1 //===- CorrelatedExprs.cpp - Pass to detect and eliminated c.e.'s ---------===//
3 // Correlated Expression Elimination propogates information from conditional
4 // branches to blocks dominated by destinations of the branch. It propogates
5 // information from the condition check itself into the body of the branch,
6 // allowing transformations like these for example:
9 // ... 4*i; // constant propogation
13 // X = M-N; // = M-M == 0;
15 // This is called Correlated Expression Elimination because we eliminate or
16 // simplify expressions that are correlated with the direction of a branch. In
17 // this way we use static information to give us some information about the
18 // dynamic value of a variable.
20 //===----------------------------------------------------------------------===//
22 #include "llvm/Transforms/Scalar.h"
23 #include "llvm/Pass.h"
24 #include "llvm/Function.h"
25 #include "llvm/iTerminators.h"
26 #include "llvm/iPHINode.h"
27 #include "llvm/iOperators.h"
28 #include "llvm/ConstantHandling.h"
29 #include "llvm/Assembly/Writer.h"
30 #include "llvm/Analysis/Dominators.h"
31 #include "llvm/Transforms/Utils/Local.h"
32 #include "llvm/Support/ConstantRange.h"
33 #include "llvm/Support/CFG.h"
34 #include "Support/PostOrderIterator.h"
35 #include "Support/StatisticReporter.h"
39 Statistic<>NumSetCCRemoved("cee\t\t- Number of setcc instruction eliminated");
40 Statistic<>NumOperandsCann("cee\t\t- Number of operands cannonicalized");
41 Statistic<>BranchRevectors("cee\t\t- Number of branches revectored");
45 Value *Val; // Relation to what value?
46 Instruction::BinaryOps Rel; // SetCC relation, or Add if no information
48 Relation(Value *V) : Val(V), Rel(Instruction::Add) {}
49 bool operator<(const Relation &R) const { return Val < R.Val; }
50 Value *getValue() const { return Val; }
51 Instruction::BinaryOps getRelation() const { return Rel; }
53 // contradicts - Return true if the relationship specified by the operand
54 // contradicts already known information.
56 bool contradicts(Instruction::BinaryOps Rel, const ValueInfo &VI) const;
58 // incorporate - Incorporate information in the argument into this relation
59 // entry. This assumes that the information doesn't contradict itself. If
60 // any new information is gained, true is returned, otherwise false is
61 // returned to indicate that nothing was updated.
63 bool incorporate(Instruction::BinaryOps Rel, ValueInfo &VI);
65 // KnownResult - Whether or not this condition determines the result of a
66 // setcc in the program. False & True are intentionally 0 & 1 so we can
67 // convert to bool by casting after checking for unknown.
69 enum KnownResult { KnownFalse = 0, KnownTrue = 1, Unknown = 2 };
71 // getImpliedResult - If this relationship between two values implies that
72 // the specified relationship is true or false, return that. If we cannot
73 // determine the result required, return Unknown.
75 KnownResult getImpliedResult(Instruction::BinaryOps Rel) const;
77 // print - Output this relation to the specified stream
78 void print(std::ostream &OS) const;
83 // ValueInfo - One instance of this record exists for every value with
84 // relationships between other values. It keeps track of all of the
85 // relationships to other values in the program (specified with Relation) that
86 // are known to be valid in a region.
89 // RelationShips - this value is know to have the specified relationships to
90 // other values. There can only be one entry per value, and this list is
91 // kept sorted by the Val field.
92 std::vector<Relation> Relationships;
94 // If information about this value is known or propogated from constant
95 // expressions, this range contains the possible values this value may hold.
98 // If we find that this value is equal to another value that has a lower
99 // rank, this value is used as it's replacement.
103 ValueInfo(const Type *Ty)
104 : Bounds(Ty->isIntegral() ? Ty : Type::IntTy), Replacement(0) {}
106 // getBounds() - Return the constant bounds of the value...
107 const ConstantRange &getBounds() const { return Bounds; }
108 ConstantRange &getBounds() { return Bounds; }
110 const std::vector<Relation> &getRelationships() { return Relationships; }
112 // getReplacement - Return the value this value is to be replaced with if it
113 // exists, otherwise return null.
115 Value *getReplacement() const { return Replacement; }
117 // setReplacement - Used by the replacement calculation pass to figure out
118 // what to replace this value with, if anything.
120 void setReplacement(Value *Repl) { Replacement = Repl; }
122 // getRelation - return the relationship entry for the specified value.
123 // This can invalidate references to other Relation's, so use it carefully.
125 Relation &getRelation(Value *V) {
126 // Binary search for V's entry...
