--- /dev/null
+//===- SCCP.cpp - Sparse Conditional Constant Propogation -----------------===//
+//
+// This file implements sparse conditional constant propogation 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
+//
+// Notice that:
+// * This pass has a habit of making definitions be dead. It is a good idea
+// to to run a DCE pass sometime after running this pass.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Opt/AllOpts.h"
+#include "llvm/Method.h"
+#include "llvm/BasicBlock.h"
+#include "llvm/ConstPoolVals.h"
+#include "llvm/ConstantPool.h"
+#include "llvm/Opt/ConstantHandling.h"
+#include "llvm/InstrTypes.h"
+#include "llvm/iOther.h"
+#include "llvm/iTerminators.h"
+//#include "llvm/Assembly/Writer.h"
+#include <algorithm>
+#include <map>
+#include <set>
+
+
+// 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.
+//
+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
+ ConstPoolVal *ConstantVal; // If Constant value, the current value
+public:
+ inline InstVal() : LatticeValue(Undefined), ConstantVal(0) {}
+
+ // markOverdefined - Return true if this is a new status to be in...
+ inline bool markOverdefined() {
+ if (LatticeValue != Overdefined) {
+ LatticeValue = Overdefined;
+ return true;
+ }
+ return false;
+ }
+
+ // markConstant - Return true if this is a new status for us...
+ inline bool markConstant(ConstPoolVal *V) {
+ if (LatticeValue != Constant) {
+ LatticeValue = Constant;
+ ConstantVal = V;
+ return true;
+ } else {
+ assert(ConstantVal->equals(V) && "Marking constant with different value");
+ }
+ return false;
+ }
+
+ inline bool isUndefined() const { return LatticeValue == Undefined; }
+ inline bool isConstant() const { return LatticeValue == Constant; }
+ inline bool isOverdefined() const { return LatticeValue == Overdefined; }
+
+ inline ConstPoolVal *getConstant() const { return ConstantVal; }
+};
+
+
+
+//===----------------------------------------------------------------------===//
+// 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.
+//
+class SCCP {
+ Method *M; // The method that we are working on...
+
+ set<BasicBlock*> BBExecutable; // The basic blocks that are executable
+ map<Value*, InstVal> ValueState; // The state each value is in...
+
+ vector<Instruction*> InstWorkList; // The instruction work list
+ vector<BasicBlock*> BBWorkList; // The BasicBlock work list
+
+ //===--------------------------------------------------------------------===//
+ // The public interface for this class
+ //
+public:
+
+ // SCCP Ctor - Save the method to operate on...
+ inline SCCP(Method *m) : M(m) {}
+
+ // doSCCP() - Run the Sparse Conditional Constant Propogation algorithm, and
+ // return true if the method was modified.
+ bool doSCCP();
+
+ //===--------------------------------------------------------------------===//
+ // The implementation of this class
+ //
+private:
+
+ // markValueOverdefined - 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, ConstPoolVal *V) {
+ //cerr << "markConstant: " << V << " = " << I;
+ if (ValueState[I].markConstant(V)) {
+ InstWorkList.push_back(I);
+ return true;
+ }
+ return false;
+ }
+
+ // 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 = V->castInstruction()) {
+ //cerr << "markOverdefined: " << V;
+ InstWorkList.push_back(I); // Only instructions go on the work list
+ }
+ return true;
+ }
+ return false;
+ }
+
+ // getValueState - Return the InstVal object that corresponds to the value.
+ // This function is neccesary because not all values should start out in the
+ // underdefined state... MethodArgument'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) {
+ map<Value*, InstVal>::iterator I = ValueState.find(V);
+ if (I != ValueState.end()) return I->second; // Common case, in the map
+
+ if (ConstPoolVal *CPV = V->castConstant()) { // Constants are constant
+ ValueState[CPV].markConstant(CPV);
+ } else if (V->isMethodArgument()) { // MethodArgs 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
+ // 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 OperandChangedState(User *U);
+ void UpdateInstruction(Instruction *I);
+};
+
+
+
+//===----------------------------------------------------------------------===//
+// SCCP Class Implementation
+
+
+// doSCCP() - Run the Sparse Conditional Constant Propogation algorithm, and
+// return true if the method was modified.
