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...
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/LLVMContext.h"
31 #include "llvm/Pass.h"
32 #include "llvm/Assembly/Writer.h"
33 #include "llvm/Support/CFG.h"
34 #include "llvm/Support/Compiler.h"
35 #include "llvm/Support/Debug.h"
36 #include "llvm/Support/ValueHandle.h"
37 #include "llvm/ADT/PostOrderIterator.h"
38 #include "llvm/ADT/Statistic.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");
49 struct VISIBILITY_HIDDEN ValueEntry {
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 std::vector<ValueEntry> &Ops) {
63 Module *M = I->getParent()->getParent()->getParent();
64 cerr << Instruction::getOpcodeName(I->getOpcode()) << " "
65 << *Ops[0].Op->getType();
66 for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
67 WriteAsOperand(*cerr.stream() << " ", Ops[i].Op, false, M);
68 cerr << "," << Ops[i].Rank;
74 class VISIBILITY_HIDDEN Reassociate : public FunctionPass {
75 std::map<BasicBlock*, unsigned> RankMap;
76 std::map<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 void ReassociateExpression(BinaryOperator *I);
91 void RewriteExprTree(BinaryOperator *I, std::vector<ValueEntry> &Ops,
93 Value *OptimizeExpression(BinaryOperator *I, std::vector<ValueEntry> &Ops);
94 void LinearizeExprTree(BinaryOperator *I, std::vector<ValueEntry> &Ops);
95 void LinearizeExpr(BinaryOperator *I);
96 Value *RemoveFactorFromExpression(Value *V, Value *Factor);
97 void ReassociateBB(BasicBlock *BB);
99 void RemoveDeadBinaryOp(Value *V);
103 char Reassociate::ID = 0;
104 static RegisterPass<Reassociate> X("reassociate", "Reassociate expressions");
106 // Public interface to the Reassociate pass
107 FunctionPass *llvm::createReassociatePass() { return new Reassociate(); }
109 void Reassociate::RemoveDeadBinaryOp(Value *V) {
110 Instruction *Op = dyn_cast<Instruction>(V);
111 if (!Op || !isa<BinaryOperator>(Op) || !isa<CmpInst>(Op) || !Op->use_empty())
114 Value *LHS = Op->getOperand(0), *RHS = Op->getOperand(1);
115 RemoveDeadBinaryOp(LHS);
116 RemoveDeadBinaryOp(RHS);
120 static bool isUnmovableInstruction(Instruction *I) {
121 if (I->getOpcode() == Instruction::PHI ||
122 I->getOpcode() == Instruction::Alloca ||
123 I->getOpcode() == Instruction::Load ||
124 I->getOpcode() == Instruction::Malloc ||
125 I->getOpcode() == Instruction::Invoke ||
126 (I->getOpcode() == Instruction::Call &&
127 !isa<DbgInfoIntrinsic>(I)) ||
128 I->getOpcode() == Instruction::UDiv ||
129 I->getOpcode() == Instruction::SDiv ||
130 I->getOpcode() == Instruction::FDiv ||
131 I->getOpcode() == Instruction::URem ||
132 I->getOpcode() == Instruction::SRem ||
133 I->getOpcode() == Instruction::FRem)
138 void Reassociate::BuildRankMap(Function &F) {
141 // Assign distinct ranks to function arguments
142 for (Function::arg_iterator I = F.arg_begin(), E = F.arg_end(); I != E; ++I)
143 ValueRankMap[&*I] = ++i;
145 ReversePostOrderTraversal<Function*> RPOT(&F);
146 for (ReversePostOrderTraversal<Function*>::rpo_iterator I = RPOT.begin(),
147 E = RPOT.end(); I != E; ++I) {
149 unsigned BBRank = RankMap[BB] = ++i << 16;
151 // Walk the basic block, adding precomputed ranks for any instructions that
152 // we cannot move. This ensures that the ranks for these instructions are
153 // all different in the block.
