| //===- CorrelatedExprs.cpp - Pass to detect and eliminated c.e.'s ---------===// |
| // |
| // Correlated Expression Elimination propogates information from conditional |
| // branches to blocks dominated by destinations of the branch. It propogates |
| // information from the condition check itself into the body of the branch, |
| // allowing transformations like these for example: |
| // |
| // if (i == 7) |
| // ... 4*i; // constant propogation |
| // |
| // M = i+1; N = j+1; |
| // if (i == j) |
| // X = M-N; // = M-M == 0; |
| // |
| // This is called Correlated Expression Elimination because we eliminate or |
| // simplify expressions that are correlated with the direction of a branch. In |
| // this way we use static information to give us some information about the |
| // dynamic value of a variable. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #include "llvm/Transforms/Scalar.h" |
| #include "llvm/Pass.h" |
| #include "llvm/Function.h" |
| #include "llvm/iTerminators.h" |
| #include "llvm/iOperators.h" |
| #include "llvm/ConstantHandling.h" |
| #include "llvm/Assembly/Writer.h" |
| #include "llvm/Analysis/Dominators.h" |
| #include "llvm/Transforms/Utils/Local.h" |
| #include "llvm/Support/ConstantRange.h" |
| #include "llvm/Support/CFG.h" |
| #include "Support/PostOrderIterator.h" |
| #include "Support/StatisticReporter.h" |
| #include <algorithm> |
| |
| namespace { |
| Statistic<>NumSetCCRemoved("cee\t\t- Number of setcc instruction eliminated"); |
| Statistic<>NumOperandsCann("cee\t\t- Number of operands cannonicalized"); |
| Statistic<>BranchRevectors("cee\t\t- Number of branches revectored"); |
| |
| class ValueInfo; |
| class Relation { |
| Value *Val; // Relation to what value? |
| Instruction::BinaryOps Rel; // SetCC relation, or Add if no information |
| public: |
| Relation(Value *V) : Val(V), Rel(Instruction::Add) {} |
| bool operator<(const Relation &R) const { return Val < R.Val; } |
| Value *getValue() const { return Val; } |
| Instruction::BinaryOps getRelation() const { return Rel; } |
| |
| // contradicts - Return true if the relationship specified by the operand |
| // contradicts already known information. |
| // |
| bool contradicts(Instruction::BinaryOps Rel, const ValueInfo &VI) const; |
| |
| // incorporate - Incorporate information in the argument into this relation |
| // entry. This assumes that the information doesn't contradict itself. If |
| // any new information is gained, true is returned, otherwise false is |
| // returned to indicate that nothing was updated. |
| // |
| bool incorporate(Instruction::BinaryOps Rel, ValueInfo &VI); |
| |
| // KnownResult - Whether or not this condition determines the result of a |
| // setcc in the program. False & True are intentionally 0 & 1 so we can |
| // convert to bool by casting after checking for unknown. |
| // |
| enum KnownResult { KnownFalse = 0, KnownTrue = 1, Unknown = 2 }; |
| |
| // getImpliedResult - If this relationship between two values implies that |
| // the specified relationship is true or false, return that. If we cannot |
| // determine the result required, return Unknown. |
| // |
| KnownResult getImpliedResult(Instruction::BinaryOps Rel) const; |
| |
| // print - Output this relation to the specified stream |
| void print(std::ostream &OS) const; |
| void dump() const; |
| }; |
| |
| |
| // ValueInfo - One instance of this record exists for every value with |
| // relationships between other values. It keeps track of all of the |
| // relationships to other values in the program (specified with Relation) that |
| // are known to be valid in a region. |
| // |
| class ValueInfo { |
| // RelationShips - this value is know to have the specified relationships to |
| // other values. There can only be one entry per value, and this list is |
| // kept sorted by the Val field. |
| std::vector<Relation> Relationships; |
| |
| // If information about this value is known or propogated from constant |
| // expressions, this range contains the possible values this value may hold. |
| ConstantRange Bounds; |
| |
| // If we find that this value is equal to another value that has a lower |
| // rank, this value is used as it's replacement. |
| // |
| Value *Replacement; |
| public: |
| ValueInfo(const Type *Ty) |
| : Bounds(Ty->isIntegral() ? Ty : Type::IntTy), Replacement(0) {} |
| |
| // getBounds() - Return the constant bounds of the value... |
| const ConstantRange &getBounds() const { return Bounds; } |
| ConstantRange &getBounds() { return Bounds; } |
| |
| const std::vector<Relation> &getRelationships() { return Relationships; } |
| |
| // getReplacement - Return the value this value is to be replaced with if it |
| // exists, otherwise return null. |
| // |
| Value *getReplacement() const { return Replacement; } |
| |
