LiveRangeCalc: Rewrite subrange calculation

This changes subrange calculation to calculate subranges sequentially
instead of in parallel. The code is easier to understand that way and
addresses the code review issues raised about LiveOutData being
hard to understand/needing more comments by removing them :)

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@224272 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/LiveIntervalAnalysis.cpp

@@ -192,8 +192,7 @@ void LiveIntervals::computeVirtRegInterval(LiveInterval &LI) {
   assert(LRCalc && "LRCalc not initialized.");
   assert(LI.empty() && "Should only compute empty intervals.");
   LRCalc->reset(MF, getSlotIndexes(), DomTree, &getVNInfoAllocator());
-  LRCalc->createDeadDefs(LI);
-  LRCalc->extendToUses(LI);
+  LRCalc->calculate(LI);
   computeDeadValues(LI, LI);
 }
 
@@ -251,22 +250,15 @@ void LiveIntervals::computeRegUnitRange(LiveRange &LR, unsigned Unit) {
   // may share super-registers. That's OK because createDeadDefs() is
   // idempotent. It is very rare for a register unit to have multiple roots, so
   // uniquing super-registers is probably not worthwhile.
-  for (MCRegUnitRootIterator Roots(Unit, TRI); Roots.isValid(); ++Roots) {
-    for (MCSuperRegIterator Supers(*Roots, TRI, /*IncludeSelf=*/true);
-         Supers.isValid(); ++Supers) {
-      if (!MRI->reg_empty(*Supers))
-        LRCalc->createDeadDefs(LR, *Supers);
-    }
-  }
-
-  // Now extend LR to reach all uses.
-  // Ignore uses of reserved registers. We only track defs of those.
   for (MCRegUnitRootIterator Roots(Unit, TRI); Roots.isValid(); ++Roots) {
     for (MCSuperRegIterator Supers(*Roots, TRI, /*IncludeSelf=*/true);
          Supers.isValid(); ++Supers) {
       unsigned Reg = *Supers;
-      if (!MRI->isReserved(Reg) && !MRI->reg_empty(Reg))
-        LRCalc->extendToUses(LR, Reg);
+      if (MRI->reg_empty(Reg))
+        continue;
+      // Ignore uses of reserved registers. We only track defs of those.
+      bool IgnoreUses = MRI->isReserved(Reg);
+      LRCalc->calculate(LR, *Supers, IgnoreUses);
     }
   }
 }