Excess registers pushed - regs_ever_live not right way?

[Andrew Hutchinson]

I gave up with DF and instead went through function tree argument to 
rediscover argument registers.
It was then simple matter to exclude these from epilog/prolog registers 
saves/restores.

The patches is posted - and seem quite portable to other targets.

http://gcc.gnu.org/ml/gcc-patches/2008-03/msg00115.html


best regards and thanks for help.



Seongbae Park (???, ???) wrote:
> 2008/3/1 Andrew Hutchinson <andrewhutchinson@cox.net>:
>   
>> I'm am still struggling with a good solution that avoids unneeded saves
>>  of parameter registers.
>>
>>  To solve problem all I need to know are the registers actually used for
>>  parameters. Since the caller assumes all of these are clobbered by
>>  callee - they should never need to be saved.
>>     
>
> I'm totally confused what is the problem here.
> I thought you were seeing extra callee-save register save/restore in prologue,
> but now it sounds like you're seeing extra caller-save register save/restore.
> Which one are you trying to solve, and what kind of target is this ?
>
>   
>>  DF_REG_DEF_COUNT is showing 1 artificial def for all POTENTIAL parameter
>>  registers - not just the ones that are really used (since it uses target
>>  FUNCTION_ARG_REGNO_P to get parameter registers)
>>     
>
> You said you wanted to know if there's a def of a register within a function.
> For an incoming parameter, there will be one artificial def,
> and if there's no other def, it means there's no real def
> of the register within the function.
>
>   
>>  So the DF artificial defs are useless in trying to find real parameter
>>  registers.
>>     
>
> I don't understand what you mean by this. What do you mean by
> "real parameter register" ?
>
>   
>>  That seem to require going over all DF chains to work out which
>>  registers are externally defined. DF does not solve problem for me.
>>     
>
> What do you mean by "externally defined" ?
> DF may not solve the problem for you,
> but now I'm completely lost on what your problem is.
>
>   
>>  There has got to be an easier way of finding parameter registers used by
>>  function.
>>     
>
> If you want to find all the uses (use as in reading a register but not
> writing to it),
> you should look at USE chain, not DEF chain, naturally.
>
> Seongbae
>
>