diff --git a/flang/lib/Optimizer/Dialect/FIROps.cpp b/flang/lib/Optimizer/Dialect/FIROps.cpp
--- a/flang/lib/Optimizer/Dialect/FIROps.cpp
+++ b/flang/lib/Optimizer/Dialect/FIROps.cpp
@@ -1563,7 +1563,8 @@
                                           mlir::OperationState &result) {
   auto &builder = parser.getBuilder();
   mlir::OpAsmParser::UnresolvedOperand inductionVariable, lb, ub, step;
-  if (parser.parseLParen() || parser.parseRegionArgument(inductionVariable) ||
+  if (parser.parseLParen() ||
+      parser.parseOperand(inductionVariable, /*allowResultNumber=*/false) ||
       parser.parseEqual())
     return mlir::failure();
 
@@ -1581,8 +1582,9 @@
 
   mlir::OpAsmParser::UnresolvedOperand iterateVar, iterateInput;
   if (parser.parseKeyword("and") || parser.parseLParen() ||
-      parser.parseRegionArgument(iterateVar) || parser.parseEqual() ||
-      parser.parseOperand(iterateInput) || parser.parseRParen() ||
+      parser.parseOperand(iterateVar, /*allowResultNumber=*/false) ||
+      parser.parseEqual() || parser.parseOperand(iterateInput) ||
+      parser.parseRParen() ||
       parser.resolveOperand(iterateInput, i1Type, result.operands))
     return mlir::failure();
 
@@ -1876,7 +1878,8 @@
   auto &builder = parser.getBuilder();
   mlir::OpAsmParser::UnresolvedOperand inductionVariable, lb, ub, step;
   // Parse the induction variable followed by '='.
-  if (parser.parseRegionArgument(inductionVariable) || parser.parseEqual())
+  if (parser.parseOperand(inductionVariable, /*allowResultNumber=*/false) ||
+      parser.parseEqual())
     return mlir::failure();
 
   // Parse loop bounds.
diff --git a/mlir/include/mlir/IR/OpImplementation.h b/mlir/include/mlir/IR/OpImplementation.h
--- a/mlir/include/mlir/IR/OpImplementation.h
+++ b/mlir/include/mlir/IR/OpImplementation.h
@@ -584,7 +584,7 @@
   }
 
   /// These are the supported delimiters around operand lists and region
-  /// argument lists, used by parseOperandList and parseRegionArgumentList.
+  /// argument lists, used by parseOperandList.
   enum class Delimiter {
     /// Zero or more operands with no delimiters.
     None,
@@ -1110,22 +1110,27 @@
       Optional<ArrayRef<NamedAttribute>> parsedAttributes = llvm::None,
       Optional<FunctionType> parsedFnType = llvm::None) = 0;
 
-  /// Parse a single operand.
-  virtual ParseResult parseOperand(UnresolvedOperand &result) = 0;
+  /// Parse a single SSA value operand name along with a result number if
+  /// `allowResultNumber` is true.
+  virtual ParseResult parseOperand(UnresolvedOperand &result,
+                                   bool allowResultNumber = true) = 0;
 
   /// Parse a single operand if present.
   virtual OptionalParseResult
-  parseOptionalOperand(UnresolvedOperand &result) = 0;
+  parseOptionalOperand(UnresolvedOperand &result,
+                       bool allowResultNumber = true) = 0;
 
   /// Parse zero or more SSA comma-separated operand references with a specified
   /// surrounding delimiter, and an optional required operand count.
-  virtual ParseResult
-  parseOperandList(SmallVectorImpl<UnresolvedOperand> &result,
-                   int requiredOperandCount = -1,
-                   Delimiter delimiter = Delimiter::None) = 0;
+  virtual ParseResult parseOperandList(
+      SmallVectorImpl<UnresolvedOperand> &result, int requiredOperandCount = -1,
+      Delimiter delimiter = Delimiter::None, bool allowResultNumber = true) = 0;
+
   ParseResult parseOperandList(SmallVectorImpl<UnresolvedOperand> &result,
-                               Delimiter delimiter) {
-    return parseOperandList(result, /*requiredOperandCount=*/-1, delimiter);
+                               Delimiter delimiter,
+                               bool allowResultNumber = true) {
+    return parseOperandList(result, /*requiredOperandCount=*/-1, delimiter,
+                            allowResultNumber);
   }
 
