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//===- SCCP.cpp - Sparse Conditional Constant Propagation -----------------===//
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// The LLVM Compiler Infrastructure
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//===----------------------------------------------------------------------===//
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// This file implements sparse conditional constant propagation and merging:
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// Specifically, this:
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// * Assumes values are constant unless proven otherwise
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// * Assumes BasicBlocks are dead unless proven otherwise
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// * Proves values to be constant, and replaces them with constants
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// * Proves conditional branches to be unconditional
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//===----------------------------------------------------------------------===//
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#define DEBUG_TYPE "sccp"
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#include "llvm/Transforms/Scalar.h"
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#include "llvm/Transforms/IPO.h"
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#include "llvm/Constants.h"
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#include "llvm/DerivedTypes.h"
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#include "llvm/Instructions.h"
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#include "llvm/Pass.h"
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#include "llvm/Analysis/ConstantFolding.h"
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#include "llvm/Analysis/ValueTracking.h"
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#include "llvm/Transforms/Utils/Local.h"
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#include "llvm/Target/TargetData.h"
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#include "llvm/Support/CallSite.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/ErrorHandling.h"
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#include "llvm/Support/InstVisitor.h"
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#include "llvm/Support/raw_ostream.h"
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#include "llvm/ADT/DenseMap.h"
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#include "llvm/ADT/DenseSet.h"
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#include "llvm/ADT/PointerIntPair.h"
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#include "llvm/ADT/SmallPtrSet.h"
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#include "llvm/ADT/SmallVector.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/ADT/STLExtras.h"
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STATISTIC(NumInstRemoved, "Number of instructions removed");
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STATISTIC(NumDeadBlocks , "Number of basic blocks unreachable");
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STATISTIC(IPNumInstRemoved, "Number of instructions removed by IPSCCP");
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STATISTIC(IPNumArgsElimed ,"Number of arguments constant propagated by IPSCCP");
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STATISTIC(IPNumGlobalConst, "Number of globals found to be constant by IPSCCP");
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/// LatticeVal class - This class represents the different lattice values that
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/// an LLVM value may occupy. It is a simple class with value semantics.
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/// undefined - This LLVM Value has no known value yet.
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/// constant - This LLVM Value has a specific constant value.
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/// forcedconstant - This LLVM Value was thought to be undef until
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/// ResolvedUndefsIn. This is treated just like 'constant', but if merged
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/// with another (different) constant, it goes to overdefined, instead of
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/// overdefined - This instruction is not known to be constant, and we know
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/// Val: This stores the current lattice value along with the Constant* for
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/// the constant if this is a 'constant' or 'forcedconstant' value.
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PointerIntPair<Constant *, 2, LatticeValueTy> Val;
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LatticeValueTy getLatticeValue() const {
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LatticeVal() : Val(0, undefined) {}
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bool isUndefined() const { return getLatticeValue() == undefined; }
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bool isConstant() const {
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return getLatticeValue() == constant || getLatticeValue() == forcedconstant;
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bool isOverdefined() const { return getLatticeValue() == overdefined; }
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Constant *getConstant() const {
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assert(isConstant() && "Cannot get the constant of a non-constant!");
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return Val.getPointer();
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/// markOverdefined - Return true if this is a change in status.
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bool markOverdefined() {
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Val.setInt(overdefined);
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/// markConstant - Return true if this is a change in status.
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bool markConstant(Constant *V) {
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if (getLatticeValue() == constant) { // Constant but not forcedconstant.
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assert(getConstant() == V && "Marking constant with different value");
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Val.setInt(constant);
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assert(V && "Marking constant with NULL");
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assert(getLatticeValue() == forcedconstant &&
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"Cannot move from overdefined to constant!");
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// Stay at forcedconstant if the constant is the same.
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if (V == getConstant()) return false;
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// Otherwise, we go to overdefined. Assumptions made based on the
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// forced value are possibly wrong. Assuming this is another constant
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// could expose a contradiction.
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Val.setInt(overdefined);
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/// getConstantInt - If this is a constant with a ConstantInt value, return it
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/// otherwise return null.
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ConstantInt *getConstantInt() const {
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return dyn_cast<ConstantInt>(getConstant());
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void markForcedConstant(Constant *V) {
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assert(isUndefined() && "Can't force a defined value!");
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Val.setInt(forcedconstant);
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} // end anonymous namespace.
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//===----------------------------------------------------------------------===//
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/// SCCPSolver - This class is a general purpose solver for Sparse Conditional
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/// Constant Propagation.
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class SCCPSolver : public InstVisitor<SCCPSolver> {
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const TargetData *TD;
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SmallPtrSet<BasicBlock*, 8> BBExecutable;// The BBs that are executable.
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DenseMap<Value*, LatticeVal> ValueState; // The state each value is in.
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/// StructValueState - This maintains ValueState for values that have
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/// StructType, for example for formal arguments, calls, insertelement, etc.
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DenseMap<std::pair<Value*, unsigned>, LatticeVal> StructValueState;
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/// GlobalValue - If we are tracking any values for the contents of a global
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/// variable, we keep a mapping from the constant accessor to the element of
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/// the global, to the currently known value. If the value becomes
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/// overdefined, it's entry is simply removed from this map.
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DenseMap<GlobalVariable*, LatticeVal> TrackedGlobals;
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/// TrackedRetVals - If we are tracking arguments into and the return
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/// value out of a function, it will have an entry in this map, indicating
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/// what the known return value for the function is.
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DenseMap<Function*, LatticeVal> TrackedRetVals;
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/// TrackedMultipleRetVals - Same as TrackedRetVals, but used for functions
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/// that return multiple values.
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DenseMap<std::pair<Function*, unsigned>, LatticeVal> TrackedMultipleRetVals;
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/// MRVFunctionsTracked - Each function in TrackedMultipleRetVals is
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/// represented here for efficient lookup.
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SmallPtrSet<Function*, 16> MRVFunctionsTracked;
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/// TrackingIncomingArguments - This is the set of functions for whose
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/// arguments we make optimistic assumptions about and try to prove as
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SmallPtrSet<Function*, 16> TrackingIncomingArguments;
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/// The reason for two worklists is that overdefined is the lowest state
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/// on the lattice, and moving things to overdefined as fast as possible
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/// makes SCCP converge much faster.
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/// By having a separate worklist, we accomplish this because everything
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/// possibly overdefined will become overdefined at the soonest possible
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SmallVector<Value*, 64> OverdefinedInstWorkList;
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SmallVector<Value*, 64> InstWorkList;
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SmallVector<BasicBlock*, 64> BBWorkList; // The BasicBlock work list
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/// UsersOfOverdefinedPHIs - Keep track of any users of PHI nodes that are not
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/// overdefined, despite the fact that the PHI node is overdefined.
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std::multimap<PHINode*, Instruction*> UsersOfOverdefinedPHIs;
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/// KnownFeasibleEdges - Entries in this set are edges which have already had
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/// PHI nodes retriggered.
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typedef std::pair<BasicBlock*, BasicBlock*> Edge;
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DenseSet<Edge> KnownFeasibleEdges;
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SCCPSolver(const TargetData *td) : TD(td) {}
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/// MarkBlockExecutable - This method can be used by clients to mark all of
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/// the blocks that are known to be intrinsically live in the processed unit.
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/// This returns true if the block was not considered live before.
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bool MarkBlockExecutable(BasicBlock *BB) {
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if (!BBExecutable.insert(BB)) return false;
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DEBUG(dbgs() << "Marking Block Executable: " << BB->getName() << "\n");
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BBWorkList.push_back(BB); // Add the block to the work list!
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/// TrackValueOfGlobalVariable - Clients can use this method to
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/// inform the SCCPSolver that it should track loads and stores to the
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/// specified global variable if it can. This is only legal to call if
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/// performing Interprocedural SCCP.
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void TrackValueOfGlobalVariable(GlobalVariable *GV) {
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// We only track the contents of scalar globals.
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if (GV->getType()->getElementType()->isSingleValueType()) {
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LatticeVal &IV = TrackedGlobals[GV];
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if (!isa<UndefValue>(GV->getInitializer()))
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IV.markConstant(GV->getInitializer());
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/// AddTrackedFunction - If the SCCP solver is supposed to track calls into
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/// and out of the specified function (which cannot have its address taken),
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/// this method must be called.
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void AddTrackedFunction(Function *F) {
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// Add an entry, F -> undef.
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if (const StructType *STy = dyn_cast<StructType>(F->getReturnType())) {
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MRVFunctionsTracked.insert(F);
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for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i)
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TrackedMultipleRetVals.insert(std::make_pair(std::make_pair(F, i),
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TrackedRetVals.insert(std::make_pair(F, LatticeVal()));
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void AddArgumentTrackedFunction(Function *F) {
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TrackingIncomingArguments.insert(F);
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/// Solve - Solve for constants and executable blocks.
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/// ResolvedUndefsIn - While solving the dataflow for a function, we assume
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/// that branches on undef values cannot reach any of their successors.
