)'.
208 // Note that if D is also part of the expression tree that we recurse to
209 // linearize it as well. Besides that case, this does not recurse into A,B, or
211 void Reassociate::LinearizeExpr(BinaryOperator *I) {
212 BinaryOperator *LHS = cast<BinaryOperator>(I->getOperand(0));
213 BinaryOperator *RHS = cast<BinaryOperator>(I->getOperand(1));
214 assert(isReassociableOp(LHS, I->getOpcode()) &&
215 isReassociableOp(RHS, I->getOpcode()) &&
216 "Not an expression that needs linearization?");
218 DOUT << "Linear" << *LHS << *RHS << *I;
220 // Move the RHS instruction to live immediately before I, avoiding breaking
221 // dominator properties.
224 // Move operands around to do the linearization.
225 I->setOperand(1, RHS->getOperand(0));
226 RHS->setOperand(0, LHS);
227 I->setOperand(0, RHS);
231 DOUT << "Linearized: " << *I;
233 // If D is part of this expression tree, tail recurse.
234 if (isReassociableOp(I->getOperand(1), I->getOpcode()))
239 /// LinearizeExprTree - Given an associative binary expression tree, traverse
240 /// all of the uses putting it into canonical form. This forces a left-linear
241 /// form of the the expression (((a+b)+c)+d), and collects information about the
242 /// rank of the non-tree operands.
244 /// NOTE: These intentionally destroys the expression tree operands (turning
245 /// them into undef values) to reduce #uses of the values. This means that the
246 /// caller MUST use something like RewriteExprTree to put the values back in.
248 void Reassociate::LinearizeExprTree(BinaryOperator *I,
249 std::vector<ValueEntry> &Ops) {
250 Value *LHS = I->getOperand(0), *RHS = I->getOperand(1);
251 unsigned Opcode = I->getOpcode();
253 // First step, linearize the expression if it is in ((A+B)+(C+D)) form.
254 BinaryOperator *LHSBO = isReassociableOp(LHS, Opcode);
255 BinaryOperator *RHSBO = isReassociableOp(RHS, Opcode);
257 // If this is a multiply expression tree and it contains internal negations,
258 // transform them into multiplies by -1 so they can be reassociated.
259 if (I->getOpcode() == Instruction::Mul) {
260 if (!LHSBO && LHS->hasOneUse() && BinaryOperator::isNeg(LHS)) {
261 LHS = LowerNegateToMultiply(cast<Instruction>(LHS));
262 LHSBO = isReassociableOp(LHS, Opcode);
264 if (!RHSBO && RHS->hasOneUse() && BinaryOperator::isNeg(RHS)) {
265 RHS = LowerNegateToMultiply(cast<Instruction>(RHS));
266 RHSBO = isReassociableOp(RHS, Opcode);
272 // Neither the LHS or RHS as part of the tree, thus this is a leaf. As
273 // such, just remember these operands and their rank.
274 Ops.push_back(ValueEntry(getRank(LHS), LHS));
275 Ops.push_back(ValueEntry(getRank(RHS), RHS));
277 // Clear the leaves out.
278 I->setOperand(0, UndefValue::get(I->getType()));
279 I->setOperand(1, UndefValue::get(I->getType()));
282 // Turn X+(Y+Z) -> (Y+Z)+X
283 std::swap(LHSBO, RHSBO);
285 bool Success = !I->swapOperands();
286 assert(Success && "swapOperands failed");
291 // Turn (A+B)+(C+D) -> (((A+B)+C)+D). This guarantees the the RHS is not
292 // part of the expression tree.
294 LHS = LHSBO = cast<BinaryOperator>(I->getOperand(0));
295 RHS = I->getOperand(1);
299 // Okay, now we know that the LHS is a nested expression and that the RHS is
300 // not. Perform reassociation.
301 assert(!isReassociableOp(RHS, Opcode) && "LinearizeExpr failed!");
303 // Move LHS right before I to make sure that the tree expression dominates all
305 LHSBO->moveBefore(I);
307 // Linearize the expression tree on the LHS.
308 LinearizeExprTree(LHSBO, Ops);
310 // Remember the RHS operand and its rank.
