1 //===------- ABCD.cpp - Removes redundant conditional branches ------------===//
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 removes redundant branch instructions. This algorithm was
11 // described by Rastislav Bodik, Rajiv Gupta and Vivek Sarkar in their paper
12 // "ABCD: Eliminating Array Bounds Checks on Demand (2000)". The original
13 // Algorithm was created to remove array bound checks for strongly typed
14 // languages. This implementation expands the idea and removes any conditional
15 // branches that can be proved redundant, not only those used in array bound
16 // checks. With the SSI representation, each variable has a
17 // constraint. By analyzing these constraints we can prove that a branch is
18 // redundant. When a branch is proved redundant it means that
19 // one direction will always be taken; thus, we can change this branch into an
20 // unconditional jump.
21 // It is advisable to run SimplifyCFG and Aggressive Dead Code Elimination
22 // after ABCD to clean up the code.
23 // This implementation was created based on the implementation of the ABCD
24 // algorithm implemented for the compiler Jitrino.
26 //===----------------------------------------------------------------------===//
28 #define DEBUG_TYPE "abcd"
29 #include "llvm/ADT/DenseMap.h"
30 #include "llvm/ADT/OwningPtr.h"
31 #include "llvm/ADT/SmallPtrSet.h"
32 #include "llvm/ADT/Statistic.h"
33 #include "llvm/Constants.h"
34 #include "llvm/Function.h"
35 #include "llvm/Instructions.h"
36 #include "llvm/Pass.h"
37 #include "llvm/Support/raw_ostream.h"
38 #include "llvm/Support/Debug.h"
39 #include "llvm/Transforms/Scalar.h"
40 #include "llvm/Transforms/Utils/SSI.h"
44 STATISTIC(NumBranchTested, "Number of conditional branches analyzed");
45 STATISTIC(NumBranchRemoved, "Number of conditional branches removed");
49 class ABCD : public FunctionPass {
51 static char ID; // Pass identification, replacement for typeid.
52 ABCD() : FunctionPass(&ID) {}
54 void getAnalysisUsage(AnalysisUsage &AU) const {
55 AU.addRequired<SSI>();
58 bool runOnFunction(Function &F);
61 /// Keep track of whether we've modified the program yet.
70 typedef ProveResult (*meet_function)(ProveResult, ProveResult);
71 static ProveResult max(ProveResult res1, ProveResult res2) {
72 return (ProveResult) std::max(res1, res2);
74 static ProveResult min(ProveResult res1, ProveResult res2) {
75 return (ProveResult) std::min(res1, res2);
80 Bound(APInt v, bool upper) : value(v), upper_bound(upper) {}
81 Bound(const Bound *b, int cnst)
82 : value(b->value - cnst), upper_bound(b->upper_bound) {}
83 Bound(const Bound *b, const APInt &cnst)
84 : value(b->value - cnst), upper_bound(b->upper_bound) {}
86 /// Test if Bound is an upper bound
87 bool isUpperBound() const { return upper_bound; }
89 /// Get the bitwidth of this bound
90 int32_t getBitWidth() const { return value.getBitWidth(); }
92 /// Creates a Bound incrementing the one received
93 static Bound *createIncrement(const Bound *b) {
94 return new Bound(b->isUpperBound() ? b->value+1 : b->value-1,
98 /// Creates a Bound decrementing the one received
99 static Bound *createDecrement(const Bound *b) {
100 return new Bound(b->isUpperBound() ? b->value-1 : b->value+1,
104 /// Test if two bounds are equal
105 static bool eq(const Bound *a, const Bound *b) {
106 if (!a || !b) return false;
108 assert(a->isUpperBound() == b->isUpperBound());
109 return a->value == b->value;
112 /// Test if val is less than or equal to Bound b
113 static bool leq(APInt val, const Bound *b) {
114 if (!b) return false;
115 return b->isUpperBound() ? val.sle(b->value) : val.sge(b->value);
118 /// Test if Bound a is less then or equal to Bound
119 static bool leq(const Bound *a, const Bound *b) {
120 if (!a || !b) return false;
122 assert(a->isUpperBound() == b->isUpperBound());
123 return a->isUpperBound() ? a->value.sle(b->value) :
124 a->value.sge(b->value);
127 /// Test if Bound a is less then Bound b
128 static bool lt(const Bound *a, const Bound *b) {
129 if (!a || !b) return false;
131 assert(a->isUpperBound() == b->isUpperBound());
132 return a->isUpperBound() ? a->value.slt(b->value) :
133 a->value.sgt(b->value);
136 /// Test if Bound b is greater then or equal val
137 static bool geq(const Bound *b, APInt val) {
141 /// Test if Bound a is greater then or equal Bound b
142 static bool geq(const Bound *a, const Bound *b) {
151 /// This class is used to store results some parts of the graph,
152 /// so information does not need to be recalculated. The maximum false,
153 /// minimum true and minimum reduced results are stored
154 class MemoizedResultChart {
156 MemoizedResultChart() {}
157 MemoizedResultChart(const MemoizedResultChart &other) {
159 max_false.reset(new Bound(*other.max_false));
161 min_true.reset(new Bound(*other.min_true));
162 if (other.min_reduced)
163 min_reduced.reset(new Bound(*other.min_reduced));
166 /// Returns the max false
167 Bound *getFalse() const { return max_false.get(); }
169 /// Returns the min true
170 Bound *getTrue() const { return min_true.get(); }
172 /// Returns the min reduced
173 Bound *getReduced() const { return min_reduced.get(); }
175 /// Return the stored result for this bound
176 ProveResult getResult(const Bound *bound) const;
178 /// Stores a false found
179 void addFalse(const Bound *bound);
181 /// Stores a true found
182 void addTrue(const Bound *bound);
184 /// Stores a Reduced found
185 void addReduced(const Bound *bound);
187 /// Clears redundant reduced
188 /// If a min_true is smaller than a min_reduced then the min_reduced
189 /// is unnecessary and then removed. It also works for min_reduced
190 /// begin smaller than max_false.
