1 files changed, 18 insertions, 1 deletions
diff --git a/include/llvm/CodeGen/CalcSpillWeights.h b/include/llvm/CodeGen/CalcSpillWeights.h
index 24264d7f97..1f5f088be7 100644
--- a/include/llvm/CodeGen/CalcSpillWeights.h
+++ b/include/llvm/CodeGen/CalcSpillWeights.h
@@ -11,7 +11,7 @@
 #ifndef LLVM_CODEGEN_CALCSPILLWEIGHTS_H
 #define LLVM_CODEGEN_CALCSPILLWEIGHTS_H
 
-#include "llvm/CodeGen/MachineFunctionPass.h"
+#include "llvm/CodeGen/SlotIndexes.h"
 #include "llvm/ADT/DenseMap.h"
 
 namespace llvm {
@@ -20,6 +20,23 @@ namespace llvm {
   class LiveIntervals;
   class MachineLoopInfo;
 
+  /// normalizeSpillWeight - The spill weight of a live interval is computed as:
+  ///
+  ///   (sum(use freq) + sum(def freq)) / (K + size)
+  ///
+  /// @param UseDefFreq Expected number of executed use and def instructions
+  ///                   per function call. Derived from block frequencies.
+  /// @param Size       Size of live interval as returnexd by getSize()
+  ///
+  static inline float normalizeSpillWeight(float UseDefFreq, unsigned Size) {
+    // The constant 25 instructions is added to avoid depending too much on
+    // accidental SlotIndex gaps for small intervals. The effect is that small
+    // intervals have a spill weight that is mostly proportional to the number
+    // of uses, while large intervals get a spill weight that is closer to a use
+    // density.
+    return UseDefFreq / (Size + 25*SlotIndex::InstrDist);
+  }
+
   /// VirtRegAuxInfo - Calculate auxiliary information for a virtual
   /// register such as its spill weight and allocation hint.
   class VirtRegAuxInfo {