Index: lib/CodeGen/MachineScheduler.cpp
===================================================================
--- lib/CodeGen/MachineScheduler.cpp
+++ lib/CodeGen/MachineScheduler.cpp
@@ -486,13 +486,17 @@
       MachineInstr &MI = *std::prev(I);
       if (isSchedBoundary(&MI, &*MBB, MF, TII))
         break;
-      if (!MI.isDebugInstr())
+      if (!MI.isDebugInstr()) {
         // MBB::size() uses instr_iterator to count. Here we need a bundle to
         // count as a single instruction.
         ++NumRegionInstrs;
+      }
     }
 
-    Regions.push_back(SchedRegion(I, RegionEnd, NumRegionInstrs));
+    // It's possible we found a scheduling region that only has debug
+    // instructions. Don't bother scheduling these.
+    if (NumRegionInstrs != 0)
+      Regions.push_back(SchedRegion(I, RegionEnd, NumRegionInstrs));
   }
 
   if (RegionsTopDown)
Index: test/CodeGen/AMDGPU/sched-assert-onlydbg-value-empty-region.mir
===================================================================
--- /dev/null
+++ test/CodeGen/AMDGPU/sched-assert-onlydbg-value-empty-region.mir
@@ -0,0 +1,135 @@
+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
+# RUN: llc -mtriple=amdgcn-amd-amdhsa -mcpu=gfx900 -run-pass=machine-scheduler -verify-machineinstrs %s -o - | FileCheck %s
+
+# The sequence of DBG_VALUEs forms a scheduling region with 0 real
+# instructions. The RegPressure tracker would end up skipping over any
+# debug instructions, so it would point to the instruction
+# before/outside of the region, hitting this assert:
+#  assert((BotRPTracker.getPos() == RegionEnd ||
+#          (RegionEnd->isDebugInstr() &&
+#           BotRPTracker.getPos() == priorNonDebug(RegionEnd, RegionBegin))) &&
+#         "Can't find the region bottom");
+
+--- |
+  define amdgpu_kernel void @only_dbg_value_sched_region() #0 {
+    ret void
+  }
+
+  !llvm.dbg.cu = !{!0}
+  !llvm.module.flags = !{!2}
+
+  !0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 8.0 ", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, nameTableKind: None)
+  !1 = !DIFile(filename: "foo", directory: "/dev/null")
+  !2 = !{i32 2, !"Debug Info Version", i32 3}
+  !3 = !{i32 0, i32 256}
+  !4 = !DILocation(line: 93, column: 2, scope: !5)
+  !5 = distinct !DISubprogram(name: "func", scope: !6, file: !6, line: 92, scopeLine: 92, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0)
+  !6 = !DIFile(filename: "arst.cl", directory: "/dev/null")
+  !7 = !DILocalVariable(name: "p", arg: 2, scope: !5, file: !6, line: 92)
+  !8 = !DILocation(line: 92, column: 47, scope: !5)
+  !9 = !{}
+
+...
+---
+name:            only_dbg_value_sched_region
+tracksRegLiveness: true