   /// Parse zero or more trailing SSA comma-separated trailing operand
@@ -1243,29 +1248,6 @@
                       ArrayRef<Type> argTypes = {},
                       bool enableNameShadowing = false) = 0;
 
-  /// Parse a region argument, this argument is resolved when calling
-  /// 'parseRegion'.
-  virtual ParseResult parseRegionArgument(UnresolvedOperand &argument) = 0;
-
-  /// Parse zero or more region arguments with a specified surrounding
-  /// delimiter, and an optional required argument count. Region arguments
-  /// define new values; so this also checks if values with the same names have
-  /// not been defined yet.
-  virtual ParseResult
-  parseRegionArgumentList(SmallVectorImpl<UnresolvedOperand> &result,
-                          int requiredOperandCount = -1,
-                          Delimiter delimiter = Delimiter::None) = 0;
-  virtual ParseResult
-  parseRegionArgumentList(SmallVectorImpl<UnresolvedOperand> &result,
-                          Delimiter delimiter) {
-    return parseRegionArgumentList(result, /*requiredOperandCount=*/-1,
-                                   delimiter);
-  }
-
-  /// Parse a region argument if present.
-  virtual ParseResult
-  parseOptionalRegionArgument(UnresolvedOperand &argument) = 0;
-
   //===--------------------------------------------------------------------===//
   // Successor Parsing
   //===--------------------------------------------------------------------===//
diff --git a/mlir/lib/Dialect/Affine/IR/AffineOps.cpp b/mlir/lib/Dialect/Affine/IR/AffineOps.cpp
--- a/mlir/lib/Dialect/Affine/IR/AffineOps.cpp
+++ b/mlir/lib/Dialect/Affine/IR/AffineOps.cpp
@@ -1433,7 +1433,8 @@
   auto &builder = parser.getBuilder();
   OpAsmParser::UnresolvedOperand inductionVariable;
   // Parse the induction variable followed by '='.
-  if (parser.parseRegionArgument(inductionVariable) || parser.parseEqual())
+  if (parser.parseOperand(inductionVariable, /*allowResultNumber=*/false) ||
+      parser.parseEqual())
     return failure();
 
   // Parse loop bounds.
@@ -3527,8 +3528,8 @@
   auto &builder = parser.getBuilder();
   auto indexType = builder.getIndexType();
   SmallVector<OpAsmParser::UnresolvedOperand, 4> ivs;
-  if (parser.parseRegionArgumentList(ivs, /*requiredOperandCount=*/-1,
-                                     OpAsmParser::Delimiter::Paren) ||
+  if (parser.parseOperandList(ivs, OpAsmParser::Delimiter::Paren,
+                              /*allowResultNumber=*/false) ||
       parser.parseEqual() ||
       parseAffineMapWithMinMax(parser, result, MinMaxKind::Max) ||
       parser.parseKeyword("to") ||
diff --git a/mlir/lib/Dialect/ControlFlow/IR/ControlFlowOps.cpp b/mlir/lib/Dialect/ControlFlow/IR/ControlFlowOps.cpp
--- a/mlir/lib/Dialect/ControlFlow/IR/ControlFlowOps.cpp
+++ b/mlir/lib/Dialect/ControlFlow/IR/ControlFlowOps.cpp
@@ -489,7 +489,8 @@
       parser.parseSuccessor(defaultDestination))
     return failure();
   if (succeeded(parser.parseOptionalLParen())) {
-    if (parser.parseRegionArgumentList(defaultOperands) ||
+    if (parser.parseOperandList(defaultOperands, OpAsmParser::Delimiter::None,
+                                /*allowResultNumber=*/false) ||
         parser.parseColonTypeList(defaultOperandTypes) || parser.parseRParen())
       return failure();
   }
@@ -509,7 +510,8 @@
         failed(parser.parseSuccessor(destination)))
       return failure();
     if (succeeded(parser.parseOptionalLParen())) {
-      if (failed(parser.parseRegionArgumentList(operands)) ||
+      if (failed(parser.parseOperandList(operands, OpAsmParser::Delimiter::None,
+                                         /*allowResultNumber=*/false)) ||
           failed(parser.parseColonTypeList(operandTypes)) ||
           failed(parser.parseRParen()))
         return failure();
diff --git a/mlir/lib/Dialect/GPU/IR/GPUDialect.cpp b/mlir/lib/Dialect/GPU/IR/GPUDialect.cpp
--- a/mlir/lib/Dialect/GPU/IR/GPUDialect.cpp
+++ b/mlir/lib/Dialect/GPU/IR/GPUDialect.cpp
@@ -539,8 +539,8 @@
                     MutableArrayRef<OpAsmParser::UnresolvedOperand> indices) {
   assert(indices.size() == 3 && "space for three indices expected");
   SmallVector<OpAsmParser::UnresolvedOperand, 3> args;
-  if (parser.parseRegionArgumentList(args, /*requiredOperandCount=*/3,
-                                     OpAsmParser::Delimiter::Paren) ||
+  if (parser.parseOperandList(args, OpAsmParser::Delimiter::Paren,
+                              /*allowResultNumber=*/false) ||
       parser.parseKeyword("in") || parser.parseLParen())
     return failure();
   std::move(args.begin(), args.end(), indices.begin());
@@ -548,8 +548,8 @@
   for (int i = 0; i < 3; ++i) {
     if (i != 0 && parser.parseComma())
       return failure();
-    if (parser.parseRegionArgument(regionSizes[i]) || parser.parseEqual() ||
-        parser.parseOperand(sizes[i]))
+    if (parser.parseOperand(regionSizes[i], /*allowResultNumber=*/false) ||
+        parser.parseEqual() || parser.parseOperand(sizes[i]))
       return failure();
   }
 
