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/Debug.h"
34 #include "llvm/Support/ValueHandle.h"
35 #include "llvm/Support/raw_ostream.h"
36 #include "llvm/ADT/PostOrderIterator.h"
37 #include "llvm/ADT/Statistic.h"
38 #include "llvm/ADT/DenseMap.h"
43 STATISTIC(NumLinear , "Number of insts linearized");
44 STATISTIC(NumChanged, "Number of insts reassociated");
45 STATISTIC(NumAnnihil, "Number of expr tree annihilated");
46 STATISTIC(NumFactor , "Number of multiplies factored");
52 ValueEntry(unsigned R, Value *O) : Rank(R), Op(O) {}
54 inline bool operator<(const ValueEntry &LHS, const ValueEntry &RHS) {
55 return LHS.Rank > RHS.Rank; // Sort so that highest rank goes to start.
60 /// PrintOps - Print out the expression identified in the Ops list.
62 static void PrintOps(Instruction *I, const SmallVectorImpl<ValueEntry> &Ops) {
63 Module *M = I->getParent()->getParent()->getParent();
64 errs() << Instruction::getOpcodeName(I->getOpcode()) << " "
65 << *Ops[0].Op->getType() << '\t';
66 for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
68 WriteAsOperand(errs(), Ops[i].Op, false, M);
69 errs() << ", #" << Ops[i].Rank << "] ";
75 class Reassociate : public FunctionPass {
76 std::map<BasicBlock*, unsigned> RankMap;
77 std::map<AssertingVH<>, unsigned> ValueRankMap;
80 static char ID; // Pass identification, replacement for typeid
81 Reassociate() : FunctionPass(&ID) {}
83 bool runOnFunction(Function &F);
85 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
89 void BuildRankMap(Function &F);
90 unsigned getRank(Value *V);
91 Value *ReassociateExpression(BinaryOperator *I);
92 void RewriteExprTree(BinaryOperator *I, SmallVectorImpl<ValueEntry> &Ops,
94 Value *OptimizeExpression(BinaryOperator *I,
95 SmallVectorImpl<ValueEntry> &Ops);
96 Value *OptimizeAdd(Instruction *I, SmallVectorImpl<ValueEntry> &Ops);
97 void LinearizeExprTree(BinaryOperator *I, SmallVectorImpl<ValueEntry> &Ops);
98 void LinearizeExpr(BinaryOperator *I);
99 Value *RemoveFactorFromExpression(Value *V, Value *Factor);
100 void ReassociateBB(BasicBlock *BB);
102 void RemoveDeadBinaryOp(Value *V);
106 char Reassociate::ID = 0;
107 static RegisterPass<Reassociate> X("reassociate", "Reassociate expressions");
109 // Public interface to the Reassociate pass
110 FunctionPass *llvm::createReassociatePass() { return new Reassociate(); }
112 void Reassociate::RemoveDeadBinaryOp(Value *V) {
113 Instruction *Op = dyn_cast<Instruction>(V);
114 if (!Op || !isa<BinaryOperator>(Op) || !Op->use_empty())
117 Value *LHS = Op->getOperand(0), *RHS = Op->getOperand(1);
119 ValueRankMap.erase(Op);
120 Op->eraseFromParent();
121 RemoveDeadBinaryOp(LHS);
122 RemoveDeadBinaryOp(RHS);
126 static bool isUnmovableInstruction(Instruction *I) {
127 if (I->getOpcode() == Instruction::PHI ||
128 I->getOpcode() == Instruction::Alloca ||
129 I->getOpcode() == Instruction::Load ||
130 I->getOpcode() == Instruction::Invoke ||
131 (I->getOpcode() == Instruction::Call &&
132 !isa<DbgInfoIntrinsic>(I)) ||
133 I->getOpcode() == Instruction::UDiv ||
134 I->getOpcode() == Instruction::SDiv ||
135 I->getOpcode() == Instruction::FDiv ||
136 I->getOpcode() == Instruction::URem ||
137 I->getOpcode() == Instruction::SRem ||
138 I->getOpcode() == Instruction::FRem)
143 void Reassociate::BuildRankMap(Function &F) {
146 // Assign distinct ranks to function arguments
147 for (Function::arg_iterator I = F.arg_begin(), E = F.arg_end(); I != E; ++I)
148 ValueRankMap[&*I] = ++i;
150 ReversePostOrderTraversal<Function*> RPOT(&F);
151 for (ReversePostOrderTraversal<Function*>::rpo_iterator I = RPOT.begin(),
152 E = RPOT.end(); I != E; ++I) {
154 unsigned BBRank = RankMap[BB] = ++i << 16;
156 // Walk the basic block, adding precomputed ranks for any instructions that
157 // we cannot move. This ensures that the ranks for these instructions are
158 // all different in the block.
