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/IntrinsicInst.h"
30 #include "llvm/Pass.h"
31 #include "llvm/Assembly/Writer.h"
32 #include "llvm/Support/CFG.h"
33 #include "llvm/Support/Compiler.h"
34 #include "llvm/Support/Debug.h"
35 #include "llvm/ADT/PostOrderIterator.h"
36 #include "llvm/ADT/Statistic.h"
41 STATISTIC(NumLinear , "Number of insts linearized");
42 STATISTIC(NumChanged, "Number of insts reassociated");
43 STATISTIC(NumAnnihil, "Number of expr tree annihilated");
44 STATISTIC(NumFactor , "Number of multiplies factored");
47 struct VISIBILITY_HIDDEN ValueEntry {
50 ValueEntry(unsigned R, Value *O) : Rank(R), Op(O) {}
52 inline bool operator<(const ValueEntry &LHS, const ValueEntry &RHS) {
53 return LHS.Rank > RHS.Rank; // Sort so that highest rank goes to start.
58 /// PrintOps - Print out the expression identified in the Ops list.
60 static void PrintOps(Instruction *I, const std::vector<ValueEntry> &Ops) {
61 Module *M = I->getParent()->getParent()->getParent();
62 cerr << Instruction::getOpcodeName(I->getOpcode()) << " "
63 << *Ops[0].Op->getType();
64 for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
65 WriteAsOperand(*cerr.stream() << " ", Ops[i].Op, false, M);
66 cerr << "," << Ops[i].Rank;
72 class VISIBILITY_HIDDEN Reassociate : public FunctionPass {
73 std::map<BasicBlock*, unsigned> RankMap;
74 std::map<Value*, unsigned> ValueRankMap;
77 static char ID; // Pass identification, replacement for typeid
78 Reassociate() : FunctionPass(&ID) {}
80 bool runOnFunction(Function &F);
82 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
86 void BuildRankMap(Function &F);
87 unsigned getRank(Value *V);
88 void ReassociateExpression(BinaryOperator *I);
89 void RewriteExprTree(BinaryOperator *I, std::vector<ValueEntry> &Ops,
91 Value *OptimizeExpression(BinaryOperator *I, std::vector<ValueEntry> &Ops);
92 void LinearizeExprTree(BinaryOperator *I, std::vector<ValueEntry> &Ops);
93 void LinearizeExpr(BinaryOperator *I);
94 Value *RemoveFactorFromExpression(Value *V, Value *Factor);
95 void ReassociateBB(BasicBlock *BB);
97 void RemoveDeadBinaryOp(Value *V);
101 char Reassociate::ID = 0;
102 static RegisterPass<Reassociate> X("reassociate", "Reassociate expressions");
104 // Public interface to the Reassociate pass
105 FunctionPass *llvm::createReassociatePass() { return new Reassociate(); }
107 void Reassociate::RemoveDeadBinaryOp(Value *V) {
108 Instruction *Op = dyn_cast<Instruction>(V);
109 if (!Op || !isa<BinaryOperator>(Op) || !isa<CmpInst>(Op) || !Op->use_empty())
112 Value *LHS = Op->getOperand(0), *RHS = Op->getOperand(1);
113 RemoveDeadBinaryOp(LHS);
114 RemoveDeadBinaryOp(RHS);
118 static bool isUnmovableInstruction(Instruction *I) {
119 if (I->getOpcode() == Instruction::PHI ||
120 I->getOpcode() == Instruction::Alloca ||
121 I->getOpcode() == Instruction::Load ||
122 I->getOpcode() == Instruction::Malloc ||
123 I->getOpcode() == Instruction::Invoke ||
124 (I->getOpcode() == Instruction::Call &&
125 !isa<DbgInfoIntrinsic>(I)) ||
126 I->getOpcode() == Instruction::UDiv ||
127 I->getOpcode() == Instruction::SDiv ||
128 I->getOpcode() == Instruction::FDiv ||
129 I->getOpcode() == Instruction::URem ||
130 I->getOpcode() == Instruction::SRem ||
131 I->getOpcode() == Instruction::FRem)
136 void Reassociate::BuildRankMap(Function &F) {
139 // Assign distinct ranks to function arguments
140 for (Function::arg_iterator I = F.arg_begin(), E = F.arg_end(); I != E; ++I)
141 ValueRankMap[I] = ++i;
143 ReversePostOrderTraversal<Function*> RPOT(&F);
144 for (ReversePostOrderTraversal<Function*>::rpo_iterator I = RPOT.begin(),
145 E = RPOT.end(); I != E; ++I) {
147 unsigned BBRank = RankMap[BB] = ++i << 16;
149 // Walk the basic block, adding precomputed ranks for any instructions that
150 // we cannot move. This ensures that the ranks for these instructions are
151 // all different in the block.
