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> RedoInsts;
79 SmallVector<WeakVH, 8> DeadInsts;
82 static char ID; // Pass identification, replacement for typeid
83 Reassociate() : FunctionPass(ID) {
84 initializeReassociatePass(*PassRegistry::getPassRegistry());
87 bool runOnFunction(Function &F);
89 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
93 void BuildRankMap(Function &F);
94 unsigned getRank(Value *V);
95 Value *ReassociateExpression(BinaryOperator *I);
96 void RewriteExprTree(BinaryOperator *I, SmallVectorImpl<ValueEntry> &Ops,
98 Value *OptimizeExpression(BinaryOperator *I,
99 SmallVectorImpl<ValueEntry> &Ops);
100 Value *OptimizeAdd(Instruction *I, SmallVectorImpl<ValueEntry> &Ops);
101 void LinearizeExprTree(BinaryOperator *I, SmallVectorImpl<ValueEntry> &Ops);
102 void LinearizeExpr(BinaryOperator *I);
103 Value *RemoveFactorFromExpression(Value *V, Value *Factor);
104 void ReassociateInst(BasicBlock::iterator &BBI);
106 void RemoveDeadBinaryOp(Value *V);
110 char Reassociate::ID = 0;
111 INITIALIZE_PASS(Reassociate, "reassociate",
112 "Reassociate expressions", false, false)
114 // Public interface to the Reassociate pass
115 FunctionPass *llvm::createReassociatePass() { return new Reassociate(); }
117 void Reassociate::RemoveDeadBinaryOp(Value *V) {
118 Instruction *Op = dyn_cast<Instruction>(V);
119 if (!Op || !isa<BinaryOperator>(Op))
122 Value *LHS = Op->getOperand(0), *RHS = Op->getOperand(1);
124 ValueRankMap.erase(Op);
125 DeadInsts.push_back(Op);
126 RemoveDeadBinaryOp(LHS);
127 RemoveDeadBinaryOp(RHS);
131 static bool isUnmovableInstruction(Instruction *I) {
132 if (I->getOpcode() == Instruction::PHI ||
133 I->getOpcode() == Instruction::Alloca ||
134 I->getOpcode() == Instruction::Load ||
135 I->getOpcode() == Instruction::Invoke ||
136 (I->getOpcode() == Instruction::Call &&
137 !isa<DbgInfoIntrinsic>(I)) ||
138 I->getOpcode() == Instruction::UDiv ||
139 I->getOpcode() == Instruction::SDiv ||
140 I->getOpcode() == Instruction::FDiv ||
141 I->getOpcode() == Instruction::URem ||
142 I->getOpcode() == Instruction::SRem ||
143 I->getOpcode() == Instruction::FRem)
148 void Reassociate::BuildRankMap(Function &F) {
151 // Assign distinct ranks to function arguments
152 for (Function::arg_iterator I = F.arg_begin(), E = F.arg_end(); I != E; ++I)
153 ValueRankMap[&*I] = ++i;
155 ReversePostOrderTraversal<Function*> RPOT(&F);
156 for (ReversePostOrderTraversal<Function*>::rpo_iterator I = RPOT.begin(),
157 E = RPOT.end(); I != E; ++I) {
159 unsigned BBRank = RankMap[BB] = ++i << 16;
161 // Walk the basic block, adding precomputed ranks for any instructions that
162 // we cannot move. This ensures that the ranks for these instructions are
163 // all different in the block.
164 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
165 if (isUnmovableInstruction(I))
166 ValueRankMap[&*I] = ++BBRank;
170 unsigned Reassociate::getRank(Value *V) {
171 Instruction *I = dyn_cast<Instruction>(V);
173 if (isa<Argument>(V)) return ValueRankMap[V]; // Function argument.
174 return 0; // Otherwise it's a global or constant, rank 0.
177 if (unsigned Rank = ValueRankMap[I])
178 return Rank; // Rank already known?
180 // If this is an expression, return the 1+MAX(rank(LHS), rank(RHS)) so that
181 // we can reassociate expressions for code motion! Since we do not recurse
182 // for PHI nodes, we cannot have infinite recursion here, because there
183 // cannot be loops in the value graph that do not go through PHI nodes.
184 unsigned Rank = 0, MaxRank = RankMap[I->getParent()];
185 for (unsigned i = 0, e = I->getNumOperands();
186 i != e && Rank != MaxRank; ++i)
187 Rank = std::max(Rank, getRank(I->getOperand(i)));
189 // If this is a not or neg instruction, do not count it for rank. This
190 // assures us that X and ~X will have the same rank.
