[AMDGPU][MC][GFX10] Enabled null with 64-bit operands

See Bug 42745: https://bugs.llvm.org/show_bug.cgi?id=42745

Reviewers: atamazov, arsenm

https://reviews.llvm.org/D65231

llvm-svn: 370660
diff --git a/llvm/lib/Target/AMDGPU/AsmParser/AMDGPUAsmParser.cpp b/llvm/lib/Target/AMDGPU/AsmParser/AMDGPUAsmParser.cpp
index ab9e0a9..519f809 100644
--- a/llvm/lib/Target/AMDGPU/AsmParser/AMDGPUAsmParser.cpp
+++ b/llvm/lib/Target/AMDGPU/AsmParser/AMDGPUAsmParser.cpp
@@ -1854,6 +1854,8 @@
   case AMDGPU::SRC_EXECZ:
   case AMDGPU::SRC_SCC:
     return true;
+  case AMDGPU::SGPR_NULL:
+    return true;
   default:
     return false;
   }