From 0a29ac76bb13f566926259a6346b8ad1838ff0f3 Mon Sep 17 00:00:00 2001
From: Kunal Pathak <Kunal.Pathak@microsoft.com>
Date: Fri, 4 Jun 2021 08:58:53 -0700
Subject: [PATCH] Consider reloadWeight while evaluating spill cost

---
 src/coreclr/jit/lsra.cpp | 26 ++++++++++++++++++++++----
 1 file changed, 22 insertions(+), 4 deletions(-)

diff --git a/src/coreclr/jit/lsra.cpp b/src/coreclr/jit/lsra.cpp
index af168348e194d..fbea4ff5615ae 100644
--- a/src/coreclr/jit/lsra.cpp
+++ b/src/coreclr/jit/lsra.cpp
@@ -11258,13 +11258,31 @@ void LinearScan::RegisterSelection::try_SPILL_COST()
             continue;
         }
 
-        float currentSpillWeight = linearScan->spillCost[spillCandidateRegNum];
-#ifdef TARGET_ARM
-        if (currentInterval->registerType == TYP_DOUBLE)
+        float currentSpillWeight = 0;
+        RefPosition* recentRefPosition = spillCandidateRegRecord->assignedInterval->recentRefPosition;
+        if ((recentRefPosition != nullptr) && (recentRefPosition->RegOptional()) &&
+            !(currentInterval->isLocalVar && recentRefPosition->IsActualRef()))
         {
-            currentSpillWeight = max(currentSpillWeight, linearScan->spillCost[REG_NEXT(spillCandidateRegNum)]);
+            // We do not "spillAfter" if previous (recent) refPosition was regOptional or if it
+            // is not an actual ref. In those cases, we will reload in future (next) refPosition.
+            // For such cases, consider the spill cost of next refposition.
+            RefPosition* reloadRefPosition = spillCandidateRegRecord->assignedInterval->getNextRefPosition();
+            if (reloadRefPosition != nullptr)
+            {
+                currentSpillWeight = linearScan->getWeight(reloadRefPosition);
+            }
         }
+        else
+        {
+            currentSpillWeight = linearScan->spillCost[spillCandidateRegNum];
+#ifdef TARGET_ARM
+            if (currentInterval->registerType == TYP_DOUBLE)
+            {
+                currentSpillWeight = max(currentSpillWeight, linearScan->spillCost[REG_NEXT(spillCandidateRegNum)]);
+            }
 #endif
+        }
+
         if (currentSpillWeight < bestSpillWeight)
         {
             bestSpillWeight    = currentSpillWeight;