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<>, unsigned> ValueRankMap;
78 SmallVector<WeakVH, 8> DeadInsts;
81 static char ID; // Pass identification, replacement for typeid
82 Reassociate() : FunctionPass(ID) {
83 initializeReassociatePass(*PassRegistry::getPassRegistry());
86 bool runOnFunction(Function &F);
88 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
92 void BuildRankMap(Function &F);
93 unsigned getRank(Value *V);
94 Value *ReassociateExpression(BinaryOperator *I);
95 void RewriteExprTree(BinaryOperator *I, SmallVectorImpl<ValueEntry> &Ops,
97 Value *OptimizeExpression(BinaryOperator *I,
98 SmallVectorImpl<ValueEntry> &Ops);
99 Value *OptimizeAdd(Instruction *I, SmallVectorImpl<ValueEntry> &Ops);
100 void LinearizeExprTree(BinaryOperator *I, SmallVectorImpl<ValueEntry> &Ops);
101 void LinearizeExpr(BinaryOperator *I);
102 Value *RemoveFactorFromExpression(Value *V, Value *Factor);
103 void ReassociateBB(BasicBlock *BB);
105 void RemoveDeadBinaryOp(Value *V);
109 char Reassociate::ID = 0;
110 INITIALIZE_PASS(Reassociate, "reassociate",
111 "Reassociate expressions", false, false)
113 // Public interface to the Reassociate pass
114 FunctionPass *llvm::createReassociatePass() { return new Reassociate(); }
116 void Reassociate::RemoveDeadBinaryOp(Value *V) {
117 Instruction *Op = dyn_cast<Instruction>(V);
118 if (!Op || !isa<BinaryOperator>(Op))
121 Value *LHS = Op->getOperand(0), *RHS = Op->getOperand(1);
123 ValueRankMap.erase(Op);
124 DeadInsts.push_back(Op);
125 RemoveDeadBinaryOp(LHS);
126 RemoveDeadBinaryOp(RHS);
130 static bool isUnmovableInstruction(Instruction *I) {
131 if (I->getOpcode() == Instruction::PHI ||
132 I->getOpcode() == Instruction::Alloca ||
133 I->getOpcode() == Instruction::Load ||
134 I->getOpcode() == Instruction::Invoke ||
135 (I->getOpcode() == Instruction::Call &&
136 !isa<DbgInfoIntrinsic>(I)) ||
137 I->getOpcode() == Instruction::UDiv ||
138 I->getOpcode() == Instruction::SDiv ||
139 I->getOpcode() == Instruction::FDiv ||
140 I->getOpcode() == Instruction::URem ||
141 I->getOpcode() == Instruction::SRem ||
142 I->getOpcode() == Instruction::FRem)
147 void Reassociate::BuildRankMap(Function &F) {
150 // Assign distinct ranks to function arguments
151 for (Function::arg_iterator I = F.arg_begin(), E = F.arg_end(); I != E; ++I)
152 ValueRankMap[&*I] = ++i;
154 ReversePostOrderTraversal<Function*> RPOT(&F);
155 for (ReversePostOrderTraversal<Function*>::rpo_iterator I = RPOT.begin(),
156 E = RPOT.end(); I != E; ++I) {
158 unsigned BBRank = RankMap[BB] = ++i << 16;
160 // Walk the basic block, adding precomputed ranks for any instructions that
161 // we cannot move. This ensures that the ranks for these instructions are
162 // all different in the block.
163 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
164 if (isUnmovableInstruction(I))
165 ValueRankMap[&*I] = ++BBRank;
169 unsigned Reassociate::getRank(Value *V) {
170 Instruction *I = dyn_cast<Instruction>(V);
172 if (isa<Argument>(V)) return ValueRankMap[V]; // Function argument.
173 return 0; // Otherwise it's a global or constant, rank 0.
176 if (unsigned Rank = ValueRankMap[I])
177 return Rank; // Rank already known?
179 // If this is an expression, return the 1+MAX(rank(LHS), rank(RHS)) so that
180 // we can reassociate expressions for code motion! Since we do not recurse
181 // for PHI nodes, we cannot have infinite recursion here, because there
182 // cannot be loops in the value graph that do not go through PHI nodes.
183 unsigned Rank = 0, MaxRank = RankMap[I->getParent()];
184 for (unsigned i = 0, e = I->getNumOperands();
185 i != e && Rank != MaxRank; ++i)
186 Rank = std::max(Rank, getRank(I->getOperand(i)));
188 // If this is a not or neg instruction, do not count it for rank. This
189 // assures us that X and ~X will have the same rank.
190 if (!I->getType()->isIntegerTy() ||
191 (!BinaryOperator::isNot(I) && !BinaryOperator::isNeg(I)))
194 //DEBUG(dbgs() << "Calculated Rank[" << V->getName() << "] = "
197 return ValueRankMap[I] = Rank;
200 /// isReassociableOp - Return true if V is an instruction of the specified
201 /// opcode and if it only has one use.
