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Substantially refactor the SCCP class into an SCCP pass and an SCCPSolver

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class.  The only changes are minor:

 * Do not try to SCCP instructions that return void in the rewrite loop.
   This is silly and fool hardy, wasting a map lookup and adding an entry
   to the map which is never used.
 * If we decide something has an undefined value, rewrite it to undef,
   potentially leading to further simplications.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@17816 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2004-11-15 04:44:20 +00:00
parent 2e83ea5211
commit 82bec2cff0
1 changed files with 209 additions and 168 deletions
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377
lib/Transforms/Scalar/SCCP.cpp
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@ -89,12 +89,11 @@ public:
//===----------------------------------------------------------------------===//
// SCCP Class
//
// This class does all of the work of Sparse Conditional Constant Propagation.
//
namespace {
class SCCP : public FunctionPass, public InstVisitor<SCCP> {
/// SCCPSolver - This class is a general purpose solver for Sparse Conditional
/// Constant Propagation.
///
class SCCPSolver : public InstVisitor<SCCPSolver> {
std::set<BasicBlock*> BBExecutable;// The basic blocks that are executable
hash_map<Value*, InstVal> ValueState; // The state each value is in...
@ -121,22 +120,31 @@ class SCCP : public FunctionPass, public InstVisitor<SCCP> {
std::set<Edge> KnownFeasibleEdges;
public:
// 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();
/// MarkBlockExecutable - This method can be used by clients to mark all of
/// the blocks that are known to be intrinsically live in the processed unit.
void MarkBlockExecutable(BasicBlock *BB) {
DEBUG(std::cerr << "Marking Block Executable: " << BB->getName() << "\n");
BBExecutable.insert(BB); // Basic block is executable!
BBWorkList.push_back(BB); // Add the block to the work list!
}
/// Solve - Solve for constants and executable blocks.
///
void Solve();
/// getExecutableBlocks - Once we have solved for constants, return the set of
/// blocks that is known to be executable.
std::set<BasicBlock*> &getExecutableBlocks() {
return BBExecutable;
}
/// getValueMapping - Once we have solved for constants, return the mapping of
/// LLVM values to InstVals.
hash_map<Value*, InstVal> &getValueMapping() {
return ValueState;
}
//===--------------------------------------------------------------------===//
// The implementation of this class
//
private:
friend struct InstVisitor<SCCP>; // Allow callbacks from visitor
// 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.
@ -158,7 +166,8 @@ private:
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
// Only instructions go on the work list
OverdefinedInstWorkList.push_back(I);
}
}
inline void markOverdefined(Instruction *I) {
@ -206,12 +215,33 @@ private:
}
} 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!
MarkBlockExecutable(Dest);
}
}
// 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) {
// Only instructions use other variable values!
Instruction &I = cast<Instruction>(*U);
if (BBExecutable.count(I.getParent())) // Inst is executable?
visit(I);
}
private:
friend class InstVisitor<SCCPSolver>;
// visit implementations - Something changed in this instruction... Either an
// operand made a transition, or the instruction is newly executable. Change
@ -249,149 +279,13 @@ private:
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) {
// 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...
FunctionPass *llvm::createSCCPPass() {
return new SCCP();
}
//===----------------------------------------------------------------------===//
// SCCP Class Implementation
// runOnFunction() - Run the Sparse Conditional Constant Propagation algorithm,
// and return true if the function was modified.
//
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();
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();
DEBUG(std::cerr << "\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...
//
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...
while (!BBWorkList.empty()) {
BasicBlock *BB = BBWorkList.back();
BBWorkList.pop_back();
DEBUG(std::cerr << "\nPopped off BBWL: " << *BB);
// Notify all instructions in this basic block that they are newly
// executable.
visit(BB);
}
}
DEBUG(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 function, replacing them with
// constants if we have found them to be of constant values.
//
bool MadeChanges = false;
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];
if (IV.isConstant()) {
Constant *Const = IV.getConstant();
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... and delete it.
BI = BB->getInstList().erase(BI);
// Hey, we just changed something!
MadeChanges = true;
++NumInstRemoved;
} else {
++BI;
}
}
// 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) {
void SCCPSolver::getFeasibleSuccessors(TerminatorInst &TI,
std::vector<bool> &Succs) {
Succs.resize(TI.getNumSuccessors());
if (BranchInst *BI = dyn_cast<BranchInst>(&TI)) {
if (BI->isUnconditional()) {
@ -441,7 +335,7 @@ void SCCP::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 SCCP::isEdgeFeasible(BasicBlock *From, BasicBlock *To) {
bool SCCPSolver::isEdgeFeasible(BasicBlock *From, BasicBlock *To) {
assert(BBExecutable.count(To) && "Dest should always be alive!");
// Make sure the source basic block is executable!!
@ -514,7 +408,7 @@ bool SCCP::isEdgeFeasible(BasicBlock *From, BasicBlock *To) {
// 7. If a conditional branch has a value that is overdefined, make all
// successors executable.
