diff --git a/llvm/lib/CodeGen/CodeGen.cpp b/llvm/lib/CodeGen/CodeGen.cpp
--- a/llvm/lib/CodeGen/CodeGen.cpp
+++ b/llvm/lib/CodeGen/CodeGen.cpp
@@ -80,6 +80,7 @@
   initializeMachineCycleInfoWrapperPassPass(Registry);
   initializeMachineDominatorTreePass(Registry);
   initializeMachineFunctionPrinterPassPass(Registry);
+  initializeMachineFunctionSplitterPass(Registry);
   initializeMachineLateInstrsCleanupPass(Registry);
   initializeMachineLICMPass(Registry);
   initializeMachineLoopInfoPass(Registry);
diff --git a/llvm/test/CodeGen/AArch64/machine-function-splitter.mir b/llvm/test/CodeGen/AArch64/machine-function-splitter.mir
new file mode 100644
--- /dev/null
+++ b/llvm/test/CodeGen/AArch64/machine-function-splitter.mir
@@ -0,0 +1,85 @@
+# RUN: llc -mtriple=aarch64-none-linux-gnu --verify-machineinstrs -run-pass machine-function-splitter %s -o - | FileCheck %s
+
+--- |  
+  ; Function Attrs: nounwind
+  define void @split_basic(i1 zeroext %0) #0 !prof !14 !section_prefix !15 {
+    br i1 %0, label %2, label %4, !prof !16
+
+  2:                                                ; preds = %1
+    %3 = call i32 @bar()
+    br label %6
+
+  4:                                                ; preds = %1
+    %5 = call i32 @baz()
+    br label %6
+
+  6:                                                ; preds = %4, %2
+    %7 = tail call i32 @qux()
+    ret void
+  }
+  
+  declare i32 @bar()
+  
+  declare i32 @baz()
+  
+  declare i32 @bam()
+  
+  declare i32 @qux()
+  
+  attributes #0 = { nounwind }
+  
+  !llvm.module.flags = !{!0}
+  
+  !0 = !{i32 1, !"ProfileSummary", !1}
+  !1 = !{!2, !3, !4, !5, !6, !7, !8, !9}
+  !2 = !{!"ProfileFormat", !"InstrProf"}
+  !3 = !{!"TotalCount", i64 10000}
+  !4 = !{!"MaxCount", i64 10}
+  !5 = !{!"MaxInternalCount", i64 1}
+  !6 = !{!"MaxFunctionCount", i64 1000}
+  !7 = !{!"NumCounts", i64 3}
+  !8 = !{!"NumFunctions", i64 5}
+  !9 = !{!"DetailedSummary", !10}
+  !10 = !{!11, !12, !13}
+  !11 = !{i32 10000, i64 100, i32 1}
+  !12 = !{i32 999900, i64 100, i32 1}
+  !13 = !{i32 999999, i64 1, i32 2}
+  !14 = !{!"function_entry_count", i64 9000}
+  !15 = !{!"function_section_prefix", !"hot"}
+  !16 = !{!"branch_weights", i32 7000, i32 0}
+  !17 = !{!"branch_weights", i32 1000, i32 4000, i32 4000, i32 0, i32 0}
+
+...
+---
+name:            split_basic
+stack:
+  - { id: 0, name: '', type: spill-slot, offset: -16, size: 8, alignment: 16,
+      stack-id: default, callee-saved-register: '$lr', callee-saved-restored: true,
+      debug-info-variable: '', debug-info-expression: '', debug-info-location: '' }
+machineFunctionInfo:
+  hasRedZone:      false
+body:             |
+  ; CHECK-LABEL: name: split_basic
+  ; COM: Check that machine function splitting splits a cold block.
+  ; CHECK: bb.0 (%ir-block.1)
+  ; CHECK-NOT: bb.1 (%ir-block.2, bbsections Cold)
+  ; CHECK: bb.2 (%ir-block.4, bbsections Cold)
+
+  bb.0 (%ir-block.1):
+    successors: %bb.1(0x80000000), %bb.2(0x00000000)
+    liveins: $w0, $lr
+
+    early-clobber $sp = frame-setup STRXpre killed $lr, $sp, -16 :: (store (s64) into %stack.0)
+    CBZW killed renamable $w0, %bb.2
+
+  bb.1 (%ir-block.2):
+    BL @bar, csr_aarch64_aapcs, implicit-def dead $lr, implicit $sp, implicit-def $sp, implicit-def dead $w0
+    early-clobber $sp, $lr = frame-destroy LDRXpost $sp, 16 :: (load (s64) from %stack.0)
+    TCRETURNdi @qux, 0, csr_aarch64_aapcs, implicit $sp
+
+  bb.2 (%ir-block.4):
+    BL @baz, csr_aarch64_aapcs, implicit-def dead $lr, implicit $sp, implicit-def $sp, implicit-def dead $w0
+    early-clobber $sp, $lr = frame-destroy LDRXpost $sp, 16 :: (load (s64) from %stack.0)
+    TCRETURNdi @qux, 0, csr_aarch64_aapcs, implicit $sp
+
+...