152 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
153 if (isUnmovableInstruction(I))
154 ValueRankMap[I] = ++BBRank;
158 unsigned Reassociate::getRank(Value *V) {
159 if (isa<Argument>(V)) return ValueRankMap[V]; // Function argument...
161 Instruction *I = dyn_cast<Instruction>(V);
162 if (I == 0) return 0; // Otherwise it's a global or constant, rank 0.
164 unsigned &CachedRank = ValueRankMap[I];
165 if (CachedRank) return CachedRank; // Rank already known?
167 // If this is an expression, return the 1+MAX(rank(LHS), rank(RHS)) so that
168 // we can reassociate expressions for code motion! Since we do not recurse
169 // for PHI nodes, we cannot have infinite recursion here, because there
170 // cannot be loops in the value graph that do not go through PHI nodes.
171 unsigned Rank = 0, MaxRank = RankMap[I->getParent()];
172 for (unsigned i = 0, e = I->getNumOperands();
173 i != e && Rank != MaxRank; ++i)
174 Rank = std::max(Rank, getRank(I->getOperand(i)));
176 // If this is a not or neg instruction, do not count it for rank. This
177 // assures us that X and ~X will have the same rank.
178 if (!I->getType()->isInteger() ||
179 (!BinaryOperator::isNot(I) && !BinaryOperator::isNeg(I)))
182 //DOUT << "Calculated Rank[" << V->getName() << "] = "
185 return CachedRank = Rank;
188 /// isReassociableOp - Return true if V is an instruction of the specified
189 /// opcode and if it only has one use.
190 static BinaryOperator *isReassociableOp(Value *V, unsigned Opcode) {
191 if ((V->hasOneUse() || V->use_empty()) && isa<Instruction>(V) &&
192 cast<Instruction>(V)->getOpcode() == Opcode)
193 return cast<BinaryOperator>(V);
197 /// LowerNegateToMultiply - Replace 0-X with X*-1.
199 static Instruction *LowerNegateToMultiply(Instruction *Neg,
200 std::map<Value*, unsigned> &ValueRankMap) {
201 Constant *Cst = ConstantInt::getAllOnesValue(Neg->getType());
203 Instruction *Res = BinaryOperator::CreateMul(Neg->getOperand(1), Cst, "",Neg);
204 ValueRankMap.erase(Neg);
206 Neg->replaceAllUsesWith(Res);
207 Neg->eraseFromParent();
211 // Given an expression of the form '(A+B)+(D+C)', turn it into '(((A+B)+C)+D)'.
212 // Note that if D is also part of the expression tree that we recurse to
213 // linearize it as well. Besides that case, this does not recurse into A,B, or
215 void Reassociate::LinearizeExpr(BinaryOperator *I) {
216 BinaryOperator *LHS = cast<BinaryOperator>(I->getOperand(0));
217 BinaryOperator *RHS = cast<BinaryOperator>(I->getOperand(1));
218 assert(isReassociableOp(LHS, I->getOpcode()) &&
219 isReassociableOp(RHS, I->getOpcode()) &&
220 "Not an expression that needs linearization?");
222 DOUT << "Linear" << *LHS << *RHS << *I;
224 // Move the RHS instruction to live immediately before I, avoiding breaking
225 // dominator properties.
228 // Move operands around to do the linearization.