191 if (!I->getType()->isIntegerTy() ||
192 (!BinaryOperator::isNot(I) && !BinaryOperator::isNeg(I)))
195 //DEBUG(dbgs() << "Calculated Rank[" << V->getName() << "] = "
198 return ValueRankMap[I] = Rank;
201 /// isReassociableOp - Return true if V is an instruction of the specified
202 /// opcode and if it only has one use.
203 static BinaryOperator *isReassociableOp(Value *V, unsigned Opcode) {
204 if ((V->hasOneUse() || V->use_empty()) && isa<Instruction>(V) &&
205 cast<Instruction>(V)->getOpcode() == Opcode)
206 return cast<BinaryOperator>(V);
210 /// LowerNegateToMultiply - Replace 0-X with X*-1.
212 static Instruction *LowerNegateToMultiply(Instruction *Neg,
213 DenseMap<AssertingVH<>, unsigned> &ValueRankMap) {
214 Constant *Cst = Constant::getAllOnesValue(Neg->getType());
216 Instruction *Res = BinaryOperator::CreateMul(Neg->getOperand(1), Cst, "",Neg);
217 ValueRankMap.erase(Neg);
219 Neg->replaceAllUsesWith(Res);
220 Neg->eraseFromParent();
224 // Given an expression of the form '(A+B)+(D+C)', turn it into '(((A+B)+C)+D)'.
225 // Note that if D is also part of the expression tree that we recurse to
226 // linearize it as well. Besides that case, this does not recurse into A,B, or
228 void Reassociate::LinearizeExpr(BinaryOperator *I) {
229 BinaryOperator *LHS = cast<BinaryOperator>(I->getOperand(0));
230 BinaryOperator *RHS = cast<BinaryOperator>(I->getOperand(1));
231 assert(isReassociableOp(LHS, I->getOpcode()) &&
232 isReassociableOp(RHS, I->getOpcode()) &&
233 "Not an expression that needs linearization?");
235 DEBUG(dbgs() << "Linear" << *LHS << '\n' << *RHS << '\n' << *I << '\n');
237 // Move the RHS instruction to live immediately before I, avoiding breaking
238 // dominator properties.
241 // Move operands around to do the linearization.
242 I->setOperand(1, RHS->getOperand(0));
243 RHS->setOperand(0, LHS);
244 I->setOperand(0, RHS);
246 // Conservatively clear all the optional flags, which may not hold
247 // after the reassociation.
248 I->clearSubclassOptionalData();
249 LHS->clearSubclassOptionalData();
250 RHS->clearSubclassOptionalData();
254 DEBUG(dbgs() << "Linearized: " << *I << '\n');
256 // If D is part of this expression tree, tail recurse.
257 if (isReassociableOp(I->getOperand(1), I->getOpcode()))
262 /// LinearizeExprTree - Given an associative binary expression tree, traverse
263 /// all of the uses putting it into canonical form. This forces a left-linear
264 /// form of the expression (((a+b)+c)+d), and collects information about the
265 /// rank of the non-tree operands.
267 /// NOTE: These intentionally destroys the expression tree operands (turning
268 /// them into undef values) to reduce #uses of the values. This means that the
269 /// caller MUST use something like RewriteExprTree to put the values back in.
271 void Reassociate::LinearizeExprTree(BinaryOperator *I,
272 SmallVectorImpl<ValueEntry> &Ops) {
273 Value *LHS = I->getOperand(0), *RHS = I->getOperand(1);
274 unsigned Opcode = I->getOpcode();
276 // First step, linearize the expression if it is in ((A+B)+(C+D)) form.
277 BinaryOperator *LHSBO = isReassociableOp(LHS, Opcode);
278 BinaryOperator *RHSBO = isReassociableOp(RHS, Opcode);
280 // If this is a multiply expression tree and it contains internal negations,
281 // transform them into multiplies by -1 so they can be reassociated.
282 if (I->getOpcode() == Instruction::Mul) {
283 if (!LHSBO && LHS->hasOneUse() && BinaryOperator::isNeg(LHS)) {
284 LHS = LowerNegateToMultiply(cast<Instruction>(LHS), ValueRankMap);
285 LHSBO = isReassociableOp(LHS, Opcode);
287 if (!RHSBO && RHS->hasOneUse() && BinaryOperator::isNeg(RHS)) {
288 RHS = LowerNegateToMultiply(cast<Instruction>(RHS), ValueRankMap);
289 RHSBO = isReassociableOp(RHS, Opcode);
295 // Neither the LHS or RHS as part of the tree, thus this is a leaf. As
296 // such, just remember these operands and their rank.
297 Ops.push_back(ValueEntry(getRank(LHS), LHS));
298 Ops.push_back(ValueEntry(getRank(RHS), RHS));
300 // Clear the leaves out.
