add unreachable to prevent no-return warnings
diff --git a/llvm/lib/Target/AMDGPU/AMDGPUTargetMachine.cpp b/llvm/lib/Target/AMDGPU/AMDGPUTargetMachine.cpp
index 6860b22..1167465 100644
--- a/llvm/lib/Target/AMDGPU/AMDGPUTargetMachine.cpp
+++ b/llvm/lib/Target/AMDGPU/AMDGPUTargetMachine.cpp
@@ -2186,6 +2186,7 @@
     return RA_OPTIONS(onlyAllocateVGPRs, "vgpr", true);
   }
 
+  llvm_unreachable("invalid phase value");
 #undef RA_OPTIONS
 }