| //===- SCCP.cpp - Sparse Conditional Constant Propagation -----------------===// |
| // |
| // The LLVM Compiler Infrastructure |
| // |
| // This file is distributed under the University of Illinois Open Source |
| // License. See LICENSE.TXT for details. |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // This file implements sparse conditional constant propagation and merging: |
| // |
| // Specifically, this: |
| // * Assumes values are constant unless proven otherwise |
| // * Assumes BasicBlocks are dead unless proven otherwise |
| // * Proves values to be constant, and replaces them with constants |
| // * Proves conditional branches to be unconditional |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #define DEBUG_TYPE "sccp" |
| #include "llvm/Transforms/Scalar.h" |
| #include "llvm/Transforms/IPO.h" |
| #include "llvm/Constants.h" |
| #include "llvm/DerivedTypes.h" |
| #include "llvm/Instructions.h" |
| #include "llvm/Pass.h" |
| #include "llvm/Analysis/ConstantFolding.h" |
| #include "llvm/Analysis/ValueTracking.h" |
| #include "llvm/Transforms/Utils/Local.h" |
| #include "llvm/Target/TargetData.h" |
| #include "llvm/Support/CallSite.h" |
| #include "llvm/Support/Debug.h" |
| #include "llvm/Support/ErrorHandling.h" |
| #include "llvm/Support/InstVisitor.h" |
| #include "llvm/Support/raw_ostream.h" |
| #include "llvm/ADT/DenseMap.h" |
| #include "llvm/ADT/DenseSet.h" |
| #include "llvm/ADT/PointerIntPair.h" |
| #include "llvm/ADT/SmallPtrSet.h" |
| #include "llvm/ADT/SmallVector.h" |
| #include "llvm/ADT/Statistic.h" |
| #include "llvm/ADT/STLExtras.h" |
| #include <algorithm> |
| #include <map> |
| using namespace llvm; |
| |
| STATISTIC(NumInstRemoved, "Number of instructions removed"); |
| STATISTIC(NumDeadBlocks , "Number of basic blocks unreachable"); |
| |
| STATISTIC(IPNumInstRemoved, "Number of instructions removed by IPSCCP"); |
| STATISTIC(IPNumArgsElimed ,"Number of arguments constant propagated by IPSCCP"); |
| STATISTIC(IPNumGlobalConst, "Number of globals found to be constant by IPSCCP"); |
| |
| namespace { |
| /// LatticeVal class - This class represents the different lattice values that |
| /// an LLVM value may occupy. It is a simple class with value semantics. |
| /// |
| class LatticeVal { |
| enum LatticeValueTy { |
| /// undefined - This LLVM Value has no known value yet. |
| undefined, |
| |
| /// constant - This LLVM Value has a specific constant value. |
| constant, |
| |
| /// forcedconstant - This LLVM Value was thought to be undef until |
| /// ResolvedUndefsIn. This is treated just like 'constant', but if merged |
| /// with another (different) constant, it goes to overdefined, instead of |
| /// asserting. |
| forcedconstant, |
| |
| /// overdefined - This instruction is not known to be constant, and we know |
| /// it has a value. |
| overdefined |
| }; |
| |
| /// Val: This stores the current lattice value along with the Constant* for |
| /// the constant if this is a 'constant' or 'forcedconstant' value. |
| PointerIntPair<Constant *, 2, LatticeValueTy> Val; |
| |
| LatticeValueTy getLatticeValue() const { |
| return Val.getInt(); |
| } |
| |
| public: |
| LatticeVal() : Val(0, undefined) {} |
| |
| bool isUndefined() const { return getLatticeValue() == undefined; } |
| bool isConstant() const { |
| return getLatticeValue() == constant || getLatticeValue() == forcedconstant; |
| } |
| bool isOverdefined() const { return getLatticeValue() == overdefined; } |
| |
| Constant *getConstant() const { |
| assert(isConstant() && "Cannot get the constant of a non-constant!"); |
| return Val.getPointer(); |
| } |
| |
| /// markOverdefined - Return true if this is a change in status. |
| bool markOverdefined() { |
| if (isOverdefined()) |
| return false; |
| |
| Val.setInt(overdefined); |
| return true; |
| } |
| |
| /// markConstant - Return true if this is a change in status. |
| bool markConstant(Constant *V) { |
| if (getLatticeValue() == constant) { // Constant but not forcedconstant. |
| assert(getConstant() == V && "Marking constant with different value"); |
| return false; |
| } |
| |
| if (isUndefined()) { |
| Val.setInt(constant); |
| assert(V && "Marking constant with NULL"); |
| Val.setPointer(V); |
| } else { |
| assert(getLatticeValue() == forcedconstant && |
| "Cannot move from overdefined to constant!"); |
| // Stay at forcedconstant if the constant is the same. |
| if (V == getConstant()) return false; |
| |
| // Otherwise, we go to overdefined. Assumptions made based on the |
| // forced value are possibly wrong. Assuming this is another constant |
| // could expose a contradiction. |
| Val.setInt(overdefined); |
| } |
| return true; |
| } |
| |
| /// getConstantInt - If this is a constant with a ConstantInt value, return it |
| /// otherwise return null. |
| ConstantInt *getConstantInt() const { |
| if (isConstant()) |
| return dyn_cast<ConstantInt>(getConstant()); |
| return 0; |
| } |
| |
| void markForcedConstant(Constant *V) { |
| assert(isUndefined() && "Can't force a defined value!"); |
| Val.setInt(forcedconstant); |
| Val.setPointer(V); |
| } |
| }; |
| } // end anonymous namespace. |
| |
| |
| namespace { |
| |
| //===----------------------------------------------------------------------===// |
| // |
| /// SCCPSolver - This class is a general purpose solver for Sparse Conditional |
| /// Constant Propagation. |
| /// |
| class SCCPSolver : public InstVisitor<SCCPSolver> { |
| const TargetData *TD; |
| SmallPtrSet<BasicBlock*, 8> BBExecutable;// The BBs that are executable. |
| DenseMap<Value*, LatticeVal> ValueState; // The state each value is in. |
| |
| /// StructValueState - This maintains ValueState for values that have |
| /// StructType, for example for formal arguments, calls, insertelement, etc. |
| /// |
| DenseMap<std::pair<Value*, unsigned>, LatticeVal> StructValueState; |
| |
| /// GlobalValue - If we are tracking any values for the contents of a global |
| /// variable, we keep a mapping from the constant accessor to the element of |
| /// the global, to the currently known value. If the value becomes |
| /// overdefined, it's entry is simply removed from this map. |
| DenseMap<GlobalVariable*, LatticeVal> TrackedGlobals; |
| |
| /// TrackedRetVals - If we are tracking arguments into and the return |
| /// value out of a function, it will have an entry in this map, indicating |
| /// what the known return value for the function is. |
| DenseMap<Function*, LatticeVal> TrackedRetVals; |
| |
| /// TrackedMultipleRetVals - Same as TrackedRetVals, but used for functions |
| /// that return multiple values. |
| DenseMap<std::pair<Function*, unsigned>, LatticeVal> TrackedMultipleRetVals; |
| |
| /// MRVFunctionsTracked - Each function in TrackedMultipleRetVals is |
| /// represented here for efficient lookup. |
| SmallPtrSet<Function*, 16> MRVFunctionsTracked; |
| |
| /// TrackingIncomingArguments - This is the set of functions for whose |
| /// arguments we make optimistic assumptions about and try to prove as |
| /// constants. |
| SmallPtrSet<Function*, 16> TrackingIncomingArguments; |
| |
| /// The reason for two worklists is that overdefined is the lowest state |
| /// on the lattice, and moving things to overdefined as fast as possible |
| /// makes SCCP converge much faster. |
| /// |
| /// By having a separate worklist, we accomplish this because everything |
| /// possibly overdefined will become overdefined at the soonest possible |
| /// point. |
| SmallVector<Value*, 64> OverdefinedInstWorkList; |
| SmallVector<Value*, 64> InstWorkList; |
| |
| |
| SmallVector<BasicBlock*, 64> BBWorkList; // The BasicBlock work list |
| |
| /// UsersOfOverdefinedPHIs - Keep track of any users of PHI nodes that are not |
| /// overdefined, despite the fact that the PHI node is overdefined. |
| std::multimap<PHINode*, Instruction*> UsersOfOverdefinedPHIs; |
| |
| /// KnownFeasibleEdges - Entries in this set are edges which have already had |
| /// PHI nodes retriggered. |
| typedef std::pair<BasicBlock*, BasicBlock*> Edge; |
| DenseSet<Edge> KnownFeasibleEdges; |
| public: |
| SCCPSolver(const TargetData *td) : TD(td) {} |
| |
| /// MarkBlockExecutable - This method can be used by clients to mark all of |
| /// the blocks that are known to be intrinsically live in the processed unit. |
| /// |
| /// This returns true if the block was not considered live before. |
| bool MarkBlockExecutable(BasicBlock *BB) { |
| if (!BBExecutable.insert(BB)) return false; |
| DEBUG(dbgs() << "Marking Block Executable: " << BB->getName() << "\n"); |
| BBWorkList.push_back(BB); // Add the block to the work list! |
| return true; |
| } |
| |
| /// TrackValueOfGlobalVariable - Clients can use this method to |
| /// inform the SCCPSolver that it should track loads and stores to the |
| /// specified global variable if it can. This is only legal to call if |
| /// performing Interprocedural SCCP. |
| void TrackValueOfGlobalVariable(GlobalVariable *GV) { |
| // We only track the contents of scalar globals. |
| if (GV->getType()->getElementType()->isSingleValueType()) { |
| LatticeVal &IV = TrackedGlobals[GV]; |
| if (!isa<UndefValue>(GV->getInitializer())) |
| IV.markConstant(GV->getInitializer()); |
| } |
| } |
| |
| /// AddTrackedFunction - If the SCCP solver is supposed to track calls into |