202 static BinaryOperator *isReassociableOp(Value *V, unsigned Opcode) {
203 if ((V->hasOneUse() || V->use_empty()) && isa<Instruction>(V) &&
204 cast<Instruction>(V)->getOpcode() == Opcode)
205 return cast<BinaryOperator>(V);
209 /// LowerNegateToMultiply - Replace 0-X with X*-1.
211 static Instruction *LowerNegateToMultiply(Instruction *Neg,
212 DenseMap<AssertingVH<>, unsigned> &ValueRankMap) {
213 Constant *Cst = Constant::getAllOnesValue(Neg->getType());
215 Instruction *Res = BinaryOperator::CreateMul(Neg->getOperand(1), Cst, "",Neg);
216 ValueRankMap.erase(Neg);
218 Neg->replaceAllUsesWith(Res);
219 Neg->eraseFromParent();
223 // Given an expression of the form '(A+B)+(D+C)', turn it into '(((A+B)+C)+D)'.
224 // Note that if D is also part of the expression tree that we recurse to
225 // linearize it as well. Besides that case, this does not recurse into A,B, or
227 void Reassociate::LinearizeExpr(BinaryOperator *I) {
228 BinaryOperator *LHS = cast<BinaryOperator>(I->getOperand(0));
229 BinaryOperator *RHS = cast<BinaryOperator>(I->getOperand(1));
230 assert(isReassociableOp(LHS, I->getOpcode()) &&
231 isReassociableOp(RHS, I->getOpcode()) &&
232 "Not an expression that needs linearization?");
234 DEBUG(dbgs() << "Linear" << *LHS << '\n' << *RHS << '\n' << *I << '\n');
236 // Move the RHS instruction to live immediately before I, avoiding breaking
237 // dominator properties.
240 // Move operands around to do the linearization.
241 I->setOperand(1, RHS->getOperand(0));
242 RHS->setOperand(0, LHS);
243 I->setOperand(0, RHS);
245 // Conservatively clear all the optional flags, which may not hold
246 // after the reassociation.
247 I->clearSubclassOptionalData();
248 LHS->clearSubclassOptionalData();
249 RHS->clearSubclassOptionalData();
253 DEBUG(dbgs() << "Linearized: " << *I << '\n');
255 // If D is part of this expression tree, tail recurse.
256 if (isReassociableOp(I->getOperand(1), I->getOpcode()))
261 /// LinearizeExprTree - Given an associative binary expression tree, traverse
262 /// all of the uses putting it into canonical form. This forces a left-linear
263 /// form of the expression (((a+b)+c)+d), and collects information about the
264 /// rank of the non-tree operands.
266 /// NOTE: These intentionally destroys the expression tree operands (turning
267 /// them into undef values) to reduce #uses of the values. This means that the
268 /// caller MUST use something like RewriteExprTree to put the values back in.
270 void Reassociate::LinearizeExprTree(BinaryOperator *I,
271 SmallVectorImpl<ValueEntry> &Ops) {
272 Value *LHS = I->getOperand(0), *RHS = I->getOperand(1);
273 unsigned Opcode = I->getOpcode();
275 // First step, linearize the expression if it is in ((A+B)+(C+D)) form.
276 BinaryOperator *LHSBO = isReassociableOp(LHS, Opcode);
277 BinaryOperator *RHSBO = isReassociableOp(RHS, Opcode);
279 // If this is a multiply expression tree and it contains internal negations,
280 // transform them into multiplies by -1 so they can be reassociated.
281 if (I->getOpcode() == Instruction::Mul) {
282 if (!LHSBO && LHS->hasOneUse() && BinaryOperator::isNeg(LHS)) {
283 LHS = LowerNegateToMultiply(cast<Instruction>(LHS), ValueRankMap);
284 LHSBO = isReassociableOp(LHS, Opcode);
286 if (!RHSBO && RHS->hasOneUse() && BinaryOperator::isNeg(RHS)) {
287 RHS = LowerNegateToMultiply(cast<Instruction>(RHS), ValueRankMap);
288 RHSBO = isReassociableOp(RHS, Opcode);
294 // Neither the LHS or RHS as part of the tree, thus this is a leaf. As
295 // such, just remember these operands and their rank.
296 Ops.push_back(ValueEntry(getRank(LHS), LHS));
297 Ops.push_back(ValueEntry(getRank(RHS), RHS));
299 // Clear the leaves out.
300 I->setOperand(0, UndefValue::get(I->getType()));
301 I->setOperand(1, UndefValue::get(I->getType()));
305 // Turn X+(Y+Z) -> (Y+Z)+X
306 std::swap(LHSBO, RHSBO);
308 bool Success = !I->swapOperands();
309 assert(Success && "swapOperands failed");
313 // Turn (A+B)+(C+D) -> (((A+B)+C)+D). This guarantees the RHS is not
314 // part of the expression tree.
