LiveIntervalAnalysis: Cleanup computeDeadValues

- This also fixes a bug introduced in r223880 where values were not
  correctly marked as Dead anymore.
- Cleanup computeDeadValues(): split up SubRange code variant, simplify
  arguments.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@224538 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/CodeGen/LiveInterval.h

@@ -472,6 +472,12 @@ namespace llvm {
       removeSegment(S.start, S.end, RemoveDeadValNo);
     }
 
+    /// Remove segment pointed to by iterator @p I from this range.  This does
+    /// not remove dead value numbers.
+    iterator removeSegment(iterator I) {
+      return segments.erase(I);
+    }
+
     /// Query Liveness at Idx.
     /// The sub-instruction slot of Idx doesn't matter, only the instruction
     /// it refers to is considered.

include/llvm/CodeGen/LiveIntervalAnalysis.h

@@ -158,7 +158,7 @@ namespace llvm {
     /// shrinkToUses(LiveInterval *li, SmallVectorImpl<MachineInstr*> *dead)
     /// that works on a subregister live range and only looks at uses matching
     /// the lane mask of the subregister range.
-    bool shrinkToUses(LiveInterval::SubRange &SR, unsigned Reg);
+    void shrinkToUses(LiveInterval::SubRange &SR, unsigned Reg);
 
     /// extendToIndices - Extend the live range of LI to reach all points in
     /// Indices. The points in the Indices array must be jointly dominated by
@@ -406,17 +406,15 @@ namespace llvm {
     /// Compute RegMaskSlots and RegMaskBits.
     void computeRegMasks();
 
-    /// \brief Walk the values in the @p LR live range and compute which ones
+    /// Walk the values in @p LI and check for dead values:
-    /// are dead in live range @p Segments.  Dead values are not deleted,
-    /// however:
     /// - Dead PHIDef values are marked as unused.
-    /// - if @p dead != nullptr then dead operands are marked as such and
+    /// - Dead operands are marked as such.
-    ///   completely dead machine instructions are added to the @p dead vector.
+    /// - Completely dead machine instructions are added to the @p dead vector
-    /// - CanSeparate is set to true if the interval may have been separated
+    ///   if it is not nullptr.
-    ///   into multiple connected components.
+    /// Returns true if any PHI value numbers have been removed which may
-    void computeDeadValues(LiveRange &Segments, LiveRange &LR,
+    /// have separated the interval into multiple connected components.
-                           bool *CanSeparate = nullptr, unsigned Reg = 0,
+    bool computeDeadValues(LiveInterval &LI,
-                           SmallVectorImpl<MachineInstr*> *dead = nullptr);
+                           SmallVectorImpl<MachineInstr*> *dead);
 
     static LiveInterval* createInterval(unsigned Reg);
 

lib/CodeGen/LiveIntervalAnalysis.cpp

@@ -193,7 +193,7 @@ void LiveIntervals::computeVirtRegInterval(LiveInterval &LI) {
   assert(LI.empty() && "Should only compute empty intervals.");
   LRCalc->reset(MF, getSlotIndexes(), DomTree, &getVNInfoAllocator());
   LRCalc->calculate(LI);
-  computeDeadValues(LI, LI);
+  computeDeadValues(LI, nullptr);
 }
 
 void LiveIntervals::computeVirtRegs() {
@@ -433,49 +433,46 @@ bool LiveIntervals::shrinkToUses(LiveInterval *li,
   createSegmentsForValues(NewLR, make_range(li->vni_begin(), li->vni_end()));
   extendSegmentsToUses(NewLR, *Indexes, WorkList, *li);
 
-  // Handle dead values.
-  bool CanSeparate;
-  computeDeadValues(NewLR, *li, &CanSeparate, li->reg, dead);
-
   // Move the trimmed segments back.
   li->segments.swap(NewLR.segments);
+
+  // Handle dead values.
+  bool CanSeparate = computeDeadValues(*li, dead);
   DEBUG(dbgs() << "Shrunk: " << *li << '\n');
   return CanSeparate;
 }
 
