On Tue, Aug 24, 2021 at 12:23 PM Thomas Schwinge
<tho...@codesourcery.com> wrote:
>
> Hi!
>
> On 2021-08-19T22:13:56+0200, I wrote:
> > On 2021-08-16T10:21:04+0200, Jakub Jelinek <ja...@redhat.com> wrote:
> >> On Mon, Aug 16, 2021 at 10:08:42AM +0200, Thomas Schwinge wrote:
> > |> Concerning the current 'gcc/omp-low.c:omp_build_component_ref', for the
> > |> current set of offloading testcases, we never see a
> > |> '!ADDR_SPACE_GENERIC_P' there, so the address space handling doesn't seem
> > |> to be necessary there (but also won't do any harm: no-op).
> >>
> >> Are you sure this can't trigger?
> >> Say
> >> extern int __seg_fs a;
> >>
> >> void
> >> foo (void)
> >> {
> >> #pragma omp parallel private (a)
> >> a = 2;
> >> }
> >
> > That test case doesn't run into 'omp_build_component_ref' at all,
> > but [I've pushed an altered and extended variant that does],
> > "Add 'libgomp.c/address-space-1.c'".
> >
> > In this case, 'omp_build_component_ref' called via host compilation
> > 'pass_lower_omp', it's the 'field_type' that has 'address-space-1', not
> > 'obj_type', so indeed Kwok's new code is a no-op:
> >
> > (gdb) call debug_tree(field_type)
> > <pointer_type 0x7ffff7686b28
> > type <integer_type 0x7ffff7686498 int address-space-1 SI
>
> >> I think keeping the qual addr space here is the wrong thing to do,
> >> it should keep the other quals and clear the address space instead,
> >> the whole struct is going to be in generic addres space, isn't it?
> >
> > Correct for 'omp_build_component_ref' called via host compilation
> > 'pass_lower_omp'
>
> > However, regarding the former comment -- shouldn't we force generic
> > address space for all 'tree' types read in via LTO streaming for
> > offloading compilation? I assume that (in the general case) address
> > spaces are never compatible between host and offloading compilation?
> > For [...] "Add 'libgomp.c/address-space-1.c'", propagating the
> > '__seg_fs' address space across the offloading boundary (assuming I did
> > interpret the dumps correctly) doesn't seem to cause any problems
>
> As I found later, actually the 'address-space-1' per host '__seg_fs' does
> cause the "Intel MIC (emulated) offloading execution failure"
> mentioned/XFAILed for 'libgomp.c/address-space-1.c': SIGSEGV, like
> (expected) for host execution. For GCN offloading target, it maps to
> GCN 'ADDR_SPACE_FLAT' which apparently doesn't cause any ill effects (for
> that simple test case). The nvptx offloading target doesn't consider
> address spaces at all.
>
> Is the attached "Host and offload targets have no common meaning of
> address spaces" OK to push?
>
>
> Then, is that the way to do this, or should we add in
> 'gcc/tree-streamer-out.c:pack_ts_base_value_fields':
>
> if (lto_stream_offload_p)
> gcc_assert (ADDR_SPACE_GENERIC_P (TYPE_ADDR_SPACE (expr)));
>
> ..., and elsewhere sanitize this for offloading compilation? Jakub's
> suggestion above, regarding 'gcc/omp-low.c:omp_build_component_ref':
>
> | I think keeping the qual addr space here is the wrong thing to do,
> | it should keep the other quals and clear the address space instead
>
> But it's not obvious to me that indeed this is the one place where this
> would need to be done? (It ought to work for
> 'libgomp.c/address-space-1.c', and any other occurrences would run into
> the 'assert', so that ought to be "fine", though?)
>
>
> And, should we have a new hook
> 'void targetm.addr_space.validate (addr_space_t as)' (better name?),
> called via 'gcc/emit-rtl.c:set_mem_attrs' (only? -- assuming this is the
> appropriate canonic function where address space use is observed?), to
> make sure that the requested 'as' is valid for the target?
> 'default_addr_space_validate' would refuse everything but
> 'ADDR_SPACE_GENERIC_P (as)'; this hook would need implementing for all
> handful of targets making use of address spaces (supposedly matching the
> logic how they call 'c_register_addr_space'?). (The closest existing
> hook seems to be 'targetm.addr_space.diagnose_usage', only defined for
> AVR, and called from "the front ends" (C only).)
Are address-spaces to be used in any way for OpenMP offload code? That is,
does the OpenMP standard talk about them and how to remap things? I'd
say I agree that any host address-space should go away when the corresponding
data is offloaded and in case OpenMP allows to specify a target address-space
that would need to be instantiated in a way so the LTO streaming knows about
a mapping from the host to the target representation.
Richard.
>
> Grüße
> Thomas
>
>
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