MachO: Add linker-optimisation hint framework to MC.

Another part of the ARM64 backend (so tests will be following soon).
This is currently used by the linker to relax adrp/ldr pairs into nops
where possible, though could well be more broadly applicable.

llvm-svn: 205084

llvm/lib/MC/MCLinkerOptimizationHint.cpp

@@ -0,0 +1,30 @@
+//===-- llvm/MC/MCLinkerOptimizationHint.cpp ----- LOH handling -*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/MC/MCLinkerOptimizationHint.h"
+#include "llvm/MC/MCAsmLayout.h"
+#include "llvm/Support/LEB128.h"
+#include "llvm/MC/MCStreamer.h"
+
+using namespace llvm;
+
+namespace llvm {
+template<>
+void MCLOHDirective::Emit_impl(raw_ostream &OutStream,
+                               const MachObjectWriter &ObjWriter,
+                               const MCAsmLayout &Layout) const {
+  const MCAssembler &Asm = Layout.getAssembler();
+  encodeULEB128(Kind, OutStream);
+  encodeULEB128(Args.size(), OutStream);
+  for (LOHArgs::const_iterator It = Args.begin(), EndIt = Args.end();
+       It != EndIt; ++It)
+    encodeULEB128(ObjWriter.getSymbolAddress(&Asm.getSymbolData(**It), Layout),
+                  OutStream);
+}
+} // end namespace llvm