154 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
155 if (isUnmovableInstruction(I))
156 ValueRankMap[&*I] = ++BBRank;
160 unsigned Reassociate::getRank(Value *V) {
161 if (isa<Argument>(V)) return ValueRankMap[V]; // Function argument...
163 Instruction *I = dyn_cast<Instruction>(V);
164 if (I == 0) return 0; // Otherwise it's a global or constant, rank 0.
166 unsigned &CachedRank = ValueRankMap[I];
167 if (CachedRank) return CachedRank; // Rank already known?
169 // If this is an expression, return the 1+MAX(rank(LHS), rank(RHS)) so that
170 // we can reassociate expressions for code motion! Since we do not recurse
171 // for PHI nodes, we cannot have infinite recursion here, because there
172 // cannot be loops in the value graph that do not go through PHI nodes.
173 unsigned Rank = 0, MaxRank = RankMap[I->getParent()];
174 for (unsigned i = 0, e = I->getNumOperands();
175 i != e && Rank != MaxRank; ++i)
176 Rank = std::max(Rank, getRank(I->getOperand(i)));
178 // If this is a not or neg instruction, do not count it for rank. This
179 // assures us that X and ~X will have the same rank.
180 if (!I->getType()->isInteger() ||
181 (!BinaryOperator::isNot(I) && !BinaryOperator::isNeg(I)))
184 //DOUT << "Calculated Rank[" << V->getName() << "] = "
187 return CachedRank = Rank;
190 /// isReassociableOp - Return true if V is an instruction of the specified
191 /// opcode and if it only has one use.
192 static BinaryOperator *isReassociableOp(Value *V, unsigned Opcode) {
193 if ((V->hasOneUse() || V->use_empty()) && isa<Instruction>(V) &&
194 cast<Instruction>(V)->getOpcode() == Opcode)
195 return cast<BinaryOperator>(V);
199 /// LowerNegateToMultiply - Replace 0-X with X*-1.
201 static Instruction *LowerNegateToMultiply(Instruction *Neg,
202 std::map<AssertingVH<>, unsigned> &ValueRankMap,
203 LLVMContext *Context) {
204 Constant *Cst = Context->getAllOnesValue(Neg->getType());
206 Instruction *Res = BinaryOperator::CreateMul(Neg->getOperand(1), Cst, "",Neg);
207 ValueRankMap.erase(Neg);
209 Neg->replaceAllUsesWith(Res);
210 Neg->eraseFromParent();
214 // Given an expression of the form '(A+B)+(D+C)', turn it into '(((A+B)+C)+D)'.
215 // Note that if D is also part of the expression tree that we recurse to
216 // linearize it as well. Besides that case, this does not recurse into A,B, or
218 void Reassociate::LinearizeExpr(BinaryOperator *I) {
219 BinaryOperator *LHS = cast<BinaryOperator>(I->getOperand(0));
220 BinaryOperator *RHS = cast<BinaryOperator>(I->getOperand(1));
221 assert(isReassociableOp(LHS, I->getOpcode()) &&
222 isReassociableOp(RHS, I->getOpcode()) &&
223 "Not an expression that needs linearization?");
225 DOUT << "Linear" << *LHS << *RHS << *I;
227 // Move the RHS instruction to live immediately before I, avoiding breaking
228 // dominator properties.
231 // Move operands around to do the linearization.
232 I->setOperand(1, RHS->getOperand(0));
233 RHS->setOperand(0, LHS);
234 I->setOperand(0, RHS);
238 DOUT << "Linearized: " << *I;
240 // If D is part of this expression tree, tail recurse.
241 if (isReassociableOp(I->getOperand(1), I->getOpcode()))
246 /// LinearizeExprTree - Given an associative binary expression tree, traverse
247 /// all of the uses putting it into canonical form. This forces a left-linear
248 /// form of the the expression (((a+b)+c)+d), and collects information about the
249 /// rank of the non-tree operands.
251 /// NOTE: These intentionally destroys the expression tree operands (turning
252 /// them into undef values) to reduce #uses of the values. This means that the
253 /// caller MUST use something like RewriteExprTree to put the values back in.