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/// However, this is not a safe assumption. After we solve dataflow, this
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/// method should be use to handle this. If this returns true, the solver
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bool ResolvedUndefsIn(Function &F);
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bool isBlockExecutable(BasicBlock *BB) const {
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return BBExecutable.count(BB);
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LatticeVal getLatticeValueFor(Value *V) const {
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DenseMap<Value*, LatticeVal>::const_iterator I = ValueState.find(V);
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assert(I != ValueState.end() && "V is not in valuemap!");
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LatticeVal getStructLatticeValueFor(Value *V, unsigned i) const {
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DenseMap<std::pair<Value*, unsigned>, LatticeVal>::const_iterator I =
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StructValueState.find(std::make_pair(V, i));
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assert(I != StructValueState.end() && "V is not in valuemap!");
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/// getTrackedRetVals - Get the inferred return value map.
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const DenseMap<Function*, LatticeVal> &getTrackedRetVals() {
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return TrackedRetVals;
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/// getTrackedGlobals - Get and return the set of inferred initializers for
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/// global variables.
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const DenseMap<GlobalVariable*, LatticeVal> &getTrackedGlobals() {
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return TrackedGlobals;
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void markOverdefined(Value *V) {
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assert(!V->getType()->isStructTy() && "Should use other method");
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markOverdefined(ValueState[V], V);
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/// markAnythingOverdefined - Mark the specified value overdefined. This
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/// works with both scalars and structs.
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void markAnythingOverdefined(Value *V) {
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if (const StructType *STy = dyn_cast<StructType>(V->getType()))
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for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i)
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markOverdefined(getStructValueState(V, i), V);
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// markConstant - Make a value be marked as "constant". If the value
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// is not already a constant, add it to the instruction work list so that
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// the users of the instruction are updated later.
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void markConstant(LatticeVal &IV, Value *V, Constant *C) {
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if (!IV.markConstant(C)) return;
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DEBUG(dbgs() << "markConstant: " << *C << ": " << *V << '\n');
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InstWorkList.push_back(V);
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void markConstant(Value *V, Constant *C) {
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assert(!V->getType()->isStructTy() && "Should use other method");
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markConstant(ValueState[V], V, C);
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void markForcedConstant(Value *V, Constant *C) {
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assert(!V->getType()->isStructTy() && "Should use other method");
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ValueState[V].markForcedConstant(C);
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DEBUG(dbgs() << "markForcedConstant: " << *C << ": " << *V << '\n');
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InstWorkList.push_back(V);
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// markOverdefined - Make a value be marked as "overdefined". If the
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// value is not already overdefined, add it to the overdefined instruction
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// work list so that the users of the instruction are updated later.
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void markOverdefined(LatticeVal &IV, Value *V) {
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if (!IV.markOverdefined()) return;
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DEBUG(dbgs() << "markOverdefined: ";
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if (Function *F = dyn_cast<Function>(V))
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dbgs() << "Function '" << F->getName() << "'\n";
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dbgs() << *V << '\n');
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// Only instructions go on the work list
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OverdefinedInstWorkList.push_back(V);
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void mergeInValue(LatticeVal &IV, Value *V, LatticeVal MergeWithV) {
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if (IV.isOverdefined() || MergeWithV.isUndefined())
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if (MergeWithV.isOverdefined())
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markOverdefined(IV, V);
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else if (IV.isUndefined())
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markConstant(IV, V, MergeWithV.getConstant());
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else if (IV.getConstant() != MergeWithV.getConstant())
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markOverdefined(IV, V);
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void mergeInValue(Value *V, LatticeVal MergeWithV) {
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assert(!V->getType()->isStructTy() && "Should use other method");
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mergeInValue(ValueState[V], V, MergeWithV);
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/// getValueState - Return the LatticeVal object that corresponds to the
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/// value. This function handles the case when the value hasn't been seen yet
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/// by properly seeding constants etc.
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LatticeVal &getValueState(Value *V) {
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assert(!V->getType()->isStructTy() && "Should use getStructValueState");
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std::pair<DenseMap<Value*, LatticeVal>::iterator, bool> I =
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ValueState.insert(std::make_pair(V, LatticeVal()));
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LatticeVal &LV = I.first->second;
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return LV; // Common case, already in the map.
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if (Constant *C = dyn_cast<Constant>(V)) {
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// Undef values remain undefined.
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if (!isa<UndefValue>(V))
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LV.markConstant(C); // Constants are constant
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// All others are underdefined by default.
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/// getStructValueState - Return the LatticeVal object that corresponds to the
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/// value/field pair. This function handles the case when the value hasn't
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/// been seen yet by properly seeding constants etc.
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LatticeVal &getStructValueState(Value *V, unsigned i) {
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assert(V->getType()->isStructTy() && "Should use getValueState");
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assert(i < cast<StructType>(V->getType())->getNumElements() &&
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"Invalid element #");
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std::pair<DenseMap<std::pair<Value*, unsigned>, LatticeVal>::iterator,
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bool> I = StructValueState.insert(
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std::make_pair(std::make_pair(V, i), LatticeVal()));
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LatticeVal &LV = I.first->second;
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return LV; // Common case, already in the map.
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if (Constant *C = dyn_cast<Constant>(V)) {
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if (isa<UndefValue>(C))
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; // Undef values remain undefined.
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else if (ConstantStruct *CS = dyn_cast<ConstantStruct>(C))
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LV.markConstant(CS->getOperand(i)); // Constants are constant.
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else if (isa<ConstantAggregateZero>(C)) {
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const Type *FieldTy = cast<StructType>(V->getType())->getElementType(i);
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LV.markConstant(Constant::getNullValue(FieldTy));
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LV.markOverdefined(); // Unknown sort of constant.
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// All others are underdefined by default.
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/// markEdgeExecutable - Mark a basic block as executable, adding it to the BB
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/// work list if it is not already executable.
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void markEdgeExecutable(BasicBlock *Source, BasicBlock *Dest) {
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if (!KnownFeasibleEdges.insert(Edge(Source, Dest)).second)
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return; // This edge is already known to be executable!
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if (!MarkBlockExecutable(Dest)) {
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// If the destination is already executable, we just made an *edge*
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// feasible that wasn't before. Revisit the PHI nodes in the block
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// because they have potentially new operands.
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DEBUG(dbgs() << "Marking Edge Executable: " << Source->getName()
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<< " -> " << Dest->getName() << "\n");
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for (BasicBlock::iterator I = Dest->begin();
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(PN = dyn_cast<PHINode>(I)); ++I)
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// getFeasibleSuccessors - Return a vector of booleans to indicate which
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// successors are reachable from a given terminator instruction.
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void getFeasibleSuccessors(TerminatorInst &TI, SmallVector<bool, 16> &Succs);
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// isEdgeFeasible - Return true if the control flow edge from the 'From' basic
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// block to the 'To' basic block is currently feasible.
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bool isEdgeFeasible(BasicBlock *From, BasicBlock *To);
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// OperandChangedState - This method is invoked on all of the users of an
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// instruction that was just changed state somehow. Based on this
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// information, we need to update the specified user of this instruction.
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void OperandChangedState(Instruction *I) {
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if (BBExecutable.count(I->getParent())) // Inst is executable?
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/// RemoveFromOverdefinedPHIs - If I has any entries in the
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/// UsersOfOverdefinedPHIs map for PN, remove them now.
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void RemoveFromOverdefinedPHIs(Instruction *I, PHINode *PN) {
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if (UsersOfOverdefinedPHIs.empty()) return;
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std::multimap<PHINode*, Instruction*>::iterator It, E;
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tie(It, E) = UsersOfOverdefinedPHIs.equal_range(PN);
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UsersOfOverdefinedPHIs.erase(It++);
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friend class InstVisitor<SCCPSolver>;
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// visit implementations - Something changed in this instruction. Either an
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// operand made a transition, or the instruction is newly executable. Change
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// the value type of I to reflect these changes if appropriate.
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void visitPHINode(PHINode &I);
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void visitReturnInst(ReturnInst &I);
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void visitTerminatorInst(TerminatorInst &TI);
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void visitCastInst(CastInst &I);
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void visitSelectInst(SelectInst &I);
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void visitBinaryOperator(Instruction &I);
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void visitCmpInst(CmpInst &I);
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void visitExtractElementInst(ExtractElementInst &I);
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void visitInsertElementInst(InsertElementInst &I);
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void visitShuffleVectorInst(ShuffleVectorInst &I);
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void visitExtractValueInst(ExtractValueInst &EVI);
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void visitInsertValueInst(InsertValueInst &IVI);
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// Instructions that cannot be folded away.
