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Kill flags are difficult to maintain, and liveness queries are better handled by live intervals. Kill flags are reinserted after register allocation by addKillFlags(). git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@163334 91177308-0d34-0410-b5e6-96231b3b80d8
355 lines
12 KiB
C++
355 lines
12 KiB
C++
//===---- LiveRangeCalc.cpp - Calculate live ranges -----------------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// Implementation of the LiveRangeCalc class.
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//
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//===----------------------------------------------------------------------===//
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#define DEBUG_TYPE "regalloc"
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#include "LiveRangeCalc.h"
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#include "llvm/CodeGen/MachineDominators.h"
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#include "llvm/CodeGen/MachineRegisterInfo.h"
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using namespace llvm;
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void LiveRangeCalc::reset(const MachineFunction *MF,
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SlotIndexes *SI,
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MachineDominatorTree *MDT,
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VNInfo::Allocator *VNIA) {
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MRI = &MF->getRegInfo();
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Indexes = SI;
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DomTree = MDT;
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Alloc = VNIA;
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unsigned N = MF->getNumBlockIDs();
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Seen.clear();
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Seen.resize(N);
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LiveOut.resize(N);
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LiveIn.clear();
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}
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void LiveRangeCalc::createDeadDefs(LiveInterval *LI, unsigned Reg) {
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assert(MRI && Indexes && "call reset() first");
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// Visit all def operands. If the same instruction has multiple defs of Reg,
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// LI->createDeadDef() will deduplicate.
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for (MachineRegisterInfo::def_iterator
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I = MRI->def_begin(Reg), E = MRI->def_end(); I != E; ++I) {
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const MachineInstr *MI = &*I;
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// Find the corresponding slot index.
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SlotIndex Idx;
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if (MI->isPHI())
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// PHI defs begin at the basic block start index.
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Idx = Indexes->getMBBStartIdx(MI->getParent());
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else
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// Instructions are either normal 'r', or early clobber 'e'.
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Idx = Indexes->getInstructionIndex(MI)
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.getRegSlot(I.getOperand().isEarlyClobber());
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// Create the def in LI. This may find an existing def.
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LI->createDeadDef(Idx, *Alloc);
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}
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}
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void LiveRangeCalc::extendToUses(LiveInterval *LI, unsigned Reg) {
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assert(MRI && Indexes && "call reset() first");
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// Visit all operands that read Reg. This may include partial defs.
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for (MachineRegisterInfo::reg_nodbg_iterator I = MRI->reg_nodbg_begin(Reg),
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E = MRI->reg_nodbg_end(); I != E; ++I) {
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MachineOperand &MO = I.getOperand();
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// Clear all kill flags. They will be reinserted after register allocation
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// by LiveIntervalAnalysis::addKillFlags().
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if (MO.isUse())
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MO.setIsKill(false);
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if (!MO.readsReg())
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continue;
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// MI is reading Reg. We may have visited MI before if it happens to be
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// reading Reg multiple times. That is OK, extend() is idempotent.
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const MachineInstr *MI = &*I;
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// Find the SlotIndex being read.
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SlotIndex Idx;
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if (MI->isPHI()) {
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assert(!MO.isDef() && "Cannot handle PHI def of partial register.");
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// PHI operands are paired: (Reg, PredMBB).
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// Extend the live range to be live-out from PredMBB.
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Idx = Indexes->getMBBEndIdx(MI->getOperand(I.getOperandNo()+1).getMBB());
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} else {
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// This is a normal instruction.
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Idx = Indexes->getInstructionIndex(MI).getRegSlot();
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// Check for early-clobber redefs.
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unsigned DefIdx;
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if (MO.isDef()) {
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if (MO.isEarlyClobber())
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Idx = Idx.getRegSlot(true);
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} else if (MI->isRegTiedToDefOperand(I.getOperandNo(), &DefIdx)) {
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// FIXME: This would be a lot easier if tied early-clobber uses also
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// had an early-clobber flag.
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if (MI->getOperand(DefIdx).isEarlyClobber())
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Idx = Idx.getRegSlot(true);
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}
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}
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extend(LI, Idx, Reg);
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}
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}
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// Transfer information from the LiveIn vector to the live ranges.
