lib/CodeGen/LiveRangeCalc.cpp - llvm - Git at Google

 //===---- LiveRangeCalc.cpp - Calculate live ranges -----------------------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // Implementation of the LiveRangeCalc class.
 //
 //===----------------------------------------------------------------------===//

 #define DEBUG_TYPE "regalloc"
 #include "LiveRangeCalc.h"
 #include "llvm/CodeGen/MachineDominators.h"

 using namespace llvm;

 void LiveRangeCalc::reset(const MachineFunction *MF) {
   unsigned N = MF->getNumBlockIDs();
   Seen.clear();
   Seen.resize(N);
   LiveOut.resize(N);
   LiveIn.clear();
 }


 // Transfer information from the LiveIn vector to the live ranges.
 void LiveRangeCalc::updateLiveIns(VNInfo *OverrideVNI, SlotIndexes *Indexes) {
   for (SmallVectorImpl<LiveInBlock>::iterator I = LiveIn.begin(),
          E = LiveIn.end(); I != E; ++I) {
     if (!I->DomNode)
       continue;
     MachineBasicBlock *MBB = I->DomNode->getBlock();

     VNInfo *VNI = OverrideVNI ? OverrideVNI : I->Value;
     assert(VNI && "No live-in value found");

     SlotIndex Start, End;
     tie(Start, End) = Indexes->getMBBRange(MBB);

     if (I->Kill.isValid())
       I->LI->addRange(LiveRange(Start, I->Kill, VNI));
     else {
       I->LI->addRange(LiveRange(Start, End, VNI));
       // The value is live-through, update LiveOut as well.  Defer the Domtree
       // lookup until it is needed.
       assert(Seen.test(MBB->getNumber()));
       LiveOut[MBB] = LiveOutPair(VNI, (MachineDomTreeNode *)0);
     }
   }
   LiveIn.clear();
 }


 void LiveRangeCalc::extend(LiveInterval *LI,
                            SlotIndex Kill,
                            SlotIndexes *Indexes,
                            MachineDominatorTree *DomTree,
                            VNInfo::Allocator *Alloc) {
   assert(LI && "Missing live range");
   assert(Kill.isValid() && "Invalid SlotIndex");
   assert(Indexes && "Missing SlotIndexes");
   assert(DomTree && "Missing dominator tree");

   MachineBasicBlock *KillMBB = Indexes->getMBBFromIndex(Kill.getPrevSlot());
   assert(Kill && "No MBB at Kill");

   // Is there a def in the same MBB we can extend?
   if (LI->extendInBlock(Indexes->getMBBStartIdx(KillMBB), Kill))
     return;

   // Find the single reaching def, or determine if Kill is jointly dominated by
   // multiple values, 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.
   VNInfo *VNI = findReachingDefs(LI, KillMBB, Kill, Indexes, DomTree);

   // When there were multiple different values, we may need new PHIs.
   if (!VNI)
     updateSSA(Indexes, DomTree, Alloc);

   updateLiveIns(VNI, Indexes);
 }


 // This function is called by a client after using the low-level API to add
 // live-out and live-in blocks.  The unique value optimization is not
 // available, SplitEditor::transferValues handles that case directly anyway.
 void LiveRangeCalc::calculateValues(SlotIndexes *Indexes,
                                     MachineDominatorTree *DomTree,
                                     VNInfo::Allocator *Alloc) {
   assert(Indexes && "Missing SlotIndexes");
   assert(DomTree && "Missing dominator tree");
   updateSSA(Indexes, DomTree, Alloc);
   updateLiveIns(0, Indexes);
 }


 VNInfo *LiveRangeCalc::findReachingDefs(LiveInterval *LI,
                                         MachineBasicBlock *KillMBB,
                                         SlotIndex Kill,
                                         SlotIndexes *Indexes,
                                         MachineDominatorTree *DomTree) {
   // Blocks where LI should be live-in.
   SmallVector<MachineBasicBlock*, 16> WorkList(1, KillMBB);

   // Remember if we have seen more than one value.
   bool UniqueVNI = true;
   VNInfo *TheVNI = 0;

   // Using Seen as a visited set, perform a BFS for all reaching defs.
   for (unsigned i = 0; i != WorkList.size(); ++i) {
     MachineBasicBlock *MBB = WorkList[i];
     assert(!MBB->pred_empty() && "Value live-in to entry block?");
     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?
        if (Seen.test(Pred->getNumber())) {
          if (VNInfo *VNI = LiveOut[Pred].first) {
            if (TheVNI && TheVNI != VNI)
              UniqueVNI = false;
            TheVNI = VNI;
          }
          continue;
        }

