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/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"
42 STATISTIC(NumLinear , "Number of insts linearized");
43 STATISTIC(NumChanged, "Number of insts reassociated");
44 STATISTIC(NumAnnihil, "Number of expr tree annihilated");
45 STATISTIC(NumFactor , "Number of multiplies factored");
51 ValueEntry(unsigned R, Value *O) : Rank(R), Op(O) {}
53 inline bool operator<(const ValueEntry &LHS, const ValueEntry &RHS) {
54 return LHS.Rank > RHS.Rank; // Sort so that highest rank goes to start.
59 /// PrintOps - Print out the expression identified in the Ops list.
61 static void PrintOps(Instruction *I, const SmallVectorImpl<ValueEntry> &Ops) {
62 Module *M = I->getParent()->getParent()->getParent();
63 dbgs() << Instruction::getOpcodeName(I->getOpcode()) << " "
64 << *Ops[0].Op->getType() << '\t';
65 for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
67 WriteAsOperand(dbgs(), Ops[i].Op, false, M);
68 dbgs() << ", #" << Ops[i].Rank << "] ";
74 class Reassociate : public FunctionPass {
75 DenseMap<BasicBlock*, unsigned> RankMap;
76 DenseMap<AssertingVH<>, unsigned> ValueRankMap;
79 static char ID; // Pass identification, replacement for typeid
80 Reassociate() : FunctionPass(ID) {
81 initializeReassociatePass(*PassRegistry::getPassRegistry());
84 bool runOnFunction(Function &F);
86 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
90 void BuildRankMap(Function &F);
91 unsigned getRank(Value *V);
92 Value *ReassociateExpression(BinaryOperator *I);
93 void RewriteExprTree(BinaryOperator *I, SmallVectorImpl<ValueEntry> &Ops,
95 Value *OptimizeExpression(BinaryOperator *I,
96 SmallVectorImpl<ValueEntry> &Ops);
97 Value *OptimizeAdd(Instruction *I, SmallVectorImpl<ValueEntry> &Ops);
98 void LinearizeExprTree(BinaryOperator *I, SmallVectorImpl<ValueEntry> &Ops);
99 void LinearizeExpr(BinaryOperator *I);
100 Value *RemoveFactorFromExpression(Value *V, Value *Factor);
101 void ReassociateBB(BasicBlock *BB);
103 void RemoveDeadBinaryOp(Value *V);
107 char Reassociate::ID = 0;
108 INITIALIZE_PASS(Reassociate, "reassociate",
109 "Reassociate expressions", false, false)
111 // Public interface to the Reassociate pass
112 FunctionPass *llvm::createReassociatePass() { return new Reassociate(); }
114 void Reassociate::RemoveDeadBinaryOp(Value *V) {
115 Instruction *Op = dyn_cast<Instruction>(V);
116 if (!Op || !isa<BinaryOperator>(Op) || !Op->use_empty())
119 Value *LHS = Op->getOperand(0), *RHS = Op->getOperand(1);
121 ValueRankMap.erase(Op);
122 Op->eraseFromParent();
123 RemoveDeadBinaryOp(LHS);
124 RemoveDeadBinaryOp(RHS);
128 static bool isUnmovableInstruction(Instruction *I) {
129 if (I->getOpcode() == Instruction::PHI ||
130 I->getOpcode() == Instruction::Alloca ||
131 I->getOpcode() == Instruction::Load ||
132 I->getOpcode() == Instruction::Invoke ||
133 (I->getOpcode() == Instruction::Call &&
134 !isa<DbgInfoIntrinsic>(I)) ||
135 I->getOpcode() == Instruction::UDiv ||
136 I->getOpcode() == Instruction::SDiv ||
137 I->getOpcode() == Instruction::FDiv ||
138 I->getOpcode() == Instruction::URem ||
139 I->getOpcode() == Instruction::SRem ||
140 I->getOpcode() == Instruction::FRem)
145 void Reassociate::BuildRankMap(Function &F) {
148 // Assign distinct ranks to function arguments
149 for (Function::arg_iterator I = F.arg_begin(), E = F.arg_end(); I != E; ++I)
150 ValueRankMap[&*I] = ++i;
152 ReversePostOrderTraversal<Function*> RPOT(&F);
153 for (ReversePostOrderTraversal<Function*>::rpo_iterator I = RPOT.begin(),
154 E = RPOT.end(); I != E; ++I) {
156 unsigned BBRank = RankMap[BB] = ++i << 16;
158 // Walk the basic block, adding precomputed ranks for any instructions that
159 // we cannot move. This ensures that the ranks for these instructions are
160 // all different in the block.
161 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
162 if (isUnmovableInstruction(I))
163 ValueRankMap[&*I] = ++BBRank;
167 unsigned Reassociate::getRank(Value *V) {
168 Instruction *I = dyn_cast<Instruction>(V);
170 if (isa<Argument>(V)) return ValueRankMap[V]; // Function argument.
171 return 0; // Otherwise it's a global or constant, rank 0.
174 if (unsigned Rank = ValueRankMap[I])
175 return Rank; // Rank already known?