127 std::vector<Relation>::iterator I =
128 std::lower_bound(Relationships.begin(), Relationships.end(), V);
130 // If we found the entry, return it...
131 if (I != Relationships.end() && I->getValue() == V)
134 // Insert and return the new relationship...
135 return *Relationships.insert(I, V);
138 const Relation *requestRelation(Value *V) const {
139 // Binary search for V's entry...
140 std::vector<Relation>::const_iterator I =
141 std::lower_bound(Relationships.begin(), Relationships.end(), V);
142 if (I != Relationships.end() && I->getValue() == V)
147 // print - Output information about this value relation...
148 void print(std::ostream &OS, Value *V) const;
152 // RegionInfo - Keeps track of all of the value relationships for a region. A
153 // region is the are dominated by a basic block. RegionInfo's keep track of
154 // the RegionInfo for their dominator, because anything known in a dominator
155 // is known to be true in a dominated block as well.
160 // ValueMap - Tracks the ValueInformation known for this region
161 typedef std::map<Value*, ValueInfo> ValueMapTy;
164 RegionInfo(BasicBlock *bb) : BB(bb) {}
166 // getEntryBlock - Return the block that dominates all of the members of
168 BasicBlock *getEntryBlock() const { return BB; }
170 const RegionInfo &operator=(const RegionInfo &RI) {
171 ValueMap = RI.ValueMap;
175 // print - Output information about this region...
176 void print(std::ostream &OS) const;
178 // Allow external access.
179 typedef ValueMapTy::iterator iterator;
180 iterator begin() { return ValueMap.begin(); }
181 iterator end() { return ValueMap.end(); }
183 ValueInfo &getValueInfo(Value *V) {
184 ValueMapTy::iterator I = ValueMap.lower_bound(V);
185 if (I != ValueMap.end() && I->first == V) return I->second;
186 return ValueMap.insert(I, std::make_pair(V, V->getType()))->second;
189 const ValueInfo *requestValueInfo(Value *V) const {
190 ValueMapTy::const_iterator I = ValueMap.find(V);
191 if (I != ValueMap.end()) return &I->second;
196 /// CEE - Correlated Expression Elimination
197 class CEE : public FunctionPass {
198 std::map<Value*, unsigned> RankMap;
199 std::map<BasicBlock*, RegionInfo> RegionInfoMap;
203 virtual bool runOnFunction(Function &F);
205 // We don't modify the program, so we preserve all analyses
206 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
208 AU.addRequired<DominatorSet>();
209 AU.addRequired<DominatorTree>();
212 // print - Implement the standard print form to print out analysis
214 virtual void print(std::ostream &O, const Module *M) const;
217 RegionInfo &getRegionInfo(BasicBlock *BB) {
218 std::map<BasicBlock*, RegionInfo>::iterator I
219 = RegionInfoMap.lower_bound(BB);
220 if (I != RegionInfoMap.end() && I->first == BB) return I->second;
221 return RegionInfoMap.insert(I, std::make_pair(BB, BB))->second;
224 void BuildRankMap(Function &F);
225 unsigned getRank(Value *V) const {
226 if (isa<Constant>(V) || isa<GlobalValue>(V)) return 0;
227 std::map<Value*, unsigned>::const_iterator I = RankMap.find(V);
228 if (I != RankMap.end()) return I->second;
229 return 0; // Must be some other global thing
232 bool TransformRegion(BasicBlock *BB, std::set<BasicBlock*> &VisitedBlocks);
234 BasicBlock *isCorrelatedBranchBlock(BasicBlock *BB, RegionInfo &RI);
235 void PropogateBranchInfo(BranchInst *BI);
236 void PropogateEquality(Value *Op0, Value *Op1, RegionInfo &RI);
237 void PropogateRelation(Instruction::BinaryOps Opcode, Value *Op0,
238 Value *Op1, RegionInfo &RI);
239 void UpdateUsersOfValue(Value *V, RegionInfo &RI);
240 void IncorporateInstruction(Instruction *Inst, RegionInfo &RI);
241 void ComputeReplacements(RegionInfo &RI);
244 // getSetCCResult - Given a setcc instruction, determine if the result is
245 // determined by facts we already know about the region under analysis.
246 // Return KnownTrue, KnownFalse, or Unknown based on what we can determine.
248 Relation::KnownResult getSetCCResult(SetCondInst *SC, const RegionInfo &RI);
251 bool SimplifyBasicBlock(BasicBlock &BB, const RegionInfo &RI);
252 bool SimplifyInstruction(Instruction *Inst, const RegionInfo &RI);
254 RegisterOpt<CEE> X("cee", "Correlated Expression Elimination");
257 Pass *createCorrelatedExpressionEliminationPass() { return new CEE(); }
260 bool CEE::runOnFunction(Function &F) {
261 // Build a rank map for the function...