255 void Reassociate::LinearizeExprTree(BinaryOperator *I,
256 std::vector<ValueEntry> &Ops) {
257 Value *LHS = I->getOperand(0), *RHS = I->getOperand(1);
258 unsigned Opcode = I->getOpcode();
260 // First step, linearize the expression if it is in ((A+B)+(C+D)) form.
261 BinaryOperator *LHSBO = isReassociableOp(LHS, Opcode);
262 BinaryOperator *RHSBO = isReassociableOp(RHS, Opcode);
264 // If this is a multiply expression tree and it contains internal negations,
265 // transform them into multiplies by -1 so they can be reassociated.
266 if (I->getOpcode() == Instruction::Mul) {
267 if (!LHSBO && LHS->hasOneUse() && BinaryOperator::isNeg(LHS)) {
268 LHS = LowerNegateToMultiply(cast<Instruction>(LHS),
269 ValueRankMap, Context);
270 LHSBO = isReassociableOp(LHS, Opcode);
272 if (!RHSBO && RHS->hasOneUse() && BinaryOperator::isNeg(RHS)) {
273 RHS = LowerNegateToMultiply(cast<Instruction>(RHS),
274 ValueRankMap, Context);
275 RHSBO = isReassociableOp(RHS, Opcode);
281 // Neither the LHS or RHS as part of the tree, thus this is a leaf. As
282 // such, just remember these operands and their rank.
283 Ops.push_back(ValueEntry(getRank(LHS), LHS));
284 Ops.push_back(ValueEntry(getRank(RHS), RHS));
286 // Clear the leaves out.
287 I->setOperand(0, Context->getUndef(I->getType()));
288 I->setOperand(1, Context->getUndef(I->getType()));
291 // Turn X+(Y+Z) -> (Y+Z)+X
292 std::swap(LHSBO, RHSBO);
294 bool Success = !I->swapOperands();
295 assert(Success && "swapOperands failed");
300 // Turn (A+B)+(C+D) -> (((A+B)+C)+D). This guarantees the the RHS is not
301 // part of the expression tree.
303 LHS = LHSBO = cast<BinaryOperator>(I->getOperand(0));
304 RHS = I->getOperand(1);
308 // Okay, now we know that the LHS is a nested expression and that the RHS is
309 // not. Perform reassociation.
310 assert(!isReassociableOp(RHS, Opcode) && "LinearizeExpr failed!");
312 // Move LHS right before I to make sure that the tree expression dominates all
314 LHSBO->moveBefore(I);
316 // Linearize the expression tree on the LHS.
317 LinearizeExprTree(LHSBO, Ops);
319 // Remember the RHS operand and its rank.
320 Ops.push_back(ValueEntry(getRank(RHS), RHS));
322 // Clear the RHS leaf out.
323 I->setOperand(1, Context->getUndef(I->getType()));
326 // RewriteExprTree - Now that the operands for this expression tree are
327 // linearized and optimized, emit them in-order. This function is written to be
329 void Reassociate::RewriteExprTree(BinaryOperator *I,
330 std::vector<ValueEntry> &Ops,
332 if (i+2 == Ops.size()) {
333 if (I->getOperand(0) != Ops[i].Op ||
334 I->getOperand(1) != Ops[i+1].Op) {
335 Value *OldLHS = I->getOperand(0);
336 DOUT << "RA: " << *I;
337 I->setOperand(0, Ops[i].Op);
338 I->setOperand(1, Ops[i+1].Op);
339 DOUT << "TO: " << *I;
343 // If we reassociated a tree to fewer operands (e.g. (1+a+2) -> (a+3)
344 // delete the extra, now dead, nodes.
345 RemoveDeadBinaryOp(OldLHS);
349 assert(i+2 < Ops.size() && "Ops index out of range!");
351 if (I->getOperand(1) != Ops[i].Op) {
352 DOUT << "RA: " << *I;
353 I->setOperand(1, Ops[i].Op);
354 DOUT << "TO: " << *I;
359 BinaryOperator *LHS = cast<BinaryOperator>(I->getOperand(0));
360 assert(LHS->getOpcode() == I->getOpcode() &&
361 "Improper expression tree!");
363 // Compactify the tree instructions together with each other to guarantee
364 // that the expression tree is dominated by all of Ops.