301 I->setOperand(0, UndefValue::get(I->getType()));
302 I->setOperand(1, UndefValue::get(I->getType()));
306 // Turn X+(Y+Z) -> (Y+Z)+X
307 std::swap(LHSBO, RHSBO);
309 bool Success = !I->swapOperands();
310 assert(Success && "swapOperands failed");
314 // Turn (A+B)+(C+D) -> (((A+B)+C)+D). This guarantees the RHS is not
315 // part of the expression tree.
317 LHS = LHSBO = cast<BinaryOperator>(I->getOperand(0));
318 RHS = I->getOperand(1);
322 // Okay, now we know that the LHS is a nested expression and that the RHS is
323 // not. Perform reassociation.
324 assert(!isReassociableOp(RHS, Opcode) && "LinearizeExpr failed!");
326 // Move LHS right before I to make sure that the tree expression dominates all
328 LHSBO->moveBefore(I);
330 // Linearize the expression tree on the LHS.
331 LinearizeExprTree(LHSBO, Ops);
333 // Remember the RHS operand and its rank.
334 Ops.push_back(ValueEntry(getRank(RHS), RHS));
336 // Clear the RHS leaf out.
337 I->setOperand(1, UndefValue::get(I->getType()));
340 // RewriteExprTree - Now that the operands for this expression tree are
341 // linearized and optimized, emit them in-order. This function is written to be
343 void Reassociate::RewriteExprTree(BinaryOperator *I,
344 SmallVectorImpl<ValueEntry> &Ops,
346 if (i+2 == Ops.size()) {
347 if (I->getOperand(0) != Ops[i].Op ||
348 I->getOperand(1) != Ops[i+1].Op) {
349 Value *OldLHS = I->getOperand(0);
350 DEBUG(dbgs() << "RA: " << *I << '\n');
351 I->setOperand(0, Ops[i].Op);
352 I->setOperand(1, Ops[i+1].Op);
354 // Clear all the optional flags, which may not hold after the
355 // reassociation if the expression involved more than just this operation.
357 I->clearSubclassOptionalData();
359 DEBUG(dbgs() << "TO: " << *I << '\n');
363 // If we reassociated a tree to fewer operands (e.g. (1+a+2) -> (a+3)
364 // delete the extra, now dead, nodes.
365 RemoveDeadBinaryOp(OldLHS);
369 assert(i+2 < Ops.size() && "Ops index out of range!");
371 if (I->getOperand(1) != Ops[i].Op) {
372 DEBUG(dbgs() << "RA: " << *I << '\n');
373 I->setOperand(1, Ops[i].Op);
375 // Conservatively clear all the optional flags, which may not hold
376 // after the reassociation.
377 I->clearSubclassOptionalData();
379 DEBUG(dbgs() << "TO: " << *I << '\n');
384 BinaryOperator *LHS = cast<BinaryOperator>(I->getOperand(0));
385 assert(LHS->getOpcode() == I->getOpcode() &&
386 "Improper expression tree!");
388 // Compactify the tree instructions together with each other to guarantee
389 // that the expression tree is dominated by all of Ops.
391 RewriteExprTree(LHS, Ops, i+1);
396 // NegateValue - Insert instructions before the instruction pointed to by BI,
397 // that computes the negative version of the value specified. The negative
398 // version of the value is returned, and BI is left pointing at the instruction
399 // that should be processed next by the reassociation pass.
401 static Value *NegateValue(Value *V, Instruction *BI) {
402 if (Constant *C = dyn_cast<Constant>(V))
403 return ConstantExpr::getNeg(C);
405 // We are trying to expose opportunity for reassociation. One of the things
406 // that we want to do to achieve this is to push a negation as deep into an
407 // expression chain as possible, to expose the add instructions. In practice,
408 // this means that we turn this:
409 // X = -(A+12+C+D) into X = -A + -12 + -C + -D = -12 + -A + -C + -D
410 // so that later, a: Y = 12+X could get reassociated with the -12 to eliminate
411 // the constants. We assume that instcombine will clean up the mess later if
412 // we introduce tons of unnecessary negation instructions.
414 if (Instruction *I = dyn_cast<Instruction>(V))
415 if (I->getOpcode() == Instruction::Add && I->hasOneUse()) {
416 // Push the negates through the add.
417 I->setOperand(0, NegateValue(I->getOperand(0), BI));
418 I->setOperand(1, NegateValue(I->getOperand(1), BI));
420 // We must move the add instruction here, because the neg instructions do
421 // not dominate the old add instruction in general. By moving it, we are
422 // assured that the neg instructions we just inserted dominate the
423 // instruction we are about to insert after them.
426 I->setName(I->getName()+".neg");
430 // Okay, we need to materialize a negated version of V with an instruction.