| /// and out of the specified function (which cannot have its address taken), |
| /// this method must be called. |
| void AddTrackedFunction(Function *F) { |
| // Add an entry, F -> undef. |
| if (StructType *STy = dyn_cast<StructType>(F->getReturnType())) { |
| MRVFunctionsTracked.insert(F); |
| for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) |
| TrackedMultipleRetVals.insert(std::make_pair(std::make_pair(F, i), |
| LatticeVal())); |
| } else |
| TrackedRetVals.insert(std::make_pair(F, LatticeVal())); |
| } |
| |
| void AddArgumentTrackedFunction(Function *F) { |
| TrackingIncomingArguments.insert(F); |
| } |
| |
| /// Solve - Solve for constants and executable blocks. |
| /// |
| void Solve(); |
| |
| /// ResolvedUndefsIn - While solving the dataflow for a function, we assume |
| /// that branches on undef values cannot reach any of their successors. |
| /// However, this is not a safe assumption. After we solve dataflow, this |
| /// method should be use to handle this. If this returns true, the solver |
| /// should be rerun. |
| bool ResolvedUndefsIn(Function &F); |
| |
| bool isBlockExecutable(BasicBlock *BB) const { |
| return BBExecutable.count(BB); |
| } |
| |
| LatticeVal getLatticeValueFor(Value *V) const { |
| DenseMap<Value*, LatticeVal>::const_iterator I = ValueState.find(V); |
| assert(I != ValueState.end() && "V is not in valuemap!"); |
| return I->second; |
| } |
| |
| /*LatticeVal getStructLatticeValueFor(Value *V, unsigned i) const { |
| DenseMap<std::pair<Value*, unsigned>, LatticeVal>::const_iterator I = |
| StructValueState.find(std::make_pair(V, i)); |
| assert(I != StructValueState.end() && "V is not in valuemap!"); |
| return I->second; |
| }*/ |
| |
| /// getTrackedRetVals - Get the inferred return value map. |
| /// |
| const DenseMap<Function*, LatticeVal> &getTrackedRetVals() { |
| return TrackedRetVals; |
| } |
| |
| /// getTrackedGlobals - Get and return the set of inferred initializers for |
| /// global variables. |
| const DenseMap<GlobalVariable*, LatticeVal> &getTrackedGlobals() { |
| return TrackedGlobals; |
| } |
| |
| void markOverdefined(Value *V) { |
| assert(!V->getType()->isStructTy() && "Should use other method"); |
| markOverdefined(ValueState[V], V); |
| } |
| |
| /// markAnythingOverdefined - Mark the specified value overdefined. This |
| /// works with both scalars and structs. |
| void markAnythingOverdefined(Value *V) { |
| if (StructType *STy = dyn_cast<StructType>(V->getType())) |
| for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) |
| markOverdefined(getStructValueState(V, i), V); |
| else |
| markOverdefined(V); |
| } |
| |
| private: |
| // markConstant - Make a value be marked as "constant". If the value |
| // is not already a constant, add it to the instruction work list so that |
| // the users of the instruction are updated later. |
| // |
| void markConstant(LatticeVal &IV, Value *V, Constant *C) { |
| if (!IV.markConstant(C)) return; |
| DEBUG(dbgs() << "markConstant: " << *C << ": " << *V << '\n'); |
| if (IV.isOverdefined()) |
| OverdefinedInstWorkList.push_back(V); |
| else |
| InstWorkList.push_back(V); |
| } |
| |
| void markConstant(Value *V, Constant *C) { |
| assert(!V->getType()->isStructTy() && "Should use other method"); |
| markConstant(ValueState[V], V, C); |
| } |
| |
| void markForcedConstant(Value *V, Constant *C) { |
| assert(!V->getType()->isStructTy() && "Should use other method"); |
| LatticeVal &IV = ValueState[V]; |
| IV.markForcedConstant(C); |
| DEBUG(dbgs() << "markForcedConstant: " << *C << ": " << *V << '\n'); |
| if (IV.isOverdefined()) |
| OverdefinedInstWorkList.push_back(V); |
| else |
| InstWorkList.push_back(V); |
| } |
| |
| |
| // markOverdefined - Make a value be marked as "overdefined". If the |
| // value is not already overdefined, add it to the overdefined instruction |
| // work list so that the users of the instruction are updated later. |
| void markOverdefined(LatticeVal &IV, Value *V) { |
| if (!IV.markOverdefined()) return; |
| |
| DEBUG(dbgs() << "markOverdefined: "; |
| if (Function *F = dyn_cast<Function>(V)) |
| dbgs() << "Function '" << F->getName() << "'\n"; |
| else |
| dbgs() << *V << '\n'); |
| // Only instructions go on the work list |
| OverdefinedInstWorkList.push_back(V); |
| } |
| |
| void mergeInValue(LatticeVal &IV, Value *V, LatticeVal MergeWithV) { |
| if (IV.isOverdefined() || MergeWithV.isUndefined()) |
| return; // Noop. |
| if (MergeWithV.isOverdefined()) |
| markOverdefined(IV, V); |
| else if (IV.isUndefined()) |
| markConstant(IV, V, MergeWithV.getConstant()); |
| else if (IV.getConstant() != MergeWithV.getConstant()) |
| markOverdefined(IV, V); |
| } |
| |
| void mergeInValue(Value *V, LatticeVal MergeWithV) { |
| assert(!V->getType()->isStructTy() && "Should use other method"); |
| mergeInValue(ValueState[V], V, MergeWithV); |
| } |
| |
| |
| /// getValueState - Return the LatticeVal object that corresponds to the |
| /// value. This function handles the case when the value hasn't been seen yet |
| /// by properly seeding constants etc. |
| LatticeVal &getValueState(Value *V) { |
| assert(!V->getType()->isStructTy() && "Should use getStructValueState"); |
| |
| std::pair<DenseMap<Value*, LatticeVal>::iterator, bool> I = |
| ValueState.insert(std::make_pair(V, LatticeVal())); |
| LatticeVal &LV = I.first->second; |
| |
| if (!I.second) |
| return LV; // Common case, already in the map. |
| |
| if (Constant *C = dyn_cast<Constant>(V)) { |
| // Undef values remain undefined. |
| if (!isa<UndefValue>(V)) |
| LV.markConstant(C); // Constants are constant |
| } |
| |
| // All others are underdefined by default. |
| return LV; |
| } |
| |
| /// getStructValueState - Return the LatticeVal object that corresponds to the |
| /// value/field pair. This function handles the case when the value hasn't |
| /// been seen yet by properly seeding constants etc. |
| LatticeVal &getStructValueState(Value *V, unsigned i) { |
| assert(V->getType()->isStructTy() && "Should use getValueState"); |
| assert(i < cast<StructType>(V->getType())->getNumElements() && |
| "Invalid element #"); |
| |
| std::pair<DenseMap<std::pair<Value*, unsigned>, LatticeVal>::iterator, |
| bool> I = StructValueState.insert( |
| std::make_pair(std::make_pair(V, i), LatticeVal())); |
| LatticeVal &LV = I.first->second; |
| |
| if (!I.second) |
| return LV; // Common case, already in the map. |
| |
| if (Constant *C = dyn_cast<Constant>(V)) { |
| if (isa<UndefValue>(C)) |
| ; // Undef values remain undefined. |
| else if (ConstantStruct *CS = dyn_cast<ConstantStruct>(C)) |
| LV.markConstant(CS->getOperand(i)); // Constants are constant. |
| else if (isa<ConstantAggregateZero>(C)) { |
| Type *FieldTy = cast<StructType>(V->getType())->getElementType(i); |
| LV.markConstant(Constant::getNullValue(FieldTy)); |
| } else |
| LV.markOverdefined(); // Unknown sort of constant. |
| } |
| |
| // All others are underdefined by default. |
| return LV; |
| } |
| |
| |
| /// markEdgeExecutable - Mark a basic block as executable, adding it to the BB |
| /// work list if it is not already executable. |
| void markEdgeExecutable(BasicBlock *Source, BasicBlock *Dest) { |
| if (!KnownFeasibleEdges.insert(Edge(Source, Dest)).second) |
| return; // This edge is already known to be executable! |
| |
| if (!MarkBlockExecutable(Dest)) { |
| // If the destination is already executable, we just made an *edge* |
| // feasible that wasn't before. Revisit the PHI nodes in the block |
| // because they have potentially new operands. |
| DEBUG(dbgs() << "Marking Edge Executable: " << Source->getName() |
| << " -> " << Dest->getName() << "\n"); |
| |
| PHINode *PN; |
| for (BasicBlock::iterator I = Dest->begin(); |
| (PN = dyn_cast<PHINode>(I)); ++I) |
| visitPHINode(*PN); |
| } |
| } |
| |
| // getFeasibleSuccessors - Return a vector of booleans to indicate which |
| // successors are reachable from a given terminator instruction. |
| // |
| void getFeasibleSuccessors(TerminatorInst &TI, SmallVector<bool, 16> &Succs); |
| |
| // isEdgeFeasible - Return true if the control flow edge from the 'From' basic |
| // block to the 'To' basic block is currently feasible. |
| // |
| bool isEdgeFeasible(BasicBlock *From, BasicBlock *To); |
| |
| // OperandChangedState - This method is invoked on all of the users of an |
| // instruction that was just changed state somehow. Based on this |
| // information, we need to update the specified user of this instruction. |
| // |
| void OperandChangedState(Instruction *I) { |
| if (BBExecutable.count(I->getParent())) // Inst is executable? |
| visit(*I); |
| } |
| |
| /// RemoveFromOverdefinedPHIs - If I has any entries in the |
| /// UsersOfOverdefinedPHIs map for PN, remove them now. |
| void RemoveFromOverdefinedPHIs(Instruction *I, PHINode *PN) { |
| if (UsersOfOverdefinedPHIs.empty()) return; |
| typedef std::multimap<PHINode*, Instruction*>::iterator ItTy; |
| std::pair<ItTy, ItTy> Range = UsersOfOverdefinedPHIs.equal_range(PN); |
| for (ItTy It = Range.first, E = Range.second; It != E;) { |
| if (It->second == I) |
| UsersOfOverdefinedPHIs.erase(It++); |
| else |
| ++It; |
| } |
| } |
| |
| /// InsertInOverdefinedPHIs - Insert an entry in the UsersOfOverdefinedPHIS |
| /// map for I and PN, but if one is there already, do not create another. |
| /// (Duplicate entries do not break anything directly, but can lead to |