229 I->setOperand(1, RHS->getOperand(0));
230 RHS->setOperand(0, LHS);
231 I->setOperand(0, RHS);
235 DOUT << "Linearized: " << *I;
237 // If D is part of this expression tree, tail recurse.
238 if (isReassociableOp(I->getOperand(1), I->getOpcode()))
243 /// LinearizeExprTree - Given an associative binary expression tree, traverse
244 /// all of the uses putting it into canonical form. This forces a left-linear
245 /// form of the the expression (((a+b)+c)+d), and collects information about the
246 /// rank of the non-tree operands.
248 /// NOTE: These intentionally destroys the expression tree operands (turning
249 /// them into undef values) to reduce #uses of the values. This means that the
250 /// caller MUST use something like RewriteExprTree to put the values back in.
252 void Reassociate::LinearizeExprTree(BinaryOperator *I,
253 std::vector<ValueEntry> &Ops) {
254 Value *LHS = I->getOperand(0), *RHS = I->getOperand(1);
255 unsigned Opcode = I->getOpcode();
257 // First step, linearize the expression if it is in ((A+B)+(C+D)) form.
258 BinaryOperator *LHSBO = isReassociableOp(LHS, Opcode);
259 BinaryOperator *RHSBO = isReassociableOp(RHS, Opcode);
261 // If this is a multiply expression tree and it contains internal negations,
262 // transform them into multiplies by -1 so they can be reassociated.
263 if (I->getOpcode() == Instruction::Mul) {
264 if (!LHSBO && LHS->hasOneUse() && BinaryOperator::isNeg(LHS)) {
265 LHS = LowerNegateToMultiply(cast<Instruction>(LHS), ValueRankMap);
266 LHSBO = isReassociableOp(LHS, Opcode);
268 if (!RHSBO && RHS->hasOneUse() && BinaryOperator::isNeg(RHS)) {
269 RHS = LowerNegateToMultiply(cast<Instruction>(RHS), ValueRankMap);
270 RHSBO = isReassociableOp(RHS, Opcode);
276 // Neither the LHS or RHS as part of the tree, thus this is a leaf. As
277 // such, just remember these operands and their rank.
278 Ops.push_back(ValueEntry(getRank(LHS), LHS));
279 Ops.push_back(ValueEntry(getRank(RHS), RHS));
281 // Clear the leaves out.
282 I->setOperand(0, UndefValue::get(I->getType()));
283 I->setOperand(1, UndefValue::get(I->getType()));
286 // Turn X+(Y+Z) -> (Y+Z)+X
287 std::swap(LHSBO, RHSBO);
289 bool Success = !I->swapOperands();
290 assert(Success && "swapOperands failed");
295 // Turn (A+B)+(C+D) -> (((A+B)+C)+D). This guarantees the the RHS is not
296 // part of the expression tree.
298 LHS = LHSBO = cast<BinaryOperator>(I->getOperand(0));
299 RHS = I->getOperand(1);
303 // Okay, now we know that the LHS is a nested expression and that the RHS is
304 // not. Perform reassociation.
305 assert(!isReassociableOp(RHS, Opcode) && "LinearizeExpr failed!");
307 // Move LHS right before I to make sure that the tree expression dominates all
309 LHSBO->moveBefore(I);
311 // Linearize the expression tree on the LHS.
312 LinearizeExprTree(LHSBO, Ops);
314 // Remember the RHS operand and its rank.
315 Ops.push_back(ValueEntry(getRank(RHS), RHS));
317 // Clear the RHS leaf out.
318 I->setOperand(1, UndefValue::get(I->getType()));
321 // RewriteExprTree - Now that the operands for this expression tree are
322 // linearized and optimized, emit them in-order. This function is written to be
324 void Reassociate::RewriteExprTree(BinaryOperator *I,
325 std::vector<ValueEntry> &Ops,
327 if (i+2 == Ops.size()) {
328 if (I->getOperand(0) != Ops[i].Op ||
329 I->getOperand(1) != Ops[i+1].Op) {
330 Value *OldLHS = I->getOperand(0);
331 DOUT << "RA: " << *I;
332 I->setOperand(0, Ops[i].Op);
333 I->setOperand(1, Ops[i+1].Op);
334 DOUT << "TO: " << *I;
338 // If we reassociated a tree to fewer operands (e.g. (1+a+2) -> (a+3)
339 // delete the extra, now dead, nodes.
