#include "llvm/iTerminators.h"
#include "llvm/iOther.h"
#include "llvm/Pass.h"
+#include "llvm/Support/InstVisitor.h"
#include "Support/STLExtras.h"
#include <algorithm>
#include <map>
// 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 {
+class SCCP : public InstVisitor<SCCP> {
Function *M; // The function that we are working on
std::set<BasicBlock*> BBExecutable;// The basic blocks that are executable
// 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
// is not already a constant, add it to the instruction work list so that
}
- // UpdateInstruction - Something changed in this instruction... Either an
+ // 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.
//
- void UpdateInstruction(Instruction *I);
+ void visitPHINode(PHINode *I);
+
+ // Terminators
+ void visitReturnInst(ReturnInst *I) { /*does not have an effect*/ }
+ void visitBranchInst(BranchInst *I);
+ void visitSwitchInst(SwitchInst *I);
+
+ void visitUnaryOperator(Instruction *I);
+ void visitCastInst(CastInst *I) { visitUnaryOperator(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) {
+ // 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
+ }
// OperandChangedState - This method is invoked on all of the users of an
// instruction that was just changed state somehow.... Based on this
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));
+ // Notify all instructions in this basic block that they are newly
+ // executable.
+ visit(BB);
}
}
}
-// UpdateInstruction - Something changed in this instruction... Either an
+// 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:
// 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->getOpcode()) {
- //===-----------------------------------------------------------------===//
- // Handle PHI nodes...
- //
- case Instruction::PHINode: {
- PHINode *PN = cast<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() != 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
- }
+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
+ // 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() != OperandIV->getConstant()) {
+ // 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
+ 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;
+ // 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(PN, OperandIV->getConstant()); // Aquire operand value
}
+}
- //===-----------------------------------------------------------------===//
- // Handle instructions that unconditionally provide overdefined values...
- //
- case Instruction::Malloc:
- case Instruction::Free:
- case Instruction::Alloca:
- case Instruction::Load:
- case Instruction::Store:
- // TODO: getfield
- case Instruction::Call:
- case Instruction::Invoke:
- markOverdefined(I); // Memory and call's are all overdefined
- return;
-
- //===-----------------------------------------------------------------===//
- // Handle Terminator instructions...
- //
- case Instruction::Ret: return; // Function return doesn't affect anything
- case Instruction::Br: { // Handle conditional branches...
- BranchInst *BI = cast<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.
+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));
- } else if (BCValue.isConstant()) {
- // Constant condition variables mean the branch can only go a single way.
- ConstantBool *CPB = cast<ConstantBool>(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 = cast<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()) {
- 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;
- }
+void SCCP::visitSwitchInst(SwitchInst *SI) {
+ 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()) {
+ 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;
}
-
- // 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->getOpcode())
-
- //===-------------------------------------------------------------------===//
- // Handle Unary and cast instructions...
- //
- if (isa<UnaryOperator>(I) || isa<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. :(
- }
- }
- return;
+ // Constant value not equal to any of the branches... must execute
+ // default branch then...
+ markExecutable(SI->getDefaultDest());
}
+}
-
- //===-----------------------------------------------------------------===//
- // Handle GetElementPtr instructions...
- //
- if (isa<GetElementPtrInst>(I)) {
+void SCCP::visitUnaryOperator(Instruction *I) {
+ Value *V = I->getOperand(0);
+ InstVal &VState = getValueState(V);
+ if (VState.isOverdefined()) { // Inherit overdefinedness of operand
markOverdefined(I);
- return;
- }
-
-
- //===-----------------------------------------------------------------===//
- // Handle Binary instructions...
- //
- if (isa<BinaryOperator>(I) || isa<ShiftInst>(I)) {
- 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()) {
- Constant *Result =
- ConstantFoldBinaryInstruction(I->getOpcode(),
- V1State.getConstant(),
- V2State.getConstant());
- if (Result) {
- // This instruction constant folds!
- markConstant(I, Result);
- } else {
- markOverdefined(I); // Don't know how to fold this instruction. :(
- }
+ } 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. :(
}
- 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
}
-
+// Handle BinaryOperators and Shift Instructions...
+void SCCP::visitBinaryOperator(Instruction *I) {
+ InstVal &V1State = getValueState(I->getOperand(0));
+ InstVal &V2State = getValueState(I->getOperand(1));
+ if (V1State.isOverdefined() || V2State.isOverdefined()) {
+ markOverdefined(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. :(
+ }
+}
// OperandChangedState - This method is invoked on all of the users of an
// instruction that was just changed state somehow.... Based on this
Instruction *I = cast<Instruction>(U);
if (!BBExecutable.count(I->getParent())) return; // Inst not executable yet!
- UpdateInstruction(I);
+ visit(I);
}
namespace {
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