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void LiveRangeCalc::updateLiveIns(VNInfo *OverrideVNI) {
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for (SmallVectorImpl<LiveInBlock>::iterator I = LiveIn.begin(),
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E = LiveIn.end(); I != E; ++I) {
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if (!I->DomNode)
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continue;
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MachineBasicBlock *MBB = I->DomNode->getBlock();
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VNInfo *VNI = OverrideVNI ? OverrideVNI : I->Value;
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assert(VNI && "No live-in value found");
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SlotIndex Start, End;
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tie(Start, End) = Indexes->getMBBRange(MBB);
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if (I->Kill.isValid())
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I->LI->addRange(LiveRange(Start, I->Kill, VNI));
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else {
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I->LI->addRange(LiveRange(Start, End, VNI));
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// The value is live-through, update LiveOut as well. Defer the Domtree
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// lookup until it is needed.
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assert(Seen.test(MBB->getNumber()));
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LiveOut[MBB] = LiveOutPair(VNI, (MachineDomTreeNode *)0);
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}
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}
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LiveIn.clear();
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}
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void LiveRangeCalc::extend(LiveInterval *LI,
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SlotIndex Kill,
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unsigned PhysReg) {
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assert(LI && "Missing live range");
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assert(Kill.isValid() && "Invalid SlotIndex");
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assert(Indexes && "Missing SlotIndexes");
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assert(DomTree && "Missing dominator tree");
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MachineBasicBlock *KillMBB = Indexes->getMBBFromIndex(Kill.getPrevSlot());
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assert(KillMBB && "No MBB at Kill");
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// Is there a def in the same MBB we can extend?
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if (LI->extendInBlock(Indexes->getMBBStartIdx(KillMBB), Kill))
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return;
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// Find the single reaching def, or determine if Kill is jointly dominated by
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// multiple values, and we may need to create even more phi-defs to preserve
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// VNInfo SSA form. Perform a search for all predecessor blocks where we
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// know the dominating VNInfo.
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VNInfo *VNI = findReachingDefs(LI, KillMBB, Kill, PhysReg);
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// When there were multiple different values, we may need new PHIs.
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if (!VNI)
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updateSSA();
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updateLiveIns(VNI);
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}
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// This function is called by a client after using the low-level API to add
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// live-out and live-in blocks. The unique value optimization is not
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// available, SplitEditor::transferValues handles that case directly anyway.
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void LiveRangeCalc::calculateValues() {
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assert(Indexes && "Missing SlotIndexes");
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assert(DomTree && "Missing dominator tree");
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updateSSA();
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updateLiveIns(0);
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}
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VNInfo *LiveRangeCalc::findReachingDefs(LiveInterval *LI,
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MachineBasicBlock *KillMBB,
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SlotIndex Kill,
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unsigned PhysReg) {
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// Blocks where LI should be live-in.
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SmallVector<MachineBasicBlock*, 16> WorkList(1, KillMBB);
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// Remember if we have seen more than one value.
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bool UniqueVNI = true;
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VNInfo *TheVNI = 0;
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// Using Seen as a visited set, perform a BFS for all reaching defs.
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for (unsigned i = 0; i != WorkList.size(); ++i) {
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MachineBasicBlock *MBB = WorkList[i];
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#ifndef NDEBUG
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if (MBB->pred_empty()) {
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MBB->getParent()->verify();
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llvm_unreachable("Use not jointly dominated by defs.");
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}
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if (TargetRegisterInfo::isPhysicalRegister(PhysReg) &&
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!MBB->isLiveIn(PhysReg)) {
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MBB->getParent()->verify();
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errs() << "The register needs to be live in to BB#" << MBB->getNumber()
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<< ", but is missing from the live-in list.\n";
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llvm_unreachable("Invalid global physical register");
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}
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#endif
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for (MachineBasicBlock::pred_iterator PI = MBB->pred_begin(),
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PE = MBB->pred_end(); PI != PE; ++PI) {
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MachineBasicBlock *Pred = *PI;
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// Is this a known live-out block?
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if (Seen.test(Pred->getNumber())) {
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if (VNInfo *VNI = LiveOut[Pred].first) {
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if (TheVNI && TheVNI != VNI)
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UniqueVNI = false;
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TheVNI = VNI;
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}
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continue;
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}
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SlotIndex Start, End;
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tie(Start, End) = Indexes->getMBBRange(Pred);
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// First time we see Pred. Try to determine the live-out value, but set
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// it as null if Pred is live-through with an unknown value.
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VNInfo *VNI = LI->extendInBlock(Start, End);
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setLiveOutValue(Pred, VNI);
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if (VNI) {
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if (TheVNI && TheVNI != VNI)
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UniqueVNI = false;
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TheVNI = VNI;
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continue;
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}
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// No, we need a live-in value for Pred as well
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if (Pred != KillMBB)
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WorkList.push_back(Pred);
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else
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// Loopback to KillMBB, so value is really live through.