340 RemoveDeadBinaryOp(OldLHS);
344 assert(i+2 < Ops.size() && "Ops index out of range!");
346 if (I->getOperand(1) != Ops[i].Op) {
347 DOUT << "RA: " << *I;
348 I->setOperand(1, Ops[i].Op);
349 DOUT << "TO: " << *I;
354 BinaryOperator *LHS = cast<BinaryOperator>(I->getOperand(0));
355 assert(LHS->getOpcode() == I->getOpcode() &&
356 "Improper expression tree!");
358 // Compactify the tree instructions together with each other to guarantee
359 // that the expression tree is dominated by all of Ops.
361 RewriteExprTree(LHS, Ops, i+1);
366 // NegateValue - Insert instructions before the instruction pointed to by BI,
367 // that computes the negative version of the value specified. The negative
368 // version of the value is returned, and BI is left pointing at the instruction
369 // that should be processed next by the reassociation pass.
371 static Value *NegateValue(Value *V, Instruction *BI) {
372 // We are trying to expose opportunity for reassociation. One of the things
373 // that we want to do to achieve this is to push a negation as deep into an
374 // expression chain as possible, to expose the add instructions. In practice,
375 // this means that we turn this:
376 // X = -(A+12+C+D) into X = -A + -12 + -C + -D = -12 + -A + -C + -D
377 // so that later, a: Y = 12+X could get reassociated with the -12 to eliminate
378 // the constants. We assume that instcombine will clean up the mess later if
379 // we introduce tons of unnecessary negation instructions...
381 if (Instruction *I = dyn_cast<Instruction>(V))
382 if (I->getOpcode() == Instruction::Add && I->hasOneUse()) {
383 // Push the negates through the add.
384 I->setOperand(0, NegateValue(I->getOperand(0), BI));
385 I->setOperand(1, NegateValue(I->getOperand(1), BI));
387 // We must move the add instruction here, because the neg instructions do
388 // not dominate the old add instruction in general. By moving it, we are
389 // assured that the neg instructions we just inserted dominate the
390 // instruction we are about to insert after them.
393 I->setName(I->getName()+".neg");
397 // Insert a 'neg' instruction that subtracts the value from zero to get the
400 return BinaryOperator::CreateNeg(V, V->getName() + ".neg", BI);
403 /// ShouldBreakUpSubtract - Return true if we should break up this subtract of
404 /// X-Y into (X + -Y).
405 static bool ShouldBreakUpSubtract(Instruction *Sub) {
406 // If this is a negation, we can't split it up!
407 if (BinaryOperator::isNeg(Sub))
410 // Don't bother to break this up unless either the LHS is an associable add or
411 // subtract or if this is only used by one.
412 if (isReassociableOp(Sub->getOperand(0), Instruction::Add) ||
413 isReassociableOp(Sub->getOperand(0), Instruction::Sub))
415 if (isReassociableOp(Sub->getOperand(1), Instruction::Add) ||
416 isReassociableOp(Sub->getOperand(1), Instruction::Sub))
418 if (Sub->hasOneUse() &&
419 (isReassociableOp(Sub->use_back(), Instruction::Add) ||
420 isReassociableOp(Sub->use_back(), Instruction::Sub)))
426 /// BreakUpSubtract - If we have (X-Y), and if either X is an add, or if this is
427 /// only used by an add, transform this into (X+(0-Y)) to promote better
429 static Instruction *BreakUpSubtract(Instruction *Sub,
430 std::map<Value*, unsigned> &ValueRankMap) {
431 // Convert a subtract into an add and a neg instruction... so that sub
432 // instructions can be commuted with other add instructions...
434 // Calculate the negative value of Operand 1 of the sub instruction...
435 // and set it as the RHS of the add instruction we just made...