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void visitStoreInst (StoreInst &I);
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void visitLoadInst (LoadInst &I);
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void visitGetElementPtrInst(GetElementPtrInst &I);
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void visitCallInst (CallInst &I) {
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visitCallSite(CallSite::get(&I));
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void visitInvokeInst (InvokeInst &II) {
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visitCallSite(CallSite::get(&II));
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visitTerminatorInst(II);
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void visitCallSite (CallSite CS);
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void visitUnwindInst (TerminatorInst &I) { /*returns void*/ }
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void visitUnreachableInst(TerminatorInst &I) { /*returns void*/ }
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void visitAllocaInst (Instruction &I) { markOverdefined(&I); }
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void visitVANextInst (Instruction &I) { markOverdefined(&I); }
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void visitVAArgInst (Instruction &I) { markAnythingOverdefined(&I); }
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void visitInstruction(Instruction &I) {
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// If a new instruction is added to LLVM that we don't handle.
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dbgs() << "SCCP: Don't know how to handle: " << I;
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markAnythingOverdefined(&I); // Just in case
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} // end anonymous namespace
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// getFeasibleSuccessors - Return a vector of booleans to indicate which
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// successors are reachable from a given terminator instruction.
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void SCCPSolver::getFeasibleSuccessors(TerminatorInst &TI,
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SmallVector<bool, 16> &Succs) {
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Succs.resize(TI.getNumSuccessors());
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if (BranchInst *BI = dyn_cast<BranchInst>(&TI)) {
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if (BI->isUnconditional()) {
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LatticeVal BCValue = getValueState(BI->getCondition());
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ConstantInt *CI = BCValue.getConstantInt();
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// Overdefined condition variables, and branches on unfoldable constant
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// conditions, mean the branch could go either way.
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if (!BCValue.isUndefined())
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Succs[0] = Succs[1] = true;
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// Constant condition variables mean the branch can only go a single way.
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Succs[CI->isZero()] = true;
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if (isa<InvokeInst>(TI)) {
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// Invoke instructions successors are always executable.
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Succs[0] = Succs[1] = true;
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if (SwitchInst *SI = dyn_cast<SwitchInst>(&TI)) {
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LatticeVal SCValue = getValueState(SI->getCondition());
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ConstantInt *CI = SCValue.getConstantInt();
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if (CI == 0) { // Overdefined or undefined condition?
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// All destinations are executable!
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if (!SCValue.isUndefined())
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Succs.assign(TI.getNumSuccessors(), true);
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Succs[SI->findCaseValue(CI)] = true;
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// TODO: This could be improved if the operand is a [cast of a] BlockAddress.
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if (isa<IndirectBrInst>(&TI)) {
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// Just mark all destinations executable!
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Succs.assign(TI.getNumSuccessors(), true);
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dbgs() << "Unknown terminator instruction: " << TI << '\n';
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llvm_unreachable("SCCP: Don't know how to handle this terminator!");
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// isEdgeFeasible - Return true if the control flow edge from the 'From' basic
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// block to the 'To' basic block is currently feasible.
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bool SCCPSolver::isEdgeFeasible(BasicBlock *From, BasicBlock *To) {
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assert(BBExecutable.count(To) && "Dest should always be alive!");
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// Make sure the source basic block is executable!!
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if (!BBExecutable.count(From)) return false;
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// Check to make sure this edge itself is actually feasible now.
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TerminatorInst *TI = From->getTerminator();
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if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
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if (BI->isUnconditional())
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LatticeVal BCValue = getValueState(BI->getCondition());
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// Overdefined condition variables mean the branch could go either way,
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// undef conditions mean that neither edge is feasible yet.
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ConstantInt *CI = BCValue.getConstantInt();
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return !BCValue.isUndefined();
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// Constant condition variables mean the branch can only go a single way.
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return BI->getSuccessor(CI->isZero()) == To;
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// Invoke instructions successors are always executable.
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if (isa<InvokeInst>(TI))
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if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
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LatticeVal SCValue = getValueState(SI->getCondition());
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ConstantInt *CI = SCValue.getConstantInt();
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return !SCValue.isUndefined();
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// Make sure to skip the "default value" which isn't a value
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for (unsigned i = 1, E = SI->getNumSuccessors(); i != E; ++i)
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if (SI->getSuccessorValue(i) == CI) // Found the taken branch.
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return SI->getSuccessor(i) == To;
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// If the constant value is not equal to any of the branches, we must
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// execute default branch.
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return SI->getDefaultDest() == To;
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// Just mark all destinations executable!
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// TODO: This could be improved if the operand is a [cast of a] BlockAddress.
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if (isa<IndirectBrInst>(&TI))
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dbgs() << "Unknown terminator instruction: " << *TI << '\n';
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// visit Implementations - Something changed in this instruction, either an
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// operand made a transition, or the instruction is newly executable. Change
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// the value type of I to reflect these changes if appropriate. This method
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// makes sure to do the following actions:
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// 1. If a phi node merges two constants in, and has conflicting value coming
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// from different branches, or if the PHI node merges in an overdefined
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// value, then the PHI node becomes overdefined.
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// 2. If a phi node merges only constants in, and they all agree on value, the
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// PHI node becomes a constant value equal to that.
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// 3. If V <- x (op) y && isConstant(x) && isConstant(y) V = Constant
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// 4. If V <- x (op) y && (isOverdefined(x) || isOverdefined(y)) V = Overdefined
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// 5. If V <- MEM or V <- CALL or V <- (unknown) then V = Overdefined
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// 6. If a conditional branch has a value that is constant, make the selected
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// destination executable
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// 7. If a conditional branch has a value that is overdefined, make all
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// successors executable.
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void SCCPSolver::visitPHINode(PHINode &PN) {
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// If this PN returns a struct, just mark the result overdefined.
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// TODO: We could do a lot better than this if code actually uses this.
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if (PN.getType()->isStructTy())
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return markAnythingOverdefined(&PN);
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if (getValueState(&PN).isOverdefined()) {
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// There may be instructions using this PHI node that are not overdefined
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// themselves. If so, make sure that they know that the PHI node operand
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std::multimap<PHINode*, Instruction*>::iterator I, E;
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tie(I, E) = UsersOfOverdefinedPHIs.equal_range(&PN);
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SmallVector<Instruction*, 16> Users;
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Users.push_back(I->second);
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while (!Users.empty())
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visit(Users.pop_back_val());
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return; // Quick exit
689
// Super-extra-high-degree PHI nodes are unlikely to ever be marked constant,
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// and slow us down a lot. Just mark them overdefined.
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if (PN.getNumIncomingValues() > 64)
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return markOverdefined(&PN);
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// Look at all of the executable operands of the PHI node. If any of them
695
// are overdefined, the PHI becomes overdefined as well. If they are all
696
// constant, and they agree with each other, the PHI becomes the identical
697
// constant. If they are constant and don't agree, the PHI is overdefined.
698
// If there are no executable operands, the PHI remains undefined.
700
Constant *OperandVal = 0;
701
for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i) {
702
LatticeVal IV = getValueState(PN.getIncomingValue(i));
703
if (IV.isUndefined()) continue; // Doesn't influence PHI node.
705
if (!isEdgeFeasible(PN.getIncomingBlock(i), PN.getParent()))
708
if (IV.isOverdefined()) // PHI node becomes overdefined!
709
return markOverdefined(&PN);
711
if (OperandVal == 0) { // Grab the first value.
712
OperandVal = IV.getConstant();
716
// There is already a reachable operand. If we conflict with it,
717
// then the PHI node becomes overdefined. If we agree with it, we
720
// Check to see if there are two different constants merging, if so, the PHI
721
// node is overdefined.
722
if (IV.getConstant() != OperandVal)
723
return markOverdefined(&PN);
726
// If we exited the loop, this means that the PHI node only has constant
727
// arguments that agree with each other(and OperandVal is the constant) or
728
// OperandVal is null because there are no defined incoming arguments. If
729
// this is the case, the PHI remains undefined.
732
markConstant(&PN, OperandVal); // Acquire operand value
738
void SCCPSolver::visitReturnInst(ReturnInst &I) {
739
if (I.getNumOperands() == 0) return; // ret void
741
Function *F = I.getParent()->getParent();
742
Value *ResultOp = I.getOperand(0);
744
// If we are tracking the return value of this function, merge it in.
745
if (!TrackedRetVals.empty() && !ResultOp->getType()->isStructTy()) {
746
DenseMap<Function*, LatticeVal>::iterator TFRVI =
747
TrackedRetVals.find(F);
748
if (TFRVI != TrackedRetVals.end()) {
749
mergeInValue(TFRVI->second, F, getValueState(ResultOp));
754
// Handle functions that return multiple values.
755
if (!TrackedMultipleRetVals.empty()) {
756
if (const StructType *STy = dyn_cast<StructType>(ResultOp->getType()))
757
if (MRVFunctionsTracked.count(F))
758
for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i)
759
mergeInValue(TrackedMultipleRetVals[std::make_pair(F, i)], F,
760
getStructValueState(ResultOp, i));
765
void SCCPSolver::visitTerminatorInst(TerminatorInst &TI) {
766
SmallVector<bool, 16> SuccFeasible;
767
getFeasibleSuccessors(TI, SuccFeasible);
769
BasicBlock *BB = TI.getParent();
771
// Mark all feasible successors executable.