366 RewriteExprTree(LHS, Ops, i+1);
371 // NegateValue - Insert instructions before the instruction pointed to by BI,
372 // that computes the negative version of the value specified. The negative
373 // version of the value is returned, and BI is left pointing at the instruction
374 // that should be processed next by the reassociation pass.
376 static Value *NegateValue(LLVMContext *Context, Value *V, Instruction *BI) {
377 // We are trying to expose opportunity for reassociation. One of the things
378 // that we want to do to achieve this is to push a negation as deep into an
379 // expression chain as possible, to expose the add instructions. In practice,
380 // this means that we turn this:
381 // X = -(A+12+C+D) into X = -A + -12 + -C + -D = -12 + -A + -C + -D
382 // so that later, a: Y = 12+X could get reassociated with the -12 to eliminate
383 // the constants. We assume that instcombine will clean up the mess later if
384 // we introduce tons of unnecessary negation instructions...
386 if (Instruction *I = dyn_cast<Instruction>(V))
387 if (I->getOpcode() == Instruction::Add && I->hasOneUse()) {
388 // Push the negates through the add.
389 I->setOperand(0, NegateValue(Context, I->getOperand(0), BI));
390 I->setOperand(1, NegateValue(Context, I->getOperand(1), BI));
392 // We must move the add instruction here, because the neg instructions do
393 // not dominate the old add instruction in general. By moving it, we are
394 // assured that the neg instructions we just inserted dominate the
395 // instruction we are about to insert after them.
398 I->setName(I->getName()+".neg");
402 // Insert a 'neg' instruction that subtracts the value from zero to get the
405 return BinaryOperator::CreateNeg(*Context, V, V->getName() + ".neg", BI);
408 /// ShouldBreakUpSubtract - Return true if we should break up this subtract of
409 /// X-Y into (X + -Y).
410 static bool ShouldBreakUpSubtract(LLVMContext *Context, Instruction *Sub) {
411 // If this is a negation, we can't split it up!
412 if (BinaryOperator::isNeg(Sub))
415 // Don't bother to break this up unless either the LHS is an associable add or
416 // subtract or if this is only used by one.
417 if (isReassociableOp(Sub->getOperand(0), Instruction::Add) ||
418 isReassociableOp(Sub->getOperand(0), Instruction::Sub))
420 if (isReassociableOp(Sub->getOperand(1), Instruction::Add) ||
421 isReassociableOp(Sub->getOperand(1), Instruction::Sub))
423 if (Sub->hasOneUse() &&
424 (isReassociableOp(Sub->use_back(), Instruction::Add) ||
425 isReassociableOp(Sub->use_back(), Instruction::Sub)))
431 /// BreakUpSubtract - If we have (X-Y), and if either X is an add, or if this is
432 /// only used by an add, transform this into (X+(0-Y)) to promote better
434 static Instruction *BreakUpSubtract(LLVMContext *Context, Instruction *Sub,
435 std::map<AssertingVH<>, unsigned> &ValueRankMap) {
436 // Convert a subtract into an add and a neg instruction... so that sub
437 // instructions can be commuted with other add instructions...
439 // Calculate the negative value of Operand 1 of the sub instruction...
440 // and set it as the RHS of the add instruction we just made...
442 Value *NegVal = NegateValue(Context, Sub->getOperand(1), Sub);
444 BinaryOperator::CreateAdd(Sub->getOperand(0), NegVal, "", Sub);
447 // Everyone now refers to the add instruction.
