[mlir][OpenACC] add unstructured attributes for acc.loop with early exits

mlir/include/mlir/Dialect/OpenACC/OpenACCOps.td

@@ -2487,6 +2487,12 @@ def OpenACC_LoopOp : OpenACC_Op<"loop",
  device-type-aware getter methods. When modifying these operands, the
  corresponding `device_type` attributes must be updated to maintain
  consistency between operands and their target device types.
+
+ The `unstructured` attribute indicates that the loops inside the OpenACC
+ construct contain early exits and cannot be lowered to structured MLIR
+ operations. When this flag is set, the acc.loop should have no induction
+ variables and the loop must be implemented via explicit control flow
+ inside its body.
  }];
 
  let arguments = (ins
@@ -2520,7 +2526,8 @@ def OpenACC_LoopOp : OpenACC_Op<"loop",
  OptionalAttr<SymbolRefArrayAttr>:$firstprivatizationRecipes,
  Variadic<AnyType>:$reductionOperands,
  OptionalAttr<SymbolRefArrayAttr>:$reductionRecipes,
- OptionalAttr<OpenACC_CombinedConstructsAttr>:$combined
+ OptionalAttr<OpenACC_CombinedConstructsAttr>:$combined,
+ UnitAttr:$unstructured
  );
 
  let results = (outs Variadic<AnyType>:$results);

mlir/lib/Dialect/OpenACC/IR/OpenACC.cpp

@@ -3065,8 +3065,12 @@ LogicalResult acc::LoopOp::verify() {
  if (getRegion().empty())
  return emitError("expected non-empty body.");
 
- // When it is container-like - it is expected to hold a loop-like operation.
- if (isContainerLike()) {
+ if (getUnstructured()) {
+ if (!isContainerLike())
+ return emitError(
+ "unstructured acc.loop must not have induction variables");
+ } else if (isContainerLike()) {
+ // When it is container-like - it is expected to hold a loop-like operation.
  // Obtain the maximum collapse count - we use this to check that there
  // are enough loops contained.
  uint64_t collapseCount = getCollapseValue().value_or(1);

mlir/test/Dialect/OpenACC/invalid.mlir

@@ -492,6 +492,15 @@ func.func @fct1(%0 : !llvm.ptr) -> () {
 
 // -----
 
+%i1 = arith.constant 1 : i32
+%i2 = arith.constant 10 : i32
+// expected-error@+1 {{unstructured acc.loop must not have induction variables}}
+acc.loop control(%iv : i32) = (%i1 : i32) to (%i2 : i32) step (%i1 : i32) {
+ acc.yield
+} attributes {independent = [#acc.device_type<none>], unstructured}
+
+// -----
+
 // expected-error@+1 {{expect at least one of num, dim or static values}}
 acc.loop gang({}) {
  "test.openacc_dummy_op"() : () -> ()

mlir/test/Dialect/OpenACC/ops.mlir

@@ -2143,6 +2143,20 @@ func.func @acc_loop_container() {
 
 // -----
 
+func.func @acc_unstructured_loop() {
+ acc.loop {
+ acc.yield
+ } attributes {independent = [#acc.device_type<none>], unstructured}
+ return
+}
+
+// CHECK-LABEL: func.func @acc_unstructured_loop
+// CHECK: acc.loop
+// CHECK: acc.yield
+// CHECK: } attributes {independent = [#acc.device_type<none>], unstructured}
+
+// -----
+
 // Test private recipe with data bounds for array slicing
 acc.private.recipe @privatization_memref_slice : memref<10x10xf32> init {
 ^bb0(%arg0: memref<10x10xf32>, %bounds0: !acc.data_bounds_ty, %bounds1: !acc.data_bounds_ty):