159 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
160 if (isUnmovableInstruction(I))
161 ValueRankMap[&*I] = ++BBRank;
165 unsigned Reassociate::getRank(Value *V) {
166 if (isa<Argument>(V)) return ValueRankMap[V]; // Function argument...
168 Instruction *I = dyn_cast<Instruction>(V);
169 if (I == 0) return 0; // Otherwise it's a global or constant, rank 0.
171 unsigned &CachedRank = ValueRankMap[I];
172 if (CachedRank) return CachedRank; // Rank already known?
174 // If this is an expression, return the 1+MAX(rank(LHS), rank(RHS)) so that
175 // we can reassociate expressions for code motion! Since we do not recurse
176 // for PHI nodes, we cannot have infinite recursion here, because there
177 // cannot be loops in the value graph that do not go through PHI nodes.
178 unsigned Rank = 0, MaxRank = RankMap[I->getParent()];
179 for (unsigned i = 0, e = I->getNumOperands();
180 i != e && Rank != MaxRank; ++i)
181 Rank = std::max(Rank, getRank(I->getOperand(i)));
183 // If this is a not or neg instruction, do not count it for rank. This
184 // assures us that X and ~X will have the same rank.
185 if (!I->getType()->isInteger() ||
186 (!BinaryOperator::isNot(I) && !BinaryOperator::isNeg(I)))
189 //DEBUG(errs() << "Calculated Rank[" << V->getName() << "] = "
192 return CachedRank = Rank;
195 /// isReassociableOp - Return true if V is an instruction of the specified
196 /// opcode and if it only has one use.
197 static BinaryOperator *isReassociableOp(Value *V, unsigned Opcode) {
198 if ((V->hasOneUse() || V->use_empty()) && isa<Instruction>(V) &&
199 cast<Instruction>(V)->getOpcode() == Opcode)
200 return cast<BinaryOperator>(V);
204 /// LowerNegateToMultiply - Replace 0-X with X*-1.
206 static Instruction *LowerNegateToMultiply(Instruction *Neg,
207 std::map<AssertingVH<>, unsigned> &ValueRankMap) {
208 Constant *Cst = Constant::getAllOnesValue(Neg->getType());
210 Instruction *Res = BinaryOperator::CreateMul(Neg->getOperand(1), Cst, "",Neg);
211 ValueRankMap.erase(Neg);
213 Neg->replaceAllUsesWith(Res);
214 Neg->eraseFromParent();
218 // Given an expression of the form '(A+B)+(D+C)', turn it into '(((A+B)+C)+D)'.
219 // Note that if D is also part of the expression tree that we recurse to
220 // linearize it as well. Besides that case, this does not recurse into A,B, or
222 void Reassociate::LinearizeExpr(BinaryOperator *I) {
223 BinaryOperator *LHS = cast<BinaryOperator>(I->getOperand(0));
224 BinaryOperator *RHS = cast<BinaryOperator>(I->getOperand(1));
225 assert(isReassociableOp(LHS, I->getOpcode()) &&
226 isReassociableOp(RHS, I->getOpcode()) &&
227 "Not an expression that needs linearization?");
229 DEBUG(errs() << "Linear" << *LHS << '\n' << *RHS << '\n' << *I << '\n');
231 // Move the RHS instruction to live immediately before I, avoiding breaking
232 // dominator properties.
235 // Move operands around to do the linearization.
236 I->setOperand(1, RHS->getOperand(0));
237 RHS->setOperand(0, LHS);
238 I->setOperand(0, RHS);
242 DEBUG(errs() << "Linearized: " << *I << '\n');
244 // If D is part of this expression tree, tail recurse.
245 if (isReassociableOp(I->getOperand(1), I->getOpcode()))
250 /// LinearizeExprTree - Given an associative binary expression tree, traverse
251 /// all of the uses putting it into canonical form. This forces a left-linear
252 /// form of the the expression (((a+b)+c)+d), and collects information about the
253 /// rank of the non-tree operands.
255 /// NOTE: These intentionally destroys the expression tree operands (turning
256 /// them into undef values) to reduce #uses of the values. This means that the
257 /// caller MUST use something like RewriteExprTree to put the values back in.
