[Mlir-commits] [mlir] f7fff18 - [mlir][OpenACC] add unstructured attributes for acc.loop with early exits (#164990)

[llvmlistbot at llvm.org]

Author: jeanPerier
Date: 2025-11-04T01:02:36+01:00
New Revision: f7fff18ad09680056f028a99a961d4120063c55b

URL: https://github.com/llvm/llvm-project/commit/f7fff18ad09680056f028a99a961d4120063c55b
DIFF: https://github.com/llvm/llvm-project/commit/f7fff18ad09680056f028a99a961d4120063c55b.diff

LOG: [mlir][OpenACC] add unstructured attributes for acc.loop with early exits (#164990)

"!$acc loop" directive may be placed above loops with early exits.

Currently flang lowers loop with early exits to explicit control flow
(this may be revisited when MLIR allows early exits in structured
region). The acc loop directive cannot simply be ignored in such case in
lowering because it may hold data clauses that should be applied when
reaching that point.

This patch adds an "unstructured" attribute to acc.loop to support that
case.
An acc.loop with such attributes may hold data operands but must have no
controls. It is expected that the loop logic is implemented in its body
in a way that the acc dialect may not understand.

Such acc.loop is just a container and the loop with early exit will be
executed sequentially.

Added: 
    

Modified: 
    mlir/include/mlir/Dialect/OpenACC/OpenACCOps.td
    mlir/lib/Dialect/OpenACC/IR/OpenACC.cpp
    mlir/test/Dialect/OpenACC/invalid.mlir
    mlir/test/Dialect/OpenACC/ops.mlir

Removed: 
    


################################################################################
diff  --git a/mlir/include/mlir/Dialect/OpenACC/OpenACCOps.td b/mlir/include/mlir/Dialect/OpenACC/OpenACCOps.td
index 2f4517ddfe754..c689b7e46ea9e 100644
--- a/mlir/include/mlir/Dialect/OpenACC/OpenACCOps.td
+++ b/mlir/include/mlir/Dialect/OpenACC/OpenACCOps.td
@@ -2557,6 +2557,12 @@ 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
@@ -2590,7 +2596,8 @@ 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);

diff  --git a/mlir/lib/Dialect/OpenACC/IR/OpenACC.cpp b/mlir/lib/Dialect/OpenACC/IR/OpenACC.cpp
index 35eba724a9059..b2f1d840f3bca 100644
--- a/mlir/lib/Dialect/OpenACC/IR/OpenACC.cpp
+++ b/mlir/lib/Dialect/OpenACC/IR/OpenACC.cpp
@@ -3068,8 +3068,12 @@ 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);

diff  --git a/mlir/test/Dialect/OpenACC/invalid.mlir b/mlir/test/Dialect/OpenACC/invalid.mlir
index 26b63fbe182ea..0e75894eaeceb 100644
--- a/mlir/test/Dialect/OpenACC/invalid.mlir
+++ b/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 at +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 at +1 {{expect at least one of num, dim or static values}}
 acc.loop gang({}) {
   "test.openacc_dummy_op"() : () -> ()

diff  --git a/mlir/test/Dialect/OpenACC/ops.mlir b/mlir/test/Dialect/OpenACC/ops.mlir
index 042ee2503cb95..df8ab9b7dd239 100644
--- a/mlir/test/Dialect/OpenACC/ops.mlir
+++ b/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):