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21cb67e16a
- Replace ConstantPointerRef usage with GlobalValue usage - Correct isa<Constant> for GlobalValue subclass git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@14947 91177308-0d34-0410-b5e6-96231b3b80d8
841 lines
32 KiB
C++
841 lines
32 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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#include "llvm/Transforms/Scalar.h"
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#include "llvm/Constants.h"
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#include "llvm/Function.h"
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#include "llvm/GlobalVariable.h"
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#include "llvm/Instructions.h"
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#include "llvm/Pass.h"
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#include "llvm/Type.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 "Support/Debug.h"
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#include "Support/hash_map"
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#include "Support/Statistic.h"
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#include "Support/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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// InstVal class - This class represents the different lattice values that an
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// instruction may occupy. It is a simple class with value semantics.
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//
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namespace {
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Statistic<> NumInstRemoved("sccp", "Number of instructions removed");
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class InstVal {
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enum {
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undefined, // This instruction has no known value
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constant, // This instruction has a constant value
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overdefined // This instruction has an unknown value
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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 InstVal() : 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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LatticeValue = constant;
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ConstantVal = V;
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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 bool isUndefined() const { return LatticeValue == undefined; }
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inline bool isConstant() const { return LatticeValue == constant; }
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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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// SCCP Class
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//
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// This class does all of the work of Sparse Conditional Constant Propagation.
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//
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namespace {
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class SCCP : public FunctionPass, public InstVisitor<SCCP> {
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std::set<BasicBlock*> BBExecutable;// The basic blocks that are executable
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hash_map<Value*, InstVal> ValueState; // The state each value is in...
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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<Instruction*> OverdefinedInstWorkList;// The overdefined
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// instruction work list
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std::vector<Instruction*> InstWorkList;// The instruction work list
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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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// runOnFunction - Run the Sparse Conditional Constant Propagation algorithm,
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// and return true if the function was modified.
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//
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bool runOnFunction(Function &F);
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virtual void getAnalysisUsage(AnalysisUsage &AU) const {
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AU.setPreservesCFG();
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}
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//===--------------------------------------------------------------------===//
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// The implementation of this class
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//
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private:
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friend class InstVisitor<SCCP>; // Allow callbacks from visitor
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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(InstVal &IV, Instruction *I, Constant *C) {
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if (IV.markConstant(C)) {
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DEBUG(std::cerr << "markConstant: " << *C << ": " << *I);
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InstWorkList.push_back(I);
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}
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}
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inline void markConstant(Instruction *I, Constant *C) {
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markConstant(ValueState[I], I, 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(InstVal &IV, Instruction *I) {
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if (IV.markOverdefined()) {
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DEBUG(std::cerr << "markOverdefined: " << *I);
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OverdefinedInstWorkList.push_back(I); // Only instructions go on the work list
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}
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}
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inline void markOverdefined(Instruction *I) {
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markOverdefined(ValueState[I], I);
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}
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// getValueState - Return the InstVal 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 InstVal &getValueState(Value *V) {
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hash_map<Value*, InstVal>::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 (GlobalValue *GV = dyn_cast<GlobalValue>(V)) {
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// The address of a global is a constant...
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ValueState[V].markConstant(GV);
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} else if (Constant *CPV = dyn_cast<Constant>(V)) { // Constants are constant
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ValueState[CPV].markConstant(CPV);
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} else if (isa<Argument>(V)) { // Arguments are overdefined
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ValueState[V].markOverdefined();
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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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DEBUG(std::cerr << "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();
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PHINode *PN = dyn_cast<PHINode>(I); ++I)
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visitPHINode(*PN);
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} else {
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DEBUG(std::cerr << "Marking Block Executable: " << Dest->getName()<<"\n");
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BBExecutable.insert(Dest); // Basic block is executable!
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BBWorkList.push_back(Dest); // Add the block to the work list!
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}
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}
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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) { /*does not have an effect*/ }
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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 visitShiftInst(ShiftInst &I) { visitBinaryOperator(I); }
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// Instructions that cannot be folded away...
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void visitStoreInst (Instruction &I) { /*returns void*/ }
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void visitLoadInst (LoadInst &I);
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void visitGetElementPtrInst(GetElementPtrInst &I);
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void visitCallInst (CallInst &I);
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void visitInvokeInst (TerminatorInst &I) {
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if (I.getType() != Type::VoidTy) markOverdefined(&I);
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visitTerminatorInst(I);
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}
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void visitUnwindInst (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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std::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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// 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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};
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RegisterOpt<SCCP> X("sccp", "Sparse Conditional Constant Propagation");
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} // end anonymous namespace
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// createSCCPPass - This is the public interface to this file...
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Pass *llvm::createSCCPPass() {
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return new SCCP();
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}
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//===----------------------------------------------------------------------===//
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// SCCP Class Implementation
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// runOnFunction() - Run the Sparse Conditional Constant Propagation algorithm,
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// and return true if the function was modified.
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//
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bool SCCP::runOnFunction(Function &F) {
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// Mark the first block of the function as being executable...
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BBExecutable.insert(F.begin()); // Basic block is executable!
