diff --git a/llvm/lib/Target/AMDGPU/AsmParser/AMDGPUAsmParser.cpp b/llvm/lib/Target/AMDGPU/AsmParser/AMDGPUAsmParser.cpp
--- a/llvm/lib/Target/AMDGPU/AsmParser/AMDGPUAsmParser.cpp
+++ b/llvm/lib/Target/AMDGPU/AsmParser/AMDGPUAsmParser.cpp
@@ -6074,8 +6074,6 @@
 };
 
 OperandMatchResultTy AMDGPUAsmParser::parseOptionalOperand(OperandVector &Operands) {
-  unsigned size = Operands.size();
-  assert(size > 0);
 
   OperandMatchResultTy res = parseOptionalOpr(Operands);
 
@@ -6090,17 +6088,13 @@
   // to make sure autogenerated parser of custom operands never hit hardcoded
   // mandatory operands.
 
-  if (size == 1 || ((AMDGPUOperand &)*Operands[size - 1]).isRegKind()) {
-
-    // We have parsed the first optional operand.
-    // Parse as many operands as necessary to skip all mandatory operands.
+  for (unsigned i = 0; i < MAX_OPR_LOOKAHEAD; ++i) {
+    if (res != MatchOperand_Success ||
+        isToken(AsmToken::EndOfStatement))
+      break;
 
-    for (unsigned i = 0; i < MAX_OPR_LOOKAHEAD; ++i) {
-      if (res != MatchOperand_Success ||
-          getLexer().is(AsmToken::EndOfStatement)) break;
-      if (getLexer().is(AsmToken::Comma)) Parser.Lex();
-      res = parseOptionalOpr(Operands);
-    }
+    trySkipToken(AsmToken::Comma);
+    res = parseOptionalOpr(Operands);
   }
 
   return res;
diff --git a/llvm/test/MC/AMDGPU/flat-global.s b/llvm/test/MC/AMDGPU/flat-global.s
--- a/llvm/test/MC/AMDGPU/flat-global.s
+++ b/llvm/test/MC/AMDGPU/flat-global.s
@@ -526,3 +526,8 @@
 // GFX10: encoding: [0x00,0x80,0x6c,0xdc,0x03,0x01,0x7d,0x00]
 // GFX9: global_store_short_d16_hi v[3:4], v1, off ; encoding: [0x00,0x80,0x6c,0xdc,0x03,0x01,0x7f,0x00]
 // VI-ERR: instruction not supported on this GPU
+
+global_atomic_add v0, v[1:2], v2, off glc slc
+// GFX10: global_atomic_add v0, v[1:2], v2, off glc slc ; encoding: [0x00,0x80,0xcb,0xdc,0x01,0x02,0x7d,0x00]
+// GFX9: global_atomic_add v0, v[1:2], v2, off glc slc ; encoding: [0x00,0x80,0x0b,0xdd,0x01,0x02,0x7f,0x00]
+// VI-ERR: error: invalid operand for instruction