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This function constructs the main liverange by merging all subranges if subregister liveness tracking is available. This should be slightly faster to compute instead of performing the liveness calculation again for the main range. More importantly it avoids cases where the main liverange would cover positions where no subrange was live. These cases happened for partial definitions where the actual defined part was dead and only the undefined parts used later. The register coalescing requires that every part covered by the main live range has at least one subrange live. I also expect this function to become usefull later for places where the subranges are modified in a way that it is hard to correctly fix the main liverange in the machine scheduler, we can simply reconstruct it from subranges then. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@224806 91177308-0d34-0410-b5e6-96231b3b80d8
465 lines
16 KiB
C++
465 lines
16 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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#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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#define DEBUG_TYPE "regalloc"
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void LiveRangeCalc::resetLiveOutMap() {
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unsigned NumBlocks = MF->getNumBlockIDs();
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Seen.clear();
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Seen.resize(NumBlocks);
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Map.resize(NumBlocks);
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}
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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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MF = mf;
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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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resetLiveOutMap();
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LiveIn.clear();
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}
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static void createDeadDef(SlotIndexes &Indexes, VNInfo::Allocator &Alloc,
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LiveRange &LR, const MachineOperand &MO) {
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const MachineInstr *MI = MO.getParent();
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SlotIndex DefIdx;
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if (MI->isPHI())
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DefIdx = Indexes.getMBBStartIdx(MI->getParent());
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else
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DefIdx = Indexes.getInstructionIndex(MI).getRegSlot(MO.isEarlyClobber());
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// Create the def in LR. This may find an existing def.
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LR.createDeadDef(DefIdx, Alloc);
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}
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void LiveRangeCalc::calculate(LiveInterval &LI) {
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assert(MRI && Indexes && "call reset() first");
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// Step 1: Create minimal live segments for every definition of Reg.
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// Visit all def operands. If the same instruction has multiple defs of Reg,
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// createDeadDef() will deduplicate.
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const TargetRegisterInfo &TRI = *MRI->getTargetRegisterInfo();
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unsigned Reg = LI.reg;
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for (const MachineOperand &MO : MRI->reg_nodbg_operands(Reg)) {
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if (!MO.isDef() && !MO.readsReg())
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continue;
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unsigned SubReg = MO.getSubReg();
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if (LI.hasSubRanges() || (SubReg != 0 && MRI->tracksSubRegLiveness())) {
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unsigned Mask = SubReg != 0 ? TRI.getSubRegIndexLaneMask(SubReg)
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: MRI->getMaxLaneMaskForVReg(Reg);
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// If this is the first time we see a subregister def, initialize
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// subranges by creating a copy of the main range.
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if (!LI.hasSubRanges() && !LI.empty()) {
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unsigned ClassMask = MRI->getMaxLaneMaskForVReg(Reg);
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LI.createSubRangeFrom(*Alloc, ClassMask, LI);
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}
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for (LiveInterval::SubRange &S : LI.subranges()) {
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// A Mask for subregs common to the existing subrange and current def.
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unsigned Common = S.LaneMask & Mask;
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if (Common == 0)
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continue;
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// A Mask for subregs covered by the subrange but not the current def.
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unsigned LRest = S.LaneMask & ~Mask;
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LiveInterval::SubRange *CommonRange;
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if (LRest != 0) {
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// Split current subrange into Common and LRest ranges.
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S.LaneMask = LRest;
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CommonRange = LI.createSubRangeFrom(*Alloc, Common, S);
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} else {
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assert(Common == S.LaneMask);
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CommonRange = &S;
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}
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if (MO.isDef())
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createDeadDef(*Indexes, *Alloc, *CommonRange, MO);
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Mask &= ~Common;
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}
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// Create a new SubRange for subregs we did not cover yet.
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if (Mask != 0) {
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LiveInterval::SubRange *NewRange = LI.createSubRange(*Alloc, Mask);
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if (MO.isDef())
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createDeadDef(*Indexes, *Alloc, *NewRange, MO);
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}
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}
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// Create the def in the main liverange. We do not have to do this if
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// subranges are tracked as we recreate the main range later in this case.
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if (MO.isDef() && !LI.hasSubRanges())
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createDeadDef(*Indexes, *Alloc, LI, MO);
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}
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// We may have created empty live ranges for partially undefined uses, we
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// can't keep them because we won't find defs in them later.
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LI.removeEmptySubRanges();
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// Step 2: Extend live segments to all uses, constructing SSA form as
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// necessary.
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if (LI.hasSubRanges()) {
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for (LiveInterval::SubRange &S : LI.subranges()) {
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resetLiveOutMap();
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extendToUses(S, Reg, S.LaneMask);
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}
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LI.clear();
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LI.constructMainRangeFromSubranges(*Indexes, *Alloc);
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} else {
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resetLiveOutMap();
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extendToUses(LI, Reg, ~0u);
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}
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}
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void LiveRangeCalc::createDeadDefs(LiveRange &LR, 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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// LR.createDeadDef() will deduplicate.
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for (MachineOperand &MO : MRI->def_operands(Reg))
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createDeadDef(*Indexes, *Alloc, LR, MO);
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}
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void LiveRangeCalc::extendToUses(LiveRange &LR, unsigned Reg, unsigned Mask) {
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// Visit all operands that read Reg. This may include partial defs.