431 // Scan the use lists of V to see if we have one already.
432 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E;++UI){
434 if (!BinaryOperator::isNeg(U)) continue;
436 // We found one! Now we have to make sure that the definition dominates
437 // this use. We do this by moving it to the entry block (if it is a
438 // non-instruction value) or right after the definition. These negates will
439 // be zapped by reassociate later, so we don't need much finesse here.
440 BinaryOperator *TheNeg = cast<BinaryOperator>(U);
442 // Verify that the negate is in this function, V might be a constant expr.
443 if (TheNeg->getParent()->getParent() != BI->getParent()->getParent())
446 BasicBlock::iterator InsertPt;
447 if (Instruction *InstInput = dyn_cast<Instruction>(V)) {
448 if (InvokeInst *II = dyn_cast<InvokeInst>(InstInput)) {
449 InsertPt = II->getNormalDest()->begin();
451 InsertPt = InstInput;
454 while (isa<PHINode>(InsertPt)) ++InsertPt;
456 InsertPt = TheNeg->getParent()->getParent()->getEntryBlock().begin();
458 TheNeg->moveBefore(InsertPt);
462 // Insert a 'neg' instruction that subtracts the value from zero to get the
464 return BinaryOperator::CreateNeg(V, V->getName() + ".neg", BI);
467 /// ShouldBreakUpSubtract - Return true if we should break up this subtract of
468 /// X-Y into (X + -Y).
469 static bool ShouldBreakUpSubtract(Instruction *Sub) {
470 // If this is a negation, we can't split it up!
471 if (BinaryOperator::isNeg(Sub))
474 // Don't bother to break this up unless either the LHS is an associable add or
475 // subtract or if this is only used by one.
476 if (isReassociableOp(Sub->getOperand(0), Instruction::Add) ||
477 isReassociableOp(Sub->getOperand(0), Instruction::Sub))
479 if (isReassociableOp(Sub->getOperand(1), Instruction::Add) ||
480 isReassociableOp(Sub->getOperand(1), Instruction::Sub))
482 if (Sub->hasOneUse() &&
483 (isReassociableOp(Sub->use_back(), Instruction::Add) ||
484 isReassociableOp(Sub->use_back(), Instruction::Sub)))
490 /// BreakUpSubtract - If we have (X-Y), and if either X is an add, or if this is
491 /// only used by an add, transform this into (X+(0-Y)) to promote better
493 static Instruction *BreakUpSubtract(Instruction *Sub,
494 DenseMap<AssertingVH<>, unsigned> &ValueRankMap) {
495 // Convert a subtract into an add and a neg instruction. This allows sub
496 // instructions to be commuted with other add instructions.
498 // Calculate the negative value of Operand 1 of the sub instruction,
499 // and set it as the RHS of the add instruction we just made.
501 Value *NegVal = NegateValue(Sub->getOperand(1), Sub);
503 BinaryOperator::CreateAdd(Sub->getOperand(0), NegVal, "", Sub);
506 // Everyone now refers to the add instruction.
507 ValueRankMap.erase(Sub);
508 Sub->replaceAllUsesWith(New);
509 Sub->eraseFromParent();
511 DEBUG(dbgs() << "Negated: " << *New << '\n');
515 /// ConvertShiftToMul - If this is a shift of a reassociable multiply or is used
516 /// by one, change this into a multiply by a constant to assist with further
518 static Instruction *ConvertShiftToMul(Instruction *Shl,
519 DenseMap<AssertingVH<>, unsigned> &ValueRankMap) {
520 // If an operand of this shift is a reassociable multiply, or if the shift
521 // is used by a reassociable multiply or add, turn into a multiply.
522 if (isReassociableOp(Shl->getOperand(0), Instruction::Mul) ||
524 (isReassociableOp(Shl->use_back(), Instruction::Mul) ||
525 isReassociableOp(Shl->use_back(), Instruction::Add)))) {
526 Constant *MulCst = ConstantInt::get(Shl->getType(), 1);
527 MulCst = ConstantExpr::getShl(MulCst, cast<Constant>(Shl->getOperand(1)));
530 BinaryOperator::CreateMul(Shl->getOperand(0), MulCst, "", Shl);
531 ValueRankMap.erase(Shl);
533 Shl->replaceAllUsesWith(Mul);
534 Shl->eraseFromParent();
540 // Scan backwards and forwards among values with the same rank as element i to
541 // see if X exists. If X does not exist, return i. This is useful when
542 // scanning for 'x' when we see '-x' because they both get the same rank.
