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2011 lines
74 KiB
C++
2011 lines
74 KiB
C++
//===- SCCP.cpp - Sparse Conditional Constant Propagation -----------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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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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//===----------------------------------------------------------------------===//
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//
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// This file implements sparse conditional constant propagation and merging:
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//
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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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//===----------------------------------------------------------------------===//
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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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#include <algorithm>
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#include <map>
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using namespace llvm;
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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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namespace {
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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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///
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class LatticeVal {
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enum LatticeValueTy {
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/// undefined - This LLVM Value has no known value yet.
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undefined,
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/// constant - This LLVM Value has a specific constant value.
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constant,
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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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/// asserting.
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forcedconstant,
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/// overdefined - This instruction is not known to be constant, and we know
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/// it has a value.
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overdefined
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};
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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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return Val.getInt();
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}
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public:
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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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}
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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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}
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/// markOverdefined - Return true if this is a change in status.
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bool markOverdefined() {
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if (isOverdefined())
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return false;
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Val.setInt(overdefined);
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return true;
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}
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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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return false;
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}
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if (isUndefined()) {
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Val.setInt(constant);
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assert(V && "Marking constant with NULL");
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Val.setPointer(V);
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} else {
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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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}
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return true;
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}
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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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if (isConstant())
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return dyn_cast<ConstantInt>(getConstant());
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return 0;
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}
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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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Val.setPointer(V);
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}
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};
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} // end anonymous namespace.
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namespace {
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//===----------------------------------------------------------------------===//
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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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///
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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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///
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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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/// constants.
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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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///
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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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/// point.
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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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public:
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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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///
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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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return true;
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}
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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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}
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}
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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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LatticeVal()));
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} else
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TrackedRetVals.insert(std::make_pair(F, LatticeVal()));
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}
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void AddArgumentTrackedFunction(Function *F) {
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TrackingIncomingArguments.insert(F);
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}
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/// Solve - Solve for constants and executable blocks.
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///
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void Solve();
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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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/// should be rerun.
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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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}
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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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return I->second;
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}
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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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return I->second;
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}*/
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/// getTrackedRetVals - Get the inferred return value map.
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///
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const DenseMap<Function*, LatticeVal> &getTrackedRetVals() {
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return TrackedRetVals;
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}
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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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}
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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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}
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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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else
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markOverdefined(V);
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}
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private:
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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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//
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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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if (IV.isOverdefined())
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OverdefinedInstWorkList.push_back(V);
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else
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InstWorkList.push_back(V);
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}
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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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}
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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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LatticeVal &IV = ValueState[V];
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IV.markForcedConstant(C);
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DEBUG(dbgs() << "markForcedConstant: " << *C << ": " << *V << '\n');
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if (IV.isOverdefined())
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OverdefinedInstWorkList.push_back(V);
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else
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InstWorkList.push_back(V);
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}
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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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else
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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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}
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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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return; // Noop.
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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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}
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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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}
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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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if (!I.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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}
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// All others are underdefined by default.
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return LV;
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}
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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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if (!I.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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} else
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LV.markOverdefined(); // Unknown sort of constant.
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}
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// All others are underdefined by default.
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return LV;
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}
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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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PHINode *PN;
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for (BasicBlock::iterator I = Dest->begin();
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(PN = dyn_cast<PHINode>(I)); ++I)
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visitPHINode(*PN);
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}
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}
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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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//
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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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//
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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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//
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void OperandChangedState(Instruction *I) {
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if (BBExecutable.count(I->getParent())) // Inst is executable?
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visit(*I);
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}
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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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while (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) {
|
|
std::multimap<PHINode*, Instruction*>::iterator J, E;
|
|
tie(J, E) = UsersOfOverdefinedPHIs.equal_range(PN);
|
|
for (; 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.
|
|
std::multimap<PHINode*, Instruction*>::iterator I, E;
|
|
tie(I, E) = UsersOfOverdefinedPHIs.equal_range(&PN);
|
|
if (I == E)
|
|
return;
|
|
|
|
SmallVector<Instruction*, 16> Users;
|
|
for (; 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 (const 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) {
|
|
const 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 (const 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];
|
|
markConstant(&I, ConstantExpr::getGetElementPtr(Ptr, &Operands[0]+1,
|
|
Operands.size()-1));
|
|
}
|
|
|
|
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.data(), Operands.size()))
|
|
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 (const 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 (const 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 (const 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.
|
|
const 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;
|
|
}
|