3.2 Variable Declarations ¶

A variable declaration with the form:

[loc|heap] amode defining identifier [:= unit];

Is in principle equivalent to the identity declaration:

ref amode defining identifier = [loc|heap] amode;

In both cases the object ascribed to the defining identifier is of mode ref amode. The ascribed object is a name which is created by a generator implied in the actual declarer in the variable declaration case, and an explicit generator in the initialization expression in the identity declaration case.

However, in this compiler these two cases are handled differently in order to reduce the amount of both indirect addressing and of storage:

• The variable declaration [loc|heap] amode foo lowers into a VAR_DECL with type CTYPE (amode) provided that the generator is loc and that the type contains no rows. Accessing the variable will then involve direct addressing, and when its address is required an ADDR_EXPR shall be used.
• The identity declaration ref amode foo = loc amode lowers into a VAR_DECL with type *CTYPE (amode). Accessing the variable will then involve indirect addressing: it is effectively a pointer.

This optimization introduces the complication that an expression (the VAR_DECL) whose type is TYPE can appear in a place where *TYPE is expected, depending on the context and the r-value and l-value interpretation of the VAR_DECL. The function a68_consolidate_ref is used in several parts of the lowering pass to guarantee a given name is an address regardless of how it was initialized.