rtl semantics

[Ian Lance Taylor]

Russell Shaw <rjshaw@netspace.net.au> writes:

> I just read all the gcc internals manual.
> I have trouble with the contextual polymorphic
> nature of rtl objects.
> 
> In h8300.md, there is:
> 
>    (define_attr "cpu" "h8300,h8300h"
>      (const (symbol_ref "cpu_type")))
> 
> yet in gccint.info, const should have a machine mode: (const:M EXP)
> 
> Do rtl keywords have a variable meaning, depending on the context
> where they're used? Is there other languages similar to rtl i could
> learn from? (scheme?)

The define_attr construct is not quite RTL.  It does not actually
describe a machine instruction, and thus does not require a mode.  It
is described here:
    http://gcc.gnu.org/onlinedocs/gccint/Defining-Attributes.html#Defining-Attributes

The const attribute in define_attr is described here:
    http://gcc.gnu.org/onlinedocs/gccint/Constant-Attributes.html#Constant-Attributes

Ian