-void LiveIntervals::computeDeadValues(LiveRange &Segments, LiveRange &LR,
+bool LiveIntervals::computeDeadValues(LiveInterval &LI,
-                                      bool *CanSeparateRes, unsigned Reg,
                                       SmallVectorImpl<MachineInstr*> *dead) {
-  bool CanSeparate = false;
+  bool PHIRemoved = false;
-  for (auto VNI : LR.valnos) {
+  for (auto VNI : LI.valnos) {
     if (VNI->isUnused())
       continue;
-    LiveRange::iterator LRI = Segments.FindSegmentContaining(VNI->def);
+    LiveRange::iterator I = LI.FindSegmentContaining(VNI->def);
-    assert(LRI != Segments.end() && "Missing segment for PHI");
+    assert(I != LI.end() && "Missing segment for VNI");
-    if (LRI->end != VNI->def.getDeadSlot())
+    if (I->end != VNI->def.getDeadSlot())
       continue;
     if (VNI->isPHIDef()) {
       // This is a dead PHI. Remove it.
       VNI->markUnused();
-      Segments.removeSegment(LRI->start, LRI->end);
+      LI.removeSegment(I);
       DEBUG(dbgs() << "Dead PHI at " << VNI->def << " may separate interval\n");
-      CanSeparate = true;
+      PHIRemoved = true;
-    } else if (dead != nullptr) {
+    } else {
       // This is a dead def. Make sure the instruction knows.
       MachineInstr *MI = getInstructionFromIndex(VNI->def);
       assert(MI && "No instruction defining live value");
-      MI->addRegisterDead(Reg, TRI);
+      MI->addRegisterDead(LI.reg, TRI);
       if (dead && MI->allDefsAreDead()) {
         DEBUG(dbgs() << "All defs dead: " << VNI->def << '\t' << *MI);
         dead->push_back(MI);
       }
     }
   }
-  if (CanSeparateRes != nullptr)
+  return PHIRemoved;
-    *CanSeparateRes = CanSeparate;
 }
 
-bool LiveIntervals::shrinkToUses(LiveInterval::SubRange &SR, unsigned Reg)
+void LiveIntervals::shrinkToUses(LiveInterval::SubRange &SR, unsigned Reg)
 {
   DEBUG(dbgs() << "Shrink: " << SR << '\n');
   assert(TargetRegisterInfo::isVirtualRegister(Reg)
@@ -522,14 +519,26 @@ bool LiveIntervals::shrinkToUses(LiveInterval::SubRange &SR, unsigned Reg)
   createSegmentsForValues(NewLR, make_range(SR.vni_begin(), SR.vni_end()));
   extendSegmentsToUses(NewLR, *Indexes, WorkList, SR);
 
-  // Handle dead values.
-  bool CanSeparate;
-  computeDeadValues(NewLR, SR, &CanSeparate);
-
   // Move the trimmed ranges back.
   SR.segments.swap(NewLR.segments);
+
+  // Remove dead PHI value numbers
+  for (auto VNI : SR.valnos) {
+    if (VNI->isUnused())
+      continue;
+    const LiveRange::Segment *Segment = SR.getSegmentContaining(VNI->def);
+    assert(Segment != nullptr && "Missing segment for VNI");
+    if (Segment->end != VNI->def.getDeadSlot())
+      continue;
+    if (VNI->isPHIDef()) {
+      // This is a dead PHI. Remove it.
+      VNI->markUnused();
+      SR.removeSegment(*Segment);
+      DEBUG(dbgs() << "Dead PHI at " << VNI->def << " may separate interval\n");
+    }
+  }
+
   DEBUG(dbgs() << "Shrunk: " << SR << '\n');
-  return CanSeparate;
 }
 
 void LiveIntervals::extendToIndices(LiveRange &LR,