543 static unsigned FindInOperandList(SmallVectorImpl<ValueEntry> &Ops, unsigned i,
545 unsigned XRank = Ops[i].Rank;
546 unsigned e = Ops.size();
547 for (unsigned j = i+1; j != e && Ops[j].Rank == XRank; ++j)
551 for (unsigned j = i-1; j != ~0U && Ops[j].Rank == XRank; --j)
557 /// EmitAddTreeOfValues - Emit a tree of add instructions, summing Ops together
558 /// and returning the result. Insert the tree before I.
559 static Value *EmitAddTreeOfValues(Instruction *I, SmallVectorImpl<Value*> &Ops){
560 if (Ops.size() == 1) return Ops.back();
562 Value *V1 = Ops.back();
564 Value *V2 = EmitAddTreeOfValues(I, Ops);
565 return BinaryOperator::CreateAdd(V2, V1, "tmp", I);
568 /// RemoveFactorFromExpression - If V is an expression tree that is a
569 /// multiplication sequence, and if this sequence contains a multiply by Factor,
570 /// remove Factor from the tree and return the new tree.
571 Value *Reassociate::RemoveFactorFromExpression(Value *V, Value *Factor) {
572 BinaryOperator *BO = isReassociableOp(V, Instruction::Mul);
575 SmallVector<ValueEntry, 8> Factors;
576 LinearizeExprTree(BO, Factors);
578 bool FoundFactor = false;
579 bool NeedsNegate = false;
580 for (unsigned i = 0, e = Factors.size(); i != e; ++i) {
581 if (Factors[i].Op == Factor) {
583 Factors.erase(Factors.begin()+i);
587 // If this is a negative version of this factor, remove it.
588 if (ConstantInt *FC1 = dyn_cast<ConstantInt>(Factor))
589 if (ConstantInt *FC2 = dyn_cast<ConstantInt>(Factors[i].Op))
590 if (FC1->getValue() == -FC2->getValue()) {
591 FoundFactor = NeedsNegate = true;
592 Factors.erase(Factors.begin()+i);
598 // Make sure to restore the operands to the expression tree.
599 RewriteExprTree(BO, Factors);
603 BasicBlock::iterator InsertPt = BO; ++InsertPt;
605 // If this was just a single multiply, remove the multiply and return the only
606 // remaining operand.
607 if (Factors.size() == 1) {
608 ValueRankMap.erase(BO);
609 DeadInsts.push_back(BO);
612 RewriteExprTree(BO, Factors);
617 V = BinaryOperator::CreateNeg(V, "neg", InsertPt);
622 /// FindSingleUseMultiplyFactors - If V is a single-use multiply, recursively
623 /// add its operands as factors, otherwise add V to the list of factors.
625 /// Ops is the top-level list of add operands we're trying to factor.
626 static void FindSingleUseMultiplyFactors(Value *V,
627 SmallVectorImpl<Value*> &Factors,
628 const SmallVectorImpl<ValueEntry> &Ops,
631 if (!(V->hasOneUse() || V->use_empty()) || // More than one use.
632 !(BO = dyn_cast<BinaryOperator>(V)) ||
633 BO->getOpcode() != Instruction::Mul) {
634 Factors.push_back(V);
638 // If this value has a single use because it is another input to the add
639 // tree we're reassociating and we dropped its use, it actually has two
640 // uses and we can't factor it.
642 for (unsigned i = 0, e = Ops.size(); i != e; ++i)
643 if (Ops[i].Op == V) {
644 Factors.push_back(V);
650 // Otherwise, add the LHS and RHS to the list of factors.
651 FindSingleUseMultiplyFactors(BO->getOperand(1), Factors, Ops, false);
652 FindSingleUseMultiplyFactors(BO->getOperand(0), Factors, Ops, false);
655 /// OptimizeAndOrXor - Optimize a series of operands to an 'and', 'or', or 'xor'
656 /// instruction. This optimizes based on identities. If it can be reduced to
657 /// a single Value, it is returned, otherwise the Ops list is mutated as
659 static Value *OptimizeAndOrXor(unsigned Opcode,
660 SmallVectorImpl<ValueEntry> &Ops) {
661 // Scan the operand lists looking for X and ~X pairs, along with X,X pairs.
662 // If we find any, we can simplify the expression. X&~X == 0, X|~X == -1.
663 for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
664 // First, check for X and ~X in the operand list.
665 assert(i < Ops.size());
666 if (BinaryOperator::isNot(Ops[i].Op)) { // Cannot occur for ^.
667 Value *X = BinaryOperator::getNotArgument(Ops[i].Op);
668 unsigned FoundX = FindInOperandList(Ops, i, X);
670 if (Opcode == Instruction::And) // ...&X&~X = 0
671 return Constant::getNullValue(X->getType());
673 if (Opcode == Instruction::Or) // ...|X|~X = -1
674 return Constant::getAllOnesValue(X->getType());
678 // Next, check for duplicate pairs of values, which we assume are next to
679 // each other, due to our sorting criteria.
