BasicBlock *llvm::SplitBlock(BasicBlock *Old, Instruction *SplitPt,
DominatorTree *DT, LoopInfo *LI) {
BasicBlock::iterator SplitIt = SplitPt->getIterator();
while (isa<PHINode>(SplitIt) || SplitIt->isEHPad())
++SplitIt;
BasicBlock *New = Old->splitBasicBlock(SplitIt, Old->getName()+".split");
// The new block lives in whichever loop the old one did. This preserves
// LCSSA as well, because we force the split point to be after any PHI nodes.
if (LI)
if (Loop *L = LI->getLoopFor(Old))
L->addBasicBlockToLoop(New, *LI);
if (DT)
// Old dominates New. New node dominates all other nodes dominated by Old.
if (DomTreeNode *OldNode = DT->getNode(Old)) {
std::vector<DomTreeNode *> Children(OldNode->begin(), OldNode->end());
DomTreeNode *NewNode = DT->addNewBlock(New, Old);
for (DomTreeNode *I : Children)
DT->changeImmediateDominator(I, NewNode);
}
return New;
}
/// Find an insertion point that dominates all uses.
SmallPtrSet<Instruction *, 8> ConstantHoistingPass::findConstantInsertionPoint(
const ConstantInfo &ConstInfo) const {
assert(!ConstInfo.RebasedConstants.empty() && "Invalid constant info entry.");
// Collect all basic blocks.
SmallPtrSet<BasicBlock *, 8> BBs;
SmallPtrSet<Instruction *, 8> InsertPts;
for (auto const &RCI : ConstInfo.RebasedConstants)
for (auto const &U : RCI.Uses)
BBs.insert(findMatInsertPt(U.Inst, U.OpndIdx)->getParent());
if (BBs.count(Entry)) {
InsertPts.insert(&Entry->front());
return InsertPts;
}
if (BFI) {
findBestInsertionSet(*DT, *BFI, Entry, BBs);
for (auto BB : BBs) {
BasicBlock::iterator InsertPt = BB->begin();
for (; isa<PHINode>(InsertPt) || InsertPt->isEHPad(); ++InsertPt)
;
InsertPts.insert(&*InsertPt);
}
return InsertPts;
}
while (BBs.size() >= 2) {
BasicBlock *BB, *BB1, *BB2;
BB1 = *BBs.begin();
BB2 = *std::next(BBs.begin());
BB = DT->findNearestCommonDominator(BB1, BB2);
if (BB == Entry) {
InsertPts.insert(&Entry->front());
return InsertPts;
}
BBs.erase(BB1);
BBs.erase(BB2);
BBs.insert(BB);
}
assert((BBs.size() == 1) && "Expected only one element.");
Instruction &FirstInst = (*BBs.begin())->front();
InsertPts.insert(findMatInsertPt(&FirstInst));
return InsertPts;
}
/// DemotePHIToStack - This function takes a virtual register computed by a PHI
/// node and replaces it with a slot in the stack frame allocated via alloca.
/// The PHI node is deleted. It returns the pointer to the alloca inserted.
AllocaInst *llvm::DemotePHIToStack(PHINode *P, Instruction *AllocaPoint) {
if (P->use_empty()) {
P->eraseFromParent();
return nullptr;
}
const DataLayout &DL = P->getModule()->getDataLayout();
// Create a stack slot to hold the value.
AllocaInst *Slot;
if (AllocaPoint) {
Slot = new AllocaInst(P->getType(), DL.getAllocaAddrSpace(), nullptr,
P->getName()+".reg2mem", AllocaPoint);
} else {
Function *F = P->getParent()->getParent();
Slot = new AllocaInst(P->getType(), DL.getAllocaAddrSpace(), nullptr,
P->getName() + ".reg2mem",
&F->getEntryBlock().front());
}
// Iterate over each operand inserting a store in each predecessor.
for (unsigned i = 0, e = P->getNumIncomingValues(); i < e; ++i) {
if (InvokeInst *II = dyn_cast<InvokeInst>(P->getIncomingValue(i))) {
assert(II->getParent() != P->getIncomingBlock(i) &&
"Invoke edge not supported yet"); (void)II;
}
new StoreInst(P->getIncomingValue(i), Slot,
P->getIncomingBlock(i)->getTerminator());
}
// Insert a load in place of the PHI and replace all uses.