448 ValueRankMap.erase(Sub);
449 Sub->replaceAllUsesWith(New);
450 Sub->eraseFromParent();
452 DOUT << "Negated: " << *New;
456 /// ConvertShiftToMul - If this is a shift of a reassociable multiply or is used
457 /// by one, change this into a multiply by a constant to assist with further
459 static Instruction *ConvertShiftToMul(Instruction *Shl,
460 std::map<AssertingVH<>, unsigned> &ValueRankMap,
461 LLVMContext *Context) {
462 // If an operand of this shift is a reassociable multiply, or if the shift
463 // is used by a reassociable multiply or add, turn into a multiply.
464 if (isReassociableOp(Shl->getOperand(0), Instruction::Mul) ||
466 (isReassociableOp(Shl->use_back(), Instruction::Mul) ||
467 isReassociableOp(Shl->use_back(), Instruction::Add)))) {
468 Constant *MulCst = Context->getConstantInt(Shl->getType(), 1);
470 Context->getConstantExprShl(MulCst, cast<Constant>(Shl->getOperand(1)));
472 Instruction *Mul = BinaryOperator::CreateMul(Shl->getOperand(0), MulCst,
474 ValueRankMap.erase(Shl);
476 Shl->replaceAllUsesWith(Mul);
477 Shl->eraseFromParent();
483 // Scan backwards and forwards among values with the same rank as element i to
484 // see if X exists. If X does not exist, return i.
485 static unsigned FindInOperandList(std::vector<ValueEntry> &Ops, unsigned i,
487 unsigned XRank = Ops[i].Rank;
488 unsigned e = Ops.size();
489 for (unsigned j = i+1; j != e && Ops[j].Rank == XRank; ++j)
493 for (unsigned j = i-1; j != ~0U && Ops[j].Rank == XRank; --j)
499 /// EmitAddTreeOfValues - Emit a tree of add instructions, summing Ops together
500 /// and returning the result. Insert the tree before I.
501 static Value *EmitAddTreeOfValues(Instruction *I, std::vector<Value*> &Ops) {
502 if (Ops.size() == 1) return Ops.back();
504 Value *V1 = Ops.back();
506 Value *V2 = EmitAddTreeOfValues(I, Ops);
507 return BinaryOperator::CreateAdd(V2, V1, "tmp", I);
510 /// RemoveFactorFromExpression - If V is an expression tree that is a
511 /// multiplication sequence, and if this sequence contains a multiply by Factor,
512 /// remove Factor from the tree and return the new tree.
513 Value *Reassociate::RemoveFactorFromExpression(Value *V, Value *Factor) {
514 BinaryOperator *BO = isReassociableOp(V, Instruction::Mul);
517 std::vector<ValueEntry> Factors;
518 LinearizeExprTree(BO, Factors);
520 bool FoundFactor = false;
521 for (unsigned i = 0, e = Factors.size(); i != e; ++i)
522 if (Factors[i].Op == Factor) {
524 Factors.erase(Factors.begin()+i);
528 // Make sure to restore the operands to the expression tree.
529 RewriteExprTree(BO, Factors);
533 if (Factors.size() == 1) return Factors[0].Op;
535 RewriteExprTree(BO, Factors);
539 /// FindSingleUseMultiplyFactors - If V is a single-use multiply, recursively
540 /// add its operands as factors, otherwise add V to the list of factors.
541 static void FindSingleUseMultiplyFactors(Value *V,
542 std::vector<Value*> &Factors) {
544 if ((!V->hasOneUse() && !V->use_empty()) ||
545 !(BO = dyn_cast<BinaryOperator>(V)) ||
546 BO->getOpcode() != Instruction::Mul) {
547 Factors.push_back(V);
551 // Otherwise, add the LHS and RHS to the list of factors.
552 FindSingleUseMultiplyFactors(BO->getOperand(1), Factors);
553 FindSingleUseMultiplyFactors(BO->getOperand(0), Factors);
558 Value *Reassociate::OptimizeExpression(BinaryOperator *I,
559 std::vector<ValueEntry> &Ops) {
560 // Now that we have the linearized expression tree, try to optimize it.
561 // Start by folding any constants that we found.
