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confusion with external linkage types. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@33663 91177308-0d34-0410-b5e6-96231b3b80d8
1679 lines
63 KiB
C++
1679 lines
63 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 was developed by the LLVM research group and is distributed under
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// the University of Illinois Open Source 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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// Notice that:
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// * This pass has a habit of making definitions be dead. It is a good idea
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// to to run a DCE pass sometime after running this pass.
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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/Support/InstVisitor.h"
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#include "llvm/Transforms/Utils/Local.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/ADT/hash_map"
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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 <set>
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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 ofinstructions removed by IPSCCP");
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STATISTIC(IPNumDeadBlocks , "Number of basic blocks unreachable 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 {
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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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} LatticeValue; // The current lattice position
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Constant *ConstantVal; // If Constant value, the current value
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public:
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inline LatticeVal() : LatticeValue(undefined), ConstantVal(0) {}
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// markOverdefined - Return true if this is a new status to be in...
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inline bool markOverdefined() {
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if (LatticeValue != overdefined) {
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LatticeValue = overdefined;
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return true;
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}
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return false;
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}
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// markConstant - Return true if this is a new status for us.
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inline bool markConstant(Constant *V) {
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if (LatticeValue != constant) {
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if (LatticeValue == undefined) {
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LatticeValue = constant;
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assert(V && "Marking constant with NULL");
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ConstantVal = V;
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} else {
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assert(LatticeValue == 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 == ConstantVal) 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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LatticeValue = overdefined;
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}
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return true;
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} else {
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assert(ConstantVal == V && "Marking constant with different value");
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}
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return false;
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}
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inline void markForcedConstant(Constant *V) {
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assert(LatticeValue == undefined && "Can't force a defined value!");
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LatticeValue = forcedconstant;
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ConstantVal = V;
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}
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inline bool isUndefined() const { return LatticeValue == undefined; }
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inline bool isConstant() const {
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return LatticeValue == constant || LatticeValue == forcedconstant;
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}
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inline bool isOverdefined() const { return LatticeValue == overdefined; }
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inline Constant *getConstant() const {
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assert(isConstant() && "Cannot get the constant of a non-constant!");
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return ConstantVal;
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}
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};
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} // end anonymous 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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std::set<BasicBlock*> BBExecutable;// The basic blocks that are executable
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hash_map<Value*, LatticeVal> ValueState; // The state each value is in...
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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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hash_map<GlobalVariable*, LatticeVal> TrackedGlobals;
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/// TrackedFunctionRetVals - 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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hash_map<Function*, LatticeVal> TrackedFunctionRetVals;
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// The reason for two worklists is that overdefined is the lowest state
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// on the lattice, and moving things to overdefined as fast as possible
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// makes SCCP converge much faster.
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// By having a separate worklist, we accomplish this because everything
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// possibly overdefined will become overdefined at the soonest possible
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// point.
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std::vector<Value*> OverdefinedInstWorkList;
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std::vector<Value*> InstWorkList;
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std::vector<BasicBlock*> 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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std::set<Edge> KnownFeasibleEdges;
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public:
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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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void MarkBlockExecutable(BasicBlock *BB) {
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DOUT << "Marking Block Executable: " << BB->getName() << "\n";
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BBExecutable.insert(BB); // Basic block is executable!
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BBWorkList.push_back(BB); // Add the block to the work list!
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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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const Type *ElTy = GV->getType()->getElementType();
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if (ElTy->isFirstClassType()) {
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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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assert(F->hasInternalLinkage() && "Can only track internal functions!");
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// Add an entry, F -> undef.
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TrackedFunctionRetVals[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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/// getExecutableBlocks - Once we have solved for constants, return the set of
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/// blocks that is known to be executable.
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std::set<BasicBlock*> &getExecutableBlocks() {
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return BBExecutable;
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}
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/// getValueMapping - Once we have solved for constants, return the mapping of
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/// LLVM values to LatticeVals.
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hash_map<Value*, LatticeVal> &getValueMapping() {
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return ValueState;
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}
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/// getTrackedFunctionRetVals - Get the inferred return value map.
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///
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const hash_map<Function*, LatticeVal> &getTrackedFunctionRetVals() {
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return TrackedFunctionRetVals;
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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 hash_map<GlobalVariable*, LatticeVal> &getTrackedGlobals() {
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return TrackedGlobals;
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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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inline void markConstant(LatticeVal &IV, Value *V, Constant *C) {
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if (IV.markConstant(C)) {
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DOUT << "markConstant: " << *C << ": " << *V;
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InstWorkList.push_back(V);
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}
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}
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inline void markForcedConstant(LatticeVal &IV, Value *V, Constant *C) {
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IV.markForcedConstant(C);
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DOUT << "markForcedConstant: " << *C << ": " << *V;
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InstWorkList.push_back(V);
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}
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inline void markConstant(Value *V, Constant *C) {
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markConstant(ValueState[V], V, C);
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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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inline void markOverdefined(LatticeVal &IV, Value *V) {
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if (IV.markOverdefined()) {
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DEBUG(DOUT << "markOverdefined: ";
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if (Function *F = dyn_cast<Function>(V))
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DOUT << "Function '" << F->getName() << "'\n";
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else
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DOUT << *V);
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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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}
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inline void markOverdefined(Value *V) {
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markOverdefined(ValueState[V], V);
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}
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inline 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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inline void mergeInValue(Value *V, LatticeVal &MergeWithV) {
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return mergeInValue(ValueState[V], V, MergeWithV);
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}
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// getValueState - Return the LatticeVal object that corresponds to the value.
