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* Enable SCCP debugging to be turned on with a simple change of #define
* 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
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@ -30,6 +30,12 @@
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#include <iostream>
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using std::cerr;
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#if 0 // Enable this to get SCCP debug output
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#define DEBUG_SCCP(X) X
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#else
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#define DEBUG_SCCP(X)
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#endif
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// InstVal class - This class represents the different lattice values that an
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// instruction may occupy. It is a simple class with value semantics.
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//
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@ -86,7 +92,7 @@ class SCCP : public FunctionPass, public InstVisitor<SCCP> {
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std::set<BasicBlock*> BBExecutable;// The basic blocks that are executable
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std::map<Value*, InstVal> ValueState; // The state each value is in...
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std::vector<Instruction*> InstWorkList;// The instruction work list
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std::set<Instruction*> InstWorkList;// The instruction work list
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std::vector<BasicBlock*> BBWorkList; // The BasicBlock work list
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public:
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@ -116,9 +122,10 @@ private:
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// the users of the instruction are updated later.
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//
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inline bool markConstant(Instruction *I, Constant *V) {
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//cerr << "markConstant: " << V << " = " << I;
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DEBUG_SCCP(cerr << "markConstant: " << V << " = " << I);
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if (ValueState[I].markConstant(V)) {
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InstWorkList.push_back(I);
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InstWorkList.insert(I);
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return true;
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}
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return false;
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@ -131,8 +138,8 @@ private:
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inline bool markOverdefined(Value *V) {
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if (ValueState[V].markOverdefined()) {
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if (Instruction *I = dyn_cast<Instruction>(V)) {
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//cerr << "markOverdefined: " << V;
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InstWorkList.push_back(I); // Only instructions go on the work list
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DEBUG_SCCP(cerr << "markOverdefined: " << V);
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InstWorkList.insert(I); // Only instructions go on the work list
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}
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return true;
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}
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@ -163,7 +170,7 @@ private:
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//
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void markExecutable(BasicBlock *BB) {
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if (BBExecutable.count(BB)) return;
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//cerr << "Marking BB Executable: " << BB;
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DEBUG_SCCP(cerr << "Marking BB Executable: " << BB);
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BBExecutable.insert(BB); // Basic block is executable!
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BBWorkList.push_back(BB); // Add the block to the work list!
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}
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@ -178,6 +185,7 @@ private:
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// Terminators
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void visitReturnInst(ReturnInst *I) { /*does not have an effect*/ }
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void visitBranchInst(BranchInst *I);
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void visitInvokeInst(InvokeInst *I);
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void visitSwitchInst(SwitchInst *I);
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void visitUnaryOperator(Instruction *I);
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@ -186,11 +194,12 @@ private:
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void visitShiftInst(ShiftInst *I) { visitBinaryOperator(I); }
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// Instructions that cannot be folded away...
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void visitStoreInst (Instruction *I) { /*returns void*/ }
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void visitMemAccessInst (Instruction *I) { markOverdefined(I); }
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void visitCallInst (Instruction *I) { markOverdefined(I); }
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void visitInvokeInst (Instruction *I) { markOverdefined(I); }
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void visitAllocationInst(Instruction *I) { markOverdefined(I); }
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void visitFreeInst (Instruction *I) { markOverdefined(I); }
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void visitFreeInst (Instruction *I) { /*returns void*/ }
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void visitInstruction(Instruction *I) {
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// If a new instruction is added to LLVM that we don't handle...
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@ -198,11 +207,21 @@ private:
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markOverdefined(I); // Just in case
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}
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// isEdgeFeasible - Return true if the control flow edge from the 'From' basic
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// block to the 'To' basic block is currently feasible...
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//
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bool isEdgeFeasible(BasicBlock *From, BasicBlock *To);
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// OperandChangedState - This method is invoked on all of the users of an
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// instruction that was just changed state somehow.... Based on this
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// information, we need to update the specified user of this instruction.
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//
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void OperandChangedState(User *U);
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void OperandChangedState(User *U) {
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// Only instructions use other variable values!
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Instruction *I = cast<Instruction>(U);
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if (!BBExecutable.count(I->getParent())) return;// Inst not executable yet!
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visit(I);
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}
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};
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} // end anonymous namespace
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@ -230,10 +249,10 @@ bool SCCP::runOnFunction(Function *F) {
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while (!BBWorkList.empty() || !InstWorkList.empty()) {
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// Process the instruction work list...
