AMDGPU: Fix crashes in invalid call cases

We have to at least tolerate calls to kernels, possibly with a
mismatched calling convention on the callsite.

llvm-svn: 355049
diff --git a/llvm/lib/Target/AMDGPU/AMDGPUISelLowering.cpp b/llvm/lib/Target/AMDGPU/AMDGPUISelLowering.cpp
index 1fc44b6..6817117 100644
--- a/llvm/lib/Target/AMDGPU/AMDGPUISelLowering.cpp
+++ b/llvm/lib/Target/AMDGPU/AMDGPUISelLowering.cpp
@@ -848,9 +848,6 @@
 CCAssignFn *AMDGPUCallLowering::CCAssignFnForCall(CallingConv::ID CC,
                                                   bool IsVarArg) {
   switch (CC) {
-  case CallingConv::AMDGPU_KERNEL:
-  case CallingConv::SPIR_KERNEL:
-    llvm_unreachable("kernels should not be handled here");
   case CallingConv::AMDGPU_VS:
   case CallingConv::AMDGPU_GS:
   case CallingConv::AMDGPU_PS:
@@ -863,8 +860,10 @@
   case CallingConv::Fast:
   case CallingConv::Cold:
     return CC_AMDGPU_Func;
+  case CallingConv::AMDGPU_KERNEL:
+  case CallingConv::SPIR_KERNEL:
   default:
-    report_fatal_error("Unsupported calling convention.");
+    report_fatal_error("Unsupported calling convention for call");
   }
 }