1 files changed, 14 insertions, 5 deletions
diff --git a/llvm/lib/CodeGen/RegAllocGreedy.cpp b/llvm/lib/CodeGen/RegAllocGreedy.cpp
index 4a54d7ebf8a9..9c6cb7c3a4e2 100644
--- a/llvm/lib/CodeGen/RegAllocGreedy.cpp
+++ b/llvm/lib/CodeGen/RegAllocGreedy.cpp
@@ -135,6 +135,12 @@ static cl::opt<bool> GreedyRegClassPriorityTrumpsGlobalness(
              "more important then whether the range is global"),
     cl::Hidden);
 
+static cl::opt<bool> GreedyReverseLocalAssignment(
+    "greedy-reverse-local-assignment",
+    cl::desc("Reverse allocation order of local live ranges, such that "
+             "shorter local live ranges will tend to be allocated first"),
+    cl::Hidden);
+
 static RegisterRegAlloc greedyRegAlloc("greedy", "greedy register allocator",
                                        createGreedyRegisterAllocator);
 
@@ -297,11 +303,10 @@ void RAGreedy::enqueue(PQueue &CurQueue, const LiveInterval *LI) {
   } else {
     // Giant live ranges fall back to the global assignment heuristic, which
     // prevents excessive spilling in pathological cases.
-    bool ReverseLocal = TRI->reverseLocalAssignment();
     const TargetRegisterClass &RC = *MRI->getRegClass(Reg);
-    bool ForceGlobal =
-        !ReverseLocal && (Size / SlotIndex::InstrDist) >
-                             (2 * RegClassInfo.getNumAllocatableRegs(&RC));
+    bool ForceGlobal = !ReverseLocalAssignment &&
+                       (Size / SlotIndex::InstrDist) >
+                           (2 * RegClassInfo.getNumAllocatableRegs(&RC));
     unsigned GlobalBit = 0;
 
     if (Stage == RS_Assign && !ForceGlobal && !LI->empty() &&
@@ -309,7 +314,7 @@ void RAGreedy::enqueue(PQueue &CurQueue, const LiveInterval *LI) {
       // Allocate original local ranges in linear instruction order. Since they
       // are singly defined, this produces optimal coloring in the absence of
       // global interference and other constraints.
-      if (!ReverseLocal)
+      if (!ReverseLocalAssignment)
         Prio = LI->beginIndex().getInstrDistance(Indexes->getLastIndex());
       else {
         // Allocating bottom up may allow many short LRGs to be assigned first
@@ -2528,6 +2533,10 @@ bool RAGreedy::runOnMachineFunction(MachineFunction &mf) {
           ? GreedyRegClassPriorityTrumpsGlobalness
           : TRI->regClassPriorityTrumpsGlobalness(*MF);
 
+  ReverseLocalAssignment = GreedyReverseLocalAssignment.getNumOccurrences()
+                               ? GreedyReverseLocalAssignment
+                               : TRI->reverseLocalAssignment();
+
   ExtraInfo.emplace();
   EvictAdvisor =
       getAnalysis<RegAllocEvictionAdvisorAnalysis>().getAdvisor(*MF, *this);