311 Ops.push_back(ValueEntry(getRank(RHS), RHS));
313 // Clear the RHS leaf out.
314 I->setOperand(1, UndefValue::get(I->getType()));
317 // RewriteExprTree - Now that the operands for this expression tree are
318 // linearized and optimized, emit them in-order. This function is written to be
320 void Reassociate::RewriteExprTree(BinaryOperator *I,
321 std::vector<ValueEntry> &Ops,
323 if (i+2 == Ops.size()) {
324 if (I->getOperand(0) != Ops[i].Op ||
325 I->getOperand(1) != Ops[i+1].Op) {
326 Value *OldLHS = I->getOperand(0);
327 DOUT << "RA: " << *I;
328 I->setOperand(0, Ops[i].Op);
329 I->setOperand(1, Ops[i+1].Op);
330 DOUT << "TO: " << *I;
334 // If we reassociated a tree to fewer operands (e.g. (1+a+2) -> (a+3)
335 // delete the extra, now dead, nodes.
336 RemoveDeadBinaryOp(OldLHS);
340 assert(i+2 < Ops.size() && "Ops index out of range!");
342 if (I->getOperand(1) != Ops[i].Op) {
343 DOUT << "RA: " << *I;
344 I->setOperand(1, Ops[i].Op);
345 DOUT << "TO: " << *I;
350 BinaryOperator *LHS = cast<BinaryOperator>(I->getOperand(0));
351 assert(LHS->getOpcode() == I->getOpcode() &&
352 "Improper expression tree!");
354 // Compactify the tree instructions together with each other to guarantee
355 // that the expression tree is dominated by all of Ops.
357 RewriteExprTree(LHS, Ops, i+1);
362 // NegateValue - Insert instructions before the instruction pointed to by BI,
363 // that computes the negative version of the value specified. The negative
364 // version of the value is returned, and BI is left pointing at the instruction
365 // that should be processed next by the reassociation pass.
367 static Value *NegateValue(Value *V, Instruction *BI) {
368 // We are trying to expose opportunity for reassociation. One of the things
369 // that we want to do to achieve this is to push a negation as deep into an
370 // expression chain as possible, to expose the add instructions. In practice,
371 // this means that we turn this:
372 // X = -(A+12+C+D) into X = -A + -12 + -C + -D = -12 + -A + -C + -D
373 // so that later, a: Y = 12+X could get reassociated with the -12 to eliminate
374 // the constants. We assume that instcombine will clean up the mess later if
375 // we introduce tons of unnecessary negation instructions...
377 if (Instruction *I = dyn_cast<Instruction>(V))
378 if (I->getOpcode() == Instruction::Add && I->hasOneUse()) {
379 // Push the negates through the add.
380 I->setOperand(0, NegateValue(I->getOperand(0), BI));
381 I->setOperand(1, NegateValue(I->getOperand(1), BI));
383 // We must move the add instruction here, because the neg instructions do
384 // not dominate the old add instruction in general. By moving it, we are
385 // assured that the neg instructions we just inserted dominate the
386 // instruction we are about to insert after them.
389 I->setName(I->getName()+".neg");
393 // Insert a 'neg' instruction that subtracts the value from zero to get the
396 return BinaryOperator::CreateNeg(V, V->getName() + ".neg", BI);
399 /// ShouldBreakUpSubtract - Return true if we should break up this subtract of
400 /// X-Y into (X + -Y).
401 static bool ShouldBreakUpSubtract(Instruction *Sub) {
402 // If this is a negation, we can't split it up!
403 if (BinaryOperator::isNeg(Sub))
406 // Don't bother to break this up unless either the LHS is an associable add or
407 // subtract or if this is only used by one.
408 if (isReassociableOp(Sub->getOperand(0), Instruction::Add) ||
409 isReassociableOp(Sub->getOperand(0), Instruction::Sub))
411 if (isReassociableOp(Sub->getOperand(1), Instruction::Add) ||
412 isReassociableOp(Sub->getOperand(1), Instruction::Sub))
414 if (Sub->hasOneUse() &&
415 (isReassociableOp(Sub->use_back(), Instruction::Add) ||
416 isReassociableOp(Sub->use_back(), Instruction::Sub)))
422 /// BreakUpSubtract - If we have (X-Y), and if either X is an add, or if this is
423 /// only used by an add, transform this into (X+(0-Y)) to promote better
425 static Instruction *BreakUpSubtract(Instruction *Sub) {
426 // Convert a subtract into an add and a neg instruction... so that sub
427 // instructions can be commuted with other add instructions...