772
for (unsigned i = 0, e = SuccFeasible.size(); i != e; ++i)
774
markEdgeExecutable(BB, TI.getSuccessor(i));
777
void SCCPSolver::visitCastInst(CastInst &I) {
778
LatticeVal OpSt = getValueState(I.getOperand(0));
779
if (OpSt.isOverdefined()) // Inherit overdefinedness of operand
781
else if (OpSt.isConstant()) // Propagate constant value
782
markConstant(&I, ConstantExpr::getCast(I.getOpcode(),
783
OpSt.getConstant(), I.getType()));
787
void SCCPSolver::visitExtractValueInst(ExtractValueInst &EVI) {
788
// If this returns a struct, mark all elements over defined, we don't track
789
// structs in structs.
790
if (EVI.getType()->isStructTy())
791
return markAnythingOverdefined(&EVI);
793
// If this is extracting from more than one level of struct, we don't know.
794
if (EVI.getNumIndices() != 1)
795
return markOverdefined(&EVI);
797
Value *AggVal = EVI.getAggregateOperand();
798
if (AggVal->getType()->isStructTy()) {
799
unsigned i = *EVI.idx_begin();
800
LatticeVal EltVal = getStructValueState(AggVal, i);
801
mergeInValue(getValueState(&EVI), &EVI, EltVal);
803
// Otherwise, must be extracting from an array.
804
return markOverdefined(&EVI);
808
void SCCPSolver::visitInsertValueInst(InsertValueInst &IVI) {
809
const StructType *STy = dyn_cast<StructType>(IVI.getType());
811
return markOverdefined(&IVI);
813
// If this has more than one index, we can't handle it, drive all results to
815
if (IVI.getNumIndices() != 1)
816
return markAnythingOverdefined(&IVI);
818
Value *Aggr = IVI.getAggregateOperand();
819
unsigned Idx = *IVI.idx_begin();
821
// Compute the result based on what we're inserting.
822
for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
823
// This passes through all values that aren't the inserted element.
825
LatticeVal EltVal = getStructValueState(Aggr, i);
826
mergeInValue(getStructValueState(&IVI, i), &IVI, EltVal);
830
Value *Val = IVI.getInsertedValueOperand();
831
if (Val->getType()->isStructTy())
832
// We don't track structs in structs.
833
markOverdefined(getStructValueState(&IVI, i), &IVI);
835
LatticeVal InVal = getValueState(Val);
836
mergeInValue(getStructValueState(&IVI, i), &IVI, InVal);
841
void SCCPSolver::visitSelectInst(SelectInst &I) {
842
// If this select returns a struct, just mark the result overdefined.
843
// TODO: We could do a lot better than this if code actually uses this.
844
if (I.getType()->isStructTy())
845
return markAnythingOverdefined(&I);
847
LatticeVal CondValue = getValueState(I.getCondition());
848
if (CondValue.isUndefined())
851
if (ConstantInt *CondCB = CondValue.getConstantInt()) {
852
Value *OpVal = CondCB->isZero() ? I.getFalseValue() : I.getTrueValue();
853
mergeInValue(&I, getValueState(OpVal));
857
// Otherwise, the condition is overdefined or a constant we can't evaluate.
858
// See if we can produce something better than overdefined based on the T/F
860
LatticeVal TVal = getValueState(I.getTrueValue());
861
LatticeVal FVal = getValueState(I.getFalseValue());
863
// select ?, C, C -> C.
864
if (TVal.isConstant() && FVal.isConstant() &&
865
TVal.getConstant() == FVal.getConstant())
866
return markConstant(&I, FVal.getConstant());
868
if (TVal.isUndefined()) // select ?, undef, X -> X.
869
return mergeInValue(&I, FVal);
870
if (FVal.isUndefined()) // select ?, X, undef -> X.
871
return mergeInValue(&I, TVal);
875
// Handle Binary Operators.
876
void SCCPSolver::visitBinaryOperator(Instruction &I) {
877
LatticeVal V1State = getValueState(I.getOperand(0));
878
LatticeVal V2State = getValueState(I.getOperand(1));
880
LatticeVal &IV = ValueState[&I];
881
if (IV.isOverdefined()) return;
883
if (V1State.isConstant() && V2State.isConstant())
884
return markConstant(IV, &I,
885
ConstantExpr::get(I.getOpcode(), V1State.getConstant(),
886
V2State.getConstant()));
888
// If something is undef, wait for it to resolve.
889
if (!V1State.isOverdefined() && !V2State.isOverdefined())
892
// Otherwise, one of our operands is overdefined. Try to produce something
893
// better than overdefined with some tricks.
895
// If this is an AND or OR with 0 or -1, it doesn't matter that the other
896
// operand is overdefined.
897
if (I.getOpcode() == Instruction::And || I.getOpcode() == Instruction::Or) {
898
LatticeVal *NonOverdefVal = 0;
899
if (!V1State.isOverdefined())
900
NonOverdefVal = &V1State;
901
else if (!V2State.isOverdefined())
902
NonOverdefVal = &V2State;
905
if (NonOverdefVal->isUndefined()) {
906
// Could annihilate value.
907
if (I.getOpcode() == Instruction::And)
908
markConstant(IV, &I, Constant::getNullValue(I.getType()));
909
else if (const VectorType *PT = dyn_cast<VectorType>(I.getType()))
910
markConstant(IV, &I, Constant::getAllOnesValue(PT));
913
Constant::getAllOnesValue(I.getType()));
917
if (I.getOpcode() == Instruction::And) {
919
if (NonOverdefVal->getConstant()->isNullValue())
920
return markConstant(IV, &I, NonOverdefVal->getConstant());
922
if (ConstantInt *CI = NonOverdefVal->getConstantInt())
923
if (CI->isAllOnesValue()) // X or -1 = -1
924
return markConstant(IV, &I, NonOverdefVal->getConstant());
930
// If both operands are PHI nodes, it is possible that this instruction has
931
// a constant value, despite the fact that the PHI node doesn't. Check for
932
// this condition now.
933
if (PHINode *PN1 = dyn_cast<PHINode>(I.getOperand(0)))
934
if (PHINode *PN2 = dyn_cast<PHINode>(I.getOperand(1)))
935
if (PN1->getParent() == PN2->getParent()) {
936
// Since the two PHI nodes are in the same basic block, they must have
937
// entries for the same predecessors. Walk the predecessor list, and
938
// if all of the incoming values are constants, and the result of
939
// evaluating this expression with all incoming value pairs is the
940
// same, then this expression is a constant even though the PHI node
941
// is not a constant!
943
for (unsigned i = 0, e = PN1->getNumIncomingValues(); i != e; ++i) {
944
LatticeVal In1 = getValueState(PN1->getIncomingValue(i));
945
BasicBlock *InBlock = PN1->getIncomingBlock(i);
946
LatticeVal In2 =getValueState(PN2->getIncomingValueForBlock(InBlock));
948
if (In1.isOverdefined() || In2.isOverdefined()) {
949
Result.markOverdefined();
950
break; // Cannot fold this operation over the PHI nodes!
953
if (In1.isConstant() && In2.isConstant()) {
954
Constant *V = ConstantExpr::get(I.getOpcode(), In1.getConstant(),
956
if (Result.isUndefined())
957
Result.markConstant(V);
958
else if (Result.isConstant() && Result.getConstant() != V) {
959
Result.markOverdefined();
965
// If we found a constant value here, then we know the instruction is
966
// constant despite the fact that the PHI nodes are overdefined.
967
if (Result.isConstant()) {
968
markConstant(IV, &I, Result.getConstant());
969
// Remember that this instruction is virtually using the PHI node
971
UsersOfOverdefinedPHIs.insert(std::make_pair(PN1, &I));
972
UsersOfOverdefinedPHIs.insert(std::make_pair(PN2, &I));
976
if (Result.isUndefined())
979
// Okay, this really is overdefined now. Since we might have
980
// speculatively thought that this was not overdefined before, and
981
// added ourselves to the UsersOfOverdefinedPHIs list for the PHIs,
982
// make sure to clean out any entries that we put there, for
984
RemoveFromOverdefinedPHIs(&I, PN1);
985
RemoveFromOverdefinedPHIs(&I, PN2);
991
// Handle ICmpInst instruction.
992
void SCCPSolver::visitCmpInst(CmpInst &I) {
993
LatticeVal V1State = getValueState(I.getOperand(0));
994
LatticeVal V2State = getValueState(I.getOperand(1));
996
LatticeVal &IV = ValueState[&I];
997
if (IV.isOverdefined()) return;
999
if (V1State.isConstant() && V2State.isConstant())
1000
return markConstant(IV, &I, ConstantExpr::getCompare(I.getPredicate(),
1001
V1State.getConstant(),
1002
V2State.getConstant()));
1004
// If operands are still undefined, wait for it to resolve.
