[AArch64] Implement GHC calling convention

Original patch by Luke Iannini.  Minor improvements and test added by
Erik de Castro Lopo.

Differential Revision: http://reviews.llvm.org/D6877

From: Erik de Castro Lopo <erikd@mega-nerd.com>
llvm-svn: 226473
diff --git a/llvm/lib/Target/AArch64/AArch64FrameLowering.cpp b/llvm/lib/Target/AArch64/AArch64FrameLowering.cpp
index 66aa216..d8e9156 100644
--- a/llvm/lib/Target/AArch64/AArch64FrameLowering.cpp
+++ b/llvm/lib/Target/AArch64/AArch64FrameLowering.cpp
@@ -215,6 +215,11 @@
   bool HasFP = hasFP(MF);
   DebugLoc DL = MBB.findDebugLoc(MBBI);
 
+  // All calls are tail calls in GHC calling conv, and functions have no
+  // prologue/epilogue.
+  if (MF.getFunction()->getCallingConv() == CallingConv::GHC)
+    return;
+
   int NumBytes = (int)MFI->getStackSize();
   if (!AFI->hasStackFrame()) {
     assert(!HasFP && "unexpected function without stack frame but with FP");
@@ -451,6 +456,11 @@
   int NumBytes = MFI->getStackSize();
   const AArch64FunctionInfo *AFI = MF.getInfo<AArch64FunctionInfo>();
 
+  // All calls are tail calls in GHC calling conv, and functions have no
+  // prologue/epilogue.
+  if (MF.getFunction()->getCallingConv() == CallingConv::GHC)
+    return;
+
   // Initial and residual are named for consitency with the prologue. Note that
   // in the epilogue, the residual adjustment is executed first.
   uint64_t ArgumentPopSize = 0;