// * 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
+// * Proves conditional branches constant, and unconditionalizes them
// * Folds multiple identical constants in the constant pool together
//
// Notice that:
//
//===----------------------------------------------------------------------===//
-#include "llvm/Transforms/Scalar/ConstantProp.h"
+#include "llvm/Transforms/Scalar.h"
#include "llvm/ConstantHandling.h"
#include "llvm/Function.h"
#include "llvm/iPHINode.h"
#include "llvm/Pass.h"
#include "llvm/Support/InstVisitor.h"
#include "Support/STLExtras.h"
+#include "Support/StatisticReporter.h"
#include <algorithm>
#include <set>
-#include <iostream>
using std::cerr;
+static Statistic<> NumInstRemoved("sccp\t\t- Number of instructions removed");
+
// InstVal class - This class represents the different lattice values that an
// instruction may occupy. It is a simple class with value semantics.
//
+namespace {
class InstVal {
enum {
undefined, // This instruction has no known value
inline Constant *getConstant() const { 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() function.
//
-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...
std::vector<Instruction*> InstWorkList;// The instruction work list
std::vector<BasicBlock*> BBWorkList; // The BasicBlock work list
+public:
- //===--------------------------------------------------------------------===//
- // The public interface for this class
+ // runOnFunction - Run the Sparse Conditional Constant Propogation algorithm,
+ // and return true if the function was modified.
//
-public:
+ bool runOnFunction(Function &F);
- // SCCP Ctor - Save the function to operate on...
- inline SCCP(Function *f) : M(f) {}
+ virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+ AU.preservesCFG();
+ }
- // doSCCP() - Run the Sparse Conditional Constant Propogation algorithm, and
- // return true if the function was modified.
- bool doSCCP();
//===--------------------------------------------------------------------===//
// The implementation of this class
// the users of the instruction are updated later.
//
inline bool markConstant(Instruction *I, Constant *V) {
- //cerr << "markConstant: " << V << " = " << I;
+ DEBUG(cerr << "markConstant: " << V << " = " << I);
+
if (ValueState[I].markConstant(V)) {
InstWorkList.push_back(I);
return true;
inline bool markOverdefined(Value *V) {
if (ValueState[V].markOverdefined()) {
if (Instruction *I = dyn_cast<Instruction>(V)) {
- //cerr << "markOverdefined: " << V;
+ DEBUG(cerr << "markOverdefined: " << V);
InstWorkList.push_back(I); // Only instructions go on the work list
}
return true;
//
void markExecutable(BasicBlock *BB) {
if (BBExecutable.count(BB)) return;
- //cerr << "Marking BB Executable: " << BB;
+ DEBUG(cerr << "Marking BB Executable: " << *BB);
BBExecutable.insert(BB); // Basic block is executable!
BBWorkList.push_back(BB); // 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 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 visitInstruction(Instruction *I) {
+ void visitStoreInst (Instruction &I) { /*returns void*/ }
+ 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) { /*returns void*/ }
+
+ 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
+ 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())) return;// Inst not executable yet!
+ visit(I);
+ }
};
+ RegisterOpt<SCCP> X("sccp", "Sparse Conditional Constant Propogation");
+} // end anonymous namespace
+
+
+// createSCCPPass - This is the public interface to this file...
+//
+Pass *createSCCPPass() {
+ return new SCCP();
+}
+
//===----------------------------------------------------------------------===//
// SCCP Class Implementation
-// doSCCP() - Run the Sparse Conditional Constant Propogation algorithm, and
-// return true if the function was modified.
+// runOnFunction() - Run the Sparse Conditional Constant Propogation algorithm,
+// and return true if the function was modified.
//
-bool SCCP::doSCCP() {
+bool SCCP::runOnFunction(Function &F) {
// Mark the first block of the function as being executable...
- markExecutable(M->front());
+ markExecutable(&F.front());
// Process the work lists until their are empty!
while (!BBWorkList.empty() || !InstWorkList.empty()) {
Instruction *I = InstWorkList.back();
InstWorkList.pop_back();
- //cerr << "\nPopped off I-WL: " << I;
+ DEBUG(cerr << "\nPopped off I-WL: " << I);
// "I" got into the work list because it either made the transition from
BasicBlock *BB = BBWorkList.back();
BBWorkList.pop_back();
- //cerr << "\nPopped off BBWL: " << BB;
+ DEBUG(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 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))
+ 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 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(cerr << "Constant: " << Const << " = " << Inst);
// Replaces all of the uses of a variable with uses of the constant.
- Inst->replaceAllUsesWith(Const);
+ Inst.replaceAllUsesWith(Const);
- // Remove the operator from the list of definitions...
- BB->getInstList().remove(BI);
-
- // 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();
+
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) {
+ assert(Succs.size() == TI.getNumSuccessors() && "Succs vector wrong size!");
+ if (BranchInst *BI = dyn_cast<BranchInst>(&TI)) {
+ if (BI->isUnconditional()) {
+ Succs[0] = true;
+ } else {
+ InstVal &BCValue = getValueState(BI->getCondition());
+ if (BCValue.isOverdefined()) {
+ // Overdefined condition variables 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?