191 void clearRedundantReduced();
200 OwningPtr<Bound> max_false, min_true, min_reduced;
203 /// This class stores the result found for a node of the graph,
204 /// so these results do not need to be recalculated, only searched for.
205 class MemoizedResult {
207 /// Test if there is true result stored from b to a
208 /// that is less then the bound
209 bool hasTrue(Value *b, const Bound *bound) const {
210 Bound *trueBound = map.lookup(b).getTrue();
211 return trueBound && Bound::leq(trueBound, bound);
214 /// Test if there is false result stored from b to a
215 /// that is less then the bound
216 bool hasFalse(Value *b, const Bound *bound) const {
217 Bound *falseBound = map.lookup(b).getFalse();
218 return falseBound && Bound::leq(falseBound, bound);
221 /// Test if there is reduced result stored from b to a
222 /// that is less then the bound
223 bool hasReduced(Value *b, const Bound *bound) const {
224 Bound *reducedBound = map.lookup(b).getReduced();
225 return reducedBound && Bound::leq(reducedBound, bound);
228 /// Returns the stored bound for b
229 ProveResult getBoundResult(Value *b, const Bound *bound) {
230 return map[b].getResult(bound);
235 DenseMapIterator<Value*, MemoizedResultChart> begin = map.begin();
236 DenseMapIterator<Value*, MemoizedResultChart> end = map.end();
237 for (; begin != end; ++begin) {
238 begin->second.clear();
243 /// Stores the bound found
244 void updateBound(Value *b, const Bound *bound, const ProveResult res);
247 // Maps a nod in the graph with its results found.
248 DenseMap<Value*, MemoizedResultChart> map;
251 /// This class represents an edge in the inequality graph used by the
252 /// ABCD algorithm. An edge connects node v to node u with a value c if
253 /// we could infer a constraint v <= u + c in the source program.
256 Edge(Value *V, APInt val, bool upper)
257 : vertex(V), value(val), upper_bound(upper) {}
259 Value *getVertex() const { return vertex; }
260 const APInt &getValue() const { return value; }
261 bool isUpperBound() const { return upper_bound; }
269 /// Weighted and Directed graph to represent constraints.
270 /// There is one type of constraint, a <= b + X, which will generate an
271 /// edge from b to a with weight X.
272 class InequalityGraph {
275 /// Adds an edge from V_from to V_to with weight value
276 void addEdge(Value *V_from, Value *V_to, APInt value, bool upper);
278 /// Test if there is a node V
279 bool hasNode(Value *V) const { return graph.count(V); }
281 /// Test if there is any edge from V in the upper direction
282 bool hasEdge(Value *V, bool upper) const;
284 /// Returns all edges pointed by vertex V
285 SmallPtrSet<Edge *, 16> getEdges(Value *V) const {
286 return graph.lookup(V);
289 /// Prints the graph in dot format.
290 /// Blue edges represent upper bound and Red lower bound.
291 void printGraph(raw_ostream &OS, Function &F) const {
303 DenseMap<Value *, SmallPtrSet<Edge *, 16> > graph;
305 /// Adds a Node to the graph.
306 DenseMap<Value *, SmallPtrSet<Edge *, 16> >::iterator addNode(Value *V) {
307 SmallPtrSet<Edge *, 16> p;
308 return graph.insert(std::make_pair(V, p)).first;
311 /// Prints the header of the dot file
312 void printHeader(raw_ostream &OS, Function &F) const;
314 /// Prints the footer of the dot file
315 void printFooter(raw_ostream &OS) const {
319 /// Prints the body of the dot file
320 void printBody(raw_ostream &OS) const;
322 /// Prints vertex source to the dot file
323 void printVertex(raw_ostream &OS, Value *source) const;
325 /// Prints the edge to the dot file
326 void printEdge(raw_ostream &OS, Value *source, Edge *edge) const;
328 void printName(raw_ostream &OS, Value *info) const;
331 /// Iterates through all BasicBlocks, if the Terminator Instruction
332 /// uses an Comparator Instruction, all operands of this comparator
333 /// are sent to be transformed to SSI. Only Instruction operands are
335 void createSSI(Function &F);
337 /// Creates the graphs for this function.
