[OpenMP][MLIR] Add omp.distribute op to the OMP dialect

This patch adds the omp.distribute operation to the OMP dialect. The purpose is
to be able to represent the distribute construct in OpenMP with the associated
clauses. The effect of the operation is to distributes the loop iterations of
the loop(s) contained inside the region across multiple teams.

mlir/include/mlir/Dialect/OpenMP/OpenMPOps.td

@@ -636,6 +636,57 @@ def YieldOp : OpenMP_Op<"yield",
   let assemblyFormat = [{ ( `(` $results^ `:` type($results) `)` )? attr-dict}];
 }
 
+//===----------------------------------------------------------------------===//
+// Distribute construct [2.9.4.1]
+//===----------------------------------------------------------------------===//
+def DistributeOp : OpenMP_Op<"distribute", [AttrSizedOperandSegments,
+                              RecursiveMemoryEffects]> {
+  let summary = "distribute construct";
+  let description = [{
+    The distribute construct specifies that the iterations of one or more loop
+    will be executed by the initial teams in the context of their implicit
+    tasks. The iterations are distributed across the initial threads of all
+    initial teams that execute the teams region to which the distribute region
+    binds.
+
+    The distribute loop construct specifies that the iterations of the loop(s)
+    will be executed in parallel by threads in the current context. These
+    iterations are spread across threads that already exist in the enclosing
+    region. The lower and upper bounds specify a half-open range: the
+    range includes the lower bound but does not include the upper bound. If the
+    `inclusive` attribute is specified then the upper bound is also included.
+
+    The `dist_schedule_static` attribute specifies the  schedule for this
+    loop, determining how the loop is distributed across the parallel threads.
+    The optional `schedule_chunk` associated with this determines further
+    controls this distribution.
+
+    // TODO: private_var, firstprivate_var, lastprivate_var, collapse
+  }];
+  let arguments = (ins
+             UnitAttr:$dist_schedule_static,
+             Optional<IntLikeType>:$chunk_size,
+             Variadic<AnyType>:$allocate_vars,
+             Variadic<AnyType>:$allocators_vars,
+             OptionalAttr<OrderKindAttr>:$order_val);
+
+  let regions = (region AnyRegion:$region);
+
+  let assemblyFormat = [{
+    oilist(`dist_schedule_static` $dist_schedule_static
+          |`chunk_size` `(` $chunk_size `:` type($chunk_size) `)`
+          |`order` `(` custom<ClauseAttr>($order_val) `)`
+          |`allocate` `(`
+             custom<AllocateAndAllocator>(
+               $allocate_vars, type($allocate_vars),
+               $allocators_vars, type($allocators_vars)
+             ) `)`
+    ) $region attr-dict
+  }];
+
+  let hasVerifier = 1;
+}
+
 //===----------------------------------------------------------------------===//
 // 2.10.1 task Construct
 //===----------------------------------------------------------------------===//

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

@@ -1053,6 +1053,22 @@ LogicalResult SimdLoopOp::verify() {
   return success();
 }
 
+//===----------------------------------------------------------------------===//
+// Verifier for Distribute construct [2.9.4.1]
+//===----------------------------------------------------------------------===//
+
+LogicalResult DistributeOp::verify() {
+  if (this->getChunkSize() && !this->getDistScheduleStatic())
+    return emitOpError() << "chunk size set without "
+                            "dist_schedule_static being present";
+
+  if (getAllocateVars().size() != getAllocatorsVars().size())
+    return emitError(
+        "expected equal sizes for allocate and allocator variables");
+
+  return success();
+}
+
 //===----------------------------------------------------------------------===//
 // ReductionOp
 //===----------------------------------------------------------------------===//

mlir/test/Dialect/OpenMP/ops.mlir

@@ -479,6 +479,36 @@ func.func @omp_simdloop_pretty_multiple(%lb1 : index, %ub1 : index, %step1 : ind
   return
 }
 
+// CHECK-LABEL: omp_distribute
+func.func @omp_distribute(%chunk_size : i32, %data_var : memref<i32>) -> () {
+  // CHECK: omp.distribute
+  "omp.distribute" () ({
+    omp.terminator
+  }) {} : () -> ()
+  // CHECK: omp.distribute
+  omp.distribute {
+    omp.terminator
+  }
+  // CHECK: omp.distribute dist_schedule_static
+  omp.distribute dist_schedule_static {
+    omp.terminator
+  }
+  // CHECK: omp.distribute dist_schedule_static chunk_size(%{{.+}} : i32)
+  omp.distribute dist_schedule_static chunk_size(%chunk_size : i32) {
+    omp.terminator
+  }
+  // CHECK: omp.distribute order(concurrent)
+  omp.distribute order(concurrent) {
+    omp.terminator
+  }
+  // CHECK: omp.distribute allocate(%{{.+}} : memref<i32> -> %{{.+}} : memref<i32>)
+  omp.distribute allocate(%data_var : memref<i32> -> %data_var : memref<i32>) {
+    omp.terminator
+  }
+return
+}
+
+
 // CHECK-LABEL: omp_target
 func.func @omp_target(%if_cond : i1, %device : si32,  %num_threads : i32, %map1: memref<?xi32>, %map2: memref<?xi32>) -> () {