LLVM API Documentation
00001 //===- CorrelatedExprs.cpp - Pass to detect and eliminated c.e.'s ---------===// 00002 // 00003 // The LLVM Compiler Infrastructure 00004 // 00005 // This file was developed by the LLVM research group and is distributed under 00006 // the University of Illinois Open Source License. See LICENSE.TXT for details. 00007 // 00008 //===----------------------------------------------------------------------===// 00009 // 00010 // Correlated Expression Elimination propagates information from conditional 00011 // branches to blocks dominated by destinations of the branch. It propagates 00012 // information from the condition check itself into the body of the branch, 00013 // allowing transformations like these for example: 00014 // 00015 // if (i == 7) 00016 // ... 4*i; // constant propagation 00017 // 00018 // M = i+1; N = j+1; 00019 // if (i == j) 00020 // X = M-N; // = M-M == 0; 00021 // 00022 // This is called Correlated Expression Elimination because we eliminate or 00023 // simplify expressions that are correlated with the direction of a branch. In 00024 // this way we use static information to give us some information about the 00025 // dynamic value of a variable. 00026 // 00027 //===----------------------------------------------------------------------===// 00028 00029 #include "llvm/Transforms/Scalar.h" 00030 #include "llvm/Constants.h" 00031 #include "llvm/Pass.h" 00032 #include "llvm/Function.h" 00033 #include "llvm/Instructions.h" 00034 #include "llvm/Type.h" 00035 #include "llvm/Analysis/Dominators.h" 00036 #include "llvm/Assembly/Writer.h" 00037 #include "llvm/Transforms/Utils/Local.h" 00038 #include "llvm/Transforms/Utils/BasicBlockUtils.h" 00039 #include "llvm/Support/ConstantRange.h" 00040 #include "llvm/Support/CFG.h" 00041 #include "llvm/Support/Debug.h" 00042 #include "llvm/ADT/PostOrderIterator.h" 00043 #include "llvm/ADT/Statistic.h" 00044 #include <algorithm> 00045 using namespace llvm; 00046 00047 namespace { 00048 Statistic<> NumSetCCRemoved("cee", "Number of setcc instruction eliminated"); 00049 Statistic<> NumOperandsCann("cee", "Number of operands canonicalized"); 00050 Statistic<> BranchRevectors("cee", "Number of branches revectored"); 00051 00052 class ValueInfo; 00053 class Relation { 00054 Value *Val; // Relation to what value? 00055 Instruction::BinaryOps Rel; // SetCC relation, or Add if no information 00056 public: 00057 Relation(Value *V) : Val(V), Rel(Instruction::Add) {} 00058 bool operator<(const Relation &R) const { return Val < R.Val; } 00059 Value *getValue() const { return Val; } 00060 Instruction::BinaryOps getRelation() const { return Rel; } 00061 00062 // contradicts - Return true if the relationship specified by the operand 00063 // contradicts already known information. 00064 // 00065 bool contradicts(Instruction::BinaryOps Rel, const ValueInfo &VI) const; 00066 00067 // incorporate - Incorporate information in the argument into this relation 00068 // entry. This assumes that the information doesn't contradict itself. If 00069 // any new information is gained, true is returned, otherwise false is 00070 // returned to indicate that nothing was updated. 00071 // 00072 bool incorporate(Instruction::BinaryOps Rel, ValueInfo &VI); 00073 00074 // KnownResult - Whether or not this condition determines the result of a 00075 // setcc in the program. False & True are intentionally 0 & 1 so we can 00076 // convert to bool by casting after checking for unknown. 00077 // 00078 enum KnownResult { KnownFalse = 0, KnownTrue = 1, Unknown = 2 }; 00079 00080 // getImpliedResult - If this relationship between two values implies that 00081 // the specified relationship is true or false, return that. If we cannot 00082 // determine the result required, return Unknown. 00083 // 00084 KnownResult getImpliedResult(Instruction::BinaryOps Rel) const; 00085 00086 // print - Output this relation to the specified stream 00087 void print(std::ostream &OS) const; 00088 void dump() const; 00089 }; 00090 00091 00092 // ValueInfo - One instance of this record exists for every value with 00093 // relationships between other values. It keeps track of all of the 00094 // relationships to other values in the program (specified with Relation) that 00095 // are known to be valid in a region. 00096 // 00097 class ValueInfo { 00098 // RelationShips - this value is know to have the specified relationships to 00099 // other values. There can only be one entry per value, and this list is 00100 // kept sorted by the Val field. 00101 std::vector<Relation> Relationships; 00102 00103 // If information about this value is known or propagated from constant 00104 // expressions, this range contains the possible values this value may hold. 00105 ConstantRange Bounds; 00106 00107 // If we find that this value is equal to another value that has a lower 00108 // rank, this value is used as it's replacement. 00109 // 00110 Value *Replacement; 00111 public: 00112 ValueInfo(const Type *Ty) 00113 : Bounds(Ty->isIntegral() ? Ty : Type::IntTy), Replacement(0) {} 00114 00115 // getBounds() - Return the constant bounds of the value... 00116 const ConstantRange &getBounds() const { return Bounds; } 00117 ConstantRange &getBounds() { return Bounds; } 00118 00119 const std::vector<Relation> &getRelationships() { return Relationships; } 00120 00121 // getReplacement - Return the value this value is to be replaced with if it 00122 // exists, otherwise return null. 00123 // 00124 Value *getReplacement() const { return Replacement; } 00125 00126 // setReplacement - Used by the replacement calculation pass to figure out 00127 // what to replace this value with, if anything. 00128 // 00129 void setReplacement(Value *Repl) { Replacement = Repl; } 00130 00131 // getRelation - return the relationship entry for the specified value. 00132 // This can invalidate references to other Relations, so use it carefully. 00133 // 00134 Relation &getRelation(Value *V) { 00135 // Binary search for V's entry... 00136 std::vector<Relation>::iterator I = 00137 std::lower_bound(Relationships.begin(), Relationships.end(), V); 00138 00139 // If we found the entry, return it... 00140 if (I != Relationships.end() && I->getValue() == V) 00141 return *I; 00142 00143 // Insert and return the new relationship... 00144 return *Relationships.insert(I, V); 00145 } 00146 00147 const Relation *requestRelation(Value *V) const { 00148 // Binary search for V's entry... 00149 std::vector<Relation>::const_iterator I = 00150 std::lower_bound(Relationships.begin(), Relationships.end(), V); 00151 if (I != Relationships.end() && I->getValue() == V) 00152 return &*I; 00153 return 0; 00154 } 00155 00156 // print - Output information about this value relation... 