RE: Java: add flag_use_atomic_builtins

["Boehm, Hans" <hans.boehm@hp.com>]

At the risk of asking a stupid question, shouldn't all the code inside gcc gradually migrate towards using the C++0x (and probably C1x) atomics, which seem to be generally supported by gcc 4.4?

There are known issues with __sync (no atomic loads and stores, underspecified ordering), which is why there wasn't much of an effort topush the __sync interface into C++0x.

Hans

> -----Original Message-----
> From: java-patches-owner@gcc.gnu.org 
> [mailto:java-patches-owner@gcc.gnu.org] On Behalf Of Andrew Haley
> Sent: Wednesday, August 12, 2009 10:15 AM
> To: Paolo Bonzini
> Cc: Joseph S. Myers; java-patches@gcc.gnu.org; Gcc Patch List
> Subject: Re: Java: add flag_use_atomic_builtins
> 
> Andrew Haley wrote:
> > Paolo Bonzini wrote:
> >> On 08/12/2009 06:52 PM, Andrew Haley wrote:
> >>> Joseph S. Myers wrote:
> >>>> On Wed, 12 Aug 2009, Andrew Haley wrote:
> >>>>
> >>>>> Some targets, particularly ARM, don't have instructions 
> for things 
> >>>>> such as sync_compare_and_swap.  Instead, a routine in libgcc is 
> >>>>> used.  This patch adds a new gcj option, -fuse-atomic-builtins, 
> >>>>> which causes gcj to use the routines in libgcc whenever atomic 
> >>>>> operations are needed.
> >>>> Wouldn't a target hook to allow a target to declare which 
> >>>> operations it provides in libgcc be better than a 
> command-line option?
> >>> Maybe it would.  I'm happy to work with anyone to create such a 
> >>> thing.  What would such a hook look like, and how would a 
> front- end 
> >>> use it?
> >> Couldn't optabs be (re)used?
> > 
> > That would be nice.
> 
> I guess that's just a matter of
> 
>   set_optab_libfunc (sync_compare_and_swap_optab, SImode,, 
> SImode, SImode "__sync_bool_compare_and_swap_4");
> 
> or somesuch?
> 
> Andrew.
>