| /// exponential growth of the table in rare cases.) |
| void InsertInOverdefinedPHIs(Instruction *I, PHINode *PN) { |
| typedef std::multimap<PHINode*, Instruction*>::iterator ItTy; |
| std::pair<ItTy, ItTy> Range = UsersOfOverdefinedPHIs.equal_range(PN); |
| for (ItTy J = Range.first, E = Range.second; J != E; ++J) |
| if (J->second == I) |
| return; |
| UsersOfOverdefinedPHIs.insert(std::make_pair(PN, I)); |
| } |
| |
| private: |
| friend class InstVisitor<SCCPSolver>; |
| |
| // visit implementations - Something changed in this instruction. Either an |
| // operand made a transition, or the instruction is newly executable. Change |
| // the value type of I to reflect these changes if appropriate. |
| void visitPHINode(PHINode &I); |
| |
| // Terminators |
| void visitReturnInst(ReturnInst &I); |
| void visitTerminatorInst(TerminatorInst &TI); |
| |
| void visitCastInst(CastInst &I); |
| void visitSelectInst(SelectInst &I); |
| void visitBinaryOperator(Instruction &I); |
| void visitCmpInst(CmpInst &I); |
| void visitExtractElementInst(ExtractElementInst &I); |
| void visitInsertElementInst(InsertElementInst &I); |
| void visitShuffleVectorInst(ShuffleVectorInst &I); |
| void visitExtractValueInst(ExtractValueInst &EVI); |
| void visitInsertValueInst(InsertValueInst &IVI); |
| |
| // Instructions that cannot be folded away. |
| void visitStoreInst (StoreInst &I); |
| void visitLoadInst (LoadInst &I); |
| void visitGetElementPtrInst(GetElementPtrInst &I); |
| void visitCallInst (CallInst &I) { |
| visitCallSite(&I); |
| } |
| void visitInvokeInst (InvokeInst &II) { |
| visitCallSite(&II); |
| visitTerminatorInst(II); |
| } |
| void visitCallSite (CallSite CS); |
| void visitUnwindInst (TerminatorInst &I) { /*returns void*/ } |
| void visitUnreachableInst(TerminatorInst &I) { /*returns void*/ } |
| void visitAllocaInst (Instruction &I) { markOverdefined(&I); } |
| void visitVAArgInst (Instruction &I) { markAnythingOverdefined(&I); } |
| |
| void visitInstruction(Instruction &I) { |
| // If a new instruction is added to LLVM that we don't handle. |
| dbgs() << "SCCP: Don't know how to handle: " << I; |
| markAnythingOverdefined(&I); // Just in case |
| } |
| }; |
| |
| } // end anonymous namespace |
| |
| |
| // getFeasibleSuccessors - Return a vector of booleans to indicate which |
| // successors are reachable from a given terminator instruction. |
| // |
| void SCCPSolver::getFeasibleSuccessors(TerminatorInst &TI, |
| SmallVector<bool, 16> &Succs) { |
| Succs.resize(TI.getNumSuccessors()); |
| if (BranchInst *BI = dyn_cast<BranchInst>(&TI)) { |
| if (BI->isUnconditional()) { |
| Succs[0] = true; |
| return; |
| } |
| |
| LatticeVal BCValue = getValueState(BI->getCondition()); |
| ConstantInt *CI = BCValue.getConstantInt(); |
| if (CI == 0) { |
| // Overdefined condition variables, and branches on unfoldable constant |
| // conditions, mean the branch could go either way. |
| if (!BCValue.isUndefined()) |
| Succs[0] = Succs[1] = true; |
| return; |
| } |
| |
| // Constant condition variables mean the branch can only go a single way. |
| Succs[CI->isZero()] = true; |
| return; |
| } |
| |
| if (isa<InvokeInst>(TI)) { |
| // Invoke instructions successors are always executable. |
| Succs[0] = Succs[1] = true; |
| return; |
| } |
| |
| if (SwitchInst *SI = dyn_cast<SwitchInst>(&TI)) { |
| LatticeVal SCValue = getValueState(SI->getCondition()); |
| ConstantInt *CI = SCValue.getConstantInt(); |
| |
| if (CI == 0) { // Overdefined or undefined condition? |
| // All destinations are executable! |
| if (!SCValue.isUndefined()) |
| Succs.assign(TI.getNumSuccessors(), true); |
| return; |
| } |
| |
| Succs[SI->findCaseValue(CI)] = true; |
| return; |
| } |
| |
| // TODO: This could be improved if the operand is a [cast of a] BlockAddress. |
| if (isa<IndirectBrInst>(&TI)) { |
| // Just mark all destinations executable! |
| Succs.assign(TI.getNumSuccessors(), true); |
| return; |
| } |
| |
| #ifndef NDEBUG |
| dbgs() << "Unknown terminator instruction: " << TI << '\n'; |
| #endif |
| llvm_unreachable("SCCP: Don't know how to handle this terminator!"); |
| } |
| |
| |
| // isEdgeFeasible - Return true if the control flow edge from the 'From' basic |
| // block to the 'To' basic block is currently feasible. |
| // |
| bool SCCPSolver::isEdgeFeasible(BasicBlock *From, BasicBlock *To) { |
| assert(BBExecutable.count(To) && "Dest should always be alive!"); |
| |
| // Make sure the source basic block is executable!! |
| if (!BBExecutable.count(From)) return false; |
| |
| // Check to make sure this edge itself is actually feasible now. |
| TerminatorInst *TI = From->getTerminator(); |
| if (BranchInst *BI = dyn_cast<BranchInst>(TI)) { |
| if (BI->isUnconditional()) |
| return true; |
| |
| LatticeVal BCValue = getValueState(BI->getCondition()); |
| |
| // Overdefined condition variables mean the branch could go either way, |
| // undef conditions mean that neither edge is feasible yet. |
| ConstantInt *CI = BCValue.getConstantInt(); |
| if (CI == 0) |
| return !BCValue.isUndefined(); |
| |
| // Constant condition variables mean the branch can only go a single way. |
| return BI->getSuccessor(CI->isZero()) == To; |
| } |
| |
| // Invoke instructions successors are always executable. |
| if (isa<InvokeInst>(TI)) |
| return true; |
| |
| if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) { |
| LatticeVal SCValue = getValueState(SI->getCondition()); |
| ConstantInt *CI = SCValue.getConstantInt(); |
| |
| if (CI == 0) |
| return !SCValue.isUndefined(); |
| |
| // Make sure to skip the "default value" which isn't a value |
| for (unsigned i = 1, E = SI->getNumSuccessors(); i != E; ++i) |
| if (SI->getSuccessorValue(i) == CI) // Found the taken branch. |
| return SI->getSuccessor(i) == To; |
| |
| // If the constant value is not equal to any of the branches, we must |
| // execute default branch. |
| return SI->getDefaultDest() == To; |
| } |
| |
| // Just mark all destinations executable! |
| // TODO: This could be improved if the operand is a [cast of a] BlockAddress. |
| if (isa<IndirectBrInst>(TI)) |
| return true; |
| |
| #ifndef NDEBUG |
| dbgs() << "Unknown terminator instruction: " << *TI << '\n'; |
| #endif |
| llvm_unreachable(0); |
| } |
| |
| // visit Implementations - Something changed in this instruction, either an |
| // operand made a transition, or the instruction is newly executable. Change |
| // the value type of I to reflect these changes if appropriate. This method |
| // makes sure to do the following actions: |
| // |
| // 1. If a phi node merges two constants in, and has conflicting value coming |
| // from different branches, or if the PHI node merges in an overdefined |
| // value, then the PHI node becomes overdefined. |
| // 2. If a phi node merges only constants in, and they all agree on value, the |
| // PHI node becomes a constant value equal to that. |
| // 3. If V <- x (op) y && isConstant(x) && isConstant(y) V = Constant |
| // 4. If V <- x (op) y && (isOverdefined(x) || isOverdefined(y)) V = Overdefined |
| // 5. If V <- MEM or V <- CALL or V <- (unknown) then V = Overdefined |
| // 6. If a conditional branch has a value that is constant, make the selected |
| // destination executable |
| // 7. If a conditional branch has a value that is overdefined, make all |
| // successors executable. |
| // |
| void SCCPSolver::visitPHINode(PHINode &PN) { |
| // If this PN returns a struct, just mark the result overdefined. |
| // TODO: We could do a lot better than this if code actually uses this. |
| if (PN.getType()->isStructTy()) |
| return markAnythingOverdefined(&PN); |
| |
| if (getValueState(&PN).isOverdefined()) { |
| // There may be instructions using this PHI node that are not overdefined |
| // themselves. If so, make sure that they know that the PHI node operand |
| // changed. |
| typedef std::multimap<PHINode*, Instruction*>::iterator ItTy; |
| std::pair<ItTy, ItTy> Range = UsersOfOverdefinedPHIs.equal_range(&PN); |
| |
| if (Range.first == Range.second) |
| return; |
| |
| SmallVector<Instruction*, 16> Users; |
| for (ItTy I = Range.first, E = Range.second; I != E; ++I) |
| Users.push_back(I->second); |
| while (!Users.empty()) |
| visit(Users.pop_back_val()); |
| return; // Quick exit |
| } |
| |
| // Super-extra-high-degree PHI nodes are unlikely to ever be marked constant, |
| // and slow us down a lot. Just mark them overdefined. |
| if (PN.getNumIncomingValues() > 64) |
| return markOverdefined(&PN); |
| |
| // Look at all of the executable operands of the PHI node. If any of them |
| // are overdefined, the PHI becomes overdefined as well. If they are all |
| // constant, and they agree with each other, the PHI becomes the identical |
| // constant. If they are constant and don't agree, the PHI is overdefined. |
| // If there are no executable operands, the PHI remains undefined. |
| // |
| Constant *OperandVal = 0; |
| for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i) { |
| LatticeVal IV = getValueState(PN.getIncomingValue(i)); |
| if (IV.isUndefined()) continue; // Doesn't influence PHI node. |
| |
| if (!isEdgeFeasible(PN.getIncomingBlock(i), PN.getParent())) |
| continue; |
| |
| if (IV.isOverdefined()) // PHI node becomes overdefined! |
| return markOverdefined(&PN); |
| |
