// enterBasicBlock - Set up LiveRegs by merging predecessor live-out values.
void ExeDepsFix::enterBasicBlock(MachineBasicBlock *MBB) {
// Detect back-edges from predecessors we haven't processed yet.
SeenUnknownBackEdge = false;
// Reset instruction counter in each basic block.
CurInstr = 0;
// Set up LiveRegs to represent registers entering MBB.
if (!LiveRegs)
LiveRegs = new LiveReg[NumRegs];
// Default values are 'nothing happened a long time ago'.
for (unsigned rx = 0; rx != NumRegs; ++rx) {
LiveRegs[rx].Value = 0;
LiveRegs[rx].Def = -(1 << 20);
}
// This is the entry block.
if (MBB->pred_empty()) {
for (MachineBasicBlock::livein_iterator i = MBB->livein_begin(),
e = MBB->livein_end(); i != e; ++i) {
int rx = regIndex(*i);
if (rx < 0)
continue;
// Treat function live-ins as if they were defined just before the first
// instruction. Usually, function arguments are set up immediately
// before the call.
LiveRegs[rx].Def = -1;
}
DEBUG(dbgs() << "BB#" << MBB->getNumber() << ": entry\n");
return;
}
// Try to coalesce live-out registers from predecessors.
for (MachineBasicBlock::const_pred_iterator pi = MBB->pred_begin(),
pe = MBB->pred_end(); pi != pe; ++pi) {
LiveOutMap::const_iterator fi = LiveOuts.find(*pi);
if (fi == LiveOuts.end()) {
SeenUnknownBackEdge = true;
continue;
}
assert(fi->second && "Can't have NULL entries");
for (unsigned rx = 0; rx != NumRegs; ++rx) {
// Use the most recent predecessor def for each register.
LiveRegs[rx].Def = std::max(LiveRegs[rx].Def, fi->second[rx].Def);
DomainValue *pdv = resolve(fi->second[rx].Value);
if (!pdv)
continue;
if (!LiveRegs[rx].Value) {
setLiveReg(rx, pdv);
continue;
}
// We have a live DomainValue from more than one predecessor.
if (LiveRegs[rx].Value->isCollapsed()) {
// We are already collapsed, but predecessor is not. Force him.
unsigned Domain = LiveRegs[rx].Value->getFirstDomain();
if (!pdv->isCollapsed() && pdv->hasDomain(Domain))
collapse(pdv, Domain);
continue;
}
// Currently open, merge in predecessor.
if (!pdv->isCollapsed())
merge(LiveRegs[rx].Value, pdv);
else
force(rx, pdv->getFirstDomain());
}
}
DEBUG(dbgs() << "BB#" << MBB->getNumber()
<< (SeenUnknownBackEdge ? ": incomplete\n" : ": all preds known\n"));
}
/// Set up LiveRegs by merging predecessor live-out values.
void ExeDepsFix::enterBasicBlock(MachineBasicBlock *MBB) {
// Reset instruction counter in each basic block.
CurInstr = 0;
// Set up UndefReads to track undefined register reads.
UndefReads.clear();
LiveRegSet.clear();
// Set up LiveRegs to represent registers entering MBB.
if (!LiveRegs)
LiveRegs = new LiveReg[NumRegs];
// Default values are 'nothing happened a long time ago'.
for (unsigned rx = 0; rx != NumRegs; ++rx) {
LiveRegs[rx].Value = nullptr;
LiveRegs[rx].Def = -(1 << 20);
}
// This is the entry block.
if (MBB->pred_empty()) {
for (const auto &LI : MBB->liveins()) {
for (int rx : regIndices(LI.PhysReg)) {
// Treat function live-ins as if they were defined just before the first
// instruction. Usually, function arguments are set up immediately
// before the call.
LiveRegs[rx].Def = -1;
}
}
DEBUG(dbgs() << "BB#" << MBB->getNumber() << ": entry\n");
return;
}
// Try to coalesce live-out registers from predecessors.
for (MachineBasicBlock::const_pred_iterator pi = MBB->pred_begin(),
pe = MBB->pred_end(); pi != pe; ++pi) {
auto fi = MBBInfos.find(*pi);
assert(fi != MBBInfos.end() &&
"Should have pre-allocated MBBInfos for all MBBs");
LiveReg *Incoming = fi->second.OutRegs;
// Incoming is null if this is a backedge from a BB
// we haven't processed yet
if (Incoming == nullptr) {
continue;
}
for (unsigned rx = 0; rx != NumRegs; ++rx) {
// Use the most recent predecessor def for each register.
LiveRegs[rx].Def = std::max(LiveRegs[rx].Def, Incoming[rx].Def);
DomainValue *pdv = resolve(Incoming[rx].Value);
if (!pdv)
continue;
if (!LiveRegs[rx].Value) {
setLiveReg(rx, pdv);
continue;
}
// We have a live DomainValue from more than one predecessor.
if (LiveRegs[rx].Value->isCollapsed()) {
// We are already collapsed, but predecessor is not. Force it.
unsigned Domain = LiveRegs[rx].Value->getFirstDomain();
if (!pdv->isCollapsed() && pdv->hasDomain(Domain))
collapse(pdv, Domain);
continue;
}
// Currently open, merge in predecessor.
if (!pdv->isCollapsed())
merge(LiveRegs[rx].Value, pdv);
else
force(rx, pdv->getFirstDomain());
}
}
DEBUG(
dbgs() << "BB#" << MBB->getNumber()
<< (!isBlockDone(MBB) ? ": incomplete\n" : ": all preds known\n"));
}