264 // Traverse the dominator tree, computing information for each node in the
265 // tree. Note that our traversal will not even touch unreachable basic
267 DS = &getAnalysis<DominatorSet>();
268 DT = &getAnalysis<DominatorTree>();
270 std::set<BasicBlock*> VisitedBlocks;
271 bool Changed = TransformRegion(&F.getEntryNode(), VisitedBlocks);
273 RegionInfoMap.clear();
278 // TransformRegion - Transform the region starting with BB according to the
279 // calculated region information for the block. Transforming the region
280 // involves analyzing any information this block provides to successors,
281 // propogating the information to successors, and finally transforming
284 // This method processes the function in depth first order, which guarantees
285 // that we process the immediate dominator of a block before the block itself.
286 // Because we are passing information from immediate dominators down to
287 // dominatees, we obviously have to process the information source before the
288 // information consumer.
290 bool CEE::TransformRegion(BasicBlock *BB, std::set<BasicBlock*> &VisitedBlocks){
291 // Prevent infinite recursion...
292 if (VisitedBlocks.count(BB)) return false;
293 VisitedBlocks.insert(BB);
295 // Get the computed region information for this block...
296 RegionInfo &RI = getRegionInfo(BB);
298 // Compute the replacement information for this block...
299 ComputeReplacements(RI);
301 // If debugging, print computed region information...
302 DEBUG(RI.print(std::cerr));
304 // Simplify the contents of this block...
305 bool Changed = SimplifyBasicBlock(*BB, RI);
307 // Get the terminator of this basic block...
308 TerminatorInst *TI = BB->getTerminator();
310 // If this is a conditional branch, make sure that there is a branch target
311 // for each successor that can hold any information gleaned from the branch,
312 // by breaking any critical edges that may be laying about.
314 if (TI->getNumSuccessors() > 1) {
315 // If any of the successors has multiple incoming branches, add a new dummy
316 // destination branch that only contains an unconditional branch to the real
318 for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) {
319 BasicBlock *Succ = TI->getSuccessor(i);
320 // If there is more than one predecessor of the destination block, break
321 // this critical edge by inserting a new block. This updates dominatorset
322 // and dominatortree information.
324 if (isCriticalEdge(TI, i))
325 SplitCriticalEdge(TI, i, this);
329 // Loop over all of the blocks that this block is the immediate dominator for.
330 // Because all information known in this region is also known in all of the
331 // blocks that are dominated by this one, we can safely propogate the
332 // information down now.
334 DominatorTree::Node *BBN = (*DT)[BB];
335 for (unsigned i = 0, e = BBN->getChildren().size(); i != e; ++i) {
336 BasicBlock *Dominated = BBN->getChildren()[i]->getNode();
337 assert(RegionInfoMap.find(Dominated) == RegionInfoMap.end() &&
338 "RegionInfo should be calculated in dominanace order!");
339 getRegionInfo(Dominated) = RI;
342 // Now that all of our successors have information if they deserve it,
343 // propogate any information our terminator instruction finds to our
345 if (BranchInst *BI = dyn_cast<BranchInst>(TI))
346 if (BI->isConditional())
347 PropogateBranchInfo(BI);
349 // If this is a branch to a block outside our region that simply performs
350 // another conditional branch, one whose outcome is known inside of this
351 // region, then vector this outgoing edge directly to the known destination.
353 for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
354 while (BasicBlock *Dest = isCorrelatedBranchBlock(TI->getSuccessor(i), RI)){
355 // If there are any PHI nodes in the Dest BB, we must duplicate the entry
356 // in the PHI node for the old successor to now include an entry from the
357 // current basic block.
359 BasicBlock *OldSucc = TI->getSuccessor(i);
361 // Loop over all of the PHI nodes...
362 for (BasicBlock::iterator I = Dest->begin();
363 PHINode *PN = dyn_cast<PHINode>(&*I); ++I) {
364 // Find the entry in the PHI node for OldSucc, create a duplicate entry
366 int BlockIndex = PN->getBasicBlockIndex(OldSucc);
367 assert(BlockIndex != -1 && "Block should have entry in PHI!");
368 PN->addIncoming(PN->getIncomingValue(BlockIndex), BB);
371 // Actually revector the branch now...
372 TI->setSuccessor(i, Dest);
377 // Now that all of our successors have information, recursively process them.