BasicBlock::iterator InsertPt = P->getIterator();
for (; isa<PHINode>(InsertPt) || InsertPt->isEHPad(); ++InsertPt)
/* empty */; // Don't insert before PHI nodes or landingpad instrs.
Value *V = new LoadInst(Slot, P->getName() + ".reload", &*InsertPt);
P->replaceAllUsesWith(V);
// Delete PHI.
P->eraseFromParent();
return Slot;
}
/// DemoteRegToStack - This function takes a virtual register computed by an
/// Instruction and replaces it with a slot in the stack frame, allocated via
/// alloca. This allows the CFG to be changed around without fear of
/// invalidating the SSA information for the value. It returns the pointer to
/// the alloca inserted to create a stack slot for I.
AllocaInst *llvm::DemoteRegToStack(Instruction &I, bool VolatileLoads,
Instruction *AllocaPoint) {
if (I.use_empty()) {
I.eraseFromParent();
return nullptr;
}
// Create a stack slot to hold the value.
AllocaInst *Slot;
if (AllocaPoint) {
Slot = new AllocaInst(I.getType(), nullptr,
I.getName()+".reg2mem", AllocaPoint);
} else {
Function *F = I.getParent()->getParent();
Slot = new AllocaInst(I.getType(), nullptr, I.getName()+".reg2mem",
F->getEntryBlock().begin());
}
// We cannot demote invoke instructions to the stack if their normal edge
// is critical. Therefore, split the critical edge and create a basic block
// into which the store can be inserted.
if (InvokeInst *II = dyn_cast<InvokeInst>(&I)) {
if (!II->getNormalDest()->getSinglePredecessor()) {
unsigned SuccNum = GetSuccessorNumber(II->getParent(), II->getNormalDest());
assert(isCriticalEdge(II, SuccNum) && "Expected a critical edge!");
BasicBlock *BB = SplitCriticalEdge(II, SuccNum);
assert(BB && "Unable to split critical edge.");
(void)BB;
}
}
// Change all of the users of the instruction to read from the stack slot.
while (!I.use_empty()) {
Instruction *U = cast<Instruction>(I.user_back());
if (PHINode *PN = dyn_cast<PHINode>(U)) {
// If this is a PHI node, we can't insert a load of the value before the
// use. Instead insert the load in the predecessor block corresponding
// to the incoming value.
//
// Note that if there are multiple edges from a basic block to this PHI
// node that we cannot have multiple loads. The problem is that the
// resulting PHI node will have multiple values (from each load) coming in
// from the same block, which is illegal SSA form. For this reason, we
// keep track of and reuse loads we insert.
DenseMap<BasicBlock*, Value*> Loads;
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
if (PN->getIncomingValue(i) == &I) {
Value *&V = Loads[PN->getIncomingBlock(i)];
if (!V) {
// Insert the load into the predecessor block
V = new LoadInst(Slot, I.getName()+".reload", VolatileLoads,
PN->getIncomingBlock(i)->getTerminator());
}
PN->setIncomingValue(i, V);
}
} else {
// If this is a normal instruction, just insert a load.
Value *V = new LoadInst(Slot, I.getName()+".reload", VolatileLoads, U);
U->replaceUsesOfWith(&I, V);
}
}
// Insert stores of the computed value into the stack slot. We have to be
// careful if I is an invoke instruction, because we can't insert the store
// AFTER the terminator instruction.
BasicBlock::iterator InsertPt;
if (!isa<TerminatorInst>(I)) {
InsertPt = &I;
++InsertPt;
for (; isa<PHINode>(InsertPt) || InsertPt->isEHPad(); ++InsertPt)
/* empty */; // Don't insert before PHI nodes or landingpad instrs.
} else {
InvokeInst &II = cast<InvokeInst>(I);
InsertPt = II.getNormalDest()->getFirstInsertionPt();
}
new StoreInst(&I, Slot, InsertPt);
return Slot;
}
