[AMDGPU][MC][GFX8+] Added syntactic sugar for 'vgpr index' operand of instructions s_set_gpr_idx_on and s_set_gpr_idx_mode

See bug 39331: https://bugs.llvm.org/show_bug.cgi?id=39331

Reviewers: artem.tamazov, arsenm

Differential Revision: https://reviews.llvm.org/D58288

llvm-svn: 354969
diff --git a/llvm/lib/Target/AMDGPU/Utils/AMDGPUAsmUtils.h b/llvm/lib/Target/AMDGPU/Utils/AMDGPUAsmUtils.h
index 9265d60..cd91c5f 100644
--- a/llvm/lib/Target/AMDGPU/Utils/AMDGPUAsmUtils.h
+++ b/llvm/lib/Target/AMDGPU/Utils/AMDGPUAsmUtils.h
@@ -30,6 +30,13 @@
 extern const char* const IdSymbolic[];
 
 } // namespace Swizzle
+
+namespace VGPRIndexMode { // Symbolic names for the gpr_idx(...) syntax.
+
+extern const char* const IdSymbolic[];
+
+} // namespace VGPRIndexMode
+
 } // namespace AMDGPU
 } // namespace llvm