| if (OperandVal == 0) { // Grab the first value. |
| OperandVal = IV.getConstant(); |
| continue; |
| } |
| |
| // There is already a reachable operand. If we conflict with it, |
| // then the PHI node becomes overdefined. If we agree with it, we |
| // can continue on. |
| |
| // Check to see if there are two different constants merging, if so, the PHI |
| // node is overdefined. |
| if (IV.getConstant() != OperandVal) |
| return markOverdefined(&PN); |
| } |
| |
| // If we exited the loop, this means that the PHI node only has constant |
| // arguments that agree with each other(and OperandVal is the constant) or |
| // OperandVal is null because there are no defined incoming arguments. If |
| // this is the case, the PHI remains undefined. |
| // |
| if (OperandVal) |
| markConstant(&PN, OperandVal); // Acquire operand value |
| } |
| |
| |
| |
| |
| void SCCPSolver::visitReturnInst(ReturnInst &I) { |
| if (I.getNumOperands() == 0) return; // ret void |
| |
| Function *F = I.getParent()->getParent(); |
| Value *ResultOp = I.getOperand(0); |
| |
| // If we are tracking the return value of this function, merge it in. |
| if (!TrackedRetVals.empty() && !ResultOp->getType()->isStructTy()) { |
| DenseMap<Function*, LatticeVal>::iterator TFRVI = |
| TrackedRetVals.find(F); |
| if (TFRVI != TrackedRetVals.end()) { |
| mergeInValue(TFRVI->second, F, getValueState(ResultOp)); |
| return; |
| } |
| } |
| |
| // Handle functions that return multiple values. |
| if (!TrackedMultipleRetVals.empty()) { |
| if (StructType *STy = dyn_cast<StructType>(ResultOp->getType())) |
| if (MRVFunctionsTracked.count(F)) |
| for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) |
| mergeInValue(TrackedMultipleRetVals[std::make_pair(F, i)], F, |
| getStructValueState(ResultOp, i)); |
| |
| } |
| } |
| |
| void SCCPSolver::visitTerminatorInst(TerminatorInst &TI) { |
| SmallVector<bool, 16> SuccFeasible; |
| getFeasibleSuccessors(TI, SuccFeasible); |
| |
| BasicBlock *BB = TI.getParent(); |
| |
| // Mark all feasible successors executable. |
| for (unsigned i = 0, e = SuccFeasible.size(); i != e; ++i) |
| if (SuccFeasible[i]) |
| markEdgeExecutable(BB, TI.getSuccessor(i)); |
| } |
| |
| void SCCPSolver::visitCastInst(CastInst &I) { |
| LatticeVal OpSt = getValueState(I.getOperand(0)); |
| if (OpSt.isOverdefined()) // Inherit overdefinedness of operand |
| markOverdefined(&I); |
| else if (OpSt.isConstant()) // Propagate constant value |
| markConstant(&I, ConstantExpr::getCast(I.getOpcode(), |
| OpSt.getConstant(), I.getType())); |
| } |
| |
| |
| void SCCPSolver::visitExtractValueInst(ExtractValueInst &EVI) { |
| // If this returns a struct, mark all elements over defined, we don't track |
| // structs in structs. |
| if (EVI.getType()->isStructTy()) |
| return markAnythingOverdefined(&EVI); |
| |
| // If this is extracting from more than one level of struct, we don't know. |
| if (EVI.getNumIndices() != 1) |
| return markOverdefined(&EVI); |
| |
| Value *AggVal = EVI.getAggregateOperand(); |
| if (AggVal->getType()->isStructTy()) { |
| unsigned i = *EVI.idx_begin(); |
| LatticeVal EltVal = getStructValueState(AggVal, i); |
| mergeInValue(getValueState(&EVI), &EVI, EltVal); |
| } else { |
| // Otherwise, must be extracting from an array. |
| return markOverdefined(&EVI); |
| } |
| } |
| |
| void SCCPSolver::visitInsertValueInst(InsertValueInst &IVI) { |
| StructType *STy = dyn_cast<StructType>(IVI.getType()); |
| if (STy == 0) |
| return markOverdefined(&IVI); |
| |
| // If this has more than one index, we can't handle it, drive all results to |
| // undef. |
| if (IVI.getNumIndices() != 1) |
| return markAnythingOverdefined(&IVI); |
| |
| Value *Aggr = IVI.getAggregateOperand(); |
| unsigned Idx = *IVI.idx_begin(); |
| |
| // Compute the result based on what we're inserting. |
| for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) { |
| // This passes through all values that aren't the inserted element. |
| if (i != Idx) { |
| LatticeVal EltVal = getStructValueState(Aggr, i); |
| mergeInValue(getStructValueState(&IVI, i), &IVI, EltVal); |
| continue; |
| } |
| |
| Value *Val = IVI.getInsertedValueOperand(); |
| if (Val->getType()->isStructTy()) |
| // We don't track structs in structs. |
| markOverdefined(getStructValueState(&IVI, i), &IVI); |
| else { |
| LatticeVal InVal = getValueState(Val); |
| mergeInValue(getStructValueState(&IVI, i), &IVI, InVal); |
| } |
| } |
| } |
| |
| void SCCPSolver::visitSelectInst(SelectInst &I) { |
| // If this select returns a struct, just mark the result overdefined. |
| // TODO: We could do a lot better than this if code actually uses this. |
| if (I.getType()->isStructTy()) |
| return markAnythingOverdefined(&I); |
| |
| LatticeVal CondValue = getValueState(I.getCondition()); |
| if (CondValue.isUndefined()) |
| return; |
| |
| if (ConstantInt *CondCB = CondValue.getConstantInt()) { |
| Value *OpVal = CondCB->isZero() ? I.getFalseValue() : I.getTrueValue(); |
| mergeInValue(&I, getValueState(OpVal)); |
| return; |
| } |
| |
| // Otherwise, the condition is overdefined or a constant we can't evaluate. |
| // See if we can produce something better than overdefined based on the T/F |
| // value. |
| LatticeVal TVal = getValueState(I.getTrueValue()); |
| LatticeVal FVal = getValueState(I.getFalseValue()); |
| |
| // select ?, C, C -> C. |
| if (TVal.isConstant() && FVal.isConstant() && |
| TVal.getConstant() == FVal.getConstant()) |
| return markConstant(&I, FVal.getConstant()); |
| |
| if (TVal.isUndefined()) // select ?, undef, X -> X. |
| return mergeInValue(&I, FVal); |
| if (FVal.isUndefined()) // select ?, X, undef -> X. |
| return mergeInValue(&I, TVal); |
| markOverdefined(&I); |
| } |
| |
| // Handle Binary Operators. |
| void SCCPSolver::visitBinaryOperator(Instruction &I) { |
| LatticeVal V1State = getValueState(I.getOperand(0)); |
| LatticeVal V2State = getValueState(I.getOperand(1)); |
| |
| LatticeVal &IV = ValueState[&I]; |
| if (IV.isOverdefined()) return; |
| |
| if (V1State.isConstant() && V2State.isConstant()) |
| return markConstant(IV, &I, |
| ConstantExpr::get(I.getOpcode(), V1State.getConstant(), |
| V2State.getConstant())); |
| |
| // If something is undef, wait for it to resolve. |
| if (!V1State.isOverdefined() && !V2State.isOverdefined()) |
| return; |
| |
| // Otherwise, one of our operands is overdefined. Try to produce something |
| // better than overdefined with some tricks. |
| |
| // If this is an AND or OR with 0 or -1, it doesn't matter that the other |
| // operand is overdefined. |
| if (I.getOpcode() == Instruction::And || I.getOpcode() == Instruction::Or) { |
| LatticeVal *NonOverdefVal = 0; |
| if (!V1State.isOverdefined()) |
| NonOverdefVal = &V1State; |
| else if (!V2State.isOverdefined()) |
| NonOverdefVal = &V2State; |
| |
| if (NonOverdefVal) { |
| if (NonOverdefVal->isUndefined()) { |
| // Could annihilate value. |
| if (I.getOpcode() == Instruction::And) |
| markConstant(IV, &I, Constant::getNullValue(I.getType())); |
| else if (VectorType *PT = dyn_cast<VectorType>(I.getType())) |
| markConstant(IV, &I, Constant::getAllOnesValue(PT)); |
| else |
| markConstant(IV, &I, |
| Constant::getAllOnesValue(I.getType())); |
| return; |
| } |
| |
| if (I.getOpcode() == Instruction::And) { |
| // X and 0 = 0 |
| if (NonOverdefVal->getConstant()->isNullValue()) |
| return markConstant(IV, &I, NonOverdefVal->getConstant()); |
| } else { |
| if (ConstantInt *CI = NonOverdefVal->getConstantInt()) |
| if (CI->isAllOnesValue()) // X or -1 = -1 |
| return markConstant(IV, &I, NonOverdefVal->getConstant()); |
| } |
| } |
| } |
| |
| |
| // If both operands are PHI nodes, it is possible that this instruction has |
| // a constant value, despite the fact that the PHI node doesn't. Check for |
| // this condition now. |
| if (PHINode *PN1 = dyn_cast<PHINode>(I.getOperand(0))) |
| if (PHINode *PN2 = dyn_cast<PHINode>(I.getOperand(1))) |
| if (PN1->getParent() == PN2->getParent()) { |
| // Since the two PHI nodes are in the same basic block, they must have |
| // entries for the same predecessors. Walk the predecessor list, and |
| // if all of the incoming values are constants, and the result of |
| // evaluating this expression with all incoming value pairs is the |
| // same, then this expression is a constant even though the PHI node |
| // is not a constant! |
| LatticeVal Result; |
| for (unsigned i = 0, e = PN1->getNumIncomingValues(); i != e; ++i) { |
| LatticeVal In1 = getValueState(PN1->getIncomingValue(i)); |
| BasicBlock *InBlock = PN1->getIncomingBlock(i); |
| LatticeVal In2 =getValueState(PN2->getIncomingValueForBlock(InBlock)); |
| |
| if (In1.isOverdefined() || In2.isOverdefined()) { |
| Result.markOverdefined(); |
| break; // Cannot fold this operation over the PHI nodes! |
| } |
| |
| if (In1.isConstant() && In2.isConstant()) { |
| Constant *V = ConstantExpr::get(I.getOpcode(), In1.getConstant(), |
| In2.getConstant()); |
| if (Result.isUndefined()) |
| Result.markConstant(V); |
| else if (Result.isConstant() && Result.getConstant() != V) { |
| Result.markOverdefined(); |
| break; |
| } |
| } |
| } |
| |
| // If we found a constant value here, then we know the instruction is |
| // constant despite the fact that the PHI nodes are overdefined. |
| if (Result.isConstant()) { |
| markConstant(IV, &I, Result.getConstant()); |
