Re: How to add target specific dependency?

["Pranav Bhandarkar" <pranav dot bhandarkar at gmail dot com>]

On 8/23/07, petruk_gile <petsbags@gmail.com> wrote:
>
> Hi all ..
>
> I'm currently porting GCC into a new processor, and I have a problem in
> instruction scheduling ...
>
> The case is like this:
> In the machine description (*.md) file, sometimes I emit a single RTL
> instruction into multiple ASM instruction. The problem is, in some case I
> need to emit an operand that actually doesn't exist in its RTL
> representation. For example :
>
> "movpqi_insn x,y" instruction will be translated as ==> "sar x, *ar15"  and
> "lar y, *ar15"
>
>       Where "sar" means "Store register" and "lar" means "load register" ...
>
> Since GCC performs instruction scheduling in RTL form, it doesn't know that
> instruction "movpqi_insn" actually reads AR15 .... Hence, sometimes GCC
> moves an instruction that actually SHOULD NOT be moved, due to data
> dependence in AR15...., and it causes incorrect scheduling  (This is my
> analysis, please tell me if you guys think I'm wrong)...
>
> So, I need to:
> (1) whether disable the scheduling for that particular dependency, or
> (2) Inform GCC that "movpqi_insn" has an additional dependency in AR15 ....
>
> The problem is, I still don't know how can i do those 2 things ... So if any
> of you have any advice, I'd be really grateful .... :D
Ideally you could either split movpqi_insn (into a store and a load)
during expansion or split the insn appropriately just before
instruction scheduling (using a define_insn_and_split) .

cheers!
Pranav