Index: lib/Transforms/Utils/BasicBlockUtils.cpp
===================================================================
--- lib/Transforms/Utils/BasicBlockUtils.cpp
+++ lib/Transforms/Utils/BasicBlockUtils.cpp
@@ -504,6 +504,9 @@
     // Insert dummy values as the incoming value.
     for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++I)
       cast<PHINode>(I)->addIncoming(UndefValue::get(I->getType()), NewBB);
+
+    if (DT && BB == DT->getRootNode()->getBlock())
+      DT->setNewRoot(NewBB);
     return NewBB;
   }
 
Index: unittests/Transforms/Utils/BasicBlockUtils.cpp
===================================================================
--- /dev/null
+++ unittests/Transforms/Utils/BasicBlockUtils.cpp
@@ -0,0 +1,51 @@
+//===- BasicBlockUtils.cpp - Unit tests for BasicBlockUtils ---------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Transforms/Utils/BasicBlockUtils.h"
+#include "llvm/AsmParser/Parser.h"
+#include "llvm/IR/BasicBlock.h"
+#include "llvm/IR/Dominators.h"
+#include "llvm/IR/LLVMContext.h"
+#include "llvm/Support/SourceMgr.h"
+#include "gtest/gtest.h"
+
+using namespace llvm;
+
+static std::unique_ptr<Module> parseIR(LLVMContext &C, const char *IR) {
+  SMDiagnostic Err;
+  std::unique_ptr<Module> Mod = parseAssemblyString(IR, Err, C);
+  if (!Mod)
+    Err.print("BasicBlockUtilsTests", errs());
+  return Mod;
+}
+
+TEST(BasicBlockUtils, SplitBlockPredecessors) {
+  LLVMContext C;
+
+  std::unique_ptr<Module> M = parseIR(
+    C,
+    "define void @basic_func(i1 %cond) {\n"
+    "entry:\n"
+    "  br i1 %cond, label %bb0, label %bb1\n"
+    "bb0:\n"
+    "  ret void\n"
+    "bb1:\n"
+    "  ret void\n"
+    "}\n"
+    "\n"
+    );
+
+  auto *F = M->getFunction("basic_func");
+  DominatorTree DT(*F);
+
+  // Make sure the dominator tree is properly updated if calling this on the
+  // entry block.
+  SplitBlockPredecessors(&F->getEntryBlock(), {}, "split.entry", &DT);
+  EXPECT_TRUE(DT.verify());
+}
Index: unittests/Transforms/Utils/CMakeLists.txt
===================================================================
--- unittests/Transforms/Utils/CMakeLists.txt
+++ unittests/Transforms/Utils/CMakeLists.txt
@@ -8,6 +8,7 @@
 
 add_llvm_unittest(UtilsTests
   ASanStackFrameLayoutTest.cpp
+  BasicBlockUtils.cpp
   Cloning.cpp
   CodeExtractor.cpp
   FunctionComparator.cpp
Index: unittests/Transforms/Utils/Local.cpp
===================================================================
--- unittests/Transforms/Utils/Local.cpp
+++ unittests/Transforms/Utils/Local.cpp
@@ -100,7 +100,7 @@
   EXPECT_EQ(3U, BB->size());
 }
 
-std::unique_ptr<Module> parseIR(LLVMContext &C, const char *IR) {
+static std::unique_ptr<Module> parseIR(LLVMContext &C, const char *IR) {
   SMDiagnostic Err;
   std::unique_ptr<Module> Mod = parseAssemblyString(IR, Err, C);
   if (!Mod)