429 // Calculate the negative value of Operand 1 of the sub instruction...
430 // and set it as the RHS of the add instruction we just made...
432 Value *NegVal = NegateValue(Sub->getOperand(1), Sub);
434 BinaryOperator::CreateAdd(Sub->getOperand(0), NegVal, "", Sub);
437 // Everyone now refers to the add instruction.
438 Sub->replaceAllUsesWith(New);
439 Sub->eraseFromParent();
441 DOUT << "Negated: " << *New;
445 /// ConvertShiftToMul - If this is a shift of a reassociable multiply or is used
446 /// by one, change this into a multiply by a constant to assist with further
448 static Instruction *ConvertShiftToMul(Instruction *Shl) {
449 // If an operand of this shift is a reassociable multiply, or if the shift
450 // is used by a reassociable multiply or add, turn into a multiply.
451 if (isReassociableOp(Shl->getOperand(0), Instruction::Mul) ||
453 (isReassociableOp(Shl->use_back(), Instruction::Mul) ||
454 isReassociableOp(Shl->use_back(), Instruction::Add)))) {
455 Constant *MulCst = ConstantInt::get(Shl->getType(), 1);
456 MulCst = ConstantExpr::getShl(MulCst, cast<Constant>(Shl->getOperand(1)));
458 Instruction *Mul = BinaryOperator::CreateMul(Shl->getOperand(0), MulCst,
461 Shl->replaceAllUsesWith(Mul);
462 Shl->eraseFromParent();
468 // Scan backwards and forwards among values with the same rank as element i to
469 // see if X exists. If X does not exist, return i.
470 static unsigned FindInOperandList(std::vector<ValueEntry> &Ops, unsigned i,
472 unsigned XRank = Ops[i].Rank;
473 unsigned e = Ops.size();
474 for (unsigned j = i+1; j != e && Ops[j].Rank == XRank; ++j)
478 for (unsigned j = i-1; j != ~0U && Ops[j].Rank == XRank; --j)
484 /// EmitAddTreeOfValues - Emit a tree of add instructions, summing Ops together
485 /// and returning the result. Insert the tree before I.
486 static Value *EmitAddTreeOfValues(Instruction *I, std::vector<Value*> &Ops) {
487 if (Ops.size() == 1) return Ops.back();
489 Value *V1 = Ops.back();
491 Value *V2 = EmitAddTreeOfValues(I, Ops);
492 return BinaryOperator::CreateAdd(V2, V1, "tmp", I);
495 /// RemoveFactorFromExpression - If V is an expression tree that is a
496 /// multiplication sequence, and if this sequence contains a multiply by Factor,
497 /// remove Factor from the tree and return the new tree.
498 Value *Reassociate::RemoveFactorFromExpression(Value *V, Value *Factor) {
499 BinaryOperator *BO = isReassociableOp(V, Instruction::Mul);
502 std::vector<ValueEntry> Factors;
503 LinearizeExprTree(BO, Factors);
505 bool FoundFactor = false;
506 for (unsigned i = 0, e = Factors.size(); i != e; ++i)
507 if (Factors[i].Op == Factor) {
509 Factors.erase(Factors.begin()+i);
513 // Make sure to restore the operands to the expression tree.
514 RewriteExprTree(BO, Factors);
518 if (Factors.size() == 1) return Factors[0].Op;
520 RewriteExprTree(BO, Factors);
524 /// FindSingleUseMultiplyFactors - If V is a single-use multiply, recursively
525 /// add its operands as factors, otherwise add V to the list of factors.
526 static void FindSingleUseMultiplyFactors(Value *V,
527 std::vector<Value*> &Factors) {
529 if ((!V->hasOneUse() && !V->use_empty()) ||
530 !(BO = dyn_cast<BinaryOperator>(V)) ||
531 BO->getOpcode() != Instruction::Mul) {
532 Factors.push_back(V);
536 // Otherwise, add the LHS and RHS to the list of factors.