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// This function is necessary because not all values should start out in the
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// underdefined state... Argument's should be overdefined, and
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// constants should be marked as constants. If a value is not known to be an
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// Instruction object, then use this accessor to get its value from the map.
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//
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inline LatticeVal &getValueState(Value *V) {
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hash_map<Value*, LatticeVal>::iterator I = ValueState.find(V);
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if (I != ValueState.end()) return I->second; // Common case, in the map
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if (Constant *C = dyn_cast<Constant>(V)) {
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if (isa<UndefValue>(V)) {
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// Nothing to do, remain undefined.
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} else {
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ValueState[C].markConstant(C); // Constants are constant
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}
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}
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// All others are underdefined by default...
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return ValueState[V];
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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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//
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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 (BBExecutable.count(Dest)) {
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DOUT << "Marking Edge Executable: " << Source->getName()
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<< " -> " << Dest->getName() << "\n";
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// The destination is already executable, but 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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for (BasicBlock::iterator I = Dest->begin(); isa<PHINode>(I); ++I)
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visitPHINode(*cast<PHINode>(I));
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} else {
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MarkBlockExecutable(Dest);
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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, std::vector<bool> &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(User *U) {
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// Only instructions use other variable values!
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Instruction &I = cast<Instruction>(*U);
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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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private:
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friend class InstVisitor<SCCPSolver>;
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// visit implementations - Something changed in this instruction... Either an
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// operand made a transition, or the instruction is newly executable. Change
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// the value type of I to reflect these changes if appropriate.
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//
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void visitPHINode(PHINode &I);
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// Terminators
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void visitReturnInst(ReturnInst &I);
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void visitTerminatorInst(TerminatorInst &TI);
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void visitCastInst(CastInst &I);
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void visitSelectInst(SelectInst &I);
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void visitBinaryOperator(Instruction &I);
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void visitCmpInst(CmpInst &I);
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void visitShiftInst(ShiftInst &I) { visitBinaryOperator(I); }
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void visitExtractElementInst(ExtractElementInst &I);
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void visitInsertElementInst(InsertElementInst &I);
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void visitShuffleVectorInst(ShuffleVectorInst &I);
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// Instructions that cannot be folded away...
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void visitStoreInst (Instruction &I);
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void visitLoadInst (LoadInst &I);
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void visitGetElementPtrInst(GetElementPtrInst &I);
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void visitCallInst (CallInst &I) { visitCallSite(CallSite::get(&I)); }
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void visitInvokeInst (InvokeInst &II) {
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visitCallSite(CallSite::get(&II));
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visitTerminatorInst(II);
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}
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void visitCallSite (CallSite CS);
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void visitUnwindInst (TerminatorInst &I) { /*returns void*/ }
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void visitUnreachableInst(TerminatorInst &I) { /*returns void*/ }
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void visitAllocationInst(Instruction &I) { markOverdefined(&I); }
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void visitVANextInst (Instruction &I) { markOverdefined(&I); }
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void visitVAArgInst (Instruction &I) { markOverdefined(&I); }
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void visitFreeInst (Instruction &I) { /*returns void*/ }
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void visitInstruction(Instruction &I) {
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// If a new instruction is added to LLVM that we don't handle...
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cerr << "SCCP: Don't know how to handle: " << I;
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markOverdefined(&I); // Just in case
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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 SCCPSolver::getFeasibleSuccessors(TerminatorInst &TI,
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std::vector<bool> &Succs) {
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Succs.resize(TI.getNumSuccessors());
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if (BranchInst *BI = dyn_cast<BranchInst>(&TI)) {
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if (BI->isUnconditional()) {
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Succs[0] = true;
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} else {
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LatticeVal &BCValue = getValueState(BI->getCondition());
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if (BCValue.isOverdefined() ||
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(BCValue.isConstant() && !isa<ConstantInt>(BCValue.getConstant()))) {
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// Overdefined condition variables, and branches on unfoldable constant
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// conditions, mean the branch could go either way.
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Succs[0] = Succs[1] = true;
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} else if (BCValue.isConstant()) {
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// Constant condition variables mean the branch can only go a single way
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Succs[BCValue.getConstant() == ConstantInt::getFalse()] = true;
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}
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}
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} else if (isa<InvokeInst>(&TI)) {
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// Invoke instructions successors are always executable.
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Succs[0] = Succs[1] = true;
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} else if (SwitchInst *SI = dyn_cast<SwitchInst>(&TI)) {
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LatticeVal &SCValue = getValueState(SI->getCondition());
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if (SCValue.isOverdefined() || // Overdefined condition?
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(SCValue.isConstant() && !isa<ConstantInt>(SCValue.getConstant()))) {
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// All destinations are executable!