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BBWorkList.push_back(F.begin()); // Add the block to the work list!
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// Process the work lists until they are empty!
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while (!BBWorkList.empty() || !InstWorkList.empty() ||
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!OverdefinedInstWorkList.empty()) {
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// Process the instruction work list...
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while (!OverdefinedInstWorkList.empty()) {
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Instruction *I = OverdefinedInstWorkList.back();
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OverdefinedInstWorkList.pop_back();
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DEBUG(std::cerr << "\nPopped off OI-WL: " << I);
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// "I" got into the work list because it either made the transition from
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// bottom to constant
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//
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// Anything on this worklist that is overdefined need not be visited
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// since all of its users will have already been marked as overdefined
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// Update all of the users of this instruction's value...
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//
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for_each(I->use_begin(), I->use_end(),
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bind_obj(this, &SCCP::OperandChangedState));
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}
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// Process the instruction work list...
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while (!InstWorkList.empty()) {
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Instruction *I = InstWorkList.back();
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InstWorkList.pop_back();
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DEBUG(std::cerr << "\nPopped off I-WL: " << *I);
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// "I" got into the work list because it either made the transition from
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// bottom to constant
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//
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// Anything on this worklist that is overdefined need not be visited
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// since all of its users will have already been marked as overdefined.
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// Update all of the users of this instruction's value...
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//
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InstVal &Ival = getValueState (I);
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if (!Ival.isOverdefined())
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for_each(I->use_begin(), I->use_end(),
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bind_obj(this, &SCCP::OperandChangedState));
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}
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// Process the basic block work list...
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while (!BBWorkList.empty()) {
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BasicBlock *BB = BBWorkList.back();
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BBWorkList.pop_back();
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DEBUG(std::cerr << "\nPopped off BBWL: " << *BB);
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// Notify all instructions in this basic block that they are newly
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// executable.
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visit(BB);
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}
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}
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if (DebugFlag) {
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for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I)
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if (!BBExecutable.count(I))
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std::cerr << "BasicBlock Dead:" << *I;
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}
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// Iterate over all of the instructions in a function, replacing them with
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// constants if we have found them to be of constant values.
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//
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bool MadeChanges = false;
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for (Function::iterator BB = F.begin(), BBE = F.end(); BB != BBE; ++BB)
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for (BasicBlock::iterator BI = BB->begin(); BI != BB->end();) {
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Instruction &Inst = *BI;
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InstVal &IV = ValueState[&Inst];
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if (IV.isConstant()) {
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Constant *Const = IV.getConstant();
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DEBUG(std::cerr << "Constant: " << *Const << " = " << Inst);
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// Replaces all of the uses of a variable with uses of the constant.
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Inst.replaceAllUsesWith(Const);
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// Remove the operator from the list of definitions... and delete it.
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BI = BB->getInstList().erase(BI);
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// Hey, we just changed something!
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MadeChanges = true;
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++NumInstRemoved;
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} else {
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++BI;
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}
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}
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// Reset state so that the next invocation will have empty data structures
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BBExecutable.clear();
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ValueState.clear();
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std::vector<Instruction*>().swap(OverdefinedInstWorkList);
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std::vector<Instruction*>().swap(InstWorkList);
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std::vector<BasicBlock*>().swap(BBWorkList);
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return MadeChanges;
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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 SCCP::getFeasibleSuccessors(TerminatorInst &TI, 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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InstVal &BCValue = getValueState(BI->getCondition());
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if (BCValue.isOverdefined() ||
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(BCValue.isConstant() && !isa<ConstantBool>(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() == ConstantBool::False] = true;
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}
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}
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} else if (InvokeInst *II = dyn_cast<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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InstVal &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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std::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 SCCP::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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InstVal &BCValue = getValueState(BI->getCondition());
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if (BCValue.isOverdefined()) {
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// Overdefined condition variables mean the branch could go either way.
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return true;
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} else if (BCValue.isConstant()) {
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// Not branching on an evaluatable constant?
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if (!isa<ConstantBool>(BCValue.getConstant())) return true;
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// Constant condition variables mean the branch can only go a single way
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return BI->getSuccessor(BCValue.getConstant() ==
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ConstantBool::False) == To;
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}
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return false;
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}
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} else if (InvokeInst *II = dyn_cast<InvokeInst>(TI)) {
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// Invoke instructions successors are always executable.
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return true;
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} else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
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InstVal &SCValue = getValueState(SI->getCondition());
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if (SCValue.isOverdefined()) { // Overdefined condition?
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// All destinations are executable!