338 /// It will look for all comparators used in branches, and create them.
339 /// These comparators will create constraints for any instruction as an
341 void executeABCD(Function &F);
343 /// Seeks redundancies in the comparator instruction CI.
344 /// If the ABCD algorithm can prove that the comparator CI always
345 /// takes one way, then the Terminator Instruction TI is substituted from
346 /// a conditional branch to a unconditional one.
347 /// This code basically receives a comparator, and verifies which kind of
348 /// instruction it is. Depending on the kind of instruction, we use different
349 /// strategies to prove its redundancy.
350 void seekRedundancy(ICmpInst *ICI, TerminatorInst *TI);
352 /// Substitutes Terminator Instruction TI, that is a conditional branch,
353 /// with one unconditional branch. Succ_edge determines if the new
354 /// unconditional edge will be the first or second edge of the former TI
356 void removeRedundancy(TerminatorInst *TI, bool Succ_edge);
358 /// When an conditional branch is removed, the BasicBlock that is no longer
359 /// reachable will have problems in phi functions. This method fixes these
360 /// phis removing the former BasicBlock from the list of incoming BasicBlocks
361 /// of all phis. In case the phi remains with no predecessor it will be
362 /// marked to be removed later.
363 void fixPhi(BasicBlock *BB, BasicBlock *Succ);
365 /// Removes phis that have no predecessor
368 /// Creates constraints for Instructions.
369 /// If the constraint for this instruction has already been created
371 void createConstraintInstruction(Instruction *I);
373 /// Creates constraints for Binary Operators.
374 /// It will create constraints only for addition and subtraction,
375 /// the other binary operations are not treated by ABCD.
376 /// For additions in the form a = b + X and a = X + b, where X is a constant,
377 /// the constraint a <= b + X can be obtained. For this constraint, an edge
378 /// a->b with weight X is added to the lower bound graph, and an edge
379 /// b->a with weight -X is added to the upper bound graph.
380 /// Only subtractions in the format a = b - X is used by ABCD.
381 /// Edges are created using the same semantic as addition.
382 void createConstraintBinaryOperator(BinaryOperator *BO);
384 /// Creates constraints for Comparator Instructions.
385 /// Only comparators that have any of the following operators
386 /// are used to create constraints: >=, >, <=, <. And only if
387 /// at least one operand is an Instruction. In a Comparator Instruction
388 /// a op b, there will be 4 sigma functions a_t, a_f, b_t and b_f. Where
389 /// t and f represent sigma for operands in true and false branches. The
390 /// following constraints can be obtained. a_t <= a, a_f <= a, b_t <= b and
391 /// b_f <= b. There are two more constraints that depend on the operator.
392 /// For the operator <= : a_t <= b_t and b_f <= a_f-1
393 /// For the operator < : a_t <= b_t-1 and b_f <= a_f
394 /// For the operator >= : b_t <= a_t and a_f <= b_f-1
395 /// For the operator > : b_t <= a_t-1 and a_f <= b_f
396 void createConstraintCmpInst(ICmpInst *ICI, TerminatorInst *TI);
398 /// Creates constraints for PHI nodes.
399 /// In a PHI node a = phi(b,c) we can create the constraint
400 /// a<= max(b,c). With this constraint there will be the edges,
401 /// b->a and c->a with weight 0 in the lower bound graph, and the edges
402 /// a->b and a->c with weight 0 in the upper bound graph.
403 void createConstraintPHINode(PHINode *PN);
405 /// Given a binary operator, we are only interest in the case
406 /// that one operand is an Instruction and the other is a ConstantInt. In
407 /// this case the method returns true, otherwise false. It also obtains the
408 /// Instruction and ConstantInt from the BinaryOperator and returns it.
409 bool createBinaryOperatorInfo(BinaryOperator *BO, Instruction **I1,
410 Instruction **I2, ConstantInt **C1,
413 /// This method creates a constraint between a Sigma and an Instruction.
414 /// These constraints are created as soon as we find a comparator that uses a
416 void createConstraintSigInst(Instruction *I_op, BasicBlock *BB_succ_t,
417 BasicBlock *BB_succ_f, PHINode **SIG_op_t,
420 /// If PN_op1 and PN_o2 are different from NULL, create a constraint
421 /// PN_op2 -> PN_op1 with value. In case any of them is NULL, replace
422 /// with the respective V_op#, if V_op# is a ConstantInt.
423 void createConstraintSigSig(PHINode *SIG_op1, PHINode *SIG_op2,
424 ConstantInt *V_op1, ConstantInt *V_op2,
427 /// Returns the sigma representing the Instruction I in BasicBlock BB.
428 /// Returns NULL in case there is no sigma for this Instruction in this
429 /// Basic Block. This methods assume that sigmas are the first instructions
430 /// in a block, and that there can be only two sigmas in a block. So it will
431 /// only look on the first two instructions of BasicBlock BB.
