rtl semantics

[Russell Shaw]

Ian Lance Taylor wrote:
> 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

Are the templates in <machine>.md real RTL, or only templates used to generate RTL?
Is "RTL" a textual language, or just some C struct?