562 bool IterateOptimization = false;
563 if (Ops.size() == 1) return Ops[0].Op;
565 unsigned Opcode = I->getOpcode();
567 if (Constant *V1 = dyn_cast<Constant>(Ops[Ops.size()-2].Op))
568 if (Constant *V2 = dyn_cast<Constant>(Ops.back().Op)) {
570 Ops.back().Op = Context->getConstantExpr(Opcode, V1, V2);
571 return OptimizeExpression(I, Ops);
574 // Check for destructive annihilation due to a constant being used.
575 if (ConstantInt *CstVal = dyn_cast<ConstantInt>(Ops.back().Op))
578 case Instruction::And:
579 if (CstVal->isZero()) { // ... & 0 -> 0
582 } else if (CstVal->isAllOnesValue()) { // ... & -1 -> ...
586 case Instruction::Mul:
587 if (CstVal->isZero()) { // ... * 0 -> 0
590 } else if (cast<ConstantInt>(CstVal)->isOne()) {
591 Ops.pop_back(); // ... * 1 -> ...
594 case Instruction::Or:
595 if (CstVal->isAllOnesValue()) { // ... | -1 -> -1
600 case Instruction::Add:
601 case Instruction::Xor:
602 if (CstVal->isZero()) // ... [|^+] 0 -> ...
606 if (Ops.size() == 1) return Ops[0].Op;
608 // Handle destructive annihilation do to identities between elements in the
609 // argument list here.
612 case Instruction::And:
613 case Instruction::Or:
614 case Instruction::Xor:
615 // Scan the operand lists looking for X and ~X pairs, along with X,X pairs.
616 // If we find any, we can simplify the expression. X&~X == 0, X|~X == -1.
617 for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
618 // First, check for X and ~X in the operand list.
619 assert(i < Ops.size());
620 if (BinaryOperator::isNot(Ops[i].Op)) { // Cannot occur for ^.
621 Value *X = BinaryOperator::getNotArgument(Ops[i].Op);
622 unsigned FoundX = FindInOperandList(Ops, i, X);
624 if (Opcode == Instruction::And) { // ...&X&~X = 0
626 return Context->getNullValue(X->getType());
627 } else if (Opcode == Instruction::Or) { // ...|X|~X = -1
629 return Context->getAllOnesValue(X->getType());
634 // Next, check for duplicate pairs of values, which we assume are next to
635 // each other, due to our sorting criteria.
636 assert(i < Ops.size());
637 if (i+1 != Ops.size() && Ops[i+1].Op == Ops[i].Op) {
638 if (Opcode == Instruction::And || Opcode == Instruction::Or) {
639 // Drop duplicate values.
640 Ops.erase(Ops.begin()+i);
642 IterateOptimization = true;
645 assert(Opcode == Instruction::Xor);
648 return Context->getNullValue(Ops[0].Op->getType());
651 Ops.erase(Ops.begin()+i, Ops.begin()+i+2);
653 IterateOptimization = true;
660 case Instruction::Add:
661 // Scan the operand lists looking for X and -X pairs. If we find any, we
662 // can simplify the expression. X+-X == 0.
663 for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
664 assert(i < Ops.size());
665 // Check for X and -X in the operand list.
666 if (BinaryOperator::isNeg(Ops[i].Op)) {
667 Value *X = BinaryOperator::getNegArgument(Ops[i].Op);
668 unsigned FoundX = FindInOperandList(Ops, i, X);
670 // Remove X and -X from the operand list.
671 if (Ops.size() == 2) {
673 return Context->getNullValue(X->getType());
675 Ops.erase(Ops.begin()+i);
679 --i; // Need to back up an extra one.
680 Ops.erase(Ops.begin()+FoundX);
681 IterateOptimization = true;
683 --i; // Revisit element.
684 e -= 2; // Removed two elements.
691 // Scan the operand list, checking to see if there are any common factors
692 // between operands. Consider something like A*A+A*B*C+D. We would like to
693 // reassociate this to A*(A+B*C)+D, which reduces the number of multiplies.
