RC::ConstHandle<CaseVector> CaseVector::Create( RC::ConstHandle<Case> const &first, RC::ConstHandle<CaseVector> const &remaining )
{
CaseVector *result = new CaseVector;
if ( first )
result->push_back( first );
if ( remaining )
{
for ( const_iterator it=remaining->begin(); it!=remaining->end(); ++it )
result->push_back( *it );
}
return result;
}
// processSwitchInst - Replace the specified switch instruction with a sequence
// of chained if-then insts in a balanced binary search.
//
void LowerSwitch::processSwitchInst(SwitchInst *SI) {
BasicBlock *CurBlock = SI->getParent();
BasicBlock *OrigBlock = CurBlock;
Function *F = CurBlock->getParent();
Value *Val = SI->getOperand(0); // The value we are switching on...
BasicBlock* Default = SI->getDefaultDest();
// If there is only the default destination, don't bother with the code below.
if (SI->getNumOperands() == 2) {
BranchInst::Create(SI->getDefaultDest(), CurBlock);
CurBlock->getInstList().erase(SI);
return;
}
// Create a new, empty default block so that the new hierarchy of
// if-then statements go to this and the PHI nodes are happy.
BasicBlock* NewDefault = BasicBlock::Create(SI->getContext(), "NewDefault");
F->getBasicBlockList().insert(Default, NewDefault);
BranchInst::Create(Default, NewDefault);
// If there is an entry in any PHI nodes for the default edge, make sure
// to update them as well.
for (BasicBlock::iterator I = Default->begin(); isa<PHINode>(I); ++I) {
PHINode *PN = cast<PHINode>(I);
int BlockIdx = PN->getBasicBlockIndex(OrigBlock);
assert(BlockIdx != -1 && "Switch didn't go to this successor??");
PN->setIncomingBlock((unsigned)BlockIdx, NewDefault);
}
// Prepare cases vector.
CaseVector Cases;
unsigned numCmps = Clusterify(Cases, SI);
DEBUG(dbgs() << "Clusterify finished. Total clusters: " << Cases.size()
<< ". Total compares: " << numCmps << "\n");
DEBUG(dbgs() << "Cases: " << Cases << "\n");
(void)numCmps;
BasicBlock* SwitchBlock = switchConvert(Cases.begin(), Cases.end(), Val,
OrigBlock, NewDefault);
// Branch to our shiny new if-then stuff...
BranchInst::Create(SwitchBlock, OrigBlock);
// We are now done with the switch instruction, delete it.
CurBlock->getInstList().erase(SI);
}
// Clusterify - Transform simple list of Cases into list of CaseRange's
unsigned LowerSwitch::Clusterify(CaseVector& Cases, SwitchInst *SI) {
unsigned numCmps = 0;
// Start with "simple" cases
for (unsigned i = 1; i < SI->getNumSuccessors(); ++i)
Cases.push_back(CaseRange(SI->getSuccessorValue(i),
SI->getSuccessorValue(i),
SI->getSuccessor(i)));
std::sort(Cases.begin(), Cases.end(), CaseCmp());
// Merge case into clusters
if (Cases.size()>=2)
for (CaseItr I=Cases.begin(), J=llvm::next(Cases.begin()); J!=Cases.end(); ) {
int64_t nextValue = cast<ConstantInt>(J->Low)->getSExtValue();
int64_t currentValue = cast<ConstantInt>(I->High)->getSExtValue();
BasicBlock* nextBB = J->BB;
BasicBlock* currentBB = I->BB;
// If the two neighboring cases go to the same destination, merge them
// into a single case.
if ((nextValue-currentValue==1) && (currentBB == nextBB)) {
I->High = J->High;
J = Cases.erase(J);
} else {
I = J++;
}
}
for (CaseItr I=Cases.begin(), E=Cases.end(); I!=E; ++I, ++numCmps) {
if (I->Low != I->High)
// A range counts double, since it requires two compares.
++numCmps;
}
return numCmps;
}
// processSwitchInst - Replace the specified switch instruction with a sequence
// of chained if-then instructions.
//
void LowerSwitchPass::processSwitchInst(SwitchInst *SI) {
BasicBlock *origBlock = SI->getParent();
BasicBlock *defaultBlock = SI->getDefaultDest();
Function *F = origBlock->getParent();
Value *switchValue = SI->getCondition();
// Create a new, empty default block so that the new hierarchy of
// if-then statements go to this and the PHI nodes are happy.
BasicBlock* newDefault = BasicBlock::Create(getGlobalContext(), "newDefault");
#if LLVM_VERSION_CODE >= LLVM_VERSION(3, 8)
F->getBasicBlockList().insert(defaultBlock->getIterator(), newDefault);
#else
F->getBasicBlockList().insert(defaultBlock, newDefault);
#endif
BranchInst::Create(defaultBlock, newDefault);
// If there is an entry in any PHI nodes for the default edge, make sure
// to update them as well.
for (BasicBlock::iterator I = defaultBlock->begin(); isa<PHINode>(I); ++I) {
PHINode *PN = cast<PHINode>(I);
int BlockIdx = PN->getBasicBlockIndex(origBlock);
assert(BlockIdx != -1 && "Switch didn't go to this successor??");
PN->setIncomingBlock((unsigned)BlockIdx, newDefault);
}
CaseVector cases;
#if LLVM_VERSION_CODE >= LLVM_VERSION(3, 1)
for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end(); i != e; ++i)
cases.push_back(SwitchCase(i.getCaseValue(),
i.getCaseSuccessor()));
#else
for (unsigned i = 1; i < SI->getNumSuccessors(); ++i)
cases.push_back(SwitchCase(SI->getSuccessorValue(i),
SI->getSuccessor(i)));
#endif
// reverse cases, as switchConvert constructs a chain of
// basic blocks by appending to the front. if we reverse,
// the if comparisons will happen in the same order
// as the cases appear in the switch
std::reverse(cases.begin(), cases.end());
switchConvert(cases.begin(), cases.end(), switchValue, origBlock, newDefault);
// We are now done with the switch instruction, so delete it
origBlock->getInstList().erase(SI);
}