| // setReplacement - Used by the replacement calculation pass to figure out |
| // what to replace this value with, if anything. |
| // |
| void setReplacement(Value *Repl) { Replacement = Repl; } |
| |
| // getRelation - return the relationship entry for the specified value. |
| // This can invalidate references to other Relation's, so use it carefully. |
| // |
| Relation &getRelation(Value *V) { |
| // Binary search for V's entry... |
| std::vector<Relation>::iterator I = |
| std::lower_bound(Relationships.begin(), Relationships.end(), V); |
| |
| // If we found the entry, return it... |
| if (I != Relationships.end() && I->getValue() == V) |
| return *I; |
| |
| // Insert and return the new relationship... |
| return *Relationships.insert(I, V); |
| } |
| |
| const Relation *requestRelation(Value *V) const { |
| // Binary search for V's entry... |
| std::vector<Relation>::const_iterator I = |
| std::lower_bound(Relationships.begin(), Relationships.end(), V); |
| if (I != Relationships.end() && I->getValue() == V) |
| return &*I; |
| return 0; |
| } |
| |
| // print - Output information about this value relation... |
| void print(std::ostream &OS, Value *V) const; |
| void dump() const; |
| }; |
| |
| // RegionInfo - Keeps track of all of the value relationships for a region. A |
| // region is the are dominated by a basic block. RegionInfo's keep track of |
| // the RegionInfo for their dominator, because anything known in a dominator |
| // is known to be true in a dominated block as well. |
| // |
| class RegionInfo { |
| BasicBlock *BB; |
| |
| // ValueMap - Tracks the ValueInformation known for this region |
| typedef std::map<Value*, ValueInfo> ValueMapTy; |
| ValueMapTy ValueMap; |
| public: |
| RegionInfo(BasicBlock *bb) : BB(bb) {} |
| |
| // getEntryBlock - Return the block that dominates all of the members of |
| // this region. |
| BasicBlock *getEntryBlock() const { return BB; } |
| |
| const RegionInfo &operator=(const RegionInfo &RI) { |
| ValueMap = RI.ValueMap; |
| return *this; |
| } |
| |
| // print - Output information about this region... |
| void print(std::ostream &OS) const; |
| |
| // Allow external access. |
| typedef ValueMapTy::iterator iterator; |
| iterator begin() { return ValueMap.begin(); } |
| iterator end() { return ValueMap.end(); } |
| |
| ValueInfo &getValueInfo(Value *V) { |
| ValueMapTy::iterator I = ValueMap.lower_bound(V); |
| if (I != ValueMap.end() && I->first == V) return I->second; |
| return ValueMap.insert(I, std::make_pair(V, V->getType()))->second; |
| } |
| |
| const ValueInfo *requestValueInfo(Value *V) const { |
| ValueMapTy::const_iterator I = ValueMap.find(V); |
| if (I != ValueMap.end()) return &I->second; |
| return 0; |
| } |
| }; |
| |
| /// CEE - Correlated Expression Elimination |
| class CEE : public FunctionPass { |
| std::map<Value*, unsigned> RankMap; |
| std::map<BasicBlock*, RegionInfo> RegionInfoMap; |
| DominatorSet *DS; |
| DominatorTree *DT; |
| public: |
| virtual bool runOnFunction(Function &F); |
| |
| // We don't modify the program, so we preserve all analyses |
| virtual void getAnalysisUsage(AnalysisUsage &AU) const { |
| //AU.preservesCFG(); |
| AU.addRequired<DominatorSet>(); |
| AU.addRequired<DominatorTree>(); |
| }; |
| |
| // print - Implement the standard print form to print out analysis |
| // information. |
| virtual void print(std::ostream &O, const Module *M) const; |
| |
| private: |
| RegionInfo &getRegionInfo(BasicBlock *BB) { |
| std::map<BasicBlock*, RegionInfo>::iterator I |
| = RegionInfoMap.lower_bound(BB); |
| if (I != RegionInfoMap.end() && I->first == BB) return I->second; |
| return RegionInfoMap.insert(I, std::make_pair(BB, BB))->second; |
| } |
| |
| void BuildRankMap(Function &F); |
| unsigned getRank(Value *V) const { |
| if (isa<Constant>(V) || isa<GlobalValue>(V)) return 0; |
| std::map<Value*, unsigned>::const_iterator I = RankMap.find(V); |
| if (I != RankMap.end()) return I->second; |
| return 0; // Must be some other global thing |
| } |
| |
| bool TransformRegion(BasicBlock *BB, std::set<BasicBlock*> &VisitedBlocks); |
| |
| BasicBlock *isCorrelatedBranchBlock(BasicBlock *BB, RegionInfo &RI); |
| void PropogateBranchInfo(BranchInst *BI); |
| void PropogateEquality(Value *Op0, Value *Op1, RegionInfo &RI); |
| void PropogateRelation(Instruction::BinaryOps Opcode, Value *Op0, |
| Value *Op1, RegionInfo &RI); |
| void UpdateUsersOfValue(Value *V, RegionInfo &RI); |
| void IncorporateInstruction(Instruction *Inst, RegionInfo &RI); |
| void ComputeReplacements(RegionInfo &RI); |
| |
| |
| // getSetCCResult - Given a setcc instruction, determine if the result is |
| // determined by facts we already know about the region under analysis. |
| // Return KnownTrue, KnownFalse, or Unknown based on what we can determine. |
| // |
| Relation::KnownResult getSetCCResult(SetCondInst *SC, const RegionInfo &RI); |