00157 void print(std::ostream &OS, Value *V) const; 00158 void dump() const; 00159 }; 00160 00161 // RegionInfo - Keeps track of all of the value relationships for a region. A 00162 // region is the are dominated by a basic block. RegionInfo's keep track of 00163 // the RegionInfo for their dominator, because anything known in a dominator 00164 // is known to be true in a dominated block as well. 00165 // 00166 class RegionInfo { 00167 BasicBlock *BB; 00168 00169 // ValueMap - Tracks the ValueInformation known for this region 00170 typedef std::map<Value*, ValueInfo> ValueMapTy; 00171 ValueMapTy ValueMap; 00172 public: 00173 RegionInfo(BasicBlock *bb) : BB(bb) {} 00174 00175 // getEntryBlock - Return the block that dominates all of the members of 00176 // this region. 00177 BasicBlock *getEntryBlock() const { return BB; } 00178 00179 // empty - return true if this region has no information known about it. 00180 bool empty() const { return ValueMap.empty(); } 00181 00182 const RegionInfo &operator=(const RegionInfo &RI) { 00183 ValueMap = RI.ValueMap; 00184 return *this; 00185 } 00186 00187 // print - Output information about this region... 00188 void print(std::ostream &OS) const; 00189 void dump() const; 00190 00191 // Allow external access. 00192 typedef ValueMapTy::iterator iterator; 00193 iterator begin() { return ValueMap.begin(); } 00194 iterator end() { return ValueMap.end(); } 00195 00196 ValueInfo &getValueInfo(Value *V) { 00197 ValueMapTy::iterator I = ValueMap.lower_bound(V); 00198 if (I != ValueMap.end() && I->first == V) return I->second; 00199 return ValueMap.insert(I, std::make_pair(V, V->getType()))->second; 00200 } 00201 00202 const ValueInfo *requestValueInfo(Value *V) const { 00203 ValueMapTy::const_iterator I = ValueMap.find(V); 00204 if (I != ValueMap.end()) return &I->second; 00205 return 0; 00206 } 00207 00208 /// removeValueInfo - Remove anything known about V from our records. This 00209 /// works whether or not we know anything about V. 00210 /// 00211 void removeValueInfo(Value *V) { 00212 ValueMap.erase(V); 00213 } 00214 }; 00215 00216 /// CEE - Correlated Expression Elimination 00217 class CEE : public FunctionPass { 00218 std::map<Value*, unsigned> RankMap; 00219 std::map<BasicBlock*, RegionInfo> RegionInfoMap; 00220 DominatorSet *DS; 00221 DominatorTree *DT; 00222 public: 00223 virtual bool runOnFunction(Function &F); 00224 00225 // We don't modify the program, so we preserve all analyses 00226 virtual void getAnalysisUsage(AnalysisUsage &AU) const { 00227 AU.addRequired<DominatorSet>(); 00228 AU.addRequired<DominatorTree>(); 00229 AU.addRequiredID(BreakCriticalEdgesID); 00230 }; 00231 00232 // print - Implement the standard print form to print out analysis 00233 // information. 00234 virtual void print(std::ostream &O, const Module *M) const; 00235 00236 private: 00237 RegionInfo &getRegionInfo(BasicBlock *BB) { 00238 std::map<BasicBlock*, RegionInfo>::iterator I 00239 = RegionInfoMap.lower_bound(BB); 00240 if (I != RegionInfoMap.end() && I->first == BB) return I->second; 00241 return RegionInfoMap.insert(I, std::make_pair(BB, BB))->second; 00242 } 00243 00244 void BuildRankMap(Function &F); 00245 unsigned getRank(Value *V) const { 00246 if (isa<Constant>(V)) return 0; 00247 std::map<Value*, unsigned>::const_iterator I = RankMap.find(V); 00248 if (I != RankMap.end()) return I->second; 00249 return 0; // Must be some other global thing 00250 } 00251 00252 bool TransformRegion(BasicBlock *BB, std::set<BasicBlock*> &VisitedBlocks); 00253 00254 bool ForwardCorrelatedEdgeDestination(TerminatorInst *TI, unsigned SuccNo, 00255 RegionInfo &RI); 00256 00257 void ForwardSuccessorTo(TerminatorInst *TI, unsigned Succ, BasicBlock *D, 00258 RegionInfo &RI); 00259 void ReplaceUsesOfValueInRegion(Value *Orig, Value *New, 00260 BasicBlock *RegionDominator); 00261 void CalculateRegionExitBlocks(BasicBlock *BB, BasicBlock *OldSucc, 00262 std::vector<BasicBlock*> &RegionExitBlocks); 00263 void InsertRegionExitMerges(PHINode *NewPHI, Instruction *OldVal, 00264 const std::vector<BasicBlock*> &RegionExitBlocks); 00265 00266 void PropagateBranchInfo(BranchInst *BI); 00267 void PropagateEquality(Value *Op0, Value *Op1, RegionInfo &RI); 00268 void PropagateRelation(Instruction::BinaryOps Opcode, Value *Op0, 00269 Value *Op1, RegionInfo &RI); 00270 void UpdateUsersOfValue(Value *V, RegionInfo &RI); 00271 void IncorporateInstruction(Instruction *Inst, RegionInfo &RI); 00272 void ComputeReplacements(RegionInfo &RI); 00273 00274 00275 // getSetCCResult - Given a setcc instruction, determine if the result is 00276 // determined by facts we already know about the region under analysis. 00277 // Return KnownTrue, KnownFalse, or Unknown based on what we can determine. 00278 // 00279 Relation::KnownResult getSetCCResult(SetCondInst *SC, const RegionInfo &RI); 00280 00281 00282 bool SimplifyBasicBlock(BasicBlock &BB, const RegionInfo &RI); 00283 bool SimplifyInstruction(Instruction *Inst, const RegionInfo &RI); 00284 }; 00285 RegisterOpt<CEE> X("cee", "Correlated Expression Elimination"); 00286 } 00287 00288 FunctionPass *llvm::createCorrelatedExpressionEliminationPass() { 00289 return new CEE(); 00290 } 00291 00292 00293 bool CEE::runOnFunction(Function &F) { 00294 // Build a rank map for the function... 00295 BuildRankMap(F); 00296 00297 // Traverse the dominator tree, computing information for each node in the 00298 // tree. Note that our traversal will not even touch unreachable basic 00299 // blocks. 00300 DS = &getAnalysis<DominatorSet>(); 00301 DT = &getAnalysis<DominatorTree>(); 00302 00303 std::set<BasicBlock*> VisitedBlocks; 00304 bool Changed = TransformRegion(&F.getEntryBlock(), VisitedBlocks); 00305 00306 RegionInfoMap.clear(); 00307 RankMap.clear(); 00308 return Changed; 00309 } 00310 00311 // TransformRegion - Transform the region starting with BB according to the 00312 // calculated region information for the block. Transforming the region 00313 // involves analyzing any information this block provides to successors, 00314 // propagating the information to successors, and finally transforming 00315 // successors. 00316 // 00317 // This method processes the function in depth first order, which guarantees 00318 // that we process the immediate dominator of a block before the block itself. 00319 // Because we are passing information from immediate dominators down to 00320 // dominatees, we obviously have to process the information source before the 00321 // information consumer. 00322 // 00323 bool CEE::TransformRegion(BasicBlock *BB, std::set<BasicBlock*> &VisitedBlocks){ 00324 // Prevent infinite recursion... 00325 if (VisitedBlocks.count(BB)) return false; 00326 VisitedBlocks.insert(BB); 00327 00328 // Get the computed region information for this block... 00329 RegionInfo &RI = getRegionInfo(BB); 00330 00331 // Compute the replacement information for this block... 00332 ComputeReplacements(RI); 00333 00334 // If debugging, print computed region information... 