+ // 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 {
+ 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 *FT = From->getTerminator();
+ std::vector<bool> SuccFeasible(FT->getNumSuccessors());
+ getFeasibleSuccessors(*FT, SuccFeasible);
+
+ // Check all edges from From to To. If any are feasible, return true.
+ for (unsigned i = 0, e = SuccFeasible.size(); i != e; ++i)
+ if (FT->getSuccessor(i) == To && SuccFeasible[i])
+ return true;
+
+ // Otherwise, none of the edges are actually feasible at this time...
+ return false;
+}
+
// 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
// successors executable.
//
-void SCCP::visitPHINode(PHINode *PN) {
- unsigned NumValues = PN->getNumIncomingValues(), i;
+void SCCP::visitPHINode(PHINode &PN) {
+ unsigned NumValues = PN.getNumIncomingValues(), i;
InstVal *OperandIV = 0;
// Look at all of the executable operands of the PHI node. If any of them
// 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 (isEdgeFeasible(PN.getIncomingBlock(i), PN.getParent())) {
+ InstVal &IV = getValueState(PN.getIncomingValue(i));
if (IV.isUndefined()) continue; // Doesn't influence PHI node.
if (IV.isOverdefined()) { // PHI node becomes overdefined!
- markOverdefined(PN);
+ markOverdefined(&PN);
return;
}
// 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(&PN); // The PHI node now becomes overdefined
return; // I'm done analyzing you
}
}
//
if (OperandIV) {
assert(OperandIV->isConstant() && "Should only be here for constants!");
- markConstant(PN, OperandIV->getConstant()); // Aquire operand value
+ markConstant(&PN, OperandIV->getConstant()); // Aquire 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(TI.getNumSuccessors());
+ 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;
- }
- }
+ // Mark all feasible successors executable...
+ for (unsigned i = 0, e = SuccFeasible.size(); i != e; ++i)
+ if (SuccFeasible[i]) {
+ BasicBlock *Succ = TI.getSuccessor(i);
+ markExecutable(Succ);
- // Constant value not equal to any of the branches... must execute
- // default branch then...
- markExecutable(SI->getDefaultDest());
- }
+ // Visit all of the PHI nodes that merge values from this block...
+ // Because this edge may be new executable, and PHI nodes that used to be
+ // constant now may not be.
+ //
+ for (BasicBlock::iterator I = Succ->begin();
+ PHINode *PN = dyn_cast<PHINode>(&*I); ++I)
+ visitPHINode(*PN);
+ }
}
-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);
+ markOverdefined(&I);
} else if (VState.isConstant()) { // Propogate constant value
- Constant *Result = isa<CastInst>(I)
- ? ConstantFoldCastInstruction(VState.getConstant(), I->getType())
- : ConstantFoldUnaryInstruction(I->getOpcode(), VState.getConstant());
+ Constant *Result =
+ ConstantFoldCastInstruction(VState.getConstant(), I.getType());
if (Result) {
// This instruction constant folds!
- markConstant(I, Result);
+ markConstant(&I, Result);
} else {
- markOverdefined(I); // Don't know how to fold this instruction. :(
+ markOverdefined(&I); // Don't know how to fold this instruction. :(
}
}
}
// 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 &V1State = getValueState(I.getOperand(0));
+ InstVal &V2State = getValueState(I.getOperand(1));
if (V1State.isOverdefined() || V2State.isOverdefined()) {
- markOverdefined(I);
+ markOverdefined(&I);
} else if (V1State.isConstant() && V2State.isConstant()) {
- Constant *Result = ConstantFoldBinaryInstruction(I->getOpcode(),
- V1State.getConstant(),
- V2State.getConstant());
+ Constant *Result = 0;
+ if (isa<BinaryOperator>(I))
+ Result = ConstantFoldBinaryInstruction(I.getOpcode(),
+ V1State.getConstant(),
+ V2State.getConstant());
+ else if (isa<ShiftInst>(I))
+ Result = ConstantFoldShiftInstruction(I.getOpcode(),
+ V1State.getConstant(),
+ V2State.getConstant());
if (Result)
- markConstant(I, Result); // This instruction constant fold!s
+ markConstant(&I, Result); // This instruction constant folds!
else
- markOverdefined(I); // Don't know how to fold this instruction. :(
+ markOverdefined(&I); // Don't know how to fold this instruction. :(
}
}
-
-// 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 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!
-
- visit(I);
-}
-
-namespace {
- // SCCPPass - Use Sparse Conditional Constant Propogation
- // to prove whether a value is constant and whether blocks are used.
- //
- struct SCCPPass : public FunctionPass {
- const char *getPassName() const {
- return "Sparse Conditional Constant Propogation";
- }
-
- inline bool runOnFunction(Function *F) {
- SCCP S(F);
- return S.doSCCP();
- }
- virtual void getAnalysisUsage(AnalysisUsage &AU) const {
- // FIXME: SCCP does not preserve the CFG because it folds terminators!
- //AU.preservesCFG();
- }
- };
-}
-
-Pass *createSCCPPass() {
- return new SCCPPass();
-}
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