[mlir][openmp] Add an interface for Outlineable OpenMP ops

[clementval]

Summary

Add an interface for outlineable OpenMP operations.
This patch was initially done in fir-dev and is now needed
for the upstreaming.

Co-authored-by: Kiran Chandramohan <[e-mail]>

[clementval]

Initial commit made by @kiranchandramohan on fir-dev. https://github.com/flang-compiler/f18-llvm-project/commit/50277a7607c93808e896da29238dfba3a4384adf#diff-092b746eb656b2c89c421329c525a9559810d03b50aa9467466c8f7cea75330e

mlir/include/mlir/Dialect/OpenMP/CMakeLists.txt

 set(LLVM_TARGET_DEFINITIONS ${LLVM_MAIN_INCLUDE_DIR}/llvm/Frontend/OpenMP/OMP.td)
 mlir_tablegen(OmpCommon.td --gen-directive-decl)
 add_public_tablegen_target(omp_common_td)
 
 set(LLVM_TARGET_DEFINITIONS OpenMPOps.td)
 mlir_tablegen(OpenMPOpsDialect.h.inc -gen-dialect-decls -dialect=omp)
 mlir_tablegen(OpenMPOpsDialect.cpp.inc -gen-dialect-defs -dialect=omp)
 mlir_tablegen(OpenMPOps.h.inc -gen-op-decls)
 mlir_tablegen(OpenMPOps.cpp.inc -gen-op-defs)
 mlir_tablegen(OpenMPOpsEnums.h.inc -gen-enum-decls)
 mlir_tablegen(OpenMPOpsEnums.cpp.inc -gen-enum-defs)
 mlir_tablegen(OpenMPTypeInterfaces.h.inc -gen-type-interface-decls)
 mlir_tablegen(OpenMPTypeInterfaces.cpp.inc -gen-type-interface-defs)
 add_mlir_doc(OpenMPOps OpenMPDialect Dialects/ -gen-dialect-doc)
 add_public_tablegen_target(MLIROpenMPOpsIncGen)
 add_dependencies(OpenMPDialectDocGen omp_common_td)
+add_mlir_interface(OpenMPOpsInterfaces)

mlir/include/mlir/Dialect/OpenMP/OpenMPDialect.h

 #include "mlir/IR/Dialect.h"
 #include "mlir/IR/OpDefinition.h"
 #include "mlir/IR/SymbolTable.h"
 #include "mlir/Interfaces/ControlFlowInterfaces.h"
 #include "mlir/Interfaces/SideEffectInterfaces.h"
 
 #include "mlir/Dialect/OpenMP/OpenMPOpsDialect.h.inc"
 #include "mlir/Dialect/OpenMP/OpenMPOpsEnums.h.inc"
+#include "mlir/Dialect/OpenMP/OpenMPOpsInterfaces.h.inc"
 #include "mlir/Dialect/OpenMP/OpenMPTypeInterfaces.h.inc"
 
 #define GET_OP_CLASSES
 #include "mlir/Dialect/OpenMP/OpenMPOps.h.inc"
 
 #endif // MLIR_DIALECT_OPENMP_OPENMPDIALECT_H_

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

 #define OPENMP_OPS
 
 include "mlir/IR/OpBase.td"
 include "mlir/Interfaces/SideEffectInterfaces.td"
 include "mlir/Interfaces/ControlFlowInterfaces.td"
 include "mlir/IR/SymbolInterfaces.td"
 include "mlir/Dialect/OpenMP/OmpCommon.td"
 include "mlir/Dialect/LLVMIR/LLVMOpBase.td"
+include "mlir/Dialect/OpenMP/OpenMPOpsInterfaces.td"
 
 def OpenMP_Dialect : Dialect {
   let name = "omp";
   let cppNamespace = "::mlir::omp";
   let dependentDialects = ["::mlir::LLVM::LLVMDialect"];
 }
 
 class OpenMP_Op<string mnemonic, list<OpTrait> traits = []> :

 def ClauseDefault : StrEnumAttr<
     "ClauseDefault",
     "default clause",
     [ClauseDefaultPrivate, ClauseDefaultFirstPrivate, ClauseDefaultShared,
      ClauseDefaultNone]> {
   let cppNamespace = "::mlir::omp";
 }
 
-def ParallelOp : OpenMP_Op<"parallel", [AttrSizedOperandSegments]> {
+def ParallelOp : OpenMP_Op<"parallel", [AttrSizedOperandSegments,
+                 DeclareOpInterfaceMethods<OutlineableOpenMPOpInterface>]> {
   let summary = "parallel construct";
   let description = [{
     The parallel construct includes a region of code which is to be executed
     by a team of threads.
 
     The optional $if_expr_var parameter specifies a boolean result of a
     conditional check. If this value is 1 or is not provided then the parallel
     region runs as normal, if it is 0 then the parallel region is executed with

mlir/include/mlir/Dialect/OpenMP/OpenMPOpsInterfaces.td

+//===-- OpenMPOpsInterfaces.td - OpenMP op interfaces ------*- tablegen -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This is the OpenMP Dialect interfaces definition file.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef OpenMP_OPS_INTERFACES
+#define OpenMP_OPS_INTERFACES
+
+include "mlir/IR/OpBase.td"
+
+def OutlineableOpenMPOpInterface : OpInterface<"OutlineableOpenMPOpInterface"> {
+  let description = [{
+    OpenMP operations whose region will be outlined will implement this
+    interface. These operations will
+  }];
+
+  let cppNamespace = "::mlir::omp";
+
+  let methods = [
+    InterfaceMethod<"Get alloca block", "::mlir::Block*", "getAllocaBlock",
+      (ins), [{
+      return &$_op.getRegion().front();
+      }]>,
+  ];
+}
+
+#endif // OpenMP_OPS_INTERFACES

mlir/lib/Dialect/OpenMP/CMakeLists.txt

 add_mlir_dialect_library(MLIROpenMP
   IR/OpenMPDialect.cpp
 
   ADDITIONAL_HEADER_DIRS
   ${MLIR_MAIN_INCLUDE_DIR}/mlir/Dialect/OpenMP
 
   DEPENDS
   MLIROpenMPOpsIncGen
+  MLIROpenMPOpsInterfacesIncGen
 
   LINK_LIBS PUBLIC
   MLIRIR
   MLIRLLVMIR
   )