Index: llvm/lib/Target/ARM/MVEVPTOptimisationsPass.cpp
===================================================================
--- llvm/lib/Target/ARM/MVEVPTOptimisationsPass.cpp
+++ llvm/lib/Target/ARM/MVEVPTOptimisationsPass.cpp
@@ -230,6 +230,10 @@
     if ((InsertPt != MBB->end() && !DT->dominates(&*InsertPt, &Use)) ||
         !DT->dominates(ML->getHeader(), Use.getParent()))
       InsertPt = &Use;
+  if (!DT->dominates(MRI->getVRegDef(CountReg), &*InsertPt)) {
+    LLVM_DEBUG(dbgs() << "  InsertPt does not dominate CountReg!\n");
+    return false;
+  }
 
   MachineInstrBuilder MI = BuildMI(*MBB, InsertPt, LoopStart->getDebugLoc(),
                                    TII->get(ARM::t2DoLoopStartTP))
Index: llvm/test/CodeGen/Thumb2/LowOverheadLoops/count_dominates_start.mir
===================================================================
--- /dev/null
+++ llvm/test/CodeGen/Thumb2/LowOverheadLoops/count_dominates_start.mir
@@ -0,0 +1,214 @@
+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
+# RUN: llc -mtriple=thumbv8.1m.main-none-eabi -mattr=+lob -run-pass=arm-mve-vpt-opts %s -verify-machineinstrs -o - | FileCheck %s
+
+--- |
+
+  define i32 @test(i16* nocapture readonly %x, i16* nocapture readonly %y, i32 %n) {
+  entry:
+    %cmp10 = icmp sgt i32 %n, 0
+    %0 = add i32 %n, 7
+    %1 = lshr i32 %0, 3
+    %2 = shl nuw i32 %1, 3
+    %3 = add i32 %2, -8
+    %4 = lshr i32 %3, 3
+    %5 = add nuw nsw i32 %4, 1
+    br i1 %cmp10, label %vector.ph, label %for.cond.cleanup
+
+  vector.ph:                                        ; preds = %entry
+    %6 = call i32 @llvm.start.loop.iterations.i32(i32 %5)
+    br label %vector.body
+
+  vector.body:                                      ; preds = %vector.body, %vector.ph
+    %lsr.iv3 = phi i16* [ %scevgep4, %vector.body ], [ %x, %vector.ph ]
+    %lsr.iv1 = phi i16* [ %scevgep, %vector.body ], [ %y, %vector.ph ]
+    %vec.phi = phi i32 [ 0, %vector.ph ], [ %16, %vector.body ]
+    %7 = phi i32 [ %6, %vector.ph ], [ %17, %vector.body ]
+    %8 = phi i32 [ %n, %vector.ph ], [ %10, %vector.body ]
+    %lsr.iv12 = bitcast i16* %lsr.iv1 to <8 x i16>*
+    %lsr.iv35 = bitcast i16* %lsr.iv3 to <8 x i16>*
+    %9 = call <8 x i1> @llvm.arm.mve.vctp16(i32 %8)
+    %10 = sub i32 %8, 8
+    %wide.masked.load = call <8 x i16> @llvm.masked.load.v8i16.p0v8i16(<8 x i16>* %lsr.iv35, i32 2, <8 x i1> %9, <8 x i16> undef)
+    %11 = sext <8 x i16> %wide.masked.load to <8 x i32>
+    %wide.masked.load13 = call <8 x i16> @llvm.masked.load.v8i16.p0v8i16(<8 x i16>* %lsr.iv12, i32 2, <8 x i1> %9, <8 x i16> undef)
+    %12 = sext <8 x i16> %wide.masked.load13 to <8 x i32>
+    %13 = mul nsw <8 x i32> %12, %11
+    %14 = select <8 x i1> %9, <8 x i32> %13, <8 x i32> zeroinitializer
+    %15 = call i32 @llvm.vector.reduce.add.v8i32(<8 x i32> %14)
+    %16 = add i32 %15, %vec.phi
+    %scevgep = getelementptr i16, i16* %lsr.iv1, i32 8
+    %scevgep4 = getelementptr i16, i16* %lsr.iv3, i32 8
+    %17 = call i32 @llvm.loop.decrement.reg.i32(i32 %7, i32 1)
+    %18 = icmp ne i32 %17, 0
+    br i1 %18, label %vector.body, label %for.cond.cleanup
+
+  for.cond.cleanup:                                 ; preds = %vector.body, %entry
+    %s.0.lcssa = phi i32 [ 0, %entry ], [ %16, %vector.body ]
+    ret i32 %s.0.lcssa
+  }
+
+  declare <8 x i1> @llvm.get.active.lane.mask.v8i1.i32(i32, i32)
+  declare <8 x i16> @llvm.masked.load.v8i16.p0v8i16(<8 x i16>*, i32 immarg, <8 x i1>, <8 x i16>)
+  declare i32 @llvm.vector.reduce.add.v8i32(<8 x i32>)
+  declare i32 @llvm.start.loop.iterations.i32(i32)
+  declare i32 @llvm.loop.decrement.reg.i32(i32, i32)
+  declare <8 x i1> @llvm.arm.mve.vctp16(i32)
+
+...
