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 #define DEBUG_TYPE "reassociate"
24 #include "llvm/Transforms/Scalar.h"
25 #include "llvm/Transforms/Utils/Local.h"
26 #include "llvm/Constants.h"
27 #include "llvm/DerivedTypes.h"
28 #include "llvm/Function.h"
29 #include "llvm/Instructions.h"
30 #include "llvm/IntrinsicInst.h"
31 #include "llvm/Pass.h"
32 #include "llvm/Assembly/Writer.h"
33 #include "llvm/Support/CFG.h"
34 #include "llvm/Support/Debug.h"
35 #include "llvm/Support/ValueHandle.h"
36 #include "llvm/Support/raw_ostream.h"
37 #include "llvm/ADT/PostOrderIterator.h"
38 #include "llvm/ADT/Statistic.h"
39 #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 dbgs() << Instruction::getOpcodeName(I->getOpcode()) << " "
65 << *Ops[0].Op->getType() << '\t';
66 for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
68 WriteAsOperand(dbgs(), Ops[i].Op, false, M);
69 dbgs() << ", #" << Ops[i].Rank << "] ";
75 class Reassociate : public FunctionPass {
76 DenseMap<BasicBlock*, unsigned> RankMap;
77 DenseMap<AssertingVH<Value>, unsigned> ValueRankMap;
78 SmallVector<WeakVH, 8> RedoInsts;
79 SmallVector<WeakVH, 8> DeadInsts;
82 static char ID; // Pass identification, replacement for typeid
83 Reassociate() : FunctionPass(ID) {
84 initializeReassociatePass(*PassRegistry::getPassRegistry());
87 bool runOnFunction(Function &F);
89 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
93 void BuildRankMap(Function &F);
94 unsigned getRank(Value *V);
95 Value *ReassociateExpression(BinaryOperator *I);
96 void RewriteExprTree(BinaryOperator *I, SmallVectorImpl<ValueEntry> &Ops,
98 Value *OptimizeExpression(BinaryOperator *I,
99 SmallVectorImpl<ValueEntry> &Ops);
100 Value *OptimizeAdd(Instruction *I, SmallVectorImpl<ValueEntry> &Ops);
101 void LinearizeExprTree(BinaryOperator *I, SmallVectorImpl<ValueEntry> &Ops);
102 void LinearizeExpr(BinaryOperator *I);
103 Value *RemoveFactorFromExpression(Value *V, Value *Factor);
104 void ReassociateInst(BasicBlock::iterator &BBI);
106 void RemoveDeadBinaryOp(Value *V);
110 char Reassociate::ID = 0;
111 INITIALIZE_PASS(Reassociate, "reassociate",
112 "Reassociate expressions", false, false)
114 // Public interface to the Reassociate pass
115 FunctionPass *llvm::createReassociatePass() { return new Reassociate(); }
117 void Reassociate::RemoveDeadBinaryOp(Value *V) {
118 Instruction *Op = dyn_cast<Instruction>(V);
119 if (!Op || !isa<BinaryOperator>(Op))
122 Value *LHS = Op->getOperand(0), *RHS = Op->getOperand(1);
124 ValueRankMap.erase(Op);
125 DeadInsts.push_back(Op);
126 RemoveDeadBinaryOp(LHS);
127 RemoveDeadBinaryOp(RHS);
131 static bool isUnmovableInstruction(Instruction *I) {
132 if (I->getOpcode() == Instruction::PHI ||
133 I->getOpcode() == Instruction::Alloca ||
134 I->getOpcode() == Instruction::Load ||
135 I->getOpcode() == Instruction::Invoke ||
136 (I->getOpcode() == Instruction::Call &&
137 !isa<DbgInfoIntrinsic>(I)) ||
138 I->getOpcode() == Instruction::UDiv ||
139 I->getOpcode() == Instruction::SDiv ||
140 I->getOpcode() == Instruction::FDiv ||
141 I->getOpcode() == Instruction::URem ||
142 I->getOpcode() == Instruction::SRem ||
143 I->getOpcode() == Instruction::FRem)
148 void Reassociate::BuildRankMap(Function &F) {
151 // Assign distinct ranks to function arguments
152 for (Function::arg_iterator I = F.arg_begin(), E = F.arg_end(); I != E; ++I)
153 ValueRankMap[&*I] = ++i;
155 ReversePostOrderTraversal<Function*> RPOT(&F);
156 for (ReversePostOrderTraversal<Function*>::rpo_iterator I = RPOT.begin(),
157 E = RPOT.end(); I != E; ++I) {
159 unsigned BBRank = RankMap[BB] = ++i << 16;
161 // Walk the basic block, adding precomputed ranks for any instructions that
162 // we cannot move. This ensures that the ranks for these instructions are
163 // all different in the block.
164 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
165 if (isUnmovableInstruction(I))
166 ValueRankMap[&*I] = ++BBRank;
170 unsigned Reassociate::getRank(Value *V) {
171 Instruction *I = dyn_cast<Instruction>(V);
173 if (isa<Argument>(V)) return ValueRankMap[V]; // Function argument.
174 return 0; // Otherwise it's a global or constant, rank 0.
177 if (unsigned Rank = ValueRankMap[I])
178 return Rank; // Rank already known?