| |
| |
| bool SimplifyBasicBlock(BasicBlock &BB, const RegionInfo &RI); |
| bool SimplifyInstruction(Instruction *Inst, const RegionInfo &RI); |
| }; |
| RegisterOpt<CEE> X("cee", "Correlated Expression Elimination"); |
| } |
| |
| Pass *createCorrelatedExpressionEliminationPass() { return new CEE(); } |
| |
| |
| bool CEE::runOnFunction(Function &F) { |
| // Build a rank map for the function... |
| BuildRankMap(F); |
| |
| // Traverse the dominator tree, computing information for each node in the |
| // tree. Note that our traversal will not even touch unreachable basic |
| // blocks. |
| DS = &getAnalysis<DominatorSet>(); |
| DT = &getAnalysis<DominatorTree>(); |
| |
| std::set<BasicBlock*> VisitedBlocks; |
| bool Changed = TransformRegion(&F.getEntryNode(), VisitedBlocks); |
| |
| RegionInfoMap.clear(); |
| RankMap.clear(); |
| return Changed; |
| } |
| |
| // TransformRegion - Transform the region starting with BB according to the |
| // calculated region information for the block. Transforming the region |
| // involves analyzing any information this block provides to successors, |
| // propogating the information to successors, and finally transforming |
| // successors. |
| // |
| // This method processes the function in depth first order, which guarantees |
| // that we process the immediate dominator of a block before the block itself. |
| // Because we are passing information from immediate dominators down to |
| // dominatees, we obviously have to process the information source before the |
| // information consumer. |
| // |
| bool CEE::TransformRegion(BasicBlock *BB, std::set<BasicBlock*> &VisitedBlocks){ |
| // Prevent infinite recursion... |
| if (VisitedBlocks.count(BB)) return false; |
| VisitedBlocks.insert(BB); |
| |
| // Get the computed region information for this block... |
| RegionInfo &RI = getRegionInfo(BB); |
| |
| // Compute the replacement information for this block... |
| ComputeReplacements(RI); |
| |
| // If debugging, print computed region information... |
| DEBUG(RI.print(std::cerr)); |
| |
| // Simplify the contents of this block... |
| bool Changed = SimplifyBasicBlock(*BB, RI); |
| |
| // Get the terminator of this basic block... |
| TerminatorInst *TI = BB->getTerminator(); |
| |
| // If this is a conditional branch, make sure that there is a branch target |
| // for each successor that can hold any information gleaned from the branch, |
| // by breaking any critical edges that may be laying about. |
| // |
| if (TI->getNumSuccessors() > 1) { |
| // If any of the successors has multiple incoming branches, add a new dummy |
| // destination branch that only contains an unconditional branch to the real |
| // target. |
| for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) { |
| BasicBlock *Succ = TI->getSuccessor(i); |
| // If there is more than one predecessor of the destination block, break |
| // this critical edge by inserting a new block. This updates dominatorset |
| // and dominatortree information. |
| // |
| if (isCriticalEdge(TI, i)) |
| SplitCriticalEdge(TI, i, this); |
| } |
| } |
| |
| // Loop over all of the blocks that this block is the immediate dominator for. |
| // Because all information known in this region is also known in all of the |
| // blocks that are dominated by this one, we can safely propogate the |
| // information down now. |
| // |
| DominatorTree::Node *BBN = (*DT)[BB]; |
| for (unsigned i = 0, e = BBN->getChildren().size(); i != e; ++i) { |
| BasicBlock *Dominated = BBN->getChildren()[i]->getNode(); |
| assert(RegionInfoMap.find(Dominated) == RegionInfoMap.end() && |
| "RegionInfo should be calculated in dominanace order!"); |
| getRegionInfo(Dominated) = RI; |
| } |
| |
| // Now that all of our successors have information if they deserve it, |
| // propogate any information our terminator instruction finds to our |
| // successors. |
| if (BranchInst *BI = dyn_cast<BranchInst>(TI)) |
| if (BI->isConditional()) |
| PropogateBranchInfo(BI); |
| |
| // If this is a branch to a block outside our region that simply performs |
| // another conditional branch, one whose outcome is known inside of this |
| // region, then vector this outgoing edge directly to the known destination. |
| // |
| for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) { |
| while (BasicBlock *Dest = isCorrelatedBranchBlock(TI->getSuccessor(i), RI)){ |
| TI->setSuccessor(i, Dest); |
| ++BranchRevectors; |
| } |
| } |
| |
| // Now that all of our successors have information, recursively process them. |
| for (unsigned i = 0, e = BBN->getChildren().size(); i != e; ++i) |
| Changed |= TransformRegion(BBN->getChildren()[i]->getNode(), VisitedBlocks); |
| |
| // for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) |
| //Changed |= TransformRegion(TI->getSuccessor(i), VisitedBlocks); |
