Index: lib/Target/AMDGPU/SIInsertWaits.cpp
===================================================================
--- lib/Target/AMDGPU/SIInsertWaits.cpp
+++ lib/Target/AMDGPU/SIInsertWaits.cpp
@@ -93,6 +93,9 @@
 
   bool LastInstWritesM0;
 
+  /// Whether or not we have flat operations outstanding.
+  bool IsFlatOutstanding;
+
   /// \brief Whether the machine function returns void
   bool ReturnsVoid;
 
@@ -294,6 +297,9 @@
   Counters Limit = ZeroCounts;
   unsigned Sum = 0;
 
+  if (TII->isFLAT(*I))
+    IsFlatOutstanding = true;
+
   for (unsigned i = 0; i < 3; ++i) {
     LastIssued.Array[i] += Increment.Array[i];
     if (Increment.Array[i])
@@ -368,8 +374,9 @@
   // Figure out if the async instructions execute in order
   bool Ordered[3];
 
-  // VM_CNT is always ordered
-  Ordered[0] = true;
+  // VM_CNT is always ordered except when there are flat instructions, which
+  // can return out of order.
+  Ordered[0] = !IsFlatOutstanding;
 
   // EXP_CNT is unordered if we have both EXP & VM-writes
   Ordered[1] = ExpInstrTypesSeen == 3;
@@ -419,6 +426,7 @@
 
   LastOpcodeType = OTHER;
   LastInstWritesM0 = false;
+  IsFlatOutstanding = true;
   return true;
 }
 
@@ -532,6 +540,7 @@
   LastIssued = ZeroCounts;
   LastOpcodeType = OTHER;
   LastInstWritesM0 = false;
+  IsFlatOutstanding = false;
   ReturnsVoid = MF.getInfo<SIMachineFunctionInfo>()->returnsVoid();
 
   memset(&UsedRegs, 0, sizeof(UsedRegs));
Index: test/CodeGen/MIR/AMDGPU/waitcnt.mir
===================================================================
--- /dev/null
+++ test/CodeGen/MIR/AMDGPU/waitcnt.mir
@@ -0,0 +1,24 @@
+# RUN: llc -march=amdgcn -mcpu=fiji -run-pass si-insert-waits  %s -o - | FileCheck %s
+
+--- |
+  define void @flat_zero_waitcnt() { ret void }
+...
+---
+
+# CHECK-LABEL: name: flat_zero_waitcnt
+
+# CHECK-LABEL: bb.0:
+# CHECK: FLAT_LOAD_DWORD
+# CHECK: FLAT_LOAD_DWORDX4
+# s_waitcnt vmcnt(0) lgkmcnt(0)
+# CHECK: S_WAITCNT 112
+
+name: flat_zero_waitcnt
+
+body: |
+  bb.0:
+    %vgpr0 = FLAT_LOAD_DWORD %vgpr1_vgpr2, 0, 0, 0, implicit %exec, implicit %flat_scr
+    %vgpr3_vgpr4_vgpr5_vgpr6 = FLAT_LOAD_DWORDX4 %vgpr7_vgpr8, 0, 0, 0, implicit %exec, implicit %flat_scr
+    %vgpr0 = V_MOV_B32_e32 %vgpr1, implicit %exec
+    S_ENDPGM
+...