316 LHS = LHSBO = cast<BinaryOperator>(I->getOperand(0));
317 RHS = I->getOperand(1);
321 // Okay, now we know that the LHS is a nested expression and that the RHS is
322 // not. Perform reassociation.
323 assert(!isReassociableOp(RHS, Opcode) && "LinearizeExpr failed!");
325 // Move LHS right before I to make sure that the tree expression dominates all
327 LHSBO->moveBefore(I);
329 // Linearize the expression tree on the LHS.
330 LinearizeExprTree(LHSBO, Ops);
332 // Remember the RHS operand and its rank.
333 Ops.push_back(ValueEntry(getRank(RHS), RHS));
335 // Clear the RHS leaf out.
336 I->setOperand(1, UndefValue::get(I->getType()));
339 // RewriteExprTree - Now that the operands for this expression tree are
340 // linearized and optimized, emit them in-order. This function is written to be
342 void Reassociate::RewriteExprTree(BinaryOperator *I,
343 SmallVectorImpl<ValueEntry> &Ops,
345 if (i+2 == Ops.size()) {
346 if (I->getOperand(0) != Ops[i].Op ||
347 I->getOperand(1) != Ops[i+1].Op) {
348 Value *OldLHS = I->getOperand(0);
349 DEBUG(dbgs() << "RA: " << *I << '\n');
350 I->setOperand(0, Ops[i].Op);
351 I->setOperand(1, Ops[i+1].Op);
353 // Clear all the optional flags, which may not hold after the
354 // reassociation if the expression involved more than just this operation.
356 I->clearSubclassOptionalData();
358 DEBUG(dbgs() << "TO: " << *I << '\n');
362 // If we reassociated a tree to fewer operands (e.g. (1+a+2) -> (a+3)
363 // delete the extra, now dead, nodes.
364 RemoveDeadBinaryOp(OldLHS);
368 assert(i+2 < Ops.size() && "Ops index out of range!");
370 if (I->getOperand(1) != Ops[i].Op) {
371 DEBUG(dbgs() << "RA: " << *I << '\n');
372 I->setOperand(1, Ops[i].Op);
374 // Conservatively clear all the optional flags, which may not hold
375 // after the reassociation.
376 I->clearSubclassOptionalData();
378 DEBUG(dbgs() << "TO: " << *I << '\n');
383 BinaryOperator *LHS = cast<BinaryOperator>(I->getOperand(0));
384 assert(LHS->getOpcode() == I->getOpcode() &&
385 "Improper expression tree!");
387 // Compactify the tree instructions together with each other to guarantee
388 // that the expression tree is dominated by all of Ops.
390 RewriteExprTree(LHS, Ops, i+1);
395 // NegateValue - Insert instructions before the instruction pointed to by BI,
396 // that computes the negative version of the value specified. The negative
397 // version of the value is returned, and BI is left pointing at the instruction
398 // that should be processed next by the reassociation pass.
400 static Value *NegateValue(Value *V, Instruction *BI) {
401 if (Constant *C = dyn_cast<Constant>(V))
402 return ConstantExpr::getNeg(C);
404 // We are trying to expose opportunity for reassociation. One of the things
405 // that we want to do to achieve this is to push a negation as deep into an
406 // expression chain as possible, to expose the add instructions. In practice,
407 // this means that we turn this:
408 // X = -(A+12+C+D) into X = -A + -12 + -C + -D = -12 + -A + -C + -D
409 // so that later, a: Y = 12+X could get reassociated with the -12 to eliminate
410 // the constants. We assume that instcombine will clean up the mess later if
411 // we introduce tons of unnecessary negation instructions.
413 if (Instruction *I = dyn_cast<Instruction>(V))
414 if (I->getOpcode() == Instruction::Add && I->hasOneUse()) {
415 // Push the negates through the add.
416 I->setOperand(0, NegateValue(I->getOperand(0), BI));
417 I->setOperand(1, NegateValue(I->getOperand(1), BI));
419 // We must move the add instruction here, because the neg instructions do
420 // not dominate the old add instruction in general. By moving it, we are
421 // assured that the neg instructions we just inserted dominate the
422 // instruction we are about to insert after them.
425 I->setName(I->getName()+".neg");
429 // Okay, we need to materialize a negated version of V with an instruction.
430 // Scan the use lists of V to see if we have one already.
431 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E;++UI){
433 if (!BinaryOperator::isNeg(U)) continue;
435 // We found one! Now we have to make sure that the definition dominates
436 // this use. We do this by moving it to the entry block (if it is a
437 // non-instruction value) or right after the definition. These negates will
438 // be zapped by reassociate later, so we don't need much finesse here.
439 BinaryOperator *TheNeg = cast<BinaryOperator>(U);
441 // Verify that the negate is in this function, V might be a constant expr.