378 for (unsigned i = 0, e = BBN->getChildren().size(); i != e; ++i)
379 Changed |= TransformRegion(BBN->getChildren()[i]->getNode(), VisitedBlocks);
384 // If this block is a simple block not in the current region, which contains
385 // only a conditional branch, we determine if the outcome of the branch can be
386 // determined from information inside of the region. Instead of going to this
387 // block, we can instead go to the destination we know is the right target.
389 BasicBlock *CEE::isCorrelatedBranchBlock(BasicBlock *BB, RegionInfo &RI) {
390 // Check to see if we dominate the block. If so, this block will get the
391 // condition turned to a constant anyway.
393 //if (DS->dominates(RI.getEntryBlock(), BB))
396 // Check to see if this is a conditional branch...
397 if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator()))
398 if (BI->isConditional()) {
399 // Make sure that the block is either empty, or only contains a setcc.
400 if (BB->size() == 1 ||
401 (BB->size() == 2 && &BB->front() == BI->getCondition() &&
402 BI->getCondition()->use_size() == 1))
403 if (SetCondInst *SCI = dyn_cast<SetCondInst>(BI->getCondition())) {
404 Relation::KnownResult Result = getSetCCResult(SCI, RI);
406 if (Result == Relation::KnownTrue)
407 return BI->getSuccessor(0);
408 else if (Result == Relation::KnownFalse)
409 return BI->getSuccessor(1);
415 // BuildRankMap - This method builds the rank map data structure which gives
416 // each instruction/value in the function a value based on how early it appears
417 // in the function. We give constants and globals rank 0, arguments are
418 // numbered starting at one, and instructions are numbered in reverse post-order
419 // from where the arguments leave off. This gives instructions in loops higher
420 // values than instructions not in loops.
422 void CEE::BuildRankMap(Function &F) {
423 unsigned Rank = 1; // Skip rank zero.
425 // Number the arguments...
426 for (Function::aiterator I = F.abegin(), E = F.aend(); I != E; ++I)
429 // Number the instructions in reverse post order...
430 ReversePostOrderTraversal<Function*> RPOT(&F);
431 for (ReversePostOrderTraversal<Function*>::rpo_iterator I = RPOT.begin(),
432 E = RPOT.end(); I != E; ++I)
433 for (BasicBlock::iterator BBI = (*I)->begin(), E = (*I)->end();
435 if (BBI->getType() != Type::VoidTy)
436 RankMap[BBI] = Rank++;
440 // PropogateBranchInfo - When this method is invoked, we need to propogate
441 // information derived from the branch condition into the true and false
442 // branches of BI. Since we know that there aren't any critical edges in the
443 // flow graph, this can proceed unconditionally.
445 void CEE::PropogateBranchInfo(BranchInst *BI) {
446 assert(BI->isConditional() && "Must be a conditional branch!");
447 BasicBlock *BB = BI->getParent();
448 BasicBlock *TrueBB = BI->getSuccessor(0);
449 BasicBlock *FalseBB = BI->getSuccessor(1);
451 // Propogate information into the true block...
453 PropogateEquality(BI->getCondition(), ConstantBool::True,
454 getRegionInfo(TrueBB));
456 // Propogate information into the false block...
458 PropogateEquality(BI->getCondition(), ConstantBool::False,
459 getRegionInfo(FalseBB));
463 // PropogateEquality - If we discover that two values are equal to each other in
464 // a specified region, propogate this knowledge recursively.
466 void CEE::PropogateEquality(Value *Op0, Value *Op1, RegionInfo &RI) {
467 if (Op0 == Op1) return; // Gee whiz. Are these really equal each other?
469 if (isa<Constant>(Op0)) // Make sure the constant is always Op1
472 // Make sure we don't already know these are equal, to avoid infinite loops...
473 ValueInfo &VI = RI.getValueInfo(Op0);
475 // Get information about the known relationship between Op0 & Op1
476 Relation &KnownRelation = VI.getRelation(Op1);
478 // If we already know they're equal, don't reprocess...
479 if (KnownRelation.getRelation() == Instruction::SetEQ)
482 // If this is boolean, check to see if one of the operands is a constant. If
483 // it's a constant, then see if the other one is one of a setcc instruction,
484 // an AND, OR, or XOR instruction.
486 if (ConstantBool *CB = dyn_cast<ConstantBool>(Op1)) {
488 if (Instruction *Inst = dyn_cast<Instruction>(Op0)) {
489 // If we know that this instruction is an AND instruction, and the result
490 // is true, this means that both operands to the OR are known to be true
493 if (CB->getValue() && Inst->getOpcode() == Instruction::And) {
494 PropogateEquality(Inst->getOperand(0), CB, RI);
495 PropogateEquality(Inst->getOperand(1), CB, RI);
498 // If we know that this instruction is an OR instruction, and the result
499 // is false, this means that both operands to the OR are know to be false
502 if (!CB->getValue() && Inst->getOpcode() == Instruction::Or) {
503 PropogateEquality(Inst->getOperand(0), CB, RI);
504 PropogateEquality(Inst->getOperand(1), CB, RI);
507 // If we know that this instruction is a NOT instruction, we know that the
508 // operand is known to be the inverse of whatever the current value is.