| // Remember that this instruction is virtually using the PHI node |
| // operands. |
| InsertInOverdefinedPHIs(&I, PN1); |
| InsertInOverdefinedPHIs(&I, PN2); |
| return; |
| } |
| |
| if (Result.isUndefined()) |
| return; |
| |
| // Okay, this really is overdefined now. Since we might have |
| // speculatively thought that this was not overdefined before, and |
| // added ourselves to the UsersOfOverdefinedPHIs list for the PHIs, |
| // make sure to clean out any entries that we put there, for |
| // efficiency. |
| RemoveFromOverdefinedPHIs(&I, PN1); |
| RemoveFromOverdefinedPHIs(&I, PN2); |
| } |
| |
| markOverdefined(&I); |
| } |
| |
| // Handle ICmpInst instruction. |
| void SCCPSolver::visitCmpInst(CmpInst &I) { |
| LatticeVal V1State = getValueState(I.getOperand(0)); |
| LatticeVal V2State = getValueState(I.getOperand(1)); |
| |
| LatticeVal &IV = ValueState[&I]; |
| if (IV.isOverdefined()) return; |
| |
| if (V1State.isConstant() && V2State.isConstant()) |
| return markConstant(IV, &I, ConstantExpr::getCompare(I.getPredicate(), |
| V1State.getConstant(), |
| V2State.getConstant())); |
| |
| // If operands are still undefined, wait for it to resolve. |
| if (!V1State.isOverdefined() && !V2State.isOverdefined()) |
| return; |
| |
| // If something is overdefined, use some tricks to avoid ending up and over |
| // defined if we can. |
| |
| // If both operands are PHI nodes, it is possible that this instruction has |
| // a constant value, despite the fact that the PHI node doesn't. Check for |
| // this condition now. |
| if (PHINode *PN1 = dyn_cast<PHINode>(I.getOperand(0))) |
| if (PHINode *PN2 = dyn_cast<PHINode>(I.getOperand(1))) |
| if (PN1->getParent() == PN2->getParent()) { |
| // Since the two PHI nodes are in the same basic block, they must have |
| // entries for the same predecessors. Walk the predecessor list, and |
| // if all of the incoming values are constants, and the result of |
| // evaluating this expression with all incoming value pairs is the |
| // same, then this expression is a constant even though the PHI node |
| // is not a constant! |
| LatticeVal Result; |
| for (unsigned i = 0, e = PN1->getNumIncomingValues(); i != e; ++i) { |
| LatticeVal In1 = getValueState(PN1->getIncomingValue(i)); |
| BasicBlock *InBlock = PN1->getIncomingBlock(i); |
| LatticeVal In2 =getValueState(PN2->getIncomingValueForBlock(InBlock)); |
| |
| if (In1.isOverdefined() || In2.isOverdefined()) { |
| Result.markOverdefined(); |
| break; // Cannot fold this operation over the PHI nodes! |
| } |
| |
| if (In1.isConstant() && In2.isConstant()) { |
| Constant *V = ConstantExpr::getCompare(I.getPredicate(), |
| In1.getConstant(), |
| In2.getConstant()); |
| if (Result.isUndefined()) |
| Result.markConstant(V); |
| else if (Result.isConstant() && Result.getConstant() != V) { |
| Result.markOverdefined(); |
| break; |
| } |
| } |
| } |
| |
| // If we found a constant value here, then we know the instruction is |
| // constant despite the fact that the PHI nodes are overdefined. |
| if (Result.isConstant()) { |
| markConstant(&I, Result.getConstant()); |
| // Remember that this instruction is virtually using the PHI node |
| // operands. |
| InsertInOverdefinedPHIs(&I, PN1); |
| InsertInOverdefinedPHIs(&I, PN2); |
| return; |
| } |
| |
| if (Result.isUndefined()) |
| return; |
| |
| // Okay, this really is overdefined now. Since we might have |
| // speculatively thought that this was not overdefined before, and |
| // added ourselves to the UsersOfOverdefinedPHIs list for the PHIs, |
| // make sure to clean out any entries that we put there, for |
| // efficiency. |
| RemoveFromOverdefinedPHIs(&I, PN1); |
| RemoveFromOverdefinedPHIs(&I, PN2); |
| } |
| |
| markOverdefined(&I); |
| } |
| |
| void SCCPSolver::visitExtractElementInst(ExtractElementInst &I) { |
| // TODO : SCCP does not handle vectors properly. |
| return markOverdefined(&I); |
| |
| #if 0 |
| LatticeVal &ValState = getValueState(I.getOperand(0)); |
| LatticeVal &IdxState = getValueState(I.getOperand(1)); |
| |
| if (ValState.isOverdefined() || IdxState.isOverdefined()) |
| markOverdefined(&I); |
| else if(ValState.isConstant() && IdxState.isConstant()) |
| markConstant(&I, ConstantExpr::getExtractElement(ValState.getConstant(), |
| IdxState.getConstant())); |
| #endif |
| } |
| |
| void SCCPSolver::visitInsertElementInst(InsertElementInst &I) { |
| // TODO : SCCP does not handle vectors properly. |
| return markOverdefined(&I); |
| #if 0 |
| LatticeVal &ValState = getValueState(I.getOperand(0)); |
| LatticeVal &EltState = getValueState(I.getOperand(1)); |
| LatticeVal &IdxState = getValueState(I.getOperand(2)); |
| |
| if (ValState.isOverdefined() || EltState.isOverdefined() || |
| IdxState.isOverdefined()) |
| markOverdefined(&I); |
| else if(ValState.isConstant() && EltState.isConstant() && |
| IdxState.isConstant()) |
| markConstant(&I, ConstantExpr::getInsertElement(ValState.getConstant(), |
| EltState.getConstant(), |
| IdxState.getConstant())); |
| else if (ValState.isUndefined() && EltState.isConstant() && |
| IdxState.isConstant()) |
| markConstant(&I,ConstantExpr::getInsertElement(UndefValue::get(I.getType()), |
| EltState.getConstant(), |
| IdxState.getConstant())); |
| #endif |
| } |
| |
| void SCCPSolver::visitShuffleVectorInst(ShuffleVectorInst &I) { |
| // TODO : SCCP does not handle vectors properly. |
| return markOverdefined(&I); |
| #if 0 |
| LatticeVal &V1State = getValueState(I.getOperand(0)); |
| LatticeVal &V2State = getValueState(I.getOperand(1)); |
| LatticeVal &MaskState = getValueState(I.getOperand(2)); |
| |
| if (MaskState.isUndefined() || |
| (V1State.isUndefined() && V2State.isUndefined())) |
| return; // Undefined output if mask or both inputs undefined. |
| |
| if (V1State.isOverdefined() || V2State.isOverdefined() || |
| MaskState.isOverdefined()) { |
| markOverdefined(&I); |
| } else { |
| // A mix of constant/undef inputs. |
| Constant *V1 = V1State.isConstant() ? |
| V1State.getConstant() : UndefValue::get(I.getType()); |
| Constant *V2 = V2State.isConstant() ? |
| V2State.getConstant() : UndefValue::get(I.getType()); |
| Constant *Mask = MaskState.isConstant() ? |
| MaskState.getConstant() : UndefValue::get(I.getOperand(2)->getType()); |
| markConstant(&I, ConstantExpr::getShuffleVector(V1, V2, Mask)); |
| } |
| #endif |
| } |
| |
| // Handle getelementptr instructions. If all operands are constants then we |
| // can turn this into a getelementptr ConstantExpr. |
| // |
| void SCCPSolver::visitGetElementPtrInst(GetElementPtrInst &I) { |
| if (ValueState[&I].isOverdefined()) return; |
| |
| SmallVector<Constant*, 8> Operands; |
| Operands.reserve(I.getNumOperands()); |
| |
| for (unsigned i = 0, e = I.getNumOperands(); i != e; ++i) { |
| LatticeVal State = getValueState(I.getOperand(i)); |
| if (State.isUndefined()) |
| return; // Operands are not resolved yet. |
| |
| if (State.isOverdefined()) |
| return markOverdefined(&I); |
| |
| assert(State.isConstant() && "Unknown state!"); |
| Operands.push_back(State.getConstant()); |
| } |
| |
| Constant *Ptr = Operands[0]; |
| ArrayRef<Constant *> Indices(Operands.begin() + 1, Operands.end()); |
| markConstant(&I, ConstantExpr::getGetElementPtr(Ptr, Indices)); |
| } |
| |
| void SCCPSolver::visitStoreInst(StoreInst &SI) { |
| // If this store is of a struct, ignore it. |
| if (SI.getOperand(0)->getType()->isStructTy()) |
| return; |
| |
| if (TrackedGlobals.empty() || !isa<GlobalVariable>(SI.getOperand(1))) |
| return; |
| |
| GlobalVariable *GV = cast<GlobalVariable>(SI.getOperand(1)); |
| DenseMap<GlobalVariable*, LatticeVal>::iterator I = TrackedGlobals.find(GV); |
| if (I == TrackedGlobals.end() || I->second.isOverdefined()) return; |
| |
| // Get the value we are storing into the global, then merge it. |
| mergeInValue(I->second, GV, getValueState(SI.getOperand(0))); |
| if (I->second.isOverdefined()) |
| TrackedGlobals.erase(I); // No need to keep tracking this! |
| } |
| |
| |
| // Handle load instructions. If the operand is a constant pointer to a constant |
| // global, we can replace the load with the loaded constant value! |
| void SCCPSolver::visitLoadInst(LoadInst &I) { |
| // If this load is of a struct, just mark the result overdefined. |
| if (I.getType()->isStructTy()) |
| return markAnythingOverdefined(&I); |
| |
| LatticeVal PtrVal = getValueState(I.getOperand(0)); |
| if (PtrVal.isUndefined()) return; // The pointer is not resolved yet! |
| |
| LatticeVal &IV = ValueState[&I]; |
| if (IV.isOverdefined()) return; |
| |
| if (!PtrVal.isConstant() || I.isVolatile()) |
| return markOverdefined(IV, &I); |
| |
| Constant *Ptr = PtrVal.getConstant(); |
| |
| // load null -> null |
| if (isa<ConstantPointerNull>(Ptr) && I.getPointerAddressSpace() == 0) |
| return markConstant(IV, &I, Constant::getNullValue(I.getType())); |
| |
| // Transform load (constant global) into the value loaded. |
| if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Ptr)) { |
| if (!TrackedGlobals.empty()) { |
| // If we are tracking this global, merge in the known value for it. |
| DenseMap<GlobalVariable*, LatticeVal>::iterator It = |
| TrackedGlobals.find(GV); |
| if (It != TrackedGlobals.end()) { |
| mergeInValue(IV, &I, It->second); |
| return; |
| } |
| } |
| } |
| |
| // Transform load from a constant into a constant if possible. |