442 if (TheNeg->getParent()->getParent() != BI->getParent()->getParent())
445 BasicBlock::iterator InsertPt;
446 if (Instruction *InstInput = dyn_cast<Instruction>(V)) {
447 if (InvokeInst *II = dyn_cast<InvokeInst>(InstInput)) {
448 InsertPt = II->getNormalDest()->begin();
450 InsertPt = InstInput;
453 while (isa<PHINode>(InsertPt)) ++InsertPt;
455 InsertPt = TheNeg->getParent()->getParent()->getEntryBlock().begin();
457 TheNeg->moveBefore(InsertPt);
461 // Insert a 'neg' instruction that subtracts the value from zero to get the
463 return BinaryOperator::CreateNeg(V, V->getName() + ".neg", BI);
466 /// ShouldBreakUpSubtract - Return true if we should break up this subtract of
467 /// X-Y into (X + -Y).
468 static bool ShouldBreakUpSubtract(Instruction *Sub) {
469 // If this is a negation, we can't split it up!
470 if (BinaryOperator::isNeg(Sub))
473 // Don't bother to break this up unless either the LHS is an associable add or
474 // subtract or if this is only used by one.
475 if (isReassociableOp(Sub->getOperand(0), Instruction::Add) ||
476 isReassociableOp(Sub->getOperand(0), Instruction::Sub))
478 if (isReassociableOp(Sub->getOperand(1), Instruction::Add) ||
479 isReassociableOp(Sub->getOperand(1), Instruction::Sub))
481 if (Sub->hasOneUse() &&
482 (isReassociableOp(Sub->use_back(), Instruction::Add) ||
483 isReassociableOp(Sub->use_back(), Instruction::Sub)))
489 /// BreakUpSubtract - If we have (X-Y), and if either X is an add, or if this is
490 /// only used by an add, transform this into (X+(0-Y)) to promote better
492 static Instruction *BreakUpSubtract(Instruction *Sub,
493 DenseMap<AssertingVH<>, unsigned> &ValueRankMap) {
494 // Convert a subtract into an add and a neg instruction. This allows sub
495 // instructions to be commuted with other add instructions.
497 // Calculate the negative value of Operand 1 of the sub instruction,
498 // and set it as the RHS of the add instruction we just made.
500 Value *NegVal = NegateValue(Sub->getOperand(1), Sub);
502 BinaryOperator::CreateAdd(Sub->getOperand(0), NegVal, "", Sub);
505 // Everyone now refers to the add instruction.
506 ValueRankMap.erase(Sub);
507 Sub->replaceAllUsesWith(New);
508 Sub->eraseFromParent();
510 DEBUG(dbgs() << "Negated: " << *New << '\n');
514 /// ConvertShiftToMul - If this is a shift of a reassociable multiply or is used
515 /// by one, change this into a multiply by a constant to assist with further
517 static Instruction *ConvertShiftToMul(Instruction *Shl,
518 DenseMap<AssertingVH<>, unsigned> &ValueRankMap) {
519 // If an operand of this shift is a reassociable multiply, or if the shift
520 // is used by a reassociable multiply or add, turn into a multiply.
521 if (isReassociableOp(Shl->getOperand(0), Instruction::Mul) ||
523 (isReassociableOp(Shl->use_back(), Instruction::Mul) ||
524 isReassociableOp(Shl->use_back(), Instruction::Add)))) {
525 Constant *MulCst = ConstantInt::get(Shl->getType(), 1);
526 MulCst = ConstantExpr::getShl(MulCst, cast<Constant>(Shl->getOperand(1)));
529 BinaryOperator::CreateMul(Shl->getOperand(0), MulCst, "", Shl);
530 ValueRankMap.erase(Shl);
532 Shl->replaceAllUsesWith(Mul);
533 Shl->eraseFromParent();
539 // Scan backwards and forwards among values with the same rank as element i to
540 // see if X exists. If X does not exist, return i. This is useful when
541 // scanning for 'x' when we see '-x' because they both get the same rank.
542 static unsigned FindInOperandList(SmallVectorImpl<ValueEntry> &Ops, unsigned i,
544 unsigned XRank = Ops[i].Rank;
545 unsigned e = Ops.size();
546 for (unsigned j = i+1; j != e && Ops[j].Rank == XRank; ++j)
550 for (unsigned j = i-1; j != ~0U && Ops[j].Rank == XRank; --j)
556 /// EmitAddTreeOfValues - Emit a tree of add instructions, summing Ops together
557 /// and returning the result. Insert the tree before I.
558 static Value *EmitAddTreeOfValues(Instruction *I, SmallVectorImpl<Value*> &Ops){
559 if (Ops.size() == 1) return Ops.back();
561 Value *V1 = Ops.back();
563 Value *V2 = EmitAddTreeOfValues(I, Ops);
564 return BinaryOperator::CreateAdd(V2, V1, "tmp", I);
567 /// RemoveFactorFromExpression - If V is an expression tree that is a
568 /// multiplication sequence, and if this sequence contains a multiply by Factor,
569 /// remove Factor from the tree and return the new tree.