+---
+name:            test
+alignment:       2
+tracksRegLiveness: true
+registers:
+  - { id: 0, class: rgpr, preferred-register: '' }
+  - { id: 1, class: gpr, preferred-register: '' }
+  - { id: 2, class: gprnopc, preferred-register: '' }
+  - { id: 3, class: gprnopc, preferred-register: '' }
+  - { id: 4, class: tgpreven, preferred-register: '' }
+  - { id: 5, class: gprlr, preferred-register: '' }
+  - { id: 6, class: rgpr, preferred-register: '' }
+  - { id: 7, class: gpr, preferred-register: '' }
+  - { id: 8, class: gpr, preferred-register: '' }
+  - { id: 9, class: gpr, preferred-register: '' }
+  - { id: 10, class: gpr, preferred-register: '' }
+  - { id: 11, class: gpr, preferred-register: '' }
+  - { id: 12, class: gpr, preferred-register: '' }
+  - { id: 13, class: gpr, preferred-register: '' }
+  - { id: 14, class: gpr, preferred-register: '' }
+  - { id: 15, class: gprnopc, preferred-register: '' }
+  - { id: 16, class: gpr, preferred-register: '' }
+  - { id: 17, class: rgpr, preferred-register: '' }
+  - { id: 18, class: rgpr, preferred-register: '' }
+  - { id: 19, class: rgpr, preferred-register: '' }
+  - { id: 20, class: rgpr, preferred-register: '' }
+  - { id: 21, class: gprnopc, preferred-register: '' }
+  - { id: 22, class: rgpr, preferred-register: '' }
+  - { id: 23, class: gpr, preferred-register: '' }
+  - { id: 24, class: gprlr, preferred-register: '' }
+  - { id: 25, class: rgpr, preferred-register: '' }
+  - { id: 26, class: vccr, preferred-register: '' }
+  - { id: 27, class: rgpr, preferred-register: '' }
+  - { id: 28, class: rgpr, preferred-register: '' }
+  - { id: 29, class: mqpr, preferred-register: '' }
+  - { id: 30, class: rgpr, preferred-register: '' }
+  - { id: 31, class: mqpr, preferred-register: '' }
+  - { id: 32, class: tgpreven, preferred-register: '' }
+  - { id: 33, class: gprlr, preferred-register: '' }
+  - { id: 34, class: gprlr, preferred-register: '' }
+  - { id: 35, class: gprnopc, preferred-register: '' }
+liveins:
+  - { reg: '$r0', virtual-reg: '%13' }
+  - { reg: '$r1', virtual-reg: '%14' }
+  - { reg: '$r2', virtual-reg: '%15' }
+body:             |
+  ; CHECK-LABEL: name: test
+  ; CHECK: bb.0.entry:
+  ; CHECK:   successors: %bb.2(0x50000000), %bb.1(0x30000000)
+  ; CHECK:   liveins: $r0, $r1, $r2
+  ; CHECK:   [[COPY:%[0-9]+]]:gprnopc = COPY $r2
+  ; CHECK:   [[COPY1:%[0-9]+]]:gpr = COPY $r1
+  ; CHECK:   [[COPY2:%[0-9]+]]:gpr = COPY $r0
+  ; CHECK:   t2CMPri [[COPY]], 1, 14 /* CC::al */, $noreg, implicit-def $cpsr
+  ; CHECK:   t2Bcc %bb.2, 10 /* CC::ge */, $cpsr