177 // If this is an expression, return the 1+MAX(rank(LHS), rank(RHS)) so that
178 // we can reassociate expressions for code motion! Since we do not recurse
179 // for PHI nodes, we cannot have infinite recursion here, because there
180 // cannot be loops in the value graph that do not go through PHI nodes.
181 unsigned Rank = 0, MaxRank = RankMap[I->getParent()];
182 for (unsigned i = 0, e = I->getNumOperands();
183 i != e && Rank != MaxRank; ++i)
184 Rank = std::max(Rank, getRank(I->getOperand(i)));
186 // If this is a not or neg instruction, do not count it for rank. This
187 // assures us that X and ~X will have the same rank.
188 if (!I->getType()->isIntegerTy() ||
189 (!BinaryOperator::isNot(I) && !BinaryOperator::isNeg(I)))
192 //DEBUG(dbgs() << "Calculated Rank[" << V->getName() << "] = "
195 return ValueRankMap[I] = Rank;
198 /// isReassociableOp - Return true if V is an instruction of the specified
199 /// opcode and if it only has one use.
200 static BinaryOperator *isReassociableOp(Value *V, unsigned Opcode) {
201 if ((V->hasOneUse() || V->use_empty()) && isa<Instruction>(V) &&
202 cast<Instruction>(V)->getOpcode() == Opcode)
203 return cast<BinaryOperator>(V);
207 /// LowerNegateToMultiply - Replace 0-X with X*-1.
209 static Instruction *LowerNegateToMultiply(Instruction *Neg,
210 DenseMap<AssertingVH<>, unsigned> &ValueRankMap) {
211 Constant *Cst = Constant::getAllOnesValue(Neg->getType());
213 Instruction *Res = BinaryOperator::CreateMul(Neg->getOperand(1), Cst, "",Neg);
214 ValueRankMap.erase(Neg);
216 Neg->replaceAllUsesWith(Res);
217 Neg->eraseFromParent();
221 // Given an expression of the form '(A+B)+(D+C)', turn it into '(((A+B)+C)+D)'.
222 // Note that if D is also part of the expression tree that we recurse to
223 // linearize it as well. Besides that case, this does not recurse into A,B, or
225 void Reassociate::LinearizeExpr(BinaryOperator *I) {
226 BinaryOperator *LHS = cast<BinaryOperator>(I->getOperand(0));
227 BinaryOperator *RHS = cast<BinaryOperator>(I->getOperand(1));
228 assert(isReassociableOp(LHS, I->getOpcode()) &&
229 isReassociableOp(RHS, I->getOpcode()) &&
230 "Not an expression that needs linearization?");
232 DEBUG(dbgs() << "Linear" << *LHS << '\n' << *RHS << '\n' << *I << '\n');
234 // Move the RHS instruction to live immediately before I, avoiding breaking
235 // dominator properties.
238 // Move operands around to do the linearization.
239 I->setOperand(1, RHS->getOperand(0));
240 RHS->setOperand(0, LHS);
241 I->setOperand(0, RHS);
243 // Conservatively clear all the optional flags, which may not hold
244 // after the reassociation.
245 I->clearSubclassOptionalData();
246 LHS->clearSubclassOptionalData();
247 RHS->clearSubclassOptionalData();
251 DEBUG(dbgs() << "Linearized: " << *I << '\n');
253 // If D is part of this expression tree, tail recurse.
254 if (isReassociableOp(I->getOperand(1), I->getOpcode()))
259 /// LinearizeExprTree - Given an associative binary expression tree, traverse
260 /// all of the uses putting it into canonical form. This forces a left-linear
261 /// form of the expression (((a+b)+c)+d), and collects information about the
262 /// rank of the non-tree operands.
264 /// NOTE: These intentionally destroys the expression tree operands (turning
265 /// them into undef values) to reduce #uses of the values. This means that the
266 /// caller MUST use something like RewriteExprTree to put the values back in.
268 void Reassociate::LinearizeExprTree(BinaryOperator *I,
269 SmallVectorImpl<ValueEntry> &Ops) {
270 Value *LHS = I->getOperand(0), *RHS = I->getOperand(1);
271 unsigned Opcode = I->getOpcode();
273 // First step, linearize the expression if it is in ((A+B)+(C+D)) form.
274 BinaryOperator *LHSBO = isReassociableOp(LHS, Opcode);
275 BinaryOperator *RHSBO = isReassociableOp(RHS, Opcode);
277 // If this is a multiply expression tree and it contains internal negations,
278 // transform them into multiplies by -1 so they can be reassociated.
279 if (I->getOpcode() == Instruction::Mul) {
280 if (!LHSBO && LHS->hasOneUse() && BinaryOperator::isNeg(LHS)) {
281 LHS = LowerNegateToMultiply(cast<Instruction>(LHS), ValueRankMap);
282 LHSBO = isReassociableOp(LHS, Opcode);
284 if (!RHSBO && RHS->hasOneUse() && BinaryOperator::isNeg(RHS)) {
285 RHS = LowerNegateToMultiply(cast<Instruction>(RHS), ValueRankMap);
286 RHSBO = isReassociableOp(RHS, Opcode);
292 // Neither the LHS or RHS as part of the tree, thus this is a leaf. As
293 // such, just remember these operands and their rank.
