https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85129
Bug ID: 85129
Summary: [openacc] Document GOMP_OPENACC_DIM
Product: gcc
Version: 8.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libgomp
Assignee: unassigned at gcc dot gnu.org
Reporter: vries at gcc dot gnu.org
CC: jakub at gcc dot gnu.org
Target Milestone: ---
I. trunk
The GOMP_OPENACC_DIM environment variable is not documented (it should have an
entry in libgomp.texi at 'OpenACC Environment Variables').
The plugin-nvptx.c source code shows:
...
/* ... . The syntax is the same as for the -fopenacc-dim compilation
option. */
...
The documentation of fopenacc-dim is:
...
@item -fopenacc-dim=@var{geom}
@opindex fopenacc-dim
@cindex OpenACC accelerator programming
Specify default compute dimensions for parallel offload regions that do
not explicitly specify. The @var{geom} value is a triple of
':'-separated sizes, in order 'gang', 'worker' and, 'vector'. A size
can be omitted, to use a target-specific default value.
...
The documentation of fopenacc-dim shows no examples.
If we grep through the testsuite, we find a couple of examples of fopenacc-dim
usage:
...
libgomp.oacc-c-c++-common/loop-dim-default.c:
/* { dg-additional-options "-fopenacc-dim=16:16" } */
libgomp.oacc-c-c++-common/tile-1.c:
/* { dg-additional-options "-fopenacc-dim=32" } */
libgomp.oacc-c-c++-common/loop-auto-1.c:
/* { dg-additional-options "-fopenacc-dim=32" } */
...
There is no test-case exercising omission at the start, f.i. ":16:" to use a
target-specific number of gangs, 16 workers, and a target-specific vector
length.
There are no testcases exercising GOMP_OPENACC_DIM.
II. og7
If we move over to branch og7, we find a different syntax for -fopenacc-dim,
allowing a '-' to force the corresponding dimension to be chosen at runtime:
...
@item -fopenacc-dim=@var{geom}
@opindex fopenacc-dim
@cindex OpenACC accelerator programming
Specify default compute dimensions for parallel offload regions that do
not explicitly specify. The @var{geom} value is a triple of
':'-separated sizes, in order 'gang', 'worker' and, 'vector'. If a size
is to be deferred until execution '-' can be used, alternatively a size
can be omitted to use a target-specific default value. When deferring
to runtime, the environment variable @var{GOMP_OPENACC_DIM} can be set.
It has the same format as the option value, except that '-' is not
permitted.
...
The last line excludes the usage of '-' in GOMP_OPENACC_DIM, but the comment in
plugin-nvptx still claims that syntax for GOMP_OPENACC_DIM and -fopenacc-dim is
the same.
The examples of '-' fopenacc-dim usage in og7:
...
libgomp.oacc-c-c++-common/loop-default-runtime.c:
/* { dg-additional-options "-fopenacc-dim=-:-" } */
libgomp.oacc-fortran/gemm.f90:
! { dg-additional-options "-fopenacc-dim=-:-:128" }
...
There are two test-cases excercising GOMP_OPENACC_DIM (using setenv rather than
dg-set-target-env-var, to allow remote testing setups to work where
dg-set-target-env-var is broken):
...
libgomp.oacc-c-c++-common/loop-default-compile.c:
setenv ("GOMP_OPENACC_DIM", "8:8", 1);
libgomp.oacc-c-c++-common/loop-default-runtime.c:
setenv ("GOMP_OPENACC_DIM", "8:16", 1);
...