| |
| return Changed; |
| } |
| |
| // If this block is a simple block not in the current region, which contains |
| // only a conditional branch, we determine if the outcome of the branch can be |
| // determined from information inside of the region. Instead of going to this |
| // block, we can instead go to the destination we know is the right target. |
| // |
| BasicBlock *CEE::isCorrelatedBranchBlock(BasicBlock *BB, RegionInfo &RI) { |
| // Check to see if we dominate the block. If so, this block will get the |
| // condition turned to a constant anyway. |
| // |
| //if (DS->dominates(RI.getEntryBlock(), BB)) |
| // return 0; |
| |
| // Check to see if this is a conditional branch... |
| if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) |
| if (BI->isConditional()) { |
| // Make sure that the block is either empty, or only contains a setcc. |
| if (BB->size() == 1 || |
| (BB->size() == 2 && &BB->front() == BI->getCondition() && |
| BI->getCondition()->use_size() == 1)) |
| if (SetCondInst *SCI = dyn_cast<SetCondInst>(BI->getCondition())) { |
| Relation::KnownResult Result = getSetCCResult(SCI, RI); |
| |
| if (Result == Relation::KnownTrue) |
| return BI->getSuccessor(0); |
| else if (Result == Relation::KnownFalse) |
| return BI->getSuccessor(1); |
| } |
| } |
| return 0; |
| } |
| |
| // BuildRankMap - This method builds the rank map data structure which gives |
| // each instruction/value in the function a value based on how early it appears |
| // in the function. We give constants and globals rank 0, arguments are |
| // numbered starting at one, and instructions are numbered in reverse post-order |
| // from where the arguments leave off. This gives instructions in loops higher |
| // values than instructions not in loops. |
| // |
| void CEE::BuildRankMap(Function &F) { |
| unsigned Rank = 1; // Skip rank zero. |
| |
| // Number the arguments... |
| for (Function::aiterator I = F.abegin(), E = F.aend(); I != E; ++I) |
| RankMap[I] = Rank++; |
| |
| // Number the instructions in reverse post order... |
| ReversePostOrderTraversal<Function*> RPOT(&F); |
| for (ReversePostOrderTraversal<Function*>::rpo_iterator I = RPOT.begin(), |
| E = RPOT.end(); I != E; ++I) |
| for (BasicBlock::iterator BBI = (*I)->begin(), E = (*I)->end(); |
| BBI != E; ++BBI) |
| if (BBI->getType() != Type::VoidTy) |
| RankMap[BBI] = Rank++; |
| } |
| |
| |
| // PropogateBranchInfo - When this method is invoked, we need to propogate |
| // information derived from the branch condition into the true and false |
| // branches of BI. Since we know that there aren't any critical edges in the |
| // flow graph, this can proceed unconditionally. |
| // |
| void CEE::PropogateBranchInfo(BranchInst *BI) { |
| assert(BI->isConditional() && "Must be a conditional branch!"); |
| BasicBlock *BB = BI->getParent(); |
| BasicBlock *TrueBB = BI->getSuccessor(0); |
| BasicBlock *FalseBB = BI->getSuccessor(1); |
| |
| // Propogate information into the true block... |
| // |
| PropogateEquality(BI->getCondition(), ConstantBool::True, |
| getRegionInfo(TrueBB)); |
| |
| // Propogate information into the false block... |
| // |
| PropogateEquality(BI->getCondition(), ConstantBool::False, |
| getRegionInfo(FalseBB)); |
| } |
| |
| |
| // PropogateEquality - If we discover that two values are equal to each other in |
| // a specified region, propogate this knowledge recursively. |
| // |
| void CEE::PropogateEquality(Value *Op0, Value *Op1, RegionInfo &RI) { |
| if (Op0 == Op1) return; // Gee whiz. Are these really equal each other? |
| |
| if (isa<Constant>(Op0)) // Make sure the constant is always Op1 |
| std::swap(Op0, Op1); |
| |
| // Make sure we don't already know these are equal, to avoid infinite loops... |
| ValueInfo &VI = RI.getValueInfo(Op0); |
| |
| // Get information about the known relationship between Op0 & Op1 |
| Relation &KnownRelation = VI.getRelation(Op1); |
| |
| // If we already know they're equal, don't reprocess... |
| if (KnownRelation.getRelation() == Instruction::SetEQ) |
| return; |
| |
| // If this is boolean, check to see if one of the operands is a constant. If |
| // it's a constant, then see if the other one is one of a setcc instruction, |
| // an AND, OR, or XOR instruction. |
| // |
| if (ConstantBool *CB = dyn_cast<ConstantBool>(Op1)) { |
| |
| if (Instruction *Inst = dyn_cast<Instruction>(Op0)) { |
| // If we know that this instruction is an AND instruction, and the result |
| // is true, this means that both operands to the OR are known to be true |
| // as well. |
| // |
| if (CB->getValue() && Inst->getOpcode() == Instruction::And) { |
| PropogateEquality(Inst->getOperand(0), CB, RI); |
| PropogateEquality(Inst->getOperand(1), CB, RI); |
| } |
| |
| // If we know that this instruction is an OR instruction, and the result |