437 Value *NegVal = NegateValue(Sub->getOperand(1), Sub);
439 BinaryOperator::CreateAdd(Sub->getOperand(0), NegVal, "", Sub);
442 // Everyone now refers to the add instruction.
443 ValueRankMap.erase(Sub);
444 Sub->replaceAllUsesWith(New);
445 Sub->eraseFromParent();
447 DOUT << "Negated: " << *New;
451 /// ConvertShiftToMul - If this is a shift of a reassociable multiply or is used
452 /// by one, change this into a multiply by a constant to assist with further
454 static Instruction *ConvertShiftToMul(Instruction *Shl,
455 std::map<Value*, unsigned> &ValueRankMap){
456 // If an operand of this shift is a reassociable multiply, or if the shift
457 // is used by a reassociable multiply or add, turn into a multiply.
458 if (isReassociableOp(Shl->getOperand(0), Instruction::Mul) ||
460 (isReassociableOp(Shl->use_back(), Instruction::Mul) ||
461 isReassociableOp(Shl->use_back(), Instruction::Add)))) {
462 Constant *MulCst = ConstantInt::get(Shl->getType(), 1);
463 MulCst = ConstantExpr::getShl(MulCst, cast<Constant>(Shl->getOperand(1)));
465 Instruction *Mul = BinaryOperator::CreateMul(Shl->getOperand(0), MulCst,
467 ValueRankMap.erase(Shl);
469 Shl->replaceAllUsesWith(Mul);
470 Shl->eraseFromParent();
476 // Scan backwards and forwards among values with the same rank as element i to
477 // see if X exists. If X does not exist, return i.
478 static unsigned FindInOperandList(std::vector<ValueEntry> &Ops, unsigned i,
480 unsigned XRank = Ops[i].Rank;
481 unsigned e = Ops.size();
482 for (unsigned j = i+1; j != e && Ops[j].Rank == XRank; ++j)
486 for (unsigned j = i-1; j != ~0U && Ops[j].Rank == XRank; --j)
492 /// EmitAddTreeOfValues - Emit a tree of add instructions, summing Ops together
493 /// and returning the result. Insert the tree before I.
494 static Value *EmitAddTreeOfValues(Instruction *I, std::vector<Value*> &Ops) {
495 if (Ops.size() == 1) return Ops.back();
497 Value *V1 = Ops.back();
499 Value *V2 = EmitAddTreeOfValues(I, Ops);
500 return BinaryOperator::CreateAdd(V2, V1, "tmp", I);
503 /// RemoveFactorFromExpression - If V is an expression tree that is a
504 /// multiplication sequence, and if this sequence contains a multiply by Factor,
505 /// remove Factor from the tree and return the new tree.
506 Value *Reassociate::RemoveFactorFromExpression(Value *V, Value *Factor) {
507 BinaryOperator *BO = isReassociableOp(V, Instruction::Mul);
510 std::vector<ValueEntry> Factors;
511 LinearizeExprTree(BO, Factors);
513 bool FoundFactor = false;
514 for (unsigned i = 0, e = Factors.size(); i != e; ++i)
515 if (Factors[i].Op == Factor) {
517 Factors.erase(Factors.begin()+i);
521 // Make sure to restore the operands to the expression tree.
522 RewriteExprTree(BO, Factors);
526 if (Factors.size() == 1) return Factors[0].Op;
528 RewriteExprTree(BO, Factors);
532 /// FindSingleUseMultiplyFactors - If V is a single-use multiply, recursively
533 /// add its operands as factors, otherwise add V to the list of factors.
534 static void FindSingleUseMultiplyFactors(Value *V,
535 std::vector<Value*> &Factors) {
537 if ((!V->hasOneUse() && !V->use_empty()) ||
538 !(BO = dyn_cast<BinaryOperator>(V)) ||
539 BO->getOpcode() != Instruction::Mul) {
540 Factors.push_back(V);
544 // Otherwise, add the LHS and RHS to the list of factors.
545 FindSingleUseMultiplyFactors(BO->getOperand(1), Factors);
546 FindSingleUseMultiplyFactors(BO->getOperand(0), Factors);
551 Value *Reassociate::OptimizeExpression(BinaryOperator *I,
552 std::vector<ValueEntry> &Ops) {
553 // Now that we have the linearized expression tree, try to optimize it.