432 PHINode *findSigma(BasicBlock *BB, Instruction *I);
434 /// Original ABCD algorithm to prove redundant checks.
435 /// This implementation works on any kind of inequality branch.
436 bool demandProve(Value *a, Value *b, int c, bool upper_bound);
438 /// Prove that distance between b and a is <= bound
439 ProveResult prove(Value *a, Value *b, const Bound &bound, unsigned level);
441 /// Updates the distance value for a and b
442 void updateMemDistance(Value *a, Value *b, const Bound *bound, unsigned level,
445 InequalityGraph inequality_graph;
446 MemoizedResult mem_result;
447 DenseMap<Value*, const Bound*> active;
448 SmallPtrSet<Value*, 16> created;
449 SmallVector<PHINode *, 16> phis_to_remove;
452 } // end anonymous namespace.
455 static RegisterPass<ABCD> X("abcd", "ABCD: Eliminating Array Bounds Checks on Demand");
458 bool ABCD::runOnFunction(Function &F) {
462 DEBUG(inequality_graph.printGraph(dbgs(), F));
465 inequality_graph.clear();
469 phis_to_remove.clear();
473 /// Iterates through all BasicBlocks, if the Terminator Instruction
474 /// uses an Comparator Instruction, all operands of this comparator
475 /// are sent to be transformed to SSI. Only Instruction operands are
477 void ABCD::createSSI(Function &F) {
478 SSI *ssi = &getAnalysis<SSI>();
480 SmallVector<Instruction *, 16> Insts;
482 for (Function::iterator begin = F.begin(), end = F.end();
483 begin != end; ++begin) {
484 BasicBlock *BB = begin;
485 TerminatorInst *TI = BB->getTerminator();
486 if (TI->getNumOperands() == 0)
489 if (ICmpInst *ICI = dyn_cast<ICmpInst>(TI->getOperand(0))) {
490 if (Instruction *I = dyn_cast<Instruction>(ICI->getOperand(0))) {
491 modified = true; // XXX: but yet createSSI might do nothing
494 if (Instruction *I = dyn_cast<Instruction>(ICI->getOperand(1))) {
500 ssi->createSSI(Insts);
503 /// Creates the graphs for this function.
504 /// It will look for all comparators used in branches, and create them.
505 /// These comparators will create constraints for any instruction as an
507 void ABCD::executeABCD(Function &F) {
508 for (Function::iterator begin = F.begin(), end = F.end();
509 begin != end; ++begin) {
510 BasicBlock *BB = begin;
511 TerminatorInst *TI = BB->getTerminator();
512 if (TI->getNumOperands() == 0)
515 ICmpInst *ICI = dyn_cast<ICmpInst>(TI->getOperand(0));
516 if (!ICI || !ICI->getOperand(0)->getType()->isIntegerTy())
519 createConstraintCmpInst(ICI, TI);
520 seekRedundancy(ICI, TI);
524 /// Seeks redundancies in the comparator instruction CI.
525 /// If the ABCD algorithm can prove that the comparator CI always
526 /// takes one way, then the Terminator Instruction TI is substituted from
527 /// a conditional branch to a unconditional one.
528 /// This code basically receives a comparator, and verifies which kind of
529 /// instruction it is. Depending on the kind of instruction, we use different
530 /// strategies to prove its redundancy.
531 void ABCD::seekRedundancy(ICmpInst *ICI, TerminatorInst *TI) {
532 CmpInst::Predicate Pred = ICI->getPredicate();
534 Value *source, *dest;
535 int distance1, distance2;
539 case CmpInst::ICMP_SGT: // signed greater than
545 case CmpInst::ICMP_SGE: // signed greater or equal
551 case CmpInst::ICMP_SLT: // signed less than
557 case CmpInst::ICMP_SLE: // signed less or equal
568 source = ICI->getOperand(0);
569 dest = ICI->getOperand(1);
570 if (demandProve(dest, source, distance1, upper)) {
571 removeRedundancy(TI, true);
572 } else if (demandProve(dest, source, distance2, !upper)) {
573 removeRedundancy(TI, false);
577 /// Substitutes Terminator Instruction TI, that is a conditional branch,
578 /// with one unconditional branch. Succ_edge determines if the new
579 /// unconditional edge will be the first or second edge of the former TI
581 void ABCD::removeRedundancy(TerminatorInst *TI, bool Succ_edge) {
584 Succ = TI->getSuccessor(0);
585 fixPhi(TI->getParent(), TI->getSuccessor(1));
587 Succ = TI->getSuccessor(1);
588 fixPhi(TI->getParent(), TI->getSuccessor(0));
591 BranchInst::Create(Succ, TI);
592 TI->eraseFromParent(); // XXX: invoke
597 /// When an conditional branch is removed, the BasicBlock that is no longer
598 /// reachable will have problems in phi functions. This method fixes these
599 /// phis removing the former BasicBlock from the list of incoming BasicBlocks
600 /// of all phis. In case the phi remains with no predecessor it will be
601 /// marked to be removed later.