@@ -869,7 +869,8 @@
     OpAsmParser::UnresolvedOperand arg;
     Type type;
 
-    if (parser.parseRegionArgument(arg) || parser.parseColonType(type))
+    if (parser.parseOperand(arg, /*allowResultNumber=*/false) ||
+        parser.parseColonType(type))
       return failure();
 
     args.push_back(arg);
diff --git a/mlir/lib/Dialect/LLVMIR/IR/LLVMDialect.cpp b/mlir/lib/Dialect/LLVMIR/IR/LLVMDialect.cpp
--- a/mlir/lib/Dialect/LLVMIR/IR/LLVMDialect.cpp
+++ b/mlir/lib/Dialect/LLVMIR/IR/LLVMDialect.cpp
@@ -332,7 +332,8 @@
     if (parser.parseColon() || parser.parseSuccessor(destination))
       return failure();
     if (!parser.parseOptionalLParen()) {
-      if (parser.parseRegionArgumentList(operands) ||
+      if (parser.parseOperandList(operands, OpAsmParser::Delimiter::None,
+                                  /*allowResultNumber=*/false) ||
           parser.parseColonTypeList(operandTypes) || parser.parseRParen())
         return failure();
     }
diff --git a/mlir/lib/Dialect/OpenACC/IR/OpenACC.cpp b/mlir/lib/Dialect/OpenACC/IR/OpenACC.cpp
--- a/mlir/lib/Dialect/OpenACC/IR/OpenACC.cpp
+++ b/mlir/lib/Dialect/OpenACC/IR/OpenACC.cpp
@@ -70,7 +70,8 @@
     OpAsmParser::UnresolvedOperand arg;
     Type type;
 
-    if (parser.parseRegionArgument(arg) || parser.parseColonType(type))
+    if (parser.parseOperand(arg, /*allowResultNumber=*/false) ||
+        parser.parseColonType(type))
       return failure();
 
     args.push_back(arg);
diff --git a/mlir/lib/Dialect/OpenMP/IR/OpenMPDialect.cpp b/mlir/lib/Dialect/OpenMP/IR/OpenMPDialect.cpp
--- a/mlir/lib/Dialect/OpenMP/IR/OpenMPDialect.cpp
+++ b/mlir/lib/Dialect/OpenMP/IR/OpenMPDialect.cpp
@@ -524,8 +524,8 @@
                    SmallVectorImpl<Type> &loopVarTypes, UnitAttr &inclusive) {
   // Parse an opening `(` followed by induction variables followed by `)`
   SmallVector<OpAsmParser::UnresolvedOperand> ivs;
-  if (parser.parseRegionArgumentList(ivs, /*requiredOperandCount=*/-1,
-                                     OpAsmParser::Delimiter::Paren))
+  if (parser.parseOperandList(ivs, OpAsmParser::Delimiter::Paren,
+                              /*allowResultNumber=*/false))
     return failure();
 
