On 11/04/2014 03:13 PM, Andrew MacLeod wrote:
>from targhooks.c:
bool
default_builtin_support_vector_misalignment (machine_mode mode,
const_tree type, <...>)
{
if (optab_handler (movmisalign_optab, mode) != CODE_FOR_nothing)
return true;
return false;
}
the idea is to move all the functionality that front ends need into
well
defined and controlled places so we can increase the separation. "can
perform a compare_and_swap operation" is clearly a target specific
question isn't it?
I would rather question what is so special about java that it needs
to ask that and other frontends not. Don't we have generic atomics
support now?
Richard.
True... I don't know if this is a thing that simply predates our
current level of support or if it is something else that is java
specific for its builtins.
Don't know enough about java to comment.
aph? Looks like you wrote the originals in 2006... Can the java CAS
builtins simply use our current atomic calls rather than doing their
own thing and querying whether the target has a sync compare and swap
operation?
Andrew
It looks like java is deciding whether or not GCC can inline atomic
operations or not, and if it can't, doesn't want the atomic
operations... which presumably means there is no dependency on
libatomic at runtime.
A call to can_compare_and_swap_p(mode) is analogous to a compile time
version of folding atomic_always_lock_free(mode) to a constant...
Frankly that seems like a reasonable question for some front end to
ask... and elect not to emit atomic calls if so desired. (which is what
java is doing I think)
whether it still needs to do that is a question for some java person.
Andrew
