-//===- SCCP.cpp - Sparse Conditional Constant Propogation -----------------===//
+//===- SCCP.cpp - Sparse Conditional Constant Propagation -----------------===//
+//
+// The LLVM Compiler Infrastructure
//
-// This file implements sparse conditional constant propogation and merging:
+// This file was developed by the LLVM research group and is distributed under
+// the University of Illinois Open Source License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements sparse conditional constant propagation and merging:
//
// Specifically, this:
// * Assumes values are constant unless proven otherwise
// * Assumes BasicBlocks are dead unless proven otherwise
// * Proves values to be constant, and replaces them with constants
-// . Proves conditional branches constant, and unconditionalizes them
-// * Folds multiple identical constants in the constant pool together
+// * Proves conditional branches to be unconditional
//
// Notice that:
// * This pass has a habit of making definitions be dead. It is a good idea
//
//===----------------------------------------------------------------------===//
-#include "llvm/Transforms/Scalar/ConstantProp.h"
-#include "llvm/ConstantHandling.h"
+#include "llvm/Transforms/Scalar.h"
+#include "llvm/Constants.h"
#include "llvm/Function.h"
-#include "llvm/BasicBlock.h"
-#include "llvm/ConstantVals.h"
-#include "llvm/iPHINode.h"
-#include "llvm/iMemory.h"
-#include "llvm/iTerminators.h"
-#include "llvm/iOther.h"
+#include "llvm/GlobalVariable.h"
+#include "llvm/Instructions.h"
#include "llvm/Pass.h"
+#include "llvm/Type.h"
#include "llvm/Support/InstVisitor.h"
-#include "Support/STLExtras.h"
+#include "llvm/Transforms/Utils/Local.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/ADT/hash_map"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/ADT/STLExtras.h"
#include <algorithm>
-#include <map>
#include <set>
-#include <iostream>
-using std::cerr;
+using namespace llvm;
// InstVal class - This class represents the different lattice values that an
-// instruction may occupy. It is a simple class with value semantics. The
-// potential constant value that is pointed to is owned by the constant pool
-// for the method being optimized.
+// instruction may occupy. It is a simple class with value semantics.
//
+namespace {
+ Statistic<> NumInstRemoved("sccp", "Number of instructions removed");
+
class InstVal {
enum {
undefined, // This instruction has no known value
constant, // This instruction has a constant value
- // Range, // This instruction is known to fall within a range
overdefined // This instruction has an unknown value
} LatticeValue; // The current lattice position
Constant *ConstantVal; // If Constant value, the current value
inline bool isConstant() const { return LatticeValue == constant; }
inline bool isOverdefined() const { return LatticeValue == overdefined; }
- inline Constant *getConstant() const { return ConstantVal; }
+ inline Constant *getConstant() const {
+ assert(isConstant() && "Cannot get the constant of a non-constant!");
+ return ConstantVal;
+ }
};
+} // end anonymous namespace
//===----------------------------------------------------------------------===//
// SCCP Class
//
-// This class does all of the work of Sparse Conditional Constant Propogation.
-// It's public interface consists of a constructor and a doSCCP() method.
+// This class does all of the work of Sparse Conditional Constant Propagation.
//
-class SCCP : public InstVisitor<SCCP> {
- Function *M; // The function that we are working on
-
+namespace {
+class SCCP : public FunctionPass, public InstVisitor<SCCP> {
std::set<BasicBlock*> BBExecutable;// The basic blocks that are executable
- std::map<Value*, InstVal> ValueState; // The state each value is in...
-
+ hash_map<Value*, InstVal> ValueState; // The state each value is in...
+
+ // The reason for two worklists is that overdefined is the lowest state
+ // on the lattice, and moving things to overdefined as fast as possible
+ // makes SCCP converge much faster.
+ // By having a separate worklist, we accomplish this because everything
+ // possibly overdefined will become overdefined at the soonest possible
+ // point.
