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) {}
82 bool runOnFunction(Function &F);
84 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
88 void BuildRankMap(Function &F);
89 unsigned getRank(Value *V);
90 Value *ReassociateExpression(BinaryOperator *I);
91 void RewriteExprTree(BinaryOperator *I, SmallVectorImpl<ValueEntry> &Ops,
93 Value *OptimizeExpression(BinaryOperator *I,
94 SmallVectorImpl<ValueEntry> &Ops);
95 Value *OptimizeAdd(Instruction *I, SmallVectorImpl<ValueEntry> &Ops);
96 void LinearizeExprTree(BinaryOperator *I, SmallVectorImpl<ValueEntry> &Ops);
97 void LinearizeExpr(BinaryOperator *I);
98 Value *RemoveFactorFromExpression(Value *V, Value *Factor);
99 void ReassociateBB(BasicBlock *BB);
101 void RemoveDeadBinaryOp(Value *V);
105 char Reassociate::ID = 0;
106 INITIALIZE_PASS(Reassociate, "reassociate",
107 "Reassociate expressions", false, false);
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 Instruction *I = dyn_cast<Instruction>(V);
168 if (isa<Argument>(V)) return ValueRankMap[V]; // Function argument.
169 return 0; // Otherwise it's a global or constant, rank 0.
172 if (unsigned Rank = ValueRankMap[I])
173 return Rank; // Rank already known?
175 // If this is an expression, return the 1+MAX(rank(LHS), rank(RHS)) so that
176 // we can reassociate expressions for code motion! Since we do not recurse
177 // for PHI nodes, we cannot have infinite recursion here, because there
178 // cannot be loops in the value graph that do not go through PHI nodes.
179 unsigned Rank = 0, MaxRank = RankMap[I->getParent()];
180 for (unsigned i = 0, e = I->getNumOperands();
181 i != e && Rank != MaxRank; ++i)
182 Rank = std::max(Rank, getRank(I->getOperand(i)));
184 // If this is a not or neg instruction, do not count it for rank. This
185 // assures us that X and ~X will have the same rank.
186 if (!I->getType()->isIntegerTy() ||
187 (!BinaryOperator::isNot(I) && !BinaryOperator::isNeg(I)))
190 //DEBUG(dbgs() << "Calculated Rank[" << V->getName() << "] = "
193 return ValueRankMap[I] = Rank;
196 /// isReassociableOp - Return true if V is an instruction of the specified
197 /// opcode and if it only has one use.
198 static BinaryOperator *isReassociableOp(Value *V, unsigned Opcode) {
199 if ((V->hasOneUse() || V->use_empty()) && isa<Instruction>(V) &&
200 cast<Instruction>(V)->getOpcode() == Opcode)
201 return cast<BinaryOperator>(V);
205 /// LowerNegateToMultiply - Replace 0-X with X*-1.
207 static Instruction *LowerNegateToMultiply(Instruction *Neg,
208 DenseMap<AssertingVH<>, unsigned> &ValueRankMap) {
209 Constant *Cst = Constant::getAllOnesValue(Neg->getType());
211 Instruction *Res = BinaryOperator::CreateMul(Neg->getOperand(1), Cst, "",Neg);
212 ValueRankMap.erase(Neg);
214 Neg->replaceAllUsesWith(Res);
215 Neg->eraseFromParent();
219 // Given an expression of the form '(A+B)+(D+C)', turn it into '(((A+B)+C)+D)'.
220 // Note that if D is also part of the expression tree that we recurse to
221 // linearize it as well. Besides that case, this does not recurse into A,B, or
223 void Reassociate::LinearizeExpr(BinaryOperator *I) {
224 BinaryOperator *LHS = cast<BinaryOperator>(I->getOperand(0));
225 BinaryOperator *RHS = cast<BinaryOperator>(I->getOperand(1));
226 assert(isReassociableOp(LHS, I->getOpcode()) &&
227 isReassociableOp(RHS, I->getOpcode()) &&
228 "Not an expression that needs linearization?");
230 DEBUG(dbgs() << "Linear" << *LHS << '\n' << *RHS << '\n' << *I << '\n');
232 // Move the RHS instruction to live immediately before I, avoiding breaking
233 // dominator properties.
236 // Move operands around to do the linearization.
237 I->setOperand(1, RHS->getOperand(0));
238 RHS->setOperand(0, LHS);
239 I->setOperand(0, RHS);
243 DEBUG(dbgs() << "Linearized: " << *I << '\n');
245 // If D is part of this expression tree, tail recurse.