570 Value *Reassociate::RemoveFactorFromExpression(Value *V, Value *Factor) {
571 BinaryOperator *BO = isReassociableOp(V, Instruction::Mul);
574 SmallVector<ValueEntry, 8> Factors;
575 LinearizeExprTree(BO, Factors);
577 bool FoundFactor = false;
578 bool NeedsNegate = false;
579 for (unsigned i = 0, e = Factors.size(); i != e; ++i) {
580 if (Factors[i].Op == Factor) {
582 Factors.erase(Factors.begin()+i);
586 // If this is a negative version of this factor, remove it.
587 if (ConstantInt *FC1 = dyn_cast<ConstantInt>(Factor))
588 if (ConstantInt *FC2 = dyn_cast<ConstantInt>(Factors[i].Op))
589 if (FC1->getValue() == -FC2->getValue()) {
590 FoundFactor = NeedsNegate = true;
591 Factors.erase(Factors.begin()+i);
597 // Make sure to restore the operands to the expression tree.
598 RewriteExprTree(BO, Factors);
602 BasicBlock::iterator InsertPt = BO; ++InsertPt;
604 // If this was just a single multiply, remove the multiply and return the only
605 // remaining operand.
606 if (Factors.size() == 1) {
607 ValueRankMap.erase(BO);
608 DeadInsts.push_back(BO);
611 RewriteExprTree(BO, Factors);
616 V = BinaryOperator::CreateNeg(V, "neg", InsertPt);
621 /// FindSingleUseMultiplyFactors - If V is a single-use multiply, recursively
622 /// add its operands as factors, otherwise add V to the list of factors.
624 /// Ops is the top-level list of add operands we're trying to factor.
625 static void FindSingleUseMultiplyFactors(Value *V,
626 SmallVectorImpl<Value*> &Factors,
627 const SmallVectorImpl<ValueEntry> &Ops,
630 if (!(V->hasOneUse() || V->use_empty()) || // More than one use.
631 !(BO = dyn_cast<BinaryOperator>(V)) ||
632 BO->getOpcode() != Instruction::Mul) {
633 Factors.push_back(V);
637 // If this value has a single use because it is another input to the add
638 // tree we're reassociating and we dropped its use, it actually has two
639 // uses and we can't factor it.
641 for (unsigned i = 0, e = Ops.size(); i != e; ++i)
642 if (Ops[i].Op == V) {
643 Factors.push_back(V);
649 // Otherwise, add the LHS and RHS to the list of factors.
650 FindSingleUseMultiplyFactors(BO->getOperand(1), Factors, Ops, false);
651 FindSingleUseMultiplyFactors(BO->getOperand(0), Factors, Ops, false);
654 /// OptimizeAndOrXor - Optimize a series of operands to an 'and', 'or', or 'xor'
655 /// instruction. This optimizes based on identities. If it can be reduced to
656 /// a single Value, it is returned, otherwise the Ops list is mutated as
658 static Value *OptimizeAndOrXor(unsigned Opcode,
659 SmallVectorImpl<ValueEntry> &Ops) {
660 // Scan the operand lists looking for X and ~X pairs, along with X,X pairs.
661 // If we find any, we can simplify the expression. X&~X == 0, X|~X == -1.
662 for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
663 // First, check for X and ~X in the operand list.
664 assert(i < Ops.size());
665 if (BinaryOperator::isNot(Ops[i].Op)) { // Cannot occur for ^.
666 Value *X = BinaryOperator::getNotArgument(Ops[i].Op);
667 unsigned FoundX = FindInOperandList(Ops, i, X);
669 if (Opcode == Instruction::And) // ...&X&~X = 0
670 return Constant::getNullValue(X->getType());
672 if (Opcode == Instruction::Or) // ...|X|~X = -1
673 return Constant::getAllOnesValue(X->getType());
677 // Next, check for duplicate pairs of values, which we assume are next to
678 // each other, due to our sorting criteria.
679 assert(i < Ops.size());
680 if (i+1 != Ops.size() && Ops[i+1].Op == Ops[i].Op) {
681 if (Opcode == Instruction::And || Opcode == Instruction::Or) {
682 // Drop duplicate values for And and Or.
683 Ops.erase(Ops.begin()+i);
689 // Drop pairs of values for Xor.
690 assert(Opcode == Instruction::Xor);
692 return Constant::getNullValue(Ops[0].Op->getType());
695 Ops.erase(Ops.begin()+i, Ops.begin()+i+2);
703 /// OptimizeAdd - Optimize a series of operands to an 'add' instruction. This
704 /// optimizes based on identities. If it can be reduced to a single Value, it
705 /// is returned, otherwise the Ops list is mutated as necessary.
706 Value *Reassociate::OptimizeAdd(Instruction *I,
707 SmallVectorImpl<ValueEntry> &Ops) {
708 // Scan the operand lists looking for X and -X pairs. If we find any, we
709 // can simplify the expression. X+-X == 0. While we're at it, scan for any
710 // duplicates. We want to canonicalize Y+Y+Y+Z -> 3*Y+Z.
712 // TODO: We could handle "X + ~X" -> "-1" if we wanted, since "-X = ~X+1".