1005
if (!V1State.isOverdefined() && !V2State.isOverdefined())
1008
// If something is overdefined, use some tricks to avoid ending up and over
1009
// defined if we can.
1011
// If both operands are PHI nodes, it is possible that this instruction has
1012
// a constant value, despite the fact that the PHI node doesn't. Check for
1013
// this condition now.
1014
if (PHINode *PN1 = dyn_cast<PHINode>(I.getOperand(0)))
1015
if (PHINode *PN2 = dyn_cast<PHINode>(I.getOperand(1)))
1016
if (PN1->getParent() == PN2->getParent()) {
1017
// Since the two PHI nodes are in the same basic block, they must have
1018
// entries for the same predecessors. Walk the predecessor list, and
1019
// if all of the incoming values are constants, and the result of
1020
// evaluating this expression with all incoming value pairs is the
1021
// same, then this expression is a constant even though the PHI node
1022
// is not a constant!
1024
for (unsigned i = 0, e = PN1->getNumIncomingValues(); i != e; ++i) {
1025
LatticeVal In1 = getValueState(PN1->getIncomingValue(i));
1026
BasicBlock *InBlock = PN1->getIncomingBlock(i);
1027
LatticeVal In2 =getValueState(PN2->getIncomingValueForBlock(InBlock));
1029
if (In1.isOverdefined() || In2.isOverdefined()) {
1030
Result.markOverdefined();
1031
break; // Cannot fold this operation over the PHI nodes!
1034
if (In1.isConstant() && In2.isConstant()) {
1035
Constant *V = ConstantExpr::getCompare(I.getPredicate(),
1038
if (Result.isUndefined())
1039
Result.markConstant(V);
1040
else if (Result.isConstant() && Result.getConstant() != V) {
1041
Result.markOverdefined();
1047
// If we found a constant value here, then we know the instruction is
1048
// constant despite the fact that the PHI nodes are overdefined.
1049
if (Result.isConstant()) {
1050
markConstant(&I, Result.getConstant());
1051
// Remember that this instruction is virtually using the PHI node
1053
UsersOfOverdefinedPHIs.insert(std::make_pair(PN1, &I));
1054
UsersOfOverdefinedPHIs.insert(std::make_pair(PN2, &I));
1058
if (Result.isUndefined())
1061
// Okay, this really is overdefined now. Since we might have
1062
// speculatively thought that this was not overdefined before, and
1063
// added ourselves to the UsersOfOverdefinedPHIs list for the PHIs,
1064
// make sure to clean out any entries that we put there, for
1066
RemoveFromOverdefinedPHIs(&I, PN1);
1067
RemoveFromOverdefinedPHIs(&I, PN2);
1070
markOverdefined(&I);
1073
void SCCPSolver::visitExtractElementInst(ExtractElementInst &I) {
1074
// TODO : SCCP does not handle vectors properly.
1075
return markOverdefined(&I);
1078
LatticeVal &ValState = getValueState(I.getOperand(0));
1079
LatticeVal &IdxState = getValueState(I.getOperand(1));
1081
if (ValState.isOverdefined() || IdxState.isOverdefined())
1082
markOverdefined(&I);
1083
else if(ValState.isConstant() && IdxState.isConstant())
1084
markConstant(&I, ConstantExpr::getExtractElement(ValState.getConstant(),
1085
IdxState.getConstant()));
1089
void SCCPSolver::visitInsertElementInst(InsertElementInst &I) {
1090
// TODO : SCCP does not handle vectors properly.
1091
return markOverdefined(&I);
1093
LatticeVal &ValState = getValueState(I.getOperand(0));
1094
LatticeVal &EltState = getValueState(I.getOperand(1));
1095
LatticeVal &IdxState = getValueState(I.getOperand(2));
1097
if (ValState.isOverdefined() || EltState.isOverdefined() ||
1098
IdxState.isOverdefined())
1099
markOverdefined(&I);
1100
else if(ValState.isConstant() && EltState.isConstant() &&
1101
IdxState.isConstant())
1102
markConstant(&I, ConstantExpr::getInsertElement(ValState.getConstant(),
1103
EltState.getConstant(),
1104
IdxState.getConstant()));
1105
else if (ValState.isUndefined() && EltState.isConstant() &&
1106
IdxState.isConstant())
1107
markConstant(&I,ConstantExpr::getInsertElement(UndefValue::get(I.getType()),
1108
EltState.getConstant(),
1109
IdxState.getConstant()));
1113
void SCCPSolver::visitShuffleVectorInst(ShuffleVectorInst &I) {
1114
// TODO : SCCP does not handle vectors properly.
1115
return markOverdefined(&I);
1117
LatticeVal &V1State = getValueState(I.getOperand(0));
1118
LatticeVal &V2State = getValueState(I.getOperand(1));
1119
LatticeVal &MaskState = getValueState(I.getOperand(2));
1121
if (MaskState.isUndefined() ||
1122
(V1State.isUndefined() && V2State.isUndefined()))
1123
return; // Undefined output if mask or both inputs undefined.
1125
if (V1State.isOverdefined() || V2State.isOverdefined() ||
1126
MaskState.isOverdefined()) {
1127
markOverdefined(&I);
1129
// A mix of constant/undef inputs.
1130
Constant *V1 = V1State.isConstant() ?
1131
V1State.getConstant() : UndefValue::get(I.getType());
1132
Constant *V2 = V2State.isConstant() ?
1133
V2State.getConstant() : UndefValue::get(I.getType());
1134
Constant *Mask = MaskState.isConstant() ?
1135
MaskState.getConstant() : UndefValue::get(I.getOperand(2)->getType());
1136
markConstant(&I, ConstantExpr::getShuffleVector(V1, V2, Mask));
1141
// Handle getelementptr instructions. If all operands are constants then we
1142
// can turn this into a getelementptr ConstantExpr.
1144
void SCCPSolver::visitGetElementPtrInst(GetElementPtrInst &I) {
1145
if (ValueState[&I].isOverdefined()) return;
1147
SmallVector<Constant*, 8> Operands;
1148
Operands.reserve(I.getNumOperands());
1150
for (unsigned i = 0, e = I.getNumOperands(); i != e; ++i) {
1151
LatticeVal State = getValueState(I.getOperand(i));
1152
if (State.isUndefined())
1153
return; // Operands are not resolved yet.
1155
if (State.isOverdefined())
1156
return markOverdefined(&I);
1158
assert(State.isConstant() && "Unknown state!");
1159
Operands.push_back(State.getConstant());
1162
Constant *Ptr = Operands[0];
1163
markConstant(&I, ConstantExpr::getGetElementPtr(Ptr, &Operands[0]+1,
1164
Operands.size()-1));
1167
void SCCPSolver::visitStoreInst(StoreInst &SI) {
1168
// If this store is of a struct, ignore it.
1169
if (SI.getOperand(0)->getType()->isStructTy())
1172
if (TrackedGlobals.empty() || !isa<GlobalVariable>(SI.getOperand(1)))
1175
GlobalVariable *GV = cast<GlobalVariable>(SI.getOperand(1));
1176
DenseMap<GlobalVariable*, LatticeVal>::iterator I = TrackedGlobals.find(GV);
1177
if (I == TrackedGlobals.end() || I->second.isOverdefined()) return;
1179
// Get the value we are storing into the global, then merge it.
1180
mergeInValue(I->second, GV, getValueState(SI.getOperand(0)));
1181
if (I->second.isOverdefined())
1182
TrackedGlobals.erase(I); // No need to keep tracking this!
1186
// Handle load instructions. If the operand is a constant pointer to a constant
1187
// global, we can replace the load with the loaded constant value!
1188
void SCCPSolver::visitLoadInst(LoadInst &I) {
1189
// If this load is of a struct, just mark the result overdefined.
1190
if (I.getType()->isStructTy())
1191
return markAnythingOverdefined(&I);
1193
LatticeVal PtrVal = getValueState(I.getOperand(0));
1194
if (PtrVal.isUndefined()) return; // The pointer is not resolved yet!
1196
LatticeVal &IV = ValueState[&I];
1197
if (IV.isOverdefined()) return;
1199
if (!PtrVal.isConstant() || I.isVolatile())
1200
return markOverdefined(IV, &I);
1202
Constant *Ptr = PtrVal.getConstant();
1204
// load null -> null
1205
if (isa<ConstantPointerNull>(Ptr) && I.getPointerAddressSpace() == 0)
1206
return markConstant(IV, &I, Constant::getNullValue(I.getType()));
1208
// Transform load (constant global) into the value loaded.
1209
if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Ptr)) {
1210
if (!TrackedGlobals.empty()) {
1211
// If we are tracking this global, merge in the known value for it.
1212
DenseMap<GlobalVariable*, LatticeVal>::iterator It =
1213
TrackedGlobals.find(GV);
1214
if (It != TrackedGlobals.end()) {
1215
mergeInValue(IV, &I, It->second);
1221
// Transform load from a constant into a constant if possible.