+  ; CHECK: bb.1:
+  ; CHECK:   successors: %bb.4(0x80000000)
+  ; CHECK:   [[t2MOVi:%[0-9]+]]:rgpr = t2MOVi 0, 14 /* CC::al */, $noreg, $noreg
+  ; CHECK:   [[COPY3:%[0-9]+]]:gpr = COPY [[t2MOVi]]
+  ; CHECK:   t2B %bb.4, 14 /* CC::al */, $noreg
+  ; CHECK: bb.2.vector.ph:
+  ; CHECK:   successors: %bb.3(0x80000000)
+  ; CHECK:   [[t2ADDri:%[0-9]+]]:rgpr = t2ADDri [[COPY]], 7, 14 /* CC::al */, $noreg, $noreg
+  ; CHECK:   [[t2BICri:%[0-9]+]]:rgpr = t2BICri [[t2ADDri]], 7, 14 /* CC::al */, $noreg, $noreg
+  ; CHECK:   [[t2SUBri:%[0-9]+]]:rgpr = t2SUBri [[t2BICri]], 8, 14 /* CC::al */, $noreg, $noreg
+  ; CHECK:   [[t2MOVi1:%[0-9]+]]:rgpr = t2MOVi 1, 14 /* CC::al */, $noreg, $noreg
+  ; CHECK:   [[t2ADDrs:%[0-9]+]]:gprnopc = nuw nsw t2ADDrs [[t2MOVi1]], [[t2SUBri]], 27, 14 /* CC::al */, $noreg, $noreg
+  ; CHECK:   [[COPY4:%[0-9]+]]:rgpr = COPY [[t2ADDrs]]
+  ; CHECK:   [[t2DoLoopStart:%[0-9]+]]:gprlr = t2DoLoopStart [[COPY4]]
+  ; CHECK:   [[t2MOVi2:%[0-9]+]]:rgpr = t2MOVi 0, 14 /* CC::al */, $noreg, $noreg
+  ; CHECK:   [[COPY5:%[0-9]+]]:gpr = COPY [[t2MOVi2]]
+  ; CHECK:   [[COPY6:%[0-9]+]]:gpr = COPY [[t2DoLoopStart]]
+  ; CHECK:   [[COPY7:%[0-9]+]]:gprnopc = COPY [[COPY]]
+  ; CHECK: bb.3.vector.body:
+  ; CHECK:   successors: %bb.3(0x7c000000), %bb.4(0x04000000)
+  ; CHECK:   [[PHI:%[0-9]+]]:gprnopc = PHI [[COPY2]], %bb.2, %10, %bb.3
+  ; CHECK:   [[PHI1:%[0-9]+]]:gprnopc = PHI [[COPY1]], %bb.2, %9, %bb.3
+  ; CHECK:   [[PHI2:%[0-9]+]]:tgpreven = PHI [[COPY5]], %bb.2, %8, %bb.3
+  ; CHECK:   [[PHI3:%[0-9]+]]:gprlr = PHI [[COPY6]], %bb.2, %11, %bb.3
+  ; CHECK:   [[PHI4:%[0-9]+]]:rgpr = PHI [[COPY7]], %bb.2, %7, %bb.3
+  ; CHECK:   [[MVE_VCTP16_:%[0-9]+]]:vccr = MVE_VCTP16 [[PHI4]], 0, $noreg
+  ; CHECK:   [[t2SUBri1:%[0-9]+]]:rgpr = t2SUBri [[PHI4]], 8, 14 /* CC::al */, $noreg, $noreg
+  ; CHECK:   [[COPY8:%[0-9]+]]:gpr = COPY [[t2SUBri1]]
+  ; CHECK:   [[MVE_VLDRHU16_post:%[0-9]+]]:rgpr, [[MVE_VLDRHU16_post1:%[0-9]+]]:mqpr = MVE_VLDRHU16_post [[PHI]], 16, 1, [[MVE_VCTP16_]] :: (load 16 from %ir.lsr.iv35, align 2)
+  ; CHECK:   [[MVE_VLDRHU16_post2:%[0-9]+]]:rgpr, [[MVE_VLDRHU16_post3:%[0-9]+]]:mqpr = MVE_VLDRHU16_post [[PHI1]], 16, 1, [[MVE_VCTP16_]] :: (load 16 from %ir.lsr.iv12, align 2)
+  ; CHECK:   [[MVE_VMLADAVas16_:%[0-9]+]]:tgpreven = MVE_VMLADAVas16 [[PHI2]], killed [[MVE_VLDRHU16_post3]], killed [[MVE_VLDRHU16_post1]], 1, [[MVE_VCTP16_]]
+  ; CHECK:   [[COPY9:%[0-9]+]]:gpr = COPY [[MVE_VMLADAVas16_]]
+  ; CHECK:   [[COPY10:%[0-9]+]]:gpr = COPY [[MVE_VLDRHU16_post2]]