246 if (isReassociableOp(I->getOperand(1), I->getOpcode()))
251 /// LinearizeExprTree - Given an associative binary expression tree, traverse
252 /// all of the uses putting it into canonical form. This forces a left-linear
253 /// form of the expression (((a+b)+c)+d), and collects information about the
254 /// rank of the non-tree operands.
256 /// NOTE: These intentionally destroys the expression tree operands (turning
257 /// them into undef values) to reduce #uses of the values. This means that the
258 /// caller MUST use something like RewriteExprTree to put the values back in.
260 void Reassociate::LinearizeExprTree(BinaryOperator *I,
261 SmallVectorImpl<ValueEntry> &Ops) {
262 Value *LHS = I->getOperand(0), *RHS = I->getOperand(1);
263 unsigned Opcode = I->getOpcode();
265 // First step, linearize the expression if it is in ((A+B)+(C+D)) form.
266 BinaryOperator *LHSBO = isReassociableOp(LHS, Opcode);
267 BinaryOperator *RHSBO = isReassociableOp(RHS, Opcode);
269 // If this is a multiply expression tree and it contains internal negations,
270 // transform them into multiplies by -1 so they can be reassociated.
271 if (I->getOpcode() == Instruction::Mul) {
272 if (!LHSBO && LHS->hasOneUse() && BinaryOperator::isNeg(LHS)) {
273 LHS = LowerNegateToMultiply(cast<Instruction>(LHS), ValueRankMap);
274 LHSBO = isReassociableOp(LHS, Opcode);
276 if (!RHSBO && RHS->hasOneUse() && BinaryOperator::isNeg(RHS)) {
277 RHS = LowerNegateToMultiply(cast<Instruction>(RHS), ValueRankMap);
278 RHSBO = isReassociableOp(RHS, Opcode);
284 // Neither the LHS or RHS as part of the tree, thus this is a leaf. As
285 // such, just remember these operands and their rank.
286 Ops.push_back(ValueEntry(getRank(LHS), LHS));
287 Ops.push_back(ValueEntry(getRank(RHS), RHS));
289 // Clear the leaves out.
290 I->setOperand(0, UndefValue::get(I->getType()));
291 I->setOperand(1, UndefValue::get(I->getType()));
295 // Turn X+(Y+Z) -> (Y+Z)+X
296 std::swap(LHSBO, RHSBO);
298 bool Success = !I->swapOperands();
299 assert(Success && "swapOperands failed");
303 // Turn (A+B)+(C+D) -> (((A+B)+C)+D). This guarantees the RHS is not
304 // part of the expression tree.
306 LHS = LHSBO = cast<BinaryOperator>(I->getOperand(0));
307 RHS = I->getOperand(1);
311 // Okay, now we know that the LHS is a nested expression and that the RHS is
312 // not. Perform reassociation.
313 assert(!isReassociableOp(RHS, Opcode) && "LinearizeExpr failed!");
315 // Move LHS right before I to make sure that the tree expression dominates all
317 LHSBO->moveBefore(I);
319 // Linearize the expression tree on the LHS.
320 LinearizeExprTree(LHSBO, Ops);
322 // Remember the RHS operand and its rank.
323 Ops.push_back(ValueEntry(getRank(RHS), RHS));
325 // Clear the RHS leaf out.
326 I->setOperand(1, UndefValue::get(I->getType()));
329 // RewriteExprTree - Now that the operands for this expression tree are
330 // linearized and optimized, emit them in-order. This function is written to be
332 void Reassociate::RewriteExprTree(BinaryOperator *I,
333 SmallVectorImpl<ValueEntry> &Ops,
335 if (i+2 == Ops.size()) {
336 if (I->getOperand(0) != Ops[i].Op ||
337 I->getOperand(1) != Ops[i+1].Op) {
338 Value *OldLHS = I->getOperand(0);
339 DEBUG(dbgs() << "RA: " << *I << '\n');
340 I->setOperand(0, Ops[i].Op);
341 I->setOperand(1, Ops[i+1].Op);
342 DEBUG(dbgs() << "TO: " << *I << '\n');
346 // If we reassociated a tree to fewer operands (e.g. (1+a+2) -> (a+3)
347 // delete the extra, now dead, nodes.