1222
if (Constant *C = ConstantFoldLoadFromConstPtr(Ptr, TD))
1223
return markConstant(IV, &I, C);
1225
// Otherwise we cannot say for certain what value this load will produce.
1227
markOverdefined(IV, &I);
1230
void SCCPSolver::visitCallSite(CallSite CS) {
1231
Function *F = CS.getCalledFunction();
1232
Instruction *I = CS.getInstruction();
1234
// The common case is that we aren't tracking the callee, either because we
1235
// are not doing interprocedural analysis or the callee is indirect, or is
1236
// external. Handle these cases first.
1237
if (F == 0 || F->isDeclaration()) {
1239
// Void return and not tracking callee, just bail.
1240
if (I->getType()->isVoidTy()) return;
1242
// Otherwise, if we have a single return value case, and if the function is
1243
// a declaration, maybe we can constant fold it.
1244
if (F && F->isDeclaration() && !I->getType()->isStructTy() &&
1245
canConstantFoldCallTo(F)) {
1247
SmallVector<Constant*, 8> Operands;
1248
for (CallSite::arg_iterator AI = CS.arg_begin(), E = CS.arg_end();
1250
LatticeVal State = getValueState(*AI);
1252
if (State.isUndefined())
1253
return; // Operands are not resolved yet.
1254
if (State.isOverdefined())
1255
return markOverdefined(I);
1256
assert(State.isConstant() && "Unknown state!");
1257
Operands.push_back(State.getConstant());
1260
// If we can constant fold this, mark the result of the call as a
1262
if (Constant *C = ConstantFoldCall(F, Operands.data(), Operands.size()))
1263
return markConstant(I, C);
1266
// Otherwise, we don't know anything about this call, mark it overdefined.
1267
return markAnythingOverdefined(I);
1270
// If this is a local function that doesn't have its address taken, mark its
1271
// entry block executable and merge in the actual arguments to the call into
1272
// the formal arguments of the function.
1273
if (!TrackingIncomingArguments.empty() && TrackingIncomingArguments.count(F)){
1274
MarkBlockExecutable(F->begin());
1276
// Propagate information from this call site into the callee.
1277
CallSite::arg_iterator CAI = CS.arg_begin();
1278
for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end();
1279
AI != E; ++AI, ++CAI) {
1280
// If this argument is byval, and if the function is not readonly, there
1281
// will be an implicit copy formed of the input aggregate.
1282
if (AI->hasByValAttr() && !F->onlyReadsMemory()) {
1283
markOverdefined(AI);
1287
if (const StructType *STy = dyn_cast<StructType>(AI->getType())) {
1288
for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
1289
LatticeVal CallArg = getStructValueState(*CAI, i);
1290
mergeInValue(getStructValueState(AI, i), AI, CallArg);
1293
mergeInValue(AI, getValueState(*CAI));
1298
// If this is a single/zero retval case, see if we're tracking the function.
1299
if (const StructType *STy = dyn_cast<StructType>(F->getReturnType())) {
1300
if (!MRVFunctionsTracked.count(F))
1301
goto CallOverdefined; // Not tracking this callee.
1303
// If we are tracking this callee, propagate the result of the function
1304
// into this call site.
1305
for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i)
1306
mergeInValue(getStructValueState(I, i), I,
1307
TrackedMultipleRetVals[std::make_pair(F, i)]);
1309
DenseMap<Function*, LatticeVal>::iterator TFRVI = TrackedRetVals.find(F);
1310
if (TFRVI == TrackedRetVals.end())
1311
goto CallOverdefined; // Not tracking this callee.
1313
// If so, propagate the return value of the callee into this call result.
1314
mergeInValue(I, TFRVI->second);
1318
void SCCPSolver::Solve() {
1319
// Process the work lists until they are empty!
1320
while (!BBWorkList.empty() || !InstWorkList.empty() ||
1321
!OverdefinedInstWorkList.empty()) {
1322
// Process the overdefined instruction's work list first, which drives other
1323
// things to overdefined more quickly.
1324
while (!OverdefinedInstWorkList.empty()) {
1325
Value *I = OverdefinedInstWorkList.pop_back_val();
1327
DEBUG(dbgs() << "\nPopped off OI-WL: " << *I << '\n');
1329
// "I" got into the work list because it either made the transition from
1330
// bottom to constant
1332
// Anything on this worklist that is overdefined need not be visited
1333
// since all of its users will have already been marked as overdefined
1334
// Update all of the users of this instruction's value.
1336
for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
1338
if (Instruction *I = dyn_cast<Instruction>(*UI))
1339
OperandChangedState(I);
1342
// Process the instruction work list.
1343
while (!InstWorkList.empty()) {
1344
Value *I = InstWorkList.pop_back_val();
1346
DEBUG(dbgs() << "\nPopped off I-WL: " << *I << '\n');
1348
// "I" got into the work list because it made the transition from undef to
1351
// Anything on this worklist that is overdefined need not be visited
1352
// since all of its users will have already been marked as overdefined.
1353
// Update all of the users of this instruction's value.
1355
if (I->getType()->isStructTy() || !getValueState(I).isOverdefined())
1356
for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
1358
if (Instruction *I = dyn_cast<Instruction>(*UI))
1359
OperandChangedState(I);
1362
// Process the basic block work list.
1363
while (!BBWorkList.empty()) {
1364
BasicBlock *BB = BBWorkList.back();
1365
BBWorkList.pop_back();
1367
DEBUG(dbgs() << "\nPopped off BBWL: " << *BB << '\n');
1369
// Notify all instructions in this basic block that they are newly
1376
/// ResolvedUndefsIn - While solving the dataflow for a function, we assume
1377
/// that branches on undef values cannot reach any of their successors.
1378
/// However, this is not a safe assumption. After we solve dataflow, this
1379
/// method should be use to handle this. If this returns true, the solver
1380
/// should be rerun.
1382
/// This method handles this by finding an unresolved branch and marking it one
1383
/// of the edges from the block as being feasible, even though the condition
1384
/// doesn't say it would otherwise be. This allows SCCP to find the rest of the
1385
/// CFG and only slightly pessimizes the analysis results (by marking one,
1386
/// potentially infeasible, edge feasible). This cannot usefully modify the
1387
/// constraints on the condition of the branch, as that would impact other users
1390
/// This scan also checks for values that use undefs, whose results are actually
1391
/// defined. For example, 'zext i8 undef to i32' should produce all zeros
1392
/// conservatively, as "(zext i8 X -> i32) & 0xFF00" must always return zero,
1393
/// even if X isn't defined.
1394
bool SCCPSolver::ResolvedUndefsIn(Function &F) {
1395
for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
1396
if (!BBExecutable.count(BB))
1399
for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
1400
// Look for instructions which produce undef values.
1401
if (I->getType()->isVoidTy()) continue;
1403
if (const StructType *STy = dyn_cast<StructType>(I->getType())) {
1404
// Only a few things that can be structs matter for undef. Just send
1405
// all their results to overdefined. We could be more precise than this
1406
// but it isn't worth bothering.
1407
if (isa<CallInst>(I) || isa<SelectInst>(I)) {
1408
for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
1409
LatticeVal &LV = getStructValueState(I, i);
1410
if (LV.isUndefined())
1411
markOverdefined(LV, I);
1417
LatticeVal &LV = getValueState(I);
1418
if (!LV.isUndefined()) continue;
1420
// No instructions using structs need disambiguation.
1421
if (I->getOperand(0)->getType()->isStructTy())
1424
// Get the lattice values of the first two operands for use below.
1425
LatticeVal Op0LV = getValueState(I->getOperand(0));
1427
if (I->getNumOperands() == 2) {
1428
// No instructions using structs need disambiguation.
1429
if (I->getOperand(1)->getType()->isStructTy())
1432
// If this is a two-operand instruction, and if both operands are
1433
// undefs, the result stays undef.
1434
Op1LV = getValueState(I->getOperand(1));
1435
if (Op0LV.isUndefined() && Op1LV.isUndefined())
1439
// If this is an instructions whose result is defined even if the input is
1440
// not fully defined, propagate the information.
1441
const Type *ITy = I->getType();
1442
switch (I->getOpcode()) {
1443
default: break; // Leave the instruction as an undef.
1444
case Instruction::ZExt:
1445
// After a zero extend, we know the top part is zero. SExt doesn't have
1446
// to be handled here, because we don't know whether the top part is 1's
1448
markForcedConstant(I, Constant::getNullValue(ITy));
1450
case Instruction::Mul:
1451
case Instruction::And:
1452
// undef * X -> 0. X could be zero.
1453
// undef & X -> 0. X could be zero.
1454
markForcedConstant(I, Constant::getNullValue(ITy));
1457
case Instruction::Or:
1458
// undef | X -> -1. X could be -1.