694 // To efficiently find this, we count the number of times a factor occurs
695 // for any ADD operands that are MULs.
696 std::map<Value*, unsigned> FactorOccurrences;
698 Value *MaxOccVal = 0;
699 for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
700 if (BinaryOperator *BOp = dyn_cast<BinaryOperator>(Ops[i].Op)) {
701 if (BOp->getOpcode() == Instruction::Mul && BOp->use_empty()) {
702 // Compute all of the factors of this added value.
703 std::vector<Value*> Factors;
704 FindSingleUseMultiplyFactors(BOp, Factors);
705 assert(Factors.size() > 1 && "Bad linearize!");
707 // Add one to FactorOccurrences for each unique factor in this op.
708 if (Factors.size() == 2) {
709 unsigned Occ = ++FactorOccurrences[Factors[0]];
710 if (Occ > MaxOcc) { MaxOcc = Occ; MaxOccVal = Factors[0]; }
711 if (Factors[0] != Factors[1]) { // Don't double count A*A.
712 Occ = ++FactorOccurrences[Factors[1]];
713 if (Occ > MaxOcc) { MaxOcc = Occ; MaxOccVal = Factors[1]; }
716 std::set<Value*> Duplicates;
717 for (unsigned i = 0, e = Factors.size(); i != e; ++i) {
718 if (Duplicates.insert(Factors[i]).second) {
719 unsigned Occ = ++FactorOccurrences[Factors[i]];
720 if (Occ > MaxOcc) { MaxOcc = Occ; MaxOccVal = Factors[i]; }
728 // If any factor occurred more than one time, we can pull it out.
730 DOUT << "\nFACTORING [" << MaxOcc << "]: " << *MaxOccVal << "\n";
732 // Create a new instruction that uses the MaxOccVal twice. If we don't do
733 // this, we could otherwise run into situations where removing a factor
734 // from an expression will drop a use of maxocc, and this can cause
735 // RemoveFactorFromExpression on successive values to behave differently.
736 Instruction *DummyInst = BinaryOperator::CreateAdd(MaxOccVal, MaxOccVal);
737 std::vector<Value*> NewMulOps;
738 for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
739 if (Value *V = RemoveFactorFromExpression(Ops[i].Op, MaxOccVal)) {
740 NewMulOps.push_back(V);
741 Ops.erase(Ops.begin()+i);
746 // No need for extra uses anymore.
749 unsigned NumAddedValues = NewMulOps.size();
750 Value *V = EmitAddTreeOfValues(I, NewMulOps);
751 Value *V2 = BinaryOperator::CreateMul(V, MaxOccVal, "tmp", I);
753 // Now that we have inserted V and its sole use, optimize it. This allows
754 // us to handle cases that require multiple factoring steps, such as this:
755 // A*A*B + A*A*C --> A*(A*B+A*C) --> A*(A*(B+C))
756 if (NumAddedValues > 1)
757 ReassociateExpression(cast<BinaryOperator>(V));
764 // Add the new value to the list of things being added.
765 Ops.insert(Ops.begin(), ValueEntry(getRank(V2), V2));
767 // Rewrite the tree so that there is now a use of V.
768 RewriteExprTree(I, Ops);
769 return OptimizeExpression(I, Ops);
772 //case Instruction::Mul:
775 if (IterateOptimization)
776 return OptimizeExpression(I, Ops);
781 /// ReassociateBB - Inspect all of the instructions in this basic block,
782 /// reassociating them as we go.
783 void Reassociate::ReassociateBB(BasicBlock *BB) {
784 for (BasicBlock::iterator BBI = BB->begin(); BBI != BB->end(); ) {
785 Instruction *BI = BBI++;
786 if (BI->getOpcode() == Instruction::Shl &&
787 isa<ConstantInt>(BI->getOperand(1)))
788 if (Instruction *NI = ConvertShiftToMul(BI, ValueRankMap, Context)) {
793 // Reject cases where it is pointless to do this.