294 Ops.push_back(ValueEntry(getRank(LHS), LHS));
295 Ops.push_back(ValueEntry(getRank(RHS), RHS));
297 // Clear the leaves out.
298 I->setOperand(0, UndefValue::get(I->getType()));
299 I->setOperand(1, UndefValue::get(I->getType()));
303 // Turn X+(Y+Z) -> (Y+Z)+X
304 std::swap(LHSBO, RHSBO);
306 bool Success = !I->swapOperands();
307 assert(Success && "swapOperands failed");
311 // Turn (A+B)+(C+D) -> (((A+B)+C)+D). This guarantees the RHS is not
312 // part of the expression tree.
314 LHS = LHSBO = cast<BinaryOperator>(I->getOperand(0));
315 RHS = I->getOperand(1);
319 // Okay, now we know that the LHS is a nested expression and that the RHS is
320 // not. Perform reassociation.
321 assert(!isReassociableOp(RHS, Opcode) && "LinearizeExpr failed!");
323 // Move LHS right before I to make sure that the tree expression dominates all
325 LHSBO->moveBefore(I);
327 // Linearize the expression tree on the LHS.
328 LinearizeExprTree(LHSBO, Ops);
330 // Remember the RHS operand and its rank.
331 Ops.push_back(ValueEntry(getRank(RHS), RHS));
333 // Clear the RHS leaf out.
334 I->setOperand(1, UndefValue::get(I->getType()));
337 // RewriteExprTree - Now that the operands for this expression tree are
338 // linearized and optimized, emit them in-order. This function is written to be
340 void Reassociate::RewriteExprTree(BinaryOperator *I,
341 SmallVectorImpl<ValueEntry> &Ops,
343 if (i+2 == Ops.size()) {
344 if (I->getOperand(0) != Ops[i].Op ||
345 I->getOperand(1) != Ops[i+1].Op) {
346 Value *OldLHS = I->getOperand(0);
347 DEBUG(dbgs() << "RA: " << *I << '\n');
348 I->setOperand(0, Ops[i].Op);
349 I->setOperand(1, Ops[i+1].Op);
351 // Clear all the optional flags, which may not hold after the
352 // reassociation if the expression involved more than just this operation.
354 I->clearSubclassOptionalData();
356 DEBUG(dbgs() << "TO: " << *I << '\n');
360 // If we reassociated a tree to fewer operands (e.g. (1+a+2) -> (a+3)
361 // delete the extra, now dead, nodes.
362 RemoveDeadBinaryOp(OldLHS);
366 assert(i+2 < Ops.size() && "Ops index out of range!");
368 if (I->getOperand(1) != Ops[i].Op) {
369 DEBUG(dbgs() << "RA: " << *I << '\n');
370 I->setOperand(1, Ops[i].Op);
372 // Conservatively clear all the optional flags, which may not hold
373 // after the reassociation.
374 I->clearSubclassOptionalData();
376 DEBUG(dbgs() << "TO: " << *I << '\n');
381 BinaryOperator *LHS = cast<BinaryOperator>(I->getOperand(0));
382 assert(LHS->getOpcode() == I->getOpcode() &&
383 "Improper expression tree!");
385 // Compactify the tree instructions together with each other to guarantee
386 // that the expression tree is dominated by all of Ops.
388 RewriteExprTree(LHS, Ops, i+1);
393 // NegateValue - Insert instructions before the instruction pointed to by BI,
394 // that computes the negative version of the value specified. The negative
395 // version of the value is returned, and BI is left pointing at the instruction
396 // that should be processed next by the reassociation pass.
398 static Value *NegateValue(Value *V, Instruction *BI) {
399 if (Constant *C = dyn_cast<Constant>(V))
400 return ConstantExpr::getNeg(C);
402 // We are trying to expose opportunity for reassociation. One of the things
403 // that we want to do to achieve this is to push a negation as deep into an
404 // expression chain as possible, to expose the add instructions. In practice,
405 // this means that we turn this:
406 // X = -(A+12+C+D) into X = -A + -12 + -C + -D = -12 + -A + -C + -D
407 // so that later, a: Y = 12+X could get reassociated with the -12 to eliminate
408 // the constants. We assume that instcombine will clean up the mess later if
409 // we introduce tons of unnecessary negation instructions.
411 if (Instruction *I = dyn_cast<Instruction>(V))
412 if (I->getOpcode() == Instruction::Add && I->hasOneUse()) {
413 // Push the negates through the add.
414 I->setOperand(0, NegateValue(I->getOperand(0), BI));
415 I->setOperand(1, NegateValue(I->getOperand(1), BI));
417 // We must move the add instruction here, because the neg instructions do
418 // not dominate the old add instruction in general. By moving it, we are
419 // assured that the neg instructions we just inserted dominate the
420 // instruction we are about to insert after them.
423 I->setName(I->getName()+".neg");
427 // Okay, we need to materialize a negated version of V with an instruction.