00335 DEBUG(RI.print(std::cerr)); 00336 00337 // Simplify the contents of this block... 00338 bool Changed = SimplifyBasicBlock(*BB, RI); 00339 00340 // Get the terminator of this basic block... 00341 TerminatorInst *TI = BB->getTerminator(); 00342 00343 // Loop over all of the blocks that this block is the immediate dominator for. 00344 // Because all information known in this region is also known in all of the 00345 // blocks that are dominated by this one, we can safely propagate the 00346 // information down now. 00347 // 00348 DominatorTree::Node *BBN = (*DT)[BB]; 00349 if (!RI.empty()) // Time opt: only propagate if we can change something 00350 for (unsigned i = 0, e = BBN->getChildren().size(); i != e; ++i) { 00351 BasicBlock *Dominated = BBN->getChildren()[i]->getBlock(); 00352 assert(RegionInfoMap.find(Dominated) == RegionInfoMap.end() && 00353 "RegionInfo should be calculated in dominanace order!"); 00354 getRegionInfo(Dominated) = RI; 00355 } 00356 00357 // Now that all of our successors have information if they deserve it, 00358 // propagate any information our terminator instruction finds to our 00359 // successors. 00360 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) 00361 if (BI->isConditional()) 00362 PropagateBranchInfo(BI); 00363 00364 // If this is a branch to a block outside our region that simply performs 00365 // another conditional branch, one whose outcome is known inside of this 00366 // region, then vector this outgoing edge directly to the known destination. 00367 // 00368 for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) 00369 while (ForwardCorrelatedEdgeDestination(TI, i, RI)) { 00370 ++BranchRevectors; 00371 Changed = true; 00372 } 00373 00374 // Now that all of our successors have information, recursively process them. 00375 for (unsigned i = 0, e = BBN->getChildren().size(); i != e; ++i) 00376 Changed |= TransformRegion(BBN->getChildren()[i]->getBlock(),VisitedBlocks); 00377 00378 return Changed; 00379 } 00380 00381 // isBlockSimpleEnoughForCheck to see if the block is simple enough for us to 00382 // revector the conditional branch in the bottom of the block, do so now. 00383 // 00384 static bool isBlockSimpleEnough(BasicBlock *BB) { 00385 assert(isa<BranchInst>(BB->getTerminator())); 00386 BranchInst *BI = cast<BranchInst>(BB->getTerminator()); 00387 assert(BI->isConditional()); 00388 00389 // Check the common case first: empty block, or block with just a setcc. 00390 if (BB->size() == 1 || 00391 (BB->size() == 2 && &BB->front() == BI->getCondition() && 00392 BI->getCondition()->hasOneUse())) 00393 return true; 00394 00395 // Check the more complex case now... 00396 BasicBlock::iterator I = BB->begin(); 00397 00398 // FIXME: This should be reenabled once the regression with SIM is fixed! 00399 #if 0 00400 // PHI Nodes are ok, just skip over them... 00401 while (isa<PHINode>(*I)) ++I; 00402 #endif 00403 00404 // Accept the setcc instruction... 00405 if (&*I == BI->getCondition()) 00406 ++I; 00407 00408 // Nothing else is acceptable here yet. We must not revector... unless we are 00409 // at the terminator instruction. 00410 if (&*I == BI) 00411 return true; 00412 00413 return false; 00414 } 00415 00416 00417 bool CEE::ForwardCorrelatedEdgeDestination(TerminatorInst *TI, unsigned SuccNo, 00418 RegionInfo &RI) { 00419 // If this successor is a simple block not in the current region, which 00420 // contains only a conditional branch, we decide if the outcome of the branch 00421 // can be determined from information inside of the region. Instead of going 00422 // to this block, we can instead go to the destination we know is the right 00423 // target. 00424 // 00425 00426 // Check to see if we dominate the block. If so, this block will get the 00427 // condition turned to a constant anyway. 00428 // 00429 //if (DS->dominates(RI.getEntryBlock(), BB)) 00430 // return 0; 00431 00432 BasicBlock *BB = TI->getParent(); 00433 00434 // Get the destination block of this edge... 00435 BasicBlock *OldSucc = TI->getSuccessor(SuccNo); 00436 00437 // Make sure that the block ends with a conditional branch and is simple 00438 // enough for use to be able to revector over. 00439 BranchInst *BI = dyn_cast<BranchInst>(OldSucc->getTerminator()); 00440 if (BI == 0 || !BI->isConditional() || !isBlockSimpleEnough(OldSucc)) 00441 return false; 00442 00443 // We can only forward the branch over the block if the block ends with a 00444 // setcc we can determine the outcome for. 00445 // 00446 // FIXME: we can make this more generic. Code below already handles more 00447 // generic case. 00448 SetCondInst *SCI = dyn_cast<SetCondInst>(BI->getCondition()); 00449 if (SCI == 0) return false; 00450 00451 // Make a new RegionInfo structure so that we can simulate the effect of the 00452 // PHI nodes in the block we are skipping over... 00453 // 00454 RegionInfo NewRI(RI); 00455 00456 // Remove value information for all of the values we are simulating... to make 00457 // sure we don't have any stale information. 00458 for (BasicBlock::iterator I = OldSucc->begin(), E = OldSucc->end(); I!=E; ++I) 00459 if (I->getType() != Type::VoidTy) 00460 NewRI.removeValueInfo(I); 00461 00462 // Put the newly discovered information into the RegionInfo... 00463 for (BasicBlock::iterator I = OldSucc->begin(), E = OldSucc->end(); I!=E; ++I) 00464 if (PHINode *PN = dyn_cast<PHINode>(I)) { 00465 int OpNum = PN->getBasicBlockIndex(BB); 00466 assert(OpNum != -1 && "PHI doesn't have incoming edge for predecessor!?"); 00467 PropagateEquality(PN, PN->getIncomingValue(OpNum), NewRI); 00468 } else if (SetCondInst *SCI = dyn_cast<SetCondInst>(I)) { 00469 Relation::KnownResult Res = getSetCCResult(SCI, NewRI); 00470 if (Res == Relation::Unknown) return false; 00471 PropagateEquality(SCI, ConstantBool::get(Res), NewRI); 00472 } else { 00473 assert(isa<BranchInst>(*I) && "Unexpected instruction type!"); 00474 } 00475 00476 // Compute the facts implied by what we have discovered... 00477 ComputeReplacements(NewRI); 00478 00479 ValueInfo &PredicateVI = NewRI.getValueInfo(BI->getCondition()); 00480 if (PredicateVI.getReplacement() && 00481 isa<Constant>(PredicateVI.getReplacement()) && 00482 !isa<GlobalValue>(PredicateVI.getReplacement())) { 00483 ConstantBool *CB = cast<ConstantBool>(PredicateVI.getReplacement()); 00484 00485 // Forward to the successor that corresponds to the branch we will take. 00486 ForwardSuccessorTo(TI, SuccNo, BI->getSuccessor(!CB->getValue()), NewRI); 00487 return true; 00488 } 00489 00490 return false; 00491 } 00492 00493 static Value *getReplacementOrValue(Value *V, RegionInfo &RI) { 00494 if (const ValueInfo *VI = RI.requestValueInfo(V)) 00495 if (Value *Repl = VI->getReplacement()) 00496 return Repl; 00497 return V; 00498 } 00499 00500 /// ForwardSuccessorTo - We have found that we can forward successor # 'SuccNo' 00501 /// of Terminator 'TI' to the 'Dest' BasicBlock. This method performs the 00502 /// mechanics of updating SSA information and revectoring the branch. 