On 11/11/15 12:00, Jakub Jelinek wrote:
On Wed, Nov 11, 2015 at 11:51:02AM +0100, Richard Biener wrote:
The option -foffload-alias=pointer instructs the compiler to assume that
objects references in an offload region do not alias.
The option -foffload-alias=all instructs the compiler to make no
assumptions about aliasing in offload regions.
The default value is -foffload-alias=none.
I think global options for this is nonsense. Please follow what
we do for #pragma GCC ivdep for example, thus allow the alias
behavior to be specified per "region" (whatever makes sense here
in the context of offloading).
So, IIUC, instead of a global option foffload-alias, you're saying
something like the following would be acceptable:
...
#pragma GCC offload-alias=<none|pointer|all>
#pragma acc kernels copyin (a[0:N], b[0:N]) copyout (c[0:N])
{
#pragma acc loop
for (COUNTERTYPE ii = 0; ii < N; ii++)
c[ii] = a[ii] + b[ii];
}
...
?
I suppose that would work (though a global option would allow us to
easily switch between none/pointer/all values in a large number of
files, something that might be useful when f.i. running an openacc test
suite).
Yeah, completely agreed. I don't see why the offloaded region would be in
any way special, they are C/C++/Fortran code as any other.
What we can and should improve is teach IPA aliasing/points to analysis
about the way we lower the host vs. offloading region boundary, so that
if alias analysis on the caller of GOMP_target_ext/GOACC_parallel_keyed
determines something it can be used on the offloaded function side and vice
versa,
I agree this would be a nice way to solve the aliasing info problem, but
considering the remark of Richard at
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=46032#c19 :
...
Not that I think IPA PTA is anywhere near production ready
...
I haven't considered proceeding in that direction.
Thanks,
- Tom
but a switch like the above is just wrong.
