diff --git a/llvm/lib/CodeGen/BasicBlockSections.cpp b/llvm/lib/CodeGen/BasicBlockSections.cpp
--- a/llvm/lib/CodeGen/BasicBlockSections.cpp
+++ b/llvm/lib/CodeGen/BasicBlockSections.cpp
@@ -128,6 +128,24 @@
                 "into clusters of basic blocks.",
                 false, false)
 
+/// Basic blocks with an explicit unconditional branch to its fallthrough block
+/// do not need an extra unconditional branch.
+static bool needInsertUncondBranch(const MachineBasicBlock &MBB) {
+  auto B = MBB.terminators().begin(), E = MBB.end(), I = B;
+  if (I == E)
+    return true;
+
+  if (I->isUnconditionalBranch())
+    return false;
+
+  while (I != E) {
+    if (I->isUnconditionalBranch())
+      return false;
+    I++;
+  }
+  return true;
+}
+
 // This function updates and optimizes the branching instructions of every basic
 // block in a given function to account for changes in the layout.
 static void updateBranches(
@@ -141,10 +159,13 @@
     // If this block had a fallthrough before we need an explicit unconditional
     // branch to that block if either
     //     1- the block ends a section, which means its next block may be
-    //        reorderd by the linker, or
+    //        reorderd by the linker,
     //     2- the fallthrough block is not adjacent to the block in the new
-    //        order.
-    if (FTMBB && (MBB.isEndSection() || &*NextMBBI != FTMBB))
+    //        order, or
+    //     3- the terminator of the block is an unconditional branch to its
+    //        fallthrough.
+    if (FTMBB && (MBB.isEndSection() || &*NextMBBI != FTMBB) &&
+        needInsertUncondBranch(MBB))
       TII->insertUnconditionalBranch(MBB, FTMBB, MBB.findBranchDebugLoc());
 
     // We do not optimize branches for machine basic blocks ending sections, as
diff --git a/llvm/test/CodeGen/X86/basic-block-sections_2.ll b/llvm/test/CodeGen/X86/basic-block-sections_2.ll
--- a/llvm/test/CodeGen/X86/basic-block-sections_2.ll
+++ b/llvm/test/CodeGen/X86/basic-block-sections_2.ll
@@ -12,11 +12,18 @@
 ;;
 ; __cxx_global_var_init has multiple basic blocks which will produce many sections.
 ; RUN: llc < %s -mtriple=x86_64-pc-linux -function-sections -basic-block-sections=all -unique-basic-block-section-names | FileCheck %s
+; RUN: llc < %s -mtriple=x86_64-pc-linux -function-sections -basic-block-sections=all -O0 -unique-basic-block-section-names | FileCheck %s --check-prefix=REDUNDANT
 
 ; CHECK-LABEL: __cxx_global_var_init:
 ; CHECK-LABEL: __cxx_global_var_init.__part.1:
 ; CHECK-LABEL: __cxx_global_var_init.1:
 
+; REDUNDANT-LABEL: __cxx_global_var_init:
+; REDUNDANT: jmp __cxx_global_var_init.__part.2
+; REDUNDANT-NOT: jmp __cxx_global_var_init.__part.1
+; REDUNDANT-LABEL: __cxx_global_var_init.__part.1:
+; REDUNDANT-LABEL: __cxx_global_var_init.1:
+
 %class.A = type { i8 }
 
 $_ZN1AC2Eb = comdat any