428 // Scan the use lists of V to see if we have one already.
429 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E;++UI){
431 if (!BinaryOperator::isNeg(U)) continue;
433 // We found one! Now we have to make sure that the definition dominates
434 // this use. We do this by moving it to the entry block (if it is a
435 // non-instruction value) or right after the definition. These negates will
436 // be zapped by reassociate later, so we don't need much finesse here.
437 BinaryOperator *TheNeg = cast<BinaryOperator>(U);
439 // Verify that the negate is in this function, V might be a constant expr.
440 if (TheNeg->getParent()->getParent() != BI->getParent()->getParent())
443 BasicBlock::iterator InsertPt;
444 if (Instruction *InstInput = dyn_cast<Instruction>(V)) {
445 if (InvokeInst *II = dyn_cast<InvokeInst>(InstInput)) {
446 InsertPt = II->getNormalDest()->begin();
448 InsertPt = InstInput;
451 while (isa<PHINode>(InsertPt)) ++InsertPt;
453 InsertPt = TheNeg->getParent()->getParent()->getEntryBlock().begin();
455 TheNeg->moveBefore(InsertPt);
459 // Insert a 'neg' instruction that subtracts the value from zero to get the
461 return BinaryOperator::CreateNeg(V, V->getName() + ".neg", BI);
464 /// ShouldBreakUpSubtract - Return true if we should break up this subtract of
465 /// X-Y into (X + -Y).
466 static bool ShouldBreakUpSubtract(Instruction *Sub) {
467 // If this is a negation, we can't split it up!
468 if (BinaryOperator::isNeg(Sub))
471 // Don't bother to break this up unless either the LHS is an associable add or
472 // subtract or if this is only used by one.
473 if (isReassociableOp(Sub->getOperand(0), Instruction::Add) ||
474 isReassociableOp(Sub->getOperand(0), Instruction::Sub))
476 if (isReassociableOp(Sub->getOperand(1), Instruction::Add) ||
477 isReassociableOp(Sub->getOperand(1), Instruction::Sub))
479 if (Sub->hasOneUse() &&
480 (isReassociableOp(Sub->use_back(), Instruction::Add) ||
481 isReassociableOp(Sub->use_back(), Instruction::Sub)))
487 /// BreakUpSubtract - If we have (X-Y), and if either X is an add, or if this is
488 /// only used by an add, transform this into (X+(0-Y)) to promote better
490 static Instruction *BreakUpSubtract(Instruction *Sub,
491 DenseMap<AssertingVH<>, unsigned> &ValueRankMap) {
492 // Convert a subtract into an add and a neg instruction. This allows sub
493 // instructions to be commuted with other add instructions.
495 // Calculate the negative value of Operand 1 of the sub instruction,
496 // and set it as the RHS of the add instruction we just made.
498 Value *NegVal = NegateValue(Sub->getOperand(1), Sub);
500 BinaryOperator::CreateAdd(Sub->getOperand(0), NegVal, "", Sub);
503 // Everyone now refers to the add instruction.
504 ValueRankMap.erase(Sub);
505 Sub->replaceAllUsesWith(New);
506 Sub->eraseFromParent();
508 DEBUG(dbgs() << "Negated: " << *New << '\n');
512 /// ConvertShiftToMul - If this is a shift of a reassociable multiply or is used
513 /// by one, change this into a multiply by a constant to assist with further
515 static Instruction *ConvertShiftToMul(Instruction *Shl,
516 DenseMap<AssertingVH<>, unsigned> &ValueRankMap) {
517 // If an operand of this shift is a reassociable multiply, or if the shift
518 // is used by a reassociable multiply or add, turn into a multiply.
519 if (isReassociableOp(Shl->getOperand(0), Instruction::Mul) ||
521 (isReassociableOp(Shl->use_back(), Instruction::Mul) ||
522 isReassociableOp(Shl->use_back(), Instruction::Add)))) {
523 Constant *MulCst = ConstantInt::get(Shl->getType(), 1);
524 MulCst = ConstantExpr::getShl(MulCst, cast<Constant>(Shl->getOperand(1)));
527 BinaryOperator::CreateMul(Shl->getOperand(0), MulCst, "", Shl);
528 ValueRankMap.erase(Shl);
530 Shl->replaceAllUsesWith(Mul);
531 Shl->eraseFromParent();
537 // Scan backwards and forwards among values with the same rank as element i to
538 // see if X exists. If X does not exist, return i. This is useful when
539 // scanning for 'x' when we see '-x' because they both get the same rank.
540 static unsigned FindInOperandList(SmallVectorImpl<ValueEntry> &Ops, unsigned i,
542 unsigned XRank = Ops[i].Rank;
543 unsigned e = Ops.size();
544 for (unsigned j = i+1; j != e && Ops[j].Rank == XRank; ++j)
548 for (unsigned j = i-1; j != ~0U && Ops[j].Rank == XRank; --j)
554 /// EmitAddTreeOfValues - Emit a tree of add instructions, summing Ops together
555 /// and returning the result. Insert the tree before I.
