1 files changed, 16 insertions, 3 deletions

diff --git a/llvm/lib/CodeGen/SplitKit.cpp b/llvm/lib/CodeGen/SplitKit.cpp
index 83964eced597..d6c0a782465e 100644
--- a/llvm/lib/CodeGen/SplitKit.cpp
+++ b/llvm/lib/CodeGen/SplitKit.cpp
@@ -45,6 +45,11 @@ using namespace llvm;
 
 #define DEBUG_TYPE "regalloc"
 
+static cl::opt<bool>
+    EnableLoopIVHeuristic("enable-split-loopiv-heuristic",
+                          cl::desc("Enable loop iv regalloc heuristic"),
+                          cl::init(true));
+
 STATISTIC(NumFinished, "Number of splits finished");
 STATISTIC(NumSimple,   "Number of splits that were simple");
 STATISTIC(NumCopies,   "Number of copies inserted for splitting");
@@ -126,7 +131,6 @@ InsertPointAnalysis::computeLastInsertPoint(const LiveInterval &CurLI,
   // If the value leaving MBB was defined after the call in MBB, it can't
   // really be live-in to the landing pad.  This can happen if the landing pad
   // has a PHI, and this register is undef on the exceptional edge.
-  // <rdar://problem/10664933>
   if (!SlotIndex::isEarlierInstr(VNI->def, LIP.second) && VNI->def < MBBEnd)
     return LIP.first;
 
@@ -294,6 +298,13 @@ void SplitAnalysis::calcLiveBlockInfo() {
       MFI = LIS.getMBBFromIndex(LVI->start)->getIterator();
   }
 
+  LooksLikeLoopIV = EnableLoopIVHeuristic && UseBlocks.size() == 2 &&
+                    any_of(UseBlocks, [this](BlockInfo &BI) {
+                      MachineLoop *L = Loops.getLoopFor(BI.MBB);
+                      return BI.LiveIn && BI.LiveOut && BI.FirstDef && L &&
+                             L->isLoopLatch(BI.MBB);
+                    });
+
   assert(getNumLiveBlocks() == countLiveBlocks(CurLI) && "Bad block count");
 }
 
@@ -796,8 +807,10 @@ SlotIndex SplitEditor::leaveIntvAtTop(MachineBasicBlock &MBB) {
     return Start;
   }
 
-  VNInfo *VNI = defFromParent(0, ParentVNI, Start, MBB,
-                              MBB.SkipPHIsLabelsAndDebug(MBB.begin()));
+  unsigned RegIdx = 0;
+  Register Reg = LIS.getInterval(Edit->get(RegIdx)).reg();
+  VNInfo *VNI = defFromParent(RegIdx, ParentVNI, Start, MBB,
+                              MBB.SkipPHIsLabelsAndDebug(MBB.begin(), Reg));
   RegAssign.insert(Start, VNI->def, OpenIdx);
   LLVM_DEBUG(dump());
   return VNI->def;