554 // Start by folding any constants that we found.
555 bool IterateOptimization = false;
556 if (Ops.size() == 1) return Ops[0].Op;
558 unsigned Opcode = I->getOpcode();
560 if (Constant *V1 = dyn_cast<Constant>(Ops[Ops.size()-2].Op))
561 if (Constant *V2 = dyn_cast<Constant>(Ops.back().Op)) {
563 Ops.back().Op = ConstantExpr::get(Opcode, V1, V2);
564 return OptimizeExpression(I, Ops);
567 // Check for destructive annihilation due to a constant being used.
568 if (ConstantInt *CstVal = dyn_cast<ConstantInt>(Ops.back().Op))
571 case Instruction::And:
572 if (CstVal->isZero()) { // ... & 0 -> 0
575 } else if (CstVal->isAllOnesValue()) { // ... & -1 -> ...
579 case Instruction::Mul:
580 if (CstVal->isZero()) { // ... * 0 -> 0
583 } else if (cast<ConstantInt>(CstVal)->isOne()) {
584 Ops.pop_back(); // ... * 1 -> ...
587 case Instruction::Or:
588 if (CstVal->isAllOnesValue()) { // ... | -1 -> -1
593 case Instruction::Add:
594 case Instruction::Xor:
595 if (CstVal->isZero()) // ... [|^+] 0 -> ...
599 if (Ops.size() == 1) return Ops[0].Op;
601 // Handle destructive annihilation do to identities between elements in the
602 // argument list here.
605 case Instruction::And:
606 case Instruction::Or:
607 case Instruction::Xor:
608 // Scan the operand lists looking for X and ~X pairs, along with X,X pairs.
609 // If we find any, we can simplify the expression. X&~X == 0, X|~X == -1.
610 for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
611 // First, check for X and ~X in the operand list.
612 assert(i < Ops.size());
613 if (BinaryOperator::isNot(Ops[i].Op)) { // Cannot occur for ^.
614 Value *X = BinaryOperator::getNotArgument(Ops[i].Op);
615 unsigned FoundX = FindInOperandList(Ops, i, X);
617 if (Opcode == Instruction::And) { // ...&X&~X = 0
619 return Constant::getNullValue(X->getType());
620 } else if (Opcode == Instruction::Or) { // ...|X|~X = -1
622 return ConstantInt::getAllOnesValue(X->getType());
627 // Next, check for duplicate pairs of values, which we assume are next to
628 // each other, due to our sorting criteria.
629 assert(i < Ops.size());
630 if (i+1 != Ops.size() && Ops[i+1].Op == Ops[i].Op) {
631 if (Opcode == Instruction::And || Opcode == Instruction::Or) {
632 // Drop duplicate values.
633 Ops.erase(Ops.begin()+i);
635 IterateOptimization = true;
638 assert(Opcode == Instruction::Xor);
641 return Constant::getNullValue(Ops[0].Op->getType());
644 Ops.erase(Ops.begin()+i, Ops.begin()+i+2);
646 IterateOptimization = true;
653 case Instruction::Add:
654 // Scan the operand lists looking for X and -X pairs. If we find any, we
655 // can simplify the expression. X+-X == 0.
656 for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
657 assert(i < Ops.size());
658 // Check for X and -X in the operand list.
659 if (BinaryOperator::isNeg(Ops[i].Op)) {
660 Value *X = BinaryOperator::getNegArgument(Ops[i].Op);
661 unsigned FoundX = FindInOperandList(Ops, i, X);
663 // Remove X and -X from the operand list.
664 if (Ops.size() == 2) {
666 return Constant::getNullValue(X->getType());
668 Ops.erase(Ops.begin()+i);
672 --i; // Need to back up an extra one.
673 Ops.erase(Ops.begin()+FoundX);
674 IterateOptimization = true;
676 --i; // Revisit element.
677 e -= 2; // Removed two elements.
