[llvm] r189101 - Add function attribute 'optnone'.

[Greg_Bedwell at sn.scee.net]

Hi,

> I think that being able to specify the optimization level on a per 
function
> basis, like in GCC, would be useful (I think several people are 
interested in
> this, so it may actually happen).  One of my gripes with optnone is that 
it is
> heading in this direction but isn't solving the general problem.  I 
would be
> much happier with a more general approach than optnone that made it 
> possible to
> say "optimize this function at -O0" but that also allowed you to 
say"optimize
> it at -O1" (or whatever).  Then you could optimize most of the program 
with
> -O2/-O3 and the problematic functions with -O1 (or -O0).  So from 
> this point of
> view I don't think optnone goes far enough.  [Having the optimization 
level on
> the function also means that per-function passes could look up 
> whether they are
> supposed to be doing -Og optimization and turn problematic transforms 
off].
> 

This sounds good to me.  Our original proposal was for this very feature:
http://llvm.1065342.n5.nabble.com/PROPOSAL-per-function-optimization-level-control-td57094.html 


Unfortunately, it didn't seem to register any particular interest at time, 
so we were advised to scale-back our ambitions and go for something less 
ambitious/controversial, hence 'optnone' which would still fulfil our 
primary use-case and possibly be a stepping stone to more fully blown 
per-function optimization later on.  Maybe now that there is firm talk of 
a new pass manager the proposal can be revisited w.r.t making sure the new 
implementation could support this type of feature as part of its design?

Thanks for bearing with us whilst we stumble around trying to integrate 
into the community properly!

Greg Bedwell
SN Systems - Sony Computer Entertainment Group


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