AMDGPU: Start defining a calling convention

Partially implement callee-side for arguments and return values.
byval doesn't work properly, and most likely sret or other on-stack
return values most as well.

llvm-svn: 303308
diff --git a/llvm/lib/Target/AMDGPU/Utils/AMDGPUBaseInfo.cpp b/llvm/lib/Target/AMDGPU/Utils/AMDGPUBaseInfo.cpp
index d565c84..2abd4af 100644
--- a/llvm/lib/Target/AMDGPU/Utils/AMDGPUBaseInfo.cpp
+++ b/llvm/lib/Target/AMDGPU/Utils/AMDGPUBaseInfo.cpp
@@ -518,7 +518,18 @@
 }
 
 bool isEntryFunctionCC(CallingConv::ID CC) {
-  return true;
+  switch (CC) {
+  case CallingConv::AMDGPU_KERNEL:
+  case CallingConv::SPIR_KERNEL:
+  case CallingConv::AMDGPU_VS:
+  case CallingConv::AMDGPU_GS:
+  case CallingConv::AMDGPU_PS:
+  case CallingConv::AMDGPU_CS:
+  case CallingConv::AMDGPU_HS:
+    return true;
+  default:
+    return false;
+  }
 }
 
 bool isSI(const MCSubtargetInfo &STI) {