684 // Scan the operand list, checking to see if there are any common factors
685 // between operands. Consider something like A*A+A*B*C+D. We would like to
686 // reassociate this to A*(A+B*C)+D, which reduces the number of multiplies.
687 // To efficiently find this, we count the number of times a factor occurs
688 // for any ADD operands that are MULs.
689 std::map<Value*, unsigned> FactorOccurrences;
691 Value *MaxOccVal = 0;
692 for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
693 if (BinaryOperator *BOp = dyn_cast<BinaryOperator>(Ops[i].Op)) {
694 if (BOp->getOpcode() == Instruction::Mul && BOp->use_empty()) {
695 // Compute all of the factors of this added value.
696 std::vector<Value*> Factors;
697 FindSingleUseMultiplyFactors(BOp, Factors);
698 assert(Factors.size() > 1 && "Bad linearize!");
700 // Add one to FactorOccurrences for each unique factor in this op.
701 if (Factors.size() == 2) {
702 unsigned Occ = ++FactorOccurrences[Factors[0]];
703 if (Occ > MaxOcc) { MaxOcc = Occ; MaxOccVal = Factors[0]; }
704 if (Factors[0] != Factors[1]) { // Don't double count A*A.
705 Occ = ++FactorOccurrences[Factors[1]];
706 if (Occ > MaxOcc) { MaxOcc = Occ; MaxOccVal = Factors[1]; }
709 std::set<Value*> Duplicates;
710 for (unsigned i = 0, e = Factors.size(); i != e; ++i) {
711 if (Duplicates.insert(Factors[i]).second) {
712 unsigned Occ = ++FactorOccurrences[Factors[i]];
713 if (Occ > MaxOcc) { MaxOcc = Occ; MaxOccVal = Factors[i]; }
721 // If any factor occurred more than one time, we can pull it out.
723 DOUT << "\nFACTORING [" << MaxOcc << "]: " << *MaxOccVal << "\n";
725 // Create a new instruction that uses the MaxOccVal twice. If we don't do
726 // this, we could otherwise run into situations where removing a factor
727 // from an expression will drop a use of maxocc, and this can cause
728 // RemoveFactorFromExpression on successive values to behave differently.
729 Instruction *DummyInst = BinaryOperator::CreateAdd(MaxOccVal, MaxOccVal);
730 std::vector<Value*> NewMulOps;
731 for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
732 if (Value *V = RemoveFactorFromExpression(Ops[i].Op, MaxOccVal)) {
733 NewMulOps.push_back(V);
734 Ops.erase(Ops.begin()+i);
739 // No need for extra uses anymore.
742 unsigned NumAddedValues = NewMulOps.size();
743 Value *V = EmitAddTreeOfValues(I, NewMulOps);
744 Value *V2 = BinaryOperator::CreateMul(V, MaxOccVal, "tmp", I);
746 // Now that we have inserted V and its sole use, optimize it. This allows
747 // us to handle cases that require multiple factoring steps, such as this:
748 // A*A*B + A*A*C --> A*(A*B+A*C) --> A*(A*(B+C))
749 if (NumAddedValues > 1)
750 ReassociateExpression(cast<BinaryOperator>(V));
757 // Add the new value to the list of things being added.
758 Ops.insert(Ops.begin(), ValueEntry(getRank(V2), V2));
760 // Rewrite the tree so that there is now a use of V.
761 RewriteExprTree(I, Ops);
762 return OptimizeExpression(I, Ops);
765 //case Instruction::Mul:
768 if (IterateOptimization)
769 return OptimizeExpression(I, Ops);
774 /// ReassociateBB - Inspect all of the instructions in this basic block,
775 /// reassociating them as we go.
776 void Reassociate::ReassociateBB(BasicBlock *BB) {
777 for (BasicBlock::iterator BBI = BB->begin(); BBI != BB->end(); ) {
778 Instruction *BI = BBI++;
779 if (BI->getOpcode() == Instruction::Shl &&
780 isa<ConstantInt>(BI->getOperand(1)))
781 if (Instruction *NI = ConvertShiftToMul(BI, ValueRankMap)) {
786 // Reject cases where it is pointless to do this.
