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LiveIntervalAnalysis: Rework constructMainRangeFromSubranges()
We now use LiveRangeCalc::extendToUses() instead of a specially designed algorithm in constructMainRangeFromSubranges(): - The original motivation for constructMainRangeFromSubranges() were differences between the main liverange and subranges because of hidden dead definitions. This case however cannot happen anymore with the DetectDeadLaneMasks pass in place. - It simplifies the code. - This fixes a longstanding bug where we did not properly create new SSA values on merging control flow (the MachineVerifier missed most of these cases). - Move constructMainRangeFromSubranges() to LiveIntervalAnalysis and LiveRangeCalc to better match the implementation/available helper functions. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@269016 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Matthias Braun
+20
-245
@@ -815,239 +815,6 @@ void LiveInterval::clearSubRanges() {
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SubRanges = nullptr;
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}
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/// Helper function for constructMainRangeFromSubranges(): Search the CFG
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/// backwards until we find a place covered by a LiveRange segment that actually
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/// has a valno set.
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static VNInfo *searchForVNI(const SlotIndexes &Indexes, LiveRange &LR,
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const MachineBasicBlock *MBB,
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SmallPtrSetImpl<const MachineBasicBlock*> &Visited) {
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// We start the search at the end of MBB.
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SlotIndex EndIdx = Indexes.getMBBEndIdx(MBB);
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// In our use case we can't live the area covered by the live segments without
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// finding an actual VNI def.
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LiveRange::iterator I = LR.find(EndIdx.getPrevSlot());
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assert(I != LR.end());
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LiveRange::Segment &S = *I;
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if (S.valno != nullptr)
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return S.valno;
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VNInfo *VNI = nullptr;
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// Continue at predecessors (we could even go to idom with domtree available).
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for (const MachineBasicBlock *Pred : MBB->predecessors()) {
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// Avoid going in circles.
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if (!Visited.insert(Pred).second)
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continue;
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VNI = searchForVNI(Indexes, LR, Pred, Visited);
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if (VNI != nullptr) {
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S.valno = VNI;
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break;
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}
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}
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return VNI;
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}
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static void determineMissingVNIs(const SlotIndexes &Indexes, LiveInterval &LI) {
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SmallPtrSet<const MachineBasicBlock*, 5> Visited;
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LiveRange::iterator OutIt;
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VNInfo *PrevValNo = nullptr;
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for (LiveRange::iterator I = LI.begin(), E = LI.end(); I != E; ++I) {
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LiveRange::Segment &S = *I;
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// Determine final VNI if necessary.
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if (S.valno == nullptr) {
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// This can only happen at the begin of a basic block.
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assert(S.start.isBlock() && "valno should only be missing at block begin");
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Visited.clear();
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const MachineBasicBlock *MBB = Indexes.getMBBFromIndex(S.start);
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for (const MachineBasicBlock *Pred : MBB->predecessors()) {
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VNInfo *VNI = searchForVNI(Indexes, LI, Pred, Visited);
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if (VNI != nullptr) {
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S.valno = VNI;
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break;
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}
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}
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assert(S.valno != nullptr && "could not determine valno");
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}
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// Merge with previous segment if it has the same VNI.
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if (PrevValNo == S.valno && OutIt->end == S.start) {
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OutIt->end = S.end;
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} else {
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// Didn't merge. Move OutIt to next segment.
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if (PrevValNo == nullptr)
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OutIt = LI.begin();
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else
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++OutIt;
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if (OutIt != I)
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*OutIt = *I;
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PrevValNo = S.valno;
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}
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}
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// If we merged some segments chop off the end.
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++OutIt;
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LI.segments.erase(OutIt, LI.end());
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}
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void LiveInterval::constructMainRangeFromSubranges(
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const SlotIndexes &Indexes, VNInfo::Allocator &VNIAllocator) {
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// The basic observations on which this algorithm is based:
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// - Each Def/ValNo in a subrange must have a corresponding def on the main
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// range, but not further defs/valnos are necessary.
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// - If any of the subranges is live at a point the main liverange has to be
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// live too, conversily if no subrange is live the main range mustn't be
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// live either.
