[MLIR][OpenMP] Check that omp.loop_nest represents at least one loop (#89082)

Author: skatrak

mlir/lib/Dialect/OpenMP/IR/OpenMPDialect.cpp

@@ -1898,6 +1898,9 @@ void LoopNestOp::build(OpBuilder &builder, OperationState &state,
 }
 
 LogicalResult LoopNestOp::verify() {
+  if (getLowerBound().empty())
+    return emitOpError() << "must represent at least one loop";
+
   if (getLowerBound().size() != getIVs().size())
     return emitOpError() << "number of range arguments and IVs do not match";
 

mlir/test/Dialect/OpenMP/invalid.mlir

@@ -138,6 +138,20 @@ func.func @iv_number_mismatch(%lb : index, %ub : index, %step : index) {
 
 // -----
 
+func.func @no_loops(%lb : index, %ub : index, %step : index) {
+  // TODO Remove induction variables from omp.wsloop.
+  omp.wsloop for (%iv) : index = (%lb) to (%ub) step (%step) {
+    // expected-error@+1 {{op must represent at least one loop}}
+    "omp.loop_nest" () ({
+    ^bb0():
+      omp.yield
+    }) : () -> ()
+    omp.terminator
+  }
+}
+
+// -----
+
 func.func @inclusive_not_a_clause(%lb : index, %ub : index, %step : index) {
   // expected-error @below {{expected 'for'}}
   omp.wsloop nowait inclusive