602 void ABCD::fixPhi(BasicBlock *BB, BasicBlock *Succ) {
603 BasicBlock::iterator begin = Succ->begin();
604 while (PHINode *PN = dyn_cast<PHINode>(begin++)) {
605 PN->removeIncomingValue(BB, false);
606 if (PN->getNumIncomingValues() == 0)
607 phis_to_remove.push_back(PN);
611 /// Removes phis that have no predecessor
612 void ABCD::removePhis() {
613 for (unsigned i = 0, e = phis_to_remove.size(); i != e; ++i) {
614 PHINode *PN = phis_to_remove[i];
615 PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
616 PN->eraseFromParent();
620 /// Creates constraints for Instructions.
621 /// If the constraint for this instruction has already been created
623 void ABCD::createConstraintInstruction(Instruction *I) {
624 // Test if this instruction has not been created before
625 if (created.insert(I)) {
626 if (BinaryOperator *BO = dyn_cast<BinaryOperator>(I)) {
627 createConstraintBinaryOperator(BO);
628 } else if (PHINode *PN = dyn_cast<PHINode>(I)) {
629 createConstraintPHINode(PN);
634 /// Creates constraints for Binary Operators.
635 /// It will create constraints only for addition and subtraction,
636 /// the other binary operations are not treated by ABCD.
637 /// For additions in the form a = b + X and a = X + b, where X is a constant,
638 /// the constraint a <= b + X can be obtained. For this constraint, an edge
639 /// a->b with weight X is added to the lower bound graph, and an edge
640 /// b->a with weight -X is added to the upper bound graph.
641 /// Only subtractions in the format a = b - X is used by ABCD.
642 /// Edges are created using the same semantic as addition.
643 void ABCD::createConstraintBinaryOperator(BinaryOperator *BO) {
644 Instruction *I1 = NULL, *I2 = NULL;
645 ConstantInt *CI1 = NULL, *CI2 = NULL;
647 // Test if an operand is an Instruction and the other is a Constant
648 if (!createBinaryOperatorInfo(BO, &I1, &I2, &CI1, &CI2))
654 switch (BO->getOpcode()) {
655 case Instruction::Add:
658 value = CI2->getValue();
661 value = CI1->getValue();
665 case Instruction::Sub:
666 // Instructions like a = X-b, where X is a constant are not represented
672 value = -CI2->getValue();
679 inequality_graph.addEdge(I, BO, value, true);
680 inequality_graph.addEdge(BO, I, -value, false);
681 createConstraintInstruction(I);
684 /// Given a binary operator, we are only interest in the case
685 /// that one operand is an Instruction and the other is a ConstantInt. In
686 /// this case the method returns true, otherwise false. It also obtains the
687 /// Instruction and ConstantInt from the BinaryOperator and returns it.
688 bool ABCD::createBinaryOperatorInfo(BinaryOperator *BO, Instruction **I1,
689 Instruction **I2, ConstantInt **C1,
691 Value *op1 = BO->getOperand(0);
692 Value *op2 = BO->getOperand(1);
694 if ((*I1 = dyn_cast<Instruction>(op1))) {
695 if ((*C2 = dyn_cast<ConstantInt>(op2)))
696 return true; // First is Instruction and second ConstantInt
698 return false; // Both are Instruction
700 if ((*C1 = dyn_cast<ConstantInt>(op1)) &&
701 (*I2 = dyn_cast<Instruction>(op2)))
702 return true; // First is ConstantInt and second Instruction
704 return false; // Both are not Instruction
708 /// Creates constraints for Comparator Instructions.
709 /// Only comparators that have any of the following operators
710 /// are used to create constraints: >=, >, <=, <. And only if
711 /// at least one operand is an Instruction. In a Comparator Instruction
712 /// a op b, there will be 4 sigma functions a_t, a_f, b_t and b_f. Where
713 /// t and f represent sigma for operands in true and false branches. The
714 /// following constraints can be obtained. a_t <= a, a_f <= a, b_t <= b and
715 /// b_f <= b. There are two more constraints that depend on the operator.
