- // Now for the fun part. We know that ParentVNI potentially has multiple defs,
- // and we may need to create even more phi-defs to preserve VNInfo SSA form.
- // Perform a search for all predecessor blocks where we know the dominating
- // VNInfo. Insert phi-def VNInfos along the path back to IdxMBB.
- DEBUG(dbgs() << "\n Reaching defs for BB#" << IdxMBB->getNumber()
- << " at " << Idx << " in " << *LI << '\n');
- DEBUG(dumpCache());
-
- // Blocks where LI should be live-in.
- SmallVector<MachineDomTreeNode*, 16> LiveIn;
- LiveIn.push_back(MDT[IdxMBB]);
-
- // Using LiveOutCache as a visited set, perform a BFS for all reaching defs.
- for (unsigned i = 0; i != LiveIn.size(); ++i) {
- MachineBasicBlock *MBB = LiveIn[i]->getBlock();
- for (MachineBasicBlock::pred_iterator PI = MBB->pred_begin(),
- PE = MBB->pred_end(); PI != PE; ++PI) {
- MachineBasicBlock *Pred = *PI;
- // Is this a known live-out block?
- std::pair<LiveOutMap::iterator,bool> LOIP =
- LiveOutCache.insert(std::make_pair(Pred, LiveOutPair()));
- // Yes, we have been here before.
- if (!LOIP.second) {
- DEBUG(if (VNInfo *VNI = LOIP.first->second.first)
- dbgs() << " known valno #" << VNI->id
- << " at BB#" << Pred->getNumber() << '\n');
- continue;
- }
-
- // Does Pred provide a live-out value?
- SlotIndex Last = LIS.getMBBEndIdx(Pred).getPrevSlot();
- if (VNInfo *VNI = extendTo(Pred, Last)) {
- MachineBasicBlock *DefMBB = LIS.getMBBFromIndex(VNI->def);
- DEBUG(dbgs() << " found valno #" << VNI->id
- << " from BB#" << DefMBB->getNumber()
- << " at BB#" << Pred->getNumber() << '\n');
- LiveOutPair &LOP = LOIP.first->second;
- LOP.first = VNI;
- LOP.second = MDT[DefMBB];
- continue;
- }
- // No, we need a live-in value for Pred as well
- if (Pred != IdxMBB)
- LiveIn.push_back(MDT[Pred]);
- }
- }
-
- // We may need to add phi-def values to preserve the SSA form.
- // This is essentially the same iterative algorithm that SSAUpdater uses,
- // except we already have a dominator tree, so we don't have to recompute it.
- VNInfo *IdxVNI = 0;
- unsigned Changes;
- do {
- Changes = 0;
- DEBUG(dbgs() << " Iterating over " << LiveIn.size() << " blocks.\n");
- // Propagate live-out values down the dominator tree, inserting phi-defs when
- // necessary. Since LiveIn was created by a BFS, going backwards makes it more
- // likely for us to visit immediate dominators before their children.
- for (unsigned i = LiveIn.size(); i; --i) {
- MachineDomTreeNode *Node = LiveIn[i-1];
- MachineBasicBlock *MBB = Node->getBlock();
- MachineDomTreeNode *IDom = Node->getIDom();
- LiveOutPair IDomValue;
- // We need a live-in value to a block with no immediate dominator?
- // This is probably an unreachable block that has survived somehow.
- bool needPHI = !IDom;
-
- // Get the IDom live-out value.
- if (!needPHI) {
- LiveOutMap::iterator I = LiveOutCache.find(IDom->getBlock());
- if (I != LiveOutCache.end())
- IDomValue = I->second;
- else
- // If IDom is outside our set of live-out blocks, there must be new
- // defs, and we need a phi-def here.
- needPHI = true;
- }
-
- // IDom dominates all of our predecessors, but it may not be the immediate
- // dominator. Check if any of them have live-out values that are properly
- // dominated by IDom. If so, we need a phi-def here.
- if (!needPHI) {
- for (MachineBasicBlock::pred_iterator PI = MBB->pred_begin(),
- PE = MBB->pred_end(); PI != PE; ++PI) {
- LiveOutPair Value = LiveOutCache[*PI];
- if (!Value.first || Value.first == IDomValue.first)
- continue;
- // This predecessor is carrying something other than IDomValue.