+ std::vector<Instruction*> OverdefinedInstWorkList;// The overdefined
+ // instruction work list
std::vector<Instruction*> InstWorkList;// The instruction work list
+
+
std::vector<BasicBlock*> BBWorkList; // The BasicBlock work list
- //===--------------------------------------------------------------------===//
- // The public interface for this class
- //
+ /// UsersOfOverdefinedPHIs - Keep track of any users of PHI nodes that are not
+ /// overdefined, despite the fact that the PHI node is overdefined.
+ std::multimap<PHINode*, Instruction*> UsersOfOverdefinedPHIs;
+
+ /// KnownFeasibleEdges - Entries in this set are edges which have already had
+ /// PHI nodes retriggered.
+ typedef std::pair<BasicBlock*,BasicBlock*> Edge;
+ std::set<Edge> KnownFeasibleEdges;
public:
- // SCCP Ctor - Save the method to operate on...
- inline SCCP(Function *f) : M(f) {}
+ // 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();
+ }
- // doSCCP() - Run the Sparse Conditional Constant Propogation algorithm, and
- // return true if the method was modified.
- bool doSCCP();
//===--------------------------------------------------------------------===//
// The implementation of this class
private:
friend class InstVisitor<SCCP>; // Allow callbacks from visitor
- // markValueOverdefined - Make a value be marked as "constant". If the value
+ // markConstant - Make a value be marked as "constant". If the value
// is not already a constant, add it to the instruction work list so that
// the users of the instruction are updated later.
//
- inline bool markConstant(Instruction *I, Constant *V) {
- //cerr << "markConstant: " << V << " = " << I;
- if (ValueState[I].markConstant(V)) {
+ inline void markConstant(InstVal &IV, Instruction *I, Constant *C) {
+ if (IV.markConstant(C)) {
+ DEBUG(std::cerr << "markConstant: " << *C << ": " << *I);
InstWorkList.push_back(I);
- return true;
}
- return false;
+ }
+ inline void markConstant(Instruction *I, Constant *C) {
+ markConstant(ValueState[I], I, C);
}
- // markValueOverdefined - Make a value be marked as "overdefined". If the
- // value is not already overdefined, add it to the instruction work list so
- // that the users of the instruction are updated later.
- //
- inline bool markOverdefined(Value *V) {
- if (ValueState[V].markOverdefined()) {
- if (Instruction *I = dyn_cast<Instruction>(V)) {
- //cerr << "markOverdefined: " << V;
- InstWorkList.push_back(I); // Only instructions go on the work list
- }
- return true;
+ // markOverdefined - Make a value be marked as "overdefined". If the
+ // value is not already overdefined, add it to the overdefined instruction
+ // work list so that the users of the instruction are updated later.
+
+ inline void markOverdefined(InstVal &IV, Instruction *I) {
+ if (IV.markOverdefined()) {
+ DEBUG(std::cerr << "markOverdefined: " << *I);
+ OverdefinedInstWorkList.push_back(I); // Only instructions go on the work list
}
- return false;
+ }
+ inline void markOverdefined(Instruction *I) {
+ markOverdefined(ValueState[I], I);
}
// getValueState - Return the InstVal object that corresponds to the value.
- // This function is neccesary because not all values should start out in the
+ // This function is necessary because not all values should start out in the
// underdefined state... Argument's should be overdefined, and
// constants should be marked as constants. If a value is not known to be an
// Instruction object, then use this accessor to get its value from the map.
//
inline InstVal &getValueState(Value *V) {
- std::map<Value*, InstVal>::iterator I = ValueState.find(V);
+ hash_map<Value*, InstVal>::iterator I = ValueState.find(V);
if (I != ValueState.end()) return I->second; // Common case, in the map
if (Constant *CPV = dyn_cast<Constant>(V)) { // Constants are constant
ValueState[CPV].markConstant(CPV);
} else if (isa<Argument>(V)) { // Arguments are overdefined
ValueState[V].markOverdefined();
- }
+ }
// All others are underdefined by default...
return ValueState[V];
}
- // markExecutable - Mark a basic block as executable, adding it to the BB
+ // markEdgeExecutable - Mark a basic block as executable, adding it to the BB
// work list if it is not already executable...