| // is false, this means that both operands to the OR are know to be false |
| // as well. |
| // |
| if (!CB->getValue() && Inst->getOpcode() == Instruction::Or) { |
| PropogateEquality(Inst->getOperand(0), CB, RI); |
| PropogateEquality(Inst->getOperand(1), CB, RI); |
| } |
| |
| // If we know that this instruction is a NOT instruction, we know that the |
| // operand is known to be the inverse of whatever the current value is. |
| // |
| if (BinaryOperator *BOp = dyn_cast<BinaryOperator>(Inst)) |
| if (BinaryOperator::isNot(BOp)) |
| PropogateEquality(BinaryOperator::getNotArgument(BOp), |
| ConstantBool::get(!CB->getValue()), RI); |
| |
| // If we know the value of a SetCC instruction, propogate the information |
| // about the relation into this region as well. |
| // |
| if (SetCondInst *SCI = dyn_cast<SetCondInst>(Inst)) { |
| if (CB->getValue()) { // If we know the condition is true... |
| // Propogate info about the LHS to the RHS & RHS to LHS |
| PropogateRelation(SCI->getOpcode(), SCI->getOperand(0), |
| SCI->getOperand(1), RI); |
| PropogateRelation(SCI->getSwappedCondition(), |
| SCI->getOperand(1), SCI->getOperand(0), RI); |
| |
| } else { // If we know the condition is false... |
| // We know the opposite of the condition is true... |
| Instruction::BinaryOps C = SCI->getInverseCondition(); |
| |
| PropogateRelation(C, SCI->getOperand(0), SCI->getOperand(1), RI); |
| PropogateRelation(SetCondInst::getSwappedCondition(C), |
| SCI->getOperand(1), SCI->getOperand(0), RI); |
| } |
| } |
| } |
| } |
| |
| // Propogate information about Op0 to Op1 & visa versa |
| PropogateRelation(Instruction::SetEQ, Op0, Op1, RI); |
| PropogateRelation(Instruction::SetEQ, Op1, Op0, RI); |
| } |
| |
| |
| // PropogateRelation - We know that the specified relation is true in all of the |
| // blocks in the specified region. Propogate the information about Op0 and |
| // anything derived from it into this region. |
| // |
| void CEE::PropogateRelation(Instruction::BinaryOps Opcode, Value *Op0, |
| Value *Op1, RegionInfo &RI) { |
| assert(Op0->getType() == Op1->getType() && "Equal types expected!"); |
| |
| // Constants are already pretty well understood. We will apply information |
| // about the constant to Op1 in another call to PropogateRelation. |
| // |
| if (isa<Constant>(Op0)) return; |
| |
| // Get the region information for this block to update... |
| ValueInfo &VI = RI.getValueInfo(Op0); |
| |
| // Get information about the known relationship between Op0 & Op1 |
| Relation &Op1R = VI.getRelation(Op1); |
| |
| // Quick bailout for common case if we are reprocessing an instruction... |
| if (Op1R.getRelation() == Opcode) |
| return; |
| |
| // If we already have information that contradicts the current information we |
| // are propogating, ignore this info. Something bad must have happened! |
| // |
| if (Op1R.contradicts(Opcode, VI)) { |
| Op1R.contradicts(Opcode, VI); |
| std::cerr << "Contradiction found for opcode: " |
| << Instruction::getOpcodeName(Opcode) << "\n"; |
| Op1R.print(std::cerr); |
| return; |
| } |
| |
| // If the information propogted is new, then we want process the uses of this |
| // instruction to propogate the information down to them. |
| // |
| if (Op1R.incorporate(Opcode, VI)) |
| UpdateUsersOfValue(Op0, RI); |
| } |
| |
| |
| // UpdateUsersOfValue - The information about V in this region has been updated. |
| // Propogate this to all consumers of the value. |
| // |
| void CEE::UpdateUsersOfValue(Value *V, RegionInfo &RI) { |
| for (Value::use_iterator I = V->use_begin(), E = V->use_end(); |
| I != E; ++I) |
| if (Instruction *Inst = dyn_cast<Instruction>(*I)) { |
| // If this is an instruction using a value that we know something about, |
| // try to propogate information to the value produced by the |
| // instruction. We can only do this if it is an instruction we can |
| // propogate information for (a setcc for example), and we only WANT to |
| // do this if the instruction dominates this region. |
| // |
| // If the instruction doesn't dominate this region, then it cannot be |
| // used in this region and we don't care about it. If the instruction |
| // is IN this region, then we will simplify the instruction before we |
| // get to uses of it anyway, so there is no reason to bother with it |
| // here. This check is also effectively checking to make sure that Inst |
| // is in the same function as our region (in case V is a global f.e.). |
| // |
| if (DS->properlyDominates(Inst->getParent(), RI.getEntryBlock())) |
| IncorporateInstruction(Inst, RI); |
| } |
| } |
| |
| // IncorporateInstruction - We just updated the information about one of the |
| // operands to the specified instruction. Update the information about the |
| // value produced by this instruction |
| // |
| void CEE::IncorporateInstruction(Instruction *Inst, RegionInfo &RI) { |