716 /// For the operator <= : a_t <= b_t and b_f <= a_f-1
717 /// For the operator < : a_t <= b_t-1 and b_f <= a_f
718 /// For the operator >= : b_t <= a_t and a_f <= b_f-1
719 /// For the operator > : b_t <= a_t-1 and a_f <= b_f
720 void ABCD::createConstraintCmpInst(ICmpInst *ICI, TerminatorInst *TI) {
721 Value *V_op1 = ICI->getOperand(0);
722 Value *V_op2 = ICI->getOperand(1);
724 if (!V_op1->getType()->isIntegerTy())
727 Instruction *I_op1 = dyn_cast<Instruction>(V_op1);
728 Instruction *I_op2 = dyn_cast<Instruction>(V_op2);
730 // Test if at least one operand is an Instruction
731 if (!I_op1 && !I_op2)
734 BasicBlock *BB_succ_t = TI->getSuccessor(0);
735 BasicBlock *BB_succ_f = TI->getSuccessor(1);
737 PHINode *SIG_op1_t = NULL, *SIG_op1_f = NULL,
738 *SIG_op2_t = NULL, *SIG_op2_f = NULL;
740 createConstraintSigInst(I_op1, BB_succ_t, BB_succ_f, &SIG_op1_t, &SIG_op1_f);
741 createConstraintSigInst(I_op2, BB_succ_t, BB_succ_f, &SIG_op2_t, &SIG_op2_f);
743 int32_t width = cast<IntegerType>(V_op1->getType())->getBitWidth();
744 APInt MinusOne = APInt::getAllOnesValue(width);
745 APInt Zero = APInt::getNullValue(width);
747 CmpInst::Predicate Pred = ICI->getPredicate();
748 ConstantInt *CI1 = dyn_cast<ConstantInt>(V_op1);
749 ConstantInt *CI2 = dyn_cast<ConstantInt>(V_op2);
751 case CmpInst::ICMP_SGT: // signed greater than
752 createConstraintSigSig(SIG_op2_t, SIG_op1_t, CI2, CI1, MinusOne);
753 createConstraintSigSig(SIG_op1_f, SIG_op2_f, CI1, CI2, Zero);
756 case CmpInst::ICMP_SGE: // signed greater or equal
757 createConstraintSigSig(SIG_op2_t, SIG_op1_t, CI2, CI1, Zero);
758 createConstraintSigSig(SIG_op1_f, SIG_op2_f, CI1, CI2, MinusOne);
761 case CmpInst::ICMP_SLT: // signed less than
762 createConstraintSigSig(SIG_op1_t, SIG_op2_t, CI1, CI2, MinusOne);
763 createConstraintSigSig(SIG_op2_f, SIG_op1_f, CI2, CI1, Zero);
766 case CmpInst::ICMP_SLE: // signed less or equal
767 createConstraintSigSig(SIG_op1_t, SIG_op2_t, CI1, CI2, Zero);
768 createConstraintSigSig(SIG_op2_f, SIG_op1_f, CI2, CI1, MinusOne);
776 createConstraintInstruction(I_op1);
778 createConstraintInstruction(I_op2);
781 /// Creates constraints for PHI nodes.
782 /// In a PHI node a = phi(b,c) we can create the constraint
783 /// a<= max(b,c). With this constraint there will be the edges,
784 /// b->a and c->a with weight 0 in the lower bound graph, and the edges
785 /// a->b and a->c with weight 0 in the upper bound graph.
786 void ABCD::createConstraintPHINode(PHINode *PN) {
787 // FIXME: We really want to disallow sigma nodes, but I don't know the best
788 // way to detect the other than this.
789 if (PN->getNumOperands() == 2) return;
791 int32_t width = cast<IntegerType>(PN->getType())->getBitWidth();
792 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
793 Value *V = PN->getIncomingValue(i);
794 if (Instruction *I = dyn_cast<Instruction>(V)) {
795 createConstraintInstruction(I);
797 inequality_graph.addEdge(V, PN, APInt(width, 0), true);
798 inequality_graph.addEdge(V, PN, APInt(width, 0), false);
802 /// This method creates a constraint between a Sigma and an Instruction.
803 /// These constraints are created as soon as we find a comparator that uses a
805 void ABCD::createConstraintSigInst(Instruction *I_op, BasicBlock *BB_succ_t,
806 BasicBlock *BB_succ_f, PHINode **SIG_op_t,
807 PHINode **SIG_op_f) {
808 *SIG_op_t = findSigma(BB_succ_t, I_op);
809 *SIG_op_f = findSigma(BB_succ_f, I_op);
812 int32_t width = cast<IntegerType>((*SIG_op_t)->getType())->getBitWidth();
813 inequality_graph.addEdge(I_op, *SIG_op_t, APInt(width, 0), true);
814 inequality_graph.addEdge(*SIG_op_t, I_op, APInt(width, 0), false);
817 int32_t width = cast<IntegerType>((*SIG_op_f)->getType())->getBitWidth();
818 inequality_graph.addEdge(I_op, *SIG_op_f, APInt(width, 0), true);
819 inequality_graph.addEdge(*SIG_op_f, I_op, APInt(width, 0), false);
823 /// If PN_op1 and PN_o2 are different from NULL, create a constraint
824 /// PN_op2 -> PN_op1 with value. In case any of them is NULL, replace
825 /// with the respective V_op#, if V_op# is a ConstantInt.
826 void ABCD::createConstraintSigSig(PHINode *SIG_op1, PHINode *SIG_op2,
827 ConstantInt *V_op1, ConstantInt *V_op2,
829 if (SIG_op1 && SIG_op2) {
830 inequality_graph.addEdge(SIG_op2, SIG_op1, value, true);
831 inequality_graph.addEdge(SIG_op1, SIG_op2, -value, false);
832 } else if (SIG_op1 && V_op2) {
833 inequality_graph.addEdge(V_op2, SIG_op1, value, true);
834 inequality_graph.addEdge(SIG_op1, V_op2, -value, false);
835 } else if (SIG_op2 && V_op1) {
836 inequality_graph.addEdge(SIG_op2, V_op1, value, true);
837 inequality_graph.addEdge(V_op1, SIG_op2, -value, false);
841 /// Returns the sigma representing the Instruction I in BasicBlock BB.
