Allow allocatable ranges from global live range splitting to be split again.

These intervals are allocatable immediately after splitting, but they may be
evicted because of later splitting. This is rare, but when it happens they
should be split again.

The remainder intervals that cannot be allocated after splitting still move
directly to spilling.

SplitEditor::finish can optionally provide a mapping from new live intervals
back to the original interval indexes returned by openIntv().

Each original interval index can map to multiple new intervals after connected
components have been separated. Dead code elimination may also add existing
intervals to the list.

The reverse mapping allows the SplitEditor client to treat the new intervals
differently depending on the split region they came from.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@129925 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/RegAllocGreedy.cpp

@@ -883,12 +883,36 @@ void RAGreedy::splitAroundRegion(LiveInterval &VirtReg,
       SE->enterIntvAtEnd(*MBB);
   }
 
-  // FIXME: Should we be more aggressive about splitting the stack region into
-  // per-block segments? The current approach allows the stack region to
-  // separate into connected components. Some components may be allocatable.
-  SE->finish();
   ++NumGlobalSplits;
 
+  SmallVector<unsigned, 8> IntvMap;
+  SE->finish(&IntvMap);
+  LRStage.resize(MRI->getNumVirtRegs());
+
+  // Sort out the new intervals created by splitting. We get four kinds:
+  // - Remainder intervals should not be split again.
+  // - Candidate intervals can be assigned to Cand.PhysReg.
+  // - Block-local splits are candidates for local splitting.
+  // - DCE leftovers should go back on the queue.
+  for (unsigned i = 0, e = LREdit.size(); i != e; ++i) {
+    unsigned Reg = LREdit.get(i)->reg;
+
+    // Ignore old intervals from DCE.
+    if (LRStage[Reg] != RS_New)
+      continue;
+
+    // Remainder interval. Don't try splitting again, spill if it doesn't
+    // allocate.
+    if (IntvMap[i] == 0) {
+      LRStage[Reg] = RS_Global;
+      continue;
+    }
+
+    // Other intervals are treated as new. This includes the main interval,
+    // local intervals created for blocks with multiple uses, and anything
+    // created by DCE.
+  }
+
   if (VerifyEnabled)
     MF->verify(this, "After splitting live range around region");
 }
@@ -946,7 +970,6 @@ unsigned RAGreedy::tryRegionSplit(LiveInterval &VirtReg, AllocationOrder &Order,
     return 0;
 
   splitAroundRegion(VirtReg, GlobalCand[BestCand], NewVRegs);
-  setStage(NewVRegs.begin(), NewVRegs.end(), RS_Global);
   return 0;
 }
 

lib/CodeGen/SplitKit.cpp

@@ -935,7 +935,7 @@ void SplitEditor::deleteRematVictims() {
   Edit->eliminateDeadDefs(Dead, LIS, VRM, TII);
 }
 
-void SplitEditor::finish() {
+void SplitEditor::finish(SmallVectorImpl<unsigned> *LRMap) {
   ++NumFinished;
 
   // At this point, the live intervals in Edit contain VNInfos corresponding to
@@ -983,6 +983,13 @@ void SplitEditor::finish() {
   for (LiveRangeEdit::iterator I = Edit->begin(), E = Edit->end(); I != E; ++I)
     (*I)->RenumberValues(LIS);
 
+  // Provide a reverse mapping from original indices to Edit ranges.
+  if (LRMap) {
+    LRMap->clear();
+    for (unsigned i = 0, e = Edit->size(); i != e; ++i)
+      LRMap->push_back(i);
+  }
+
   // Now check if any registers were separated into multiple components.
   ConnectedVNInfoEqClasses ConEQ(LIS);
   for (unsigned i = 0, e = Edit->size(); i != e; ++i) {
@@ -997,10 +1004,15 @@ void SplitEditor::finish() {
     for (unsigned i = 1; i != NumComp; ++i)
       dups.push_back(&Edit->create(LIS, VRM));
     ConEQ.Distribute(&dups[0], MRI);
+    // The new intervals all map back to i.
+    if (LRMap)
+      LRMap->resize(Edit->size(), i);
   }
 
   // Calculate spill weight and allocation hints for new intervals.
   Edit->calculateRegClassAndHint(VRM.getMachineFunction(), LIS, SA.Loops);
+
+  assert(!LRMap || LRMap->size() == Edit->size());
 }
 
 

lib/CodeGen/SplitKit.h

@@ -368,7 +368,10 @@ public:
 
   /// finish - after all the new live ranges have been created, compute the
   /// remaining live range, and rewrite instructions to use the new registers.
-  void finish();
+  /// @param LRMap When not null, this vector will map each live range in Edit
+  ///              back to the indices returned by openIntv.
+  ///              There may be extra indices created by dead code elimination.
+  void finish(SmallVectorImpl<unsigned> *LRMap = 0);
 
   /// dump - print the current interval maping to dbgs().
   void dump() const;