259 void Reassociate::LinearizeExprTree(BinaryOperator *I,
260 SmallVectorImpl<ValueEntry> &Ops) {
261 Value *LHS = I->getOperand(0), *RHS = I->getOperand(1);
262 unsigned Opcode = I->getOpcode();
264 // First step, linearize the expression if it is in ((A+B)+(C+D)) form.
265 BinaryOperator *LHSBO = isReassociableOp(LHS, Opcode);
266 BinaryOperator *RHSBO = isReassociableOp(RHS, Opcode);
268 // If this is a multiply expression tree and it contains internal negations,
269 // transform them into multiplies by -1 so they can be reassociated.
270 if (I->getOpcode() == Instruction::Mul) {
271 if (!LHSBO && LHS->hasOneUse() && BinaryOperator::isNeg(LHS)) {
272 LHS = LowerNegateToMultiply(cast<Instruction>(LHS), ValueRankMap);
273 LHSBO = isReassociableOp(LHS, Opcode);
275 if (!RHSBO && RHS->hasOneUse() && BinaryOperator::isNeg(RHS)) {
276 RHS = LowerNegateToMultiply(cast<Instruction>(RHS), ValueRankMap);
277 RHSBO = isReassociableOp(RHS, Opcode);
283 // Neither the LHS or RHS as part of the tree, thus this is a leaf. As
284 // such, just remember these operands and their rank.
285 Ops.push_back(ValueEntry(getRank(LHS), LHS));
286 Ops.push_back(ValueEntry(getRank(RHS), RHS));
288 // Clear the leaves out.
289 I->setOperand(0, UndefValue::get(I->getType()));
290 I->setOperand(1, UndefValue::get(I->getType()));
294 // Turn X+(Y+Z) -> (Y+Z)+X
295 std::swap(LHSBO, RHSBO);
297 bool Success = !I->swapOperands();
298 assert(Success && "swapOperands failed");
302 // Turn (A+B)+(C+D) -> (((A+B)+C)+D). This guarantees the the RHS is not
303 // part of the expression tree.
305 LHS = LHSBO = cast<BinaryOperator>(I->getOperand(0));
306 RHS = I->getOperand(1);
310 // Okay, now we know that the LHS is a nested expression and that the RHS is
311 // not. Perform reassociation.
312 assert(!isReassociableOp(RHS, Opcode) && "LinearizeExpr failed!");
314 // Move LHS right before I to make sure that the tree expression dominates all
316 LHSBO->moveBefore(I);
318 // Linearize the expression tree on the LHS.
319 LinearizeExprTree(LHSBO, Ops);
321 // Remember the RHS operand and its rank.
322 Ops.push_back(ValueEntry(getRank(RHS), RHS));
324 // Clear the RHS leaf out.
325 I->setOperand(1, UndefValue::get(I->getType()));
328 // RewriteExprTree - Now that the operands for this expression tree are
329 // linearized and optimized, emit them in-order. This function is written to be
331 void Reassociate::RewriteExprTree(BinaryOperator *I,
332 SmallVectorImpl<ValueEntry> &Ops,
334 if (i+2 == Ops.size()) {
335 if (I->getOperand(0) != Ops[i].Op ||
336 I->getOperand(1) != Ops[i+1].Op) {
337 Value *OldLHS = I->getOperand(0);
338 DEBUG(errs() << "RA: " << *I << '\n');
339 I->setOperand(0, Ops[i].Op);
340 I->setOperand(1, Ops[i+1].Op);
341 DEBUG(errs() << "TO: " << *I << '\n');
345 // If we reassociated a tree to fewer operands (e.g. (1+a+2) -> (a+3)
346 // delete the extra, now dead, nodes.
347 RemoveDeadBinaryOp(OldLHS);
351 assert(i+2 < Ops.size() && "Ops index out of range!");
353 if (I->getOperand(1) != Ops[i].Op) {
354 DEBUG(errs() << "RA: " << *I << '\n');
355 I->setOperand(1, Ops[i].Op);
356 DEBUG(errs() << "TO: " << *I << '\n');
361 BinaryOperator *LHS = cast<BinaryOperator>(I->getOperand(0));
362 assert(LHS->getOpcode() == I->getOpcode() &&
363 "Improper expression tree!");
365 // Compactify the tree instructions together with each other to guarantee
366 // that the expression tree is dominated by all of Ops.
368 RewriteExprTree(LHS, Ops, i+1);
373 // NegateValue - Insert instructions before the instruction pointed to by BI,
374 // that computes the negative version of the value specified. The negative
375 // version of the value is returned, and BI is left pointing at the instruction
376 // that should be processed next by the reassociation pass.