00503 /// 00504 void CEE::ForwardSuccessorTo(TerminatorInst *TI, unsigned SuccNo, 00505 BasicBlock *Dest, RegionInfo &RI) { 00506 // If there are any PHI nodes in the Dest BB, we must duplicate the entry 00507 // in the PHI node for the old successor to now include an entry from the 00508 // current basic block. 00509 // 00510 BasicBlock *OldSucc = TI->getSuccessor(SuccNo); 00511 BasicBlock *BB = TI->getParent(); 00512 00513 DEBUG(std::cerr << "Forwarding branch in basic block %" << BB->getName() 00514 << " from block %" << OldSucc->getName() << " to block %" 00515 << Dest->getName() << "\n"); 00516 00517 DEBUG(std::cerr << "Before forwarding: " << *BB->getParent()); 00518 00519 // Because we know that there cannot be critical edges in the flow graph, and 00520 // that OldSucc has multiple outgoing edges, this means that Dest cannot have 00521 // multiple incoming edges. 00522 // 00523 #ifndef NDEBUG 00524 pred_iterator DPI = pred_begin(Dest); ++DPI; 00525 assert(DPI == pred_end(Dest) && "Critical edge found!!"); 00526 #endif 00527 00528 // Loop over any PHI nodes in the destination, eliminating them, because they 00529 // may only have one input. 00530 // 00531 while (PHINode *PN = dyn_cast<PHINode>(&Dest->front())) { 00532 assert(PN->getNumIncomingValues() == 1 && "Crit edge found!"); 00533 // Eliminate the PHI node 00534 PN->replaceAllUsesWith(PN->getIncomingValue(0)); 00535 Dest->getInstList().erase(PN); 00536 } 00537 00538 // If there are values defined in the "OldSucc" basic block, we need to insert 00539 // PHI nodes in the regions we are dealing with to emulate them. This can 00540 // insert dead phi nodes, but it is more trouble to see if they are used than 00541 // to just blindly insert them. 00542 // 00543 if (DS->dominates(OldSucc, Dest)) { 00544 // RegionExitBlocks - Find all of the blocks that are not dominated by Dest, 00545 // but have predecessors that are. Additionally, prune down the set to only 00546 // include blocks that are dominated by OldSucc as well. 00547 // 00548 std::vector<BasicBlock*> RegionExitBlocks; 00549 CalculateRegionExitBlocks(Dest, OldSucc, RegionExitBlocks); 00550 00551 for (BasicBlock::iterator I = OldSucc->begin(), E = OldSucc->end(); 00552 I != E; ++I) 00553 if (I->getType() != Type::VoidTy) { 00554 // Create and insert the PHI node into the top of Dest. 00555 PHINode *NewPN = new PHINode(I->getType(), I->getName()+".fw_merge", 00556 Dest->begin()); 00557 // There is definitely an edge from OldSucc... add the edge now 00558 NewPN->addIncoming(I, OldSucc); 00559 00560 // There is also an edge from BB now, add the edge with the calculated 00561 // value from the RI. 00562 NewPN->addIncoming(getReplacementOrValue(I, RI), BB); 00563 00564 // Make everything in the Dest region use the new PHI node now... 00565 ReplaceUsesOfValueInRegion(I, NewPN, Dest); 00566 00567 // Make sure that exits out of the region dominated by NewPN get PHI 00568 // nodes that merge the values as appropriate. 00569 InsertRegionExitMerges(NewPN, I, RegionExitBlocks); 00570 } 00571 } 00572 00573 // If there were PHI nodes in OldSucc, we need to remove the entry for this 00574 // edge from the PHI node, and we need to replace any references to the PHI 00575 // node with a new value. 00576 // 00577 for (BasicBlock::iterator I = OldSucc->begin(); isa<PHINode>(I); ) { 00578 PHINode *PN = cast<PHINode>(I); 00579 00580 // Get the value flowing across the old edge and remove the PHI node entry 00581 // for this edge: we are about to remove the edge! Don't remove the PHI 00582 // node yet though if this is the last edge into it. 00583 Value *EdgeValue = PN->removeIncomingValue(BB, false); 00584 00585 // Make sure that anything that used to use PN now refers to EdgeValue 00586 ReplaceUsesOfValueInRegion(PN, EdgeValue, Dest); 00587 00588 // If there is only one value left coming into the PHI node, replace the PHI 00589 // node itself with the one incoming value left. 00590 // 00591 if (PN->getNumIncomingValues() == 1) { 00592 assert(PN->getNumIncomingValues() == 1); 00593 PN->replaceAllUsesWith(PN->getIncomingValue(0)); 00594 PN->getParent()->getInstList().erase(PN); 00595 I = OldSucc->begin(); 00596 } else if (PN->getNumIncomingValues() == 0) { // Nuke the PHI 00597 // If we removed the last incoming value to this PHI, nuke the PHI node 00598 // now. 00599 PN->replaceAllUsesWith(Constant::getNullValue(PN->getType())); 00600 PN->getParent()->getInstList().erase(PN); 00601 I = OldSucc->begin(); 00602 } else { 00603 ++I; // Otherwise, move on to the next PHI node 00604 } 00605 } 00606 00607 // Actually revector the branch now... 00608 TI->setSuccessor(SuccNo, Dest); 00609 00610 // If we just introduced a critical edge in the flow graph, make sure to break 00611 // it right away... 00612 SplitCriticalEdge(TI, SuccNo, this); 00613 00614 // Make sure that we don't introduce critical edges from oldsucc now! 00615 for (unsigned i = 0, e = OldSucc->getTerminator()->getNumSuccessors(); 00616 i != e; ++i) 00617 if (isCriticalEdge(OldSucc->getTerminator(), i)) 00618 SplitCriticalEdge(OldSucc->getTerminator(), i, this); 00619 00620 // Since we invalidated the CFG, recalculate the dominator set so that it is 00621 // useful for later processing! 00622 // FIXME: This is much worse than it really should be! 00623 //DS->recalculate(); 00624 00625 DEBUG(std::cerr << "After forwarding: " << *BB->getParent()); 00626 } 00627 00628 /// ReplaceUsesOfValueInRegion - This method replaces all uses of Orig with uses 00629 /// of New. It only affects instructions that are defined in basic blocks that 00630 /// are dominated by Head. 00631 /// 00632 void CEE::ReplaceUsesOfValueInRegion(Value *Orig, Value *New, 00633 BasicBlock *RegionDominator) { 00634 assert(Orig != New && "Cannot replace value with itself"); 00635 std::vector<Instruction*> InstsToChange; 00636 std::vector<PHINode*> PHIsToChange; 00637 InstsToChange.reserve(Orig->use_size()); 00638 00639 // Loop over instructions adding them to InstsToChange vector, this allows us 00640 // an easy way to avoid invalidating the use_iterator at a bad time. 00641 for (Value::use_iterator I = Orig->use_begin(), E = Orig->use_end(); 00642 I != E; ++I) 00643 if (Instruction *User = dyn_cast<Instruction>(*I)) 00644 if (DS->dominates(RegionDominator, User->getParent())) 00645 InstsToChange.push_back(User); 00646 else if (PHINode *PN = dyn_cast<PHINode>(User)) { 00647 PHIsToChange.push_back(PN); 00648 } 00649 00650 // PHIsToChange contains PHI nodes that use Orig that do not live in blocks 00651 // dominated by orig. If the block the value flows in from is dominated by 00652 // RegionDominator, then we rewrite the PHI 00653 for (unsigned i = 0, e = PHIsToChange.size(); i != e; ++i) { 00654 PHINode *PN = PHIsToChange[i]; 00655 for (unsigned j = 0, e = PN->getNumIncomingValues(); j != e; ++j) 00656 if (PN->getIncomingValue(j) == Orig && 00657 DS->dominates(RegionDominator, PN->getIncomingBlock(j))) 00658 PN->setIncomingValue(j, New); 00659 } 00660 00661 // Loop over the InstsToChange list, replacing all uses of Orig with uses of 00662 // New. This list contains all of the instructions in our region that use 00663 // Orig. 00664 for (unsigned i = 0, e = InstsToChange.size(); i != e; ++i) 00665 if (PHINode *PN = dyn_cast<PHINode>(InstsToChange[i])) { 00666 // PHINodes must be handled carefully. If the PHI node itself is in the 00667 // region, we have to make sure to only do the replacement for incoming 00668 // values that correspond to basic blocks in the region. 