//
void SCCP::visitPHINode(PHINode &PN) {
void SCCPSolver::visitPHINode(PHINode &PN) {
InstVal &PNIV = getValueState(&PN);
if (PNIV.isOverdefined()) {
// There may be instructions using this PHI node that are not overdefined
@ -586,7 +480,7 @@ void SCCP::visitPHINode(PHINode &PN) {
markConstant(PNIV, &PN, OperandVal); // Acquire operand value
}
void SCCP::visitTerminatorInst(TerminatorInst &TI) {
void SCCPSolver::visitTerminatorInst(TerminatorInst &TI) {
std::vector<bool> SuccFeasible;
getFeasibleSuccessors(TI, SuccFeasible);
@ -598,7 +492,7 @@ void SCCP::visitTerminatorInst(TerminatorInst &TI) {
markEdgeExecutable(BB, TI.getSuccessor(i));
}
void SCCP::visitCastInst(CastInst &I) {
void SCCPSolver::visitCastInst(CastInst &I) {
Value *V = I.getOperand(0);
InstVal &VState = getValueState(V);
if (VState.isOverdefined()) // Inherit overdefinedness of operand
@ -607,7 +501,7 @@ void SCCP::visitCastInst(CastInst &I) {
markConstant(&I, ConstantExpr::getCast(VState.getConstant(), I.getType()));
}
void SCCP::visitSelectInst(SelectInst &I) {
void SCCPSolver::visitSelectInst(SelectInst &I) {
InstVal &CondValue = getValueState(I.getCondition());
if (CondValue.isOverdefined())
markOverdefined(&I);
@ -630,7 +524,7 @@ void SCCP::visitSelectInst(SelectInst &I) {
}
// Handle BinaryOperators and Shift Instructions...
void SCCP::visitBinaryOperator(Instruction &I) {
void SCCPSolver::visitBinaryOperator(Instruction &I) {
InstVal &IV = ValueState[&I];
if (IV.isOverdefined()) return;
@ -716,7 +610,7 @@ void SCCP::visitBinaryOperator(Instruction &I) {
// Handle getelementptr instructions... if all operands are constants then we
// can turn this into a getelementptr ConstantExpr.
//
void SCCP::visitGetElementPtrInst(GetElementPtrInst &I) {
void SCCPSolver::visitGetElementPtrInst(GetElementPtrInst &I) {
InstVal &IV = ValueState[&I];
if (IV.isOverdefined()) return;
@ -769,7 +663,7 @@ static Constant *GetGEPGlobalInitializer(Constant *C, ConstantExpr *CE) {
// 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) {
void SCCPSolver::visitLoadInst(LoadInst &I) {
InstVal &IV = ValueState[&I];
if (IV.isOverdefined()) return;
@ -807,7 +701,7 @@ void SCCP::visitLoadInst(LoadInst &I) {
markOverdefined(IV, &I);
}
void SCCP::visitCallInst(CallInst &I) {
void SCCPSolver::visitCallInst(CallInst &I) {
InstVal &IV = ValueState[&I];
if (IV.isOverdefined()) return;
@ -837,3 +731,150 @@ void SCCP::visitCallInst(CallInst &I) {
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()) {
Instruction *I = OverdefinedInstWorkList.back();
OverdefinedInstWorkList.pop_back();
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 (Value::use_iterator UI = I->use_begin(), E = I->use_end();
UI != E; ++UI)
OperandChangedState(*UI);
}
// Process the instruction work list...
while (!InstWorkList.empty()) {
Instruction *I = InstWorkList.back();
InstWorkList.pop_back();
DEBUG(std::cerr << "\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();
DEBUG(std::cerr << "\nPopped off BBWL: " << *BB);
// Notify all instructions in this basic block that they are newly
// executable.
visit(BB);
}
}
}
namespace {
//===----------------------------------------------------------------------===//
//
/// SCCP Class - This class does all of the work of Sparse Conditional Constant
/// Propagation.
///
class SCCP : public FunctionPass, public InstVisitor<SCCP> {
public:
// 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();
}
};
RegisterOpt<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();
}
//===----------------------------------------------------------------------===//
// SCCP Class Implementation
// runOnFunction() - Run the Sparse Conditional Constant Propagation algorithm,
// and return true if the function was modified.
//
bool SCCP::runOnFunction(Function &F) {
SCCPSolver Solver;
// Mark the first block of the function as being executable.
Solver.MarkBlockExecutable(F.begin());
// Solve for constants.
Solver.Solve();
DEBUG(std::cerr << "SCCP on function '" << F.getName() << "'\n");
DEBUG(std::set<BasicBlock*> &ExecutableBBs = Solver.getExecutableBlocks();
for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I)
if (!ExecutableBBs.count(I))
std::cerr << " BasicBlock Dead:" << *I);
// 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;
hash_map<Value*, InstVal> &Values = Solver.getValueMapping();
for (Function::iterator BB = F.begin(), BBE = F.end(); BB != BBE; ++BB)
for (BasicBlock::iterator BI = BB->begin(), E = BB->end(); BI != E; ) {
Instruction *Inst = BI++;
if (Inst->getType() != Type::VoidTy) {
InstVal &IV = Values[Inst];
if (IV.isConstant() || IV.isUndefined()) {
Constant *Const;
if (IV.isConstant()) {
Const = IV.getConstant();
DEBUG(std::cerr << " Constant: " << *Const << " = " << *Inst);
} else {
Const = UndefValue::get(Inst->getType());
DEBUG(std::cerr << " Undefined: " << *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;
}