714 for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
715 Value *TheOp = Ops[i].Op;
716 // Check to see if we've seen this operand before. If so, we factor all
717 // instances of the operand together. Due to our sorting criteria, we know
718 // that these need to be next to each other in the vector.
719 if (i+1 != Ops.size() && Ops[i+1].Op == TheOp) {
720 // Rescan the list, remove all instances of this operand from the expr.
721 unsigned NumFound = 0;
723 Ops.erase(Ops.begin()+i);
725 } while (i != Ops.size() && Ops[i].Op == TheOp);
727 DEBUG(errs() << "\nFACTORING [" << NumFound << "]: " << *TheOp << '\n');
730 // Insert a new multiply.
731 Value *Mul = ConstantInt::get(cast<IntegerType>(I->getType()), NumFound);
732 Mul = BinaryOperator::CreateMul(TheOp, Mul, "factor", I);
734 // Now that we have inserted a multiply, optimize it. This allows us to
735 // handle cases that require multiple factoring steps, such as this:
736 // (X*2) + (X*2) + (X*2) -> (X*2)*3 -> X*6
737 Mul = ReassociateExpression(cast<BinaryOperator>(Mul));
739 // If every add operand was a duplicate, return the multiply.
743 // Otherwise, we had some input that didn't have the dupe, such as
744 // "A + A + B" -> "A*2 + B". Add the new multiply to the list of
745 // things being added by this operation.
746 Ops.insert(Ops.begin(), ValueEntry(getRank(Mul), Mul));
753 // Check for X and -X in the operand list.
754 if (!BinaryOperator::isNeg(TheOp))
757 Value *X = BinaryOperator::getNegArgument(TheOp);
758 unsigned FoundX = FindInOperandList(Ops, i, X);
762 // Remove X and -X from the operand list.
764 return Constant::getNullValue(X->getType());
766 Ops.erase(Ops.begin()+i);
770 --i; // Need to back up an extra one.
771 Ops.erase(Ops.begin()+FoundX);
773 --i; // Revisit element.
774 e -= 2; // Removed two elements.
777 // Scan the operand list, checking to see if there are any common factors
778 // between operands. Consider something like A*A+A*B*C+D. We would like to
779 // reassociate this to A*(A+B*C)+D, which reduces the number of multiplies.
780 // To efficiently find this, we count the number of times a factor occurs
781 // for any ADD operands that are MULs.
782 DenseMap<Value*, unsigned> FactorOccurrences;
784 // Keep track of each multiply we see, to avoid triggering on (X*4)+(X*4)
785 // where they are actually the same multiply.
787 Value *MaxOccVal = 0;
788 for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
789 BinaryOperator *BOp = dyn_cast<BinaryOperator>(Ops[i].Op);
790 if (BOp == 0 || BOp->getOpcode() != Instruction::Mul || !BOp->use_empty())
793 // Compute all of the factors of this added value.
794 SmallVector<Value*, 8> Factors;
795 FindSingleUseMultiplyFactors(BOp, Factors, Ops, true);
796 assert(Factors.size() > 1 && "Bad linearize!");
798 // Add one to FactorOccurrences for each unique factor in this op.
799 SmallPtrSet<Value*, 8> Duplicates;
800 for (unsigned i = 0, e = Factors.size(); i != e; ++i) {
801 Value *Factor = Factors[i];
802 if (!Duplicates.insert(Factor)) continue;
804 unsigned Occ = ++FactorOccurrences[Factor];
805 if (Occ > MaxOcc) { MaxOcc = Occ; MaxOccVal = Factor; }
807 // If Factor is a negative constant, add the negated value as a factor
808 // because we can percolate the negate out. Watch for minint, which
809 // cannot be positivified.
810 if (ConstantInt *CI = dyn_cast<ConstantInt>(Factor))
811 if (CI->getValue().isNegative() && !CI->getValue().isMinSignedValue()) {
812 Factor = ConstantInt::get(CI->getContext(), -CI->getValue());
813 assert(!Duplicates.count(Factor) &&
814 "Shouldn't have two constant factors, missed a canonicalize");
816 unsigned Occ = ++FactorOccurrences[Factor];
817 if (Occ > MaxOcc) { MaxOcc = Occ; MaxOccVal = Factor; }
822 // If any factor occurred more than one time, we can pull it out.
824 DEBUG(errs() << "\nFACTORING [" << MaxOcc << "]: " << *MaxOccVal << '\n');
827 // Create a new instruction that uses the MaxOccVal twice. If we don't do
828 // this, we could otherwise run into situations where removing a factor
829 // from an expression will drop a use of maxocc, and this can cause
830 // RemoveFactorFromExpression on successive values to behave differently.
831 Instruction *DummyInst = BinaryOperator::CreateAdd(MaxOccVal, MaxOccVal);
832 SmallVector<Value*, 4> NewMulOps;
833 for (unsigned i = 0; i != Ops.size(); ++i) {
834 // Only try to remove factors from expressions we're allowed to.