556 static Value *EmitAddTreeOfValues(Instruction *I, SmallVectorImpl<Value*> &Ops){
557 if (Ops.size() == 1) return Ops.back();
559 Value *V1 = Ops.back();
561 Value *V2 = EmitAddTreeOfValues(I, Ops);
562 return BinaryOperator::CreateAdd(V2, V1, "tmp", I);
565 /// RemoveFactorFromExpression - If V is an expression tree that is a
566 /// multiplication sequence, and if this sequence contains a multiply by Factor,
567 /// remove Factor from the tree and return the new tree.
568 Value *Reassociate::RemoveFactorFromExpression(Value *V, Value *Factor) {
569 BinaryOperator *BO = isReassociableOp(V, Instruction::Mul);
572 SmallVector<ValueEntry, 8> Factors;
573 LinearizeExprTree(BO, Factors);
575 bool FoundFactor = false;
576 bool NeedsNegate = false;
577 for (unsigned i = 0, e = Factors.size(); i != e; ++i) {
578 if (Factors[i].Op == Factor) {
580 Factors.erase(Factors.begin()+i);
584 // If this is a negative version of this factor, remove it.
585 if (ConstantInt *FC1 = dyn_cast<ConstantInt>(Factor))
586 if (ConstantInt *FC2 = dyn_cast<ConstantInt>(Factors[i].Op))
587 if (FC1->getValue() == -FC2->getValue()) {
588 FoundFactor = NeedsNegate = true;
589 Factors.erase(Factors.begin()+i);
595 // Make sure to restore the operands to the expression tree.
596 RewriteExprTree(BO, Factors);
600 BasicBlock::iterator InsertPt = BO; ++InsertPt;
602 // If this was just a single multiply, remove the multiply and return the only
603 // remaining operand.
604 if (Factors.size() == 1) {
605 ValueRankMap.erase(BO);
606 BO->eraseFromParent();
609 RewriteExprTree(BO, Factors);
614 V = BinaryOperator::CreateNeg(V, "neg", InsertPt);
619 /// FindSingleUseMultiplyFactors - If V is a single-use multiply, recursively
620 /// add its operands as factors, otherwise add V to the list of factors.
622 /// Ops is the top-level list of add operands we're trying to factor.
623 static void FindSingleUseMultiplyFactors(Value *V,
624 SmallVectorImpl<Value*> &Factors,
625 const SmallVectorImpl<ValueEntry> &Ops,
628 if (!(V->hasOneUse() || V->use_empty()) || // More than one use.
629 !(BO = dyn_cast<BinaryOperator>(V)) ||
630 BO->getOpcode() != Instruction::Mul) {
631 Factors.push_back(V);
635 // If this value has a single use because it is another input to the add
636 // tree we're reassociating and we dropped its use, it actually has two
637 // uses and we can't factor it.
639 for (unsigned i = 0, e = Ops.size(); i != e; ++i)
640 if (Ops[i].Op == V) {
641 Factors.push_back(V);
647 // Otherwise, add the LHS and RHS to the list of factors.
648 FindSingleUseMultiplyFactors(BO->getOperand(1), Factors, Ops, false);
649 FindSingleUseMultiplyFactors(BO->getOperand(0), Factors, Ops, false);
652 /// OptimizeAndOrXor - Optimize a series of operands to an 'and', 'or', or 'xor'
653 /// instruction. This optimizes based on identities. If it can be reduced to
654 /// a single Value, it is returned, otherwise the Ops list is mutated as
656 static Value *OptimizeAndOrXor(unsigned Opcode,
657 SmallVectorImpl<ValueEntry> &Ops) {
658 // Scan the operand lists looking for X and ~X pairs, along with X,X pairs.
659 // If we find any, we can simplify the expression. X&~X == 0, X|~X == -1.
660 for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
661 // First, check for X and ~X in the operand list.
662 assert(i < Ops.size());
663 if (BinaryOperator::isNot(Ops[i].Op)) { // Cannot occur for ^.
664 Value *X = BinaryOperator::getNotArgument(Ops[i].Op);
665 unsigned FoundX = FindInOperandList(Ops, i, X);
667 if (Opcode == Instruction::And) // ...&X&~X = 0
668 return Constant::getNullValue(X->getType());
670 if (Opcode == Instruction::Or) // ...|X|~X = -1
671 return Constant::getAllOnesValue(X->getType());
675 // Next, check for duplicate pairs of values, which we assume are next to
676 // each other, due to our sorting criteria.
677 assert(i < Ops.size());
678 if (i+1 != Ops.size() && Ops[i+1].Op == Ops[i].Op) {
679 if (Opcode == Instruction::And || Opcode == Instruction::Or) {
680 // Drop duplicate values for And and Or.
681 Ops.erase(Ops.begin()+i);
687 // Drop pairs of values for Xor.
688 assert(Opcode == Instruction::Xor);
690 return Constant::getNullValue(Ops[0].Op->getType());
693 Ops.erase(Ops.begin()+i, Ops.begin()+i+2);
701 /// OptimizeAdd - Optimize a series of operands to an 'add' instruction. This
702 /// optimizes based on identities. If it can be reduced to a single Value, it
703 /// is returned, otherwise the Ops list is mutated as necessary.