510 if (BinaryOperator *BOp = dyn_cast<BinaryOperator>(Inst))
511 if (BinaryOperator::isNot(BOp))
512 PropogateEquality(BinaryOperator::getNotArgument(BOp),
513 ConstantBool::get(!CB->getValue()), RI);
515 // If we know the value of a SetCC instruction, propogate the information
516 // about the relation into this region as well.
518 if (SetCondInst *SCI = dyn_cast<SetCondInst>(Inst)) {
519 if (CB->getValue()) { // If we know the condition is true...
520 // Propogate info about the LHS to the RHS & RHS to LHS
521 PropogateRelation(SCI->getOpcode(), SCI->getOperand(0),
522 SCI->getOperand(1), RI);
523 PropogateRelation(SCI->getSwappedCondition(),
524 SCI->getOperand(1), SCI->getOperand(0), RI);
526 } else { // If we know the condition is false...
527 // We know the opposite of the condition is true...
528 Instruction::BinaryOps C = SCI->getInverseCondition();
530 PropogateRelation(C, SCI->getOperand(0), SCI->getOperand(1), RI);
531 PropogateRelation(SetCondInst::getSwappedCondition(C),
532 SCI->getOperand(1), SCI->getOperand(0), RI);
538 // Propogate information about Op0 to Op1 & visa versa
539 PropogateRelation(Instruction::SetEQ, Op0, Op1, RI);
540 PropogateRelation(Instruction::SetEQ, Op1, Op0, RI);
544 // PropogateRelation - We know that the specified relation is true in all of the
545 // blocks in the specified region. Propogate the information about Op0 and
546 // anything derived from it into this region.
548 void CEE::PropogateRelation(Instruction::BinaryOps Opcode, Value *Op0,
549 Value *Op1, RegionInfo &RI) {
550 assert(Op0->getType() == Op1->getType() && "Equal types expected!");
552 // Constants are already pretty well understood. We will apply information
553 // about the constant to Op1 in another call to PropogateRelation.
555 if (isa<Constant>(Op0)) return;
557 // Get the region information for this block to update...
558 ValueInfo &VI = RI.getValueInfo(Op0);
560 // Get information about the known relationship between Op0 & Op1
561 Relation &Op1R = VI.getRelation(Op1);
563 // Quick bailout for common case if we are reprocessing an instruction...
564 if (Op1R.getRelation() == Opcode)
567 // If we already have information that contradicts the current information we
568 // are propogating, ignore this info. Something bad must have happened!
570 if (Op1R.contradicts(Opcode, VI)) {
571 Op1R.contradicts(Opcode, VI);
572 std::cerr << "Contradiction found for opcode: "
573 << Instruction::getOpcodeName(Opcode) << "\n";
574 Op1R.print(std::cerr);
578 // If the information propogted is new, then we want process the uses of this
579 // instruction to propogate the information down to them.
581 if (Op1R.incorporate(Opcode, VI))
582 UpdateUsersOfValue(Op0, RI);
586 // UpdateUsersOfValue - The information about V in this region has been updated.
587 // Propogate this to all consumers of the value.
589 void CEE::UpdateUsersOfValue(Value *V, RegionInfo &RI) {
590 for (Value::use_iterator I = V->use_begin(), E = V->use_end();
592 if (Instruction *Inst = dyn_cast<Instruction>(*I)) {
593 // If this is an instruction using a value that we know something about,
594 // try to propogate information to the value produced by the
595 // instruction. We can only do this if it is an instruction we can
596 // propogate information for (a setcc for example), and we only WANT to
597 // do this if the instruction dominates this region.
599 // If the instruction doesn't dominate this region, then it cannot be
600 // used in this region and we don't care about it. If the instruction
601 // is IN this region, then we will simplify the instruction before we
602 // get to uses of it anyway, so there is no reason to bother with it
603 // here. This check is also effectively checking to make sure that Inst
604 // is in the same function as our region (in case V is a global f.e.).
