diff --git a/llvm/lib/Target/AMDGPU/SIMemoryLegalizer.cpp b/llvm/lib/Target/AMDGPU/SIMemoryLegalizer.cpp
--- a/llvm/lib/Target/AMDGPU/SIMemoryLegalizer.cpp
+++ b/llvm/lib/Target/AMDGPU/SIMemoryLegalizer.cpp
@@ -898,6 +898,10 @@
 
   const GCNSubtarget &STM = MBB.getParent()->getSubtarget<GCNSubtarget>();
 
+  // Graphics environments never added a principled use of volatile vs.
+  // non-volatile, and the default MTYPE in buffer descriptors (MTYPE value 0)
+  // is NC_NV (non-coherent, non-volatile) on gfx8 (and maybe on gfx7, but not
+  // on gfx9), so a non-volatile wbinv is required.
   const unsigned InvalidateL1 = STM.isAmdPalOS() || STM.isMesa3DOS()
                                     ? AMDGPU::BUFFER_WBINVL1
                                     : AMDGPU::BUFFER_WBINVL1_VOL;