   size_t numIVs = ivs.size();
@@ -587,8 +587,8 @@
 ParseResult SimdLoopOp::parse(OpAsmParser &parser, OperationState &result) {
   // Parse an opening `(` followed by induction variables followed by `)`
   SmallVector<OpAsmParser::UnresolvedOperand> ivs;
-  if (parser.parseRegionArgumentList(ivs, /*requiredOperandCount=*/-1,
-                                     OpAsmParser::Delimiter::Paren))
+  if (parser.parseOperandList(ivs, OpAsmParser::Delimiter::Paren,
+                              /*allowResultNumber=*/false))
     return failure();
   int numIVs = static_cast<int>(ivs.size());
   Type loopVarType;
diff --git a/mlir/lib/Dialect/PDLInterp/IR/PDLInterp.cpp b/mlir/lib/Dialect/PDLInterp/IR/PDLInterp.cpp
--- a/mlir/lib/Dialect/PDLInterp/IR/PDLInterp.cpp
+++ b/mlir/lib/Dialect/PDLInterp/IR/PDLInterp.cpp
@@ -103,7 +103,7 @@
   // Parse the loop variable followed by type.
   OpAsmParser::UnresolvedOperand loopVariable;
   Type loopVariableType;
-  if (parser.parseRegionArgument(loopVariable) ||
+  if (parser.parseOperand(loopVariable, /*allowResultNumber=*/false) ||
       parser.parseColonType(loopVariableType))
     return failure();
 
diff --git a/mlir/lib/Dialect/SCF/SCF.cpp b/mlir/lib/Dialect/SCF/SCF.cpp
--- a/mlir/lib/Dialect/SCF/SCF.cpp
+++ b/mlir/lib/Dialect/SCF/SCF.cpp
@@ -401,7 +401,8 @@
   auto &builder = parser.getBuilder();
   OpAsmParser::UnresolvedOperand inductionVariable, lb, ub, step;
   // Parse the induction variable followed by '='.
-  if (parser.parseRegionArgument(inductionVariable) || parser.parseEqual())
+  if (parser.parseOperand(inductionVariable, /*allowResultNumber=*/false) ||
+      parser.parseEqual())
     return failure();
 
   // Parse loop bounds.
@@ -1975,8 +1976,8 @@
   auto &builder = parser.getBuilder();
   // Parse an opening `(` followed by induction variables followed by `)`
   SmallVector<OpAsmParser::UnresolvedOperand, 4> ivs;
-  if (parser.parseRegionArgumentList(ivs, /*requiredOperandCount=*/-1,
-                                     OpAsmParser::Delimiter::Paren))
+  if (parser.parseOperandList(ivs, OpAsmParser::Delimiter::Paren,
+                              /*allowResultNumber=*/false))
     return failure();
 
   // Parse loop bounds.
diff --git a/mlir/lib/Dialect/Vector/IR/VectorOps.cpp b/mlir/lib/Dialect/Vector/IR/VectorOps.cpp
--- a/mlir/lib/Dialect/Vector/IR/VectorOps.cpp
+++ b/mlir/lib/Dialect/Vector/IR/VectorOps.cpp
@@ -4698,7 +4698,8 @@
   OpAsmParser::UnresolvedOperand laneId;
 