537 FindSingleUseMultiplyFactors(BO->getOperand(1), Factors);
538 FindSingleUseMultiplyFactors(BO->getOperand(0), Factors);
543 Value *Reassociate::OptimizeExpression(BinaryOperator *I,
544 std::vector<ValueEntry> &Ops) {
545 // Now that we have the linearized expression tree, try to optimize it.
546 // Start by folding any constants that we found.
547 bool IterateOptimization = false;
548 if (Ops.size() == 1) return Ops[0].Op;
550 unsigned Opcode = I->getOpcode();
552 if (Constant *V1 = dyn_cast<Constant>(Ops[Ops.size()-2].Op))
553 if (Constant *V2 = dyn_cast<Constant>(Ops.back().Op)) {
555 Ops.back().Op = ConstantExpr::get(Opcode, V1, V2);
556 return OptimizeExpression(I, Ops);
559 // Check for destructive annihilation due to a constant being used.
560 if (ConstantInt *CstVal = dyn_cast<ConstantInt>(Ops.back().Op))
563 case Instruction::And:
564 if (CstVal->isZero()) { // ... & 0 -> 0
567 } else if (CstVal->isAllOnesValue()) { // ... & -1 -> ...
571 case Instruction::Mul:
572 if (CstVal->isZero()) { // ... * 0 -> 0
575 } else if (cast<ConstantInt>(CstVal)->isOne()) {
576 Ops.pop_back(); // ... * 1 -> ...
579 case Instruction::Or:
580 if (CstVal->isAllOnesValue()) { // ... | -1 -> -1
585 case Instruction::Add:
586 case Instruction::Xor:
587 if (CstVal->isZero()) // ... [|^+] 0 -> ...
591 if (Ops.size() == 1) return Ops[0].Op;
593 // Handle destructive annihilation do to identities between elements in the
594 // argument list here.
597 case Instruction::And:
598 case Instruction::Or:
599 case Instruction::Xor:
600 // Scan the operand lists looking for X and ~X pairs, along with X,X pairs.
601 // If we find any, we can simplify the expression. X&~X == 0, X|~X == -1.
602 for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
603 // First, check for X and ~X in the operand list.
604 assert(i < Ops.size());
605 if (BinaryOperator::isNot(Ops[i].Op)) { // Cannot occur for ^.
606 Value *X = BinaryOperator::getNotArgument(Ops[i].Op);
607 unsigned FoundX = FindInOperandList(Ops, i, X);
609 if (Opcode == Instruction::And) { // ...&X&~X = 0
611 return Constant::getNullValue(X->getType());
612 } else if (Opcode == Instruction::Or) { // ...|X|~X = -1
614 return ConstantInt::getAllOnesValue(X->getType());
619 // Next, check for duplicate pairs of values, which we assume are next to
620 // each other, due to our sorting criteria.
621 assert(i < Ops.size());
622 if (i+1 != Ops.size() && Ops[i+1].Op == Ops[i].Op) {
623 if (Opcode == Instruction::And || Opcode == Instruction::Or) {
624 // Drop duplicate values.
625 Ops.erase(Ops.begin()+i);
627 IterateOptimization = true;
630 assert(Opcode == Instruction::Xor);
633 return Constant::getNullValue(Ops[0].Op->getType());
636 Ops.erase(Ops.begin()+i, Ops.begin()+i+2);
638 IterateOptimization = true;
645 case Instruction::Add:
646 // Scan the operand lists looking for X and -X pairs. If we find any, we
647 // can simplify the expression. X+-X == 0.
648 for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
649 assert(i < Ops.size());
650 // Check for X and -X in the operand list.
651 if (BinaryOperator::isNeg(Ops[i].Op)) {
652 Value *X = BinaryOperator::getNegArgument(Ops[i].Op);
653 unsigned FoundX = FindInOperandList(Ops, i, X);
655 // Remove X and -X from the operand list.
656 if (Ops.size() == 2) {
658 return Constant::getNullValue(X->getType());
660 Ops.erase(Ops.begin()+i);
664 --i; // Need to back up an extra one.
