Index: llvm/lib/Target/AMDGPU/AMDGPUAsmPrinter.cpp
===================================================================
--- llvm/lib/Target/AMDGPU/AMDGPUAsmPrinter.cpp
+++ llvm/lib/Target/AMDGPU/AMDGPUAsmPrinter.cpp
@@ -715,6 +715,7 @@
         case AMDGPU::SRC_PRIVATE_BASE:
         case AMDGPU::SRC_PRIVATE_LIMIT:
         case AMDGPU::SGPR_NULL:
+        case AMDGPU::MODE:
           continue;
 
         case AMDGPU::SRC_POPS_EXITING_WAVE_ID:
Index: llvm/lib/Target/AMDGPU/SIRegisterInfo.cpp
===================================================================
--- llvm/lib/Target/AMDGPU/SIRegisterInfo.cpp
+++ llvm/lib/Target/AMDGPU/SIRegisterInfo.cpp
@@ -205,6 +205,7 @@
 
 BitVector SIRegisterInfo::getReservedRegs(const MachineFunction &MF) const {
   BitVector Reserved(getNumRegs());
+  Reserved.set(AMDGPU::MODE);
 
   // EXEC_LO and EXEC_HI could be allocated and used as regular register, but
   // this seems likely to result in bugs, so I'm marking them as reserved.
@@ -1648,15 +1649,16 @@
 bool SIRegisterInfo::isVGPR(const MachineRegisterInfo &MRI,
                             Register Reg) const {
   const TargetRegisterClass *RC = getRegClassForReg(MRI, Reg);
-  assert(RC && "Register class for the reg not found");
-  return hasVGPRs(RC);
+  // Registers without classes are unaddressable, SGPR-like registers.
+  return RC && hasVGPRs(RC);
 }
 
 bool SIRegisterInfo::isAGPR(const MachineRegisterInfo &MRI,
                             Register Reg) const {
   const TargetRegisterClass *RC = getRegClassForReg(MRI, Reg);
-  assert(RC && "Register class for the reg not found");
-  return hasAGPRs(RC);
+
+  // Registers without classes are unaddressable, SGPR-like registers.
+  return RC && hasAGPRs(RC);
 }
 
 bool SIRegisterInfo::shouldCoalesce(MachineInstr *MI,
Index: llvm/lib/Target/AMDGPU/SIRegisterInfo.td
===================================================================
--- llvm/lib/Target/AMDGPU/SIRegisterInfo.td
+++ llvm/lib/Target/AMDGPU/SIRegisterInfo.td
@@ -208,6 +208,9 @@
 defm SRC_PRIVATE_LIMIT : SIRegLoHi16<"src_private_limit", 238>;
 defm SRC_POPS_EXITING_WAVE_ID : SIRegLoHi16<"src_pops_exiting_wave_id", 239>;
 
+// Not addressable
+def MODE : SIReg <"mode", 0>;
+
 def LDS_DIRECT : SIReg <"src_lds_direct", 254> {
   // There is no physical register corresponding to this. This is an
   // encoding value in a source field, which will ultimately trigger a