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Succs.assign(TI.getNumSuccessors(), true);
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} else if (SCValue.isConstant()) {
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Constant *CPV = SCValue.getConstant();
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// Make sure to skip the "default value" which isn't a value
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for (unsigned i = 1, E = SI->getNumSuccessors(); i != E; ++i) {
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if (SI->getSuccessorValue(i) == CPV) {// Found the right branch...
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Succs[i] = true;
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return;
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}
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}
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// Constant value not equal to any of the branches... must execute
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// default branch then...
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Succs[0] = true;
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}
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} else {
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cerr << "SCCP: Don't know how to handle: " << TI;
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Succs.assign(TI.getNumSuccessors(), true);
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}
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}
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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 SCCPSolver::isEdgeFeasible(BasicBlock *From, BasicBlock *To) {
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assert(BBExecutable.count(To) && "Dest should always be alive!");
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// Make sure the source basic block is executable!!
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if (!BBExecutable.count(From)) return false;
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// Check to make sure this edge itself is actually feasible now...
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TerminatorInst *TI = From->getTerminator();
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if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
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if (BI->isUnconditional())
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return true;
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else {
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LatticeVal &BCValue = getValueState(BI->getCondition());
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if (BCValue.isOverdefined()) {
|
|
// Overdefined condition variables mean the branch could go either way.
|
|
return true;
|
|
} else if (BCValue.isConstant()) {
|
|
// Not branching on an evaluatable constant?
|
|
if (!isa<ConstantInt>(BCValue.getConstant())) return true;
|
|
|
|
// Constant condition variables mean the branch can only go a single way
|
|
return BI->getSuccessor(BCValue.getConstant() ==
|
|
ConstantInt::getFalse()) == To;
|
|
}
|
|
return false;
|
|
}
|
|
} else if (isa<InvokeInst>(TI)) {
|
|
// Invoke instructions successors are always executable.
|
|
return true;
|
|
} else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
|
|
LatticeVal &SCValue = getValueState(SI->getCondition());
|
|
if (SCValue.isOverdefined()) { // Overdefined condition?
|
|
// All destinations are executable!
|
|
return true;
|
|
} else if (SCValue.isConstant()) {
|
|
Constant *CPV = SCValue.getConstant();
|
|
if (!isa<ConstantInt>(CPV))
|
|
return true; // not a foldable constant?
|
|
|
|
// 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) == CPV) // Found the taken branch...
|
|
return SI->getSuccessor(i) == To;
|
|
|
|
// Constant value not equal to any of the branches... must execute
|
|
// default branch then...
|
|
return SI->getDefaultDest() == To;
|
|
}
|
|
return false;
|
|
} else {
|
|
cerr << "Unknown terminator instruction: " << *TI;
|
|
abort();
|
|
}
|
|
}
|
|
|
|
// 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) {
|
|
LatticeVal &PNIV = getValueState(&PN);
|
|
if (PNIV.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) {
|
|
std::vector<Instruction*> Users;
|
|
Users.reserve(std::distance(I, E));
|
|
for (; I != E; ++I) Users.push_back(I->second);
|
|
while (!Users.empty()) {
|
|
visit(Users.back());
|
|
Users.pop_back();
|
|
}
|
|
}
|
|
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) {
|
|
markOverdefined(PNIV, &PN);
|
|
return;
|
|
}
|
|
|
|
// 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())) {
|
|
if (IV.isOverdefined()) { // PHI node becomes overdefined!
|
|
markOverdefined(PNIV, &PN);
|
|
return;
|
|
}
|
|
|
|
if (OperandVal == 0) { // Grab the first value...
|
|
OperandVal = IV.getConstant();
|
|
} else { // Another value is being merged in!
|
|
// 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 (IV.getConstant() != OperandVal) {
|
|
// Yes there is. This means the PHI node is not constant.
|
|
// You must be overdefined poor PHI.
|
|
//
|
|
markOverdefined(PNIV, &PN); // The PHI node now becomes overdefined
|
|
return; // I'm done analyzing you
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
// 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(PNIV, &PN, OperandVal); // Acquire operand value
|
|
}
|
|
|
|
void SCCPSolver::visitReturnInst(ReturnInst &I) {
|
|
if (I.getNumOperands() == 0) return; // Ret void
|
|
|
|
// If we are tracking the return value of this function, merge it in.
|
|
Function *F = I.getParent()->getParent();
|
|
if (F->hasInternalLinkage() && !TrackedFunctionRetVals.empty()) {
|
|
hash_map<Function*, LatticeVal>::iterator TFRVI =
|
|
TrackedFunctionRetVals.find(F);
|
|
if (TFRVI != TrackedFunctionRetVals.end() &&
|
|
!TFRVI->second.isOverdefined()) {
|
|
LatticeVal &IV = getValueState(I.getOperand(0));
|
|
mergeInValue(TFRVI->second, F, IV);
|
|
}
|
|
}
|
|
}
|
|
|
|
|
|
void SCCPSolver::visitTerminatorInst(TerminatorInst &TI) {
|
|
std::vector<bool> 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) {
|
|
Value *V = I.getOperand(0);
|
|
LatticeVal &VState = getValueState(V);
|
|
if (VState.isOverdefined()) // Inherit overdefinedness of operand
|
|
markOverdefined(&I);
|
|
else if (VState.isConstant()) // Propagate constant value
|
|
markConstant(&I, ConstantExpr::getCast(I.getOpcode(),
|
|
VState.getConstant(), I.getType()));
|
|
}
|
|
|
|
void SCCPSolver::visitSelectInst(SelectInst &I) {
|
|
LatticeVal &CondValue = getValueState(I.getCondition());
|
|
if (CondValue.isUndefined())
|
|
return;
|
|
if (CondValue.isConstant()) {
|
|
if (ConstantInt *CondCB = dyn_cast<ConstantInt>(CondValue.getConstant())){
|
|
mergeInValue(&I, getValueState(CondCB->getZExtValue() ? I.getTrueValue()
|
|
: I.getFalseValue()));
|
|
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()) {
|
|
markConstant(&I, FVal.getConstant());
|
|
return;
|
|
}
|
|
|
|
if (TVal.isUndefined()) { // select ?, undef, X -> X.