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Kill = SlotIndex();
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}
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}
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// Transfer WorkList to LiveInBlocks in reverse order.
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// This ordering works best with updateSSA().
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LiveIn.clear();
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LiveIn.reserve(WorkList.size());
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while(!WorkList.empty())
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addLiveInBlock(LI, DomTree->getNode(WorkList.pop_back_val()));
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// The kill block may not be live-through.
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assert(LiveIn.back().DomNode->getBlock() == KillMBB);
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LiveIn.back().Kill = Kill;
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return UniqueVNI ? TheVNI : 0;
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}
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// This is essentially the same iterative algorithm that SSAUpdater uses,
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// except we already have a dominator tree, so we don't have to recompute it.
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void LiveRangeCalc::updateSSA() {
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assert(Indexes && "Missing SlotIndexes");
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assert(DomTree && "Missing dominator tree");
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// Interate until convergence.
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unsigned Changes;
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do {
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Changes = 0;
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// Propagate live-out values down the dominator tree, inserting phi-defs
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// when necessary.
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for (SmallVectorImpl<LiveInBlock>::iterator I = LiveIn.begin(),
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E = LiveIn.end(); I != E; ++I) {
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MachineDomTreeNode *Node = I->DomNode;
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// Skip block if the live-in value has already been determined.
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if (!Node)
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continue;
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MachineBasicBlock *MBB = Node->getBlock();
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MachineDomTreeNode *IDom = Node->getIDom();
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LiveOutPair IDomValue;
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// We need a live-in value to a block with no immediate dominator?
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// This is probably an unreachable block that has survived somehow.
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bool needPHI = !IDom || !Seen.test(IDom->getBlock()->getNumber());
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// IDom dominates all of our predecessors, but it may not be their
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// immediate dominator. Check if any of them have live-out values that are
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// properly dominated by IDom. If so, we need a phi-def here.
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if (!needPHI) {
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IDomValue = LiveOut[IDom->getBlock()];
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// Cache the DomTree node that defined the value.
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if (IDomValue.first && !IDomValue.second)
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LiveOut[IDom->getBlock()].second = IDomValue.second =
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DomTree->getNode(Indexes->getMBBFromIndex(IDomValue.first->def));
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for (MachineBasicBlock::pred_iterator PI = MBB->pred_begin(),
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PE = MBB->pred_end(); PI != PE; ++PI) {
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LiveOutPair &Value = LiveOut[*PI];
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if (!Value.first || Value.first == IDomValue.first)
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continue;
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// Cache the DomTree node that defined the value.
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if (!Value.second)
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Value.second =
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DomTree->getNode(Indexes->getMBBFromIndex(Value.first->def));
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// This predecessor is carrying something other than IDomValue.
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// It could be because IDomValue hasn't propagated yet, or it could be
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// because MBB is in the dominance frontier of that value.
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if (DomTree->dominates(IDom, Value.second)) {
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needPHI = true;
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break;
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}
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}
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}
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// The value may be live-through even if Kill is set, as can happen when
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// we are called from extendRange. In that case LiveOutSeen is true, and
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// LiveOut indicates a foreign or missing value.
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LiveOutPair &LOP = LiveOut[MBB];
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// Create a phi-def if required.
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if (needPHI) {
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++Changes;
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assert(Alloc && "Need VNInfo allocator to create PHI-defs");
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SlotIndex Start, End;
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tie(Start, End) = Indexes->getMBBRange(MBB);
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VNInfo *VNI = I->LI->getNextValue(Start, *Alloc);
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I->Value = VNI;
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// This block is done, we know the final value.
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I->DomNode = 0;
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// Add liveness since updateLiveIns now skips this node.
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if (I->Kill.isValid())
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I->LI->addRange(LiveRange(Start, I->Kill, VNI));
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else {
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I->LI->addRange(LiveRange(Start, End, VNI));
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LOP = LiveOutPair(VNI, Node);
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}
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} else if (IDomValue.first) {
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// No phi-def here. Remember incoming value.
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I->Value = IDomValue.first;
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// If the IDomValue is killed in the block, don't propagate through.
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if (I->Kill.isValid())
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continue;
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// Propagate IDomValue if it isn't killed:
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// MBB is live-out and doesn't define its own value.
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if (LOP.first == IDomValue.first)
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continue;
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++Changes;
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LOP = IDomValue;
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}
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}
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} while (Changes);
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}
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