348 RemoveDeadBinaryOp(OldLHS);
352 assert(i+2 < Ops.size() && "Ops index out of range!");
354 if (I->getOperand(1) != Ops[i].Op) {
355 DEBUG(dbgs() << "RA: " << *I << '\n');
356 I->setOperand(1, Ops[i].Op);
357 DEBUG(dbgs() << "TO: " << *I << '\n');
362 BinaryOperator *LHS = cast<BinaryOperator>(I->getOperand(0));
363 assert(LHS->getOpcode() == I->getOpcode() &&
364 "Improper expression tree!");
366 // Compactify the tree instructions together with each other to guarantee
367 // that the expression tree is dominated by all of Ops.
369 RewriteExprTree(LHS, Ops, i+1);
374 // NegateValue - Insert instructions before the instruction pointed to by BI,
375 // that computes the negative version of the value specified. The negative
376 // version of the value is returned, and BI is left pointing at the instruction
377 // that should be processed next by the reassociation pass.
379 static Value *NegateValue(Value *V, Instruction *BI) {
380 if (Constant *C = dyn_cast<Constant>(V))
381 return ConstantExpr::getNeg(C);
383 // We are trying to expose opportunity for reassociation. One of the things
384 // that we want to do to achieve this is to push a negation as deep into an
385 // expression chain as possible, to expose the add instructions. In practice,
386 // this means that we turn this:
387 // X = -(A+12+C+D) into X = -A + -12 + -C + -D = -12 + -A + -C + -D
388 // so that later, a: Y = 12+X could get reassociated with the -12 to eliminate
389 // the constants. We assume that instcombine will clean up the mess later if
390 // we introduce tons of unnecessary negation instructions.
392 if (Instruction *I = dyn_cast<Instruction>(V))
393 if (I->getOpcode() == Instruction::Add && I->hasOneUse()) {
394 // Push the negates through the add.
395 I->setOperand(0, NegateValue(I->getOperand(0), BI));
396 I->setOperand(1, NegateValue(I->getOperand(1), BI));
398 // We must move the add instruction here, because the neg instructions do
399 // not dominate the old add instruction in general. By moving it, we are
400 // assured that the neg instructions we just inserted dominate the
401 // instruction we are about to insert after them.
404 I->setName(I->getName()+".neg");
408 // Okay, we need to materialize a negated version of V with an instruction.
409 // Scan the use lists of V to see if we have one already.
410 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E;++UI){
412 if (!BinaryOperator::isNeg(U)) continue;
414 // We found one! Now we have to make sure that the definition dominates
415 // this use. We do this by moving it to the entry block (if it is a
416 // non-instruction value) or right after the definition. These negates will
417 // be zapped by reassociate later, so we don't need much finesse here.
418 BinaryOperator *TheNeg = cast<BinaryOperator>(U);
420 // Verify that the negate is in this function, V might be a constant expr.
421 if (TheNeg->getParent()->getParent() != BI->getParent()->getParent())
424 BasicBlock::iterator InsertPt;
425 if (Instruction *InstInput = dyn_cast<Instruction>(V)) {
426 if (InvokeInst *II = dyn_cast<InvokeInst>(InstInput)) {
427 InsertPt = II->getNormalDest()->begin();
429 InsertPt = InstInput;
432 while (isa<PHINode>(InsertPt)) ++InsertPt;
434 InsertPt = TheNeg->getParent()->getParent()->getEntryBlock().begin();
436 TheNeg->moveBefore(InsertPt);
440 // Insert a 'neg' instruction that subtracts the value from zero to get the
442 return BinaryOperator::CreateNeg(V, V->getName() + ".neg", BI);
445 /// ShouldBreakUpSubtract - Return true if we should break up this subtract of
446 /// X-Y into (X + -Y).
447 static bool ShouldBreakUpSubtract(Instruction *Sub) {
448 // If this is a negation, we can't split it up!
449 if (BinaryOperator::isNeg(Sub))
452 // Don't bother to break this up unless either the LHS is an associable add or
453 // subtract or if this is only used by one.
454 if (isReassociableOp(Sub->getOperand(0), Instruction::Add) ||
455 isReassociableOp(Sub->getOperand(0), Instruction::Sub))
457 if (isReassociableOp(Sub->getOperand(1), Instruction::Add) ||
458 isReassociableOp(Sub->getOperand(1), Instruction::Sub))
460 if (Sub->hasOneUse() &&
461 (isReassociableOp(Sub->use_back(), Instruction::Add) ||
462 isReassociableOp(Sub->use_back(), Instruction::Sub)))
468 /// BreakUpSubtract - If we have (X-Y), and if either X is an add, or if this is
469 /// only used by an add, transform this into (X+(0-Y)) to promote better
471 static Instruction *BreakUpSubtract(Instruction *Sub,
472 DenseMap<AssertingVH<>, unsigned> &ValueRankMap) {
473 // Convert a subtract into an add and a neg instruction. This allows sub
474 // instructions to be commuted with other add instructions.