| if (Constant *C = ConstantFoldLoadFromConstPtr(Ptr, TD)) |
| return markConstant(IV, &I, C); |
| |
| // Otherwise we cannot say for certain what value this load will produce. |
| // Bail out. |
| markOverdefined(IV, &I); |
| } |
| |
| void SCCPSolver::visitCallSite(CallSite CS) { |
| Function *F = CS.getCalledFunction(); |
| Instruction *I = CS.getInstruction(); |
| |
| // The common case is that we aren't tracking the callee, either because we |
| // are not doing interprocedural analysis or the callee is indirect, or is |
| // external. Handle these cases first. |
| if (F == 0 || F->isDeclaration()) { |
| CallOverdefined: |
| // Void return and not tracking callee, just bail. |
| if (I->getType()->isVoidTy()) return; |
| |
| // Otherwise, if we have a single return value case, and if the function is |
| // a declaration, maybe we can constant fold it. |
| if (F && F->isDeclaration() && !I->getType()->isStructTy() && |
| canConstantFoldCallTo(F)) { |
| |
| SmallVector<Constant*, 8> Operands; |
| for (CallSite::arg_iterator AI = CS.arg_begin(), E = CS.arg_end(); |
| AI != E; ++AI) { |
| LatticeVal State = getValueState(*AI); |
| |
| if (State.isUndefined()) |
| return; // Operands are not resolved yet. |
| if (State.isOverdefined()) |
| return markOverdefined(I); |
| assert(State.isConstant() && "Unknown state!"); |
| Operands.push_back(State.getConstant()); |
| } |
| |
| // If we can constant fold this, mark the result of the call as a |
| // constant. |
| if (Constant *C = ConstantFoldCall(F, Operands)) |
| return markConstant(I, C); |
| } |
| |
| // Otherwise, we don't know anything about this call, mark it overdefined. |
| return markAnythingOverdefined(I); |
| } |
| |
| // If this is a local function that doesn't have its address taken, mark its |
| // entry block executable and merge in the actual arguments to the call into |
| // the formal arguments of the function. |
| if (!TrackingIncomingArguments.empty() && TrackingIncomingArguments.count(F)){ |
| MarkBlockExecutable(F->begin()); |
| |
| // Propagate information from this call site into the callee. |
| CallSite::arg_iterator CAI = CS.arg_begin(); |
| for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end(); |
| AI != E; ++AI, ++CAI) { |
| // If this argument is byval, and if the function is not readonly, there |
| // will be an implicit copy formed of the input aggregate. |
| if (AI->hasByValAttr() && !F->onlyReadsMemory()) { |
| markOverdefined(AI); |
| continue; |
| } |
| |
| if (StructType *STy = dyn_cast<StructType>(AI->getType())) { |
| for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) { |
| LatticeVal CallArg = getStructValueState(*CAI, i); |
| mergeInValue(getStructValueState(AI, i), AI, CallArg); |
| } |
| } else { |
| mergeInValue(AI, getValueState(*CAI)); |
| } |
| } |
| } |
| |
| // If this is a single/zero retval case, see if we're tracking the function. |
| if (StructType *STy = dyn_cast<StructType>(F->getReturnType())) { |
| if (!MRVFunctionsTracked.count(F)) |
| goto CallOverdefined; // Not tracking this callee. |
| |
| // If we are tracking this callee, propagate the result of the function |
| // into this call site. |
| for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) |
| mergeInValue(getStructValueState(I, i), I, |
| TrackedMultipleRetVals[std::make_pair(F, i)]); |
| } else { |
| DenseMap<Function*, LatticeVal>::iterator TFRVI = TrackedRetVals.find(F); |
| if (TFRVI == TrackedRetVals.end()) |
| goto CallOverdefined; // Not tracking this callee. |
| |
| // If so, propagate the return value of the callee into this call result. |
| mergeInValue(I, TFRVI->second); |
| } |
| } |
| |
| void SCCPSolver::Solve() { |
| // Process the work lists until they are empty! |
| while (!BBWorkList.empty() || !InstWorkList.empty() || |
| !OverdefinedInstWorkList.empty()) { |
| // Process the overdefined instruction's work list first, which drives other |
| // things to overdefined more quickly. |
| while (!OverdefinedInstWorkList.empty()) { |
| Value *I = OverdefinedInstWorkList.pop_back_val(); |
| |
| DEBUG(dbgs() << "\nPopped off OI-WL: " << *I << '\n'); |
| |
| // "I" got into the work list because it either made the transition from |
| // bottom to constant |
| // |
| // Anything on this worklist that is overdefined need not be visited |
| // since all of its users will have already been marked as overdefined |
| // Update all of the users of this instruction's value. |
| // |
| for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); |
| UI != E; ++UI) |
| if (Instruction *I = dyn_cast<Instruction>(*UI)) |
| OperandChangedState(I); |
| } |
| |
| // Process the instruction work list. |
| while (!InstWorkList.empty()) { |
| Value *I = InstWorkList.pop_back_val(); |
| |
| DEBUG(dbgs() << "\nPopped off I-WL: " << *I << '\n'); |
| |
| // "I" got into the work list because it made the transition from undef to |
| // constant. |
| // |
| // Anything on this worklist that is overdefined need not be visited |
| // since all of its users will have already been marked as overdefined. |
| // Update all of the users of this instruction's value. |
| // |
| if (I->getType()->isStructTy() || !getValueState(I).isOverdefined()) |
| for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); |
| UI != E; ++UI) |
| if (Instruction *I = dyn_cast<Instruction>(*UI)) |
| OperandChangedState(I); |
| } |
| |
| // Process the basic block work list. |
| while (!BBWorkList.empty()) { |
| BasicBlock *BB = BBWorkList.back(); |
| BBWorkList.pop_back(); |
| |
| DEBUG(dbgs() << "\nPopped off BBWL: " << *BB << '\n'); |
| |
| // Notify all instructions in this basic block that they are newly |
| // executable. |
| visit(BB); |
| } |
| } |
| } |
| |
| /// ResolvedUndefsIn - While solving the dataflow for a function, we assume |
| /// that branches on undef values cannot reach any of their successors. |
| /// However, this is not a safe assumption. After we solve dataflow, this |
| /// method should be use to handle this. If this returns true, the solver |
| /// should be rerun. |
| /// |
| /// This method handles this by finding an unresolved branch and marking it one |
| /// of the edges from the block as being feasible, even though the condition |
| /// doesn't say it would otherwise be. This allows SCCP to find the rest of the |
| /// CFG and only slightly pessimizes the analysis results (by marking one, |
| /// potentially infeasible, edge feasible). This cannot usefully modify the |
| /// constraints on the condition of the branch, as that would impact other users |
| /// of the value. |
| /// |
| /// This scan also checks for values that use undefs, whose results are actually |
| /// defined. For example, 'zext i8 undef to i32' should produce all zeros |
| /// conservatively, as "(zext i8 X -> i32) & 0xFF00" must always return zero, |
| /// even if X isn't defined. |
| bool SCCPSolver::ResolvedUndefsIn(Function &F) { |
| for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) { |
| if (!BBExecutable.count(BB)) |
| continue; |
| |
| for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) { |
| // Look for instructions which produce undef values. |
| if (I->getType()->isVoidTy()) continue; |
| |
| if (StructType *STy = dyn_cast<StructType>(I->getType())) { |
| // Only a few things that can be structs matter for undef. Just send |
| // all their results to overdefined. We could be more precise than this |
| // but it isn't worth bothering. |
| if (isa<CallInst>(I) || isa<SelectInst>(I)) { |
| for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) { |
| LatticeVal &LV = getStructValueState(I, i); |
| if (LV.isUndefined()) |
| markOverdefined(LV, I); |
| } |
| } |
| continue; |
| } |
| |
| LatticeVal &LV = getValueState(I); |
| if (!LV.isUndefined()) continue; |
| |
| // No instructions using structs need disambiguation. |
| if (I->getOperand(0)->getType()->isStructTy()) |
| continue; |
| |
| // Get the lattice values of the first two operands for use below. |
| LatticeVal Op0LV = getValueState(I->getOperand(0)); |
| LatticeVal Op1LV; |
| if (I->getNumOperands() == 2) { |
| // No instructions using structs need disambiguation. |
| if (I->getOperand(1)->getType()->isStructTy()) |
| continue; |
| |
| // If this is a two-operand instruction, and if both operands are |
| // undefs, the result stays undef. |
| Op1LV = getValueState(I->getOperand(1)); |
| if (Op0LV.isUndefined() && Op1LV.isUndefined()) |
| continue; |
| } |
| |
| // If this is an instructions whose result is defined even if the input is |
| // not fully defined, propagate the information. |
| Type *ITy = I->getType(); |
| switch (I->getOpcode()) { |
| default: break; // Leave the instruction as an undef. |
| case Instruction::ZExt: |
| // After a zero extend, we know the top part is zero. SExt doesn't have |
| // to be handled here, because we don't know whether the top part is 1's |
| // or 0's. |
| case Instruction::SIToFP: // some FP values are not possible, just use 0. |
| case Instruction::UIToFP: // some FP values are not possible, just use 0. |
| markForcedConstant(I, Constant::getNullValue(ITy)); |
| return true; |
| case Instruction::Mul: |
| case Instruction::And: |
| // undef * X -> 0. X could be zero. |
| // undef & X -> 0. X could be zero. |
| markForcedConstant(I, Constant::getNullValue(ITy)); |
| return true; |
| |
| case Instruction::Or: |
