Index: lib/Target/AMDGPU/SIInsertWaitcnts.cpp
===================================================================
--- lib/Target/AMDGPU/SIInsertWaitcnts.cpp
+++ lib/Target/AMDGPU/SIInsertWaitcnts.cpp
@@ -1216,6 +1216,9 @@
       StrictDom = true;
   }
 
+  VgprUB = std::max(getMaxVGPR(), Other.getMaxVGPR());
+  SgprUB = std::max(getMaxSGPR(), Other.getMaxSGPR());
+
   return StrictDom;
 }
 
Index: test/CodeGen/AMDGPU/waitcnt-loop-irreducible.mir
===================================================================
--- test/CodeGen/AMDGPU/waitcnt-loop-irreducible.mir
+++ test/CodeGen/AMDGPU/waitcnt-loop-irreducible.mir
@@ -1,20 +1,26 @@
-# RUN: llc -march=amdgcn -verify-machineinstrs -run-pass si-insert-waitcnts -o - %s | FileCheck -check-prefixes=GCN %s
+# RUN: llc -march=amdgcn -mcpu=gfx803 -verify-machineinstrs -run-pass si-insert-waitcnts -o - %s | FileCheck -check-prefixes=GCN,GFX8 %s
+# RUN: llc -march=amdgcn -mcpu=gfx900 -verify-machineinstrs -run-pass si-insert-waitcnts -o - %s | FileCheck -check-prefixes=GCN,GFX9 %s
 
-# GCN-LABEL: name: irreducible_loop{{$}}
-# GCN: S_LOAD_DWORDX4_IMM
-# GCN: S_WAITCNT 127{{$}}
-# GCN: S_BUFFER_LOAD_DWORD_IMM
-# GCN: S_WAITCNT 127{{$}}
-# GCN: S_CMP_GE_I32
 --- |
 
   define amdgpu_ps void @irreducible_loop() {
-  main:
+    ret void
+  }
+  define amdgpu_ps void @irreducible_loop_extended() {
     ret void
   }
 
 ...
 ---
+
+# GCN-LABEL: name: irreducible_loop{{$}}
+# GCN: S_LOAD_DWORDX4_IMM
+# GFX8: S_WAITCNT 127{{$}}
+# GFX9: S_WAITCNT 49279{{$}}
+# GCN: S_BUFFER_LOAD_DWORD_IMM
+# GFX8: S_WAITCNT 127{{$}}
+# GFX9: S_WAITCNT 49279{{$}}
+# GCN: S_CMP_GE_I32
 name:            irreducible_loop
 body:             |
   bb.0:
@@ -45,3 +51,53 @@
     S_ENDPGM
 
 ...
+
+# GCN-LABEL: name: irreducible_loop_extended
+
+# GCN: S_LOAD_DWORDX4_IMM
+# GFX8: S_WAITCNT 127{{$}}
+# GFX9: S_WAITCNT 49279{{$}}
+# GCN: BUFFER_STORE_DWORD_OFFEN_exact
+# GFX8: S_WAITCNT 127{{$}}
+# GFX9: S_WAITCNT 49279{{$}}
+# GCN: BUFFER_STORE_DWORD_OFFEN_exact
+# GCN: S_LOAD_DWORDX4_IMM
+# GFX8: S_WAITCNT 127{{$}}
+# GFX9: S_WAITCNT 49279{{$}}
+# GCN: BUFFER_ATOMIC_ADD_OFFSET_RTN
+# GCN: S_WAITCNT 3952
+# GCN: FLAT_STORE_DWORD
+# GCN: S_ENDPGM
+name: irreducible_loop_extended
+
+body: |
+  bb.0:
+    successors: %bb.1, %bb.2
+    $sgpr4_sgpr5_sgpr6_sgpr7 = S_LOAD_DWORDX4_IMM renamable $sgpr2_sgpr3, 0, 0
+    S_CBRANCH_VCCZ %bb.2, implicit $vcc
+
+  bb.1:
+    successors: %bb.2
+    BUFFER_STORE_DWORD_OFFEN_exact killed renamable $vgpr3, renamable $vgpr2, renamable $sgpr4_sgpr5_sgpr6_sgpr7, 0, 0, 0, 0, 0, implicit $exec
+
+  bb.2:
+    successors: %bb.3, %bb.6
+    S_CBRANCH_VCCNZ %bb.6, implicit $vcc
+
+  bb.3:
+    successors: %bb.4, %bb.5
+    BUFFER_STORE_DWORD_OFFEN_exact killed renamable $vgpr3, killed renamable $vgpr2, killed renamable $sgpr4_sgpr5_sgpr6_sgpr7, 0, 0, 0, 0, 0, implicit $exec
+    S_CBRANCH_VCCNZ %bb.5, implicit $vcc
+
+  bb.4:
+    successors: %bb.5
+    renamable $sgpr12_sgpr13_sgpr14_sgpr15 = S_LOAD_DWORDX4_IMM killed renamable $sgpr2_sgpr3, 64, 0
+    renamable $vgpr2 = BUFFER_ATOMIC_ADD_OFFSET_RTN killed renamable $vgpr2, killed renamable $sgpr12_sgpr13_sgpr14_sgpr15, 0, 0, 0, implicit $exec
+
+  bb.5:
+    successors: %bb.6
+
+  bb.6:
+    FLAT_STORE_DWORD $vgpr3_vgpr4, $vgpr2, 0, 0, 0, implicit $exec, implicit $flat_scr
+    S_ENDPGM
+...