665 Ops.erase(Ops.begin()+FoundX);
666 IterateOptimization = true;
668 --i; // Revisit element.
669 e -= 2; // Removed two elements.
676 // Scan the operand list, checking to see if there are any common factors
677 // between operands. Consider something like A*A+A*B*C+D. We would like to
678 // reassociate this to A*(A+B*C)+D, which reduces the number of multiplies.
679 // To efficiently find this, we count the number of times a factor occurs
680 // for any ADD operands that are MULs.
681 std::map<Value*, unsigned> FactorOccurrences;
683 Value *MaxOccVal = 0;
684 for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
685 if (BinaryOperator *BOp = dyn_cast<BinaryOperator>(Ops[i].Op)) {
686 if (BOp->getOpcode() == Instruction::Mul && BOp->use_empty()) {
687 // Compute all of the factors of this added value.
688 std::vector<Value*> Factors;
689 FindSingleUseMultiplyFactors(BOp, Factors);
690 assert(Factors.size() > 1 && "Bad linearize!");
692 // Add one to FactorOccurrences for each unique factor in this op.
693 if (Factors.size() == 2) {
694 unsigned Occ = ++FactorOccurrences[Factors[0]];
695 if (Occ > MaxOcc) { MaxOcc = Occ; MaxOccVal = Factors[0]; }
696 if (Factors[0] != Factors[1]) { // Don't double count A*A.
697 Occ = ++FactorOccurrences[Factors[1]];
698 if (Occ > MaxOcc) { MaxOcc = Occ; MaxOccVal = Factors[1]; }
701 std::set<Value*> Duplicates;
702 for (unsigned i = 0, e = Factors.size(); i != e; ++i) {
703 if (Duplicates.insert(Factors[i]).second) {
704 unsigned Occ = ++FactorOccurrences[Factors[i]];
705 if (Occ > MaxOcc) { MaxOcc = Occ; MaxOccVal = Factors[i]; }
713 // If any factor occurred more than one time, we can pull it out.
715 DOUT << "\nFACTORING [" << MaxOcc << "]: " << *MaxOccVal << "\n";
717 // Create a new instruction that uses the MaxOccVal twice. If we don't do
718 // this, we could otherwise run into situations where removing a factor
719 // from an expression will drop a use of maxocc, and this can cause
720 // RemoveFactorFromExpression on successive values to behave differently.
721 Instruction *DummyInst = BinaryOperator::CreateAdd(MaxOccVal, MaxOccVal);
722 std::vector<Value*> NewMulOps;
723 for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
724 if (Value *V = RemoveFactorFromExpression(Ops[i].Op, MaxOccVal)) {
725 NewMulOps.push_back(V);
726 Ops.erase(Ops.begin()+i);
731 // No need for extra uses anymore.
734 unsigned NumAddedValues = NewMulOps.size();
735 Value *V = EmitAddTreeOfValues(I, NewMulOps);
736 Value *V2 = BinaryOperator::CreateMul(V, MaxOccVal, "tmp", I);
738 // Now that we have inserted V and its sole use, optimize it. This allows
739 // us to handle cases that require multiple factoring steps, such as this:
740 // A*A*B + A*A*C --> A*(A*B+A*C) --> A*(A*(B+C))
741 if (NumAddedValues > 1)
742 ReassociateExpression(cast<BinaryOperator>(V));
749 // Add the new value to the list of things being added.
750 Ops.insert(Ops.begin(), ValueEntry(getRank(V2), V2));
752 // Rewrite the tree so that there is now a use of V.
753 RewriteExprTree(I, Ops);
754 return OptimizeExpression(I, Ops);
757 //case Instruction::Mul:
760 if (IterateOptimization)
761 return OptimizeExpression(I, Ops);
766 /// ReassociateBB - Inspect all of the instructions in this basic block,
767 /// reassociating them as we go.
768 void Reassociate::ReassociateBB(BasicBlock *BB) {
769 for (BasicBlock::iterator BBI = BB->begin(); BBI != BB->end(); ) {
770 Instruction *BI = BBI++;
771 if (BI->getOpcode() == Instruction::Shl &&
772 isa<ConstantInt>(BI->getOperand(1)))
773 if (Instruction *NI = ConvertShiftToMul(BI)) {
778 // Reject cases where it is pointless to do this.