|
|
mergeInValue(&I, FVal);
|
|
} else if (FVal.isUndefined()) { // select ?, X, undef -> X.
|
|
mergeInValue(&I, TVal);
|
|
} else {
|
|
markOverdefined(&I);
|
|
}
|
|
}
|
|
|
|
// Handle BinaryOperators and Shift Instructions...
|
|
void SCCPSolver::visitBinaryOperator(Instruction &I) {
|
|
LatticeVal &IV = ValueState[&I];
|
|
if (IV.isOverdefined()) return;
|
|
|
|
LatticeVal &V1State = getValueState(I.getOperand(0));
|
|
LatticeVal &V2State = getValueState(I.getOperand(1));
|
|
|
|
if (V1State.isOverdefined() || V2State.isOverdefined()) {
|
|
// 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 PackedType *PT = dyn_cast<PackedType>(I.getType()))
|
|
markConstant(IV, &I, ConstantPacked::getAllOnesValue(PT));
|
|
else
|
|
markConstant(IV, &I, ConstantInt::getAllOnesValue(I.getType()));
|
|
return;
|
|
} else {
|
|
if (I.getOpcode() == Instruction::And) {
|
|
if (NonOverdefVal->getConstant()->isNullValue()) {
|
|
markConstant(IV, &I, NonOverdefVal->getConstant());
|
|
return; // X and 0 = 0
|
|
}
|
|
} else {
|
|
if (ConstantInt *CI =
|
|
dyn_cast<ConstantInt>(NonOverdefVal->getConstant()))
|
|
if (CI->isAllOnesValue()) {
|
|
markConstant(IV, &I, NonOverdefVal->getConstant());
|
|
return; // X or -1 = -1
|
|
}
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
|
|
// 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!
|
|
} else 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.
|
|
UsersOfOverdefinedPHIs.insert(std::make_pair(PN1, &I));
|
|
UsersOfOverdefinedPHIs.insert(std::make_pair(PN2, &I));
|
|
return;
|
|
} else 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.
|
|
std::multimap<PHINode*, Instruction*>::iterator It, E;
|
|
tie(It, E) = UsersOfOverdefinedPHIs.equal_range(PN1);
|
|
while (It != E) {
|
|
if (It->second == &I) {
|
|
UsersOfOverdefinedPHIs.erase(It++);
|
|
} else
|
|
++It;
|
|
}
|
|
tie(It, E) = UsersOfOverdefinedPHIs.equal_range(PN2);
|
|
while (It != E) {
|
|
if (It->second == &I) {
|
|
UsersOfOverdefinedPHIs.erase(It++);
|
|
} else
|
|
++It;
|
|
}
|
|
}
|
|
|
|
markOverdefined(IV, &I);
|
|
} else if (V1State.isConstant() && V2State.isConstant()) {
|
|
markConstant(IV, &I, ConstantExpr::get(I.getOpcode(), V1State.getConstant(),
|
|
V2State.getConstant()));
|
|
}
|
|
}
|
|
|
|
// Handle ICmpInst instruction...
|
|
void SCCPSolver::visitCmpInst(CmpInst &I) {
|
|
LatticeVal &IV = ValueState[&I];
|
|
if (IV.isOverdefined()) return;
|
|
|
|
LatticeVal &V1State = getValueState(I.getOperand(0));
|
|
LatticeVal &V2State = getValueState(I.getOperand(1));
|
|
|
|
if (V1State.isOverdefined() || V2State.isOverdefined()) {
|
|
// 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!
|
|
} else 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(IV, &I, Result.getConstant());
|
|
// Remember that this instruction is virtually using the PHI node
|
|
// operands.
|
|
UsersOfOverdefinedPHIs.insert(std::make_pair(PN1, &I));
|
|
UsersOfOverdefinedPHIs.insert(std::make_pair(PN2, &I));
|
|
return;
|
|
} else 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.