00669 for (unsigned j = 0, e = PN->getNumIncomingValues(); j != e; ++j) 00670 if (PN->getIncomingValue(j) == Orig && 00671 DS->dominates(RegionDominator, PN->getIncomingBlock(j))) 00672 PN->setIncomingValue(j, New); 00673 00674 } else { 00675 InstsToChange[i]->replaceUsesOfWith(Orig, New); 00676 } 00677 } 00678 00679 static void CalcRegionExitBlocks(BasicBlock *Header, BasicBlock *BB, 00680 std::set<BasicBlock*> &Visited, 00681 DominatorSet &DS, 00682 std::vector<BasicBlock*> &RegionExitBlocks) { 00683 if (Visited.count(BB)) return; 00684 Visited.insert(BB); 00685 00686 if (DS.dominates(Header, BB)) { // Block in the region, recursively traverse 00687 for (succ_iterator I = succ_begin(BB), E = succ_end(BB); I != E; ++I) 00688 CalcRegionExitBlocks(Header, *I, Visited, DS, RegionExitBlocks); 00689 } else { 00690 // Header does not dominate this block, but we have a predecessor that does 00691 // dominate us. Add ourself to the list. 00692 RegionExitBlocks.push_back(BB); 00693 } 00694 } 00695 00696 /// CalculateRegionExitBlocks - Find all of the blocks that are not dominated by 00697 /// BB, but have predecessors that are. Additionally, prune down the set to 00698 /// only include blocks that are dominated by OldSucc as well. 00699 /// 00700 void CEE::CalculateRegionExitBlocks(BasicBlock *BB, BasicBlock *OldSucc, 00701 std::vector<BasicBlock*> &RegionExitBlocks){ 00702 std::set<BasicBlock*> Visited; // Don't infinite loop 00703 00704 // Recursively calculate blocks we are interested in... 00705 CalcRegionExitBlocks(BB, BB, Visited, *DS, RegionExitBlocks); 00706 00707 // Filter out blocks that are not dominated by OldSucc... 00708 for (unsigned i = 0; i != RegionExitBlocks.size(); ) { 00709 if (DS->dominates(OldSucc, RegionExitBlocks[i])) 00710 ++i; // Block is ok, keep it. 00711 else { 00712 // Move to end of list... 00713 std::swap(RegionExitBlocks[i], RegionExitBlocks.back()); 00714 RegionExitBlocks.pop_back(); // Nuke the end 00715 } 00716 } 00717 } 00718 00719 void CEE::InsertRegionExitMerges(PHINode *BBVal, Instruction *OldVal, 00720 const std::vector<BasicBlock*> &RegionExitBlocks) { 00721 assert(BBVal->getType() == OldVal->getType() && "Should be derived values!"); 00722 BasicBlock *BB = BBVal->getParent(); 00723 BasicBlock *OldSucc = OldVal->getParent(); 00724 00725 // Loop over all of the blocks we have to place PHIs in, doing it. 00726 for (unsigned i = 0, e = RegionExitBlocks.size(); i != e; ++i) { 00727 BasicBlock *FBlock = RegionExitBlocks[i]; // Block on the frontier 00728 00729 // Create the new PHI node 00730 PHINode *NewPN = new PHINode(BBVal->getType(), 00731 OldVal->getName()+".fw_frontier", 00732 FBlock->begin()); 00733 00734 // Add an incoming value for every predecessor of the block... 00735 for (pred_iterator PI = pred_begin(FBlock), PE = pred_end(FBlock); 00736 PI != PE; ++PI) { 00737 // If the incoming edge is from the region dominated by BB, use BBVal, 00738 // otherwise use OldVal. 00739 NewPN->addIncoming(DS->dominates(BB, *PI) ? BBVal : OldVal, *PI); 00740 } 00741 00742 // Now make everyone dominated by this block use this new value! 00743 ReplaceUsesOfValueInRegion(OldVal, NewPN, FBlock); 00744 } 00745 } 00746 00747 00748 00749 // BuildRankMap - This method builds the rank map data structure which gives 00750 // each instruction/value in the function a value based on how early it appears 00751 // in the function. We give constants and globals rank 0, arguments are 00752 // numbered starting at one, and instructions are numbered in reverse post-order 00753 // from where the arguments leave off. This gives instructions in loops higher 00754 // values than instructions not in loops. 00755 // 00756 void CEE::BuildRankMap(Function &F) { 00757 unsigned Rank = 1; // Skip rank zero. 00758 00759 // Number the arguments... 00760 for (Function::aiterator I = F.abegin(), E = F.aend(); I != E; ++I) 00761 RankMap[I] = Rank++; 00762 00763 // Number the instructions in reverse post order... 00764 ReversePostOrderTraversal<Function*> RPOT(&F); 00765 for (ReversePostOrderTraversal<Function*>::rpo_iterator I = RPOT.begin(), 00766 E = RPOT.end(); I != E; ++I) 00767 for (BasicBlock::iterator BBI = (*I)->begin(), E = (*I)->end(); 00768 BBI != E; ++BBI) 00769 if (BBI->getType() != Type::VoidTy) 00770 RankMap[BBI] = Rank++; 00771 } 00772 00773 00774 // PropagateBranchInfo - When this method is invoked, we need to propagate 00775 // information derived from the branch condition into the true and false 00776 // branches of BI. Since we know that there aren't any critical edges in the 00777 // flow graph, this can proceed unconditionally. 00778 // 00779 void CEE::PropagateBranchInfo(BranchInst *BI) { 00780 assert(BI->isConditional() && "Must be a conditional branch!"); 00781 00782 // Propagate information into the true block... 00783 // 00784 PropagateEquality(BI->getCondition(), ConstantBool::True, 00785 getRegionInfo(BI->getSuccessor(0))); 00786 00787 // Propagate information into the false block... 00788 // 00789 PropagateEquality(BI->getCondition(), ConstantBool::False, 00790 getRegionInfo(BI->getSuccessor(1))); 00791 } 00792 00793 00794 // PropagateEquality - If we discover that two values are equal to each other in 00795 // a specified region, propagate this knowledge recursively. 00796 // 00797 void CEE::PropagateEquality(Value *Op0, Value *Op1, RegionInfo &RI) { 00798 if (Op0 == Op1) return; // Gee whiz. Are these really equal each other? 00799 00800 if (isa<Constant>(Op0)) // Make sure the constant is always Op1 00801 std::swap(Op0, Op1); 00802 00803 // Make sure we don't already know these are equal, to avoid infinite loops... 00804 ValueInfo &VI = RI.getValueInfo(Op0); 00805 00806 // Get information about the known relationship between Op0 & Op1 00807 Relation &KnownRelation = VI.getRelation(Op1); 00808 00809 // If we already know they're equal, don't reprocess... 00810 if (KnownRelation.getRelation() == Instruction::SetEQ) 00811 return; 00812 00813 // If this is boolean, check to see if one of the operands is a constant. If 00814 // it's a constant, then see if the other one is one of a setcc instruction, 00815 // an AND, OR, or XOR instruction. 