378 static Value *NegateValue(Value *V, Instruction *BI) {
379 // We are trying to expose opportunity for reassociation. One of the things
380 // that we want to do to achieve this is to push a negation as deep into an
381 // expression chain as possible, to expose the add instructions. In practice,
382 // this means that we turn this:
383 // X = -(A+12+C+D) into X = -A + -12 + -C + -D = -12 + -A + -C + -D
384 // so that later, a: Y = 12+X could get reassociated with the -12 to eliminate
385 // the constants. We assume that instcombine will clean up the mess later if
386 // we introduce tons of unnecessary negation instructions...
388 if (Instruction *I = dyn_cast<Instruction>(V))
389 if (I->getOpcode() == Instruction::Add && I->hasOneUse()) {
390 // Push the negates through the add.
391 I->setOperand(0, NegateValue(I->getOperand(0), BI));
392 I->setOperand(1, NegateValue(I->getOperand(1), BI));
394 // We must move the add instruction here, because the neg instructions do
395 // not dominate the old add instruction in general. By moving it, we are
396 // assured that the neg instructions we just inserted dominate the
397 // instruction we are about to insert after them.
400 I->setName(I->getName()+".neg");
404 // Insert a 'neg' instruction that subtracts the value from zero to get the
407 return BinaryOperator::CreateNeg(V, V->getName() + ".neg", BI);
410 /// ShouldBreakUpSubtract - Return true if we should break up this subtract of
411 /// X-Y into (X + -Y).
412 static bool ShouldBreakUpSubtract(Instruction *Sub) {
413 // If this is a negation, we can't split it up!
414 if (BinaryOperator::isNeg(Sub))
417 // Don't bother to break this up unless either the LHS is an associable add or
418 // subtract or if this is only used by one.
419 if (isReassociableOp(Sub->getOperand(0), Instruction::Add) ||
420 isReassociableOp(Sub->getOperand(0), Instruction::Sub))
422 if (isReassociableOp(Sub->getOperand(1), Instruction::Add) ||
423 isReassociableOp(Sub->getOperand(1), Instruction::Sub))
425 if (Sub->hasOneUse() &&
426 (isReassociableOp(Sub->use_back(), Instruction::Add) ||
427 isReassociableOp(Sub->use_back(), Instruction::Sub)))
433 /// BreakUpSubtract - If we have (X-Y), and if either X is an add, or if this is
434 /// only used by an add, transform this into (X+(0-Y)) to promote better
436 static Instruction *BreakUpSubtract(Instruction *Sub,
437 std::map<AssertingVH<>, unsigned> &ValueRankMap) {
438 // Convert a subtract into an add and a neg instruction... so that sub
439 // instructions can be commuted with other add instructions...
441 // Calculate the negative value of Operand 1 of the sub instruction...
442 // and set it as the RHS of the add instruction we just made...
444 Value *NegVal = NegateValue(Sub->getOperand(1), Sub);
446 BinaryOperator::CreateAdd(Sub->getOperand(0), NegVal, "", Sub);
449 // Everyone now refers to the add instruction.
450 ValueRankMap.erase(Sub);
451 Sub->replaceAllUsesWith(New);
452 Sub->eraseFromParent();
454 DEBUG(errs() << "Negated: " << *New << '\n');
458 /// ConvertShiftToMul - If this is a shift of a reassociable multiply or is used
459 /// by one, change this into a multiply by a constant to assist with further
461 static Instruction *ConvertShiftToMul(Instruction *Shl,
462 std::map<AssertingVH<>, unsigned> &ValueRankMap) {
463 // If an operand of this shift is a reassociable multiply, or if the shift
464 // is used by a reassociable multiply or add, turn into a multiply.
465 if (isReassociableOp(Shl->getOperand(0), Instruction::Mul) ||
467 (isReassociableOp(Shl->use_back(), Instruction::Mul) ||
468 isReassociableOp(Shl->use_back(), Instruction::Add)))) {
469 Constant *MulCst = ConstantInt::get(Shl->getType(), 1);
470 MulCst = ConstantExpr::getShl(MulCst, cast<Constant>(Shl->getOperand(1)));
473 BinaryOperator::CreateMul(Shl->getOperand(0), MulCst, "", Shl);
474 ValueRankMap.erase(Shl);
476 Shl->replaceAllUsesWith(Mul);
477 Shl->eraseFromParent();
483 // Scan backwards and forwards among values with the same rank as element i to
484 // see if X exists. If X does not exist, return i.
