3 files changed, 8 insertions, 3 deletions
diff --git a/lib/CodeGen/RegAllocGreedy.cpp b/lib/CodeGen/RegAllocGreedy.cpp
index 1cbd5a925f..4c130d0026 100644
--- a/lib/CodeGen/RegAllocGreedy.cpp
+++ b/lib/CodeGen/RegAllocGreedy.cpp
@@ -806,7 +806,9 @@ void RAGreedy::growRegion(GlobalSplitCandidate &Cand) {
     if (Cand.PhysReg)
       addThroughConstraints(Cand.Intf, NewBlocks);
     else
-      SpillPlacer->addPrefSpill(NewBlocks);
+      // Provide a strong negative bias on through blocks to prevent unwanted
+      // liveness on loop backedges.
+      SpillPlacer->addPrefSpill(NewBlocks, /* Strong= */ true);
     AddedTo = ActiveBlocks.size();
 
     // Perhaps iterating can enable more bundles?
diff --git a/lib/CodeGen/SpillPlacement.cpp b/lib/CodeGen/SpillPlacement.cpp
index 10a3c18962..6f33f5465c 100644
--- a/lib/CodeGen/SpillPlacement.cpp
+++ b/lib/CodeGen/SpillPlacement.cpp
@@ -241,10 +241,12 @@ void SpillPlacement::addConstraints(ArrayRef<BlockConstraint> LiveBlocks) {
 }
 
 /// addPrefSpill - Same as addConstraints(PrefSpill)
-void SpillPlacement::addPrefSpill(ArrayRef<unsigned> Blocks) {
+void SpillPlacement::addPrefSpill(ArrayRef<unsigned> Blocks, bool Strong) {
   for (ArrayRef<unsigned>::iterator I = Blocks.begin(), E = Blocks.end();
        I != E; ++I) {
     float Freq = getBlockFrequency(*I);
+    if (Strong)
+      Freq += Freq;
     unsigned ib = bundles->getBundle(*I, 0);
     unsigned ob = bundles->getBundle(*I, 1);
     activate(ib);
diff --git a/lib/CodeGen/SpillPlacement.h b/lib/CodeGen/SpillPlacement.h
index 9d1d676c54..fc412f817c 100644
--- a/lib/CodeGen/SpillPlacement.h
+++ b/lib/CodeGen/SpillPlacement.h
@@ -107,7 +107,8 @@ public:
   /// Entry = Exit = PrefSpill, and ChangesValue = false.
   ///
   /// @param Blocks Array of block numbers that prefer to spill in and out.
-  void addPrefSpill(ArrayRef<unsigned> Blocks);
+  /// @param Strong When true, double the negative bias for these blocks.
+  void addPrefSpill(ArrayRef<unsigned> Blocks, bool Strong);
 
   /// addLinks - Add transparent blocks with the given numbers.
   void addLinks(ArrayRef<unsigned> Links);