00816 // 00817 if (ConstantBool *CB = dyn_cast<ConstantBool>(Op1)) { 00818 00819 if (Instruction *Inst = dyn_cast<Instruction>(Op0)) { 00820 // If we know that this instruction is an AND instruction, and the result 00821 // is true, this means that both operands to the OR are known to be true 00822 // as well. 00823 // 00824 if (CB->getValue() && Inst->getOpcode() == Instruction::And) { 00825 PropagateEquality(Inst->getOperand(0), CB, RI); 00826 PropagateEquality(Inst->getOperand(1), CB, RI); 00827 } 00828 00829 // If we know that this instruction is an OR instruction, and the result 00830 // is false, this means that both operands to the OR are know to be false 00831 // as well. 00832 // 00833 if (!CB->getValue() && Inst->getOpcode() == Instruction::Or) { 00834 PropagateEquality(Inst->getOperand(0), CB, RI); 00835 PropagateEquality(Inst->getOperand(1), CB, RI); 00836 } 00837 00838 // If we know that this instruction is a NOT instruction, we know that the 00839 // operand is known to be the inverse of whatever the current value is. 00840 // 00841 if (BinaryOperator *BOp = dyn_cast<BinaryOperator>(Inst)) 00842 if (BinaryOperator::isNot(BOp)) 00843 PropagateEquality(BinaryOperator::getNotArgument(BOp), 00844 ConstantBool::get(!CB->getValue()), RI); 00845 00846 // If we know the value of a SetCC instruction, propagate the information 00847 // about the relation into this region as well. 00848 // 00849 if (SetCondInst *SCI = dyn_cast<SetCondInst>(Inst)) { 00850 if (CB->getValue()) { // If we know the condition is true... 00851 // Propagate info about the LHS to the RHS & RHS to LHS 00852 PropagateRelation(SCI->getOpcode(), SCI->getOperand(0), 00853 SCI->getOperand(1), RI); 00854 PropagateRelation(SCI->getSwappedCondition(), 00855 SCI->getOperand(1), SCI->getOperand(0), RI); 00856 00857 } else { // If we know the condition is false... 00858 // We know the opposite of the condition is true... 00859 Instruction::BinaryOps C = SCI->getInverseCondition(); 00860 00861 PropagateRelation(C, SCI->getOperand(0), SCI->getOperand(1), RI); 00862 PropagateRelation(SetCondInst::getSwappedCondition(C), 00863 SCI->getOperand(1), SCI->getOperand(0), RI); 00864 } 00865 } 00866 } 00867 } 00868 00869 // Propagate information about Op0 to Op1 & visa versa 00870 PropagateRelation(Instruction::SetEQ, Op0, Op1, RI); 00871 PropagateRelation(Instruction::SetEQ, Op1, Op0, RI); 00872 } 00873 00874 00875 // PropagateRelation - We know that the specified relation is true in all of the 00876 // blocks in the specified region. Propagate the information about Op0 and 00877 // anything derived from it into this region. 00878 // 00879 void CEE::PropagateRelation(Instruction::BinaryOps Opcode, Value *Op0, 00880 Value *Op1, RegionInfo &RI) { 00881 assert(Op0->getType() == Op1->getType() && "Equal types expected!"); 00882 00883 // Constants are already pretty well understood. We will apply information 00884 // about the constant to Op1 in another call to PropagateRelation. 00885 // 00886 if (isa<Constant>(Op0)) return; 00887 00888 // Get the region information for this block to update... 00889 ValueInfo &VI = RI.getValueInfo(Op0); 00890 00891 // Get information about the known relationship between Op0 & Op1 00892 Relation &Op1R = VI.getRelation(Op1); 00893 00894 // Quick bailout for common case if we are reprocessing an instruction... 00895 if (Op1R.getRelation() == Opcode) 00896 return; 00897 00898 // If we already have information that contradicts the current information we 00899 // are propagating, ignore this info. Something bad must have happened! 00900 // 00901 if (Op1R.contradicts(Opcode, VI)) { 00902 Op1R.contradicts(Opcode, VI); 00903 std::cerr << "Contradiction found for opcode: " 00904 << Instruction::getOpcodeName(Opcode) << "\n"; 00905 Op1R.print(std::cerr); 00906 return; 00907 } 00908 00909 // If the information propagated is new, then we want process the uses of this 00910 // instruction to propagate the information down to them. 00911 // 00912 if (Op1R.incorporate(Opcode, VI)) 00913 UpdateUsersOfValue(Op0, RI); 00914 } 00915 00916 00917 // UpdateUsersOfValue - The information about V in this region has been updated. 00918 // Propagate this to all consumers of the value. 00919 // 00920 void CEE::UpdateUsersOfValue(Value *V, RegionInfo &RI) { 00921 for (Value::use_iterator I = V->use_begin(), E = V->use_end(); 00922 I != E; ++I) 00923 if (Instruction *Inst = dyn_cast<Instruction>(*I)) { 00924 // If this is an instruction using a value that we know something about, 00925 // try to propagate information to the value produced by the 00926 // instruction. We can only do this if it is an instruction we can 00927 // propagate information for (a setcc for example), and we only WANT to 00928 // do this if the instruction dominates this region. 00929 // 00930 // If the instruction doesn't dominate this region, then it cannot be 00931 // used in this region and we don't care about it. If the instruction 00932 // is IN this region, then we will simplify the instruction before we 00933 // get to uses of it anyway, so there is no reason to bother with it 00934 // here. This check is also effectively checking to make sure that Inst 00935 // is in the same function as our region (in case V is a global f.e.). 00936 // 00937 if (DS->properlyDominates(Inst->getParent(), RI.getEntryBlock())) 00938 IncorporateInstruction(Inst, RI); 00939 } 00940 } 00941 00942 // IncorporateInstruction - We just updated the information about one of the 00943 // operands to the specified instruction. Update the information about the 00944 // value produced by this instruction 00945 // 00946 void CEE::IncorporateInstruction(Instruction *Inst, RegionInfo &RI) { 00947 if (SetCondInst *SCI = dyn_cast<SetCondInst>(Inst)) { 00948 // See if we can figure out a result for this instruction... 00949 Relation::KnownResult Result = getSetCCResult(SCI, RI); 00950 if (Result != Relation::Unknown) { 00951 PropagateEquality(SCI, Result ? ConstantBool::True : ConstantBool::False, 00952 RI); 00953 } 00954 } 00955 } 00956 00957 00958 // ComputeReplacements - Some values are known to be equal to other values in a 00959 // region. For example if there is a comparison of equality between a variable 00960 // X and a constant C, we can replace all uses of X with C in the region we are 00961 // interested in. We generalize this replacement to replace variables with 00962 // other variables if they are equal and there is a variable with lower rank 00963 // than the current one. This offers a canonicalizing property that exposes 00964 // more redundancies for later transformations to take advantage of. 00965 // 00966 void CEE::ComputeReplacements(RegionInfo &RI) { 00967 // Loop over all of the values in the region info map... 00968 for (RegionInfo::iterator I = RI.begin(), E = RI.end(); I != E; ++I) { 00969 ValueInfo &VI = I->second; 00970 00971 // If we know that this value is a particular constant, set Replacement to 00972 // the constant... 