3 files changed, 32 insertions, 2 deletions

diff --git a/llvm/lib/CodeGen/RegAllocGreedy.cpp b/llvm/lib/CodeGen/RegAllocGreedy.cpp
index c1372cd038c..378219b97be 100644
--- a/llvm/lib/CodeGen/RegAllocGreedy.cpp
+++ b/llvm/lib/CodeGen/RegAllocGreedy.cpp
@@ -426,8 +426,13 @@ float RAGreedy::calcInterferenceInfo(LiveInterval &VirtReg, unsigned PhysReg) {
         if (!IntI.valid())
           break;
         // Not live in, but before the first use.
-        if (IntI.start() < BI.FirstUse)
+        if (IntI.start() < BI.FirstUse) {
           BC.Entry = SpillPlacement::PrefSpill;
+          // If the block contains a kill from an earlier split, never split
+          // again in the same block.
+          if (!BI.LiveThrough && !SA->isOriginalEndpoint(BI.Kill))
+            BC.Entry = SpillPlacement::MustSpill;
+        }
       }
 
       // Does interference overlap the uses in the entry segment
@@ -458,8 +463,12 @@ float RAGreedy::calcInterferenceInfo(LiveInterval &VirtReg, unsigned PhysReg) {
           IntI.advanceTo(BI.LastUse);
           if (!IntI.valid())
             break;
-          if (IntI.start() < Stop)
+          if (IntI.start() < Stop) {
             BC.Exit = SpillPlacement::PrefSpill;
+            // Avoid splitting twice in the same block.
+            if (!BI.LiveThrough && !SA->isOriginalEndpoint(BI.Def))
+              BC.Exit = SpillPlacement::MustSpill;
+          }
         }
       }
     }
diff --git a/llvm/lib/CodeGen/SplitKit.cpp b/llvm/lib/CodeGen/SplitKit.cpp
index 5663936bf3a..a97d890c25b 100644
--- a/llvm/lib/CodeGen/SplitKit.cpp
+++ b/llvm/lib/CodeGen/SplitKit.cpp
@@ -167,6 +167,20 @@ void SplitAnalysis::calcLiveBlockInfo() {
   }
 }
 
+bool SplitAnalysis::isOriginalEndpoint(SlotIndex Idx) const {
+  unsigned OrigReg = VRM.getOriginal(CurLI->reg);
+  const LiveInterval &Orig = LIS.getInterval(OrigReg);
+  assert(!Orig.empty() && "Splitting empty interval?");
+  LiveInterval::const_iterator I = Orig.find(Idx);
+
+  // Range containing Idx should begin at Idx.
+  if (I != Orig.end() && I->start <= Idx)
+    return I->start == Idx;
+
+  // Range does not contain Idx, previous must end at Idx.
+  return I != Orig.begin() && (--I)->end == Idx;
+}
+
 void SplitAnalysis::print(const BlockPtrSet &B, raw_ostream &OS) const {
   for (BlockPtrSet::const_iterator I = B.begin(), E = B.end(); I != E; ++I) {
     unsigned count = UsingBlocks.lookup(*I);
diff --git a/llvm/lib/CodeGen/SplitKit.h b/llvm/lib/CodeGen/SplitKit.h
index 5c34afd1c81..e02e6297035 100644
--- a/llvm/lib/CodeGen/SplitKit.h
+++ b/llvm/lib/CodeGen/SplitKit.h
@@ -125,6 +125,13 @@ public:
     return UsingBlocks.lookup(MBB);
   }
 
+  /// isOriginalEndpoint - Return true if the original live range was killed or
+  /// (re-)defined at Idx. Idx should be the 'def' slot for a normal kill/def,
+  /// and 'use' for an early-clobber def.
+  /// This can be used to recognize code inserted by earlier live range
+  /// splitting.
+  bool isOriginalEndpoint(SlotIndex Idx) const;
+
   typedef SmallPtrSet<const MachineBasicBlock*, 16> BlockPtrSet;
 
   // Print a set of blocks with use counts.