794 if (!isa<BinaryOperator>(BI) || BI->getType()->isFloatingPoint() ||
795 isa<VectorType>(BI->getType()))
796 continue; // Floating point ops are not associative.
798 // If this is a subtract instruction which is not already in negate form,
799 // see if we can convert it to X+-Y.
800 if (BI->getOpcode() == Instruction::Sub) {
801 if (ShouldBreakUpSubtract(Context, BI)) {
802 BI = BreakUpSubtract(Context, BI, ValueRankMap);
804 } else if (BinaryOperator::isNeg(BI)) {
805 // Otherwise, this is a negation. See if the operand is a multiply tree
806 // and if this is not an inner node of a multiply tree.
807 if (isReassociableOp(BI->getOperand(1), Instruction::Mul) &&
809 !isReassociableOp(BI->use_back(), Instruction::Mul))) {
810 BI = LowerNegateToMultiply(BI, ValueRankMap, Context);
816 // If this instruction is a commutative binary operator, process it.
817 if (!BI->isAssociative()) continue;
818 BinaryOperator *I = cast<BinaryOperator>(BI);
820 // If this is an interior node of a reassociable tree, ignore it until we
821 // get to the root of the tree, to avoid N^2 analysis.
822 if (I->hasOneUse() && isReassociableOp(I->use_back(), I->getOpcode()))
825 // If this is an add tree that is used by a sub instruction, ignore it
826 // until we process the subtract.
827 if (I->hasOneUse() && I->getOpcode() == Instruction::Add &&
828 cast<Instruction>(I->use_back())->getOpcode() == Instruction::Sub)
831 ReassociateExpression(I);
835 void Reassociate::ReassociateExpression(BinaryOperator *I) {
837 // First, walk the expression tree, linearizing the tree, collecting
838 std::vector<ValueEntry> Ops;
839 LinearizeExprTree(I, Ops);
841 DOUT << "RAIn:\t"; DEBUG(PrintOps(I, Ops)); DOUT << "\n";
843 // Now that we have linearized the tree to a list and have gathered all of
844 // the operands and their ranks, sort the operands by their rank. Use a
845 // stable_sort so that values with equal ranks will have their relative
846 // positions maintained (and so the compiler is deterministic). Note that
847 // this sorts so that the highest ranking values end up at the beginning of
849 std::stable_sort(Ops.begin(), Ops.end());
851 // OptimizeExpression - Now that we have the expression tree in a convenient
852 // sorted form, optimize it globally if possible.
853 if (Value *V = OptimizeExpression(I, Ops)) {
854 // This expression tree simplified to something that isn't a tree,
856 DOUT << "Reassoc to scalar: " << *V << "\n";
857 I->replaceAllUsesWith(V);
858 RemoveDeadBinaryOp(I);
862 // We want to sink immediates as deeply as possible except in the case where
863 // this is a multiply tree used only by an add, and the immediate is a -1.
864 // In this case we reassociate to put the negation on the outside so that we
865 // can fold the negation into the add: (-X)*Y + Z -> Z-X*Y
866 if (I->getOpcode() == Instruction::Mul && I->hasOneUse() &&
867 cast<Instruction>(I->use_back())->getOpcode() == Instruction::Add &&
868 isa<ConstantInt>(Ops.back().Op) &&
869 cast<ConstantInt>(Ops.back().Op)->isAllOnesValue()) {
870 Ops.insert(Ops.begin(), Ops.back());
874 DOUT << "RAOut:\t"; DEBUG(PrintOps(I, Ops)); DOUT << "\n";
876 if (Ops.size() == 1) {
877 // This expression tree simplified to something that isn't a tree,
879 I->replaceAllUsesWith(Ops[0].Op);
880 RemoveDeadBinaryOp(I);
882 // Now that we ordered and optimized the expressions, splat them back into
883 // the expression tree, removing any unneeded nodes.
884 RewriteExprTree(I, Ops);
889 bool Reassociate::runOnFunction(Function &F) {
890 // Recalculate the rank map for F
894 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI)
897 // We are done with the rank map...
899 ValueRankMap.clear();