180 // If this is an expression, return the 1+MAX(rank(LHS), rank(RHS)) so that
181 // we can reassociate expressions for code motion! Since we do not recurse
182 // for PHI nodes, we cannot have infinite recursion here, because there
183 // cannot be loops in the value graph that do not go through PHI nodes.
184 unsigned Rank = 0, MaxRank = RankMap[I->getParent()];
185 for (unsigned i = 0, e = I->getNumOperands();
186 i != e && Rank != MaxRank; ++i)
187 Rank = std::max(Rank, getRank(I->getOperand(i)));
189 // If this is a not or neg instruction, do not count it for rank. This
190 // assures us that X and ~X will have the same rank.
191 if (!I->getType()->isIntegerTy() ||
192 (!BinaryOperator::isNot(I) && !BinaryOperator::isNeg(I)))
195 //DEBUG(dbgs() << "Calculated Rank[" << V->getName() << "] = "
198 return ValueRankMap[I] = Rank;
201 /// isReassociableOp - Return true if V is an instruction of the specified
202 /// opcode and if it only has one use.
203 static BinaryOperator *isReassociableOp(Value *V, unsigned Opcode) {
204 if ((V->hasOneUse() || V->use_empty()) && isa<Instruction>(V) &&
205 cast<Instruction>(V)->getOpcode() == Opcode)
206 return cast<BinaryOperator>(V);
210 /// LowerNegateToMultiply - Replace 0-X with X*-1.
212 static Instruction *LowerNegateToMultiply(Instruction *Neg,
213 DenseMap<AssertingVH<Value>, unsigned> &ValueRankMap) {
214 Constant *Cst = Constant::getAllOnesValue(Neg->getType());
216 Instruction *Res = BinaryOperator::CreateMul(Neg->getOperand(1), Cst, "",Neg);
217 ValueRankMap.erase(Neg);
219 Neg->replaceAllUsesWith(Res);
220 Res->setDebugLoc(Neg->getDebugLoc());
221 Neg->eraseFromParent();
225 // Given an expression of the form '(A+B)+(D+C)', turn it into '(((A+B)+C)+D)'.
226 // Note that if D is also part of the expression tree that we recurse to
227 // linearize it as well. Besides that case, this does not recurse into A,B, or
229 void Reassociate::LinearizeExpr(BinaryOperator *I) {
230 BinaryOperator *LHS = cast<BinaryOperator>(I->getOperand(0));
231 BinaryOperator *RHS = cast<BinaryOperator>(I->getOperand(1));
232 assert(isReassociableOp(LHS, I->getOpcode()) &&
233 isReassociableOp(RHS, I->getOpcode()) &&
234 "Not an expression that needs linearization?");
236 DEBUG(dbgs() << "Linear" << *LHS << '\n' << *RHS << '\n' << *I << '\n');
238 // Move the RHS instruction to live immediately before I, avoiding breaking
239 // dominator properties.
242 // Move operands around to do the linearization.
243 I->setOperand(1, RHS->getOperand(0));
244 RHS->setOperand(0, LHS);
245 I->setOperand(0, RHS);
247 // Conservatively clear all the optional flags, which may not hold
248 // after the reassociation.
249 I->clearSubclassOptionalData();
250 LHS->clearSubclassOptionalData();
251 RHS->clearSubclassOptionalData();
255 DEBUG(dbgs() << "Linearized: " << *I << '\n');
257 // If D is part of this expression tree, tail recurse.
258 if (isReassociableOp(I->getOperand(1), I->getOpcode()))
263 /// LinearizeExprTree - Given an associative binary expression tree, traverse
264 /// all of the uses putting it into canonical form. This forces a left-linear
265 /// form of the expression (((a+b)+c)+d), and collects information about the
266 /// rank of the non-tree operands.
268 /// NOTE: These intentionally destroys the expression tree operands (turning
269 /// them into undef values) to reduce #uses of the values. This means that the
270 /// caller MUST use something like RewriteExprTree to put the values back in.
272 void Reassociate::LinearizeExprTree(BinaryOperator *I,
273 SmallVectorImpl<ValueEntry> &Ops) {
274 Value *LHS = I->getOperand(0), *RHS = I->getOperand(1);
275 unsigned Opcode = I->getOpcode();
277 // First step, linearize the expression if it is in ((A+B)+(C+D)) form.
278 BinaryOperator *LHSBO = isReassociableOp(LHS, Opcode);
279 BinaryOperator *RHSBO = isReassociableOp(RHS, Opcode);
281 // If this is a multiply expression tree and it contains internal negations,
282 // transform them into multiplies by -1 so they can be reassociated.
283 if (I->getOpcode() == Instruction::Mul) {
284 if (!LHSBO && LHS->hasOneUse() && BinaryOperator::isNeg(LHS)) {
285 LHS = LowerNegateToMultiply(cast<Instruction>(LHS), ValueRankMap);
286 LHSBO = isReassociableOp(LHS, Opcode);
288 if (!RHSBO && RHS->hasOneUse() && BinaryOperator::isNeg(RHS)) {
289 RHS = LowerNegateToMultiply(cast<Instruction>(RHS), ValueRankMap);
290 RHSBO = isReassociableOp(RHS, Opcode);
296 // Neither the LHS or RHS as part of the tree, thus this is a leaf. As
297 // such, just remember these operands and their rank.