   // Parse predicate operand.
-  if (parser.parseLParen() || parser.parseRegionArgument(laneId) ||
+  if (parser.parseLParen() ||
+      parser.parseOperand(laneId, /*allowResultNumber=*/false) ||
       parser.parseRParen())
     return failure();
 
diff --git a/mlir/lib/IR/FunctionImplementation.cpp b/mlir/lib/IR/FunctionImplementation.cpp
--- a/mlir/lib/IR/FunctionImplementation.cpp
+++ b/mlir/lib/IR/FunctionImplementation.cpp
@@ -30,8 +30,12 @@
     // Parse argument name if present.
     OpAsmParser::UnresolvedOperand argument;
     Type argumentType;
-    if (succeeded(parser.parseOptionalRegionArgument(argument)) &&
-        !argument.name.empty()) {
+    auto hadSSAValue = parser.parseOptionalOperand(argument,
+                                                   /*allowResultNumber=*/false);
+    if (hadSSAValue.hasValue()) {
+      if (failed(hadSSAValue.getValue()))
+        return failure(); // Argument was present but malformed.
+
       // Reject this if the preceding argument was missing a name.
       if (argNames.empty() && !argTypes.empty())
         return parser.emitError(loc, "expected type instead of SSA identifier");
diff --git a/mlir/lib/Parser/Parser.cpp b/mlir/lib/Parser/Parser.cpp
--- a/mlir/lib/Parser/Parser.cpp
+++ b/mlir/lib/Parser/Parser.cpp
@@ -268,8 +268,10 @@
   ParseResult
   parseOptionalSSAUseList(SmallVectorImpl<UnresolvedOperand> &results);
 
-  /// Parse a single SSA use into 'result'.
-  ParseResult parseSSAUse(UnresolvedOperand &result);
+  /// Parse a single SSA use into 'result'.  If 'allowResultNumber' is true then
+  /// we allow #42 syntax.
+  ParseResult parseSSAUse(UnresolvedOperand &result,
+                          bool allowResultNumber = true);
 
   /// Given a reference to an SSA value and its type, return a reference. This
   /// returns null on failure.
@@ -699,7 +701,8 @@
 ///
 ///   ssa-use ::= ssa-id
 ///
-ParseResult OperationParser::parseSSAUse(UnresolvedOperand &result) {
+ParseResult OperationParser::parseSSAUse(UnresolvedOperand &result,
+                                         bool allowResultNumber) {
   result.name = getTokenSpelling();
   result.number = 0;
   result.location = getToken().getLoc();
@@ -708,6 +711,9 @@
 
   // If we have an attribute ID, it is a result number.
   if (getToken().is(Token::hash_identifier)) {
+    if (!allowResultNumber)
+      return emitError("result number not allowed in argument list");
+
     if (auto value = getToken().getHashIdentifierNumber())
       result.number = value.getValue();
     else
@@ -1267,9 +1273,10 @@
   //===--------------------------------------------------------------------===//
 
   /// Parse a single operand.
-  ParseResult parseOperand(UnresolvedOperand &result) override {
+  ParseResult parseOperand(UnresolvedOperand &result,
+                           bool allowResultNumber = true) override {
     OperationParser::UnresolvedOperand useInfo;
-    if (parser.parseSSAUse(useInfo))
+    if (parser.parseSSAUse(useInfo, allowResultNumber))
       return failure();
 
     result = {useInfo.location, useInfo.name, useInfo.number, {}};
@@ -1279,9 +1286,11 @@
   }
 
   /// Parse a single operand if present.
-  OptionalParseResult parseOptionalOperand(UnresolvedOperand &result) override {
+  OptionalParseResult
+  parseOptionalOperand(UnresolvedOperand &result,
+                       bool allowResultNumber = true) override {
     if (parser.getToken().is(Token::percent_identifier))
-      return parseOperand(result);
+      return parseOperand(result, allowResultNumber);
     return llvm::None;
   }
 
@@ -1289,17 +1298,8 @@
   /// surrounding delimiter, and an optional required operand count.
   ParseResult parseOperandList(SmallVectorImpl<UnresolvedOperand> &result,
                                int requiredOperandCount = -1,
-                               Delimiter delimiter = Delimiter::None) override {
-    return parseOperandOrRegionArgList(result, /*isOperandList=*/true,
-                                       requiredOperandCount, delimiter);
-  }
-
-  /// Parse zero or more SSA comma-separated operand or region arguments with
-  ///  optional surrounding delimiter and required operand count.
-  ParseResult
-  parseOperandOrRegionArgList(SmallVectorImpl<UnresolvedOperand> &result,
-                              bool isOperandList, int requiredOperandCount = -1,
-                              Delimiter delimiter = Delimiter::None) {
+                               Delimiter delimiter = Delimiter::None,
+                               bool allowResultNumber = true) override {
     auto startLoc = parser.getToken().getLoc();
 
