AMDGPU: Error on calls from graphics shaders

In principle nothing should stop these from working, but
work is necessary to create an ABI for dealing with the stack
related registers.

llvm-svn: 335829
diff --git a/llvm/lib/Target/AMDGPU/SIISelLowering.cpp b/llvm/lib/Target/AMDGPU/SIISelLowering.cpp
index 2936e17..9481e2c 100644
--- a/llvm/lib/Target/AMDGPU/SIISelLowering.cpp
+++ b/llvm/lib/Target/AMDGPU/SIISelLowering.cpp
@@ -2310,6 +2310,13 @@
                               "unsupported required tail call to function ");
   }
 
+  if (AMDGPU::isShader(MF.getFunction().getCallingConv())) {
+    // Note the issue is with the CC of the calling function, not of the call
+    // itself.
+    return lowerUnhandledCall(CLI, InVals,
+                          "unsupported call from graphics shader of function ");
+  }
+
   // The first 4 bytes are reserved for the callee's emergency stack slot.
   const unsigned CalleeUsableStackOffset = 4;