//
- void markExecutable(BasicBlock *BB) {
- if (BBExecutable.count(BB)) return;
- //cerr << "Marking BB Executable: " << BB;
- BBExecutable.insert(BB); // Basic block is executable!
- BBWorkList.push_back(BB); // Add the block to the work list!
+ void markEdgeExecutable(BasicBlock *Source, BasicBlock *Dest) {
+ if (!KnownFeasibleEdges.insert(Edge(Source, Dest)).second)
+ return; // This edge is already known to be executable!
+
+ if (BBExecutable.count(Dest)) {
+ DEBUG(std::cerr << "Marking Edge Executable: " << Source->getName()
+ << " -> " << Dest->getName() << "\n");
+
+ // The destination is already executable, but we just made an edge
+ // feasible that wasn't before. Revisit the PHI nodes in the block
+ // because they have potentially new operands.
+ for (BasicBlock::iterator I = Dest->begin();
+ PHINode *PN = dyn_cast<PHINode>(I); ++I)
+ visitPHINode(*PN);
+
+ } else {
+ DEBUG(std::cerr << "Marking Block Executable: " << Dest->getName()<<"\n");
+ BBExecutable.insert(Dest); // Basic block is executable!
+ BBWorkList.push_back(Dest); // Add the block to the work list!
+ }
}
// operand made a transition, or the instruction is newly executable. Change
// the value type of I to reflect these changes if appropriate.
//
- void visitPHINode(PHINode *I);
+ void visitPHINode(PHINode &I);
// Terminators
- void visitReturnInst(ReturnInst *I) { /*does not have an effect*/ }
- void visitBranchInst(BranchInst *I);
- void visitSwitchInst(SwitchInst *I);
+ void visitReturnInst(ReturnInst &I) { /*does not have an effect*/ }
+ void visitTerminatorInst(TerminatorInst &TI);
- void visitUnaryOperator(Instruction *I);
- void visitCastInst(CastInst *I) { visitUnaryOperator(I); }
- void visitBinaryOperator(Instruction *I);
- void visitShiftInst(ShiftInst *I) { visitBinaryOperator(I); }
+ void visitCastInst(CastInst &I);
+ void visitSelectInst(SelectInst &I);
+ void visitBinaryOperator(Instruction &I);
+ void visitShiftInst(ShiftInst &I) { visitBinaryOperator(I); }
// Instructions that cannot be folded away...
- void visitMemAccessInst (Instruction *I) { markOverdefined(I); }
- void visitCallInst (Instruction *I) { markOverdefined(I); }
- void visitInvokeInst (Instruction *I) { markOverdefined(I); }
- void visitAllocationInst(Instruction *I) { markOverdefined(I); }
- void visitFreeInst (Instruction *I) { markOverdefined(I); }
+ void visitStoreInst (Instruction &I) { /*returns void*/ }
+ void visitLoadInst (LoadInst &I);
+ void visitGetElementPtrInst(GetElementPtrInst &I);
+ void visitCallInst (CallInst &I);
+ void visitInvokeInst (TerminatorInst &I) {
+ if (I.getType() != Type::VoidTy) markOverdefined(&I);
+ visitTerminatorInst(I);
+ }
+ void visitUnwindInst (TerminatorInst &I) { /*returns void*/ }
+ void visitAllocationInst(Instruction &I) { markOverdefined(&I); }
+ void visitVANextInst (Instruction &I) { markOverdefined(&I); }
+ void visitVAArgInst (Instruction &I) { markOverdefined(&I); }
+ void visitFreeInst (Instruction &I) { /*returns void*/ }
- void visitInstruction(Instruction *I) {
+ void visitInstruction(Instruction &I) {
// If a new instruction is added to LLVM that we don't handle...