|
|
std::multimap<PHINode*, Instruction*>::iterator It, E;
|
|
tie(It, E) = UsersOfOverdefinedPHIs.equal_range(PN1);
|
|
while (It != E) {
|
|
if (It->second == &I) {
|
|
UsersOfOverdefinedPHIs.erase(It++);
|
|
} else
|
|
++It;
|
|
}
|
|
tie(It, E) = UsersOfOverdefinedPHIs.equal_range(PN2);
|
|
while (It != E) {
|
|
if (It->second == &I) {
|
|
UsersOfOverdefinedPHIs.erase(It++);
|
|
} else
|
|
++It;
|
|
}
|
|
}
|
|
|
|
markOverdefined(IV, &I);
|
|
} else if (V1State.isConstant() && V2State.isConstant()) {
|
|
markConstant(IV, &I, ConstantExpr::getCompare(I.getPredicate(),
|
|
V1State.getConstant(),
|
|
V2State.getConstant()));
|
|
}
|
|
}
|
|
|
|
void SCCPSolver::visitExtractElementInst(ExtractElementInst &I) {
|
|
// FIXME : SCCP does not handle vectors properly.
|
|
markOverdefined(&I);
|
|
return;
|
|
|
|
#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) {
|
|
// FIXME : SCCP does not handle vectors properly.
|
|
markOverdefined(&I);
|
|
return;
|
|
#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) {
|
|
// FIXME : SCCP does not handle vectors properly.
|
|
markOverdefined(&I);
|
|
return;
|
|
#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) {
|
|
LatticeVal &IV = ValueState[&I];
|
|
if (IV.isOverdefined()) return;
|
|
|
|
std::vector<Constant*> 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...
|
|
else if (State.isOverdefined()) {
|
|
markOverdefined(IV, &I);
|
|
return;
|
|
}
|
|
assert(State.isConstant() && "Unknown state!");
|
|
Operands.push_back(State.getConstant());
|
|
}
|
|
|
|
Constant *Ptr = Operands[0];
|
|
Operands.erase(Operands.begin()); // Erase the pointer from idx list...
|
|
|
|
markConstant(IV, &I, ConstantExpr::getGetElementPtr(Ptr, Operands));
|
|
}
|
|
|
|
void SCCPSolver::visitStoreInst(Instruction &SI) {
|
|
if (TrackedGlobals.empty() || !isa<GlobalVariable>(SI.getOperand(1)))
|
|
return;
|
|
GlobalVariable *GV = cast<GlobalVariable>(SI.getOperand(1));
|
|
hash_map<GlobalVariable*, LatticeVal>::iterator I = TrackedGlobals.find(GV);
|
|
if (I == TrackedGlobals.end() || I->second.isOverdefined()) return;
|
|
|
|
// Get the value we are storing into the global.
|
|
LatticeVal &PtrVal = getValueState(SI.getOperand(0));
|
|
|
|
mergeInValue(I->second, GV, PtrVal);
|
|
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) {
|
|
LatticeVal &IV = ValueState[&I];
|
|
if (IV.isOverdefined()) return;
|
|
|
|
LatticeVal &PtrVal = getValueState(I.getOperand(0));
|
|
if (PtrVal.isUndefined()) return; // The pointer is not resolved yet!
|
|
if (PtrVal.isConstant() && !I.isVolatile()) {
|
|
Value *Ptr = PtrVal.getConstant();
|
|
if (isa<ConstantPointerNull>(Ptr)) {
|
|
// load null -> null
|
|
markConstant(IV, &I, Constant::getNullValue(I.getType()));
|
|
return;
|
|
}
|
|
|
|
// Transform load (constant global) into the value loaded.
|
|
if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Ptr)) {
|
|
if (GV->isConstant()) {
|
|
if (!GV->isDeclaration()) {
|
|
markConstant(IV, &I, GV->getInitializer());
|
|
return;
|
|
}
|
|
} else if (!TrackedGlobals.empty()) {
|
|
// If we are tracking this global, merge in the known value for it.
|
|
hash_map<GlobalVariable*, LatticeVal>::iterator It =
|
|
TrackedGlobals.find(GV);
|
|
if (It != TrackedGlobals.end()) {
|
|
mergeInValue(IV, &I, It->second);
|
|
return;
|
|
}
|
|
}
|
|
}
|
|
|
|
// Transform load (constantexpr_GEP global, 0, ...) into the value loaded.
|
|
if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ptr))
|
|
if (CE->getOpcode() == Instruction::GetElementPtr)
|
|
if (GlobalVariable *GV = dyn_cast<GlobalVariable>(CE->getOperand(0)))
|
|
if (GV->isConstant() && !GV->isDeclaration())
|
|
if (Constant *V =
|
|
ConstantFoldLoadThroughGEPConstantExpr(GV->getInitializer(), CE)) {
|
|
markConstant(IV, &I, V);
|
|
return;
|
|
}
|
|
}
|
|
|
|
// 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();
|
|
|
|
// If we are tracking this function, we must make sure to bind arguments as
|
|
// appropriate.
|
|
hash_map<Function*, LatticeVal>::iterator TFRVI =TrackedFunctionRetVals.end();
|
|
if (F && F->hasInternalLinkage())
|
|
TFRVI = TrackedFunctionRetVals.find(F);
|
|
|
|
if (TFRVI != TrackedFunctionRetVals.end()) {
|
|
// If this is the first call to the function hit, mark its entry block
|
|
// executable.