+machineFunctionInfo:
+  isEntryFunction: true
+  waveLimiter:     true
+body:             |
+  ; CHECK-LABEL: name: only_dbg_value_sched_region
+  ; CHECK: bb.0:
+  ; CHECK:   successors: %bb.1(0x80000000)
+  ; CHECK:   liveins: $vgpr0
+  ; CHECK:   [[COPY:%[0-9]+]]:vgpr_32 = COPY $vgpr0
+  ; CHECK:   [[DEF:%[0-9]+]]:vreg_64 = IMPLICIT_DEF
+  ; CHECK:   [[GLOBAL_LOAD_DWORDX2_:%[0-9]+]]:vreg_64 = GLOBAL_LOAD_DWORDX2 [[DEF]], 0, 0, 0, implicit $exec
+  ; CHECK:   [[GLOBAL_LOAD_DWORD:%[0-9]+]]:vgpr_32 = GLOBAL_LOAD_DWORD [[DEF]], 8, 0, 0, implicit $exec
+  ; CHECK:   undef %4.sub1:vreg_64 = V_ADD_U32_e32 [[COPY]], [[COPY]], implicit $exec
+  ; CHECK:   %4.sub0:vreg_64 = V_MOV_B32_e32 111, implicit $exec
+  ; CHECK:   [[DEF1:%[0-9]+]]:vreg_64 = IMPLICIT_DEF
+  ; CHECK:   [[DEF2:%[0-9]+]]:vreg_64 = IMPLICIT_DEF
+  ; CHECK:   [[DEF3:%[0-9]+]]:vreg_64 = IMPLICIT_DEF
+  ; CHECK:   undef %11.sub1:vreg_64 = IMPLICIT_DEF
+  ; CHECK:   [[DEF4:%[0-9]+]]:vreg_64 = IMPLICIT_DEF
+  ; CHECK:   [[DEF5:%[0-9]+]]:vreg_64 = IMPLICIT_DEF
+  ; CHECK:   [[V_MOV_B32_e32_:%[0-9]+]]:vgpr_32 = V_MOV_B32_e32 0, implicit $exec
+  ; CHECK:   [[V_MOV_B32_e32_1:%[0-9]+]]:vgpr_32 = V_MOV_B32_e32 0, implicit $exec
+  ; CHECK:   [[DEF6:%[0-9]+]]:vgpr_32 = IMPLICIT_DEF
+  ; CHECK:   [[DEF7:%[0-9]+]]:vgpr_32 = IMPLICIT_DEF
+  ; CHECK:   [[COPY1:%[0-9]+]]:vreg_64 = COPY [[GLOBAL_LOAD_DWORDX2_]]
+  ; CHECK:   undef %6.sub0:vreg_64 = V_ADD_F32_e32 [[DEF]].sub0, [[COPY1]].sub0, implicit $exec
+  ; CHECK:   dead undef %6.sub1:vreg_64 = V_ADD_F32_e32 [[DEF]].sub1, [[COPY1]].sub0, implicit $exec
+  ; CHECK:   [[GLOBAL_LOAD_DWORD1:%[0-9]+]]:vgpr_32 = GLOBAL_LOAD_DWORD [[COPY1]], 0, 0, 0, implicit $exec
+  ; CHECK:   [[DEF8:%[0-9]+]]:vgpr_32 = IMPLICIT_DEF
+  ; CHECK:   undef %19.sub0:vreg_64 = V_ADD_F32_e32 [[GLOBAL_LOAD_DWORD1]], [[GLOBAL_LOAD_DWORDX2_]].sub0, implicit $exec
+  ; CHECK:   %19.sub1:vreg_64 = V_ADD_F32_e32 [[GLOBAL_LOAD_DWORD]], [[GLOBAL_LOAD_DWORD]], implicit $exec
+  ; CHECK:   GLOBAL_STORE_DWORDX2 %19, %4, 32, 0, 0, implicit $exec
+  ; CHECK:   %11.sub0:vreg_64 = GLOBAL_LOAD_DWORD [[DEF1]], 0, 0, 0, implicit $exec
+  ; CHECK:   [[DEF2]].sub0:vreg_64 = GLOBAL_LOAD_DWORD [[DEF3]], 0, 0, 0, implicit $exec
+  ; CHECK:   dead %20:vgpr_32 = GLOBAL_LOAD_DWORD %11, 0, 0, 0, implicit $exec
+  ; CHECK:   dead %21:vgpr_32 = GLOBAL_LOAD_DWORD [[DEF4]], 0, 0, 0, implicit $exec
+  ; CHECK:   [[V_LSHLREV_B64_:%[0-9]+]]:vreg_64 = V_LSHLREV_B64 2, [[DEF2]], implicit $exec
+  ; CHECK:   dead %22:vgpr_32 = GLOBAL_LOAD_DWORD [[DEF5]], 0, 0, 0, implicit $exec
+  ; CHECK:   S_NOP 0, implicit [[DEF7]], implicit [[V_LSHLREV_B64_]].sub0, implicit [[DEF6]], implicit [[V_MOV_B32_e32_]]