- cerr << "SCCP: Don't know how to handle: " << I;
- markOverdefined(I); // Just in case
+ std::cerr << "SCCP: Don't know how to handle: " << I;
+ markOverdefined(&I); // Just in case
}
+ // getFeasibleSuccessors - Return a vector of booleans to indicate which
+ // successors are reachable from a given terminator instruction.
+ //
+ void getFeasibleSuccessors(TerminatorInst &TI, std::vector<bool> &Succs);
+
+ // isEdgeFeasible - Return true if the control flow edge from the 'From' basic
+ // block to the 'To' basic block is currently feasible...
+ //
+ bool isEdgeFeasible(BasicBlock *From, BasicBlock *To);
+
// OperandChangedState - This method is invoked on all of the users of an
// instruction that was just changed state somehow.... Based on this
// information, we need to update the specified user of this instruction.
//
- void OperandChangedState(User *U);
+ void OperandChangedState(User *U) {
+ // Only instructions use other variable values!
+ Instruction &I = cast<Instruction>(*U);
+ if (BBExecutable.count(I.getParent())) // Inst is executable?
+ visit(I);
+ }
};
+ RegisterOpt<SCCP> X("sccp", "Sparse Conditional Constant Propagation");
+} // end anonymous namespace
+
+
+// createSCCPPass - This is the public interface to this file...
+Pass *llvm::createSCCPPass() {
+ return new SCCP();
+}
+
//===----------------------------------------------------------------------===//
// SCCP Class Implementation
-// doSCCP() - Run the Sparse Conditional Constant Propogation algorithm, and
-// return true if the method was modified.
+// runOnFunction() - Run the Sparse Conditional Constant Propagation algorithm,
+// and return true if the function was modified.
//
-bool SCCP::doSCCP() {
- // Mark the first block of the method as being executable...
- markExecutable(M->front());
+bool SCCP::runOnFunction(Function &F) {
+ // Mark the first block of the function as being executable...
+ BBExecutable.insert(F.begin()); // Basic block is executable!
+ BBWorkList.push_back(F.begin()); // Add the block to the work list!
+
+ // Process the work lists until they are empty!
+ while (!BBWorkList.empty() || !InstWorkList.empty() ||
+ !OverdefinedInstWorkList.empty()) {
+ // Process the instruction work list...
+ while (!OverdefinedInstWorkList.empty()) {
+ Instruction *I = OverdefinedInstWorkList.back();
+ OverdefinedInstWorkList.pop_back();
- // Process the work lists until their are empty!
- while (!BBWorkList.empty() || !InstWorkList.empty()) {
+ DEBUG(std::cerr << "\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_each(I->use_begin(), I->use_end(),
+ bind_obj(this, &SCCP::OperandChangedState));
+ }
// Process the instruction work list...
while (!InstWorkList.empty()) {
Instruction *I = InstWorkList.back();
InstWorkList.pop_back();
- //cerr << "\nPopped off I-WL: " << I;
-
+ DEBUG(std::cerr << "\nPopped off I-WL: " << *I);
// "I" got into the work list because it either made the transition from
- // bottom to constant, or to Overdefined.
+ // 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_each(I->use_begin(), I->use_end(),
- bind_obj(this, &SCCP::OperandChangedState));
+ InstVal &Ival = getValueState (I);
+ if (!Ival.isOverdefined())
+ for_each(I->use_begin(), I->use_end(),
+ bind_obj(this, &SCCP::OperandChangedState));
}
// Process the basic block work list...
BasicBlock *BB = BBWorkList.back();
BBWorkList.pop_back();
- //cerr << "\nPopped off BBWL: " << BB;
-
- // If this block only has a single successor, mark it as executable as
- // well... if not, terminate the do loop.