|
|
if (!BBExecutable.count(F->begin()))
|
|
MarkBlockExecutable(F->begin());
|
|
|
|
CallSite::arg_iterator CAI = CS.arg_begin();
|
|
for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end();
|
|
AI != E; ++AI, ++CAI) {
|
|
LatticeVal &IV = ValueState[AI];
|
|
if (!IV.isOverdefined())
|
|
mergeInValue(IV, AI, getValueState(*CAI));
|
|
}
|
|
}
|
|
Instruction *I = CS.getInstruction();
|
|
if (I->getType() == Type::VoidTy) return;
|
|
|
|
LatticeVal &IV = ValueState[I];
|
|
if (IV.isOverdefined()) return;
|
|
|
|
// Propagate the return value of the function to the value of the instruction.
|
|
if (TFRVI != TrackedFunctionRetVals.end()) {
|
|
mergeInValue(IV, I, TFRVI->second);
|
|
return;
|
|
}
|
|
|
|
if (F == 0 || !F->isDeclaration() || !canConstantFoldCallTo(F)) {
|
|
markOverdefined(IV, I);
|
|
return;
|
|
}
|
|
|
|
std::vector<Constant*> Operands;
|
|
Operands.reserve(I->getNumOperands()-1);
|
|
|
|
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...
|
|
else if (State.isOverdefined()) {
|
|
markOverdefined(IV, I);
|
|
return;
|
|
}
|
|
assert(State.isConstant() && "Unknown state!");
|
|
Operands.push_back(State.getConstant());
|
|
}
|
|
|
|
if (Constant *C = ConstantFoldCall(F, Operands))
|
|
markConstant(IV, I, C);
|
|
else
|
|
markOverdefined(IV, I);
|
|
}
|
|
|
|
|
|
void SCCPSolver::Solve() {
|
|
// Process the work lists until they are empty!
|
|
while (!BBWorkList.empty() || !InstWorkList.empty() ||
|
|
!OverdefinedInstWorkList.empty()) {
|
|
// Process the instruction work list...
|
|
while (!OverdefinedInstWorkList.empty()) {
|
|
Value *I = OverdefinedInstWorkList.back();
|
|
OverdefinedInstWorkList.pop_back();
|
|
|
|
DOUT << "\nPopped off OI-WL: " << *I;
|
|
|
|
// "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)
|
|
OperandChangedState(*UI);
|
|
}
|
|
// Process the instruction work list...
|
|
while (!InstWorkList.empty()) {
|
|
Value *I = InstWorkList.back();
|
|
InstWorkList.pop_back();
|
|
|
|
DOUT << "\nPopped off I-WL: " << *I;
|
|
|
|
// "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...
|
|
//
|
|
if (!getValueState(I).isOverdefined())
|
|
for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
|
|
UI != E; ++UI)
|
|
OperandChangedState(*UI);
|
|
}
|
|
|
|
// Process the basic block work list...
|
|
while (!BBWorkList.empty()) {
|
|
BasicBlock *BB = BBWorkList.back();
|
|
BBWorkList.pop_back();
|
|
|
|
DOUT << "\nPopped off BBWL: " << *BB;
|
|
|
|
// 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() == Type::VoidTy) continue;
|
|
|
|
LatticeVal &LV = getValueState(I);
|
|
if (!LV.isUndefined()) 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) {
|
|
// 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.
|
|
assert(Op0LV.isUndefined());
|
|
markForcedConstant(LV, 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(LV, I, Constant::getNullValue(ITy));
|
|
return true;
|
|
|
|
case Instruction::Or:
|
|
// undef | X -> -1. X could be -1.
|
|
if (const PackedType *PTy = dyn_cast<PackedType>(ITy))
|
|
markForcedConstant(LV, I, ConstantPacked::getAllOnesValue(PTy));
|
|
else
|
|
markForcedConstant(LV, I, ConstantInt::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(LV, 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(LV, I, Op0LV.getConstant());
|
|
else
|
|
markOverdefined(LV, 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(LV, 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(LV, I, Op1LV.getConstant());
|
|
else
|
|
markOverdefined(LV, I);
|
|
return true;
|
|
}
|
|
}
|
|
|
|
TerminatorInst *TI = BB->getTerminator();
|
|
if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
|
|
if (!BI->isConditional()) continue;
|
|
if (!getValueState(BI->getCondition()).isUndefined())
|
|
continue;
|
|
} else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
|
|
if (!getValueState(SI->getCondition()).isUndefined())
|
|
continue;
|
|
} else {
|
|
continue;
|
|
}
|
|
|
|
// If the edge to the first successor isn't thought to be feasible yet, mark
|
|
// it so now.
|
|
if (KnownFeasibleEdges.count(Edge(BB, TI->getSuccessor(0))))
|
|
continue;
|
|
|
|
// Otherwise, it isn't already thought to be feasible. Mark it as such now
|
|
// and return. This will make other blocks reachable, which will allow new
|
|
// values to be discovered and existing ones to be moved in the lattice.
|
|
markEdgeExecutable(BB, TI->getSuccessor(0));
|
|
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 {
|
|
// runOnFunction - Run the Sparse Conditional Constant Propagation
|
|
// algorithm, and return true if the function was modified.