485 static unsigned FindInOperandList(SmallVectorImpl<ValueEntry> &Ops, unsigned i,
487 unsigned XRank = Ops[i].Rank;
488 unsigned e = Ops.size();
489 for (unsigned j = i+1; j != e && Ops[j].Rank == XRank; ++j)
493 for (unsigned j = i-1; j != ~0U && Ops[j].Rank == XRank; --j)
499 /// EmitAddTreeOfValues - Emit a tree of add instructions, summing Ops together
500 /// and returning the result. Insert the tree before I.
501 static Value *EmitAddTreeOfValues(Instruction *I, SmallVectorImpl<Value*> &Ops){
502 if (Ops.size() == 1) return Ops.back();
504 Value *V1 = Ops.back();
506 Value *V2 = EmitAddTreeOfValues(I, Ops);
507 return BinaryOperator::CreateAdd(V2, V1, "tmp", I);
510 /// RemoveFactorFromExpression - If V is an expression tree that is a
511 /// multiplication sequence, and if this sequence contains a multiply by Factor,
512 /// remove Factor from the tree and return the new tree.
513 Value *Reassociate::RemoveFactorFromExpression(Value *V, Value *Factor) {
514 BinaryOperator *BO = isReassociableOp(V, Instruction::Mul);
517 SmallVector<ValueEntry, 8> Factors;
518 LinearizeExprTree(BO, Factors);
520 bool FoundFactor = false;
521 for (unsigned i = 0, e = Factors.size(); i != e; ++i)
522 if (Factors[i].Op == Factor) {
524 Factors.erase(Factors.begin()+i);
528 // Make sure to restore the operands to the expression tree.
529 RewriteExprTree(BO, Factors);
533 if (Factors.size() == 1) return Factors[0].Op;
535 RewriteExprTree(BO, Factors);
539 /// FindSingleUseMultiplyFactors - If V is a single-use multiply, recursively
540 /// add its operands as factors, otherwise add V to the list of factors.
541 static void FindSingleUseMultiplyFactors(Value *V,
542 SmallVectorImpl<Value*> &Factors) {
544 if ((!V->hasOneUse() && !V->use_empty()) ||
545 !(BO = dyn_cast<BinaryOperator>(V)) ||
546 BO->getOpcode() != Instruction::Mul) {
547 Factors.push_back(V);
551 // Otherwise, add the LHS and RHS to the list of factors.
552 FindSingleUseMultiplyFactors(BO->getOperand(1), Factors);
553 FindSingleUseMultiplyFactors(BO->getOperand(0), Factors);
556 /// OptimizeAndOrXor - Optimize a series of operands to an 'and', 'or', or 'xor'
557 /// instruction. This optimizes based on identities. If it can be reduced to
558 /// a single Value, it is returned, otherwise the Ops list is mutated as
560 static Value *OptimizeAndOrXor(unsigned Opcode,
561 SmallVectorImpl<ValueEntry> &Ops) {
562 // Scan the operand lists looking for X and ~X pairs, along with X,X pairs.
563 // If we find any, we can simplify the expression. X&~X == 0, X|~X == -1.
564 for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
565 // First, check for X and ~X in the operand list.
566 assert(i < Ops.size());
567 if (BinaryOperator::isNot(Ops[i].Op)) { // Cannot occur for ^.
568 Value *X = BinaryOperator::getNotArgument(Ops[i].Op);
569 unsigned FoundX = FindInOperandList(Ops, i, X);
571 if (Opcode == Instruction::And) // ...&X&~X = 0
572 return Constant::getNullValue(X->getType());
574 if (Opcode == Instruction::Or) // ...|X|~X = -1
575 return Constant::getAllOnesValue(X->getType());
579 // Next, check for duplicate pairs of values, which we assume are next to
580 // each other, due to our sorting criteria.
581 assert(i < Ops.size());
582 if (i+1 != Ops.size() && Ops[i+1].Op == Ops[i].Op) {
583 if (Opcode == Instruction::And || Opcode == Instruction::Or) {
584 // Drop duplicate values.
585 Ops.erase(Ops.begin()+i);
589 assert(Opcode == Instruction::Xor);
591 return Constant::getNullValue(Ops[0].Op->getType());
594 Ops.erase(Ops.begin()+i, Ops.begin()+i+2);
603 /// OptimizeAdd - Optimize a series of operands to an 'add' instruction. This
604 /// optimizes based on identities. If it can be reduced to a single Value, it
605 /// is returned, otherwise the Ops list is mutated as necessary.