835 BinaryOperator *BOp = dyn_cast<BinaryOperator>(Ops[i].Op);
836 if (BOp == 0 || BOp->getOpcode() != Instruction::Mul || !BOp->use_empty())
839 if (Value *V = RemoveFactorFromExpression(Ops[i].Op, MaxOccVal)) {
840 // The factorized operand may occur several times. Convert them all in
842 for (unsigned j = Ops.size(); j != i;) {
844 if (Ops[j].Op == Ops[i].Op) {
845 NewMulOps.push_back(V);
846 Ops.erase(Ops.begin()+j);
853 // No need for extra uses anymore.
856 unsigned NumAddedValues = NewMulOps.size();
857 Value *V = EmitAddTreeOfValues(I, NewMulOps);
859 // Now that we have inserted the add tree, optimize it. This allows us to
860 // handle cases that require multiple factoring steps, such as this:
861 // A*A*B + A*A*C --> A*(A*B+A*C) --> A*(A*(B+C))
862 assert(NumAddedValues > 1 && "Each occurrence should contribute a value");
863 (void)NumAddedValues;
864 V = ReassociateExpression(cast<BinaryOperator>(V));
866 // Create the multiply.
867 Value *V2 = BinaryOperator::CreateMul(V, MaxOccVal, "tmp", I);
869 // Rerun associate on the multiply in case the inner expression turned into
870 // a multiply. We want to make sure that we keep things in canonical form.
871 V2 = ReassociateExpression(cast<BinaryOperator>(V2));
873 // If every add operand included the factor (e.g. "A*B + A*C"), then the
874 // entire result expression is just the multiply "A*(B+C)".
878 // Otherwise, we had some input that didn't have the factor, such as
879 // "A*B + A*C + D" -> "A*(B+C) + D". Add the new multiply to the list of
880 // things being added by this operation.
881 Ops.insert(Ops.begin(), ValueEntry(getRank(V2), V2));
887 Value *Reassociate::OptimizeExpression(BinaryOperator *I,
888 SmallVectorImpl<ValueEntry> &Ops) {
889 // Now that we have the linearized expression tree, try to optimize it.
890 // Start by folding any constants that we found.
891 bool IterateOptimization = false;
892 if (Ops.size() == 1) return Ops[0].Op;
894 unsigned Opcode = I->getOpcode();
896 if (Constant *V1 = dyn_cast<Constant>(Ops[Ops.size()-2].Op))
897 if (Constant *V2 = dyn_cast<Constant>(Ops.back().Op)) {
899 Ops.back().Op = ConstantExpr::get(Opcode, V1, V2);
900 return OptimizeExpression(I, Ops);
903 // Check for destructive annihilation due to a constant being used.
904 if (ConstantInt *CstVal = dyn_cast<ConstantInt>(Ops.back().Op))
907 case Instruction::And:
908 if (CstVal->isZero()) // X & 0 -> 0
910 if (CstVal->isAllOnesValue()) // X & -1 -> X
913 case Instruction::Mul:
914 if (CstVal->isZero()) { // X * 0 -> 0
919 if (cast<ConstantInt>(CstVal)->isOne())
920 Ops.pop_back(); // X * 1 -> X
922 case Instruction::Or:
923 if (CstVal->isAllOnesValue()) // X | -1 -> -1
926 case Instruction::Add:
927 case Instruction::Xor:
928 if (CstVal->isZero()) // X [|^+] 0 -> X
932 if (Ops.size() == 1) return Ops[0].Op;
934 // Handle destructive annihilation due to identities between elements in the
935 // argument list here.
938 case Instruction::And:
939 case Instruction::Or:
940 case Instruction::Xor: {
941 unsigned NumOps = Ops.size();
942 if (Value *Result = OptimizeAndOrXor(Opcode, Ops))
944 IterateOptimization |= Ops.size() != NumOps;
948 case Instruction::Add: {
949 unsigned NumOps = Ops.size();
950 if (Value *Result = OptimizeAdd(I, Ops))
952 IterateOptimization |= Ops.size() != NumOps;
956 //case Instruction::Mul:
959 if (IterateOptimization)
960 return OptimizeExpression(I, Ops);
965 /// ReassociateBB - Inspect all of the instructions in this basic block,
966 /// reassociating them as we go.
967 void Reassociate::ReassociateBB(BasicBlock *BB) {
968 for (BasicBlock::iterator BBI = BB->begin(); BBI != BB->end(); ) {
969 Instruction *BI = BBI++;
970 if (BI->getOpcode() == Instruction::Shl &&
971 isa<ConstantInt>(BI->getOperand(1)))
972 if (Instruction *NI = ConvertShiftToMul(BI, ValueRankMap)) {
977 // Reject cases where it is pointless to do this.
978 if (!isa<BinaryOperator>(BI) || BI->getType()->isFloatingPointTy() ||
979 BI->getType()->isVectorTy())
980 continue; // Floating point ops are not associative.