298 Ops.push_back(ValueEntry(getRank(LHS), LHS));
299 Ops.push_back(ValueEntry(getRank(RHS), RHS));
301 // Clear the leaves out.
302 I->setOperand(0, UndefValue::get(I->getType()));
303 I->setOperand(1, UndefValue::get(I->getType()));
307 // Turn X+(Y+Z) -> (Y+Z)+X
308 std::swap(LHSBO, RHSBO);
310 bool Success = !I->swapOperands();
311 assert(Success && "swapOperands failed");
315 // Turn (A+B)+(C+D) -> (((A+B)+C)+D). This guarantees the RHS is not
316 // part of the expression tree.
318 LHS = LHSBO = cast<BinaryOperator>(I->getOperand(0));
319 RHS = I->getOperand(1);
323 // Okay, now we know that the LHS is a nested expression and that the RHS is
324 // not. Perform reassociation.
325 assert(!isReassociableOp(RHS, Opcode) && "LinearizeExpr failed!");
327 // Move LHS right before I to make sure that the tree expression dominates all
329 LHSBO->moveBefore(I);
331 // Linearize the expression tree on the LHS.
332 LinearizeExprTree(LHSBO, Ops);
334 // Remember the RHS operand and its rank.
335 Ops.push_back(ValueEntry(getRank(RHS), RHS));
337 // Clear the RHS leaf out.
338 I->setOperand(1, UndefValue::get(I->getType()));
341 // RewriteExprTree - Now that the operands for this expression tree are
342 // linearized and optimized, emit them in-order. This function is written to be
344 void Reassociate::RewriteExprTree(BinaryOperator *I,
345 SmallVectorImpl<ValueEntry> &Ops,
347 if (i+2 == Ops.size()) {
348 if (I->getOperand(0) != Ops[i].Op ||
349 I->getOperand(1) != Ops[i+1].Op) {
350 Value *OldLHS = I->getOperand(0);
351 DEBUG(dbgs() << "RA: " << *I << '\n');
352 I->setOperand(0, Ops[i].Op);
353 I->setOperand(1, Ops[i+1].Op);
355 // Clear all the optional flags, which may not hold after the
356 // reassociation if the expression involved more than just this operation.
358 I->clearSubclassOptionalData();
360 DEBUG(dbgs() << "TO: " << *I << '\n');
364 // If we reassociated a tree to fewer operands (e.g. (1+a+2) -> (a+3)
365 // delete the extra, now dead, nodes.
366 RemoveDeadBinaryOp(OldLHS);
370 assert(i+2 < Ops.size() && "Ops index out of range!");
372 if (I->getOperand(1) != Ops[i].Op) {
373 DEBUG(dbgs() << "RA: " << *I << '\n');
374 I->setOperand(1, Ops[i].Op);
376 // Conservatively clear all the optional flags, which may not hold
377 // after the reassociation.
378 I->clearSubclassOptionalData();
380 DEBUG(dbgs() << "TO: " << *I << '\n');
385 BinaryOperator *LHS = cast<BinaryOperator>(I->getOperand(0));
386 assert(LHS->getOpcode() == I->getOpcode() &&
387 "Improper expression tree!");
389 // Compactify the tree instructions together with each other to guarantee
390 // that the expression tree is dominated by all of Ops.
392 RewriteExprTree(LHS, Ops, i+1);
397 // NegateValue - Insert instructions before the instruction pointed to by BI,
398 // that computes the negative version of the value specified. The negative
399 // version of the value is returned, and BI is left pointing at the instruction
400 // that should be processed next by the reassociation pass.
402 static Value *NegateValue(Value *V, Instruction *BI) {
403 if (Constant *C = dyn_cast<Constant>(V))
404 return ConstantExpr::getNeg(C);
406 // We are trying to expose opportunity for reassociation. One of the things
407 // that we want to do to achieve this is to push a negation as deep into an
408 // expression chain as possible, to expose the add instructions. In practice,
409 // this means that we turn this:
410 // X = -(A+12+C+D) into X = -A + -12 + -C + -D = -12 + -A + -C + -D
411 // so that later, a: Y = 12+X could get reassociated with the -12 to eliminate
412 // the constants. We assume that instcombine will clean up the mess later if
413 // we introduce tons of unnecessary negation instructions.
415 if (Instruction *I = dyn_cast<Instruction>(V))
416 if (I->getOpcode() == Instruction::Add && I->hasOneUse()) {
417 // Push the negates through the add.
418 I->setOperand(0, NegateValue(I->getOperand(0), BI));
419 I->setOperand(1, NegateValue(I->getOperand(1), BI));
421 // We must move the add instruction here, because the neg instructions do
422 // not dominate the old add instruction in general. By moving it, we are
423 // assured that the neg instructions we just inserted dominate the
424 // instruction we are about to insert after them.
427 I->setName(I->getName()+".neg");
431 // Okay, we need to materialize a negated version of V with an instruction.
432 // Scan the use lists of V to see if we have one already.