476 // Calculate the negative value of Operand 1 of the sub instruction,
477 // and set it as the RHS of the add instruction we just made.
479 Value *NegVal = NegateValue(Sub->getOperand(1), Sub);
481 BinaryOperator::CreateAdd(Sub->getOperand(0), NegVal, "", Sub);
484 // Everyone now refers to the add instruction.
485 ValueRankMap.erase(Sub);
486 Sub->replaceAllUsesWith(New);
487 Sub->eraseFromParent();
489 DEBUG(dbgs() << "Negated: " << *New << '\n');
493 /// ConvertShiftToMul - If this is a shift of a reassociable multiply or is used
494 /// by one, change this into a multiply by a constant to assist with further
496 static Instruction *ConvertShiftToMul(Instruction *Shl,
497 DenseMap<AssertingVH<>, unsigned> &ValueRankMap) {
498 // If an operand of this shift is a reassociable multiply, or if the shift
499 // is used by a reassociable multiply or add, turn into a multiply.
500 if (isReassociableOp(Shl->getOperand(0), Instruction::Mul) ||
502 (isReassociableOp(Shl->use_back(), Instruction::Mul) ||
503 isReassociableOp(Shl->use_back(), Instruction::Add)))) {
504 Constant *MulCst = ConstantInt::get(Shl->getType(), 1);
505 MulCst = ConstantExpr::getShl(MulCst, cast<Constant>(Shl->getOperand(1)));
508 BinaryOperator::CreateMul(Shl->getOperand(0), MulCst, "", Shl);
509 ValueRankMap.erase(Shl);
511 Shl->replaceAllUsesWith(Mul);
512 Shl->eraseFromParent();
518 // Scan backwards and forwards among values with the same rank as element i to
519 // see if X exists. If X does not exist, return i. This is useful when
520 // scanning for 'x' when we see '-x' because they both get the same rank.
521 static unsigned FindInOperandList(SmallVectorImpl<ValueEntry> &Ops, unsigned i,
523 unsigned XRank = Ops[i].Rank;
524 unsigned e = Ops.size();
525 for (unsigned j = i+1; j != e && Ops[j].Rank == XRank; ++j)
529 for (unsigned j = i-1; j != ~0U && Ops[j].Rank == XRank; --j)
535 /// EmitAddTreeOfValues - Emit a tree of add instructions, summing Ops together
536 /// and returning the result. Insert the tree before I.
537 static Value *EmitAddTreeOfValues(Instruction *I, SmallVectorImpl<Value*> &Ops){
538 if (Ops.size() == 1) return Ops.back();
540 Value *V1 = Ops.back();
542 Value *V2 = EmitAddTreeOfValues(I, Ops);
543 return BinaryOperator::CreateAdd(V2, V1, "tmp", I);
546 /// RemoveFactorFromExpression - If V is an expression tree that is a
547 /// multiplication sequence, and if this sequence contains a multiply by Factor,
548 /// remove Factor from the tree and return the new tree.
549 Value *Reassociate::RemoveFactorFromExpression(Value *V, Value *Factor) {
550 BinaryOperator *BO = isReassociableOp(V, Instruction::Mul);
553 SmallVector<ValueEntry, 8> Factors;
554 LinearizeExprTree(BO, Factors);
556 bool FoundFactor = false;
557 bool NeedsNegate = false;
558 for (unsigned i = 0, e = Factors.size(); i != e; ++i) {
559 if (Factors[i].Op == Factor) {
561 Factors.erase(Factors.begin()+i);
565 // If this is a negative version of this factor, remove it.
566 if (ConstantInt *FC1 = dyn_cast<ConstantInt>(Factor))
567 if (ConstantInt *FC2 = dyn_cast<ConstantInt>(Factors[i].Op))
568 if (FC1->getValue() == -FC2->getValue()) {
569 FoundFactor = NeedsNegate = true;
570 Factors.erase(Factors.begin()+i);
576 // Make sure to restore the operands to the expression tree.
577 RewriteExprTree(BO, Factors);
581 BasicBlock::iterator InsertPt = BO; ++InsertPt;
583 // If this was just a single multiply, remove the multiply and return the only
584 // remaining operand.