606 Value *Reassociate::OptimizeAdd(Instruction *I,
607 SmallVectorImpl<ValueEntry> &Ops) {
608 SmallPtrSet<Value*, 8> OperandsSeen;
611 OperandsSeen.clear();
613 // Scan the operand lists looking for X and -X pairs. If we find any, we
614 // can simplify the expression. X+-X == 0. While we're at it, scan for any
615 // duplicates. We want to canonicalize Y+Y+Y+Z -> 3*Y+Z.
616 for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
617 Value *TheOp = Ops[i].Op;
618 // Check to see if we've seen this operand before. If so, we factor all
619 // instances of the operand together.
620 if (!OperandsSeen.insert(TheOp)) {
621 // Rescan the list, removing all instances of this operand from the expr.
622 unsigned NumFound = 0;
623 for (unsigned j = 0, je = Ops.size(); j != je; ++j) {
624 if (Ops[j].Op != TheOp) continue;
626 Ops.erase(Ops.begin()+j);
630 /*DEBUG*/(errs() << "\nFACTORING [" << NumFound << "]: " << *TheOp << '\n');
634 // Insert a new multiply.
635 Value *Mul = ConstantInt::get(cast<IntegerType>(I->getType()), NumFound);
636 Mul = BinaryOperator::CreateMul(TheOp, Mul, "factor", I);
638 // Now that we have inserted a multiply, optimize it. This allows us to
639 // handle cases that require multiple factoring steps, such as this:
640 // (X*2) + (X*2) + (X*2) -> (X*2)*3 -> X*6
641 Mul = ReassociateExpression(cast<BinaryOperator>(Mul));
643 // If every add operand was a duplicate, return the multiply.
647 // Otherwise, we had some input that didn't have the dupe, such as
648 // "A + A + B" -> "A*2 + B". Add the new multiply to the list of
649 // things being added by this operation.
650 Ops.insert(Ops.begin(), ValueEntry(getRank(Mul), Mul));
654 // Check for X and -X in the operand list.
655 if (!BinaryOperator::isNeg(TheOp))
658 Value *X = BinaryOperator::getNegArgument(TheOp);
659 unsigned FoundX = FindInOperandList(Ops, i, X);
663 // Remove X and -X from the operand list.
665 return Constant::getNullValue(X->getType());
667 Ops.erase(Ops.begin()+i);
671 --i; // Need to back up an extra one.
672 Ops.erase(Ops.begin()+FoundX);
674 --i; // Revisit element.
675 e -= 2; // Removed two elements.
678 // Scan the operand list, checking to see if there are any common factors
679 // between operands. Consider something like A*A+A*B*C+D. We would like to
680 // reassociate this to A*(A+B*C)+D, which reduces the number of multiplies.
681 // To efficiently find this, we count the number of times a factor occurs
682 // for any ADD operands that are MULs.
683 DenseMap<Value*, unsigned> FactorOccurrences;
685 // Keep track of each multiply we see, to avoid triggering on (X*4)+(X*4)
686 // where they are actually the same multiply.
688 Value *MaxOccVal = 0;
689 for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
690 BinaryOperator *BOp = dyn_cast<BinaryOperator>(Ops[i].Op);
691 if (BOp == 0 || BOp->getOpcode() != Instruction::Mul || !BOp->use_empty())
694 // Compute all of the factors of this added value.
695 SmallVector<Value*, 8> Factors;
696 FindSingleUseMultiplyFactors(BOp, Factors);
697 assert(Factors.size() > 1 && "Bad linearize!");
699 // Add one to FactorOccurrences for each unique factor in this op.
700 if (Factors.size() == 2) {
701 unsigned Occ = ++FactorOccurrences[Factors[0]];
702 if (Occ > MaxOcc) { MaxOcc = Occ; MaxOccVal = Factors[0]; }
703 if (Factors[0] != Factors[1]) { // Don't double count A*A.
704 Occ = ++FactorOccurrences[Factors[1]];
705 if (Occ > MaxOcc) { MaxOcc = Occ; MaxOccVal = Factors[1]; }
708 SmallPtrSet<Value*, 4> Duplicates;
709 for (unsigned i = 0, e = Factors.size(); i != e; ++i) {
710 if (!Duplicates.insert(Factors[i])) continue;
712 unsigned Occ = ++FactorOccurrences[Factors[i]];
713 if (Occ > MaxOcc) { MaxOcc = Occ; MaxOccVal = Factors[i]; }
718 // If any factor occurred more than one time, we can pull it out.
