Re: GCC 3.5 Status (2004-08-29)

[Mark Mitchell <mark@codesourcery.com>]

Daniel Berlin wrote:

>>> I am confident that there
>>>are alternatives that, while perhaps less comprehensive, get enough of
>>>the common cases to achieve most of the benefits.
>>>      
>>>
>>What is your confidence based on?  What common cases?  Did Dan tell you
>>about the issues that he's fighting?  No "less comprehensive" solution
>>exists that will not run into the exact same problems.
>>
>>    
>>
>
>I didn't tell him about the issues i'm fighting, so he's probably just
>stating the typical result, ie "It takes less time to get the common
>cases than it does to get all the cases".
>
>Of course, the issues i'm dealing with are things that were punted on
>earlier in the design of tree-ssa, because they were either hard to get
>right, we didn't have time then, etc.
>
>Let me give an example issue from an email i sent to diego and richard,
>as a motivating example.
>  
>
Yes, there's some design work to be done.  That's why I believed your 
estimate about how long it will take, and why parallelizing the work 
will only help so much: you still have to agree on a design up front.

I still think there are likely to be expedient hacks that get you a lot 
of the win.  Note that the RTL optimizers didn't know about fields at 
all until recently (3.4?).  So, perhaps we can deal with the 
compile-time issue by accepting somewhat inferior generated code.  
Perhaps you can wait until SRA runs, and then just DTRT for objects that 
get SRA'd.  I don't have the answer; I'm just saying that there's likely 
to be one out there somewhere.  GCC got by for years with exactly this 
kind of solution, and actually managed to generate relatively decent 
code relatively often.

-- 
Mark Mitchell
CodeSourcery, LLC
(916) 791-8304
mark@codesourcery.com