704 Value *Reassociate::OptimizeAdd(Instruction *I,
705 SmallVectorImpl<ValueEntry> &Ops) {
706 // Scan the operand lists looking for X and -X pairs. If we find any, we
707 // can simplify the expression. X+-X == 0. While we're at it, scan for any
708 // duplicates. We want to canonicalize Y+Y+Y+Z -> 3*Y+Z.
710 // TODO: We could handle "X + ~X" -> "-1" if we wanted, since "-X = ~X+1".
712 for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
713 Value *TheOp = Ops[i].Op;
714 // Check to see if we've seen this operand before. If so, we factor all
715 // instances of the operand together. Due to our sorting criteria, we know
716 // that these need to be next to each other in the vector.
717 if (i+1 != Ops.size() && Ops[i+1].Op == TheOp) {
718 // Rescan the list, remove all instances of this operand from the expr.
719 unsigned NumFound = 0;
721 Ops.erase(Ops.begin()+i);
723 } while (i != Ops.size() && Ops[i].Op == TheOp);
725 DEBUG(errs() << "\nFACTORING [" << NumFound << "]: " << *TheOp << '\n');
728 // Insert a new multiply.
729 Value *Mul = ConstantInt::get(cast<IntegerType>(I->getType()), NumFound);
730 Mul = BinaryOperator::CreateMul(TheOp, Mul, "factor", I);
732 // Now that we have inserted a multiply, optimize it. This allows us to
733 // handle cases that require multiple factoring steps, such as this:
734 // (X*2) + (X*2) + (X*2) -> (X*2)*3 -> X*6
735 Mul = ReassociateExpression(cast<BinaryOperator>(Mul));
737 // If every add operand was a duplicate, return the multiply.
741 // Otherwise, we had some input that didn't have the dupe, such as
742 // "A + A + B" -> "A*2 + B". Add the new multiply to the list of
743 // things being added by this operation.
744 Ops.insert(Ops.begin(), ValueEntry(getRank(Mul), Mul));
751 // Check for X and -X in the operand list.
752 if (!BinaryOperator::isNeg(TheOp))
755 Value *X = BinaryOperator::getNegArgument(TheOp);
756 unsigned FoundX = FindInOperandList(Ops, i, X);
760 // Remove X and -X from the operand list.
762 return Constant::getNullValue(X->getType());
764 Ops.erase(Ops.begin()+i);
768 --i; // Need to back up an extra one.
769 Ops.erase(Ops.begin()+FoundX);
771 --i; // Revisit element.
772 e -= 2; // Removed two elements.
775 // Scan the operand list, checking to see if there are any common factors
776 // between operands. Consider something like A*A+A*B*C+D. We would like to
777 // reassociate this to A*(A+B*C)+D, which reduces the number of multiplies.
778 // To efficiently find this, we count the number of times a factor occurs
779 // for any ADD operands that are MULs.
780 DenseMap<Value*, unsigned> FactorOccurrences;
782 // Keep track of each multiply we see, to avoid triggering on (X*4)+(X*4)
783 // where they are actually the same multiply.
785 Value *MaxOccVal = 0;
786 for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
787 BinaryOperator *BOp = dyn_cast<BinaryOperator>(Ops[i].Op);
788 if (BOp == 0 || BOp->getOpcode() != Instruction::Mul || !BOp->use_empty())
791 // Compute all of the factors of this added value.
792 SmallVector<Value*, 8> Factors;
793 FindSingleUseMultiplyFactors(BOp, Factors, Ops, true);
794 assert(Factors.size() > 1 && "Bad linearize!");
796 // Add one to FactorOccurrences for each unique factor in this op.
797 SmallPtrSet<Value*, 8> Duplicates;
798 for (unsigned i = 0, e = Factors.size(); i != e; ++i) {
799 Value *Factor = Factors[i];
800 if (!Duplicates.insert(Factor)) continue;
802 unsigned Occ = ++FactorOccurrences[Factor];
803 if (Occ > MaxOcc) { MaxOcc = Occ; MaxOccVal = Factor; }
805 // If Factor is a negative constant, add the negated value as a factor
806 // because we can percolate the negate out. Watch for minint, which
807 // cannot be positivified.
808 if (ConstantInt *CI = dyn_cast<ConstantInt>(Factor))
809 if (CI->getValue().isNegative() && !CI->getValue().isMinSignedValue()) {
810 Factor = ConstantInt::get(CI->getContext(), -CI->getValue());
811 assert(!Duplicates.count(Factor) &&
812 "Shouldn't have two constant factors, missed a canonicalize");
814 unsigned Occ = ++FactorOccurrences[Factor];
815 if (Occ > MaxOcc) { MaxOcc = Occ; MaxOccVal = Factor; }
820 // If any factor occurred more than one time, we can pull it out.