606 if (DS->properlyDominates(Inst->getParent(), RI.getEntryBlock()))
607 IncorporateInstruction(Inst, RI);
611 // IncorporateInstruction - We just updated the information about one of the
612 // operands to the specified instruction. Update the information about the
613 // value produced by this instruction
615 void CEE::IncorporateInstruction(Instruction *Inst, RegionInfo &RI) {
616 if (SetCondInst *SCI = dyn_cast<SetCondInst>(Inst)) {
617 // See if we can figure out a result for this instruction...
618 Relation::KnownResult Result = getSetCCResult(SCI, RI);
619 if (Result != Relation::Unknown) {
620 PropogateEquality(SCI, Result ? ConstantBool::True : ConstantBool::False,
627 // ComputeReplacements - Some values are known to be equal to other values in a
628 // region. For example if there is a comparison of equality between a variable
629 // X and a constant C, we can replace all uses of X with C in the region we are
630 // interested in. We generalize this replacement to replace variables with
631 // other variables if they are equal and there is a variable with lower rank
632 // than the current one. This offers a cannonicalizing property that exposes
633 // more redundancies for later transformations to take advantage of.
635 void CEE::ComputeReplacements(RegionInfo &RI) {
636 // Loop over all of the values in the region info map...
637 for (RegionInfo::iterator I = RI.begin(), E = RI.end(); I != E; ++I) {
638 ValueInfo &VI = I->second;
640 // If we know that this value is a particular constant, set Replacement to
642 Value *Replacement = VI.getBounds().getSingleElement();
644 // If this value is not known to be some constant, figure out the lowest
645 // rank value that it is known to be equal to (if anything).
647 if (Replacement == 0) {
648 // Find out if there are any equality relationships with values of lower
649 // rank than VI itself...
650 unsigned MinRank = getRank(I->first);
652 // Loop over the relationships known about Op0.
653 const std::vector<Relation> &Relationships = VI.getRelationships();
654 for (unsigned i = 0, e = Relationships.size(); i != e; ++i)
655 if (Relationships[i].getRelation() == Instruction::SetEQ) {
656 unsigned R = getRank(Relationships[i].getValue());
659 Replacement = Relationships[i].getValue();
664 // If we found something to replace this value with, keep track of it.
666 VI.setReplacement(Replacement);
670 // SimplifyBasicBlock - Given information about values in region RI, simplify
671 // the instructions in the specified basic block.
673 bool CEE::SimplifyBasicBlock(BasicBlock &BB, const RegionInfo &RI) {
674 bool Changed = false;
675 for (BasicBlock::iterator I = BB.begin(), E = BB.end(); I != E; ) {
676 Instruction *Inst = &*I++;
678 // Convert instruction arguments to canonical forms...
679 Changed |= SimplifyInstruction(Inst, RI);
681 if (SetCondInst *SCI = dyn_cast<SetCondInst>(Inst)) {
682 // Try to simplify a setcc instruction based on inherited information
683 Relation::KnownResult Result = getSetCCResult(SCI, RI);
684 if (Result != Relation::Unknown) {
685 DEBUG(std::cerr << "Replacing setcc with " << Result
686 << " constant: " << SCI);
688 SCI->replaceAllUsesWith(ConstantBool::get((bool)Result));
689 // The instruction is now dead, remove it from the program.
690 SCI->getParent()->getInstList().erase(SCI);
700 // SimplifyInstruction - Inspect the operands of the instruction, converting
701 // them to their cannonical form if possible. This takes care of, for example,
702 // replacing a value 'X' with a constant 'C' if the instruction in question is
703 // dominated by a true seteq 'X', 'C'.
705 bool CEE::SimplifyInstruction(Instruction *I, const RegionInfo &RI) {
706 bool Changed = false;
708 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
709 if (const ValueInfo *VI = RI.requestValueInfo(I->getOperand(i)))
710 if (Value *Repl = VI->getReplacement()) {
711 // If we know if a replacement with lower rank than Op0, make the
713 DEBUG(std::cerr << "In Inst: " << I << " Replacing operand #" << i
714 << " with " << Repl << "\n");
715 I->setOperand(i, Repl);
724 // SimplifySetCC - Try to simplify a setcc instruction based on information
725 // inherited from a dominating setcc instruction. V is one of the operands to
726 // the setcc instruction, and VI is the set of information known about it. We
727 // take two cases into consideration here. If the comparison is against a
728 // constant value, we can use the constant range to see if the comparison is
729 // possible to succeed. If it is not a comparison against a constant, we check
730 // to see if there is a known relationship between the two values. If so, we
731 // may be able to eliminate the check.
