Index: llvm/lib/Target/AMDGPU/SIRegisterInfo.cpp
===================================================================
--- llvm/lib/Target/AMDGPU/SIRegisterInfo.cpp
+++ llvm/lib/Target/AMDGPU/SIRegisterInfo.cpp
@@ -138,6 +138,7 @@
 
 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.
Index: llvm/lib/Target/AMDGPU/SIRegisterInfo.td
===================================================================
--- llvm/lib/Target/AMDGPU/SIRegisterInfo.td
+++ llvm/lib/Target/AMDGPU/SIRegisterInfo.td
@@ -125,6 +125,9 @@
 def M0 : SIReg <"m0", 124>;
 def SGPR_NULL : SIReg<"null", 125>;
 
+// Not addressable
+def MODE : SIReg <"mode", 0>;
+
 def SRC_SHARED_BASE : SIReg<"src_shared_base", 235>;
 def SRC_SHARED_LIMIT : SIReg<"src_shared_limit", 236>;
 def SRC_PRIVATE_BASE : SIReg<"src_private_base", 237>;