842 /// Returns NULL in case there is no sigma for this Instruction in this
843 /// Basic Block. This methods assume that sigmas are the first instructions
844 /// in a block, and that there can be only two sigmas in a block. So it will
845 /// only look on the first two instructions of BasicBlock BB.
846 PHINode *ABCD::findSigma(BasicBlock *BB, Instruction *I) {
847 // BB has more than one predecessor, BB cannot have sigmas.
848 if (I == NULL || BB->getSinglePredecessor() == NULL)
851 BasicBlock::iterator begin = BB->begin();
852 BasicBlock::iterator end = BB->end();
854 for (unsigned i = 0; i < 2 && begin != end; ++i, ++begin) {
855 Instruction *I_succ = begin;
856 if (PHINode *PN = dyn_cast<PHINode>(I_succ))
857 if (PN->getIncomingValue(0) == I)
864 /// Original ABCD algorithm to prove redundant checks.
865 /// This implementation works on any kind of inequality branch.
866 bool ABCD::demandProve(Value *a, Value *b, int c, bool upper_bound) {
867 int32_t width = cast<IntegerType>(a->getType())->getBitWidth();
868 Bound bound(APInt(width, c), upper_bound);
873 ProveResult res = prove(a, b, bound, 0);
877 /// Prove that distance between b and a is <= bound
878 ABCD::ProveResult ABCD::prove(Value *a, Value *b, const Bound &bound,
880 // if (C[b-a<=e] == True for some e <= bound
881 // Same or stronger difference was already proven
882 if (mem_result.hasTrue(b, &bound))
885 // if (C[b-a<=e] == False for some e >= bound
886 // Same or weaker difference was already disproved
887 if (mem_result.hasFalse(b, &bound))
890 // if (C[b-a<=e] == Reduced for some e <= bound
891 // b is on a cycle that was reduced for same or stronger difference
892 if (mem_result.hasReduced(b, &bound))
895 // traversal reached the source vertex
896 if (a == b && Bound::geq(&bound, APInt(bound.getBitWidth(), 0, true)))
899 // if b has no predecessor then fail
900 if (!inequality_graph.hasEdge(b, bound.isUpperBound()))
903 // a cycle was encountered
904 if (active.count(b)) {
905 if (Bound::leq(active.lookup(b), &bound))
906 return Reduced; // a "harmless" cycle
908 return False; // an amplifying cycle
912 PHINode *PN = dyn_cast<PHINode>(b);
914 // Test if a Value is a Phi. If it is a PHINode with more than 1 incoming
915 // value, then it is a phi, if it has 1 incoming value it is a sigma.
916 if (PN && PN->getNumIncomingValues() > 1)
917 updateMemDistance(a, b, &bound, level, min);
919 updateMemDistance(a, b, &bound, level, max);
923 ABCD::ProveResult res = mem_result.getBoundResult(b, &bound);
927 /// Updates the distance value for a and b
928 void ABCD::updateMemDistance(Value *a, Value *b, const Bound *bound,
929 unsigned level, meet_function meet) {
930 ABCD::ProveResult res = (meet == max) ? False : True;
932 SmallPtrSet<Edge *, 16> Edges = inequality_graph.getEdges(b);
933 SmallPtrSet<Edge *, 16>::iterator begin = Edges.begin(), end = Edges.end();
935 for (; begin != end ; ++begin) {
936 if (((res >= Reduced) && (meet == max)) ||
937 ((res == False) && (meet == min))) {
941 if (in->isUpperBound() == bound->isUpperBound()) {
942 Value *succ = in->getVertex();
943 res = meet(res, prove(a, succ, Bound(bound, in->getValue()),
948 mem_result.updateBound(b, bound, res);
951 /// Return the stored result for this bound
952 ABCD::ProveResult ABCD::MemoizedResultChart::getResult(const Bound *bound)const{
953 if (max_false && Bound::leq(bound, max_false.get()))
955 if (min_true && Bound::leq(min_true.get(), bound))
957 if (min_reduced && Bound::leq(min_reduced.get(), bound))
962 /// Stores a false found
963 void ABCD::MemoizedResultChart::addFalse(const Bound *bound) {
964 if (!max_false || Bound::leq(max_false.get(), bound))
965 max_false.reset(new Bound(*bound));
967 if (Bound::eq(max_false.get(), min_reduced.get()))
968 min_reduced.reset(Bound::createIncrement(min_reduced.get()));
969 if (Bound::eq(max_false.get(), min_true.get()))
970 min_true.reset(Bound::createIncrement(min_true.get()));
971 if (Bound::eq(min_reduced.get(), min_true.get()))
973 clearRedundantReduced();
976 /// Stores a true found
977 void ABCD::MemoizedResultChart::addTrue(const Bound *bound) {
978 if (!min_true || Bound::leq(bound, min_true.get()))
979 min_true.reset(new Bound(*bound));
981 if (Bound::eq(min_true.get(), min_reduced.get()))
982 min_reduced.reset(Bound::createDecrement(min_reduced.get()));
983 if (Bound::eq(min_true.get(), max_false.get()))
984 max_false.reset(Bound::createDecrement(max_false.get()));
985 if (Bound::eq(max_false.get(), min_reduced.get()))
987 clearRedundantReduced();
990 /// Stores a Reduced found
991 void ABCD::MemoizedResultChart::addReduced(const Bound *bound) {
992 if (!min_reduced || Bound::leq(bound, min_reduced.get()))
993 min_reduced.reset(new Bound(*bound));
995 if (Bound::eq(min_reduced.get(), min_true.get()))
996 min_true.reset(Bound::createIncrement(min_true.get()));
997 if (Bound::eq(min_reduced.get(), max_false.get()))
998 max_false.reset(Bound::createDecrement(max_false.get()));
1001 /// Clears redundant reduced
1002 /// If a min_true is smaller than a min_reduced then the min_reduced
1003 /// is unnecessary and then removed. It also works for min_reduced
1004 /// begin smaller than max_false.