|
|
//
|
|
bool runOnFunction(Function &F);
|
|
|
|
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
|
|
AU.setPreservesCFG();
|
|
}
|
|
};
|
|
|
|
RegisterPass<SCCP> X("sccp", "Sparse Conditional Constant Propagation");
|
|
} // end anonymous namespace
|
|
|
|
|
|
// createSCCPPass - This is the public interface to this file...
|
|
FunctionPass *llvm::createSCCPPass() {
|
|
return new SCCP();
|
|
}
|
|
|
|
|
|
// runOnFunction() - Run the Sparse Conditional Constant Propagation algorithm,
|
|
// and return true if the function was modified.
|
|
//
|
|
bool SCCP::runOnFunction(Function &F) {
|
|
DOUT << "SCCP on function '" << F.getName() << "'\n";
|
|
SCCPSolver Solver;
|
|
|
|
// Mark the first block of the function as being executable.
|
|
Solver.MarkBlockExecutable(F.begin());
|
|
|
|
// Mark all arguments to the function as being overdefined.
|
|
hash_map<Value*, LatticeVal> &Values = Solver.getValueMapping();
|
|
for (Function::arg_iterator AI = F.arg_begin(), E = F.arg_end(); AI != E; ++AI)
|
|
Values[AI].markOverdefined();
|
|
|
|
// Solve for constants.
|
|
bool ResolvedUndefs = true;
|
|
while (ResolvedUndefs) {
|
|
Solver.Solve();
|
|
DOUT << "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.
|
|
//
|
|
std::set<BasicBlock*> &ExecutableBBs = Solver.getExecutableBlocks();
|
|
for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
|
|
if (!ExecutableBBs.count(BB)) {
|
|
DOUT << " 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.
|
|
std::vector<Instruction*> Insts;
|
|
for (BasicBlock::iterator I = BB->begin(), E = BB->getTerminator();
|
|
I != E; ++I)
|
|
Insts.push_back(I);
|
|
while (!Insts.empty()) {
|
|
Instruction *I = Insts.back();
|
|
Insts.pop_back();
|
|
if (!I->use_empty())
|
|
I->replaceAllUsesWith(UndefValue::get(I->getType()));
|
|
BB->getInstList().erase(I);
|
|
MadeChanges = true;
|
|
++NumInstRemoved;
|
|
}
|
|
} else {
|
|
// 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() != Type::VoidTy) {
|
|
LatticeVal &IV = Values[Inst];
|
|
if (IV.isConstant() || IV.isUndefined() &&
|
|
!isa<TerminatorInst>(Inst)) {
|
|
Constant *Const = IV.isConstant()
|
|
? IV.getConstant() : UndefValue::get(Inst->getType());
|
|
DOUT << " Constant: " << *Const << " = " << *Inst;
|
|
|
|
// Replaces all of the uses of a variable with uses of the constant.
|
|
Inst->replaceAllUsesWith(Const);
|
|
|
|
// Delete the instruction.
|
|
BB->getInstList().erase(Inst);
|
|
|
|
// 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 {
|
|
bool runOnModule(Module &M);
|
|
};
|
|
|
|
RegisterPass<IPSCCP>
|
|
Y("ipsccp", "Interprocedural Sparse Conditional Constant Propagation");
|
|
} // end anonymous namespace
|
|
|
|
// createIPSCCPPass - This is the public interface to this file...
|
|
ModulePass *llvm::createIPSCCPPass() {
|
|
return new IPSCCP();
|
|
}
|
|
|
|
|
|
static bool AddressIsTaken(GlobalValue *GV) {
|
|
// Delete any dead constantexpr klingons.
|
|
GV->removeDeadConstantUsers();
|
|
|
|
for (Value::use_iterator UI = GV->use_begin(), E = GV->use_end();
|
|
UI != E; ++UI)
|
|
if (StoreInst *SI = dyn_cast<StoreInst>(*UI)) {
|
|
if (SI->getOperand(0) == GV || SI->isVolatile())
|
|
return true; // Storing addr of GV.
|
|
} else if (isa<InvokeInst>(*UI) || isa<CallInst>(*UI)) {
|
|
// Make sure we are calling the function, not passing the address.
|
|
CallSite CS = CallSite::get(cast<Instruction>(*UI));
|
|
for (CallSite::arg_iterator AI = CS.arg_begin(),
|
|
E = CS.arg_end(); AI != E; ++AI)
|
|
if (*AI == GV)
|
|
return true;
|
|
} else if (LoadInst *LI = dyn_cast<LoadInst>(*UI)) {
|
|
if (LI->isVolatile())
|
|
return true;
|
|
} else {
|
|
return true;
|
|
}
|
|
return false;
|
|
}
|
|
|
|
bool IPSCCP::runOnModule(Module &M) {
|
|
SCCPSolver Solver;
|
|
|
|
// Loop over all functions, marking arguments to those with their addresses
|
|
// taken or that are external as overdefined.
|
|
//
|
|
hash_map<Value*, LatticeVal> &Values = Solver.getValueMapping();
|
|
for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F)
|
|
if (!F->hasInternalLinkage() || AddressIsTaken(F)) {
|
|
if (!F->isDeclaration())
|
|
Solver.MarkBlockExecutable(F->begin());
|
|
for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end();
|
|
AI != E; ++AI)
|
|
Values[AI].markOverdefined();
|
|
} else {
|
|
Solver.AddTrackedFunction(F);
|
|
}
|
|
|
|
// 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->hasInternalLinkage() && !AddressIsTaken(G))
|
|
Solver.TrackValueOfGlobalVariable(G);
|
|
|
|
// Solve for constants.