1459
markForcedConstant(I, Constant::getAllOnesValue(ITy));
1462
case Instruction::SDiv:
1463
case Instruction::UDiv:
1464
case Instruction::SRem:
1465
case Instruction::URem:
1466
// X / undef -> undef. No change.
1467
// X % undef -> undef. No change.
1468
if (Op1LV.isUndefined()) break;
1470
// undef / X -> 0. X could be maxint.
1471
// undef % X -> 0. X could be 1.
1472
markForcedConstant(I, Constant::getNullValue(ITy));
1475
case Instruction::AShr:
1476
// undef >>s X -> undef. No change.
1477
if (Op0LV.isUndefined()) break;
1479
// X >>s undef -> X. X could be 0, X could have the high-bit known set.
1480
if (Op0LV.isConstant())
1481
markForcedConstant(I, Op0LV.getConstant());
1485
case Instruction::LShr:
1486
case Instruction::Shl:
1487
// undef >> X -> undef. No change.
1488
// undef << X -> undef. No change.
1489
if (Op0LV.isUndefined()) break;
1491
// X >> undef -> 0. X could be 0.
1492
// X << undef -> 0. X could be 0.
1493
markForcedConstant(I, Constant::getNullValue(ITy));
1495
case Instruction::Select:
1496
// undef ? X : Y -> X or Y. There could be commonality between X/Y.
1497
if (Op0LV.isUndefined()) {
1498
if (!Op1LV.isConstant()) // Pick the constant one if there is any.
1499
Op1LV = getValueState(I->getOperand(2));
1500
} else if (Op1LV.isUndefined()) {
1501
// c ? undef : undef -> undef. No change.
1502
Op1LV = getValueState(I->getOperand(2));
1503
if (Op1LV.isUndefined())
1505
// Otherwise, c ? undef : x -> x.
1507
// Leave Op1LV as Operand(1)'s LatticeValue.
1510
if (Op1LV.isConstant())
1511
markForcedConstant(I, Op1LV.getConstant());
1515
case Instruction::Call:
1516
// If a call has an undef result, it is because it is constant foldable
1517
// but one of the inputs was undef. Just force the result to
1524
TerminatorInst *TI = BB->getTerminator();
1525
if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
1526
if (!BI->isConditional()) continue;
1527
if (!getValueState(BI->getCondition()).isUndefined())
1529
} else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
1530
if (SI->getNumSuccessors() < 2) // no cases
1532
if (!getValueState(SI->getCondition()).isUndefined())
1538
// If the edge to the second successor isn't thought to be feasible yet,
1539
// mark it so now. We pick the second one so that this goes to some
1540
// enumerated value in a switch instead of going to the default destination.
1541
if (KnownFeasibleEdges.count(Edge(BB, TI->getSuccessor(1))))
1544
// Otherwise, it isn't already thought to be feasible. Mark it as such now
1545
// and return. This will make other blocks reachable, which will allow new
1546
// values to be discovered and existing ones to be moved in the lattice.
1547
markEdgeExecutable(BB, TI->getSuccessor(1));
1549
// This must be a conditional branch of switch on undef. At this point,
1550
// force the old terminator to branch to the first successor. This is
1551
// required because we are now influencing the dataflow of the function with
1552
// the assumption that this edge is taken. If we leave the branch condition
1553
// as undef, then further analysis could think the undef went another way
1554
// leading to an inconsistent set of conclusions.
1555
if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
1556
BI->setCondition(ConstantInt::getFalse(BI->getContext()));
1558
SwitchInst *SI = cast<SwitchInst>(TI);
1559
SI->setCondition(SI->getCaseValue(1));
1570
//===--------------------------------------------------------------------===//
1572
/// SCCP Class - This class uses the SCCPSolver to implement a per-function
1573
/// Sparse Conditional Constant Propagator.
1575
struct SCCP : public FunctionPass {
1576
static char ID; // Pass identification, replacement for typeid
1577
SCCP() : FunctionPass(&ID) {}
1579
// runOnFunction - Run the Sparse Conditional Constant Propagation
1580
// algorithm, and return true if the function was modified.
1582
bool runOnFunction(Function &F);
1584
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
1585
AU.setPreservesCFG();
1588
} // end anonymous namespace
1591
static RegisterPass<SCCP>
1592
X("sccp", "Sparse Conditional Constant Propagation");
1594
// createSCCPPass - This is the public interface to this file.
1595
FunctionPass *llvm::createSCCPPass() {
1599
static void DeleteInstructionInBlock(BasicBlock *BB) {
1600
DEBUG(dbgs() << " BasicBlock Dead:" << *BB);
1603
// Delete the instructions backwards, as it has a reduced likelihood of
1604
// having to update as many def-use and use-def chains.
1605
while (!isa<TerminatorInst>(BB->begin())) {
1606
Instruction *I = --BasicBlock::iterator(BB->getTerminator());
1608
if (!I->use_empty())
1609
I->replaceAllUsesWith(UndefValue::get(I->getType()));
1610
BB->getInstList().erase(I);
1615
// runOnFunction() - Run the Sparse Conditional Constant Propagation algorithm,
1616
// and return true if the function was modified.
1618
bool SCCP::runOnFunction(Function &F) {
1619
DEBUG(dbgs() << "SCCP on function '" << F.getName() << "'\n");
1620
SCCPSolver Solver(getAnalysisIfAvailable<TargetData>());
1622
// Mark the first block of the function as being executable.
1623
Solver.MarkBlockExecutable(F.begin());
1625
// Mark all arguments to the function as being overdefined.
1626
for (Function::arg_iterator AI = F.arg_begin(), E = F.arg_end(); AI != E;++AI)
1627
Solver.markAnythingOverdefined(AI);
1629
// Solve for constants.
1630
bool ResolvedUndefs = true;
1631
while (ResolvedUndefs) {
1633
DEBUG(dbgs() << "RESOLVING UNDEFs\n");
1634
ResolvedUndefs = Solver.ResolvedUndefsIn(F);
1637
bool MadeChanges = false;
1639
// If we decided that there are basic blocks that are dead in this function,
1640
// delete their contents now. Note that we cannot actually delete the blocks,
1641
// as we cannot modify the CFG of the function.
1643
for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
1644
if (!Solver.isBlockExecutable(BB)) {
1645
DeleteInstructionInBlock(BB);
1650
// Iterate over all of the instructions in a function, replacing them with
1651
// constants if we have found them to be of constant values.
1653
for (BasicBlock::iterator BI = BB->begin(), E = BB->end(); BI != E; ) {
1654
Instruction *Inst = BI++;
1655
if (Inst->getType()->isVoidTy() || isa<TerminatorInst>(Inst))
1658
// TODO: Reconstruct structs from their elements.
1659
if (Inst->getType()->isStructTy())
1662
LatticeVal IV = Solver.getLatticeValueFor(Inst);
1663
if (IV.isOverdefined())
1666
Constant *Const = IV.isConstant()
1667
? IV.getConstant() : UndefValue::get(Inst->getType());
1668
DEBUG(dbgs() << " Constant: " << *Const << " = " << *Inst);
1670
// Replaces all of the uses of a variable with uses of the constant.
1671
Inst->replaceAllUsesWith(Const);
1673
// Delete the instruction.
1674
Inst->eraseFromParent();
1676
// Hey, we just changed something!
1686
//===--------------------------------------------------------------------===//
1688
/// IPSCCP Class - This class implements interprocedural Sparse Conditional
1689
/// Constant Propagation.
1691
struct IPSCCP : public ModulePass {
1693
IPSCCP() : ModulePass(&ID) {}
1694
bool runOnModule(Module &M);
1696
} // end anonymous namespace
1698
char IPSCCP::ID = 0;
1699
static RegisterPass<IPSCCP>
1700
Y("ipsccp", "Interprocedural Sparse Conditional Constant Propagation");
1702
// createIPSCCPPass - This is the public interface to this file.
1703
ModulePass *llvm::createIPSCCPPass() {
1704
return new IPSCCP();
1708
static bool AddressIsTaken(GlobalValue *GV) {
1709
// Delete any dead constantexpr klingons.
1710
GV->removeDeadConstantUsers();
1712
for (Value::use_iterator UI = GV->use_begin(), E = GV->use_end();
1714
if (StoreInst *SI = dyn_cast<StoreInst>(*UI)) {
1715
if (SI->getOperand(0) == GV || SI->isVolatile())
1716
return true; // Storing addr of GV.
1717
} else if (isa<InvokeInst>(*UI) || isa<CallInst>(*UI)) {
1718
// Make sure we are calling the function, not passing the address.
1719
if (UI.getOperandNo() != 0)
1721
} else if (LoadInst *LI = dyn_cast<LoadInst>(*UI)) {
1722
if (LI->isVolatile())
1724
} else if (isa<BlockAddress>(*UI)) {
1725
// blockaddress doesn't take the address of the function, it takes addr
1733
bool IPSCCP::runOnModule(Module &M) {
1734
SCCPSolver Solver(getAnalysisIfAvailable<TargetData>());
1736
// Loop over all functions, marking arguments to those with their addresses
1737
// taken or that are external as overdefined.