| if (SetCondInst *SCI = dyn_cast<SetCondInst>(Inst)) { |
| // See if we can figure out a result for this instruction... |
| Relation::KnownResult Result = getSetCCResult(SCI, RI); |
| if (Result != Relation::Unknown) { |
| PropogateEquality(SCI, Result ? ConstantBool::True : ConstantBool::False, |
| RI); |
| } |
| } |
| } |
| |
| |
| // ComputeReplacements - Some values are known to be equal to other values in a |
| // region. For example if there is a comparison of equality between a variable |
| // X and a constant C, we can replace all uses of X with C in the region we are |
| // interested in. We generalize this replacement to replace variables with |
| // other variables if they are equal and there is a variable with lower rank |
| // than the current one. This offers a cannonicalizing property that exposes |
| // more redundancies for later transformations to take advantage of. |
| // |
| void CEE::ComputeReplacements(RegionInfo &RI) { |
| // Loop over all of the values in the region info map... |
| for (RegionInfo::iterator I = RI.begin(), E = RI.end(); I != E; ++I) { |
| ValueInfo &VI = I->second; |
| |
| // If we know that this value is a particular constant, set Replacement to |
| // the constant... |
| Value *Replacement = VI.getBounds().getSingleElement(); |
| |
| // If this value is not known to be some constant, figure out the lowest |
| // rank value that it is known to be equal to (if anything). |
| // |
| if (Replacement == 0) { |
| // Find out if there are any equality relationships with values of lower |
| // rank than VI itself... |
| unsigned MinRank = getRank(I->first); |
| |
| // Loop over the relationships known about Op0. |
| const std::vector<Relation> &Relationships = VI.getRelationships(); |
| for (unsigned i = 0, e = Relationships.size(); i != e; ++i) |
| if (Relationships[i].getRelation() == Instruction::SetEQ) { |
| unsigned R = getRank(Relationships[i].getValue()); |
| if (R < MinRank) { |
| MinRank = R; |
| Replacement = Relationships[i].getValue(); |
| } |
| } |
| } |
| |
| // If we found something to replace this value with, keep track of it. |
| if (Replacement) |
| VI.setReplacement(Replacement); |
| } |
| } |
| |
| // SimplifyBasicBlock - Given information about values in region RI, simplify |
| // the instructions in the specified basic block. |
| // |
| bool CEE::SimplifyBasicBlock(BasicBlock &BB, const RegionInfo &RI) { |
| bool Changed = false; |
| for (BasicBlock::iterator I = BB.begin(), E = BB.end(); I != E; ) { |
| Instruction *Inst = &*I++; |
| |
| // Convert instruction arguments to canonical forms... |
| Changed |= SimplifyInstruction(Inst, RI); |
| |
| if (SetCondInst *SCI = dyn_cast<SetCondInst>(Inst)) { |
| // Try to simplify a setcc instruction based on inherited information |
| Relation::KnownResult Result = getSetCCResult(SCI, RI); |
| if (Result != Relation::Unknown) { |
| DEBUG(std::cerr << "Replacing setcc with " << Result |
| << " constant: " << SCI); |
| |
| SCI->replaceAllUsesWith(ConstantBool::get((bool)Result)); |
| // The instruction is now dead, remove it from the program. |
| SCI->getParent()->getInstList().erase(SCI); |
| ++NumSetCCRemoved; |
| Changed = true; |
| } |
| } |
| } |
| |
| return Changed; |
| } |
| |
| // SimplifyInstruction - Inspect the operands of the instruction, converting |
| // them to their cannonical form if possible. This takes care of, for example, |
| // replacing a value 'X' with a constant 'C' if the instruction in question is |
| // dominated by a true seteq 'X', 'C'. |
| // |
| bool CEE::SimplifyInstruction(Instruction *I, const RegionInfo &RI) { |
| bool Changed = false; |
| |
| for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) |
| if (const ValueInfo *VI = RI.requestValueInfo(I->getOperand(i))) |
| if (Value *Repl = VI->getReplacement()) { |
| // If we know if a replacement with lower rank than Op0, make the |
| // replacement now. |
| DEBUG(std::cerr << "In Inst: " << I << " Replacing operand #" << i |
| << " with " << Repl << "\n"); |
| I->setOperand(i, Repl); |
| Changed = true; |
| ++NumOperandsCann; |
| } |
| |
| return Changed; |
| } |
| |
| |
| // SimplifySetCC - Try to simplify a setcc instruction based on information |
| // inherited from a dominating setcc instruction. V is one of the operands to |
| // the setcc instruction, and VI is the set of information known about it. We |
| // take two cases into consideration here. If the comparison is against a |
| // constant value, we can use the constant range to see if the comparison is |
| // possible to succeed. If it is not a comparison against a constant, we check |
| // to see if there is a known relationship between the two values. If so, we |
| // may be able to eliminate the check. |
| // |
| Relation::KnownResult CEE::getSetCCResult(SetCondInst *SCI, |