585 if (Factors.size() == 1) {
586 ValueRankMap.erase(BO);
587 BO->eraseFromParent();
590 RewriteExprTree(BO, Factors);
595 V = BinaryOperator::CreateNeg(V, "neg", InsertPt);
600 /// FindSingleUseMultiplyFactors - If V is a single-use multiply, recursively
601 /// add its operands as factors, otherwise add V to the list of factors.
603 /// Ops is the top-level list of add operands we're trying to factor.
604 static void FindSingleUseMultiplyFactors(Value *V,
605 SmallVectorImpl<Value*> &Factors,
606 const SmallVectorImpl<ValueEntry> &Ops,
609 if (!(V->hasOneUse() || V->use_empty()) || // More than one use.
610 !(BO = dyn_cast<BinaryOperator>(V)) ||
611 BO->getOpcode() != Instruction::Mul) {
612 Factors.push_back(V);
616 // If this value has a single use because it is another input to the add
617 // tree we're reassociating and we dropped its use, it actually has two
618 // uses and we can't factor it.
620 for (unsigned i = 0, e = Ops.size(); i != e; ++i)
621 if (Ops[i].Op == V) {
622 Factors.push_back(V);
628 // Otherwise, add the LHS and RHS to the list of factors.
629 FindSingleUseMultiplyFactors(BO->getOperand(1), Factors, Ops, false);
630 FindSingleUseMultiplyFactors(BO->getOperand(0), Factors, Ops, false);
633 /// OptimizeAndOrXor - Optimize a series of operands to an 'and', 'or', or 'xor'
634 /// instruction. This optimizes based on identities. If it can be reduced to
635 /// a single Value, it is returned, otherwise the Ops list is mutated as
637 static Value *OptimizeAndOrXor(unsigned Opcode,
638 SmallVectorImpl<ValueEntry> &Ops) {
639 // Scan the operand lists looking for X and ~X pairs, along with X,X pairs.
640 // If we find any, we can simplify the expression. X&~X == 0, X|~X == -1.
641 for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
642 // First, check for X and ~X in the operand list.
643 assert(i < Ops.size());
644 if (BinaryOperator::isNot(Ops[i].Op)) { // Cannot occur for ^.
645 Value *X = BinaryOperator::getNotArgument(Ops[i].Op);
646 unsigned FoundX = FindInOperandList(Ops, i, X);
648 if (Opcode == Instruction::And) // ...&X&~X = 0
649 return Constant::getNullValue(X->getType());
651 if (Opcode == Instruction::Or) // ...|X|~X = -1
652 return Constant::getAllOnesValue(X->getType());
656 // Next, check for duplicate pairs of values, which we assume are next to
657 // each other, due to our sorting criteria.
658 assert(i < Ops.size());
659 if (i+1 != Ops.size() && Ops[i+1].Op == Ops[i].Op) {
660 if (Opcode == Instruction::And || Opcode == Instruction::Or) {
661 // Drop duplicate values for And and Or.
662 Ops.erase(Ops.begin()+i);
668 // Drop pairs of values for Xor.
669 assert(Opcode == Instruction::Xor);
671 return Constant::getNullValue(Ops[0].Op->getType());
674 Ops.erase(Ops.begin()+i, Ops.begin()+i+2);
682 /// OptimizeAdd - Optimize a series of operands to an 'add' instruction. This
683 /// optimizes based on identities. If it can be reduced to a single Value, it
684 /// is returned, otherwise the Ops list is mutated as necessary.
685 Value *Reassociate::OptimizeAdd(Instruction *I,
686 SmallVectorImpl<ValueEntry> &Ops) {
687 // Scan the operand lists looking for X and -X pairs. If we find any, we
688 // can simplify the expression. X+-X == 0. While we're at it, scan for any
689 // duplicates. We want to canonicalize Y+Y+Y+Z -> 3*Y+Z.
691 // TODO: We could handle "X + ~X" -> "-1" if we wanted, since "-X = ~X+1".
693 for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
694 Value *TheOp = Ops[i].Op;
695 // Check to see if we've seen this operand before. If so, we factor all
696 // instances of the operand together. Due to our sorting criteria, we know
697 // that these need to be next to each other in the vector.
698 if (i+1 != Ops.size() && Ops[i+1].Op == TheOp) {
699 // Rescan the list, remove all instances of this operand from the expr.
700 unsigned NumFound = 0;
702 Ops.erase(Ops.begin()+i);
704 } while (i != Ops.size() && Ops[i].Op == TheOp);
706 DEBUG(errs() << "\nFACTORING [" << NumFound << "]: " << *TheOp << '\n');
709 // Insert a new multiply.