00973 Value *Replacement = VI.getBounds().getSingleElement(); 00974 00975 // If this value is not known to be some constant, figure out the lowest 00976 // rank value that it is known to be equal to (if anything). 00977 // 00978 if (Replacement == 0) { 00979 // Find out if there are any equality relationships with values of lower 00980 // rank than VI itself... 00981 unsigned MinRank = getRank(I->first); 00982 00983 // Loop over the relationships known about Op0. 00984 const std::vector<Relation> &Relationships = VI.getRelationships(); 00985 for (unsigned i = 0, e = Relationships.size(); i != e; ++i) 00986 if (Relationships[i].getRelation() == Instruction::SetEQ) { 00987 unsigned R = getRank(Relationships[i].getValue()); 00988 if (R < MinRank) { 00989 MinRank = R; 00990 Replacement = Relationships[i].getValue(); 00991 } 00992 } 00993 } 00994 00995 // If we found something to replace this value with, keep track of it. 00996 if (Replacement) 00997 VI.setReplacement(Replacement); 00998 } 00999 } 01000 01001 // SimplifyBasicBlock - Given information about values in region RI, simplify 01002 // the instructions in the specified basic block. 01003 // 01004 bool CEE::SimplifyBasicBlock(BasicBlock &BB, const RegionInfo &RI) { 01005 bool Changed = false; 01006 for (BasicBlock::iterator I = BB.begin(), E = BB.end(); I != E; ) { 01007 Instruction *Inst = I++; 01008 01009 // Convert instruction arguments to canonical forms... 01010 Changed |= SimplifyInstruction(Inst, RI); 01011 01012 if (SetCondInst *SCI = dyn_cast<SetCondInst>(Inst)) { 01013 // Try to simplify a setcc instruction based on inherited information 01014 Relation::KnownResult Result = getSetCCResult(SCI, RI); 01015 if (Result != Relation::Unknown) { 01016 DEBUG(std::cerr << "Replacing setcc with " << Result 01017 << " constant: " << *SCI); 01018 01019 SCI->replaceAllUsesWith(ConstantBool::get((bool)Result)); 01020 // The instruction is now dead, remove it from the program. 01021 SCI->getParent()->getInstList().erase(SCI); 01022 ++NumSetCCRemoved; 01023 Changed = true; 01024 } 01025 } 01026 } 01027 01028 return Changed; 01029 } 01030 01031 // SimplifyInstruction - Inspect the operands of the instruction, converting 01032 // them to their canonical form if possible. This takes care of, for example, 01033 // replacing a value 'X' with a constant 'C' if the instruction in question is 01034 // dominated by a true seteq 'X', 'C'. 01035 // 01036 bool CEE::SimplifyInstruction(Instruction *I, const RegionInfo &RI) { 01037 bool Changed = false; 01038 01039 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) 01040 if (const ValueInfo *VI = RI.requestValueInfo(I->getOperand(i))) 01041 if (Value *Repl = VI->getReplacement()) { 01042 // If we know if a replacement with lower rank than Op0, make the 01043 // replacement now. 01044 DEBUG(std::cerr << "In Inst: " << *I << " Replacing operand #" << i 01045 << " with " << *Repl << "\n"); 01046 I->setOperand(i, Repl); 01047 Changed = true; 01048 ++NumOperandsCann; 01049 } 01050 01051 return Changed; 01052 } 01053 01054 01055 // getSetCCResult - Try to simplify a setcc instruction based on information 01056 // inherited from a dominating setcc instruction. V is one of the operands to 01057 // the setcc instruction, and VI is the set of information known about it. We 01058 // take two cases into consideration here. If the comparison is against a 01059 // constant value, we can use the constant range to see if the comparison is 01060 // possible to succeed. If it is not a comparison against a constant, we check 01061 // to see if there is a known relationship between the two values. If so, we 01062 // may be able to eliminate the check. 01063 // 01064 Relation::KnownResult CEE::getSetCCResult(SetCondInst *SCI, 01065 const RegionInfo &RI) { 01066 Value *Op0 = SCI->getOperand(0), *Op1 = SCI->getOperand(1); 01067 Instruction::BinaryOps Opcode = SCI->getOpcode(); 01068 01069 if (isa<Constant>(Op0)) { 01070 if (isa<Constant>(Op1)) { 01071 if (Constant *Result = ConstantFoldInstruction(SCI)) { 01072 // Wow, this is easy, directly eliminate the SetCondInst. 01073 DEBUG(std::cerr << "Replacing setcc with constant fold: " << *SCI); 01074 return cast<ConstantBool>(Result)->getValue() 01075 ? Relation::KnownTrue : Relation::KnownFalse; 01076 } 01077 } else { 01078 // We want to swap this instruction so that operand #0 is the constant. 01079 std::swap(Op0, Op1); 01080 Opcode = SCI->getSwappedCondition(); 01081 } 01082 } 01083 01084 // Try to figure out what the result of this comparison will be... 01085 Relation::KnownResult Result = Relation::Unknown; 01086 01087 // We have to know something about the relationship to prove anything... 01088 if (const ValueInfo *Op0VI = RI.requestValueInfo(Op0)) { 01089 01090 // At this point, we know that if we have a constant argument that it is in 01091 // Op1. Check to see if we know anything about comparing value with a 01092 // constant, and if we can use this info to fold the setcc. 01093 // 01094 if (ConstantIntegral *C = dyn_cast<ConstantIntegral>(Op1)) { 01095 // Check to see if we already know the result of this comparison... 01096 ConstantRange R = ConstantRange(Opcode, C); 01097 ConstantRange Int = R.intersectWith(Op0VI->getBounds()); 01098 01099 // If the intersection of the two ranges is empty, then the condition 01100 // could never be true! 01101 // 01102 if (Int.isEmptySet()) { 01103 Result = Relation::KnownFalse; 01104 01105 // Otherwise, if VI.getBounds() (the possible values) is a subset of R 01106 // (the allowed values) then we know that the condition must always be 01107 // true! 01108 // 01109 } else if (Int == Op0VI->getBounds()) { 01110 Result = Relation::KnownTrue; 01111 } 01112 } else { 01113 // If we are here, we know that the second argument is not a constant 01114 // integral. See if we know anything about Op0 & Op1 that allows us to 01115 // fold this anyway. 01116 // 01117 // Do we have value information about Op0 and a relation to Op1? 01118 if (const Relation *Op2R = Op0VI->requestRelation(Op1)) 01119 Result = Op2R->getImpliedResult(Opcode); 01120 } 01121 } 01122 return Result; 01123 } 01124 01125 //===----------------------------------------------------------------------===// 01126 // Relation Implementation 01127 //===----------------------------------------------------------------------===// 01128 01129 // CheckCondition - Return true if the specified condition is false. Bound may 01130 // be null. 01131 static bool CheckCondition(Constant *Bound, Constant *C, 01132 Instruction::BinaryOps BO) { 01133 assert(C != 0 && "C is not specified!"); 01134 if (Bound == 0) return false; 01135 01136 Constant *Val = ConstantExpr::get(BO, Bound, C); 01137 if (ConstantBool *CB = dyn_cast<ConstantBool>(Val)) 01138 return !CB->getValue(); // Return true if the condition is false... 