/// isSafeToClone - Return true if the loop body is safe to clone in practice.
/// Routines that reform the loop CFG and split edges often fail on indirectbr.
bool Loop::isSafeToClone() const {
// Return false if any loop blocks contain indirectbrs, or there are any calls
// to noduplicate functions.
for (Loop::block_iterator I = block_begin(), E = block_end(); I != E; ++I) {
if (isa<IndirectBrInst>((*I)->getTerminator()))
return false;
if (const InvokeInst *II = dyn_cast<InvokeInst>((*I)->getTerminator()))
if (II->cannotDuplicate())
return false;
for (BasicBlock::iterator BI = (*I)->begin(), BE = (*I)->end(); BI != BE; ++BI) {
if (const CallInst *CI = dyn_cast<CallInst>(BI)) {
if (CI->cannotDuplicate())
return false;
}
if (BI->getType()->isTokenTy() && BI->isUsedOutsideOfBlock(*I))
return false;
}
}
return true;
}
void fixStack(Function *f) {
// Try to remove phi node and demote reg to stack
std::vector<PHINode *> tmpPhi;
std::vector<Instruction *> tmpReg;
BasicBlock *bbEntry = f->begin();
do {
tmpPhi.clear();
tmpReg.clear();
for (Function::iterator i = f->begin(); i != f->end(); ++i) {
for (BasicBlock::iterator j = i->begin(); j != i->end(); ++j) {
if (isa<PHINode>(j)) {
PHINode *phi = cast<PHINode>(j);
tmpPhi.push_back(phi);
continue;
}
if (!(isa<AllocaInst>(j) && j->getParent() == bbEntry) &&
(valueEscapes(j) || j->isUsedOutsideOfBlock(i))) {
tmpReg.push_back(j);
continue;
}
}
}
for (unsigned int i = 0; i != tmpReg.size(); ++i) {
DemoteRegToStack(*tmpReg.at(i), f->begin()->getTerminator());
}
for (unsigned int i = 0; i != tmpPhi.size(); ++i) {
DemotePHIToStack(tmpPhi.at(i), f->begin()->getTerminator());
}
} while (tmpReg.size() != 0 || tmpPhi.size() != 0);
}
/// eliminateUnconditionalBranch - Clone the instructions from the destination
/// block into the source block, eliminating the specified unconditional branch.
/// If the destination block defines values used by successors of the dest
/// block, we may need to insert PHI nodes.
///
void TailDup::eliminateUnconditionalBranch(BranchInst *Branch) {
BasicBlock *SourceBlock = Branch->getParent();
BasicBlock *DestBlock = Branch->getSuccessor(0);
assert(SourceBlock != DestBlock && "Our predicate is broken!");
DEBUG(errs() << "TailDuplication[" << SourceBlock->getParent()->getName()
<< "]: Eliminating branch: " << *Branch);
// See if we can avoid duplicating code by moving it up to a dominator of both
// blocks.
if (BasicBlock *DomBlock = FindObviousSharedDomOf(SourceBlock, DestBlock)) {
DEBUG(errs() << "Found shared dominator: " << DomBlock->getName() << "\n");
// If there are non-phi instructions in DestBlock that have no operands
// defined in DestBlock, and if the instruction has no side effects, we can
// move the instruction to DomBlock instead of duplicating it.
BasicBlock::iterator BBI = DestBlock->getFirstNonPHI();
while (!isa<TerminatorInst>(BBI)) {
Instruction *I = BBI++;
bool CanHoist = I->isSafeToSpeculativelyExecute() &&
!I->mayReadFromMemory();
if (CanHoist) {
for (unsigned op = 0, e = I->getNumOperands(); op != e; ++op)
if (Instruction *OpI = dyn_cast<Instruction>(I->getOperand(op)))
if (OpI->getParent() == DestBlock ||
(isa<InvokeInst>(OpI) && OpI->getParent() == DomBlock)) {
CanHoist = false;
break;
}
if (CanHoist) {
// Remove from DestBlock, move right before the term in DomBlock.
