1 //===---- LiveRangeCalc.cpp - Calculate live ranges -----------------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // Implementation of the LiveRangeCalc class.
12 //===----------------------------------------------------------------------===//
14 #define DEBUG_TYPE "regalloc"
15 #include "LiveRangeCalc.h"
16 #include "llvm/CodeGen/MachineDominators.h"
20 void LiveRangeCalc::reset(const MachineFunction *MF,
22 MachineDominatorTree *MDT,
23 VNInfo::Allocator *VNIA) {
24 MRI = &MF->getRegInfo();
29 unsigned N = MF->getNumBlockIDs();
37 // Transfer information from the LiveIn vector to the live ranges.
38 void LiveRangeCalc::updateLiveIns(VNInfo *OverrideVNI) {
39 for (SmallVectorImpl<LiveInBlock>::iterator I = LiveIn.begin(),
40 E = LiveIn.end(); I != E; ++I) {
43 MachineBasicBlock *MBB = I->DomNode->getBlock();
45 VNInfo *VNI = OverrideVNI ? OverrideVNI : I->Value;
46 assert(VNI && "No live-in value found");
49 tie(Start, End) = Indexes->getMBBRange(MBB);
51 if (I->Kill.isValid())
52 I->LI->addRange(LiveRange(Start, I->Kill, VNI));
54 I->LI->addRange(LiveRange(Start, End, VNI));
55 // The value is live-through, update LiveOut as well. Defer the Domtree
56 // lookup until it is needed.
57 assert(Seen.test(MBB->getNumber()));
58 LiveOut[MBB] = LiveOutPair(VNI, (MachineDomTreeNode *)0);
65 void LiveRangeCalc::extend(LiveInterval *LI,
67 assert(LI && "Missing live range");
68 assert(Kill.isValid() && "Invalid SlotIndex");
69 assert(Indexes && "Missing SlotIndexes");
70 assert(DomTree && "Missing dominator tree");
72 MachineBasicBlock *KillMBB = Indexes->getMBBFromIndex(Kill.getPrevSlot());
73 assert(KillMBB && "No MBB at Kill");
75 // Is there a def in the same MBB we can extend?
76 if (LI->extendInBlock(Indexes->getMBBStartIdx(KillMBB), Kill))
79 // Find the single reaching def, or determine if Kill is jointly dominated by
80 // multiple values, and we may need to create even more phi-defs to preserve
81 // VNInfo SSA form. Perform a search for all predecessor blocks where we
82 // know the dominating VNInfo.
83 VNInfo *VNI = findReachingDefs(LI, KillMBB, Kill);
85 // When there were multiple different values, we may need new PHIs.
93 // This function is called by a client after using the low-level API to add
94 // live-out and live-in blocks. The unique value optimization is not
95 // available, SplitEditor::transferValues handles that case directly anyway.
96 void LiveRangeCalc::calculateValues() {
97 assert(Indexes && "Missing SlotIndexes");
98 assert(DomTree && "Missing dominator tree");
104 VNInfo *LiveRangeCalc::findReachingDefs(LiveInterval *LI,
105 MachineBasicBlock *KillMBB,
107 // Blocks where LI should be live-in.
108 SmallVector<MachineBasicBlock*, 16> WorkList(1, KillMBB);
110 // Remember if we have seen more than one value.
111 bool UniqueVNI = true;
114 // Using Seen as a visited set, perform a BFS for all reaching defs.
115 for (unsigned i = 0; i != WorkList.size(); ++i) {
116 MachineBasicBlock *MBB = WorkList[i];
117 assert(!MBB->pred_empty() && "Value live-in to entry block?");
118 for (MachineBasicBlock::pred_iterator PI = MBB->pred_begin(),
119 PE = MBB->pred_end(); PI != PE; ++PI) {
120 MachineBasicBlock *Pred = *PI;
122 // Is this a known live-out block?
123 if (Seen.test(Pred->getNumber())) {
124 if (VNInfo *VNI = LiveOut[Pred].first) {
125 if (TheVNI && TheVNI != VNI)
132 SlotIndex Start, End;
133 tie(Start, End) = Indexes->getMBBRange(Pred);
135 // First time we see Pred. Try to determine the live-out value, but set
136 // it as null if Pred is live-through with an unknown value.