720 DEBUG(errs() << "\nFACTORING [" << MaxOcc << "]: " << *MaxOccVal << '\n');
723 // Create a new instruction that uses the MaxOccVal twice. If we don't do
724 // this, we could otherwise run into situations where removing a factor
725 // from an expression will drop a use of maxocc, and this can cause
726 // RemoveFactorFromExpression on successive values to behave differently.
727 Instruction *DummyInst = BinaryOperator::CreateAdd(MaxOccVal, MaxOccVal);
728 SmallVector<Value*, 4> NewMulOps;
729 for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
730 if (Value *V = RemoveFactorFromExpression(Ops[i].Op, MaxOccVal)) {
731 NewMulOps.push_back(V);
732 Ops.erase(Ops.begin()+i);
737 // No need for extra uses anymore.
740 unsigned NumAddedValues = NewMulOps.size();
741 Value *V = EmitAddTreeOfValues(I, NewMulOps);
743 // Now that we have inserted the add tree, optimize it. This allows us to
744 // handle cases that require multiple factoring steps, such as this:
745 // A*A*B + A*A*C --> A*(A*B+A*C) --> A*(A*(B+C))
746 assert(NumAddedValues > 1 && "Each occurrence should contribute a value");
747 V = ReassociateExpression(cast<BinaryOperator>(V));
749 // Create the multiply.
750 Value *V2 = BinaryOperator::CreateMul(V, MaxOccVal, "tmp", I);
752 // FIXME: Should rerun 'ReassociateExpression' on the mul too??
754 // If every add operand included the factor (e.g. "A*B + A*C"), then the
755 // entire result expression is just the multiply "A*(B+C)".
759 // Otherwise, we had some input that didn't have the factor, such as
760 // "A*B + A*C + D" -> "A*(B+C) + D". Add the new multiply to the list of
761 // things being added by this operation.
762 Ops.insert(Ops.begin(), ValueEntry(getRank(V2), V2));
768 Value *Reassociate::OptimizeExpression(BinaryOperator *I,
769 SmallVectorImpl<ValueEntry> &Ops) {
770 // Now that we have the linearized expression tree, try to optimize it.
771 // Start by folding any constants that we found.
772 bool IterateOptimization = false;
773 if (Ops.size() == 1) return Ops[0].Op;
775 unsigned Opcode = I->getOpcode();
777 if (Constant *V1 = dyn_cast<Constant>(Ops[Ops.size()-2].Op))
778 if (Constant *V2 = dyn_cast<Constant>(Ops.back().Op)) {
780 Ops.back().Op = ConstantExpr::get(Opcode, V1, V2);
781 return OptimizeExpression(I, Ops);
784 // Check for destructive annihilation due to a constant being used.
785 if (ConstantInt *CstVal = dyn_cast<ConstantInt>(Ops.back().Op))
788 case Instruction::And:
789 if (CstVal->isZero()) // ... & 0 -> 0
791 if (CstVal->isAllOnesValue()) // ... & -1 -> ...
794 case Instruction::Mul:
795 if (CstVal->isZero()) { // ... * 0 -> 0
800 if (cast<ConstantInt>(CstVal)->isOne())
801 Ops.pop_back(); // ... * 1 -> ...
803 case Instruction::Or:
804 if (CstVal->isAllOnesValue()) // ... | -1 -> -1
807 case Instruction::Add:
808 case Instruction::Xor:
809 if (CstVal->isZero()) // ... [|^+] 0 -> ...
813 if (Ops.size() == 1) return Ops[0].Op;
815 // Handle destructive annihilation due to identities between elements in the
816 // argument list here.
819 case Instruction::And:
820 case Instruction::Or:
821 case Instruction::Xor: {
822 unsigned NumOps = Ops.size();
823 if (Value *Result = OptimizeAndOrXor(Opcode, Ops))
825 IterateOptimization |= Ops.size() != NumOps;
829 case Instruction::Add: {
830 unsigned NumOps = Ops.size();
831 if (Value *Result = OptimizeAdd(I, Ops))
833 IterateOptimization |= Ops.size() != NumOps;
837 //case Instruction::Mul:
840 if (IterateOptimization)
841 return OptimizeExpression(I, Ops);
846 /// ReassociateBB - Inspect all of the instructions in this basic block,
847 /// reassociating them as we go.