822 DEBUG(errs() << "\nFACTORING [" << MaxOcc << "]: " << *MaxOccVal << '\n');
825 // Create a new instruction that uses the MaxOccVal twice. If we don't do
826 // this, we could otherwise run into situations where removing a factor
827 // from an expression will drop a use of maxocc, and this can cause
828 // RemoveFactorFromExpression on successive values to behave differently.
829 Instruction *DummyInst = BinaryOperator::CreateAdd(MaxOccVal, MaxOccVal);
830 SmallVector<Value*, 4> NewMulOps;
831 for (unsigned i = 0; i != Ops.size(); ++i) {
832 // Only try to remove factors from expressions we're allowed to.
833 BinaryOperator *BOp = dyn_cast<BinaryOperator>(Ops[i].Op);
834 if (BOp == 0 || BOp->getOpcode() != Instruction::Mul || !BOp->use_empty())
837 if (Value *V = RemoveFactorFromExpression(Ops[i].Op, MaxOccVal)) {
838 // The factorized operand may occur several times. Convert them all in
840 for (unsigned j = Ops.size(); j != i;) {
842 if (Ops[j].Op == Ops[i].Op) {
843 NewMulOps.push_back(V);
844 Ops.erase(Ops.begin()+j);
851 // No need for extra uses anymore.
854 unsigned NumAddedValues = NewMulOps.size();
855 Value *V = EmitAddTreeOfValues(I, NewMulOps);
857 // Now that we have inserted the add tree, optimize it. This allows us to
858 // handle cases that require multiple factoring steps, such as this:
859 // A*A*B + A*A*C --> A*(A*B+A*C) --> A*(A*(B+C))
860 assert(NumAddedValues > 1 && "Each occurrence should contribute a value");
861 (void)NumAddedValues;
862 V = ReassociateExpression(cast<BinaryOperator>(V));
864 // Create the multiply.
865 Value *V2 = BinaryOperator::CreateMul(V, MaxOccVal, "tmp", I);
867 // Rerun associate on the multiply in case the inner expression turned into
868 // a multiply. We want to make sure that we keep things in canonical form.
869 V2 = ReassociateExpression(cast<BinaryOperator>(V2));
871 // If every add operand included the factor (e.g. "A*B + A*C"), then the
872 // entire result expression is just the multiply "A*(B+C)".
876 // Otherwise, we had some input that didn't have the factor, such as
877 // "A*B + A*C + D" -> "A*(B+C) + D". Add the new multiply to the list of
878 // things being added by this operation.
879 Ops.insert(Ops.begin(), ValueEntry(getRank(V2), V2));
885 Value *Reassociate::OptimizeExpression(BinaryOperator *I,
886 SmallVectorImpl<ValueEntry> &Ops) {
887 // Now that we have the linearized expression tree, try to optimize it.
888 // Start by folding any constants that we found.
889 bool IterateOptimization = false;
890 if (Ops.size() == 1) return Ops[0].Op;
892 unsigned Opcode = I->getOpcode();
894 if (Constant *V1 = dyn_cast<Constant>(Ops[Ops.size()-2].Op))
895 if (Constant *V2 = dyn_cast<Constant>(Ops.back().Op)) {
897 Ops.back().Op = ConstantExpr::get(Opcode, V1, V2);
898 return OptimizeExpression(I, Ops);
901 // Check for destructive annihilation due to a constant being used.
902 if (ConstantInt *CstVal = dyn_cast<ConstantInt>(Ops.back().Op))
905 case Instruction::And:
906 if (CstVal->isZero()) // X & 0 -> 0
908 if (CstVal->isAllOnesValue()) // X & -1 -> X
911 case Instruction::Mul:
912 if (CstVal->isZero()) { // X * 0 -> 0
917 if (cast<ConstantInt>(CstVal)->isOne())
918 Ops.pop_back(); // X * 1 -> X
920 case Instruction::Or:
921 if (CstVal->isAllOnesValue()) // X | -1 -> -1
924 case Instruction::Add:
925 case Instruction::Xor:
926 if (CstVal->isZero()) // X [|^+] 0 -> X
930 if (Ops.size() == 1) return Ops[0].Op;
932 // Handle destructive annihilation due to identities between elements in the
933 // argument list here.
936 case Instruction::And:
937 case Instruction::Or:
938 case Instruction::Xor: {
939 unsigned NumOps = Ops.size();
940 if (Value *Result = OptimizeAndOrXor(Opcode, Ops))
942 IterateOptimization |= Ops.size() != NumOps;
946 case Instruction::Add: {
947 unsigned NumOps = Ops.size();
948 if (Value *Result = OptimizeAdd(I, Ops))
950 IterateOptimization |= Ops.size() != NumOps;
954 //case Instruction::Mul:
957 if (IterateOptimization)
958 return OptimizeExpression(I, Ops);
963 /// ReassociateBB - Inspect all of the instructions in this basic block,
964 /// reassociating them as we go.
965 void Reassociate::ReassociateBB(BasicBlock *BB) {
966 for (BasicBlock::iterator BBI = BB->begin(); BBI != BB->end(); ) {
967 Instruction *BI = BBI++;
968 if (BI->getOpcode() == Instruction::Shl &&
969 isa<ConstantInt>(BI->getOperand(1)))
970 if (Instruction *NI = ConvertShiftToMul(BI, ValueRankMap)) {
975 // Reject cases where it is pointless to do this.