137 VNInfo *VNI = LI->extendInBlock(Start, End);
138 setLiveOutValue(Pred, VNI);
140 if (TheVNI && TheVNI != VNI)
146 // No, we need a live-in value for Pred as well
148 WorkList.push_back(Pred);
150 // Loopback to KillMBB, so value is really live through.
155 // Transfer WorkList to LiveInBlocks in reverse order.
156 // This ordering works best with updateSSA().
158 LiveIn.reserve(WorkList.size());
159 while(!WorkList.empty())
160 addLiveInBlock(LI, DomTree->getNode(WorkList.pop_back_val()));
162 // The kill block may not be live-through.
163 assert(LiveIn.back().DomNode->getBlock() == KillMBB);
164 LiveIn.back().Kill = Kill;
166 return UniqueVNI ? TheVNI : 0;
170 // This is essentially the same iterative algorithm that SSAUpdater uses,
171 // except we already have a dominator tree, so we don't have to recompute it.
172 void LiveRangeCalc::updateSSA() {
173 assert(Indexes && "Missing SlotIndexes");
174 assert(DomTree && "Missing dominator tree");
176 // Interate until convergence.
180 // Propagate live-out values down the dominator tree, inserting phi-defs
182 for (SmallVectorImpl<LiveInBlock>::iterator I = LiveIn.begin(),
183 E = LiveIn.end(); I != E; ++I) {
184 MachineDomTreeNode *Node = I->DomNode;
185 // Skip block if the live-in value has already been determined.
188 MachineBasicBlock *MBB = Node->getBlock();
189 MachineDomTreeNode *IDom = Node->getIDom();
190 LiveOutPair IDomValue;
192 // We need a live-in value to a block with no immediate dominator?
193 // This is probably an unreachable block that has survived somehow.
194 bool needPHI = !IDom || !Seen.test(IDom->getBlock()->getNumber());
196 // IDom dominates all of our predecessors, but it may not be their
197 // immediate dominator. Check if any of them have live-out values that are
198 // properly dominated by IDom. If so, we need a phi-def here.
200 IDomValue = LiveOut[IDom->getBlock()];
202 // Cache the DomTree node that defined the value.
203 if (IDomValue.first && !IDomValue.second)
204 LiveOut[IDom->getBlock()].second = IDomValue.second =
205 DomTree->getNode(Indexes->getMBBFromIndex(IDomValue.first->def));
207 for (MachineBasicBlock::pred_iterator PI = MBB->pred_begin(),
208 PE = MBB->pred_end(); PI != PE; ++PI) {
209 LiveOutPair &Value = LiveOut[*PI];
210 if (!Value.first || Value.first == IDomValue.first)
213 // Cache the DomTree node that defined the value.
216 DomTree->getNode(Indexes->getMBBFromIndex(Value.first->def));
218 // This predecessor is carrying something other than IDomValue.
219 // It could be because IDomValue hasn't propagated yet, or it could be
220 // because MBB is in the dominance frontier of that value.
221 if (DomTree->dominates(IDom, Value.second)) {
228 // The value may be live-through even if Kill is set, as can happen when
229 // we are called from extendRange. In that case LiveOutSeen is true, and
230 // LiveOut indicates a foreign or missing value.
231 LiveOutPair &LOP = LiveOut[MBB];
233 // Create a phi-def if required.
236 assert(Alloc && "Need VNInfo allocator to create PHI-defs");
237 SlotIndex Start, End;
238 tie(Start, End) = Indexes->getMBBRange(MBB);
239 VNInfo *VNI = I->LI->getNextValue(Start, *Alloc);
240 VNI->setIsPHIDef(true);
242 // This block is done, we know the final value.
245 // Add liveness since updateLiveIns now skips this node.
246 if (I->Kill.isValid())
247 I->LI->addRange(LiveRange(Start, I->Kill, VNI));
249 I->LI->addRange(LiveRange(Start, End, VNI));
250 LOP = LiveOutPair(VNI, Node);
252 } else if (IDomValue.first) {
253 // No phi-def here. Remember incoming value.
254 I->Value = IDomValue.first;
256 // If the IDomValue is killed in the block, don't propagate through.
257 if (I->Kill.isValid())
260 // Propagate IDomValue if it isn't killed:
261 // MBB is live-out and doesn't define its own value.
262 if (LOP.first == IDomValue.first)