- //
- if (BB->getTerminator()->getNumSuccessors() == 1)
- markExecutable(BB->getTerminator()->getSuccessor(0));
+ DEBUG(std::cerr << "\nPopped off BBWL: " << *BB);
// Notify all instructions in this basic block that they are newly
// executable.
}
}
-#if 0
- for (Function::iterator BBI = M->begin(), BBEnd = M->end();
- BBI != BBEnd; ++BBI)
- if (!BBExecutable.count(*BBI))
- cerr << "BasicBlock Dead:" << *BBI;
-#endif
-
+ if (DebugFlag) {
+ for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I)
+ if (!BBExecutable.count(I))
+ std::cerr << "BasicBlock Dead:" << *I;
+ }
- // Iterate over all of the instructions in a method, replacing them with
+ // Iterate over all of the instructions in a function, replacing them with
// constants if we have found them to be of constant values.
//
bool MadeChanges = false;
- for (Function::iterator MI = M->begin(), ME = M->end(); MI != ME; ++MI) {
- BasicBlock *BB = *MI;
+ for (Function::iterator BB = F.begin(), BBE = F.end(); BB != BBE; ++BB)
for (BasicBlock::iterator BI = BB->begin(); BI != BB->end();) {
- Instruction *Inst = *BI;
- InstVal &IV = ValueState[Inst];
+ Instruction &Inst = *BI;
+ InstVal &IV = ValueState[&Inst];
if (IV.isConstant()) {
Constant *Const = IV.getConstant();
- // cerr << "Constant: " << Inst << " is: " << Const;
+ DEBUG(std::cerr << "Constant: " << *Const << " = " << Inst);
// Replaces all of the uses of a variable with uses of the constant.
- Inst->replaceAllUsesWith(Const);
-
- // Remove the operator from the list of definitions...
- BB->getInstList().remove(BI);
+ Inst.replaceAllUsesWith(Const);
- // The new constant inherits the old name of the operator...
- if (Inst->hasName() && !Const->hasName())
- Const->setName(Inst->getName(), M->getSymbolTableSure());
-
- // Delete the operator now...
- delete Inst;
+ // Remove the operator from the list of definitions... and delete it.
+ BI = BB->getInstList().erase(BI);
// Hey, we just changed something!
MadeChanges = true;
- } else if (TerminatorInst *TI = dyn_cast<TerminatorInst>(Inst)) {
- MadeChanges |= ConstantFoldTerminator(BB, BI, TI);
+ ++NumInstRemoved;
+ } else {
+ ++BI;
}
-
- ++BI;
}
- }
- // Merge identical constants last: this is important because we may have just
- // introduced constants that already exist, and we don't want to pollute later
- // stages with extraneous constants.
- //
+ // Reset state so that the next invocation will have empty data structures
+ BBExecutable.clear();
+ ValueState.clear();
+ std::vector<Instruction*>().swap(OverdefinedInstWorkList);
+ std::vector<Instruction*>().swap(InstWorkList);
+ std::vector<BasicBlock*>().swap(BBWorkList);
+
return MadeChanges;
}
+// getFeasibleSuccessors - Return a vector of booleans to indicate which
+// successors are reachable from a given terminator instruction.
+//
+void SCCP::getFeasibleSuccessors(TerminatorInst &TI, std::vector<bool> &Succs) {
+ Succs.resize(TI.getNumSuccessors());
+ if (BranchInst *BI = dyn_cast<BranchInst>(&TI)) {
+ if (BI->isUnconditional()) {
+ Succs[0] = true;
+ } else {
+ InstVal &BCValue = getValueState(BI->getCondition());
+ if (BCValue.isOverdefined() ||
+ (BCValue.isConstant() && !isa<ConstantBool>(BCValue.getConstant()))) {
+ // Overdefined condition variables, and branches on unfoldable constant
+ // conditions, mean the branch could go either way.