| // undef | X -> -1. X could be -1. |
| markForcedConstant(I, Constant::getAllOnesValue(ITy)); |
| return true; |
| |
| case Instruction::SDiv: |
| case Instruction::UDiv: |
| case Instruction::SRem: |
| case Instruction::URem: |
| // X / undef -> undef. No change. |
| // X % undef -> undef. No change. |
| if (Op1LV.isUndefined()) break; |
| |
| // undef / X -> 0. X could be maxint. |
| // undef % X -> 0. X could be 1. |
| markForcedConstant(I, Constant::getNullValue(ITy)); |
| return true; |
| |
| case Instruction::AShr: |
| // undef >>s X -> undef. No change. |
| if (Op0LV.isUndefined()) break; |
| |
| // X >>s undef -> X. X could be 0, X could have the high-bit known set. |
| if (Op0LV.isConstant()) |
| markForcedConstant(I, Op0LV.getConstant()); |
| else |
| markOverdefined(I); |
| return true; |
| case Instruction::LShr: |
| case Instruction::Shl: |
| // undef >> X -> undef. No change. |
| // undef << X -> undef. No change. |
| if (Op0LV.isUndefined()) break; |
| |
| // X >> undef -> 0. X could be 0. |
| // X << undef -> 0. X could be 0. |
| markForcedConstant(I, Constant::getNullValue(ITy)); |
| return true; |
| case Instruction::Select: |
| // undef ? X : Y -> X or Y. There could be commonality between X/Y. |
| if (Op0LV.isUndefined()) { |
| if (!Op1LV.isConstant()) // Pick the constant one if there is any. |
| Op1LV = getValueState(I->getOperand(2)); |
| } else if (Op1LV.isUndefined()) { |
| // c ? undef : undef -> undef. No change. |
| Op1LV = getValueState(I->getOperand(2)); |
| if (Op1LV.isUndefined()) |
| break; |
| // Otherwise, c ? undef : x -> x. |
| } else { |
| // Leave Op1LV as Operand(1)'s LatticeValue. |
| } |
| |
| if (Op1LV.isConstant()) |
| markForcedConstant(I, Op1LV.getConstant()); |
| else |
| markOverdefined(I); |
| return true; |
| case Instruction::Call: |
| // If a call has an undef result, it is because it is constant foldable |
| // but one of the inputs was undef. Just force the result to |
| // overdefined. |
| markOverdefined(I); |
| return true; |
| } |
| } |
| |
| // Check to see if we have a branch or switch on an undefined value. If so |
| // we force the branch to go one way or the other to make the successor |
| // values live. It doesn't really matter which way we force it. |
| TerminatorInst *TI = BB->getTerminator(); |
| if (BranchInst *BI = dyn_cast<BranchInst>(TI)) { |
| if (!BI->isConditional()) continue; |
| if (!getValueState(BI->getCondition()).isUndefined()) |
| continue; |
| |
| // If the input to SCCP is actually branch on undef, fix the undef to |
| // false. |
| if (isa<UndefValue>(BI->getCondition())) { |
| BI->setCondition(ConstantInt::getFalse(BI->getContext())); |
| markEdgeExecutable(BB, TI->getSuccessor(1)); |
| return true; |
| } |
| |
| // Otherwise, it is a branch on a symbolic value which is currently |
| // considered to be undef. Handle this by forcing the input value to the |
| // branch to false. |
| markForcedConstant(BI->getCondition(), |
| ConstantInt::getFalse(TI->getContext())); |
| return true; |
| } |
| |
| if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) { |
| if (SI->getNumSuccessors() < 2) // no cases |
| continue; |
| if (!getValueState(SI->getCondition()).isUndefined()) |
| continue; |
| |
| // If the input to SCCP is actually switch on undef, fix the undef to |
| // the first constant. |
| if (isa<UndefValue>(SI->getCondition())) { |
| SI->setCondition(SI->getCaseValue(1)); |
| markEdgeExecutable(BB, TI->getSuccessor(1)); |
| return true; |
| } |
| |
| markForcedConstant(SI->getCondition(), SI->getCaseValue(1)); |
| return true; |
| } |
| } |
| |
| return false; |
| } |
| |
| |
| namespace { |
| //===--------------------------------------------------------------------===// |
| // |
| /// SCCP Class - This class uses the SCCPSolver to implement a per-function |
| /// Sparse Conditional Constant Propagator. |
| /// |
| struct SCCP : public FunctionPass { |
| static char ID; // Pass identification, replacement for typeid |
| SCCP() : FunctionPass(ID) { |
| initializeSCCPPass(*PassRegistry::getPassRegistry()); |
| } |
| |
| // runOnFunction - Run the Sparse Conditional Constant Propagation |
| // algorithm, and return true if the function was modified. |
| // |
| bool runOnFunction(Function &F); |
| }; |
| } // end anonymous namespace |
| |
| char SCCP::ID = 0; |
| INITIALIZE_PASS(SCCP, "sccp", |
| "Sparse Conditional Constant Propagation", false, false) |
| |
| // createSCCPPass - This is the public interface to this file. |
| FunctionPass *llvm::createSCCPPass() { |
| return new SCCP(); |
| } |
| |
| static void DeleteInstructionInBlock(BasicBlock *BB) { |
| DEBUG(dbgs() << " BasicBlock Dead:" << *BB); |
| ++NumDeadBlocks; |
| |
| // Delete the instructions backwards, as it has a reduced likelihood of |
| // having to update as many def-use and use-def chains. |
| while (!isa<TerminatorInst>(BB->begin())) { |
| Instruction *I = --BasicBlock::iterator(BB->getTerminator()); |
| |
| if (!I->use_empty()) |
| I->replaceAllUsesWith(UndefValue::get(I->getType())); |
| BB->getInstList().erase(I); |
| ++NumInstRemoved; |
| } |
| } |
| |
| // runOnFunction() - Run the Sparse Conditional Constant Propagation algorithm, |
| // and return true if the function was modified. |
| // |
| bool SCCP::runOnFunction(Function &F) { |
| DEBUG(dbgs() << "SCCP on function '" << F.getName() << "'\n"); |
| SCCPSolver Solver(getAnalysisIfAvailable<TargetData>()); |
| |
| // Mark the first block of the function as being executable. |
| Solver.MarkBlockExecutable(F.begin()); |
| |
| // Mark all arguments to the function as being overdefined. |
| for (Function::arg_iterator AI = F.arg_begin(), E = F.arg_end(); AI != E;++AI) |
| Solver.markAnythingOverdefined(AI); |
| |
| // Solve for constants. |
| bool ResolvedUndefs = true; |
| while (ResolvedUndefs) { |
| Solver.Solve(); |
| DEBUG(dbgs() << "RESOLVING UNDEFs\n"); |
| ResolvedUndefs = Solver.ResolvedUndefsIn(F); |
| } |
| |
| bool MadeChanges = false; |
| |
| // If we decided that there are basic blocks that are dead in this function, |
| // delete their contents now. Note that we cannot actually delete the blocks, |
| // as we cannot modify the CFG of the function. |
| |
| for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) { |
| if (!Solver.isBlockExecutable(BB)) { |
| DeleteInstructionInBlock(BB); |
| MadeChanges = true; |
| continue; |
| } |
| |
| // Iterate over all of the instructions in a function, replacing them with |
| // constants if we have found them to be of constant values. |
| // |
| for (BasicBlock::iterator BI = BB->begin(), E = BB->end(); BI != E; ) { |
| Instruction *Inst = BI++; |
| if (Inst->getType()->isVoidTy() || isa<TerminatorInst>(Inst)) |
| continue; |
| |
| // TODO: Reconstruct structs from their elements. |
| if (Inst->getType()->isStructTy()) |
| continue; |
| |
| LatticeVal IV = Solver.getLatticeValueFor(Inst); |
| if (IV.isOverdefined()) |
| continue; |
| |
| Constant *Const = IV.isConstant() |
| ? IV.getConstant() : UndefValue::get(Inst->getType()); |
| DEBUG(dbgs() << " Constant: " << *Const << " = " << *Inst); |
| |
| // Replaces all of the uses of a variable with uses of the constant. |
| Inst->replaceAllUsesWith(Const); |
| |
| // Delete the instruction. |
| Inst->eraseFromParent(); |
| |
| // Hey, we just changed something! |
| MadeChanges = true; |
| ++NumInstRemoved; |
| } |
| } |
| |
| return MadeChanges; |
| } |
| |
| namespace { |
| //===--------------------------------------------------------------------===// |
| // |
| /// IPSCCP Class - This class implements interprocedural Sparse Conditional |
| /// Constant Propagation. |
| /// |
| struct IPSCCP : public ModulePass { |
| static char ID; |
| IPSCCP() : ModulePass(ID) { |
| initializeIPSCCPPass(*PassRegistry::getPassRegistry()); |
| } |
| bool runOnModule(Module &M); |
| }; |
| } // end anonymous namespace |
| |
| char IPSCCP::ID = 0; |
| INITIALIZE_PASS(IPSCCP, "ipsccp", |
| "Interprocedural Sparse Conditional Constant Propagation", |
| false, false) |
| |
| // createIPSCCPPass - This is the public interface to this file. |
| ModulePass *llvm::createIPSCCPPass() { |
| return new IPSCCP(); |
| } |
| |
| |
| static bool AddressIsTaken(const GlobalValue *GV) { |
| // Delete any dead constantexpr klingons. |
| GV->removeDeadConstantUsers(); |
| |
| for (Value::const_use_iterator UI = GV->use_begin(), E = GV->use_end(); |
| UI != E; ++UI) { |
| const User *U = *UI; |
| if (const StoreInst *SI = dyn_cast<StoreInst>(U)) { |
| if (SI->getOperand(0) == GV || SI->isVolatile()) |
| return true; // Storing addr of GV. |
| } else if (isa<InvokeInst>(U) || isa<CallInst>(U)) { |
| // Make sure we are calling the function, not passing the address. |
| ImmutableCallSite CS(cast<Instruction>(U)); |
| if (!CS.isCallee(UI)) |
| return true; |
| } else if (const LoadInst *LI = dyn_cast<LoadInst>(U)) { |
| if (LI->isVolatile()) |
| return true; |
| } else if (isa<BlockAddress>(U)) { |
| // blockaddress doesn't take the address of the function, it takes addr |
| // of label. |
| } else { |
| return true; |
| } |
| } |
| return false; |
| } |
| |
| bool IPSCCP::runOnModule(Module &M) { |
| SCCPSolver Solver(getAnalysisIfAvailable<TargetData>()); |
| |
| // AddressTakenFunctions - This set keeps track of the address-taken functions |
| // that are in the input. As IPSCCP runs through and simplifies code, |