+//
+bool SCCP::doSCCP() {
+ // Mark the first block of the method as being executable...
+ markExecutable(M->front());
+
+ // Process the work lists until their are empty!
+ while (!BBWorkList.empty() || !InstWorkList.empty()) {
+ // Process the instruction work list...
+ while (!InstWorkList.empty()) {
+ Instruction *I = InstWorkList.back();
+ InstWorkList.pop_back();
+
+ //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.
+ //
+ // 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 basic block work list...
+ while (!BBWorkList.empty()) {
+ 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));
+
+ // Loop over all of the instructions and notify them that they are newly
+ // executable...
+ for_each(BB->begin(), BB->end(),
+ bind_obj(this, &SCCP::UpdateInstruction));
+ }
+ }
+
+#if 0
+ for (Method::iterator BBI = M->begin(), BBEnd = M->end(); BBI != BBEnd; ++BBI)
+ if (!BBExecutable.count(*BBI))
+ cerr << "BasicBlock Dead:" << *BBI;
+#endif
+
+
+ // Iterate over all of the instructions in a method, replacing them with
+ // constants if we have found them to be of constant values.
+ //
+ bool MadeChanges = false;
+ for (Method::inst_iterator II = M->inst_begin(); II != M->inst_end(); ) {
+ Instruction *Inst = *II;
+ InstVal &IV = ValueState[Inst];
+ if (IV.isConstant()) {
+ ConstPoolVal *Const = IV.getConstant();
+ // cerr << "Constant: " << Inst << " is: " << Const;
+
+ // Replaces all of the uses of a variable with uses of the constant.
+ Inst->replaceAllUsesWith(Const);
+
+ // Remove the operator from the list of definitions...
+ Inst->getParent()->getInstList().remove(II.getInstructionIterator());
+
+ // The new constant inherits the old name of the operator...
+ if (Inst->hasName() && !Const->hasName())
+ Const->setName(Inst->getName());
+
+ // Delete the operator now...
+ delete Inst;
+
+ // Incrementing the iterator in an unchecked manner could mess up the
+ // internals of 'II'. To make sure everything is happy, tell it we might
+ // have broken it.
+ II.resyncInstructionIterator();
+
+ // Hey, we just changed something!
+ MadeChanges = true;
+ } else {
+ ++II;
+ }
+ }
+
+ // 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.
+ //
+ return MadeChanges | DoConstantPoolMerging(M->getConstantPool());
+}
+
+
+// UpdateInstruction - 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::UpdateInstruction(Instruction *I) {
+ InstVal &IValue = ValueState[I];
+ if (IValue.isOverdefined())
+ return; // If already overdefined, we aren't going to effect anything
+
+ switch (I->getInstType()) {
+ //===-----------------------------------------------------------------===//
+ // Handle PHI nodes...
+ //
+ case Instruction::PHINode: {
+ PHINode *PN = (PHINode*)I;
+ unsigned NumValues = PN->getNumIncomingValues(), i;
+ InstVal *OperandIV = 0;
+
+ // 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.
+ //
+ 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.
+ if (IV.isOverdefined()) { // PHI node becomes overdefined!
+ markOverdefined(PN);
+ return;
+ }
+
+ if (OperandIV == 0) { // Grab the first value...
+ OperandIV = &IV;
+ } 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()->equals(OperandIV->getConstant())) {
+ // Yes there is. This means the PHI node is not constant.
+ // You must be overdefined poor PHI.
+ //
+ markOverdefined(I); // 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.
+ //
+ if (OperandIV) {
+ assert(OperandIV->isConstant() && "Should only be here for constants!");
+ markConstant(I, OperandIV->getConstant()); // Aquire operand value
+ }
+ return;
+ }
+
+ //===-----------------------------------------------------------------===//
+ // Handle instructions that unconditionally provide overdefined values...
+ //
+ case Instruction::Malloc:
+ case Instruction::Free:
+ case Instruction::Alloca:
+ case Instruction::Load:
+ case Instruction::Store:
+ // TODO: getfield/putfield?
