[AMDGPU] Add support for a16 modifiear for gfx9

Summary:
Adding support for a16 for gfx9. A16 bit replaces r128 bit for gfx9.

Change-Id: Ie8b881e4e6d2f023fb5e0150420893513e5f4841

Subscribers: arsenm, kzhuravl, wdng, nhaehnle, yaxunl, dstuttard, tpr, t-tye, jfb, llvm-commits

Differential Revision: https://reviews.llvm.org/D50575

llvm-svn: 340831
diff --git a/llvm/lib/Target/AMDGPU/AMDGPUSubtarget.h b/llvm/lib/Target/AMDGPU/AMDGPUSubtarget.h
index 03809d8..db9ebd1 100644
--- a/llvm/lib/Target/AMDGPU/AMDGPUSubtarget.h
+++ b/llvm/lib/Target/AMDGPU/AMDGPUSubtarget.h
@@ -358,6 +358,7 @@
   bool HasSDWAMac;
   bool HasSDWAOutModsVOPC;
   bool HasDPP;
+  bool HasR128A16;
   bool HasDLInsts;
   bool D16PreservesUnusedBits;
   bool FlatAddressSpace;
@@ -791,6 +792,10 @@
     return HasDPP;
   }
 
+  bool hasR128A16() const {
+    return HasR128A16;
+  }
+
   bool enableSIScheduler() const {
     return EnableSIScheduler;
   }