779 if (!isa<BinaryOperator>(BI) || BI->getType()->isFloatingPoint() ||
780 isa<VectorType>(BI->getType()))
781 continue; // Floating point ops are not associative.
783 // If this is a subtract instruction which is not already in negate form,
784 // see if we can convert it to X+-Y.
785 if (BI->getOpcode() == Instruction::Sub) {
786 if (ShouldBreakUpSubtract(BI)) {
787 BI = BreakUpSubtract(BI);
789 } else if (BinaryOperator::isNeg(BI)) {
790 // Otherwise, this is a negation. See if the operand is a multiply tree
791 // and if this is not an inner node of a multiply tree.
792 if (isReassociableOp(BI->getOperand(1), Instruction::Mul) &&
794 !isReassociableOp(BI->use_back(), Instruction::Mul))) {
795 BI = LowerNegateToMultiply(BI);
801 // If this instruction is a commutative binary operator, process it.
802 if (!BI->isAssociative()) continue;
803 BinaryOperator *I = cast<BinaryOperator>(BI);
805 // If this is an interior node of a reassociable tree, ignore it until we
806 // get to the root of the tree, to avoid N^2 analysis.
807 if (I->hasOneUse() && isReassociableOp(I->use_back(), I->getOpcode()))
810 // If this is an add tree that is used by a sub instruction, ignore it
811 // until we process the subtract.
812 if (I->hasOneUse() && I->getOpcode() == Instruction::Add &&
813 cast<Instruction>(I->use_back())->getOpcode() == Instruction::Sub)
816 ReassociateExpression(I);
820 void Reassociate::ReassociateExpression(BinaryOperator *I) {
822 // First, walk the expression tree, linearizing the tree, collecting
823 std::vector<ValueEntry> Ops;
824 LinearizeExprTree(I, Ops);
826 DOUT << "RAIn:\t"; DEBUG(PrintOps(I, Ops)); DOUT << "\n";
828 // Now that we have linearized the tree to a list and have gathered all of
829 // the operands and their ranks, sort the operands by their rank. Use a
830 // stable_sort so that values with equal ranks will have their relative
831 // positions maintained (and so the compiler is deterministic). Note that
832 // this sorts so that the highest ranking values end up at the beginning of
834 std::stable_sort(Ops.begin(), Ops.end());
836 // OptimizeExpression - Now that we have the expression tree in a convenient
837 // sorted form, optimize it globally if possible.
838 if (Value *V = OptimizeExpression(I, Ops)) {
839 // This expression tree simplified to something that isn't a tree,
841 DOUT << "Reassoc to scalar: " << *V << "\n";
842 I->replaceAllUsesWith(V);
843 RemoveDeadBinaryOp(I);
847 // We want to sink immediates as deeply as possible except in the case where
848 // this is a multiply tree used only by an add, and the immediate is a -1.
849 // In this case we reassociate to put the negation on the outside so that we
850 // can fold the negation into the add: (-X)*Y + Z -> Z-X*Y
851 if (I->getOpcode() == Instruction::Mul && I->hasOneUse() &&
852 cast<Instruction>(I->use_back())->getOpcode() == Instruction::Add &&
853 isa<ConstantInt>(Ops.back().Op) &&
854 cast<ConstantInt>(Ops.back().Op)->isAllOnesValue()) {
855 Ops.insert(Ops.begin(), Ops.back());
859 DOUT << "RAOut:\t"; DEBUG(PrintOps(I, Ops)); DOUT << "\n";
861 if (Ops.size() == 1) {
862 // This expression tree simplified to something that isn't a tree,
864 I->replaceAllUsesWith(Ops[0].Op);
865 RemoveDeadBinaryOp(I);
867 // Now that we ordered and optimized the expressions, splat them back into
868 // the expression tree, removing any unneeded nodes.
869 RewriteExprTree(I, Ops);
874 bool Reassociate::runOnFunction(Function &F) {
875 // Recalculate the rank map for F
879 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI)
882 // We are done with the rank map...
884 ValueRankMap.clear();