+ Succs[0] = Succs[1] = true;
+ } else if (BCValue.isConstant()) {
+ // Constant condition variables mean the branch can only go a single way
+ Succs[BCValue.getConstant() == ConstantBool::False] = true;
+ }
+ }
+ } else if (InvokeInst *II = dyn_cast<InvokeInst>(&TI)) {
+ // Invoke instructions successors are always executable.
+ Succs[0] = Succs[1] = true;
+ } else if (SwitchInst *SI = dyn_cast<SwitchInst>(&TI)) {
+ InstVal &SCValue = getValueState(SI->getCondition());
+ if (SCValue.isOverdefined() || // Overdefined condition?
+ (SCValue.isConstant() && !isa<ConstantInt>(SCValue.getConstant()))) {
+ // All destinations are executable!
+ Succs.assign(TI.getNumSuccessors(), true);
+ } else if (SCValue.isConstant()) {
+ Constant *CPV = SCValue.getConstant();
+ // 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 right branch...
+ Succs[i] = true;
+ return;
+ }
+ }
+
+ // Constant value not equal to any of the branches... must execute
+ // default branch then...
+ Succs[0] = true;
+ }
+ } else {
+ std::cerr << "SCCP: Don't know how to handle: " << TI;
+ Succs.assign(TI.getNumSuccessors(), true);
+ }
+}
+
+
+// isEdgeFeasible - Return true if the control flow edge from the 'From' basic
+// block to the 'To' basic block is currently feasible...
+//
+bool SCCP::isEdgeFeasible(BasicBlock *From, BasicBlock *To) {
+ assert(BBExecutable.count(To) && "Dest should always be alive!");
+
+ // Make sure the source basic block is executable!!
+ if (!BBExecutable.count(From)) return false;
+
+ // Check to make sure this edge itself is actually feasible now...
+ TerminatorInst *TI = From->getTerminator();
+ if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
+ if (BI->isUnconditional())
+ return true;
+ else {
+ InstVal &BCValue = getValueState(BI->getCondition());
+ 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<ConstantBool>(BCValue.getConstant())) return true;
+
+ // Constant condition variables mean the branch can only go a single way
+ return BI->getSuccessor(BCValue.getConstant() ==
+ ConstantBool::False) == To;
+ }
+ return false;
+ }
+ } else if (InvokeInst *II = dyn_cast<InvokeInst>(TI)) {
+ // Invoke instructions successors are always executable.
+ return true;
+ } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
+ InstVal &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 {
+ 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
// 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
+ }
-void SCCP::visitPHINode(PHINode *PN) {
- unsigned NumValues = PN->getNumIncomingValues(), i;
- InstVal *OperandIV = 0;
+ // 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. If they are constant and don't agree, the PHI is overdefined.
// If there are no executable operands, the PHI remains undefined.
//
- for (i = 0; i < NumValues; ++i) {
- if (BBExecutable.count(PN->getIncomingBlock(i))) {
- InstVal &IV = getValueState(PN->getIncomingValue(i));
- if (IV.isUndefined()) continue; // Doesn't influence PHI node.
+ 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(PN);
+ markOverdefined(PNIV, &PN);
return;
}
- if (OperandIV == 0) { // Grab the first value...
- OperandIV = &IV;
+ 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() != OperandIV->getConstant()) {
+ if (IV.getConstant() != OperandVal) {
// Yes there is. This means the PHI node is not constant.
// You must be overdefined poor PHI.
//
- markOverdefined(PN); // The PHI node now becomes overdefined
+ 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 OperandIV is a pointer to one
- // of their InstVal's) or OperandIV is null because there are no defined
- // incoming arguments. If this is the case, the PHI remains undefined.
+ // 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 (OperandIV) {
- assert(OperandIV->isConstant() && "Should only be here for constants!");
- markConstant(PN, OperandIV->getConstant()); // Aquire operand value
- }
+ if (OperandVal)
+ markConstant(PNIV, &PN, OperandVal); // Acquire operand value
}
-void SCCP::visitBranchInst(BranchInst *BI) {
- if (BI->isUnconditional())
- return; // Unconditional branches are already handled!