848 void Reassociate::ReassociateBB(BasicBlock *BB) {
849 for (BasicBlock::iterator BBI = BB->begin(); BBI != BB->end(); ) {
850 Instruction *BI = BBI++;
851 if (BI->getOpcode() == Instruction::Shl &&
852 isa<ConstantInt>(BI->getOperand(1)))
853 if (Instruction *NI = ConvertShiftToMul(BI, ValueRankMap)) {
858 // Reject cases where it is pointless to do this.
859 if (!isa<BinaryOperator>(BI) || BI->getType()->isFloatingPoint() ||
860 isa<VectorType>(BI->getType()))
861 continue; // Floating point ops are not associative.
863 // If this is a subtract instruction which is not already in negate form,
864 // see if we can convert it to X+-Y.
865 if (BI->getOpcode() == Instruction::Sub) {
866 if (ShouldBreakUpSubtract(BI)) {
867 BI = BreakUpSubtract(BI, ValueRankMap);
869 } else if (BinaryOperator::isNeg(BI)) {
870 // Otherwise, this is a negation. See if the operand is a multiply tree
871 // and if this is not an inner node of a multiply tree.
872 if (isReassociableOp(BI->getOperand(1), Instruction::Mul) &&
874 !isReassociableOp(BI->use_back(), Instruction::Mul))) {
875 BI = LowerNegateToMultiply(BI, ValueRankMap);
881 // If this instruction is a commutative binary operator, process it.
882 if (!BI->isAssociative()) continue;
883 BinaryOperator *I = cast<BinaryOperator>(BI);
885 // If this is an interior node of a reassociable tree, ignore it until we
886 // get to the root of the tree, to avoid N^2 analysis.
887 if (I->hasOneUse() && isReassociableOp(I->use_back(), I->getOpcode()))
890 // If this is an add tree that is used by a sub instruction, ignore it
891 // until we process the subtract.
892 if (I->hasOneUse() && I->getOpcode() == Instruction::Add &&
893 cast<Instruction>(I->use_back())->getOpcode() == Instruction::Sub)
896 ReassociateExpression(I);
900 Value *Reassociate::ReassociateExpression(BinaryOperator *I) {
902 // First, walk the expression tree, linearizing the tree, collecting the
903 // operand information.
904 SmallVector<ValueEntry, 8> Ops;
905 LinearizeExprTree(I, Ops);
907 DEBUG(errs() << "RAIn:\t"; PrintOps(I, Ops); errs() << '\n');
909 // Now that we have linearized the tree to a list and have gathered all of
910 // the operands and their ranks, sort the operands by their rank. Use a
911 // stable_sort so that values with equal ranks will have their relative
912 // positions maintained (and so the compiler is deterministic). Note that
913 // this sorts so that the highest ranking values end up at the beginning of
915 std::stable_sort(Ops.begin(), Ops.end());
917 // OptimizeExpression - Now that we have the expression tree in a convenient
918 // sorted form, optimize it globally if possible.
919 if (Value *V = OptimizeExpression(I, Ops)) {
920 // This expression tree simplified to something that isn't a tree,
922 DEBUG(errs() << "Reassoc to scalar: " << *V << '\n');
923 I->replaceAllUsesWith(V);
924 RemoveDeadBinaryOp(I);
929 // We want to sink immediates as deeply as possible except in the case where
930 // this is a multiply tree used only by an add, and the immediate is a -1.
931 // In this case we reassociate to put the negation on the outside so that we
932 // can fold the negation into the add: (-X)*Y + Z -> Z-X*Y
933 if (I->getOpcode() == Instruction::Mul && I->hasOneUse() &&
934 cast<Instruction>(I->use_back())->getOpcode() == Instruction::Add &&
935 isa<ConstantInt>(Ops.back().Op) &&
936 cast<ConstantInt>(Ops.back().Op)->isAllOnesValue()) {
937 ValueEntry Tmp = Ops.pop_back_val();
938 Ops.insert(Ops.begin(), Tmp);
941 DEBUG(errs() << "RAOut:\t"; PrintOps(I, Ops); errs() << '\n');
943 if (Ops.size() == 1) {
944 // This expression tree simplified to something that isn't a tree,
946 I->replaceAllUsesWith(Ops[0].Op);
947 RemoveDeadBinaryOp(I);
951 // Now that we ordered and optimized the expressions, splat them back into
952 // the expression tree, removing any unneeded nodes.
953 RewriteExprTree(I, Ops);
958 bool Reassociate::runOnFunction(Function &F) {
959 // Recalculate the rank map for F
963 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI)
966 // We are done with the rank map...
968 ValueRankMap.clear();