710 Value *Mul = ConstantInt::get(cast<IntegerType>(I->getType()), NumFound);
711 Mul = BinaryOperator::CreateMul(TheOp, Mul, "factor", I);
713 // Now that we have inserted a multiply, optimize it. This allows us to
714 // handle cases that require multiple factoring steps, such as this:
715 // (X*2) + (X*2) + (X*2) -> (X*2)*3 -> X*6
716 Mul = ReassociateExpression(cast<BinaryOperator>(Mul));
718 // If every add operand was a duplicate, return the multiply.
722 // Otherwise, we had some input that didn't have the dupe, such as
723 // "A + A + B" -> "A*2 + B". Add the new multiply to the list of
724 // things being added by this operation.
725 Ops.insert(Ops.begin(), ValueEntry(getRank(Mul), Mul));
732 // Check for X and -X in the operand list.
733 if (!BinaryOperator::isNeg(TheOp))
736 Value *X = BinaryOperator::getNegArgument(TheOp);
737 unsigned FoundX = FindInOperandList(Ops, i, X);
741 // Remove X and -X from the operand list.
743 return Constant::getNullValue(X->getType());
745 Ops.erase(Ops.begin()+i);
749 --i; // Need to back up an extra one.
750 Ops.erase(Ops.begin()+FoundX);
752 --i; // Revisit element.
753 e -= 2; // Removed two elements.
756 // Scan the operand list, checking to see if there are any common factors
757 // between operands. Consider something like A*A+A*B*C+D. We would like to
758 // reassociate this to A*(A+B*C)+D, which reduces the number of multiplies.
759 // To efficiently find this, we count the number of times a factor occurs
760 // for any ADD operands that are MULs.
761 DenseMap<Value*, unsigned> FactorOccurrences;
763 // Keep track of each multiply we see, to avoid triggering on (X*4)+(X*4)
764 // where they are actually the same multiply.
766 Value *MaxOccVal = 0;
767 for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
768 BinaryOperator *BOp = dyn_cast<BinaryOperator>(Ops[i].Op);
769 if (BOp == 0 || BOp->getOpcode() != Instruction::Mul || !BOp->use_empty())
772 // Compute all of the factors of this added value.
773 SmallVector<Value*, 8> Factors;
774 FindSingleUseMultiplyFactors(BOp, Factors, Ops, true);
775 assert(Factors.size() > 1 && "Bad linearize!");
777 // Add one to FactorOccurrences for each unique factor in this op.
778 SmallPtrSet<Value*, 8> Duplicates;
779 for (unsigned i = 0, e = Factors.size(); i != e; ++i) {
780 Value *Factor = Factors[i];
781 if (!Duplicates.insert(Factor)) continue;
783 unsigned Occ = ++FactorOccurrences[Factor];
784 if (Occ > MaxOcc) { MaxOcc = Occ; MaxOccVal = Factor; }
786 // If Factor is a negative constant, add the negated value as a factor
787 // because we can percolate the negate out. Watch for minint, which
788 // cannot be positivified.
789 if (ConstantInt *CI = dyn_cast<ConstantInt>(Factor))
790 if (CI->getValue().isNegative() && !CI->getValue().isMinSignedValue()) {
791 Factor = ConstantInt::get(CI->getContext(), -CI->getValue());
792 assert(!Duplicates.count(Factor) &&
793 "Shouldn't have two constant factors, missed a canonicalize");
795 unsigned Occ = ++FactorOccurrences[Factor];
796 if (Occ > MaxOcc) { MaxOcc = Occ; MaxOccVal = Factor; }
801 // If any factor occurred more than one time, we can pull it out.
803 DEBUG(errs() << "\nFACTORING [" << MaxOcc << "]: " << *MaxOccVal << '\n');
806 // Create a new instruction that uses the MaxOccVal twice. If we don't do
807 // this, we could otherwise run into situations where removing a factor
808 // from an expression will drop a use of maxocc, and this can cause
809 // RemoveFactorFromExpression on successive values to behave differently.
810 Instruction *DummyInst = BinaryOperator::CreateAdd(MaxOccVal, MaxOccVal);
811 SmallVector<Value*, 4> NewMulOps;
812 for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
813 // Only try to remove factors from expressions we're allowed to.
814 BinaryOperator *BOp = dyn_cast<BinaryOperator>(Ops[i].Op);
815 if (BOp == 0 || BOp->getOpcode() != Instruction::Mul || !BOp->use_empty())
818 if (Value *V = RemoveFactorFromExpression(Ops[i].Op, MaxOccVal)) {
819 NewMulOps.push_back(V);
820 Ops.erase(Ops.begin()+i);
825 // No need for extra uses anymore.
