[LiveInterval] Add RemoveDeadValNo argument to removeSegment(iterator)

[foad]

Summary

Add an optional bool RemoveDeadValNo argument to the
removeSegment(iterator) overload, for consistency with the other
overloads. This gives clients a way to remove dead valnos while also
getting an updated iterator returned (in the manner of vector::erase).

Use this to clean up some inefficient code in
LiveIntervals::repairOldRegInRange. NFC.

[foad]

Switch to using llvm::none_of.

[foad]

Ping! This is NFC, just cleaning up the "FIXME: This could be more efficient" comment in LiveIntervals by doing what it suggests.

llvm/include/llvm/CodeGen/LiveInterval.h

public:
     /// must be a single Segment in its entirety.
     void removeSegment(SlotIndex Start, SlotIndex End,
                        bool RemoveDeadValNo = false);
 
     void removeSegment(Segment S, bool RemoveDeadValNo = false) {
       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);
-    }
+    /// Remove segment pointed to by iterator @p I from this range.
+    iterator removeSegment(iterator I, bool RemoveDeadValNo = false);
+
+    /// Mark \p ValNo for deletion if no segments in this range use it.
+    void removeValNoIfDead(VNInfo *ValNo);
 
     /// Query Liveness at Idx.
     /// The sub-instruction slot of Idx doesn't matter, only the instruction
     /// it refers to is considered.
     LiveQueryResult Query(SlotIndex Idx) const {
       // Find the segment that enters the instruction.
       const_iterator I = find(Idx.getBaseIndex());
       const_iterator E = end();

llvm/lib/CodeGen/LiveInterval.cpp

void LiveRange::removeSegment(SlotIndex Start, SlotIndex End,
   assert(I != end() && "Segment is not in range!");
   assert(I->containsInterval(Start, End)
          && "Segment is not entirely in range!");
 
   // If the span we are removing is at the start of the Segment, adjust it.
   VNInfo *ValNo = I->valno;
   if (I->start == Start) {
     if (I->end == End) {
-      if (RemoveDeadValNo) {
-        // Check if val# is dead.
-        bool isDead = true;
-        for (const_iterator II = begin(), EE = end(); II != EE; ++II)
-          if (II != I && II->valno == ValNo) {
-            isDead = false;
-            break;
-          }
-        if (isDead) {
-          // Now that ValNo is dead, remove it.
-          markValNoForDeletion(ValNo);
-        }
-      }
-
       segments.erase(I);  // Removed the whole Segment.
+
+      if (RemoveDeadValNo)
+        removeValNoIfDead(ValNo);
     } else
       I->start = End;
     return;
   }
 
   // Otherwise if the span we are removing is at the end of the Segment,
   // adjust the other way.
   if (I->end == End) {
     I->end = Start;
     return;
   }
 
   // Otherwise, we are splitting the Segment into two pieces.
   SlotIndex OldEnd = I->end;
   I->end = Start;   // Trim the old segment.
 
   // Insert the new one.
   segments.insert(std::next(I), Segment(End, OldEnd, ValNo));
 }
 
+LiveRange::iterator LiveRange::removeSegment(iterator I, bool RemoveDeadValNo) {
+  VNInfo *ValNo = I->valno;
+  I = segments.erase(I);
+  if (RemoveDeadValNo)
+    removeValNoIfDead(ValNo);
+  return I;
+}
+
+void LiveRange::removeValNoIfDead(VNInfo *ValNo) {
+  if (none_of(*this, [=](const Segment &S) { return S.valno == ValNo; }))
+    markValNoForDeletion(ValNo);
+}
+
 /// removeValNo - Remove all the segments defined by the specified value#.
 /// Also remove the value# from value# list.
 void LiveRange::removeValNo(VNInfo *ValNo) {
   if (empty()) return;
   segments.erase(remove_if(*this, [ValNo](const Segment &S) {
     return S.valno == ValNo;
   }), end());
   // Now that ValNo is dead, remove it.

llvm/lib/CodeGen/LiveIntervals.cpp

for (MachineInstr::mop_iterator OI = MI.operands_begin(),
       unsigned SubReg = MO.getSubReg();
       LaneBitmask Mask = TRI->getSubRegIndexLaneMask(SubReg);
       if ((Mask & LaneMask).none())
         continue;
 
       if (MO.isDef()) {
         if (!isStartValid) {
           if (LII->end.isDead()) {
-            SlotIndex prevStart;
+            LII = LR.removeSegment(LII, true);
             if (LII != LR.begin())
-              prevStart = std::prev(LII)->start;
-
-            // FIXME: This could be more efficient if there was a
-            // removeSegment method that returned an iterator.
-            LR.removeSegment(*LII, true);
-            if (prevStart.isValid())
-              LII = LR.find(prevStart);
-            else
-              LII = LR.begin();
+              --LII;
           } else {
             LII->start = instrIdx.getRegSlot();
             LII->valno->def = instrIdx.getRegSlot();
             if (MO.getSubReg() && !MO.isUndef())
               lastUseIdx = instrIdx.getRegSlot();
             else
               lastUseIdx = SlotIndex();
             continue;