| const RegionInfo &RI) { |
| Value *Op0 = SCI->getOperand(0), *Op1 = SCI->getOperand(1); |
| Instruction::BinaryOps Opcode = SCI->getOpcode(); |
| |
| if (isa<Constant>(Op0)) { |
| if (isa<Constant>(Op1)) { |
| if (Constant *Result = ConstantFoldInstruction(SCI)) { |
| // Wow, this is easy, directly eliminate the SetCondInst. |
| DEBUG(std::cerr << "Replacing setcc with constant fold: " << SCI); |
| return cast<ConstantBool>(Result)->getValue() |
| ? Relation::KnownTrue : Relation::KnownFalse; |
| } |
| } else { |
| // We want to swap this instruction so that operand #0 is the constant. |
| std::swap(Op0, Op1); |
| Opcode = SCI->getSwappedCondition(); |
| } |
| } |
| |
| // Try to figure out what the result of this comparison will be... |
| Relation::KnownResult Result = Relation::Unknown; |
| |
| // We have to know something about the relationship to prove anything... |
| if (const ValueInfo *Op0VI = RI.requestValueInfo(Op0)) { |
| |
| // At this point, we know that if we have a constant argument that it is in |
| // Op1. Check to see if we know anything about comparing value with a |
| // constant, and if we can use this info to fold the setcc. |
| // |
| if (ConstantIntegral *C = dyn_cast<ConstantIntegral>(Op1)) { |
| // Check to see if we already know the result of this comparison... |
| ConstantRange R = ConstantRange(Opcode, C); |
| ConstantRange Int = R.intersectWith(Op0VI->getBounds()); |
| |
| // If the intersection of the two ranges is empty, then the condition |
| // could never be true! |
| // |
| if (Int.isEmptySet()) { |
| Result = Relation::KnownFalse; |
| |
| // Otherwise, if VI.getBounds() (the possible values) is a subset of R |
| // (the allowed values) then we know that the condition must always be |
| // true! |
| // |
| } else if (Int == Op0VI->getBounds()) { |
| Result = Relation::KnownTrue; |
| } |
| } else { |
| // If we are here, we know that the second argument is not a constant |
| // integral. See if we know anything about Op0 & Op1 that allows us to |
| // fold this anyway. |
| // |
| // Do we have value information about Op0 and a relation to Op1? |
| if (const Relation *Op2R = Op0VI->requestRelation(Op1)) |
| Result = Op2R->getImpliedResult(Opcode); |
| } |
| } |
| return Result; |
| } |
| |
| //===----------------------------------------------------------------------===// |
| // Relation Implementation |
| //===----------------------------------------------------------------------===// |
| |
| // CheckCondition - Return true if the specified condition is false. Bound may |
| // be null. |
| static bool CheckCondition(Constant *Bound, Constant *C, |
| Instruction::BinaryOps BO) { |
| assert(C != 0 && "C is not specified!"); |
| if (Bound == 0) return false; |
| |
| ConstantBool *Val; |
| switch (BO) { |
| default: assert(0 && "Unknown Condition code!"); |
| case Instruction::SetEQ: Val = *Bound == *C; break; |
| case Instruction::SetNE: Val = *Bound != *C; break; |
| case Instruction::SetLT: Val = *Bound < *C; break; |
| case Instruction::SetGT: Val = *Bound > *C; break; |
| case Instruction::SetLE: Val = *Bound <= *C; break; |
| case Instruction::SetGE: Val = *Bound >= *C; break; |
| } |
| |
| // ConstantHandling code may not succeed in the comparison... |
| if (Val == 0) return false; |
| return !Val->getValue(); // Return true if the condition is false... |
| } |
| |
| // contradicts - Return true if the relationship specified by the operand |
| // contradicts already known information. |
| // |
| bool Relation::contradicts(Instruction::BinaryOps Op, |
| const ValueInfo &VI) const { |
| assert (Op != Instruction::Add && "Invalid relation argument!"); |
| |
| // If this is a relationship with a constant, make sure that this relationship |
| // does not contradict properties known about the bounds of the constant. |
| // |
| if (ConstantIntegral *C = dyn_cast<ConstantIntegral>(Val)) |
| if (ConstantRange(Op, C).intersectWith(VI.getBounds()).isEmptySet()) |
| return true; |
| |
| switch (Rel) { |
| default: assert(0 && "Unknown Relationship code!"); |
| case Instruction::Add: return false; // Nothing known, nothing contradicts |
| case Instruction::SetEQ: |
| return Op == Instruction::SetLT || Op == Instruction::SetGT || |
| Op == Instruction::SetNE; |
| case Instruction::SetNE: return Op == Instruction::SetEQ; |
| case Instruction::SetLE: return Op == Instruction::SetGT; |
| case Instruction::SetGE: return Op == Instruction::SetLT; |
| case Instruction::SetLT: |
| return Op == Instruction::SetEQ || Op == Instruction::SetGT || |
| Op == Instruction::SetGE; |
| case Instruction::SetGT: |
| return Op == Instruction::SetEQ || Op == Instruction::SetLT || |
| Op == Instruction::SetLE; |
| } |
| } |
| |
| // incorporate - Incorporate information in the argument into this relation |
| // entry. This assumes that the information doesn't contradict itself. If any |