        SlotIndex Start, End;
        tie(Start, End) = Indexes->getMBBRange(Pred);

        // First time we see Pred.  Try to determine the live-out value, but set
        // it as null if Pred is live-through with an unknown value.
        VNInfo *VNI = LI->extendInBlock(Start, End);
        setLiveOutValue(Pred, VNI);
        if (VNI) {
          if (TheVNI && TheVNI != VNI)
            UniqueVNI = false;
          TheVNI = VNI;
          continue;
        }

        // No, we need a live-in value for Pred as well
        if (Pred != KillMBB)
           WorkList.push_back(Pred);
        else
           // Loopback to KillMBB, so value is really live through.
          Kill = SlotIndex();
     }
   }

   // Transfer WorkList to LiveInBlocks in reverse order.
   // This ordering works best with updateSSA().
   LiveIn.clear();
   LiveIn.reserve(WorkList.size());
   while(!WorkList.empty())
     addLiveInBlock(LI, DomTree->getNode(WorkList.pop_back_val()));

   // The kill block may not be live-through.
   assert(LiveIn.back().DomNode->getBlock() == KillMBB);
   LiveIn.back().Kill = Kill;

   return UniqueVNI ? TheVNI : 0;
 }


 // 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.
 void LiveRangeCalc::updateSSA(SlotIndexes *Indexes,
                               MachineDominatorTree *DomTree,
                               VNInfo::Allocator *Alloc) {
   assert(Indexes && "Missing SlotIndexes");
   assert(DomTree && "Missing dominator tree");

   // Interate until convergence.
   unsigned Changes;
   do {
     Changes = 0;
     // Propagate live-out values down the dominator tree, inserting phi-defs
     // when necessary.
     for (SmallVectorImpl<LiveInBlock>::iterator I = LiveIn.begin(),
            E = LiveIn.end(); I != E; ++I) {
       MachineDomTreeNode *Node = I->DomNode;
       // Skip block if the live-in value has already been determined.
       if (!Node)
         continue;
       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 || !Seen.test(IDom->getBlock()->getNumber());

       // IDom dominates all of our predecessors, but it may not be their
       // 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) {
         IDomValue = LiveOut[IDom->getBlock()];

         // Cache the DomTree node that defined the value.
         if (IDomValue.first && !IDomValue.second)
           LiveOut[IDom->getBlock()].second = IDomValue.second =
             DomTree->getNode(Indexes->getMBBFromIndex(IDomValue.first->def));

         for (MachineBasicBlock::pred_iterator PI = MBB->pred_begin(),
                PE = MBB->pred_end(); PI != PE; ++PI) {
           LiveOutPair &Value = LiveOut[*PI];
           if (!Value.first || Value.first == IDomValue.first)
             continue;

           // Cache the DomTree node that defined the value.
           if (!Value.second)
             Value.second =
               DomTree->getNode(Indexes->getMBBFromIndex(Value.first->def));

           // 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 (DomTree->dominates(IDom, Value.second)) {
             needPHI = true;
             break;
           }
         }
       }

       // The value may be live-through even if Kill is set, as can happen when
       // we are called from extendRange. In that case LiveOutSeen is true, and
       // LiveOut indicates a foreign or missing value.
       LiveOutPair &LOP = LiveOut[MBB];

       // Create a phi-def if required.
       if (needPHI) {
         ++Changes;
         assert(Alloc && "Need VNInfo allocator to create PHI-defs");
         SlotIndex Start, End;
         tie(Start, End) = Indexes->getMBBRange(MBB);
         VNInfo *VNI = I->LI->getNextValue(Start, 0, *Alloc);
         VNI->setIsPHIDef(true);
         I->Value = VNI;
         // This block is done, we know the final value.
         I->DomNode = 0;

         // Add liveness since updateLiveIns now skips this node.
         if (I->Kill.isValid())
           I->LI->addRange(LiveRange(Start, I->Kill, VNI));
         else {
           I->LI->addRange(LiveRange(Start, End, VNI));
           LOP = LiveOutPair(VNI, Node);
         }
       } else if (IDomValue.first) {
         // No phi-def here. Remember incoming value.
         I->Value = IDomValue.first;

         // If the IDomValue is killed in the block, don't propagate through.
         if (I->Kill.isValid())
           continue;