DestBlock->getInstList().remove(I);
DomBlock->getInstList().insert(DomBlock->getTerminator(), I);
DEBUG(errs() << "Hoisted: " << *I);
}
}
}
}
// Tail duplication can not update SSA properties correctly if the values
// defined in the duplicated tail are used outside of the tail itself. For
// this reason, we spill all values that are used outside of the tail to the
// stack.
for (BasicBlock::iterator I = DestBlock->begin(); I != DestBlock->end(); ++I)
if (I->isUsedOutsideOfBlock(DestBlock)) {
// We found a use outside of the tail. Create a new stack slot to
// break this inter-block usage pattern.
DemoteRegToStack(*I);
}
// We are going to have to map operands from the original block B to the new
// copy of the block B'. If there are PHI nodes in the DestBlock, these PHI
// nodes also define part of this mapping. Loop over these PHI nodes, adding
// them to our mapping.
//
std::map<Value*, Value*> ValueMapping;
BasicBlock::iterator BI = DestBlock->begin();
bool HadPHINodes = isa<PHINode>(BI);
for (; PHINode *PN = dyn_cast<PHINode>(BI); ++BI)
ValueMapping[PN] = PN->getIncomingValueForBlock(SourceBlock);
// Clone the non-phi instructions of the dest block into the source block,
// keeping track of the mapping...
//
for (; BI != DestBlock->end(); ++BI) {
Instruction *New = BI->clone();
New->setName(BI->getName());
SourceBlock->getInstList().push_back(New);
ValueMapping[BI] = New;
}
// Now that we have built the mapping information and cloned all of the
// instructions (giving us a new terminator, among other things), walk the new
// instructions, rewriting references of old instructions to use new
// instructions.
//
BI = Branch; ++BI; // Get an iterator to the first new instruction
for (; BI != SourceBlock->end(); ++BI)
for (unsigned i = 0, e = BI->getNumOperands(); i != e; ++i) {
std::map<Value*, Value*>::const_iterator I =
ValueMapping.find(BI->getOperand(i));
if (I != ValueMapping.end())
BI->setOperand(i, I->second);
}
// Next we check to see if any of the successors of DestBlock had PHI nodes.
// If so, we need to add entries to the PHI nodes for SourceBlock now.
for (succ_iterator SI = succ_begin(DestBlock), SE = succ_end(DestBlock);
SI != SE; ++SI) {
BasicBlock *Succ = *SI;
for (BasicBlock::iterator PNI = Succ->begin(); isa<PHINode>(PNI); ++PNI) {
PHINode *PN = cast<PHINode>(PNI);
// Ok, we have a PHI node. Figure out what the incoming value was for the
// DestBlock.
Value *IV = PN->getIncomingValueForBlock(DestBlock);
// Remap the value if necessary...
std::map<Value*, Value*>::const_iterator I = ValueMapping.find(IV);
if (I != ValueMapping.end())
IV = I->second;
PN->addIncoming(IV, SourceBlock);
}
}
// Next, remove the old branch instruction, and any PHI node entries that we
// had.
BI = Branch; ++BI; // Get an iterator to the first new instruction
DestBlock->removePredecessor(SourceBlock); // Remove entries in PHI nodes...
SourceBlock->getInstList().erase(Branch); // Destroy the uncond branch...
// Final step: now that we have finished everything up, walk the cloned
// instructions one last time, constant propagating and DCE'ing them, because
// they may not be needed anymore.
//
if (HadPHINodes) {
while (BI != SourceBlock->end()) {
Instruction *Inst = BI++;
if (isInstructionTriviallyDead(Inst))
Inst->eraseFromParent();
else if (Constant *C = ConstantFoldInstruction(Inst)) {
Inst->replaceAllUsesWith(C);
Inst->eraseFromParent();
}
}
}
++NumEliminated; // We just killed a branch!
}