[mlir][Vector] Fix vector.mask parser for incorrect passthru cases

This MR fixes a crash when parsing an invalid `vector.mask` with a
passtru operand.

Author: dcaballe

mlir/lib/Dialect/Vector/IR/VectorOps.cpp

@@ -6516,9 +6516,15 @@ ParseResult MaskOp::parse(OpAsmParser &parser, OperationState &result) {
   if (parser.resolveOperand(mask, maskType, result.operands))
     return failure();
 
-  if (parsePassthru.succeeded())
+  if (parsePassthru.succeeded()) {
+    if (resultTypes.empty())
+      return parser.emitError(
+          parser.getNameLoc(),
+          "expects a result if passthru operand is provided");
+
     if (parser.resolveOperand(passthru, resultTypes[0], result.operands))
       return failure();
+  }
 
   return success();
 }

mlir/test/Dialect/Vector/invalid.mlir

@@ -1747,6 +1747,24 @@ func.func @vector_mask_0d_mask(%arg0: tensor<2x4xi32>,
 
 // -----
 
+func.func @vector_mask_empty_passthru_no_return_type(%mask : vector<8xi1>,
+                                                     %passthru : vector<8xi32>) {
+  // expected-error@+1 {{'vector.mask' expects a result if passthru operand is provided}}
+  vector.mask %mask, %passthru { } : vector<8xi1>
+  return
+}
+
+// -----
+
+func.func @vector_mask_empty_passthru_empty_return_type(%mask : vector<8xi1>,
+                                                        %passthru : vector<8xi32>) {
+  // expected-error@+1 {{'vector.mask' expects a result if passthru operand is provided}}
+  vector.mask %mask, %passthru { } : vector<8xi1> -> ()
+  return
+}
+
+// -----
+
 func.func @vector_scalable_insert_unaligned(%subv: vector<4xi32>, %vec: vector<[16]xi32>) {
   // expected-error@+1 {{op failed to verify that position is a multiple of the source length.}}
   %0 = vector.scalable.insert %subv, %vec[2] : vector<4xi32> into vector<[16]xi32>