[PATCH, 4/16] Implement -foffload-alias
Tom de Vries
Thu Nov 12 16:04:00 GMT 2015
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
> 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
I agree this would be a nice way to solve the aliasing info problem, but
considering the remark of Richard at
Not that I think IPA PTA is anywhere near production ready
I haven't considered proceeding in that direction.
> but a switch like the above is just wrong.
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