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// We do this by scanning through all the subranges simultaneously creating new
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// segments in the main range as segments start/ends come up in the subranges.
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assert(hasSubRanges() && "expected subranges to be present");
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assert(segments.empty() && valnos.empty() && "expected empty main range");
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// Collect subrange, iterator pairs for the walk and determine first and last
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// SlotIndex involved.
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SmallVector<std::pair<const SubRange*, const_iterator>, 4> SRs;
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SlotIndex First;
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SlotIndex Last;
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for (const SubRange &SR : subranges()) {
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if (SR.empty())
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continue;
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SRs.push_back(std::make_pair(&SR, SR.begin()));
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if (!First.isValid() || SR.segments.front().start < First)
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First = SR.segments.front().start;
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if (!Last.isValid() || SR.segments.back().end > Last)
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Last = SR.segments.back().end;
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}
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// Walk over all subranges simultaneously.
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Segment CurrentSegment;
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bool ConstructingSegment = false;
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bool NeedVNIFixup = false;
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LaneBitmask ActiveMask = 0;
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SlotIndex Pos = First;
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while (true) {
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SlotIndex NextPos = Last;
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enum {
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NOTHING,
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BEGIN_SEGMENT,
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END_SEGMENT,
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} Event = NOTHING;
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// Which subregister lanes are affected by the current event.
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LaneBitmask EventMask = 0;
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// Whether a BEGIN_SEGMENT is also a valno definition point.
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bool IsDef = false;
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// Find the next begin or end of a subrange segment. Combine masks if we
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// have multiple begins/ends at the same position. Ends take precedence over
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// Begins.
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for (auto &SRP : SRs) {
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const SubRange &SR = *SRP.first;
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const_iterator &I = SRP.second;
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// Advance iterator of subrange to a segment involving Pos; the earlier
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// segments are already merged at this point.
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while (I != SR.end() &&
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(I->end < Pos ||
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(I->end == Pos && (ActiveMask & SR.LaneMask) == 0)))
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++I;
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if (I == SR.end())
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continue;
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if ((ActiveMask & SR.LaneMask) == 0 &&
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Pos <= I->start && I->start <= NextPos) {
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// Merge multiple begins at the same position.
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if (I->start == NextPos && Event == BEGIN_SEGMENT) {
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EventMask |= SR.LaneMask;
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IsDef |= I->valno->def == I->start;
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} else if (I->start < NextPos || Event != END_SEGMENT) {
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Event = BEGIN_SEGMENT;
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NextPos = I->start;
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EventMask = SR.LaneMask;
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IsDef = I->valno->def == I->start;
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}
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}
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if ((ActiveMask & SR.LaneMask) != 0 &&
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Pos <= I->end && I->end <= NextPos) {
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// Merge multiple ends at the same position.
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if (I->end == NextPos && Event == END_SEGMENT)
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EventMask |= SR.LaneMask;
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else {
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Event = END_SEGMENT;
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NextPos = I->end;
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EventMask = SR.LaneMask;
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}
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}
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}
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// Advance scan position.
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Pos = NextPos;
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if (Event == BEGIN_SEGMENT) {
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if (ConstructingSegment && IsDef) {
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// Finish previous segment because we have to start a new one.
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CurrentSegment.end = Pos;
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append(CurrentSegment);
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ConstructingSegment = false;
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}
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// Start a new segment if necessary.
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if (!ConstructingSegment) {
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// Determine value number for the segment.
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VNInfo *VNI;
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if (IsDef) {
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VNI = getNextValue(Pos, VNIAllocator);
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} else {
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// We have to reuse an existing value number, if we are lucky
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// then we already passed one of the predecessor blocks and determined
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// its value number (with blocks in reverse postorder this would be
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// always true but we have no such guarantee).
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assert(Pos.isBlock());
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const MachineBasicBlock *MBB = Indexes.getMBBFromIndex(Pos);
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// See if any of the predecessor blocks has a lower number and a VNI
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for (const MachineBasicBlock *Pred : MBB->predecessors()) {
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SlotIndex PredEnd = Indexes.getMBBEndIdx(Pred);
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VNI = getVNInfoBefore(PredEnd);
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if (VNI != nullptr)
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break;
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}
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// Def will come later: We have to do an extra fixup pass.