733 Relation::KnownResult CEE::getSetCCResult(SetCondInst *SCI,
734 const RegionInfo &RI) {
735 Value *Op0 = SCI->getOperand(0), *Op1 = SCI->getOperand(1);
736 Instruction::BinaryOps Opcode = SCI->getOpcode();
738 if (isa<Constant>(Op0)) {
739 if (isa<Constant>(Op1)) {
740 if (Constant *Result = ConstantFoldInstruction(SCI)) {
741 // Wow, this is easy, directly eliminate the SetCondInst.
742 DEBUG(std::cerr << "Replacing setcc with constant fold: " << SCI);
743 return cast<ConstantBool>(Result)->getValue()
744 ? Relation::KnownTrue : Relation::KnownFalse;
747 // We want to swap this instruction so that operand #0 is the constant.
749 Opcode = SCI->getSwappedCondition();
753 // Try to figure out what the result of this comparison will be...
754 Relation::KnownResult Result = Relation::Unknown;
756 // We have to know something about the relationship to prove anything...
757 if (const ValueInfo *Op0VI = RI.requestValueInfo(Op0)) {
759 // At this point, we know that if we have a constant argument that it is in
760 // Op1. Check to see if we know anything about comparing value with a
761 // constant, and if we can use this info to fold the setcc.
763 if (ConstantIntegral *C = dyn_cast<ConstantIntegral>(Op1)) {
764 // Check to see if we already know the result of this comparison...
765 ConstantRange R = ConstantRange(Opcode, C);
766 ConstantRange Int = R.intersectWith(Op0VI->getBounds());
768 // If the intersection of the two ranges is empty, then the condition
769 // could never be true!
771 if (Int.isEmptySet()) {
772 Result = Relation::KnownFalse;
774 // Otherwise, if VI.getBounds() (the possible values) is a subset of R
775 // (the allowed values) then we know that the condition must always be
778 } else if (Int == Op0VI->getBounds()) {
779 Result = Relation::KnownTrue;
782 // If we are here, we know that the second argument is not a constant
783 // integral. See if we know anything about Op0 & Op1 that allows us to
786 // Do we have value information about Op0 and a relation to Op1?
787 if (const Relation *Op2R = Op0VI->requestRelation(Op1))
788 Result = Op2R->getImpliedResult(Opcode);
794 //===----------------------------------------------------------------------===//
795 // Relation Implementation
796 //===----------------------------------------------------------------------===//
798 // CheckCondition - Return true if the specified condition is false. Bound may
800 static bool CheckCondition(Constant *Bound, Constant *C,
801 Instruction::BinaryOps BO) {
802 assert(C != 0 && "C is not specified!");
803 if (Bound == 0) return false;
807 default: assert(0 && "Unknown Condition code!");
808 case Instruction::SetEQ: Val = *Bound == *C; break;
809 case Instruction::SetNE: Val = *Bound != *C; break;
810 case Instruction::SetLT: Val = *Bound < *C; break;
811 case Instruction::SetGT: Val = *Bound > *C; break;
812 case Instruction::SetLE: Val = *Bound <= *C; break;
813 case Instruction::SetGE: Val = *Bound >= *C; break;
816 // ConstantHandling code may not succeed in the comparison...
817 if (Val == 0) return false;
818 return !Val->getValue(); // Return true if the condition is false...
821 // contradicts - Return true if the relationship specified by the operand
822 // contradicts already known information.
824 bool Relation::contradicts(Instruction::BinaryOps Op,
825 const ValueInfo &VI) const {
826 assert (Op != Instruction::Add && "Invalid relation argument!");
828 // If this is a relationship with a constant, make sure that this relationship
829 // does not contradict properties known about the bounds of the constant.
831 if (ConstantIntegral *C = dyn_cast<ConstantIntegral>(Val))
832 if (ConstantRange(Op, C).intersectWith(VI.getBounds()).isEmptySet())
836 default: assert(0 && "Unknown Relationship code!");
837 case Instruction::Add: return false; // Nothing known, nothing contradicts
838 case Instruction::SetEQ:
839 return Op == Instruction::SetLT || Op == Instruction::SetGT ||
840 Op == Instruction::SetNE;
841 case Instruction::SetNE: return Op == Instruction::SetEQ;
842 case Instruction::SetLE: return Op == Instruction::SetGT;
843 case Instruction::SetGE: return Op == Instruction::SetLT;
844 case Instruction::SetLT:
845 return Op == Instruction::SetEQ || Op == Instruction::SetGT ||
846 Op == Instruction::SetGE;
847 case Instruction::SetGT:
848 return Op == Instruction::SetEQ || Op == Instruction::SetLT ||
849 Op == Instruction::SetLE;
853 // incorporate - Incorporate information in the argument into this relation
854 // entry. This assumes that the information doesn't contradict itself. If any
855 // new information is gained, true is returned, otherwise false is returned to
856 // indicate that nothing was updated.
