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* Enable SCCP debugging to be turned on with a simple change of #define

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* Change worklist to a set so that duplicates cannot happen
* Add support for the invoke instruction
* Avoid marking store and free instructions as overdefined, since they
  cannot produce a value anyway.
* Inline the OperandChangedState implementation
* Add isEdgeFeasible in preparation to fix a bug.  Right now it behaves
  exactly as before.
* Remove obsolete comment about constant pools


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@2445 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2002-05-02 21:18:01 +00:00
parent a1ab959de3
commit 59f0ce2a41
1 changed files with 52 additions and 32 deletions
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84
lib/Transforms/Scalar/SCCP.cpp
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@ -30,6 +30,12 @@
#include <iostream>
using std::cerr;
#if 0 // Enable this to get SCCP debug output
#define DEBUG_SCCP(X) X
#else
#define DEBUG_SCCP(X)
#endif
// InstVal class - This class represents the different lattice values that an
// instruction may occupy. It is a simple class with value semantics.
//
@ -86,7 +92,7 @@ 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::set<Instruction*> InstWorkList;// The instruction work list
std::vector<BasicBlock*> BBWorkList; // The BasicBlock work list
public:
@ -116,9 +122,10 @@ private:
// the users of the instruction are updated later.
//
inline bool markConstant(Instruction *I, Constant *V) {
//cerr << "markConstant: " << V << " = " << I;
DEBUG_SCCP(cerr << "markConstant: " << V << " = " << I);
if (ValueState[I].markConstant(V)) {
InstWorkList.push_back(I);
InstWorkList.insert(I);
return true;
}
return false;
@ -131,8 +138,8 @@ private:
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
DEBUG_SCCP(cerr << "markOverdefined: " << V);
InstWorkList.insert(I); // Only instructions go on the work list
}
return true;
}
@ -163,7 +170,7 @@ private:
//
void markExecutable(BasicBlock *BB) {
if (BBExecutable.count(BB)) return;
//cerr << "Marking BB Executable: " << BB;
DEBUG_SCCP(cerr << "Marking BB Executable: " << BB);
BBExecutable.insert(BB); // Basic block is executable!
BBWorkList.push_back(BB); // Add the block to the work list!
}
@ -178,6 +185,7 @@ private:
// Terminators
void visitReturnInst(ReturnInst *I) { /*does not have an effect*/ }
void visitBranchInst(BranchInst *I);
void visitInvokeInst(InvokeInst *I);
void visitSwitchInst(SwitchInst *I);
void visitUnaryOperator(Instruction *I);
@ -186,11 +194,12 @@ private:
void visitShiftInst(ShiftInst *I) { visitBinaryOperator(I); }
// Instructions that cannot be folded away...
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) { 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...
@ -198,11 +207,21 @@ private:
markOverdefined(I); // Just in case
}
// 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);
}
};
} // end anonymous namespace
@ -230,10 +249,10 @@ bool SCCP::runOnFunction(Function *F) {
while (!BBWorkList.empty() || !InstWorkList.empty()) {
// Process the instruction work list...
while (!InstWorkList.empty()) {
Instruction *I = InstWorkList.back();
InstWorkList.pop_back();
Instruction *I = *InstWorkList.begin();
InstWorkList.erase(InstWorkList.begin());
//cerr << "\nPopped off I-WL: " << I;
DEBUG_SCCP(cerr << "\nPopped off I-WL: " << I);
// "I" got into the work list because it either made the transition from
@ -250,7 +269,7 @@ bool SCCP::runOnFunction(Function *F) {
BasicBlock *BB = BBWorkList.back();
BBWorkList.pop_back();
//cerr << "\nPopped off BBWL: " << BB;
DEBUG_SCCP(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.
@ -264,7 +283,7 @@ bool SCCP::runOnFunction(Function *F) {
}
}
#if 0
#ifdef DEBUG_SCCP
for (Function::iterator BBI = F->begin(), BBEnd = F->end();
BBI != BBEnd; ++BBI)
if (!BBExecutable.count(*BBI))
@ -283,7 +302,7 @@ bool SCCP::runOnFunction(Function *F) {
InstVal &IV = ValueState[Inst];
if (IV.isConstant()) {
Constant *Const = IV.getConstant();
// cerr << "Constant: " << Inst << " is: " << Const;
DEBUG_SCCP(cerr << "Constant: " << Inst << " is: " << Const);
// Replaces all of the uses of a variable with uses of the constant.
Inst->replaceAllUsesWith(Const);
@ -305,17 +324,25 @@ bool SCCP::runOnFunction(Function *F) {
}
}
// Reset state so that the next invokation will have empty data structures
// Reset state so that the next invocation will have empty data structures
BBExecutable.clear();
ValueState.clear();
// 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;
}
// 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;
// This should check the terminator in From!
return true;
}
// visit Implementations - Something changed in this instruction... Either an
// operand made a transition, or the instruction is newly executable. Change
@ -347,7 +374,7 @@ void SCCP::visitPHINode(PHINode *PN) {
// If there are no executable operands, the PHI remains undefined.
//
for (i = 0; i < NumValues; ++i) {
if (BBExecutable.count(PN->getIncomingBlock(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!
@ -403,6 +430,11 @@ void SCCP::visitBranchInst(BranchInst *BI) {
}
}
void SCCP::visitInvokeInst(InvokeInst *II) {
markExecutable(II->getNormalDest());
markExecutable(II->getExceptionalDest());
}
void SCCP::visitSwitchInst(SwitchInst *SI) {
InstVal &SCValue = getValueState(SI->getCondition());
if (SCValue.isOverdefined()) { // Overdefined condition? All dests are exe
@ -459,15 +491,3 @@ void SCCP::visitBinaryOperator(Instruction *I) {
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);
}