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if (VNI == nullptr)
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NeedVNIFixup = true;
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}
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// In rare cases we can produce adjacent segments with the same value
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// number (if they come from different subranges, but happen to have
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// the same defining instruction). VNIFixup will fix those cases.
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if (!empty() && segments.back().end == Pos &&
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segments.back().valno == VNI)
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NeedVNIFixup = true;
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CurrentSegment.start = Pos;
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CurrentSegment.valno = VNI;
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ConstructingSegment = true;
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}
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ActiveMask |= EventMask;
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} else if (Event == END_SEGMENT) {
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assert(ConstructingSegment);
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// Finish segment if no lane is active anymore.
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ActiveMask &= ~EventMask;
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if (ActiveMask == 0) {
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CurrentSegment.end = Pos;
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append(CurrentSegment);
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ConstructingSegment = false;
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}
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} else {
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// We reached the end of the last subranges and can stop.
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assert(Event == NOTHING);
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break;
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}
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}
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// We might not be able to assign new valnos for all segments if the basic
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// block containing the definition comes after a segment using the valno.
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// Do a fixup pass for this uncommon case.
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if (NeedVNIFixup)
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determineMissingVNIs(Indexes, *this);
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assert(ActiveMask == 0 && !ConstructingSegment && "all segments ended");
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verify();
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}
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unsigned LiveInterval::getSize() const {
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unsigned Sum = 0;
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for (const Segment &S : segments)
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@@ -1654,37 +1421,45 @@ void ConnectedSubRegClasses::distribute(const IntEqClasses &Classes,
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}
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}
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static bool subRangeLiveAt(const LiveInterval &LI, SlotIndex Pos) {
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for (const LiveInterval::SubRange &SR : LI.subranges()) {
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if (SR.liveAt(Pos))
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return true;
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}
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return false;
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}
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void ConnectedSubRegClasses::computeMainRangesFixFlags(
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const IntEqClasses &Classes,
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const SmallVectorImpl<SubRangeInfo> &SubRangeInfos,
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const SmallVectorImpl<LiveInterval*> &Intervals) const {
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BumpPtrAllocator &Allocator = LIS.getVNInfoAllocator();
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for (size_t I = 0, E = Intervals.size(); I < E; ++I) {
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LiveInterval *LI = Intervals[I];
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LI->removeEmptySubRanges();
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if (I == 0)
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LI->clear();
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LI->constructMainRangeFromSubranges(*LIS.getSlotIndexes(), Allocator);
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LiveInterval &LI = *Intervals[I];
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LI.removeEmptySubRanges();
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for (MachineOperand &MO : MRI.reg_nodbg_operands(LI->reg)) {
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for (MachineOperand &MO : MRI.reg_nodbg_operands(LI.reg)) {
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if (!MO.isDef())
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continue;
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unsigned SubRegIdx = MO.getSubReg();
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if (SubRegIdx == 0)
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continue;
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// After assigning the new vreg we may not have any other sublanes living
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// in and out of the instruction anymore. We need to add new dead and kill
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// flags in these cases.
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// in and out of the instruction anymore. We need to add new dead and
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// undef flags in these cases.
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if (!MO.isUndef()) {
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SlotIndex Pos = LIS.getInstructionIndex(*MO.getParent());
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if (!LI->liveAt(Pos.getBaseIndex()))
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if (!subRangeLiveAt(LI, Pos))
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MO.setIsUndef();
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}
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if (!MO.isDead()) {
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SlotIndex Pos = LIS.getInstructionIndex(*MO.getParent());
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if (!LI->liveAt(Pos.getDeadSlot()))
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SlotIndex Pos = LIS.getInstructionIndex(*MO.getParent()).getDeadSlot();
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if (!subRangeLiveAt(LI, Pos))
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MO.setIsDead();
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}
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}
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if (I == 0)
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LI.clear();
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LIS.constructMainRangeFromSubranges(LI);
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}
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}
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