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const TargetRegisterInfo &TRI = *MRI->getTargetRegisterInfo();
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for (MachineOperand &MO : MRI->reg_nodbg_operands(Reg)) {
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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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else {
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// We only care about uses, but on the main range (mask ~0u) this includes
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// the "virtual" reads happening for subregister defs.
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if (Mask != ~0u)
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continue;
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}
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if (!MO.readsReg())
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continue;
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unsigned SubReg = MO.getSubReg();
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if (SubReg != 0) {
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unsigned SubRegMask = TRI.getSubRegIndexLaneMask(SubReg);
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// Ignore uses not covering the current subrange.
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if ((SubRegMask & Mask) == 0)
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continue;
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}
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// Determine the actual place of the use.
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const MachineInstr *MI = MO.getParent();
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unsigned OpNo = (&MO - &MI->getOperand(0));
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SlotIndex UseIdx;
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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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// The actual place where a phi operand is used is the end of the pred
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// MBB. PHI operands are paired: (Reg, PredMBB).
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UseIdx = Indexes->getMBBEndIdx(MI->getOperand(OpNo+1).getMBB());
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} else {
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// Check for early-clobber redefs.
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bool isEarlyClobber = false;
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unsigned DefIdx;
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if (MO.isDef())
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isEarlyClobber = MO.isEarlyClobber();
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else if (MI->isRegTiedToDefOperand(OpNo, &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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isEarlyClobber = MI->getOperand(DefIdx).isEarlyClobber();
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}
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UseIdx = Indexes->getInstructionIndex(MI).getRegSlot(isEarlyClobber);
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}
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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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extend(LR, UseIdx, Reg);
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}
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}
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void LiveRangeCalc::updateFromLiveIns() {
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LiveRangeUpdater Updater;
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for (const LiveInBlock &I : LiveIn) {
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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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assert(I.Value && "No live-in value found");
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SlotIndex Start, End;
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std::tie(Start, End) = Indexes->getMBBRange(MBB);
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if (I.Kill.isValid())
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// Value is killed inside this block.
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End = I.Kill;
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else {
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// The value is live-through, update LiveOut as well.
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// Defer the Domtree lookup until it is needed.
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assert(Seen.test(MBB->getNumber()));
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Map[MBB] = LiveOutPair(I.Value, nullptr);
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}
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Updater.setDest(&I.LR);
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Updater.add(Start, End, I.Value);
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}
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LiveIn.clear();
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}
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void LiveRangeCalc::extend(LiveRange &LR, SlotIndex Kill, unsigned PhysReg) {
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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 (LR.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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if (findReachingDefs(LR, *KillMBB, Kill, PhysReg))
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return;
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// When there were multiple different values, we may need new PHIs.
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calculateValues();
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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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updateFromLiveIns();
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}
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bool LiveRangeCalc::findReachingDefs(LiveRange &LR, MachineBasicBlock &KillMBB,
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SlotIndex Kill, unsigned PhysReg) {
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unsigned KillMBBNum = KillMBB.getNumber();
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// Block numbers where LR should be live-in.
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SmallVector<unsigned, 16> WorkList(1, KillMBBNum);
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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 = nullptr;
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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 = MF->getBlockNumbered(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 = Map[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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std::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 = LR.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->getNumber());
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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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LiveIn.clear();
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// Both updateSSA() and LiveRangeUpdater benefit from ordered blocks, but
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// neither require it. Skip the sorting overhead for small updates.
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if (WorkList.size() > 4)
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array_pod_sort(WorkList.begin(), WorkList.end());
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// If a unique reaching def was found, blit in the live ranges immediately.
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if (UniqueVNI) {
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LiveRangeUpdater Updater(&LR);
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for (SmallVectorImpl<unsigned>::const_iterator I = WorkList.begin(),
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E = WorkList.end(); I != E; ++I) {
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SlotIndex Start, End;
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std::tie(Start, End) = Indexes->getMBBRange(*I);
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// Trim the live range in KillMBB.
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if (*I == KillMBBNum && Kill.isValid())
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End = Kill;
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else
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Map[MF->getBlockNumbered(*I)] = LiveOutPair(TheVNI, nullptr);
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Updater.add(Start, End, TheVNI);
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}
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return true;
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}
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// Multiple values were found, so transfer the work list to the LiveIn array
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// where UpdateSSA will use it as a work list.
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LiveIn.reserve(WorkList.size());
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for (SmallVectorImpl<unsigned>::const_iterator
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I = WorkList.begin(), E = WorkList.end(); I != E; ++I) {
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MachineBasicBlock *MBB = MF->getBlockNumbered(*I);
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addLiveInBlock(LR, DomTree->getNode(MBB));
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if (MBB == &KillMBB)
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LiveIn.back().Kill = Kill;
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}
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return false;
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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 (LiveInBlock &I : LiveIn) {
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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 = Map[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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Map[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 = Map[*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 = Map[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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std::tie(Start, End) = Indexes->getMBBRange(MBB);
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LiveRange &LR = I.LR;
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VNInfo *VNI = LR.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 = nullptr;
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// Add liveness since updateFromLiveIns now skips this node.
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if (I.Kill.isValid())
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LR.addSegment(LiveInterval::Segment(Start, I.Kill, VNI));
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else {
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LR.addSegment(LiveInterval::Segment(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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