Keep track of the number of positively biased nodes when adding constraints.

If there are no positive nodes, the algorithm can be aborted early.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@129021 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/RegAllocGreedy.cpp b/lib/CodeGen/RegAllocGreedy.cpp
index 4e8891f..31729ec 100644
--- a/lib/CodeGen/RegAllocGreedy.cpp
+++ b/lib/CodeGen/RegAllocGreedy.cpp
@@ -772,6 +772,7 @@
 
     SpillPlacer->prepare(LiveBundles);
     SpillPlacer->addConstraints(SplitConstraints);
+    DEBUG(dbgs() << ", " << SpillPlacer->getPositiveNodes() << " biased nodes");
     SpillPlacer->finish();
 
     // No live bundles, defer to splitSingleBlocks().