858 bool Relation::incorporate(Instruction::BinaryOps Op, ValueInfo &VI) {
859 assert(!contradicts(Op, VI) &&
860 "Cannot incorporate contradictory information!");
862 // If this is a relationship with a constant, make sure that we update the
863 // range that is possible for the value to have...
865 if (ConstantIntegral *C = dyn_cast<ConstantIntegral>(Val))
866 VI.getBounds() = ConstantRange(Op, C).intersectWith(VI.getBounds());
869 default: assert(0 && "Unknown prior value!");
870 case Instruction::Add: Rel = Op; return true;
871 case Instruction::SetEQ: return false; // Nothing is more precise
872 case Instruction::SetNE: return false; // Nothing is more precise
873 case Instruction::SetLT: return false; // Nothing is more precise
874 case Instruction::SetGT: return false; // Nothing is more precise
875 case Instruction::SetLE:
876 if (Op == Instruction::SetEQ || Op == Instruction::SetLT) {
879 } else if (Op == Instruction::SetNE) {
880 Rel = Instruction::SetLT;
884 case Instruction::SetGE: return Op == Instruction::SetLT;
885 if (Op == Instruction::SetEQ || Op == Instruction::SetGT) {
888 } else if (Op == Instruction::SetNE) {
889 Rel = Instruction::SetGT;
896 // getImpliedResult - If this relationship between two values implies that
897 // the specified relationship is true or false, return that. If we cannot
898 // determine the result required, return Unknown.
900 Relation::KnownResult
901 Relation::getImpliedResult(Instruction::BinaryOps Op) const {
902 if (Rel == Op) return KnownTrue;
903 if (Rel == SetCondInst::getInverseCondition(Op)) return KnownFalse;
906 default: assert(0 && "Unknown prior value!");
907 case Instruction::SetEQ:
908 if (Op == Instruction::SetLE || Op == Instruction::SetGE) return KnownTrue;
909 if (Op == Instruction::SetLT || Op == Instruction::SetGT) return KnownFalse;
911 case Instruction::SetLT:
912 if (Op == Instruction::SetNE || Op == Instruction::SetLE) return KnownTrue;
913 if (Op == Instruction::SetEQ) return KnownFalse;
915 case Instruction::SetGT:
916 if (Op == Instruction::SetNE || Op == Instruction::SetGE) return KnownTrue;
917 if (Op == Instruction::SetEQ) return KnownFalse;
919 case Instruction::SetNE:
920 case Instruction::SetLE:
921 case Instruction::SetGE:
922 case Instruction::Add:
929 //===----------------------------------------------------------------------===//
930 // Printing Support...
931 //===----------------------------------------------------------------------===//
933 // print - Implement the standard print form to print out analysis information.
934 void CEE::print(std::ostream &O, const Module *M) const {
935 O << "\nPrinting Correlated Expression Info:\n";
936 for (std::map<BasicBlock*, RegionInfo>::const_iterator I =
937 RegionInfoMap.begin(), E = RegionInfoMap.end(); I != E; ++I)
941 // print - Output information about this region...
942 void RegionInfo::print(std::ostream &OS) const {
943 if (ValueMap.empty()) return;
945 OS << " RegionInfo for basic block: " << BB->getName() << "\n";
946 for (std::map<Value*, ValueInfo>::const_iterator
947 I = ValueMap.begin(), E = ValueMap.end(); I != E; ++I)
948 I->second.print(OS, I->first);
952 // print - Output information about this value relation...
953 void ValueInfo::print(std::ostream &OS, Value *V) const {
954 if (Relationships.empty()) return;
957 OS << " ValueInfo for: ";
958 WriteAsOperand(OS, V);
960 OS << "\n Bounds = " << Bounds << "\n";
962 OS << " Replacement = ";
963 WriteAsOperand(OS, Replacement);
966 for (unsigned i = 0, e = Relationships.size(); i != e; ++i)
967 Relationships[i].print(OS);
970 // print - Output this relation to the specified stream
971 void Relation::print(std::ostream &OS) const {
974 default: OS << "*UNKNOWN*"; break;
975 case Instruction::SetEQ: OS << "== "; break;
976 case Instruction::SetNE: OS << "!= "; break;
977 case Instruction::SetLT: OS << "< "; break;
978 case Instruction::SetGT: OS << "> "; break;
979 case Instruction::SetLE: OS << "<= "; break;
980 case Instruction::SetGE: OS << ">= "; break;
983 WriteAsOperand(OS, Val);
987 void Relation::dump() const { print(std::cerr); }
988 void ValueInfo::dump() const { print(std::cerr, 0); }