     // The no-delimiter case has some special handling for better diagnostics.
@@ -1322,8 +1322,7 @@
 
     auto parseOneOperand = [&]() -> ParseResult {
       UnresolvedOperand operandOrArg;
-      if (isOperandList ? parseOperand(operandOrArg)
-                        : parseRegionArgument(operandOrArg))
+      if (parseOperand(operandOrArg, allowResultNumber))
         return failure();
       result.push_back(operandOrArg);
       return success();
@@ -1472,28 +1471,6 @@
     return success();
   }
 
-  /// Parse a region argument. The type of the argument will be resolved later
-  /// by a call to `parseRegion`.
-  ParseResult parseRegionArgument(UnresolvedOperand &argument) override {
-    return parseOperand(argument);
-  }
-
-  /// Parse a region argument if present.
-  ParseResult
-  parseOptionalRegionArgument(UnresolvedOperand &argument) override {
-    if (parser.getToken().isNot(Token::percent_identifier))
-      return success();
-    return parseRegionArgument(argument);
-  }
-
-  ParseResult
-  parseRegionArgumentList(SmallVectorImpl<UnresolvedOperand> &result,
-                          int requiredOperandCount = -1,
-                          Delimiter delimiter = Delimiter::None) override {
-    return parseOperandOrRegionArgList(result, /*isOperandList=*/false,
-                                       requiredOperandCount, delimiter);
-  }
-
   //===--------------------------------------------------------------------===//
   // Successor Parsing
   //===--------------------------------------------------------------------===//
@@ -1539,8 +1516,8 @@
 
     auto parseElt = [&]() -> ParseResult {
       UnresolvedOperand regionArg, operand;
-      if (parseRegionArgument(regionArg) || parseEqual() ||
-          parseOperand(operand))
+      if (parseOperand(regionArg, /*allowResultNumber=*/false) ||
+          parseEqual() || parseOperand(operand))
         return failure();
       lhs.push_back(regionArg);
       rhs.push_back(operand);
@@ -1561,8 +1538,9 @@
     auto parseElt = [&]() -> ParseResult {
       UnresolvedOperand regionArg, operand;
       Type type;
-      if (parseRegionArgument(regionArg) || parseEqual() ||
-          parseOperand(operand) || parseColon() || parseType(type))
+      if (parseOperand(regionArg, /*allowResultNumber=*/false) ||
+          parseEqual() || parseOperand(operand) || parseColon() ||
+          parseType(type))
         return failure();
       lhs.push_back(regionArg);
       rhs.push_back(operand);
diff --git a/mlir/test/Dialect/Affine/invalid.mlir b/mlir/test/Dialect/Affine/invalid.mlir
--- a/mlir/test/Dialect/Affine/invalid.mlir
+++ b/mlir/test/Dialect/Affine/invalid.mlir
@@ -380,3 +380,13 @@
   }
   return %res : f32
 }
+
+
+// -----
+
+func.func @result_number() {
+  // expected-error@+1 {{result number not allowed}}
+  affine.for %n0#0 = 0 to 7 {
+  }
+  return
+}
diff --git a/mlir/test/lib/Dialect/Test/TestDialect.cpp b/mlir/test/lib/Dialect/Test/TestDialect.cpp
--- a/mlir/test/lib/Dialect/Test/TestDialect.cpp
+++ b/mlir/test/lib/Dialect/Test/TestDialect.cpp
@@ -875,7 +875,8 @@
 ParseResult PolyForOp::parse(OpAsmParser &parser, OperationState &result) {
   SmallVector<OpAsmParser::UnresolvedOperand, 4> ivsInfo;
   // Parse list of region arguments without a delimiter.
-  if (parser.parseRegionArgumentList(ivsInfo))
+  if (parser.parseOperandList(ivsInfo, OpAsmParser::Delimiter::None,
+                              /*allowResultNumber=*/false))
     return failure();
 
   // Parse the body region.