433 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E;++UI){
435 if (!BinaryOperator::isNeg(U)) continue;
437 // We found one! Now we have to make sure that the definition dominates
438 // this use. We do this by moving it to the entry block (if it is a
439 // non-instruction value) or right after the definition. These negates will
440 // be zapped by reassociate later, so we don't need much finesse here.
441 BinaryOperator *TheNeg = cast<BinaryOperator>(U);
443 // Verify that the negate is in this function, V might be a constant expr.
444 if (TheNeg->getParent()->getParent() != BI->getParent()->getParent())
447 BasicBlock::iterator InsertPt;
448 if (Instruction *InstInput = dyn_cast<Instruction>(V)) {
449 if (InvokeInst *II = dyn_cast<InvokeInst>(InstInput)) {
450 InsertPt = II->getNormalDest()->begin();
452 InsertPt = InstInput;
455 while (isa<PHINode>(InsertPt)) ++InsertPt;
457 InsertPt = TheNeg->getParent()->getParent()->getEntryBlock().begin();
459 TheNeg->moveBefore(InsertPt);
463 // Insert a 'neg' instruction that subtracts the value from zero to get the
465 return BinaryOperator::CreateNeg(V, V->getName() + ".neg", BI);
468 /// ShouldBreakUpSubtract - Return true if we should break up this subtract of
469 /// X-Y into (X + -Y).
470 static bool ShouldBreakUpSubtract(Instruction *Sub) {
471 // If this is a negation, we can't split it up!
472 if (BinaryOperator::isNeg(Sub))
475 // Don't bother to break this up unless either the LHS is an associable add or
476 // subtract or if this is only used by one.
477 if (isReassociableOp(Sub->getOperand(0), Instruction::Add) ||
478 isReassociableOp(Sub->getOperand(0), Instruction::Sub))
480 if (isReassociableOp(Sub->getOperand(1), Instruction::Add) ||
481 isReassociableOp(Sub->getOperand(1), Instruction::Sub))
483 if (Sub->hasOneUse() &&
484 (isReassociableOp(Sub->use_back(), Instruction::Add) ||
485 isReassociableOp(Sub->use_back(), Instruction::Sub)))
491 /// BreakUpSubtract - If we have (X-Y), and if either X is an add, or if this is
492 /// only used by an add, transform this into (X+(0-Y)) to promote better
494 static Instruction *BreakUpSubtract(Instruction *Sub,
495 DenseMap<AssertingVH<Value>, unsigned> &ValueRankMap) {
496 // Convert a subtract into an add and a neg instruction. This allows sub
497 // instructions to be commuted with other add instructions.
499 // Calculate the negative value of Operand 1 of the sub instruction,
500 // and set it as the RHS of the add instruction we just made.
502 Value *NegVal = NegateValue(Sub->getOperand(1), Sub);
504 BinaryOperator::CreateAdd(Sub->getOperand(0), NegVal, "", Sub);
507 // Everyone now refers to the add instruction.
508 ValueRankMap.erase(Sub);
509 Sub->replaceAllUsesWith(New);
510 New->setDebugLoc(Sub->getDebugLoc());
511 Sub->eraseFromParent();
513 DEBUG(dbgs() << "Negated: " << *New << '\n');
517 /// ConvertShiftToMul - If this is a shift of a reassociable multiply or is used
518 /// by one, change this into a multiply by a constant to assist with further
520 static Instruction *ConvertShiftToMul(Instruction *Shl,
521 DenseMap<AssertingVH<Value>, unsigned> &ValueRankMap) {
522 // If an operand of this shift is a reassociable multiply, or if the shift
523 // is used by a reassociable multiply or add, turn into a multiply.
524 if (isReassociableOp(Shl->getOperand(0), Instruction::Mul) ||
526 (isReassociableOp(Shl->use_back(), Instruction::Mul) ||
527 isReassociableOp(Shl->use_back(), Instruction::Add)))) {
528 Constant *MulCst = ConstantInt::get(Shl->getType(), 1);
529 MulCst = ConstantExpr::getShl(MulCst, cast<Constant>(Shl->getOperand(1)));
532 BinaryOperator::CreateMul(Shl->getOperand(0), MulCst, "", Shl);
533 ValueRankMap.erase(Shl);
535 Shl->replaceAllUsesWith(Mul);
536 Mul->setDebugLoc(Shl->getDebugLoc());
537 Shl->eraseFromParent();
543 // Scan backwards and forwards among values with the same rank as element i to
544 // see if X exists. If X does not exist, return i. This is useful when
545 // scanning for 'x' when we see '-x' because they both get the same rank.
546 static unsigned FindInOperandList(SmallVectorImpl<ValueEntry> &Ops, unsigned i,
548 unsigned XRank = Ops[i].Rank;
549 unsigned e = Ops.size();
550 for (unsigned j = i+1; j != e && Ops[j].Rank == XRank; ++j)
554 for (unsigned j = i-1; j != ~0U && Ops[j].Rank == XRank; --j)
560 /// EmitAddTreeOfValues - Emit a tree of add instructions, summing Ops together
561 /// and returning the result. Insert the tree before I.