         // Propagate IDomValue if it isn't killed:
         // MBB is live-out and doesn't define its own value.
         if (LOP.first == IDomValue.first)
           continue;
         ++Changes;
         LOP = IDomValue;
       }
     }
   } while (Changes);
 }
	//===---- LiveRangeCalc.cpp - Calculate live ranges -----------------------===//
	//
	// The LLVM Compiler Infrastructure
	//
	// This file is distributed under the University of Illinois Open Source
	// License. See LICENSE.TXT for details.
	//
	//===----------------------------------------------------------------------===//
	//
	// Implementation of the LiveRangeCalc class.
	//
	//===----------------------------------------------------------------------===//

	#define DEBUG_TYPE "regalloc"
	#include "LiveRangeCalc.h"
	#include "llvm/CodeGen/MachineDominators.h"

	using namespace llvm;

	void LiveRangeCalc::reset(const MachineFunction *MF) {
	unsigned N = MF->getNumBlockIDs();
	Seen.clear();
	Seen.resize(N);
	LiveOut.resize(N);
	LiveIn.clear();
	}


	// Transfer information from the LiveIn vector to the live ranges.
	void LiveRangeCalc::updateLiveIns(VNInfo OverrideVNI, SlotIndexes Indexes) {
	for (SmallVectorImpl<LiveInBlock>::iterator I = LiveIn.begin(),
	E = LiveIn.end(); I != E; ++I) {
	if (!I->DomNode)
	continue;
	MachineBasicBlock *MBB = I->DomNode->getBlock();

	VNInfo *VNI = OverrideVNI ? OverrideVNI : I->Value;
	assert(VNI && "No live-in value found");

	SlotIndex Start, End;
	tie(Start, End) = Indexes->getMBBRange(MBB);

	if (I->Kill.isValid())
	I->LI->addRange(LiveRange(Start, I->Kill, VNI));
	else {
	I->LI->addRange(LiveRange(Start, End, VNI));
	// The value is live-through, update LiveOut as well. Defer the Domtree
	// lookup until it is needed.
	assert(Seen.test(MBB->getNumber()));
	LiveOut[MBB] = LiveOutPair(VNI, (MachineDomTreeNode *)0);
	}
	}
	LiveIn.clear();
	}


	void LiveRangeCalc::extend(LiveInterval *LI,
	SlotIndex Kill,
	SlotIndexes *Indexes,
	MachineDominatorTree *DomTree,
	VNInfo::Allocator *Alloc) {
	assert(LI && "Missing live range");
	assert(Kill.isValid() && "Invalid SlotIndex");
	assert(Indexes && "Missing SlotIndexes");
	assert(DomTree && "Missing dominator tree");

	MachineBasicBlock *KillMBB = Indexes->getMBBFromIndex(Kill.getPrevSlot());
	assert(Kill && "No MBB at Kill");

	// Is there a def in the same MBB we can extend?
	if (LI->extendInBlock(Indexes->getMBBStartIdx(KillMBB), Kill))
	return;

	// Find the single reaching def, or determine if Kill is jointly dominated by
	// multiple values, 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.
	VNInfo *VNI = findReachingDefs(LI, KillMBB, Kill, Indexes, DomTree);

	// When there were multiple different values, we may need new PHIs.
	if (!VNI)
	updateSSA(Indexes, DomTree, Alloc);

	updateLiveIns(VNI, Indexes);
	}


	// This function is called by a client after using the low-level API to add
	// live-out and live-in blocks. The unique value optimization is not
	// available, SplitEditor::transferValues handles that case directly anyway.
	void LiveRangeCalc::calculateValues(SlotIndexes *Indexes,
	MachineDominatorTree *DomTree,
	VNInfo::Allocator *Alloc) {
	assert(Indexes && "Missing SlotIndexes");
	assert(DomTree && "Missing dominator tree");
	updateSSA(Indexes, DomTree, Alloc);
	updateLiveIns(0, Indexes);
	}


	VNInfo LiveRangeCalc::findReachingDefs(LiveInterval LI,
	MachineBasicBlock *KillMBB,
	SlotIndex Kill,
	SlotIndexes *Indexes,
	MachineDominatorTree *DomTree) {
	// Blocks where LI should be live-in.
	SmallVector<MachineBasicBlock*, 16> WorkList(1, KillMBB);

	// Remember if we have seen more than one value.
	bool UniqueVNI = true;
	VNInfo *TheVNI = 0;

	// Using Seen as a visited set, perform a BFS for all reaching defs.
	for (unsigned i = 0; i != WorkList.size(); ++i) {
	MachineBasicBlock *MBB = WorkList[i];
	assert(!MBB->pred_empty() && "Value live-in to entry block?");
	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?
	if (Seen.test(Pred->getNumber())) {
	if (VNInfo *VNI = LiveOut[Pred].first) {
	if (TheVNI && TheVNI != VNI)
	UniqueVNI = false;
	TheVNI = VNI;
	}
	continue;
	}