828 unsigned NumAddedValues = NewMulOps.size();
829 Value *V = EmitAddTreeOfValues(I, NewMulOps);
831 // Now that we have inserted the add tree, optimize it. This allows us to
832 // handle cases that require multiple factoring steps, such as this:
833 // A*A*B + A*A*C --> A*(A*B+A*C) --> A*(A*(B+C))
834 assert(NumAddedValues > 1 && "Each occurrence should contribute a value");
835 (void)NumAddedValues;
836 V = ReassociateExpression(cast<BinaryOperator>(V));
838 // Create the multiply.
839 Value *V2 = BinaryOperator::CreateMul(V, MaxOccVal, "tmp", I);
841 // Rerun associate on the multiply in case the inner expression turned into
842 // a multiply. We want to make sure that we keep things in canonical form.
843 V2 = ReassociateExpression(cast<BinaryOperator>(V2));
845 // If every add operand included the factor (e.g. "A*B + A*C"), then the
846 // entire result expression is just the multiply "A*(B+C)".
850 // Otherwise, we had some input that didn't have the factor, such as
851 // "A*B + A*C + D" -> "A*(B+C) + D". Add the new multiply to the list of
852 // things being added by this operation.
853 Ops.insert(Ops.begin(), ValueEntry(getRank(V2), V2));
859 Value *Reassociate::OptimizeExpression(BinaryOperator *I,
860 SmallVectorImpl<ValueEntry> &Ops) {
861 // Now that we have the linearized expression tree, try to optimize it.
862 // Start by folding any constants that we found.
863 bool IterateOptimization = false;
864 if (Ops.size() == 1) return Ops[0].Op;
866 unsigned Opcode = I->getOpcode();
868 if (Constant *V1 = dyn_cast<Constant>(Ops[Ops.size()-2].Op))
869 if (Constant *V2 = dyn_cast<Constant>(Ops.back().Op)) {
871 Ops.back().Op = ConstantExpr::get(Opcode, V1, V2);
872 return OptimizeExpression(I, Ops);
875 // Check for destructive annihilation due to a constant being used.
876 if (ConstantInt *CstVal = dyn_cast<ConstantInt>(Ops.back().Op))
879 case Instruction::And:
880 if (CstVal->isZero()) // X & 0 -> 0
882 if (CstVal->isAllOnesValue()) // X & -1 -> X
885 case Instruction::Mul:
886 if (CstVal->isZero()) { // X * 0 -> 0
891 if (cast<ConstantInt>(CstVal)->isOne())
892 Ops.pop_back(); // X * 1 -> X
894 case Instruction::Or:
895 if (CstVal->isAllOnesValue()) // X | -1 -> -1
898 case Instruction::Add:
899 case Instruction::Xor:
900 if (CstVal->isZero()) // X [|^+] 0 -> X
904 if (Ops.size() == 1) return Ops[0].Op;
906 // Handle destructive annihilation due to identities between elements in the
907 // argument list here.
910 case Instruction::And:
911 case Instruction::Or:
912 case Instruction::Xor: {
913 unsigned NumOps = Ops.size();
914 if (Value *Result = OptimizeAndOrXor(Opcode, Ops))
916 IterateOptimization |= Ops.size() != NumOps;
920 case Instruction::Add: {
921 unsigned NumOps = Ops.size();
922 if (Value *Result = OptimizeAdd(I, Ops))
924 IterateOptimization |= Ops.size() != NumOps;
928 //case Instruction::Mul:
931 if (IterateOptimization)
932 return OptimizeExpression(I, Ops);
937 /// ReassociateBB - Inspect all of the instructions in this basic block,
938 /// reassociating them as we go.
939 void Reassociate::ReassociateBB(BasicBlock *BB) {
940 for (BasicBlock::iterator BBI = BB->begin(); BBI != BB->end(); ) {
941 Instruction *BI = BBI++;
942 if (BI->getOpcode() == Instruction::Shl &&
943 isa<ConstantInt>(BI->getOperand(1)))
944 if (Instruction *NI = ConvertShiftToMul(BI, ValueRankMap)) {
949 // Reject cases where it is pointless to do this.
950 if (!isa<BinaryOperator>(BI) || BI->getType()->isFloatingPointTy() ||
951 BI->getType()->isVectorTy())
952 continue; // Floating point ops are not associative.