-
- InstVal &BCValue = getValueState(BI->getCondition());
- if (BCValue.isOverdefined()) {
- // Overdefined condition variables mean the branch could go either way.
- markExecutable(BI->getSuccessor(0));
- markExecutable(BI->getSuccessor(1));
- } else if (BCValue.isConstant()) {
- // Constant condition variables mean the branch can only go a single way.
- if (BCValue.getConstant() == ConstantBool::True)
- markExecutable(BI->getSuccessor(0));
- else
- markExecutable(BI->getSuccessor(1));
- }
-}
+void SCCP::visitTerminatorInst(TerminatorInst &TI) {
+ std::vector<bool> SuccFeasible;
+ getFeasibleSuccessors(TI, SuccFeasible);
-void SCCP::visitSwitchInst(SwitchInst *SI) {
- InstVal &SCValue = getValueState(SI->getCondition());
- if (SCValue.isOverdefined()) { // Overdefined condition? All dests are exe
- for(unsigned i = 0, E = SI->getNumSuccessors(); i != E; ++i)
- markExecutable(SI->getSuccessor(i));
- } else if (SCValue.isConstant()) {
- Constant *CPV = SCValue.getConstant();
- // 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 right branch...
- markExecutable(SI->getSuccessor(i));
- return;
- }
- }
+ BasicBlock *BB = TI.getParent();
- // Constant value not equal to any of the branches... must execute
- // default branch then...
- markExecutable(SI->getDefaultDest());
- }
+ // 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::visitUnaryOperator(Instruction *I) {
- Value *V = I->getOperand(0);
+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()) { // Propogate constant value
- Constant *Result = isa<CastInst>(I)
- ? ConstantFoldCastInstruction(VState.getConstant(), I->getType())
- : ConstantFoldUnaryInstruction(I->getOpcode(), VState.getConstant());
-
- if (Result) {
- // This instruction constant folds!
- markConstant(I, Result);
- } else {
- markOverdefined(I); // Don't know how to fold this instruction. :(
- }
+ 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 &V1State = getValueState(I->getOperand(0));
- InstVal &V2State = getValueState(I->getOperand(1));
+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()) {
- markOverdefined(I);
+ // 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()) {
- Constant *Result = ConstantFoldBinaryInstruction(I->getOpcode(),
- V1State.getConstant(),
- V2State.getConstant());
- if (Result)
- markConstant(I, Result); // This instruction constant fold!s
- else
- markOverdefined(I); // Don't know how to fold this instruction. :(
+ markConstant(IV, &I, ConstantExpr::get(I.getOpcode(), V1State.getConstant(),
+ V2State.getConstant()));
}
}
-// OperandChangedState - This method is invoked on all of the users of an
-// instruction that was just changed state somehow.... Based on this
-// information, we need to update the specified user of this instruction.
+// Handle getelementptr instructions... if all operands are constants then we
+// can turn this into a getelementptr ConstantExpr.
//
-void SCCP::OperandChangedState(User *U) {
- // Only instructions use other variable values!
- Instruction *I = cast<Instruction>(U);
- if (!BBExecutable.count(I->getParent())) return; // Inst not executable yet!
+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...
- visit(I);
+ markConstant(IV, &I, ConstantExpr::getGetElementPtr(Ptr, Operands));
}
-namespace {
- // SCCPPass - Use Sparse Conditional Constant Propogation
- // to prove whether a value is constant and whether blocks are used.
- //
- struct SCCPPass : public MethodPass {
- inline bool runOnMethod(Function *F) {
- SCCP S(F);
- return S.doSCCP();
+/// 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->getNumOperands()) return 0;
+ C = CS->getOperand(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->getNumOperands()) return 0;
+ C = CA->getOperand(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);
}
-Pass *createSCCPPass() {
- return new SCCPPass();
+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);
}
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