[flang] Switch return to ExtendedValue in AbstractConverter and Bridge

[clementval]

Summary

Change the signature of genExprAddr, genExprValue to return a fir::ExtendedValue instead of a simple mlir::Value

This patch is a preparation for more lowering to be upstream. It supports D118786 and D118787.

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

[clementval]

Remove comment that is not actual.

[kiranchandramohan]

LGTM.

flang/include/flang/Lower/AbstractConverter.h

public:
 
   /// Get the mlir instance of a symbol.
   virtual mlir::Value getSymbolAddress(SymbolRef sym) = 0;
 
   //===--------------------------------------------------------------------===//
   // Expressions
   //===--------------------------------------------------------------------===//
 
-  /// Generate the address of the location holding the expression, someExpr
-  virtual mlir::Value genExprAddr(const SomeExpr &,
+  /// Generate the address of the location holding the expression, someExpr.
+  virtual fir::ExtendedValue genExprAddr(const SomeExpr &,
                                          mlir::Location *loc = nullptr) = 0;
   /// Generate the address of the location holding the expression, someExpr
-  mlir::Value genExprAddr(const SomeExpr *someExpr, mlir::Location loc) {
+  fir::ExtendedValue genExprAddr(const SomeExpr *someExpr, mlir::Location loc) {
     return genExprAddr(*someExpr, &loc);
   }
 
   /// Generate the computations of the expression to produce a value
-  virtual mlir::Value genExprValue(const SomeExpr &,
+  virtual fir::ExtendedValue genExprValue(const SomeExpr &,
                                           mlir::Location *loc = nullptr) = 0;
   /// Generate the computations of the expression, someExpr, to produce a value
-  mlir::Value genExprValue(const SomeExpr *someExpr, mlir::Location loc) {
+  fir::ExtendedValue genExprValue(const SomeExpr *someExpr,
+                                  mlir::Location loc) {
     return genExprValue(*someExpr, &loc);
   }
 
   /// Get FoldingContext that is required for some expression
   /// analysis.
   virtual Fortran::evaluate::FoldingContext &getFoldingContext() = 0;
 
   //===--------------------------------------------------------------------===//

flang/lib/Lower/Bridge.cpp

public:
   //===--------------------------------------------------------------------===//
   // AbstractConverter overrides
   //===--------------------------------------------------------------------===//
 
   mlir::Value getSymbolAddress(Fortran::lower::SymbolRef sym) override final {
     return lookupSymbol(sym).getAddr();
   }
 
-  mlir::Value genExprAddr(const Fortran::lower::SomeExpr &expr,
+  fir::ExtendedValue genExprAddr(const Fortran::lower::SomeExpr &expr,
                                  mlir::Location *loc = nullptr) override final {
     TODO_NOLOC("Not implemented. Needed for more complex expression lowering");
   }
-  mlir::Value genExprValue(const Fortran::lower::SomeExpr &expr,
-                           mlir::Location *loc = nullptr) override final {
+  fir::ExtendedValue
+  genExprValue(const Fortran::lower::SomeExpr &expr,
     TODO_NOLOC("Not implemented. Needed for more complex expression lowering");
   }
 
   Fortran::evaluate::FoldingContext &getFoldingContext() override final {
     return foldingContext;
   }
 
   mlir::Type genType(const Fortran::evaluate::DataRef &) override final {