01139 return false; 01140 } 01141 01142 // contradicts - Return true if the relationship specified by the operand 01143 // contradicts already known information. 01144 // 01145 bool Relation::contradicts(Instruction::BinaryOps Op, 01146 const ValueInfo &VI) const { 01147 assert (Op != Instruction::Add && "Invalid relation argument!"); 01148 01149 // If this is a relationship with a constant, make sure that this relationship 01150 // does not contradict properties known about the bounds of the constant. 01151 // 01152 if (ConstantIntegral *C = dyn_cast<ConstantIntegral>(Val)) 01153 if (ConstantRange(Op, C).intersectWith(VI.getBounds()).isEmptySet()) 01154 return true; 01155 01156 switch (Rel) { 01157 default: assert(0 && "Unknown Relationship code!"); 01158 case Instruction::Add: return false; // Nothing known, nothing contradicts 01159 case Instruction::SetEQ: 01160 return Op == Instruction::SetLT || Op == Instruction::SetGT || 01161 Op == Instruction::SetNE; 01162 case Instruction::SetNE: return Op == Instruction::SetEQ; 01163 case Instruction::SetLE: return Op == Instruction::SetGT; 01164 case Instruction::SetGE: return Op == Instruction::SetLT; 01165 case Instruction::SetLT: 01166 return Op == Instruction::SetEQ || Op == Instruction::SetGT || 01167 Op == Instruction::SetGE; 01168 case Instruction::SetGT: 01169 return Op == Instruction::SetEQ || Op == Instruction::SetLT || 01170 Op == Instruction::SetLE; 01171 } 01172 } 01173 01174 // incorporate - Incorporate information in the argument into this relation 01175 // entry. This assumes that the information doesn't contradict itself. If any 01176 // new information is gained, true is returned, otherwise false is returned to 01177 // indicate that nothing was updated. 01178 // 01179 bool Relation::incorporate(Instruction::BinaryOps Op, ValueInfo &VI) { 01180 assert(!contradicts(Op, VI) && 01181 "Cannot incorporate contradictory information!"); 01182 01183 // If this is a relationship with a constant, make sure that we update the 01184 // range that is possible for the value to have... 01185 // 01186 if (ConstantIntegral *C = dyn_cast<ConstantIntegral>(Val)) 01187 VI.getBounds() = ConstantRange(Op, C).intersectWith(VI.getBounds()); 01188 01189 switch (Rel) { 01190 default: assert(0 && "Unknown prior value!"); 01191 case Instruction::Add: Rel = Op; return true; 01192 case Instruction::SetEQ: return false; // Nothing is more precise 01193 case Instruction::SetNE: return false; // Nothing is more precise 01194 case Instruction::SetLT: return false; // Nothing is more precise 01195 case Instruction::SetGT: return false; // Nothing is more precise 01196 case Instruction::SetLE: 01197 if (Op == Instruction::SetEQ || Op == Instruction::SetLT) { 01198 Rel = Op; 01199 return true; 01200 } else if (Op == Instruction::SetNE) { 01201 Rel = Instruction::SetLT; 01202 return true; 01203 } 01204 return false; 01205 case Instruction::SetGE: return Op == Instruction::SetLT; 01206 if (Op == Instruction::SetEQ || Op == Instruction::SetGT) { 01207 Rel = Op; 01208 return true; 01209 } else if (Op == Instruction::SetNE) { 01210 Rel = Instruction::SetGT; 01211 return true; 01212 } 01213 return false; 01214 } 01215 } 01216 01217 // getImpliedResult - If this relationship between two values implies that 01218 // the specified relationship is true or false, return that. If we cannot 01219 // determine the result required, return Unknown. 01220 // 01221 Relation::KnownResult 01222 Relation::getImpliedResult(Instruction::BinaryOps Op) const { 01223 if (Rel == Op) return KnownTrue; 01224 if (Rel == SetCondInst::getInverseCondition(Op)) return KnownFalse; 01225 01226 switch (Rel) { 01227 default: assert(0 && "Unknown prior value!"); 01228 case Instruction::SetEQ: 01229 if (Op == Instruction::SetLE || Op == Instruction::SetGE) return KnownTrue; 01230 if (Op == Instruction::SetLT || Op == Instruction::SetGT) return KnownFalse; 01231 break; 01232 case Instruction::SetLT: 01233 if (Op == Instruction::SetNE || Op == Instruction::SetLE) return KnownTrue; 01234 if (Op == Instruction::SetEQ) return KnownFalse; 01235 break; 01236 case Instruction::SetGT: 01237 if (Op == Instruction::SetNE || Op == Instruction::SetGE) return KnownTrue; 01238 if (Op == Instruction::SetEQ) return KnownFalse; 01239 break; 01240 case Instruction::SetNE: 01241 case Instruction::SetLE: 01242 case Instruction::SetGE: 01243 case Instruction::Add: 01244 break; 01245 } 01246 return Unknown; 01247 } 01248 01249 01250 //===----------------------------------------------------------------------===// 01251 // Printing Support... 01252 //===----------------------------------------------------------------------===// 01253 01254 // print - Implement the standard print form to print out analysis information. 01255 void CEE::print(std::ostream &O, const Module *M) const { 01256 O << "\nPrinting Correlated Expression Info:\n"; 01257 for (std::map<BasicBlock*, RegionInfo>::const_iterator I = 01258 RegionInfoMap.begin(), E = RegionInfoMap.end(); I != E; ++I) 01259 I->second.print(O); 01260 } 01261 01262 // print - Output information about this region... 01263 void RegionInfo::print(std::ostream &OS) const { 01264 if (ValueMap.empty()) return; 01265 01266 OS << " RegionInfo for basic block: " << BB->getName() << "\n"; 01267 for (std::map<Value*, ValueInfo>::const_iterator 01268 I = ValueMap.begin(), E = ValueMap.end(); I != E; ++I) 01269 I->second.print(OS, I->first); 01270 OS << "\n"; 01271 } 01272 01273 // print - Output information about this value relation... 01274 void ValueInfo::print(std::ostream &OS, Value *V) const { 01275 if (Relationships.empty()) return; 01276 01277 if (V) { 01278 OS << " ValueInfo for: "; 01279 WriteAsOperand(OS, V); 01280 } 01281 OS << "\n Bounds = " << Bounds << "\n"; 01282 if (Replacement) { 01283 OS << " Replacement = "; 01284 WriteAsOperand(OS, Replacement); 01285 OS << "\n"; 01286 } 01287 for (unsigned i = 0, e = Relationships.size(); i != e; ++i) 01288 Relationships[i].print(OS); 01289 } 01290 01291 // print - Output this relation to the specified stream 01292 void Relation::print(std::ostream &OS) const { 01293 OS << " is "; 01294 switch (Rel) { 01295 default: OS << "*UNKNOWN*"; break; 01296 case Instruction::SetEQ: OS << "== "; break; 01297 case Instruction::SetNE: OS << "!= "; break; 01298 case Instruction::SetLT: OS << "< "; break; 01299 case Instruction::SetGT: OS << "> "; break; 01300 case Instruction::SetLE: OS << "<= "; break; 01301 case Instruction::SetGE: OS << ">= "; break; 01302 } 01303 01304 WriteAsOperand(OS, Val); 01305 OS << "\n"; 01306 } 01307 01308 // Don't inline these methods or else we won't be able to call them from GDB! 01309 void Relation::dump() const { print(std::cerr); } 01310 void ValueInfo::dump() const { print(std::cerr, 0); } 01311 void RegionInfo::dump() const { print(std::cerr); }