- // It could be because IDomValue hasn't propagated yet, or it could be
- // because MBB is in the dominance frontier of that value.
- if (MDT.dominates(IDom, Value.second)) {
- needPHI = true;
- break;
- }
- }
- }
-
- // Create a phi-def if required.
- if (needPHI) {
- ++Changes;
- SlotIndex Start = LIS.getMBBStartIdx(MBB);
- VNInfo *VNI = LI->getNextValue(Start, 0, LIS.getVNInfoAllocator());
- VNI->setIsPHIDef(true);
- DEBUG(dbgs() << " - BB#" << MBB->getNumber()
- << " phi-def #" << VNI->id << " at " << Start << '\n');
- // We no longer need LI to be live-in.
- LiveIn.erase(LiveIn.begin()+(i-1));
- // Blocks in LiveIn are either IdxMBB, or have a value live-through.
- if (MBB == IdxMBB)
- IdxVNI = VNI;
- // Check if we need to update live-out info.
- LiveOutMap::iterator I = LiveOutCache.find(MBB);
- if (I == LiveOutCache.end() || I->second.second == Node) {
- // We already have a live-out defined in MBB, so this must be IdxMBB.
- assert(MBB == IdxMBB && "Adding phi-def to known live-out");
- LI->addRange(LiveRange(Start, Idx.getNextSlot(), VNI));
- } else {
- // This phi-def is also live-out, so color the whole block.
- LI->addRange(LiveRange(Start, LIS.getMBBEndIdx(MBB), VNI));
- I->second = LiveOutPair(VNI, Node);
- }
- } else if (IDomValue.first) {
- // No phi-def here. Remember incoming value for IdxMBB.
- if (MBB == IdxMBB)
- IdxVNI = IDomValue.first;
- // Propagate IDomValue if needed:
- // MBB is live-out and doesn't define its own value.
- LiveOutMap::iterator I = LiveOutCache.find(MBB);
- if (I != LiveOutCache.end() && I->second.second != Node &&
- I->second.first != IDomValue.first) {
- ++Changes;
- I->second = IDomValue;
- DEBUG(dbgs() << " - BB#" << MBB->getNumber()
- << " idom valno #" << IDomValue.first->id
- << " from BB#" << IDom->getBlock()->getNumber() << '\n');
- }
- }
- }
- DEBUG(dbgs() << " - made " << Changes << " changes.\n");
- } while (Changes);
-
- assert(IdxVNI && "Didn't find value for Idx");
-
-#ifndef NDEBUG
- DEBUG(dumpCache());
- // Check the LiveOutCache invariants.
- for (LiveOutMap::iterator I = LiveOutCache.begin(), E = LiveOutCache.end();
- I != E; ++I) {
- assert(I->first && "Null MBB entry in cache");
- assert(I->second.first && "Null VNInfo in cache");
- assert(I->second.second && "Null DomTreeNode in cache");
- if (I->second.second->getBlock() == I->first)
- continue;
- for (MachineBasicBlock::pred_iterator PI = I->first->pred_begin(),
- PE = I->first->pred_end(); PI != PE; ++PI)
- assert(LiveOutCache.lookup(*PI) == I->second && "Bad invariant");
- }
-#endif
-
- // Since we went through the trouble of a full BFS visiting all reaching defs,
- // the values in LiveIn are now accurate. No more phi-defs are needed
- // for these blocks, so we can color the live ranges.
- // This makes the next mapValue call much faster.
- for (unsigned i = 0, e = LiveIn.size(); i != e; ++i) {
- MachineBasicBlock *MBB = LiveIn[i]->getBlock();
- SlotIndex Start = LIS.getMBBStartIdx(MBB);
- if (MBB == IdxMBB) {
- LI->addRange(LiveRange(Start, Idx.getNextSlot(), IdxVNI));
- continue;
- }
- // Anything in LiveIn other than IdxMBB is live-through.
- VNInfo *VNI = LiveOutCache.lookup(MBB).first;
- assert(VNI && "Missing block value");
- LI->addRange(LiveRange(Start, LIS.getMBBEndIdx(MBB), VNI));