562 static Value *EmitAddTreeOfValues(Instruction *I,
563 SmallVectorImpl<WeakVH> &Ops){
564 if (Ops.size() == 1) return Ops.back();
566 Value *V1 = Ops.back();
568 Value *V2 = EmitAddTreeOfValues(I, Ops);
569 return BinaryOperator::CreateAdd(V2, V1, "tmp", I);
572 /// RemoveFactorFromExpression - If V is an expression tree that is a
573 /// multiplication sequence, and if this sequence contains a multiply by Factor,
574 /// remove Factor from the tree and return the new tree.
575 Value *Reassociate::RemoveFactorFromExpression(Value *V, Value *Factor) {
576 BinaryOperator *BO = isReassociableOp(V, Instruction::Mul);
579 SmallVector<ValueEntry, 8> Factors;
580 LinearizeExprTree(BO, Factors);
582 bool FoundFactor = false;
583 bool NeedsNegate = false;
584 for (unsigned i = 0, e = Factors.size(); i != e; ++i) {
585 if (Factors[i].Op == Factor) {
587 Factors.erase(Factors.begin()+i);
591 // If this is a negative version of this factor, remove it.
592 if (ConstantInt *FC1 = dyn_cast<ConstantInt>(Factor))
593 if (ConstantInt *FC2 = dyn_cast<ConstantInt>(Factors[i].Op))
594 if (FC1->getValue() == -FC2->getValue()) {
595 FoundFactor = NeedsNegate = true;
596 Factors.erase(Factors.begin()+i);
602 // Make sure to restore the operands to the expression tree.
603 RewriteExprTree(BO, Factors);
607 BasicBlock::iterator InsertPt = BO; ++InsertPt;
609 // If this was just a single multiply, remove the multiply and return the only
610 // remaining operand.
611 if (Factors.size() == 1) {
612 ValueRankMap.erase(BO);
613 DeadInsts.push_back(BO);
616 RewriteExprTree(BO, Factors);
621 V = BinaryOperator::CreateNeg(V, "neg", InsertPt);
626 /// FindSingleUseMultiplyFactors - If V is a single-use multiply, recursively
627 /// add its operands as factors, otherwise add V to the list of factors.
629 /// Ops is the top-level list of add operands we're trying to factor.
630 static void FindSingleUseMultiplyFactors(Value *V,
631 SmallVectorImpl<Value*> &Factors,
632 const SmallVectorImpl<ValueEntry> &Ops,
635 if (!(V->hasOneUse() || V->use_empty()) || // More than one use.
636 !(BO = dyn_cast<BinaryOperator>(V)) ||
637 BO->getOpcode() != Instruction::Mul) {
638 Factors.push_back(V);
642 // If this value has a single use because it is another input to the add
643 // tree we're reassociating and we dropped its use, it actually has two
644 // uses and we can't factor it.
646 for (unsigned i = 0, e = Ops.size(); i != e; ++i)
647 if (Ops[i].Op == V) {
648 Factors.push_back(V);
654 // Otherwise, add the LHS and RHS to the list of factors.
655 FindSingleUseMultiplyFactors(BO->getOperand(1), Factors, Ops, false);
656 FindSingleUseMultiplyFactors(BO->getOperand(0), Factors, Ops, false);
659 /// OptimizeAndOrXor - Optimize a series of operands to an 'and', 'or', or 'xor'
660 /// instruction. This optimizes based on identities. If it can be reduced to
661 /// a single Value, it is returned, otherwise the Ops list is mutated as
663 static Value *OptimizeAndOrXor(unsigned Opcode,
664 SmallVectorImpl<ValueEntry> &Ops) {
665 // Scan the operand lists looking for X and ~X pairs, along with X,X pairs.
666 // If we find any, we can simplify the expression. X&~X == 0, X|~X == -1.
667 for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
668 // First, check for X and ~X in the operand list.
669 assert(i < Ops.size());
670 if (BinaryOperator::isNot(Ops[i].Op)) { // Cannot occur for ^.
671 Value *X = BinaryOperator::getNotArgument(Ops[i].Op);
672 unsigned FoundX = FindInOperandList(Ops, i, X);
674 if (Opcode == Instruction::And) // ...&X&~X = 0
675 return Constant::getNullValue(X->getType());
677 if (Opcode == Instruction::Or) // ...|X|~X = -1
678 return Constant::getAllOnesValue(X->getType());
682 // Next, check for duplicate pairs of values, which we assume are next to
683 // each other, due to our sorting criteria.
684 assert(i < Ops.size());
685 if (i+1 != Ops.size() && Ops[i+1].Op == Ops[i].Op) {
686 if (Opcode == Instruction::And || Opcode == Instruction::Or) {
687 // Drop duplicate values for And and Or.
688 Ops.erase(Ops.begin()+i);
694 // Drop pairs of values for Xor.
695 assert(Opcode == Instruction::Xor);
697 return Constant::getNullValue(Ops[0].Op->getType());
700 Ops.erase(Ops.begin()+i, Ops.begin()+i+2);
708 /// OptimizeAdd - Optimize a series of operands to an 'add' instruction. This
709 /// optimizes based on identities. If it can be reduced to a single Value, it
710 /// is returned, otherwise the Ops list is mutated as necessary.
711 Value *Reassociate::OptimizeAdd(Instruction *I,
712 SmallVectorImpl<ValueEntry> &Ops) {
713 // Scan the operand lists looking for X and -X pairs. If we find any, we
714 // can simplify the expression. X+-X == 0. While we're at it, scan for any
715 // duplicates. We want to canonicalize Y+Y+Y+Z -> 3*Y+Z.