1005 void ABCD::MemoizedResultChart::clearRedundantReduced() {
1006 if (min_true && min_reduced && Bound::lt(min_true.get(), min_reduced.get()))
1007 min_reduced.reset();
1008 if (max_false && min_reduced && Bound::lt(min_reduced.get(), max_false.get()))
1009 min_reduced.reset();
1012 /// Stores the bound found
1013 void ABCD::MemoizedResult::updateBound(Value *b, const Bound *bound,
1014 const ProveResult res) {
1016 map[b].addFalse(bound);
1017 } else if (res == True) {
1018 map[b].addTrue(bound);
1020 map[b].addReduced(bound);
1024 /// Adds an edge from V_from to V_to with weight value
1025 void ABCD::InequalityGraph::addEdge(Value *V_to, Value *V_from,
1026 APInt value, bool upper) {
1027 assert(V_from->getType() == V_to->getType());
1028 assert(cast<IntegerType>(V_from->getType())->getBitWidth() ==
1029 value.getBitWidth());
1031 DenseMap<Value *, SmallPtrSet<Edge *, 16> >::iterator from;
1032 from = addNode(V_from);
1033 from->second.insert(new Edge(V_to, value, upper));
1036 /// Test if there is any edge from V in the upper direction
1037 bool ABCD::InequalityGraph::hasEdge(Value *V, bool upper) const {
1038 SmallPtrSet<Edge *, 16> it = graph.lookup(V);
1040 SmallPtrSet<Edge *, 16>::iterator begin = it.begin();
1041 SmallPtrSet<Edge *, 16>::iterator end = it.end();
1042 for (; begin != end; ++begin) {
1043 if ((*begin)->isUpperBound() == upper) {
1050 /// Prints the header of the dot file
1051 void ABCD::InequalityGraph::printHeader(raw_ostream &OS, Function &F) const {
1052 OS << "digraph dotgraph {\n";
1053 OS << "label=\"Inequality Graph for \'";
1054 OS << F.getNameStr() << "\' function\";\n";
1055 OS << "node [shape=record,fontname=\"Times-Roman\",fontsize=14];\n";
1058 /// Prints the body of the dot file
1059 void ABCD::InequalityGraph::printBody(raw_ostream &OS) const {
1060 DenseMap<Value *, SmallPtrSet<Edge *, 16> >::const_iterator begin =
1061 graph.begin(), end = graph.end();
1063 for (; begin != end ; ++begin) {
1064 SmallPtrSet<Edge *, 16>::iterator begin_par =
1065 begin->second.begin(), end_par = begin->second.end();
1066 Value *source = begin->first;
1068 printVertex(OS, source);
1070 for (; begin_par != end_par ; ++begin_par) {
1071 Edge *edge = *begin_par;
1072 printEdge(OS, source, edge);
1077 /// Prints vertex source to the dot file
1079 void ABCD::InequalityGraph::printVertex(raw_ostream &OS, Value *source) const {
1081 printName(OS, source);
1083 OS << " [label=\"{";
1084 printName(OS, source);
1088 /// Prints the edge to the dot file
1089 void ABCD::InequalityGraph::printEdge(raw_ostream &OS, Value *source,
1091 Value *dest = edge->getVertex();
1092 APInt value = edge->getValue();
1093 bool upper = edge->isUpperBound();
1096 printName(OS, source);
1100 printName(OS, dest);
1102 OS << " [label=\"" << value << "\"";
1104 OS << "color=\"blue\"";
1106 OS << "color=\"red\"";
1111 void ABCD::InequalityGraph::printName(raw_ostream &OS, Value *info) const {
1112 if (ConstantInt *CI = dyn_cast<ConstantInt>(info)) {
1115 if (!info->hasName()) {
1118 OS << info->getNameStr();
1122 /// createABCDPass - The public interface to this file...
1123 FunctionPass *llvm::createABCDPass() {