954 // Do not reassociate boolean (i1) expressions. We want to preserve the
955 // original order of evaluation for short-circuited comparisons that
956 // SimplifyCFG has folded to AND/OR expressions. If the expression
957 // is not further optimized, it is likely to be transformed back to a
958 // short-circuited form for code gen, and the source order may have been
959 // optimized for the most likely conditions.
960 if (BI->getType()->isIntegerTy(1))
963 // If this is a subtract instruction which is not already in negate form,
964 // see if we can convert it to X+-Y.
965 if (BI->getOpcode() == Instruction::Sub) {
966 if (ShouldBreakUpSubtract(BI)) {
967 BI = BreakUpSubtract(BI, ValueRankMap);
968 // Reset the BBI iterator in case BreakUpSubtract changed the
969 // instruction it points to.
973 } else if (BinaryOperator::isNeg(BI)) {
974 // Otherwise, this is a negation. See if the operand is a multiply tree
975 // and if this is not an inner node of a multiply tree.
976 if (isReassociableOp(BI->getOperand(1), Instruction::Mul) &&
978 !isReassociableOp(BI->use_back(), Instruction::Mul))) {
979 BI = LowerNegateToMultiply(BI, ValueRankMap);
985 // If this instruction is a commutative binary operator, process it.
986 if (!BI->isAssociative()) continue;
987 BinaryOperator *I = cast<BinaryOperator>(BI);
989 // If this is an interior node of a reassociable tree, ignore it until we
990 // get to the root of the tree, to avoid N^2 analysis.
991 if (I->hasOneUse() && isReassociableOp(I->use_back(), I->getOpcode()))
994 // If this is an add tree that is used by a sub instruction, ignore it
995 // until we process the subtract.
996 if (I->hasOneUse() && I->getOpcode() == Instruction::Add &&
997 cast<Instruction>(I->use_back())->getOpcode() == Instruction::Sub)
1000 ReassociateExpression(I);
1004 Value *Reassociate::ReassociateExpression(BinaryOperator *I) {
1006 // First, walk the expression tree, linearizing the tree, collecting the
1007 // operand information.
1008 SmallVector<ValueEntry, 8> Ops;
1009 LinearizeExprTree(I, Ops);
1011 DEBUG(dbgs() << "RAIn:\t"; PrintOps(I, Ops); dbgs() << '\n');
1013 // Now that we have linearized the tree to a list and have gathered all of
1014 // the operands and their ranks, sort the operands by their rank. Use a
1015 // stable_sort so that values with equal ranks will have their relative
1016 // positions maintained (and so the compiler is deterministic). Note that
1017 // this sorts so that the highest ranking values end up at the beginning of
1019 std::stable_sort(Ops.begin(), Ops.end());
1021 // OptimizeExpression - Now that we have the expression tree in a convenient
1022 // sorted form, optimize it globally if possible.
1023 if (Value *V = OptimizeExpression(I, Ops)) {
1024 // This expression tree simplified to something that isn't a tree,
1026 DEBUG(dbgs() << "Reassoc to scalar: " << *V << '\n');
1027 I->replaceAllUsesWith(V);
1028 RemoveDeadBinaryOp(I);
1033 // We want to sink immediates as deeply as possible except in the case where
1034 // this is a multiply tree used only by an add, and the immediate is a -1.
1035 // In this case we reassociate to put the negation on the outside so that we
1036 // can fold the negation into the add: (-X)*Y + Z -> Z-X*Y
1037 if (I->getOpcode() == Instruction::Mul && I->hasOneUse() &&
1038 cast<Instruction>(I->use_back())->getOpcode() == Instruction::Add &&
1039 isa<ConstantInt>(Ops.back().Op) &&
1040 cast<ConstantInt>(Ops.back().Op)->isAllOnesValue()) {
1041 ValueEntry Tmp = Ops.pop_back_val();
1042 Ops.insert(Ops.begin(), Tmp);
1045 DEBUG(dbgs() << "RAOut:\t"; PrintOps(I, Ops); dbgs() << '\n');
1047 if (Ops.size() == 1) {
1048 // This expression tree simplified to something that isn't a tree,
1050 I->replaceAllUsesWith(Ops[0].Op);
1051 RemoveDeadBinaryOp(I);
1055 // Now that we ordered and optimized the expressions, splat them back into
1056 // the expression tree, removing any unneeded nodes.
1057 RewriteExprTree(I, Ops);
1062 bool Reassociate::runOnFunction(Function &F) {
1063 // Recalculate the rank map for F
1067 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI)
1070 // We are done with the rank map.
1072 ValueRankMap.clear();