https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106316
Bug ID: 106316
Summary: [OpenMP] Auto "declare target" should honor 'declare
variant' kind(nohost)
Product: gcc
Version: 13.0
Status: UNCONFIRMED
Keywords: openmp
Severity: normal
Priority: P3
Component: middle-end
Assignee: unassigned at gcc dot gnu.org
Reporter: burnus at gcc dot gnu.org
CC: jakub at gcc dot gnu.org
Target Milestone: ---
The following fails during device lto1 with:
ld: error: undefined symbol: external
>>> referenced by decl-var.c:3
>>> /tmp/cc6C3J6T.o:(onhost)
However, 'external' is never executed on the device.
This seems to be more a 'declare variant' tagging issue than a symbol issue
as it works when keeping only
int onhost(void); /* Only declaration, no definition */
in the second file (and having the definition alongside 'external' in the
first).
→ omp_discover_declare_target_tgt_fn_r, omp_discover_declare_target_fn_r
functions.
---- First file. Compile with 'gcc -c first.c' ------
void external(void)
{
__builtin_printf("Hello World\n");
}
/* See remark:
int onhost(void) { external(); return 5; } */
-----------------------------------------------------
---- Second file. Compile with 'gcc -fopenmp second.c first.o' ------
void external(void);
int onhost(void) { external(); return 5; }
int ondevice(void) { return 7; }
#pragma omp declare variant (onhost) match (device={kind(host)})
#pragma omp declare variant (ondevice) match (device={kind(nohost)})
int stub (void) { return 9; }
#pragma omp declare target
int
caller(void)
{
return stub();
}
#pragma omp end declare target
int
main()
{
__builtin_printf("On host: %d (expected: 5)\n", caller());
#pragma omp target
__builtin_printf("On device: %d (expected: 7)\n", caller());
return 0;
}
---------------------------------------------------------------------
* * *
A variant would be:
#pragma omp declare variant (ondevice) match (device={kind(nohost)})
int stub (void) { external(); return 9; }
where the 'stub();' is called in the target region but is still unreachable
because of the 'nohost'.
* * *
While some generic solution would be good - i.e. if offload host is only GCN,
it would be nice if the following works - even if it will fail once
-foffload=nvptx is used
#pragma omp declare variant (ondevice) match
(construct={target},device={arch(gcn)})
int stub (void) { external(); return 9; }
handling an explicit 'kind(host)' is very useful.