717 // TODO: We could handle "X + ~X" -> "-1" if we wanted, since "-X = ~X+1".
719 for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
720 Value *TheOp = Ops[i].Op;
721 // Check to see if we've seen this operand before. If so, we factor all
722 // instances of the operand together. Due to our sorting criteria, we know
723 // that these need to be next to each other in the vector.
724 if (i+1 != Ops.size() && Ops[i+1].Op == TheOp) {
725 // Rescan the list, remove all instances of this operand from the expr.
726 unsigned NumFound = 0;
728 Ops.erase(Ops.begin()+i);
730 } while (i != Ops.size() && Ops[i].Op == TheOp);
732 DEBUG(errs() << "\nFACTORING [" << NumFound << "]: " << *TheOp << '\n');
735 // Insert a new multiply.
736 Value *Mul = ConstantInt::get(cast<IntegerType>(I->getType()), NumFound);
737 Mul = BinaryOperator::CreateMul(TheOp, Mul, "factor", I);
739 // Now that we have inserted a multiply, optimize it. This allows us to
740 // handle cases that require multiple factoring steps, such as this:
741 // (X*2) + (X*2) + (X*2) -> (X*2)*3 -> X*6
742 RedoInsts.push_back(Mul);
744 // If every add operand was a duplicate, return the multiply.
748 // Otherwise, we had some input that didn't have the dupe, such as
749 // "A + A + B" -> "A*2 + B". Add the new multiply to the list of
750 // things being added by this operation.
751 Ops.insert(Ops.begin(), ValueEntry(getRank(Mul), Mul));
758 // Check for X and -X in the operand list.
759 if (!BinaryOperator::isNeg(TheOp))
762 Value *X = BinaryOperator::getNegArgument(TheOp);
763 unsigned FoundX = FindInOperandList(Ops, i, X);
767 // Remove X and -X from the operand list.
769 return Constant::getNullValue(X->getType());
771 Ops.erase(Ops.begin()+i);
775 --i; // Need to back up an extra one.
776 Ops.erase(Ops.begin()+FoundX);
778 --i; // Revisit element.
779 e -= 2; // Removed two elements.
782 // Scan the operand list, checking to see if there are any common factors
783 // between operands. Consider something like A*A+A*B*C+D. We would like to
784 // reassociate this to A*(A+B*C)+D, which reduces the number of multiplies.
785 // To efficiently find this, we count the number of times a factor occurs
786 // for any ADD operands that are MULs.
787 DenseMap<Value*, unsigned> FactorOccurrences;
789 // Keep track of each multiply we see, to avoid triggering on (X*4)+(X*4)
790 // where they are actually the same multiply.
792 Value *MaxOccVal = 0;
793 for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
794 BinaryOperator *BOp = dyn_cast<BinaryOperator>(Ops[i].Op);
795 if (BOp == 0 || BOp->getOpcode() != Instruction::Mul || !BOp->use_empty())
798 // Compute all of the factors of this added value.
799 SmallVector<Value*, 8> Factors;
800 FindSingleUseMultiplyFactors(BOp, Factors, Ops, true);
801 assert(Factors.size() > 1 && "Bad linearize!");
803 // Add one to FactorOccurrences for each unique factor in this op.
804 SmallPtrSet<Value*, 8> Duplicates;
805 for (unsigned i = 0, e = Factors.size(); i != e; ++i) {
806 Value *Factor = Factors[i];
807 if (!Duplicates.insert(Factor)) continue;
809 unsigned Occ = ++FactorOccurrences[Factor];
810 if (Occ > MaxOcc) { MaxOcc = Occ; MaxOccVal = Factor; }
812 // If Factor is a negative constant, add the negated value as a factor
813 // because we can percolate the negate out. Watch for minint, which
814 // cannot be positivified.
815 if (ConstantInt *CI = dyn_cast<ConstantInt>(Factor))
816 if (CI->isNegative() && !CI->isMinValue(true)) {
817 Factor = ConstantInt::get(CI->getContext(), -CI->getValue());
818 assert(!Duplicates.count(Factor) &&
819 "Shouldn't have two constant factors, missed a canonicalize");
821 unsigned Occ = ++FactorOccurrences[Factor];
822 if (Occ > MaxOcc) { MaxOcc = Occ; MaxOccVal = Factor; }
827 // If any factor occurred more than one time, we can pull it out.
829 DEBUG(errs() << "\nFACTORING [" << MaxOcc << "]: " << *MaxOccVal << '\n');
832 // Create a new instruction that uses the MaxOccVal twice. If we don't do
833 // this, we could otherwise run into situations where removing a factor
834 // from an expression will drop a use of maxocc, and this can cause
835 // RemoveFactorFromExpression on successive values to behave differently.
836 Instruction *DummyInst = BinaryOperator::CreateAdd(MaxOccVal, MaxOccVal);
837 SmallVector<WeakVH, 4> NewMulOps;
838 for (unsigned i = 0; i != Ops.size(); ++i) {
839 // Only try to remove factors from expressions we're allowed to.