680 assert(i < Ops.size());
681 if (i+1 != Ops.size() && Ops[i+1].Op == Ops[i].Op) {
682 if (Opcode == Instruction::And || Opcode == Instruction::Or) {
683 // Drop duplicate values for And and Or.
684 Ops.erase(Ops.begin()+i);
690 // Drop pairs of values for Xor.
691 assert(Opcode == Instruction::Xor);
693 return Constant::getNullValue(Ops[0].Op->getType());
696 Ops.erase(Ops.begin()+i, Ops.begin()+i+2);
704 /// OptimizeAdd - Optimize a series of operands to an 'add' instruction. This
705 /// optimizes based on identities. If it can be reduced to a single Value, it
706 /// is returned, otherwise the Ops list is mutated as necessary.
707 Value *Reassociate::OptimizeAdd(Instruction *I,
708 SmallVectorImpl<ValueEntry> &Ops) {
709 // Scan the operand lists looking for X and -X pairs. If we find any, we
710 // can simplify the expression. X+-X == 0. While we're at it, scan for any
711 // duplicates. We want to canonicalize Y+Y+Y+Z -> 3*Y+Z.
713 // TODO: We could handle "X + ~X" -> "-1" if we wanted, since "-X = ~X+1".
715 for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
716 Value *TheOp = Ops[i].Op;
717 // Check to see if we've seen this operand before. If so, we factor all
718 // instances of the operand together. Due to our sorting criteria, we know
719 // that these need to be next to each other in the vector.
720 if (i+1 != Ops.size() && Ops[i+1].Op == TheOp) {
721 // Rescan the list, remove all instances of this operand from the expr.
722 unsigned NumFound = 0;
724 Ops.erase(Ops.begin()+i);
726 } while (i != Ops.size() && Ops[i].Op == TheOp);
728 DEBUG(errs() << "\nFACTORING [" << NumFound << "]: " << *TheOp << '\n');
731 // Insert a new multiply.
732 Value *Mul = ConstantInt::get(cast<IntegerType>(I->getType()), NumFound);
733 Mul = BinaryOperator::CreateMul(TheOp, Mul, "factor", I);
735 // Now that we have inserted a multiply, optimize it. This allows us to
736 // handle cases that require multiple factoring steps, such as this:
737 // (X*2) + (X*2) + (X*2) -> (X*2)*3 -> X*6
738 RedoInsts.push_back(Mul);
740 // If every add operand was a duplicate, return the multiply.
744 // Otherwise, we had some input that didn't have the dupe, such as
745 // "A + A + B" -> "A*2 + B". Add the new multiply to the list of
746 // things being added by this operation.
747 Ops.insert(Ops.begin(), ValueEntry(getRank(Mul), Mul));
754 // Check for X and -X in the operand list.
755 if (!BinaryOperator::isNeg(TheOp))
758 Value *X = BinaryOperator::getNegArgument(TheOp);
759 unsigned FoundX = FindInOperandList(Ops, i, X);
763 // Remove X and -X from the operand list.
765 return Constant::getNullValue(X->getType());
767 Ops.erase(Ops.begin()+i);
771 --i; // Need to back up an extra one.
772 Ops.erase(Ops.begin()+FoundX);
774 --i; // Revisit element.
775 e -= 2; // Removed two elements.
778 // Scan the operand list, checking to see if there are any common factors
779 // between operands. Consider something like A*A+A*B*C+D. We would like to
780 // reassociate this to A*(A+B*C)+D, which reduces the number of multiplies.
781 // To efficiently find this, we count the number of times a factor occurs
782 // for any ADD operands that are MULs.
783 DenseMap<Value*, unsigned> FactorOccurrences;
785 // Keep track of each multiply we see, to avoid triggering on (X*4)+(X*4)
786 // where they are actually the same multiply.
788 Value *MaxOccVal = 0;
789 for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
790 BinaryOperator *BOp = dyn_cast<BinaryOperator>(Ops[i].Op);
791 if (BOp == 0 || BOp->getOpcode() != Instruction::Mul || !BOp->use_empty())
794 // Compute all of the factors of this added value.
795 SmallVector<Value*, 8> Factors;
796 FindSingleUseMultiplyFactors(BOp, Factors, Ops, true);
797 assert(Factors.size() > 1 && "Bad linearize!");
799 // Add one to FactorOccurrences for each unique factor in this op.
