diff --git a/llvm/include/llvm/CodeGen/LiveIntervals.h b/llvm/include/llvm/CodeGen/LiveIntervals.h
--- a/llvm/include/llvm/CodeGen/LiveIntervals.h
+++ b/llvm/include/llvm/CodeGen/LiveIntervals.h
@@ -256,9 +256,8 @@
       return Indexes->getMBBFromIndex(index);
     }
 
-    void insertMBBInMaps(MachineBasicBlock *MBB,
-                         MachineInstr *InsertionPoint = nullptr) {
-      Indexes->insertMBBInMaps(MBB, InsertionPoint);
+    void insertMBBInMaps(MachineBasicBlock *MBB) {
+      Indexes->insertMBBInMaps(MBB);
       assert(unsigned(MBB->getNumber()) == RegMaskBlocks.size() &&
              "Blocks must be added in order.");
       RegMaskBlocks.push_back(std::make_pair(RegMaskSlots.size(), 0));
diff --git a/llvm/include/llvm/CodeGen/SlotIndexes.h b/llvm/include/llvm/CodeGen/SlotIndexes.h
--- a/llvm/include/llvm/CodeGen/SlotIndexes.h
+++ b/llvm/include/llvm/CodeGen/SlotIndexes.h
@@ -604,38 +604,27 @@
     }
 
     /// Add the given MachineBasicBlock into the maps.
-    /// If \p InsertionPoint is specified then the block will be placed
-    /// before the given machine instr, otherwise it will be placed
-    /// before the next block in MachineFunction insertion order.
-    void insertMBBInMaps(MachineBasicBlock *mbb,
-                         MachineInstr *InsertionPoint = nullptr) {
-      MachineFunction::iterator nextMBB =
-        std::next(MachineFunction::iterator(mbb));
-
-      IndexListEntry *startEntry = nullptr;
-      IndexListEntry *endEntry = nullptr;
-      IndexList::iterator newItr;
-      if (InsertionPoint) {
-        startEntry = createEntry(nullptr, 0);
-        endEntry = getInstructionIndex(*InsertionPoint).listEntry();
-        newItr = indexList.insert(endEntry->getIterator(), startEntry);
-      } else if (nextMBB == mbb->getParent()->end()) {
-        startEntry = &indexList.back();
-        endEntry = createEntry(nullptr, 0);
-        newItr = indexList.insertAfter(startEntry->getIterator(), endEntry);
-      } else {
-        startEntry = createEntry(nullptr, 0);
-        endEntry = getMBBStartIdx(&*nextMBB).listEntry();
-        newItr = indexList.insert(endEntry->getIterator(), startEntry);
-      }
+    /// If it contains any instructions then they must already be in the maps.
+    /// This is used after a block has been split by moving some suffix of its
+    /// instructions into a newly created block.
+    void insertMBBInMaps(MachineBasicBlock *mbb) {
+      assert(mbb != &mbb->getParent()->front() &&
+             "Can't insert a new block at the beginning of a function.");
+      auto prevMBB = std::prev(MachineFunction::iterator(mbb));
+
+      // Create a new entry to be used for the start of mbb and the end of
+      // prevMBB.
+      IndexListEntry *startEntry = createEntry(nullptr, 0);
+      IndexListEntry *endEntry = getMBBEndIdx(&*prevMBB).listEntry();
+      IndexListEntry *insEntry =
+          mbb->empty() ? endEntry
+                       : getInstructionIndex(mbb->front()).listEntry();
+      IndexList::iterator newItr =
+          indexList.insert(insEntry->getIterator(), startEntry);
 
       SlotIndex startIdx(startEntry, SlotIndex::Slot_Block);
       SlotIndex endIdx(endEntry, SlotIndex::Slot_Block);
 
-      MachineFunction::iterator prevMBB(mbb);
-      assert(prevMBB != mbb->getParent()->end() &&
-             "Can't insert a new block at the beginning of a function.");
-      --prevMBB;
       MBBRanges[prevMBB->getNumber()].second = startIdx;
 
       assert(unsigned(mbb->getNumber()) == MBBRanges.size() &&
diff --git a/llvm/lib/CodeGen/MachineBasicBlock.cpp b/llvm/lib/CodeGen/MachineBasicBlock.cpp
--- a/llvm/lib/CodeGen/MachineBasicBlock.cpp
+++ b/llvm/lib/CodeGen/MachineBasicBlock.cpp
@@ -980,7 +980,7 @@
     addLiveIns(*SplitBB, LiveRegs);
 
   if (LIS)
-    LIS->insertMBBInMaps(SplitBB, &MI);
+    LIS->insertMBBInMaps(SplitBB);
 
   return SplitBB;
 }
diff --git a/llvm/unittests/MI/LiveIntervalTest.cpp b/llvm/unittests/MI/LiveIntervalTest.cpp
--- a/llvm/unittests/MI/LiveIntervalTest.cpp
+++ b/llvm/unittests/MI/LiveIntervalTest.cpp
@@ -149,6 +149,19 @@
   LIS.handleMoveIntoNewBundle(*BundleStart, true);
 }
 
+/**
+ * Split block numbered \p BlockNum at instruction \p SplitAt using
+ * MachineBasicBlock::splitAt updating liveness intervals.
+ */
+static void testSplitAt(MachineFunction &MF, LiveIntervals &LIS,
+                        unsigned SplitAt, unsigned BlockNum) {
+  MachineInstr &SplitInstr = getMI(MF, SplitAt, BlockNum);
+  MachineBasicBlock &MBB = *SplitInstr.getParent();
+
+  // Split block and update live intervals
+  MBB.splitAt(SplitInstr, false, &LIS);
+}
+
 static void liveIntervalTest(StringRef MIRFunc, LiveIntervalTest T) {
   LLVMContext Context;
   std::unique_ptr<LLVMTargetMachine> TM = createTargetMachine();
@@ -608,6 +621,34 @@
   });
 }
 
+TEST(LiveIntervalTest, SplitAtOneInstruction) {
+  liveIntervalTest(R"MIR(
+    successors: %bb.1
+    %0 = IMPLICIT_DEF
+    S_BRANCH %bb.1
+  bb.1:
+    S_NOP 0
+)MIR", [](MachineFunction &MF, LiveIntervals &LIS) {
+    testSplitAt(MF, LIS, 1, 0);
+  });
+}
+
+TEST(LiveIntervalTest, SplitAtMultiInstruction) {
+  liveIntervalTest(R"MIR(
+    successors: %bb.1
+    %0 = IMPLICIT_DEF
+    S_NOP 0
+    S_NOP 0
+    S_NOP 0
+    S_NOP 0
+    S_BRANCH %bb.1
+  bb.1:
+    S_NOP 0
+)MIR", [](MachineFunction &MF, LiveIntervals &LIS) {
+    testSplitAt(MF, LIS, 0, 0);
+  });
+}
+
 int main(int argc, char **argv) {
   ::testing::InitGoogleTest(&argc, argv);
   initLLVM();