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return true;
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} else if (SCValue.isConstant()) {
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Constant *CPV = SCValue.getConstant();
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if (!isa<ConstantInt>(CPV))
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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 {
|
|
std::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 SCCP::visitPHINode(PHINode &PN) {
|
|
InstVal &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) {
|
|
InstVal &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 SCCP::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 SCCP::visitCastInst(CastInst &I) {
|
|
Value *V = I.getOperand(0);
|
|
InstVal &VState = getValueState(V);
|
|
if (VState.isOverdefined()) // Inherit overdefinedness of operand
|
|
markOverdefined(&I);
|
|
else if (VState.isConstant()) // Propagate constant value
|
|
markConstant(&I, ConstantExpr::getCast(VState.getConstant(), I.getType()));
|
|
}
|
|
|
|
void SCCP::visitSelectInst(SelectInst &I) {
|
|
InstVal &CondValue = getValueState(I.getCondition());
|
|
if (CondValue.isOverdefined())
|
|
markOverdefined(&I);
|
|
else if (CondValue.isConstant()) {
|
|
if (CondValue.getConstant() == ConstantBool::True) {
|
|
InstVal &Val = getValueState(I.getTrueValue());
|
|
if (Val.isOverdefined())
|
|
markOverdefined(&I);
|
|
else if (Val.isConstant())
|
|
markConstant(&I, Val.getConstant());
|
|
} else if (CondValue.getConstant() == ConstantBool::False) {
|
|
InstVal &Val = getValueState(I.getFalseValue());
|
|
if (Val.isOverdefined())
|
|
markOverdefined(&I);
|
|
else if (Val.isConstant())
|
|
markConstant(&I, Val.getConstant());
|
|
} else
|
|
markOverdefined(&I);
|
|
}
|
|
}
|
|
|
|
// Handle BinaryOperators and Shift Instructions...
|
|
void SCCP::visitBinaryOperator(Instruction &I) {
|
|
InstVal &IV = ValueState[&I];
|
|
if (IV.isOverdefined()) return;
|
|
|
|
InstVal &V1State = getValueState(I.getOperand(0));
|
|
InstVal &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!
|
|
InstVal Result;
|
|
for (unsigned i = 0, e = PN1->getNumIncomingValues(); i != e; ++i) {
|
|
InstVal &In1 = getValueState(PN1->getIncomingValue(i));
|
|
BasicBlock *InBlock = PN1->getIncomingBlock(i);
|
|
InstVal &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 getelementptr instructions... if all operands are constants then we
|
|
// can turn this into a getelementptr ConstantExpr.
|
|
//
|
|
void SCCP::visitGetElementPtrInst(GetElementPtrInst &I) {
|
|
InstVal &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) {
|
|
InstVal &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));
|
|
}
|
|
|
|
/// GetGEPGlobalInitializer - Given a constant and a getelementptr constantexpr,
|
|
/// return the constant value being addressed by the constant expression, or
|
|
/// null if something is funny.
|
|
///
|
|
static Constant *GetGEPGlobalInitializer(Constant *C, ConstantExpr *CE) {
|
|
if (CE->getOperand(1) != Constant::getNullValue(CE->getOperand(1)->getType()))
|
|
return 0; // Do not allow stepping over the value!
|
|
|
|
// Loop over all of the operands, tracking down which value we are
|
|
// addressing...
|
|
for (unsigned i = 2, e = CE->getNumOperands(); i != e; ++i)
|
|
if (ConstantUInt *CU = dyn_cast<ConstantUInt>(CE->getOperand(i))) {
|
|
ConstantStruct *CS = dyn_cast<ConstantStruct>(C);
|
|
if (CS == 0) return 0;
|
|
if (CU->getValue() >= CS->getValues().size()) return 0;
|
|
C = cast<Constant>(CS->getValues()[CU->getValue()]);
|
|
} else if (ConstantSInt *CS = dyn_cast<ConstantSInt>(CE->getOperand(i))) {
|
|
ConstantArray *CA = dyn_cast<ConstantArray>(C);
|
|
if (CA == 0) return 0;
|
|
if ((uint64_t)CS->getValue() >= CA->getValues().size()) return 0;
|
|
C = cast<Constant>(CA->getValues()[CS->getValue()]);
|
|
} else
|
|
return 0;
|
|
return C;
|
|
}
|
|
|
|
// 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 SCCP::visitLoadInst(LoadInst &I) {
|
|
InstVal &IV = ValueState[&I];
|
|
if (IV.isOverdefined()) return;
|
|
|
|
InstVal &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() && !GV->isExternal()) {
|
|
markConstant(IV, &I, GV->getInitializer());
|
|
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->isExternal())
|
|
if (Constant *V =
|
|
GetGEPGlobalInitializer(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 SCCP::visitCallInst(CallInst &I) {
|
|
InstVal &IV = ValueState[&I];
|
|
if (IV.isOverdefined()) return;
|
|
|
|
Function *F = I.getCalledFunction();
|
|
if (F == 0 || !canConstantFoldCallTo(F)) {
|
|
markOverdefined(IV, &I);
|
|
return;
|
|
}
|
|
|
|
std::vector<Constant*> Operands;
|
|
Operands.reserve(I.getNumOperands()-1);
|
|
|
|
for (unsigned i = 1, e = I.getNumOperands(); i != e; ++i) {
|
|
InstVal &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());
|
|
}
|
|
|
|
if (Constant *C = ConstantFoldCall(F, Operands))
|
|
markConstant(IV, &I, C);
|
|
else
|
|
markOverdefined(IV, &I);
|
|
}
|