840 BinaryOperator *BOp = dyn_cast<BinaryOperator>(Ops[i].Op);
841 if (BOp == 0 || BOp->getOpcode() != Instruction::Mul || !BOp->use_empty())
844 if (Value *V = RemoveFactorFromExpression(Ops[i].Op, MaxOccVal)) {
845 // The factorized operand may occur several times. Convert them all in
847 for (unsigned j = Ops.size(); j != i;) {
849 if (Ops[j].Op == Ops[i].Op) {
850 NewMulOps.push_back(V);
851 Ops.erase(Ops.begin()+j);
858 // No need for extra uses anymore.
861 unsigned NumAddedValues = NewMulOps.size();
862 Value *V = EmitAddTreeOfValues(I, NewMulOps);
864 // Now that we have inserted the add tree, optimize it. This allows us to
865 // handle cases that require multiple factoring steps, such as this:
866 // A*A*B + A*A*C --> A*(A*B+A*C) --> A*(A*(B+C))
867 assert(NumAddedValues > 1 && "Each occurrence should contribute a value");
868 (void)NumAddedValues;
869 V = ReassociateExpression(cast<BinaryOperator>(V));
871 // Create the multiply.
872 Value *V2 = BinaryOperator::CreateMul(V, MaxOccVal, "tmp", I);
874 // Rerun associate on the multiply in case the inner expression turned into
875 // a multiply. We want to make sure that we keep things in canonical form.
876 V2 = ReassociateExpression(cast<BinaryOperator>(V2));
878 // If every add operand included the factor (e.g. "A*B + A*C"), then the
879 // entire result expression is just the multiply "A*(B+C)".
883 // Otherwise, we had some input that didn't have the factor, such as
884 // "A*B + A*C + D" -> "A*(B+C) + D". Add the new multiply to the list of
885 // things being added by this operation.
886 Ops.insert(Ops.begin(), ValueEntry(getRank(V2), V2));
892 Value *Reassociate::OptimizeExpression(BinaryOperator *I,
893 SmallVectorImpl<ValueEntry> &Ops) {
894 // Now that we have the linearized expression tree, try to optimize it.
895 // Start by folding any constants that we found.
896 bool IterateOptimization = false;
897 if (Ops.size() == 1) return Ops[0].Op;
899 unsigned Opcode = I->getOpcode();
901 if (Constant *V1 = dyn_cast<Constant>(Ops[Ops.size()-2].Op))
902 if (Constant *V2 = dyn_cast<Constant>(Ops.back().Op)) {
904 Ops.back().Op = ConstantExpr::get(Opcode, V1, V2);
905 return OptimizeExpression(I, Ops);
908 // Check for destructive annihilation due to a constant being used.
909 if (ConstantInt *CstVal = dyn_cast<ConstantInt>(Ops.back().Op))
912 case Instruction::And:
913 if (CstVal->isZero()) // X & 0 -> 0
915 if (CstVal->isAllOnesValue()) // X & -1 -> X
918 case Instruction::Mul:
919 if (CstVal->isZero()) { // X * 0 -> 0
924 if (cast<ConstantInt>(CstVal)->isOne())
925 Ops.pop_back(); // X * 1 -> X
927 case Instruction::Or:
928 if (CstVal->isAllOnesValue()) // X | -1 -> -1
931 case Instruction::Add:
932 case Instruction::Xor:
933 if (CstVal->isZero()) // X [|^+] 0 -> X
937 if (Ops.size() == 1) return Ops[0].Op;
939 // Handle destructive annihilation due to identities between elements in the
940 // argument list here.
943 case Instruction::And:
944 case Instruction::Or:
945 case Instruction::Xor: {
946 unsigned NumOps = Ops.size();
947 if (Value *Result = OptimizeAndOrXor(Opcode, Ops))
949 IterateOptimization |= Ops.size() != NumOps;
953 case Instruction::Add: {
954 unsigned NumOps = Ops.size();
955 if (Value *Result = OptimizeAdd(I, Ops))
957 IterateOptimization |= Ops.size() != NumOps;
961 //case Instruction::Mul:
964 if (IterateOptimization)
965 return OptimizeExpression(I, Ops);
970 /// ReassociateInst - Inspect and reassociate the instruction at the
971 /// given position, post-incrementing the position.
972 void Reassociate::ReassociateInst(BasicBlock::iterator &BBI) {
973 Instruction *BI = BBI++;
974 if (BI->getOpcode() == Instruction::Shl &&
975 isa<ConstantInt>(BI->getOperand(1)))
976 if (Instruction *NI = ConvertShiftToMul(BI, ValueRankMap)) {
981 // Reject cases where it is pointless to do this.
982 if (!isa<BinaryOperator>(BI) || BI->getType()->isFloatingPointTy() ||
983 BI->getType()->isVectorTy())
984 return; // Floating point ops are not associative.
986 // Do not reassociate boolean (i1) expressions. We want to preserve the
987 // original order of evaluation for short-circuited comparisons that
988 // SimplifyCFG has folded to AND/OR expressions. If the expression
989 // is not further optimized, it is likely to be transformed back to a
990 // short-circuited form for code gen, and the source order may have been
991 // optimized for the most likely conditions.
992 if (BI->getType()->isIntegerTy(1))
995 // If this is a subtract instruction which is not already in negate form,
996 // see if we can convert it to X+-Y.