	SlotIndex Start, End;
	tie(Start, End) = Indexes->getMBBRange(Pred);

	// First time we see Pred. Try to determine the live-out value, but set
	// it as null if Pred is live-through with an unknown value.
	VNInfo *VNI = LI->extendInBlock(Start, End);
	setLiveOutValue(Pred, VNI);
	if (VNI) {
	if (TheVNI && TheVNI != VNI)
	UniqueVNI = false;
	TheVNI = VNI;
	continue;
	}

	// No, we need a live-in value for Pred as well
	if (Pred != KillMBB)
	WorkList.push_back(Pred);
	else
	// Loopback to KillMBB, so value is really live through.
	Kill = SlotIndex();
	}
	}

	// Transfer WorkList to LiveInBlocks in reverse order.
	// This ordering works best with updateSSA().
	LiveIn.clear();
	LiveIn.reserve(WorkList.size());
	while(!WorkList.empty())
	addLiveInBlock(LI, DomTree->getNode(WorkList.pop_back_val()));

	// The kill block may not be live-through.
	assert(LiveIn.back().DomNode->getBlock() == KillMBB);
	LiveIn.back().Kill = Kill;

	return UniqueVNI ? TheVNI : 0;
	}


	// 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.
	void LiveRangeCalc::updateSSA(SlotIndexes *Indexes,
	MachineDominatorTree *DomTree,
	VNInfo::Allocator *Alloc) {
	assert(Indexes && "Missing SlotIndexes");
	assert(DomTree && "Missing dominator tree");

	// Interate until convergence.
	unsigned Changes;
	do {
	Changes = 0;
	// Propagate live-out values down the dominator tree, inserting phi-defs
	// when necessary.
	for (SmallVectorImpl<LiveInBlock>::iterator I = LiveIn.begin(),
	E = LiveIn.end(); I != E; ++I) {
	MachineDomTreeNode *Node = I->DomNode;
	// Skip block if the live-in value has already been determined.
	if (!Node)
	continue;
	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 \|\| !Seen.test(IDom->getBlock()->getNumber());

	// IDom dominates all of our predecessors, but it may not be their
	// 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) {
	IDomValue = LiveOut[IDom->getBlock()];

	// Cache the DomTree node that defined the value.
	if (IDomValue.first && !IDomValue.second)
	LiveOut[IDom->getBlock()].second = IDomValue.second =
	DomTree->getNode(Indexes->getMBBFromIndex(IDomValue.first->def));

	for (MachineBasicBlock::pred_iterator PI = MBB->pred_begin(),
	PE = MBB->pred_end(); PI != PE; ++PI) {
	LiveOutPair &Value = LiveOut[*PI];
	if (!Value.first \|\| Value.first == IDomValue.first)
	continue;

	// Cache the DomTree node that defined the value.
	if (!Value.second)
	Value.second =
	DomTree->getNode(Indexes->getMBBFromIndex(Value.first->def));

	// 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 (DomTree->dominates(IDom, Value.second)) {
	needPHI = true;
	break;
	}
	}
	}

	// The value may be live-through even if Kill is set, as can happen when
	// we are called from extendRange. In that case LiveOutSeen is true, and
	// LiveOut indicates a foreign or missing value.
	LiveOutPair &LOP = LiveOut[MBB];

	// Create a phi-def if required.
	if (needPHI) {
	++Changes;
	assert(Alloc && "Need VNInfo allocator to create PHI-defs");
	SlotIndex Start, End;
	tie(Start, End) = Indexes->getMBBRange(MBB);
	VNInfo VNI = I->LI->getNextValue(Start, 0, Alloc);
	VNI->setIsPHIDef(true);
	I->Value = VNI;
	// This block is done, we know the final value.
	I->DomNode = 0;

	// Add liveness since updateLiveIns now skips this node.
	if (I->Kill.isValid())
	I->LI->addRange(LiveRange(Start, I->Kill, VNI));
	else {
	I->LI->addRange(LiveRange(Start, End, VNI));
	LOP = LiveOutPair(VNI, Node);
	}
	} else if (IDomValue.first) {
	// No phi-def here. Remember incoming value.
	I->Value = IDomValue.first;

	// If the IDomValue is killed in the block, don't propagate through.
	if (I->Kill.isValid())
	continue;

	// Propagate IDomValue if it isn't killed:
	// MBB is live-out and doesn't define its own value.
	if (LOP.first == IDomValue.first)
	continue;
	++Changes;
	LOP = IDomValue;
	}
	}
	} while (Changes);
	}