976 if (!isa<BinaryOperator>(BI) || BI->getType()->isFloatingPointTy() ||
977 BI->getType()->isVectorTy())
978 continue; // Floating point ops are not associative.
980 // Do not reassociate boolean (i1) expressions. We want to preserve the
981 // original order of evaluation for short-circuited comparisons that
982 // SimplifyCFG has folded to AND/OR expressions. If the expression
983 // is not further optimized, it is likely to be transformed back to a
984 // short-circuited form for code gen, and the source order may have been
985 // optimized for the most likely conditions.
986 if (BI->getType()->isIntegerTy(1))
989 // If this is a subtract instruction which is not already in negate form,
990 // see if we can convert it to X+-Y.
991 if (BI->getOpcode() == Instruction::Sub) {
992 if (ShouldBreakUpSubtract(BI)) {
993 BI = BreakUpSubtract(BI, ValueRankMap);
994 // Reset the BBI iterator in case BreakUpSubtract changed the
995 // instruction it points to.
999 } else if (BinaryOperator::isNeg(BI)) {
1000 // Otherwise, this is a negation. See if the operand is a multiply tree
1001 // and if this is not an inner node of a multiply tree.
1002 if (isReassociableOp(BI->getOperand(1), Instruction::Mul) &&
1003 (!BI->hasOneUse() ||
1004 !isReassociableOp(BI->use_back(), Instruction::Mul))) {
1005 BI = LowerNegateToMultiply(BI, ValueRankMap);
1011 // If this instruction is a commutative binary operator, process it.
1012 if (!BI->isAssociative()) continue;
1013 BinaryOperator *I = cast<BinaryOperator>(BI);
1015 // If this is an interior node of a reassociable tree, ignore it until we
1016 // get to the root of the tree, to avoid N^2 analysis.
1017 if (I->hasOneUse() && isReassociableOp(I->use_back(), I->getOpcode()))
1020 // If this is an add tree that is used by a sub instruction, ignore it
1021 // until we process the subtract.
1022 if (I->hasOneUse() && I->getOpcode() == Instruction::Add &&
1023 cast<Instruction>(I->use_back())->getOpcode() == Instruction::Sub)
1026 ReassociateExpression(I);
1030 Value *Reassociate::ReassociateExpression(BinaryOperator *I) {
1032 // First, walk the expression tree, linearizing the tree, collecting the
1033 // operand information.
1034 SmallVector<ValueEntry, 8> Ops;
1035 LinearizeExprTree(I, Ops);
1037 DEBUG(dbgs() << "RAIn:\t"; PrintOps(I, Ops); dbgs() << '\n');
1039 // Now that we have linearized the tree to a list and have gathered all of
1040 // the operands and their ranks, sort the operands by their rank. Use a
1041 // stable_sort so that values with equal ranks will have their relative
1042 // positions maintained (and so the compiler is deterministic). Note that
1043 // this sorts so that the highest ranking values end up at the beginning of
1045 std::stable_sort(Ops.begin(), Ops.end());
1047 // OptimizeExpression - Now that we have the expression tree in a convenient
1048 // sorted form, optimize it globally if possible.
1049 if (Value *V = OptimizeExpression(I, Ops)) {
1050 // This expression tree simplified to something that isn't a tree,
1052 DEBUG(dbgs() << "Reassoc to scalar: " << *V << '\n');
1053 I->replaceAllUsesWith(V);
1054 RemoveDeadBinaryOp(I);
1059 // We want to sink immediates as deeply as possible except in the case where
1060 // this is a multiply tree used only by an add, and the immediate is a -1.
1061 // In this case we reassociate to put the negation on the outside so that we
1062 // can fold the negation into the add: (-X)*Y + Z -> Z-X*Y
1063 if (I->getOpcode() == Instruction::Mul && I->hasOneUse() &&
1064 cast<Instruction>(I->use_back())->getOpcode() == Instruction::Add &&
1065 isa<ConstantInt>(Ops.back().Op) &&
1066 cast<ConstantInt>(Ops.back().Op)->isAllOnesValue()) {
1067 ValueEntry Tmp = Ops.pop_back_val();
1068 Ops.insert(Ops.begin(), Tmp);
1071 DEBUG(dbgs() << "RAOut:\t"; PrintOps(I, Ops); dbgs() << '\n');
1073 if (Ops.size() == 1) {
1074 // This expression tree simplified to something that isn't a tree,
1076 I->replaceAllUsesWith(Ops[0].Op);
1077 RemoveDeadBinaryOp(I);
1081 // Now that we ordered and optimized the expressions, splat them back into
1082 // the expression tree, removing any unneeded nodes.
1083 RewriteExprTree(I, Ops);
1088 bool Reassociate::runOnFunction(Function &F) {
1089 // Recalculate the rank map for F
1093 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI)
1096 // We are done with the rank map.
1098 ValueRankMap.clear();