997 if (BI->getOpcode() == Instruction::Sub) {
998 if (ShouldBreakUpSubtract(BI)) {
999 BI = BreakUpSubtract(BI, ValueRankMap);
1000 // Reset the BBI iterator in case BreakUpSubtract changed the
1001 // instruction it points to.
1005 } else if (BinaryOperator::isNeg(BI)) {
1006 // Otherwise, this is a negation. See if the operand is a multiply tree
1007 // and if this is not an inner node of a multiply tree.
1008 if (isReassociableOp(BI->getOperand(1), Instruction::Mul) &&
1009 (!BI->hasOneUse() ||
1010 !isReassociableOp(BI->use_back(), Instruction::Mul))) {
1011 BI = LowerNegateToMultiply(BI, ValueRankMap);
1017 // If this instruction is a commutative binary operator, process it.
1018 if (!BI->isAssociative()) return;
1019 BinaryOperator *I = cast<BinaryOperator>(BI);
1021 // If this is an interior node of a reassociable tree, ignore it until we
1022 // get to the root of the tree, to avoid N^2 analysis.
1023 if (I->hasOneUse() && isReassociableOp(I->use_back(), I->getOpcode()))
1026 // If this is an add tree that is used by a sub instruction, ignore it
1027 // until we process the subtract.
1028 if (I->hasOneUse() && I->getOpcode() == Instruction::Add &&
1029 cast<Instruction>(I->use_back())->getOpcode() == Instruction::Sub)
1032 ReassociateExpression(I);
1035 Value *Reassociate::ReassociateExpression(BinaryOperator *I) {
1037 // First, walk the expression tree, linearizing the tree, collecting the
1038 // operand information.
1039 SmallVector<ValueEntry, 8> Ops;
1040 LinearizeExprTree(I, Ops);
1042 DEBUG(dbgs() << "RAIn:\t"; PrintOps(I, Ops); dbgs() << '\n');
1044 // Now that we have linearized the tree to a list and have gathered all of
1045 // the operands and their ranks, sort the operands by their rank. Use a
1046 // stable_sort so that values with equal ranks will have their relative
1047 // positions maintained (and so the compiler is deterministic). Note that
1048 // this sorts so that the highest ranking values end up at the beginning of
1050 std::stable_sort(Ops.begin(), Ops.end());
1052 // OptimizeExpression - Now that we have the expression tree in a convenient
1053 // sorted form, optimize it globally if possible.
1054 if (Value *V = OptimizeExpression(I, Ops)) {
1055 // This expression tree simplified to something that isn't a tree,
1057 DEBUG(dbgs() << "Reassoc to scalar: " << *V << '\n');
1058 I->replaceAllUsesWith(V);
1059 if (Instruction *VI = dyn_cast<Instruction>(V))
1060 VI->setDebugLoc(I->getDebugLoc());
1061 RemoveDeadBinaryOp(I);
1066 // We want to sink immediates as deeply as possible except in the case where
1067 // this is a multiply tree used only by an add, and the immediate is a -1.
1068 // In this case we reassociate to put the negation on the outside so that we
1069 // can fold the negation into the add: (-X)*Y + Z -> Z-X*Y
1070 if (I->getOpcode() == Instruction::Mul && I->hasOneUse() &&
1071 cast<Instruction>(I->use_back())->getOpcode() == Instruction::Add &&
1072 isa<ConstantInt>(Ops.back().Op) &&
1073 cast<ConstantInt>(Ops.back().Op)->isAllOnesValue()) {
1074 ValueEntry Tmp = Ops.pop_back_val();
1075 Ops.insert(Ops.begin(), Tmp);
1078 DEBUG(dbgs() << "RAOut:\t"; PrintOps(I, Ops); dbgs() << '\n');
1080 if (Ops.size() == 1) {
1081 // This expression tree simplified to something that isn't a tree,
1083 I->replaceAllUsesWith(Ops[0].Op);
1084 if (Instruction *OI = dyn_cast<Instruction>(Ops[0].Op))
1085 OI->setDebugLoc(I->getDebugLoc());
1086 RemoveDeadBinaryOp(I);
1090 // Now that we ordered and optimized the expressions, splat them back into
1091 // the expression tree, removing any unneeded nodes.
1092 RewriteExprTree(I, Ops);
1097 bool Reassociate::runOnFunction(Function &F) {
1098 // Recalculate the rank map for F
1102 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI)
1103 for (BasicBlock::iterator BBI = FI->begin(); BBI != FI->end(); )
1104 ReassociateInst(BBI);
1106 // Now that we're done, revisit any instructions which are likely to
1107 // have secondary reassociation opportunities.
1108 while (!RedoInsts.empty())
1109 if (Value *V = RedoInsts.pop_back_val()) {
1110 BasicBlock::iterator BBI = cast<Instruction>(V);
1111 ReassociateInst(BBI);
1114 // Now that we're done, delete any instructions which are no longer used.
1115 while (!DeadInsts.empty())
1116 if (Value *V = DeadInsts.pop_back_val())
1117 RecursivelyDeleteTriviallyDeadInstructions(V);
1119 // We are done with the rank map.
1121 ValueRankMap.clear();