787 if (!isa<BinaryOperator>(BI) || BI->getType()->isFloatingPoint() ||
788 isa<VectorType>(BI->getType()))
789 continue; // Floating point ops are not associative.
791 // If this is a subtract instruction which is not already in negate form,
792 // see if we can convert it to X+-Y.
793 if (BI->getOpcode() == Instruction::Sub) {
794 if (ShouldBreakUpSubtract(BI)) {
795 BI = BreakUpSubtract(BI, ValueRankMap);
797 } else if (BinaryOperator::isNeg(BI)) {
798 // Otherwise, this is a negation. See if the operand is a multiply tree
799 // and if this is not an inner node of a multiply tree.
800 if (isReassociableOp(BI->getOperand(1), Instruction::Mul) &&
802 !isReassociableOp(BI->use_back(), Instruction::Mul))) {
803 BI = LowerNegateToMultiply(BI, ValueRankMap);
809 // If this instruction is a commutative binary operator, process it.
810 if (!BI->isAssociative()) continue;
811 BinaryOperator *I = cast<BinaryOperator>(BI);
813 // If this is an interior node of a reassociable tree, ignore it until we
814 // get to the root of the tree, to avoid N^2 analysis.
815 if (I->hasOneUse() && isReassociableOp(I->use_back(), I->getOpcode()))
818 // If this is an add tree that is used by a sub instruction, ignore it
819 // until we process the subtract.
820 if (I->hasOneUse() && I->getOpcode() == Instruction::Add &&
821 cast<Instruction>(I->use_back())->getOpcode() == Instruction::Sub)
824 ReassociateExpression(I);
828 void Reassociate::ReassociateExpression(BinaryOperator *I) {
830 // First, walk the expression tree, linearizing the tree, collecting
831 std::vector<ValueEntry> Ops;
832 LinearizeExprTree(I, Ops);
834 DOUT << "RAIn:\t"; DEBUG(PrintOps(I, Ops)); DOUT << "\n";
836 // Now that we have linearized the tree to a list and have gathered all of
837 // the operands and their ranks, sort the operands by their rank. Use a
838 // stable_sort so that values with equal ranks will have their relative
839 // positions maintained (and so the compiler is deterministic). Note that
840 // this sorts so that the highest ranking values end up at the beginning of
842 std::stable_sort(Ops.begin(), Ops.end());
844 // OptimizeExpression - Now that we have the expression tree in a convenient
845 // sorted form, optimize it globally if possible.
846 if (Value *V = OptimizeExpression(I, Ops)) {
847 // This expression tree simplified to something that isn't a tree,
849 DOUT << "Reassoc to scalar: " << *V << "\n";
850 I->replaceAllUsesWith(V);
851 RemoveDeadBinaryOp(I);
855 // We want to sink immediates as deeply as possible except in the case where
856 // this is a multiply tree used only by an add, and the immediate is a -1.
857 // In this case we reassociate to put the negation on the outside so that we
858 // can fold the negation into the add: (-X)*Y + Z -> Z-X*Y
859 if (I->getOpcode() == Instruction::Mul && I->hasOneUse() &&
860 cast<Instruction>(I->use_back())->getOpcode() == Instruction::Add &&
861 isa<ConstantInt>(Ops.back().Op) &&
862 cast<ConstantInt>(Ops.back().Op)->isAllOnesValue()) {
863 Ops.insert(Ops.begin(), Ops.back());
867 DOUT << "RAOut:\t"; DEBUG(PrintOps(I, Ops)); DOUT << "\n";
869 if (Ops.size() == 1) {
870 // This expression tree simplified to something that isn't a tree,
872 I->replaceAllUsesWith(Ops[0].Op);
873 RemoveDeadBinaryOp(I);
875 // Now that we ordered and optimized the expressions, splat them back into
876 // the expression tree, removing any unneeded nodes.
877 RewriteExprTree(I, Ops);
882 bool Reassociate::runOnFunction(Function &F) {
883 // Recalculate the rank map for F
887 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI)
890 // We are done with the rank map...
892 ValueRankMap.clear();