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while (!InstWorkList.empty()) {
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Instruction *I = InstWorkList.back();
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InstWorkList.pop_back();
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Instruction *I = *InstWorkList.begin();
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InstWorkList.erase(InstWorkList.begin());
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//cerr << "\nPopped off I-WL: " << I;
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DEBUG_SCCP(cerr << "\nPopped off I-WL: " << I);
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// "I" got into the work list because it either made the transition from
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@ -250,7 +269,7 @@ bool SCCP::runOnFunction(Function *F) {
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BasicBlock *BB = BBWorkList.back();
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BBWorkList.pop_back();
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//cerr << "\nPopped off BBWL: " << BB;
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DEBUG_SCCP(cerr << "\nPopped off BBWL: " << BB);
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// If this block only has a single successor, mark it as executable as
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// well... if not, terminate the do loop.
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@ -264,7 +283,7 @@ bool SCCP::runOnFunction(Function *F) {
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}
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}
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#if 0
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#ifdef DEBUG_SCCP
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for (Function::iterator BBI = F->begin(), BBEnd = F->end();
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BBI != BBEnd; ++BBI)
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if (!BBExecutable.count(*BBI))
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@ -283,7 +302,7 @@ bool SCCP::runOnFunction(Function *F) {
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InstVal &IV = ValueState[Inst];
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if (IV.isConstant()) {
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Constant *Const = IV.getConstant();
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// cerr << "Constant: " << Inst << " is: " << Const;
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DEBUG_SCCP(cerr << "Constant: " << Inst << " is: " << Const);
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// Replaces all of the uses of a variable with uses of the constant.
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Inst->replaceAllUsesWith(Const);
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@ -305,17 +324,25 @@ bool SCCP::runOnFunction(Function *F) {
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}
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}
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// Reset state so that the next invokation will have empty data structures
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// Reset state so that the next invocation will have empty data structures
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BBExecutable.clear();
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ValueState.clear();
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// Merge identical constants last: this is important because we may have just
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// introduced constants that already exist, and we don't want to pollute later
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// stages with extraneous constants.
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//
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return MadeChanges;
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}
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// isEdgeFeasible - Return true if the control flow edge from the 'From' basic
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// block to the 'To' basic block is currently feasible...
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//
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bool SCCP::isEdgeFeasible(BasicBlock *From, BasicBlock *To) {
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assert(BBExecutable.count(To) && "Dest should always be alive!");
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// Make sure the source basic block is executable!!
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if (!BBExecutable.count(From)) return false;
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// This should check the terminator in From!
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return true;
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}
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// visit Implementations - Something changed in this instruction... Either an
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// operand made a transition, or the instruction is newly executable. Change
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@ -347,7 +374,7 @@ void SCCP::visitPHINode(PHINode *PN) {
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// If there are no executable operands, the PHI remains undefined.
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//
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for (i = 0; i < NumValues; ++i) {
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if (BBExecutable.count(PN->getIncomingBlock(i))) {
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if (isEdgeFeasible(PN->getIncomingBlock(i), PN->getParent())) {
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InstVal &IV = getValueState(PN->getIncomingValue(i));
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if (IV.isUndefined()) continue; // Doesn't influence PHI node.
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if (IV.isOverdefined()) { // PHI node becomes overdefined!
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@ -403,6 +430,11 @@ void SCCP::visitBranchInst(BranchInst *BI) {
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}
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}
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void SCCP::visitInvokeInst(InvokeInst *II) {
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markExecutable(II->getNormalDest());
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markExecutable(II->getExceptionalDest());
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}
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void SCCP::visitSwitchInst(SwitchInst *SI) {
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InstVal &SCValue = getValueState(SI->getCondition());
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if (SCValue.isOverdefined()) { // Overdefined condition? All dests are exe
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@ -459,15 +491,3 @@ void SCCP::visitBinaryOperator(Instruction *I) {
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markOverdefined(I); // Don't know how to fold this instruction. :(
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}
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}
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// OperandChangedState - This method is invoked on all of the users of an
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// instruction that was just changed state somehow.... Based on this
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// information, we need to update the specified user of this instruction.
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//
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void SCCP::OperandChangedState(User *U) {
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// Only instructions use other variable values!
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Instruction *I = cast<Instruction>(U);
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if (!BBExecutable.count(I->getParent())) return; // Inst not executable yet!
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visit(I);
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}
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