| // functions that were address taken can end up losing their |
| // address-taken-ness. Because of this, we keep track of their addresses from |
| // the first pass so we can use them for the later simplification pass. |
| SmallPtrSet<Function*, 32> AddressTakenFunctions; |
| |
| // Loop over all functions, marking arguments to those with their addresses |
| // taken or that are external as overdefined. |
| // |
| for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F) { |
| if (F->isDeclaration()) |
| continue; |
| |
| // If this is a strong or ODR definition of this function, then we can |
| // propagate information about its result into callsites of it. |
| if (!F->mayBeOverridden()) |
| Solver.AddTrackedFunction(F); |
| |
| // If this function only has direct calls that we can see, we can track its |
| // arguments and return value aggressively, and can assume it is not called |
| // unless we see evidence to the contrary. |
| if (F->hasLocalLinkage()) { |
| if (AddressIsTaken(F)) |
| AddressTakenFunctions.insert(F); |
| else { |
| Solver.AddArgumentTrackedFunction(F); |
| continue; |
| } |
| } |
| |
| // Assume the function is called. |
| Solver.MarkBlockExecutable(F->begin()); |
| |
| // Assume nothing about the incoming arguments. |
| for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end(); |
| AI != E; ++AI) |
| Solver.markAnythingOverdefined(AI); |
| } |
| |
| // Loop over global variables. We inform the solver about any internal global |
| // variables that do not have their 'addresses taken'. If they don't have |
| // their addresses taken, we can propagate constants through them. |
| for (Module::global_iterator G = M.global_begin(), E = M.global_end(); |
| G != E; ++G) |
| if (!G->isConstant() && G->hasLocalLinkage() && !AddressIsTaken(G)) |
| Solver.TrackValueOfGlobalVariable(G); |
| |
| // Solve for constants. |
| bool ResolvedUndefs = true; |
| while (ResolvedUndefs) { |
| Solver.Solve(); |
| |
| DEBUG(dbgs() << "RESOLVING UNDEFS\n"); |
| ResolvedUndefs = false; |
| for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F) |
| ResolvedUndefs |= Solver.ResolvedUndefsIn(*F); |
| } |
| |
| bool MadeChanges = false; |
| |
| // Iterate over all of the instructions in the module, replacing them with |
| // constants if we have found them to be of constant values. |
| // |
| SmallVector<BasicBlock*, 512> BlocksToErase; |
| |
| for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F) { |
| if (Solver.isBlockExecutable(F->begin())) { |
| for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end(); |
| AI != E; ++AI) { |
| if (AI->use_empty() || AI->getType()->isStructTy()) continue; |
| |
| // TODO: Could use getStructLatticeValueFor to find out if the entire |
| // result is a constant and replace it entirely if so. |
| |
| LatticeVal IV = Solver.getLatticeValueFor(AI); |
| if (IV.isOverdefined()) continue; |
| |
| Constant *CST = IV.isConstant() ? |
| IV.getConstant() : UndefValue::get(AI->getType()); |
| DEBUG(dbgs() << "*** Arg " << *AI << " = " << *CST <<"\n"); |
| |
| // Replaces all of the uses of a variable with uses of the |
| // constant. |
| AI->replaceAllUsesWith(CST); |
| ++IPNumArgsElimed; |
| } |
| } |
| |
| for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB) { |
| if (!Solver.isBlockExecutable(BB)) { |
| DeleteInstructionInBlock(BB); |
| MadeChanges = true; |
| |
| TerminatorInst *TI = BB->getTerminator(); |
| for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) { |
| BasicBlock *Succ = TI->getSuccessor(i); |
| if (!Succ->empty() && isa<PHINode>(Succ->begin())) |
| TI->getSuccessor(i)->removePredecessor(BB); |
| } |
| if (!TI->use_empty()) |
| TI->replaceAllUsesWith(UndefValue::get(TI->getType())); |
| TI->eraseFromParent(); |
| |
| if (&*BB != &F->front()) |
| BlocksToErase.push_back(BB); |
| else |
| new UnreachableInst(M.getContext(), BB); |
| continue; |
| } |
| |
| for (BasicBlock::iterator BI = BB->begin(), E = BB->end(); BI != E; ) { |
| Instruction *Inst = BI++; |
| if (Inst->getType()->isVoidTy() || Inst->getType()->isStructTy()) |
| continue; |
| |
| // TODO: Could use getStructLatticeValueFor to find out if the entire |
| // result is a constant and replace it entirely if so. |
| |
| LatticeVal IV = Solver.getLatticeValueFor(Inst); |
| if (IV.isOverdefined()) |
| continue; |
| |
| Constant *Const = IV.isConstant() |
| ? IV.getConstant() : UndefValue::get(Inst->getType()); |
| DEBUG(dbgs() << " Constant: " << *Const << " = " << *Inst); |
| |
| // Replaces all of the uses of a variable with uses of the |
| // constant. |
| Inst->replaceAllUsesWith(Const); |
| |
| // Delete the instruction. |
| if (!isa<CallInst>(Inst) && !isa<TerminatorInst>(Inst)) |
| Inst->eraseFromParent(); |
| |
| // Hey, we just changed something! |
| MadeChanges = true; |
| ++IPNumInstRemoved; |
| } |
| } |
| |
| // Now that all instructions in the function are constant folded, erase dead |
| // blocks, because we can now use ConstantFoldTerminator to get rid of |
| // in-edges. |
| for (unsigned i = 0, e = BlocksToErase.size(); i != e; ++i) { |
| // If there are any PHI nodes in this successor, drop entries for BB now. |
| BasicBlock *DeadBB = BlocksToErase[i]; |
| for (Value::use_iterator UI = DeadBB->use_begin(), UE = DeadBB->use_end(); |
| UI != UE; ) { |
| // Grab the user and then increment the iterator early, as the user |
| // will be deleted. Step past all adjacent uses from the same user. |
| Instruction *I = dyn_cast<Instruction>(*UI); |
| do { ++UI; } while (UI != UE && *UI == I); |
| |
| // Ignore blockaddress users; BasicBlock's dtor will handle them. |
| if (!I) continue; |
| |
| bool Folded = ConstantFoldTerminator(I->getParent()); |
| if (!Folded) { |
| // The constant folder may not have been able to fold the terminator |
| // if this is a branch or switch on undef. Fold it manually as a |
| // branch to the first successor. |
| #ifndef NDEBUG |
| if (BranchInst *BI = dyn_cast<BranchInst>(I)) { |
| assert(BI->isConditional() && isa<UndefValue>(BI->getCondition()) && |
| "Branch should be foldable!"); |
| } else if (SwitchInst *SI = dyn_cast<SwitchInst>(I)) { |
| assert(isa<UndefValue>(SI->getCondition()) && "Switch should fold"); |
| } else { |
| llvm_unreachable("Didn't fold away reference to block!"); |
| } |
| #endif |
| |
| // Make this an uncond branch to the first successor. |
| TerminatorInst *TI = I->getParent()->getTerminator(); |
| BranchInst::Create(TI->getSuccessor(0), TI); |
| |
| // Remove entries in successor phi nodes to remove edges. |
| for (unsigned i = 1, e = TI->getNumSuccessors(); i != e; ++i) |
| TI->getSuccessor(i)->removePredecessor(TI->getParent()); |
| |
| // Remove the old terminator. |
| TI->eraseFromParent(); |
| } |
| } |
| |
| // Finally, delete the basic block. |
| F->getBasicBlockList().erase(DeadBB); |
| } |
| BlocksToErase.clear(); |
| } |
| |
| // If we inferred constant or undef return values for a function, we replaced |
| // all call uses with the inferred value. This means we don't need to bother |
| // actually returning anything from the function. Replace all return |
| // instructions with return undef. |
| // |
| // Do this in two stages: first identify the functions we should process, then |
| // actually zap their returns. This is important because we can only do this |
| // if the address of the function isn't taken. In cases where a return is the |
| // last use of a function, the order of processing functions would affect |
| // whether other functions are optimizable. |
| SmallVector<ReturnInst*, 8> ReturnsToZap; |
| |
| // TODO: Process multiple value ret instructions also. |
| const DenseMap<Function*, LatticeVal> &RV = Solver.getTrackedRetVals(); |
| for (DenseMap<Function*, LatticeVal>::const_iterator I = RV.begin(), |
| E = RV.end(); I != E; ++I) { |
| Function *F = I->first; |
| if (I->second.isOverdefined() || F->getReturnType()->isVoidTy()) |
| continue; |
| |
| // We can only do this if we know that nothing else can call the function. |
| if (!F->hasLocalLinkage() || AddressTakenFunctions.count(F)) |
| continue; |
| |
| for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB) |
| if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) |
| if (!isa<UndefValue>(RI->getOperand(0))) |
| ReturnsToZap.push_back(RI); |
| } |
| |
| // Zap all returns which we've identified as zap to change. |
| for (unsigned i = 0, e = ReturnsToZap.size(); i != e; ++i) { |
| Function *F = ReturnsToZap[i]->getParent()->getParent(); |
| ReturnsToZap[i]->setOperand(0, UndefValue::get(F->getReturnType())); |
| } |
| |
| // If we inferred constant or undef values for globals variables, we can delete |
| // the global and any stores that remain to it. |
| const DenseMap<GlobalVariable*, LatticeVal> &TG = Solver.getTrackedGlobals(); |
| for (DenseMap<GlobalVariable*, LatticeVal>::const_iterator I = TG.begin(), |
| E = TG.end(); I != E; ++I) { |
| GlobalVariable *GV = I->first; |
| assert(!I->second.isOverdefined() && |
| "Overdefined values should have been taken out of the map!"); |
| DEBUG(dbgs() << "Found that GV '" << GV->getName() << "' is constant!\n"); |
| while (!GV->use_empty()) { |
| StoreInst *SI = cast<StoreInst>(GV->use_back()); |
| SI->eraseFromParent(); |
| } |
| M.getGlobalList().erase(GV); |
| ++IPNumGlobalConst; |
| } |
| |
| return MadeChanges; |
| } |