+  ; CHECK:   GLOBAL_STORE_DWORD [[DEF5]], [[V_MOV_B32_e32_1]], 0, 0, 0, implicit $exec
+  ; CHECK: bb.1:
+  ; CHECK:   successors: %bb.2(0x80000000)
+  ; CHECK:   S_SETREG_IMM32_B32 0, 1
+  ; CHECK:   DBG_VALUE %21, $noreg
+  ; CHECK:   DBG_VALUE %22, $noreg
+  ; CHECK:   DBG_VALUE [[V_LSHLREV_B64_]], $noreg
+  ; CHECK:   S_SETREG_IMM32_B32 0, 1
+  ; CHECK: bb.2:
+  ; CHECK:   S_NOP 0, implicit [[COPY]]
+  ; CHECK:   S_NOP 0, implicit [[DEF8]]
+  ; CHECK:   S_ENDPGM 0
+  bb.0:
+    liveins: $vgpr0
+
+    %0:vgpr_32 = COPY $vgpr0
+    %1:vreg_64 = IMPLICIT_DEF
+    %2:vreg_64 = GLOBAL_LOAD_DWORDX2 %1, 0, 0, 0, implicit $exec
+    %3:vgpr_32 = GLOBAL_LOAD_DWORD %1, 8, 0, 0, implicit $exec
+    undef %4.sub1:vreg_64 = V_ADD_U32_e32 %0, %0, implicit $exec
+    %4.sub0:vreg_64 = V_MOV_B32_e32 111, implicit $exec
+    %5:vreg_64 = COPY %2
+    undef %6.sub0:vreg_64 = V_ADD_F32_e32 %1.sub0, %5.sub0, implicit $exec
+    %6.sub1:vreg_64 = V_ADD_F32_e32 %1.sub1, %5.sub0, implicit $exec
+    %7:vgpr_32 = GLOBAL_LOAD_DWORD %5, 0, 0, 0, implicit $exec
+    %8:vreg_64 = IMPLICIT_DEF
+    %9:vreg_64 = IMPLICIT_DEF
+    %10:vreg_64 = IMPLICIT_DEF
+    undef %11.sub1:vreg_64 = IMPLICIT_DEF
+    %12:vgpr_32 = IMPLICIT_DEF
+    %13:vgpr_32 = IMPLICIT_DEF
+    %14:vreg_64 = IMPLICIT_DEF
+    %15:vreg_64 = IMPLICIT_DEF
+    %16:vgpr_32 = IMPLICIT_DEF
+    %17:vgpr_32 = V_MOV_B32_e32 0, implicit $exec
+    %18:vgpr_32 = V_MOV_B32_e32 0, implicit $exec
+    undef %19.sub0:vreg_64 = V_ADD_F32_e32 %7, %2.sub0, implicit $exec
+    %19.sub1:vreg_64 = V_ADD_F32_e32 %3, %3, implicit $exec
+    GLOBAL_STORE_DWORDX2 %19, %4, 32, 0, 0, implicit $exec
+    %11.sub0:vreg_64 = GLOBAL_LOAD_DWORD %9, 0, 0, 0, implicit $exec
+    %8.sub0:vreg_64 = GLOBAL_LOAD_DWORD %10, 0, 0, 0, implicit $exec
+    %20:vgpr_32 = GLOBAL_LOAD_DWORD %11, 0, 0, 0, implicit $exec
+    %21:vgpr_32 = GLOBAL_LOAD_DWORD %14, 0, 0, 0, implicit $exec
+    %22:vgpr_32 = GLOBAL_LOAD_DWORD %15, 0, 0, 0, implicit $exec
+    %23:vreg_64 = V_LSHLREV_B64 2, %8, implicit $exec
+    S_NOP 0, implicit %13, implicit %23.sub0, implicit %12, implicit %17
+    GLOBAL_STORE_DWORD %15, %18, 0, 0, 0, implicit $exec
+
+  bb.1:
+    S_SETREG_IMM32_B32 0, 1
+    DBG_VALUE %21, $noreg, !7, !DIExpression(DW_OP_constu, 1, DW_OP_swap, DW_OP_xderef), debug-location !8
+    DBG_VALUE %22, $noreg, !7, !DIExpression(DW_OP_constu, 1, DW_OP_swap, DW_OP_xderef), debug-location !8
+    DBG_VALUE %23, $noreg, !7, !DIExpression(DW_OP_constu, 1, DW_OP_swap, DW_OP_xderef), debug-location !8
+    S_SETREG_IMM32_B32 0, 1
+
+  bb.2:
+    S_NOP 0, implicit %0
+    S_NOP 0, implicit %16
+    S_ENDPGM 0
+
+...