[flang] Add lowering for integer constant

This patch enables the lowering of integer constant.

The `ScalarExprLowering` class is introduced in `ConvertExpr.cpp` to help
the lowering of expression. This patch adds all the placeholder as well for future
expression lowering with the appropriate TODOs.

Integer constant expression are lowered to `arith.constant` with an integer type corresponding to the kind value.

This patch is in support of D118787

This patch is part of the upstreaming effort from fir-dev branch.

Reviewed By: schweitz, kiranchandramohan

Differential Revision: https://reviews.llvm.org/D118786

1 files changed, 43 insertions, 5 deletions

diff --git a/flang/lib/Lower/ConvertType.cpp b/flang/lib/Lower/ConvertType.cpp
index 299b9e3..a411c0f 100644
--- a/flang/lib/Lower/ConvertType.cpp
+++ b/flang/lib/Lower/ConvertType.cpp
@@ -475,11 +475,49 @@ private:
 
 } // namespace
 
-mlir::Type Fortran::lower::getFIRType(
-    mlir::MLIRContext *context,
-    const Fortran::common::IntrinsicTypeDefaultKinds &defaults,
-    Fortran::common::TypeCategory tc, int kind) {
-  return TypeBuilder{context, defaults}.genFIRTy(tc, kind);
+template <int KIND>
+int getIntegerBits() {
+  return Fortran::evaluate::Type<Fortran::common::TypeCategory::Integer,
+                                 KIND>::Scalar::bits;
+}
+static mlir::Type genIntegerType(mlir::MLIRContext *context, int kind) {
+  if (Fortran::evaluate::IsValidKindOfIntrinsicType(
+          Fortran::common::TypeCategory::Integer, kind)) {
+    switch (kind) {
+    case 1:
+      return mlir::IntegerType::get(context, getIntegerBits<1>());
+    case 2:
+      return mlir::IntegerType::get(context, getIntegerBits<2>());
+    case 4:
+      return mlir::IntegerType::get(context, getIntegerBits<4>());
+    case 8:
+      return mlir::IntegerType::get(context, getIntegerBits<8>());
+    case 16:
+      return mlir::IntegerType::get(context, getIntegerBits<16>());
+    }
+  }
+  llvm_unreachable("INTEGER kind not translated");
+}
+
+static mlir::Type genFIRType(mlir::MLIRContext *context,
+                             Fortran::common::TypeCategory tc, int kind) {
+  switch (tc) {
+  case Fortran::common::TypeCategory::Integer:
+    return genIntegerType(context, kind);
+  case Fortran::common::TypeCategory::Real:
+  case Fortran::common::TypeCategory::Complex:
+  case Fortran::common::TypeCategory::Logical:
+  case Fortran::common::TypeCategory::Character:
+  default:
+    break;
+  }
+  llvm_unreachable("unhandled type category");
+}
+
+mlir::Type Fortran::lower::getFIRType(mlir::MLIRContext *context,
+                                      Fortran::common::TypeCategory tc,
+                                      int kind) {
+  return genFIRType(context, tc, kind);
 }
 
 mlir::Type Fortran::lower::getFIRType(