[RFC] CFG hooks for rtl/tree specificities

[Jan Hubicka]

> Hi,
> 
> I would like to have your opinion on the following reorganization of the CFG functions.
> 
> I propose to keep all the functions that deal with IR specificities into a hook structure
> a little bit the same way we handle the specificities of a language front-end in langhooks.  

I like it :)

> These functions are initialized during the CFG construction.  This would allow the CFG 
> analyzers and optimizers to work at both the RTL and the tree levels.  

I think all we need is to have two cfg_hooks pointer and switch betwen
cfg_rtl_hooks, cfg_rtl_layout_hooks and cfg_tree_hooks so we don't need
to fill up the structure each time.
> 
> 
> cfghooks.h will contain something like:
> ----
> 
> /* Initializations specific to either the tree or the rtl level.  */
> extern void tree_register_cfg_hooks    PARAMS ((void));
> extern void rtl_register_cfg_hooks     PARAMS ((void));
> 
> struct cfg_hooks
> {
>   basic_block (*cfgh_split_edge)       PARAMS ((edge));
>   void (*cfgh_cfg_layout_initialize)   PARAMS ((struct loops *));
>   void (*cfgh_cfg_layout_finalize)     PARAMS ((void));
>   void (*cfgh_verify_flow_info)        PARAMS ((void));
> }; 
> 
> /* The following macros act either at the tree level or at the rtl level.  */
> #define split_edge(e)                  cfg_hooks.cfgh_split_edge (e) 
> #define cfg_layout_initialize(l)       cfg_hooks.cfgh_cfg_layout_initialize (l) 
> #define cfg_layout_finalize()          cfg_hooks.cfgh_cfg_layout_finalize () 
> #define verify_flow_info()             cfg_hooks.cfgh_verify_flow_info () 
> 
> extern struct cfg_hooks cfg_hooks;

This looks nice.
It would be interesting to think about what operations do we really need
- for instance split_edge should be probably implementable already via
the primitive operations (basic block creation, edge redirection).  Our
current API is not 100% ready for that so we will probably need cleanup
on the way.

I would be happy about switching to the hooks first and leaving it to me
to cleanup the APIs if you preffer.

Honza