|
|
bool ResolvedUndefs = true;
|
|
while (ResolvedUndefs) {
|
|
Solver.Solve();
|
|
|
|
DOUT << "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.
|
|
//
|
|
std::set<BasicBlock*> &ExecutableBBs = Solver.getExecutableBlocks();
|
|
for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F) {
|
|
for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end();
|
|
AI != E; ++AI)
|
|
if (!AI->use_empty()) {
|
|
LatticeVal &IV = Values[AI];
|
|
if (IV.isConstant() || IV.isUndefined()) {
|
|
Constant *CST = IV.isConstant() ?
|
|
IV.getConstant() : UndefValue::get(AI->getType());
|
|
DOUT << "*** Arg " << *AI << " = " << *CST <<"\n";
|
|
|
|
// Replaces all of the uses of a variable with uses of the
|
|
// constant.
|
|
AI->replaceAllUsesWith(CST);
|
|
++IPNumArgsElimed;
|
|
}
|
|
}
|
|
|
|
std::vector<BasicBlock*> BlocksToErase;
|
|
for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
|
|
if (!ExecutableBBs.count(BB)) {
|
|
DOUT << " BasicBlock Dead:" << *BB;
|
|
++IPNumDeadBlocks;
|
|
|
|
// Delete the instructions backwards, as it has a reduced likelihood of
|
|
// having to update as many def-use and use-def chains.
|
|
std::vector<Instruction*> Insts;
|
|
TerminatorInst *TI = BB->getTerminator();
|
|
for (BasicBlock::iterator I = BB->begin(), E = TI; I != E; ++I)
|
|
Insts.push_back(I);
|
|
|
|
while (!Insts.empty()) {
|
|
Instruction *I = Insts.back();
|
|
Insts.pop_back();
|
|
if (!I->use_empty())
|
|
I->replaceAllUsesWith(UndefValue::get(I->getType()));
|
|
BB->getInstList().erase(I);
|
|
MadeChanges = true;
|
|
++IPNumInstRemoved;
|
|
}
|
|
|
|
for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) {
|
|
BasicBlock *Succ = TI->getSuccessor(i);
|
|
if (Succ->begin() != Succ->end() && isa<PHINode>(Succ->begin()))
|
|
TI->getSuccessor(i)->removePredecessor(BB);
|
|
}
|
|
if (!TI->use_empty())
|
|
TI->replaceAllUsesWith(UndefValue::get(TI->getType()));
|
|
BB->getInstList().erase(TI);
|
|
|
|
if (&*BB != &F->front())
|
|
BlocksToErase.push_back(BB);
|
|
else
|
|
new UnreachableInst(BB);
|
|
|
|
} else {
|
|
for (BasicBlock::iterator BI = BB->begin(), E = BB->end(); BI != E; ) {
|
|
Instruction *Inst = BI++;
|
|
if (Inst->getType() != Type::VoidTy) {
|
|
LatticeVal &IV = Values[Inst];
|
|
if (IV.isConstant() || IV.isUndefined() &&
|
|
!isa<TerminatorInst>(Inst)) {
|
|
Constant *Const = IV.isConstant()
|
|
? IV.getConstant() : UndefValue::get(Inst->getType());
|
|
DOUT << " Constant: " << *Const << " = " << *Inst;
|
|
|
|
// Replaces all of the uses of a variable with uses of the
|
|
// constant.
|
|
Inst->replaceAllUsesWith(Const);
|
|
|
|
// Delete the instruction.
|
|
if (!isa<TerminatorInst>(Inst) && !isa<CallInst>(Inst))
|
|
BB->getInstList().erase(Inst);
|
|
|
|
// 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];
|
|
while (!DeadBB->use_empty()) {
|
|
Instruction *I = cast<Instruction>(DeadBB->use_back());
|
|
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.
|
|
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 {
|
|
assert(0 && "Didn't fold away reference to block!");
|
|
}
|
|
|
|
// Make this an uncond branch to the first successor.
|
|
TerminatorInst *TI = I->getParent()->getTerminator();
|
|
new BranchInst(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);
|
|
}
|
|
}
|
|
|
|
// 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.
|
|
const hash_map<Function*, LatticeVal> &RV =Solver.getTrackedFunctionRetVals();
|
|
for (hash_map<Function*, LatticeVal>::const_iterator I = RV.begin(),
|
|
E = RV.end(); I != E; ++I)
|
|
if (!I->second.isOverdefined() &&
|
|
I->first->getReturnType() != Type::VoidTy) {
|
|
Function *F = I->first;
|
|
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)))
|
|
RI->setOperand(0, UndefValue::get(F->getReturnType()));
|
|
}
|
|
|
|
// If we infered constant or undef values for globals variables, we can delete
|
|
// the global and any stores that remain to it.
|
|
const hash_map<GlobalVariable*, LatticeVal> &TG = Solver.getTrackedGlobals();
|
|
for (hash_map<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!");
|
|
DOUT << "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;
|
|
}
|