| // new information is gained, true is returned, otherwise false is returned to |
| // indicate that nothing was updated. |
| // |
| bool Relation::incorporate(Instruction::BinaryOps Op, ValueInfo &VI) { |
| assert(!contradicts(Op, VI) && |
| "Cannot incorporate contradictory information!"); |
| |
| // If this is a relationship with a constant, make sure that we update the |
| // range that is possible for the value to have... |
| // |
| if (ConstantIntegral *C = dyn_cast<ConstantIntegral>(Val)) |
| VI.getBounds() = ConstantRange(Op, C).intersectWith(VI.getBounds()); |
| |
| switch (Rel) { |
| default: assert(0 && "Unknown prior value!"); |
| case Instruction::Add: Rel = Op; return true; |
| case Instruction::SetEQ: return false; // Nothing is more precise |
| case Instruction::SetNE: return false; // Nothing is more precise |
| case Instruction::SetLT: return false; // Nothing is more precise |
| case Instruction::SetGT: return false; // Nothing is more precise |
| case Instruction::SetLE: |
| if (Op == Instruction::SetEQ || Op == Instruction::SetLT) { |
| Rel = Op; |
| return true; |
| } else if (Op == Instruction::SetNE) { |
| Rel = Instruction::SetLT; |
| return true; |
| } |
| return false; |
| case Instruction::SetGE: return Op == Instruction::SetLT; |
| if (Op == Instruction::SetEQ || Op == Instruction::SetGT) { |
| Rel = Op; |
| return true; |
| } else if (Op == Instruction::SetNE) { |
| Rel = Instruction::SetGT; |
| return true; |
| } |
| return false; |
| } |
| } |
| |
| // getImpliedResult - If this relationship between two values implies that |
| // the specified relationship is true or false, return that. If we cannot |
| // determine the result required, return Unknown. |
| // |
| Relation::KnownResult |
| Relation::getImpliedResult(Instruction::BinaryOps Op) const { |
| if (Rel == Op) return KnownTrue; |
| if (Rel == SetCondInst::getInverseCondition(Op)) return KnownFalse; |
| |
| switch (Rel) { |
| default: assert(0 && "Unknown prior value!"); |
| case Instruction::SetEQ: |
| if (Op == Instruction::SetLE || Op == Instruction::SetGE) return KnownTrue; |
| if (Op == Instruction::SetLT || Op == Instruction::SetGT) return KnownFalse; |
| break; |
| case Instruction::SetLT: |
| if (Op == Instruction::SetNE || Op == Instruction::SetLE) return KnownTrue; |
| if (Op == Instruction::SetEQ) return KnownFalse; |
| break; |
| case Instruction::SetGT: |
| if (Op == Instruction::SetNE || Op == Instruction::SetGE) return KnownTrue; |
| if (Op == Instruction::SetEQ) return KnownFalse; |
| break; |
| case Instruction::SetNE: |
| case Instruction::SetLE: |
| case Instruction::SetGE: |
| case Instruction::Add: |
| break; |
| } |
| return Unknown; |
| } |
| |
| |
| //===----------------------------------------------------------------------===// |
| // Printing Support... |
| //===----------------------------------------------------------------------===// |
| |
| // print - Implement the standard print form to print out analysis information. |
| void CEE::print(std::ostream &O, const Module *M) const { |
| O << "\nPrinting Correlated Expression Info:\n"; |
| for (std::map<BasicBlock*, RegionInfo>::const_iterator I = |
| RegionInfoMap.begin(), E = RegionInfoMap.end(); I != E; ++I) |
| I->second.print(O); |
| } |
| |
| // print - Output information about this region... |
| void RegionInfo::print(std::ostream &OS) const { |
| if (ValueMap.empty()) return; |
| |
| OS << " RegionInfo for basic block: " << BB->getName() << "\n"; |
| for (std::map<Value*, ValueInfo>::const_iterator |
| I = ValueMap.begin(), E = ValueMap.end(); I != E; ++I) |
| I->second.print(OS, I->first); |
| OS << "\n"; |
| } |
| |
| // print - Output information about this value relation... |
| void ValueInfo::print(std::ostream &OS, Value *V) const { |
| if (Relationships.empty()) return; |
| |
| if (V) { |
| OS << " ValueInfo for: "; |
| WriteAsOperand(OS, V); |
| } |
| OS << "\n Bounds = " << Bounds << "\n"; |
| if (Replacement) { |
| OS << " Replacement = "; |
| WriteAsOperand(OS, Replacement); |
| OS << "\n"; |
| } |
| for (unsigned i = 0, e = Relationships.size(); i != e; ++i) |
| Relationships[i].print(OS); |
| } |
| |
| // print - Output this relation to the specified stream |
| void Relation::print(std::ostream &OS) const { |
| OS << " is "; |
| switch (Rel) { |
| default: OS << "*UNKNOWN*"; break; |
| case Instruction::SetEQ: OS << "== "; break; |
| case Instruction::SetNE: OS << "!= "; break; |
| case Instruction::SetLT: OS << "< "; break; |
| case Instruction::SetGT: OS << "> "; break; |
| case Instruction::SetLE: OS << "<= "; break; |
| case Instruction::SetGE: OS << ">= "; break; |
| } |
| |
| WriteAsOperand(OS, Val); |
| OS << "\n"; |
| } |
| |
| void Relation::dump() const { print(std::cerr); } |
| void ValueInfo::dump() const { print(std::cerr, 0); } |