800 SmallPtrSet<Value*, 8> Duplicates;
801 for (unsigned i = 0, e = Factors.size(); i != e; ++i) {
802 Value *Factor = Factors[i];
803 if (!Duplicates.insert(Factor)) continue;
805 unsigned Occ = ++FactorOccurrences[Factor];
806 if (Occ > MaxOcc) { MaxOcc = Occ; MaxOccVal = Factor; }
808 // If Factor is a negative constant, add the negated value as a factor
809 // because we can percolate the negate out. Watch for minint, which
810 // cannot be positivified.
811 if (ConstantInt *CI = dyn_cast<ConstantInt>(Factor))
812 if (CI->getValue().isNegative() && !CI->getValue().isMinSignedValue()) {
813 Factor = ConstantInt::get(CI->getContext(), -CI->getValue());
814 assert(!Duplicates.count(Factor) &&
815 "Shouldn't have two constant factors, missed a canonicalize");
817 unsigned Occ = ++FactorOccurrences[Factor];
818 if (Occ > MaxOcc) { MaxOcc = Occ; MaxOccVal = Factor; }
823 // If any factor occurred more than one time, we can pull it out.
825 DEBUG(errs() << "\nFACTORING [" << MaxOcc << "]: " << *MaxOccVal << '\n');
828 // Create a new instruction that uses the MaxOccVal twice. If we don't do
829 // this, we could otherwise run into situations where removing a factor
830 // from an expression will drop a use of maxocc, and this can cause
831 // RemoveFactorFromExpression on successive values to behave differently.
832 Instruction *DummyInst = BinaryOperator::CreateAdd(MaxOccVal, MaxOccVal);
833 SmallVector<Value*, 4> NewMulOps;
834 for (unsigned i = 0; i != Ops.size(); ++i) {
835 // Only try to remove factors from expressions we're allowed to.
836 BinaryOperator *BOp = dyn_cast<BinaryOperator>(Ops[i].Op);
837 if (BOp == 0 || BOp->getOpcode() != Instruction::Mul || !BOp->use_empty())
840 if (Value *V = RemoveFactorFromExpression(Ops[i].Op, MaxOccVal)) {
841 // The factorized operand may occur several times. Convert them all in
843 for (unsigned j = Ops.size(); j != i;) {
845 if (Ops[j].Op == Ops[i].Op) {
846 NewMulOps.push_back(V);
847 Ops.erase(Ops.begin()+j);
854 // No need for extra uses anymore.
857 unsigned NumAddedValues = NewMulOps.size();
858 Value *V = EmitAddTreeOfValues(I, NewMulOps);
860 // Now that we have inserted the add tree, optimize it. This allows us to
861 // handle cases that require multiple factoring steps, such as this:
862 // A*A*B + A*A*C --> A*(A*B+A*C) --> A*(A*(B+C))
863 assert(NumAddedValues > 1 && "Each occurrence should contribute a value");
864 (void)NumAddedValues;
865 V = ReassociateExpression(cast<BinaryOperator>(V));
867 // Create the multiply.
868 Value *V2 = BinaryOperator::CreateMul(V, MaxOccVal, "tmp", I);
870 // Rerun associate on the multiply in case the inner expression turned into
871 // a multiply. We want to make sure that we keep things in canonical form.
872 V2 = ReassociateExpression(cast<BinaryOperator>(V2));
874 // If every add operand included the factor (e.g. "A*B + A*C"), then the
875 // entire result expression is just the multiply "A*(B+C)".
879 // Otherwise, we had some input that didn't have the factor, such as
880 // "A*B + A*C + D" -> "A*(B+C) + D". Add the new multiply to the list of
881 // things being added by this operation.
882 Ops.insert(Ops.begin(), ValueEntry(getRank(V2), V2));
888 Value *Reassociate::OptimizeExpression(BinaryOperator *I,
889 SmallVectorImpl<ValueEntry> &Ops) {
890 // Now that we have the linearized expression tree, try to optimize it.
891 // Start by folding any constants that we found.
892 bool IterateOptimization = false;
893 if (Ops.size() == 1) return Ops[0].Op;
895 unsigned Opcode = I->getOpcode();
897 if (Constant *V1 = dyn_cast<Constant>(Ops[Ops.size()-2].Op))
898 if (Constant *V2 = dyn_cast<Constant>(Ops.back().Op)) {
900 Ops.back().Op = ConstantExpr::get(Opcode, V1, V2);
901 return OptimizeExpression(I, Ops);
904 // Check for destructive annihilation due to a constant being used.