1739
for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F) {
1740
if (F->isDeclaration())
1743
// If this is a strong or ODR definition of this function, then we can
1744
// propagate information about its result into callsites of it.
1745
if (!F->mayBeOverridden())
1746
Solver.AddTrackedFunction(F);
1748
// If this function only has direct calls that we can see, we can track its
1749
// arguments and return value aggressively, and can assume it is not called
1750
// unless we see evidence to the contrary.
1751
if (F->hasLocalLinkage() && !AddressIsTaken(F)) {
1752
Solver.AddArgumentTrackedFunction(F);
1756
// Assume the function is called.
1757
Solver.MarkBlockExecutable(F->begin());
1759
// Assume nothing about the incoming arguments.
1760
for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end();
1762
Solver.markAnythingOverdefined(AI);
1765
// Loop over global variables. We inform the solver about any internal global
1766
// variables that do not have their 'addresses taken'. If they don't have
1767
// their addresses taken, we can propagate constants through them.
1768
for (Module::global_iterator G = M.global_begin(), E = M.global_end();
1770
if (!G->isConstant() && G->hasLocalLinkage() && !AddressIsTaken(G))
1771
Solver.TrackValueOfGlobalVariable(G);
1773
// Solve for constants.
1774
bool ResolvedUndefs = true;
1775
while (ResolvedUndefs) {
1778
DEBUG(dbgs() << "RESOLVING UNDEFS\n");
1779
ResolvedUndefs = false;
1780
for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F)
1781
ResolvedUndefs |= Solver.ResolvedUndefsIn(*F);
1784
bool MadeChanges = false;
1786
// Iterate over all of the instructions in the module, replacing them with
1787
// constants if we have found them to be of constant values.
1789
SmallVector<BasicBlock*, 512> BlocksToErase;
1791
for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F) {
1792
if (Solver.isBlockExecutable(F->begin())) {
1793
for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end();
1795
if (AI->use_empty() || AI->getType()->isStructTy()) continue;
1797
// TODO: Could use getStructLatticeValueFor to find out if the entire
1798
// result is a constant and replace it entirely if so.
1800
LatticeVal IV = Solver.getLatticeValueFor(AI);
1801
if (IV.isOverdefined()) continue;
1803
Constant *CST = IV.isConstant() ?
1804
IV.getConstant() : UndefValue::get(AI->getType());
1805
DEBUG(dbgs() << "*** Arg " << *AI << " = " << *CST <<"\n");
1807
// Replaces all of the uses of a variable with uses of the
1809
AI->replaceAllUsesWith(CST);
1814
for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB) {
1815
if (!Solver.isBlockExecutable(BB)) {
1816
DeleteInstructionInBlock(BB);
1819
TerminatorInst *TI = BB->getTerminator();
1820
for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) {
1821
BasicBlock *Succ = TI->getSuccessor(i);
1822
if (!Succ->empty() && isa<PHINode>(Succ->begin()))
1823
TI->getSuccessor(i)->removePredecessor(BB);
1825
if (!TI->use_empty())
1826
TI->replaceAllUsesWith(UndefValue::get(TI->getType()));
1827
TI->eraseFromParent();
1829
if (&*BB != &F->front())
1830
BlocksToErase.push_back(BB);
1832
new UnreachableInst(M.getContext(), BB);
1836
for (BasicBlock::iterator BI = BB->begin(), E = BB->end(); BI != E; ) {
1837
Instruction *Inst = BI++;
1838
if (Inst->getType()->isVoidTy() || Inst->getType()->isStructTy())
1841
// TODO: Could use getStructLatticeValueFor to find out if the entire
1842
// result is a constant and replace it entirely if so.
1844
LatticeVal IV = Solver.getLatticeValueFor(Inst);
1845
if (IV.isOverdefined())
1848
Constant *Const = IV.isConstant()
1849
? IV.getConstant() : UndefValue::get(Inst->getType());
1850
DEBUG(dbgs() << " Constant: " << *Const << " = " << *Inst);
1852
// Replaces all of the uses of a variable with uses of the
1854
Inst->replaceAllUsesWith(Const);
1856
// Delete the instruction.
1857
if (!isa<CallInst>(Inst) && !isa<TerminatorInst>(Inst))
1858
Inst->eraseFromParent();
1860
// Hey, we just changed something!
1866
// Now that all instructions in the function are constant folded, erase dead
1867
// blocks, because we can now use ConstantFoldTerminator to get rid of
1869
for (unsigned i = 0, e = BlocksToErase.size(); i != e; ++i) {
1870
// If there are any PHI nodes in this successor, drop entries for BB now.
1871
BasicBlock *DeadBB = BlocksToErase[i];
1872
for (Value::use_iterator UI = DeadBB->use_begin(), UE = DeadBB->use_end();
1874
// Grab the user and then increment the iterator early, as the user
1875
// will be deleted. Step past all adjacent uses from the same user.
1876
Instruction *I = dyn_cast<Instruction>(*UI);
1877
do { ++UI; } while (UI != UE && *UI == I);
1879
// Ignore blockaddress users; BasicBlock's dtor will handle them.
1882
bool Folded = ConstantFoldTerminator(I->getParent());
1884
// The constant folder may not have been able to fold the terminator
1885
// if this is a branch or switch on undef. Fold it manually as a
1886
// branch to the first successor.
1888
if (BranchInst *BI = dyn_cast<BranchInst>(I)) {
1889
assert(BI->isConditional() && isa<UndefValue>(BI->getCondition()) &&
1890
"Branch should be foldable!");
1891
} else if (SwitchInst *SI = dyn_cast<SwitchInst>(I)) {
1892
assert(isa<UndefValue>(SI->getCondition()) && "Switch should fold");
1894
llvm_unreachable("Didn't fold away reference to block!");
1898
// Make this an uncond branch to the first successor.
1899
TerminatorInst *TI = I->getParent()->getTerminator();
1900
BranchInst::Create(TI->getSuccessor(0), TI);
1902
// Remove entries in successor phi nodes to remove edges.
1903
for (unsigned i = 1, e = TI->getNumSuccessors(); i != e; ++i)
1904
TI->getSuccessor(i)->removePredecessor(TI->getParent());
1906
// Remove the old terminator.
1907
TI->eraseFromParent();
1911
// Finally, delete the basic block.
1912
F->getBasicBlockList().erase(DeadBB);
1914
BlocksToErase.clear();
1917
// If we inferred constant or undef return values for a function, we replaced
1918
// all call uses with the inferred value. This means we don't need to bother
1919
// actually returning anything from the function. Replace all return
1920
// instructions with return undef.
1922
// Do this in two stages: first identify the functions we should process, then
1923
// actually zap their returns. This is important because we can only do this
1924
// if the address of the function isn't taken. In cases where a return is the
1925
// last use of a function, the order of processing functions would affect
1926
// whether other functions are optimizable.
1927
SmallVector<ReturnInst*, 8> ReturnsToZap;
1929
// TODO: Process multiple value ret instructions also.
1930
const DenseMap<Function*, LatticeVal> &RV = Solver.getTrackedRetVals();
1931
for (DenseMap<Function*, LatticeVal>::const_iterator I = RV.begin(),
1932
E = RV.end(); I != E; ++I) {
1933
Function *F = I->first;
1934
if (I->second.isOverdefined() || F->getReturnType()->isVoidTy())
1937
// We can only do this if we know that nothing else can call the function.
1938
if (!F->hasLocalLinkage() || AddressIsTaken(F))
1941
for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
1942
if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator()))
1943
if (!isa<UndefValue>(RI->getOperand(0)))
1944
ReturnsToZap.push_back(RI);
1947
// Zap all returns which we've identified as zap to change.
1948
for (unsigned i = 0, e = ReturnsToZap.size(); i != e; ++i) {
1949
Function *F = ReturnsToZap[i]->getParent()->getParent();
1950
ReturnsToZap[i]->setOperand(0, UndefValue::get(F->getReturnType()));
1953
// If we infered constant or undef values for globals variables, we can delete
1954
// the global and any stores that remain to it.
1955
const DenseMap<GlobalVariable*, LatticeVal> &TG = Solver.getTrackedGlobals();
1956
for (DenseMap<GlobalVariable*, LatticeVal>::const_iterator I = TG.begin(),
1957
E = TG.end(); I != E; ++I) {
1958
GlobalVariable *GV = I->first;
1959
assert(!I->second.isOverdefined() &&
1960
"Overdefined values should have been taken out of the map!");
1961
DEBUG(dbgs() << "Found that GV '" << GV->getName() << "' is constant!\n");
1962
while (!GV->use_empty()) {
1963
StoreInst *SI = cast<StoreInst>(GV->use_back());
1964
SI->eraseFromParent();
1966
M.getGlobalList().erase(GV);
added
removed
libclamav/c++/llvm/lib/Transforms/Scalar/SCCP.cpp