+  ; CHECK:   [[COPY11:%[0-9]+]]:gpr = COPY [[MVE_VLDRHU16_post]]
+  ; CHECK:   [[t2LoopDec:%[0-9]+]]:gprlr = t2LoopDec [[PHI3]], 1
+  ; CHECK:   [[COPY12:%[0-9]+]]:gpr = COPY [[t2LoopDec]]
+  ; CHECK:   t2LoopEnd [[t2LoopDec]], %bb.3, implicit-def dead $cpsr
+  ; CHECK:   t2B %bb.4, 14 /* CC::al */, $noreg
+  ; CHECK: bb.4.for.cond.cleanup:
+  ; CHECK:   [[PHI5:%[0-9]+]]:gpr = PHI [[COPY3]], %bb.1, [[COPY9]], %bb.3
+  ; CHECK:   $r0 = COPY [[PHI5]]
+  ; CHECK:   tBX_RET 14 /* CC::al */, $noreg, implicit $r0
+  bb.0.entry:
+    successors: %bb.1(0x50000000), %bb.4(0x30000000)
+    liveins: $r0, $r1, $r2
+
+    %15:gprnopc = COPY $r2
+    %14:gpr = COPY $r1
+    %13:gpr = COPY $r0
+    t2CMPri %15, 1, 14 /* CC::al */, $noreg, implicit-def $cpsr
+    t2Bcc %bb.1, 10 /* CC::ge */, $cpsr
+
+  bb.4:
+    successors: %bb.3(0x80000000)
+
+    %22:rgpr = t2MOVi 0, 14 /* CC::al */, $noreg, $noreg
+    %16:gpr = COPY %22
+    t2B %bb.3, 14 /* CC::al */, $noreg
+
+  bb.1.vector.ph:
+    successors: %bb.2(0x80000000)
+
+    %17:rgpr = t2ADDri %15, 7, 14 /* CC::al */, $noreg, $noreg
+    %18:rgpr = t2BICri %17, 7, 14 /* CC::al */, $noreg, $noreg
+    %19:rgpr = t2SUBri %18, 8, 14 /* CC::al */, $noreg, $noreg
+    %20:rgpr = t2MOVi 1, 14 /* CC::al */, $noreg, $noreg
+    %21:gprnopc = nuw nsw t2ADDrs %20, %19, 27, 14 /* CC::al */, $noreg, $noreg
+    %0:rgpr = COPY %21
+    %24:gprlr = t2DoLoopStart %0
+    %25:rgpr = t2MOVi 0, 14 /* CC::al */, $noreg, $noreg
+    %23:gpr = COPY %25
+    %1:gpr = COPY %24
+    %35:gprnopc = COPY %15
+
+  bb.2.vector.body:
+    successors: %bb.2(0x7c000000), %bb.3(0x04000000)
+
+    %2:gprnopc = PHI %13, %bb.1, %10, %bb.2
+    %3:gprnopc = PHI %14, %bb.1, %9, %bb.2
+    %4:tgpreven = PHI %23, %bb.1, %8, %bb.2
+    %5:gprlr = PHI %1, %bb.1, %11, %bb.2
+    %6:rgpr = PHI %35, %bb.1, %7, %bb.2
+    %26:vccr = MVE_VCTP16 %6, 0, $noreg
+    %27:rgpr = t2SUBri %6, 8, 14 /* CC::al */, $noreg, $noreg
+    %7:gpr = COPY %27
+    %28:rgpr, %29:mqpr = MVE_VLDRHU16_post %2, 16, 1, %26 :: (load 16 from %ir.lsr.iv35, align 2)
+    %30:rgpr, %31:mqpr = MVE_VLDRHU16_post %3, 16, 1, %26 :: (load 16 from %ir.lsr.iv12, align 2)
+    %32:tgpreven = MVE_VMLADAVas16 %4, killed %31, killed %29, 1, %26
+    %8:gpr = COPY %32
+    %9:gpr = COPY %30
+    %10:gpr = COPY %28
+    %33:gprlr = t2LoopDec %5, 1
+    %11:gpr = COPY %33
+    t2LoopEnd %33, %bb.2, implicit-def dead $cpsr
+    t2B %bb.3, 14 /* CC::al */, $noreg
+
+  bb.3.for.cond.cleanup:
+    %12:gpr = PHI %16, %bb.4, %8, %bb.2
+    $r0 = COPY %12
+    tBX_RET 14 /* CC::al */, $noreg, implicit $r0
+
+...