Lowering of basic elemental functions (intrinsic and user-defined).

This handles the lowering of the basic cases. There are several TODOs in
the code for other variants.

This lowers expressions like the following where a and b are arrays.

  a = f(b)
  a = abs(b)

These are transformed into loop (nests) where the right-hand side is
fully evaluated by applying the function to each element in the array
and then the resulting array is copied-out to the left-hand side.

Author: schweitzpgi

flang/include/flang/Lower/CallInterface.h

@@ -106,7 +106,9 @@ class CallInterface {
     AddressAndLength,
     /// Value means passed by value at the mlir level, it is not necessarily
     /// implied by Fortran Value attribute.
-    Value
+    Value,
+    /// ValueAttribute means dummy has the the Fortran VALUE attribute.
+    ValueAttribute
   };
   /// Different properties of an entity that can be passed/returned.
   /// One-to-One mapping with PassEntityBy but for

flang/include/flang/Lower/ConvertExpr.h

@@ -64,6 +64,9 @@ createSomeMutableBox(mlir::Location loc, AbstractConverter &converter,
 
 /// Create and return a projection of a subspace of an array value. This is the
 /// lhs onto which a newly constructed array value can be merged.
+/// This implements copy-in, copy-out semantics. In case that require it,
+/// results will be buffered so that the rhs values are preserved and the lhs is
+/// updated only after all intermediate computation is concluded.
 fir::ArrayLoadOp
 createSomeArraySubspace(AbstractConverter &converter,
                         const evaluate::Expr<evaluate::SomeType> &expr,

flang/include/flang/Lower/FIRBuilder.h

@@ -122,14 +122,21 @@ class FirOpBuilder : public mlir::OpBuilder {
   /// given a name via a front-end `Symbol` or a `StringRef`.
   mlir::Value createTemporary(mlir::Location loc, mlir::Type type,
                               llvm::StringRef name = {},
-                              llvm::ArrayRef<mlir::Value> shape = {});
+                              mlir::ValueRange shape = {},
+                              mlir::ValueRange lenParams = {},
+                              llvm::ArrayRef<mlir::NamedAttribute> attrs = {});
 
   /// Create an unnamed and untracked temporary on the stack.
   mlir::Value createTemporary(mlir::Location loc, mlir::Type type,
-                              llvm::ArrayRef<mlir::Value> shape) {
+                              mlir::ValueRange shape) {
     return createTemporary(loc, type, llvm::StringRef{}, shape);
   }
 
+  mlir::Value createTemporary(mlir::Location loc, mlir::Type type,
+                              llvm::ArrayRef<mlir::NamedAttribute> attrs) {
+    return createTemporary(loc, type, llvm::StringRef{}, {}, {}, attrs);
+  }
+
   /// Create a global value.
   fir::GlobalOp createGlobal(mlir::Location loc, mlir::Type type,
                              llvm::StringRef name,

flang/lib/Lower/CallInterface.cpp

@@ -544,6 +544,7 @@ class Fortran::lower::CallInterfaceImpl {
     using Attrs = Fortran::evaluate::characteristics::DummyDataObject::Attr;
 
     bool isOptional = false;
+    bool isValueAttr = false;
     [[maybe_unused]] auto loc = interface.converter.genLocation();
     llvm::SmallVector<mlir::NamedAttribute> attrs;
     auto addMLIRAttr = [&](llvm::StringRef attr) {
@@ -559,7 +560,7 @@ class Fortran::lower::CallInterfaceImpl {
     if (obj.attrs.test(Attrs::Contiguous))
       addMLIRAttr(fir::getContiguousAttrName());
     if (obj.attrs.test(Attrs::Value))
-      TODO(loc, "Value in procedure interface");
+      isValueAttr = true; // TODO: do we want an mlir::Attribute as well?
     if (obj.attrs.test(Attrs::Volatile))
       TODO(loc, "Volatile in procedure interface");
     if (obj.attrs.test(Attrs::Target))
@@ -609,7 +610,9 @@ class Fortran::lower::CallInterfaceImpl {
       auto refType = fir::ReferenceType::get(type);
       addFirInput(refType, nextPassedArgPosition(), Property::BaseAddress,
                   attrs);
-      addPassedArg(PassEntityBy::BaseAddress, entity, isOptional);
+      addPassedArg(isValueAttr ? PassEntityBy::ValueAttribute
+                               : PassEntityBy::BaseAddress,
+                   entity, isOptional);
     }
   }