+ case Instruction::Call:
+ markOverdefined(I); // Memory and call's are all overdefined
+ return;
+
+ //===-----------------------------------------------------------------===//
+ // Handle Terminator instructions...
+ //
+ case Instruction::Ret: return; // Method return doesn't affect anything
+ case Instruction::Br: { // Handle conditional branches...
+ BranchInst *BI = (BranchInst*)I;
+ 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.
+ ConstPoolBool *CPB = (ConstPoolBool*)BCValue.getConstant();
+ if (CPB->getValue()) // If the branch condition is TRUE...
+ markExecutable(BI->getSuccessor(0));
+ else // Else if the br cond is FALSE...
+ markExecutable(BI->getSuccessor(1));
+ }
+ return;
+ }
+
+ case Instruction::Switch: {
+ SwitchInst *SI = (SwitchInst*)I;
+ InstVal &SCValue = getValueState(SI->getCondition());
+ if (SCValue.isOverdefined()) { // Overdefined condition? All dests are exe
+ for(unsigned i = 0; BasicBlock *Succ = SI->getSuccessor(i); ++i)
+ markExecutable(Succ);
+ } else if (SCValue.isConstant()) {
+ ConstPoolVal *CPV = SCValue.getConstant();
+ for (SwitchInst::dest_iterator I = SI->dest_begin(), E = SI->dest_end();
+ I != E; ++I) {
+ if (I->first->equals(CPV)) { // Found the right branch...
+ markExecutable(I->second);
+ return;
+ }
+ }
+
+ // Constant value not equal to any of the branches... must execute
+ // default branch then...
+ markExecutable(SI->getDefaultDest());
+ }
+ return;
+ }
+
+ default: break; // Handle math operators as groups.
+ } // end switch(I->getInstType())
+
+
+ //===-------------------------------------------------------------------===//
+ // Handle Unary instructions...
+ //
+ if (I->isUnaryOp()) {
+ 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
+ ConstPoolVal *Result =
+ ConstantFoldUnaryInstruction(I->getInstType(), VState.getConstant());
+
+ if (Result) {
+ // This instruction constant folds! The only problem is that the value
+ // returned is newly allocated. Make sure to stick it into the methods
+ // constant pool...
+ M->getConstantPool().insert(Result);
+ markConstant(I, Result);
+ } else {
+ markOverdefined(I); // Don't know how to fold this instruction. :(
+ }
+ }
+ return;
+ }
+
+ //===-----------------------------------------------------------------===//
+ // Handle Binary instructions...
+ //
+ if (I->isBinaryOp()) {
+ Value *V1 = I->getOperand(0);
+ Value *V2 = I->getOperand(1);
+
+ InstVal &V1State = getValueState(V1);
+ InstVal &V2State = getValueState(V2);
+ if (V1State.isOverdefined() || V2State.isOverdefined()) {
+ markOverdefined(I);
+ } else if (V1State.isConstant() && V2State.isConstant()) {
+ ConstPoolVal *Result =
+ ConstantFoldBinaryInstruction(I->getInstType(), V1State.getConstant(),
+ V2State.getConstant());
+
+ if (Result) {
+ // This instruction constant folds! The only problem is that the value
+ // returned is newly allocated. Make sure to stick it into the methods
+ // constant pool...
+ M->getConstantPool().insert(Result);
+ markConstant(I, Result);
+ } else {
+ markOverdefined(I); // Don't know how to fold this instruction. :(
+ }
+ }
+ return;
+ }
+
+ // Shouldn't get here... either the switch statement or one of the group
+ // handlers should have kicked in...
+ //
+ cerr << "SCCP: Don't know how to handle: " << I;
+ markOverdefined(I); // Just in case
+}
+
+
+
+// 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 = U->castInstructionAsserting();
+ if (!BBExecutable.count(I->getParent())) return; // Inst not executable yet!
+
+ UpdateInstruction(I);
+}
+
+
+
+// DoSparseConditionalConstantProp - Use Sparse Conditional Constant Propogation
+// to prove whether a value is constant and whether blocks are used.
+//
+bool DoSparseConditionalConstantProp(Method *M) {
+ SCCP S(M);
+ return S.doSCCP();
+}
+
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