[AMDGPU] calling conventions for AMDPAL OS type

Summary:
This commit adds comments on how the AMDPAL OS type overloads the
existing AMDGPU_ calling conventions used by Mesa, and adds a couple of
new ones.

Reviewers: arsenm, nhaehnle, dstuttard

Subscribers: mehdi_amini, kzhuravl, wdng, yaxunl, t-tye, llvm-commits

Differential Revision: https://reviews.llvm.org/D37752

llvm-svn: 314502
diff --git a/llvm/lib/IR/AsmWriter.cpp b/llvm/lib/IR/AsmWriter.cpp
index f351aa1..f6ed6a2 100644
--- a/llvm/lib/IR/AsmWriter.cpp
+++ b/llvm/lib/IR/AsmWriter.cpp
@@ -373,7 +373,9 @@
   case CallingConv::HHVM:          Out << "hhvmcc"; break;
   case CallingConv::HHVM_C:        Out << "hhvm_ccc"; break;
   case CallingConv::AMDGPU_VS:     Out << "amdgpu_vs"; break;
+  case CallingConv::AMDGPU_LS:     Out << "amdgpu_ls"; break;
   case CallingConv::AMDGPU_HS:     Out << "amdgpu_hs"; break;
+  case CallingConv::AMDGPU_ES:     Out << "amdgpu_es"; break;
   case CallingConv::AMDGPU_GS:     Out << "amdgpu_gs"; break;
   case CallingConv::AMDGPU_PS:     Out << "amdgpu_ps"; break;
   case CallingConv::AMDGPU_CS:     Out << "amdgpu_cs"; break;