982 // Do not reassociate boolean (i1) expressions. We want to preserve the
983 // original order of evaluation for short-circuited comparisons that
984 // SimplifyCFG has folded to AND/OR expressions. If the expression
985 // is not further optimized, it is likely to be transformed back to a
986 // short-circuited form for code gen, and the source order may have been
987 // optimized for the most likely conditions.
988 if (BI->getType()->isIntegerTy(1))
991 // If this is a subtract instruction which is not already in negate form,
992 // see if we can convert it to X+-Y.
993 if (BI->getOpcode() == Instruction::Sub) {
994 if (ShouldBreakUpSubtract(BI)) {
995 BI = BreakUpSubtract(BI, ValueRankMap);
996 // Reset the BBI iterator in case BreakUpSubtract changed the
997 // instruction it points to.
1001 } else if (BinaryOperator::isNeg(BI)) {
1002 // Otherwise, this is a negation. See if the operand is a multiply tree
1003 // and if this is not an inner node of a multiply tree.
1004 if (isReassociableOp(BI->getOperand(1), Instruction::Mul) &&
1005 (!BI->hasOneUse() ||
1006 !isReassociableOp(BI->use_back(), Instruction::Mul))) {
1007 BI = LowerNegateToMultiply(BI, ValueRankMap);
1013 // If this instruction is a commutative binary operator, process it.
1014 if (!BI->isAssociative()) continue;
1015 BinaryOperator *I = cast<BinaryOperator>(BI);
1017 // If this is an interior node of a reassociable tree, ignore it until we
1018 // get to the root of the tree, to avoid N^2 analysis.
1019 if (I->hasOneUse() && isReassociableOp(I->use_back(), I->getOpcode()))
1022 // If this is an add tree that is used by a sub instruction, ignore it
1023 // until we process the subtract.
1024 if (I->hasOneUse() && I->getOpcode() == Instruction::Add &&
1025 cast<Instruction>(I->use_back())->getOpcode() == Instruction::Sub)
1028 ReassociateExpression(I);
1032 Value *Reassociate::ReassociateExpression(BinaryOperator *I) {
1034 // First, walk the expression tree, linearizing the tree, collecting the
1035 // operand information.
1036 SmallVector<ValueEntry, 8> Ops;
1037 LinearizeExprTree(I, Ops);
1039 DEBUG(dbgs() << "RAIn:\t"; PrintOps(I, Ops); dbgs() << '\n');
1041 // Now that we have linearized the tree to a list and have gathered all of
1042 // the operands and their ranks, sort the operands by their rank. Use a
1043 // stable_sort so that values with equal ranks will have their relative
1044 // positions maintained (and so the compiler is deterministic). Note that
1045 // this sorts so that the highest ranking values end up at the beginning of
1047 std::stable_sort(Ops.begin(), Ops.end());
1049 // OptimizeExpression - Now that we have the expression tree in a convenient
1050 // sorted form, optimize it globally if possible.
1051 if (Value *V = OptimizeExpression(I, Ops)) {
1052 // This expression tree simplified to something that isn't a tree,
1054 DEBUG(dbgs() << "Reassoc to scalar: " << *V << '\n');
1055 I->replaceAllUsesWith(V);
1056 RemoveDeadBinaryOp(I);
1061 // We want to sink immediates as deeply as possible except in the case where
1062 // this is a multiply tree used only by an add, and the immediate is a -1.
1063 // In this case we reassociate to put the negation on the outside so that we
1064 // can fold the negation into the add: (-X)*Y + Z -> Z-X*Y
1065 if (I->getOpcode() == Instruction::Mul && I->hasOneUse() &&
1066 cast<Instruction>(I->use_back())->getOpcode() == Instruction::Add &&
1067 isa<ConstantInt>(Ops.back().Op) &&
1068 cast<ConstantInt>(Ops.back().Op)->isAllOnesValue()) {
1069 ValueEntry Tmp = Ops.pop_back_val();
1070 Ops.insert(Ops.begin(), Tmp);
1073 DEBUG(dbgs() << "RAOut:\t"; PrintOps(I, Ops); dbgs() << '\n');
1075 if (Ops.size() == 1) {
1076 // This expression tree simplified to something that isn't a tree,
1078 I->replaceAllUsesWith(Ops[0].Op);
1079 RemoveDeadBinaryOp(I);
1083 // Now that we ordered and optimized the expressions, splat them back into
1084 // the expression tree, removing any unneeded nodes.
1085 RewriteExprTree(I, Ops);
1090 bool Reassociate::runOnFunction(Function &F) {
1091 // Recalculate the rank map for F
1095 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI)
1098 // Now that we're done, delete any instructions which are no longer used.
1099 while (!DeadInsts.empty())
1100 if (Instruction *Inst =
1101 cast_or_null<Instruction>((Value *)DeadInsts.pop_back_val()))
1102 RecursivelyDeleteTriviallyDeadInstructions(Inst);
1104 // We are done with the rank map.
1106 ValueRankMap.clear();