[flang][hlfir] Array constructor lowering [part 1/4]

This is the first and biggest chunk that introduces support for
array constructor to HLFIR.

This patch:
- adds a new ConvertArrayConstructor.cpp that centralizes the
  code dealing with array constructor lowering.
- introduces a framework to lower array constructor according to
  different strategies: A common analysis of the array constructor is
  done, and based on that, a lowering startegy is selected and driven
  through the ac-values of the array constructor. See
  ConvertArrayConstructor.cpp comments for more details.
- implements the first strategy that creates a temporary inlined and
  updates it with inlined code. This strategy can only be used if the
  temporary can be pre-allocated (i.e: the extents and length parameters
  can be pre-computed without evaluating any ac-values), and if all the
  ac-value expressions are scalars.

For the sake of simplicity, characters and derived type will be enabled
once all the strategies are added.

Reviewed By: clementval, PeteSteinfeld

Differential Revision: https://reviews.llvm.org/D144102

flang/include/flang/Lower/ConvertArrayConstructor.h

@@ -0,0 +1,46 @@
+//===-- ConvertArrayConstructor.h -- Array constructor lowering -*- C++ -*-===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+//
+// Coding style: https://mlir.llvm.org/getting_started/DeveloperGuide/
+//
+//===----------------------------------------------------------------------===//
+///
+/// Implements the conversion from evaluate::ArrayConstructor to HLFIR.
+///
+//===----------------------------------------------------------------------===//
+#ifndef FORTRAN_LOWER_CONVERTARRAYCONSTRUCTOR_H
+#define FORTRAN_LOWER_CONVERTARRAYCONSTRUCTOR_H
+
+#include "flang/Evaluate/type.h"
+#include "flang/Optimizer/Builder/HLFIRTools.h"
+
+namespace Fortran::evaluate {
+template <typename T>
+class ArrayConstructor;
+}
+
+namespace Fortran::lower {
+class AbstractConverter;
+class SymMap;
+class StatementContext;
+
+/// Class to lower evaluate::ArrayConstructor<T> to hlfir::EntityWithAttributes.
+template <typename T>
+class ArrayConstructorBuilder {
+public:
+  static hlfir::EntityWithAttributes
+  gen(mlir::Location loc, Fortran::lower::AbstractConverter &converter,
+      const Fortran::evaluate::ArrayConstructor<T> &expr,
+      Fortran::lower::SymMap &symMap,
+      Fortran::lower::StatementContext &stmtCtx);
+};
+using namespace evaluate;
+FOR_EACH_SPECIFIC_TYPE(extern template class ArrayConstructorBuilder, )
+} // namespace Fortran::lower
+
+#endif // FORTRAN_LOWER_CONVERTARRAYCONSTRUCTOR_H

flang/lib/Lower/CMakeLists.txt

@@ -5,6 +5,7 @@ add_flang_library(FortranLower
   Bridge.cpp
   CallInterface.cpp
   Coarray.cpp
+  ConvertArrayConstructor.cpp
   ConvertCall.cpp
   ConvertConstant.cpp
   ConvertExpr.cpp