905 if (ConstantInt *CstVal = dyn_cast<ConstantInt>(Ops.back().Op))
908 case Instruction::And:
909 if (CstVal->isZero()) // X & 0 -> 0
911 if (CstVal->isAllOnesValue()) // X & -1 -> X
914 case Instruction::Mul:
915 if (CstVal->isZero()) { // X * 0 -> 0
920 if (cast<ConstantInt>(CstVal)->isOne())
921 Ops.pop_back(); // X * 1 -> X
923 case Instruction::Or:
924 if (CstVal->isAllOnesValue()) // X | -1 -> -1
927 case Instruction::Add:
928 case Instruction::Xor:
929 if (CstVal->isZero()) // X [|^+] 0 -> X
933 if (Ops.size() == 1) return Ops[0].Op;
935 // Handle destructive annihilation due to identities between elements in the
936 // argument list here.
939 case Instruction::And:
940 case Instruction::Or:
941 case Instruction::Xor: {
942 unsigned NumOps = Ops.size();
943 if (Value *Result = OptimizeAndOrXor(Opcode, Ops))
945 IterateOptimization |= Ops.size() != NumOps;
949 case Instruction::Add: {
950 unsigned NumOps = Ops.size();
951 if (Value *Result = OptimizeAdd(I, Ops))
953 IterateOptimization |= Ops.size() != NumOps;
957 //case Instruction::Mul:
960 if (IterateOptimization)
961 return OptimizeExpression(I, Ops);
966 /// ReassociateInst - Inspect and reassociate the instruction at the
967 /// given position, post-incrementing the position.
968 void Reassociate::ReassociateInst(BasicBlock::iterator &BBI) {
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 return; // 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()) return;
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);
1031 Value *Reassociate::ReassociateExpression(BinaryOperator *I) {
1033 // First, walk the expression tree, linearizing the tree, collecting the
1034 // operand information.
1035 SmallVector<ValueEntry, 8> Ops;
1036 LinearizeExprTree(I, Ops);
1038 DEBUG(dbgs() << "RAIn:\t"; PrintOps(I, Ops); dbgs() << '\n');
1040 // Now that we have linearized the tree to a list and have gathered all of
1041 // the operands and their ranks, sort the operands by their rank. Use a
1042 // stable_sort so that values with equal ranks will have their relative
1043 // positions maintained (and so the compiler is deterministic). Note that
1044 // this sorts so that the highest ranking values end up at the beginning of
1046 std::stable_sort(Ops.begin(), Ops.end());
1048 // OptimizeExpression - Now that we have the expression tree in a convenient
1049 // sorted form, optimize it globally if possible.
1050 if (Value *V = OptimizeExpression(I, Ops)) {
1051 // This expression tree simplified to something that isn't a tree,
1053 DEBUG(dbgs() << "Reassoc to scalar: " << *V << '\n');
1054 I->replaceAllUsesWith(V);
1055 RemoveDeadBinaryOp(I);
1060 // We want to sink immediates as deeply as possible except in the case where
1061 // this is a multiply tree used only by an add, and the immediate is a -1.
1062 // In this case we reassociate to put the negation on the outside so that we
1063 // can fold the negation into the add: (-X)*Y + Z -> Z-X*Y
1064 if (I->getOpcode() == Instruction::Mul && I->hasOneUse() &&
1065 cast<Instruction>(I->use_back())->getOpcode() == Instruction::Add &&
1066 isa<ConstantInt>(Ops.back().Op) &&
1067 cast<ConstantInt>(Ops.back().Op)->isAllOnesValue()) {
1068 ValueEntry Tmp = Ops.pop_back_val();
1069 Ops.insert(Ops.begin(), Tmp);
1072 DEBUG(dbgs() << "RAOut:\t"; PrintOps(I, Ops); dbgs() << '\n');
1074 if (Ops.size() == 1) {
1075 // This expression tree simplified to something that isn't a tree,
1077 I->replaceAllUsesWith(Ops[0].Op);
1078 RemoveDeadBinaryOp(I);
1082 // Now that we ordered and optimized the expressions, splat them back into
1083 // the expression tree, removing any unneeded nodes.
1084 RewriteExprTree(I, Ops);
1089 bool Reassociate::runOnFunction(Function &F) {
1090 // Recalculate the rank map for F
1094 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI)
1095 for (BasicBlock::iterator BBI = FI->begin(); BBI != FI->end(); )
1096 ReassociateInst(BBI);
1098 // Now that we're done, revisit any instructions which are likely to
1099 // have secondary reassociation opportunities.
1100 while (!RedoInsts.empty())
1101 if (Value *V = RedoInsts.pop_back_val()) {
1102 BasicBlock::iterator BBI = cast<Instruction>(V);
1103 ReassociateInst(BBI);
1106 // Now that we're done, delete any instructions which are no longer used.
1107 while (!DeadInsts.empty())
1108 if (Value *V = DeadInsts.pop_back_val())
1109 RecursivelyDeleteTriviallyDeadInstructions(V);
1111 // We are done with the rank map.
1113 ValueRankMap.clear();