Re: [PATCH] openmp: Implement support for OMP_TARGET_OFFLOAD
Hi Jakub, >> the patch also breaks bootstrap on both i386-pc-solaris2.11 and >> sparc-sun-solaris2.11: >> >> /vol/gcc/src/hg/master/local/libgomp/env.c: In function 'initialize_env': >> /vol/gcc/src/hg/master/local/libgomp/env.c:414:16: error: 'new_offload' >> may be used uninitialized in this function [-Werror=maybe-uninitialized] >> 414 | *offload = new_offload; >> | ~^ >> /vol/gcc/src/hg/master/local/libgomp/env.c:384:30: note: 'new_offload' >> was declared here >> 384 | enum gomp_target_offload_t new_offload; >> | ^~~ > > I can't reproduce that, but I fail to see why we need two separate > variables, one with actual value and one tracking if the value is valid. I'd also tried i686-pc-linux-gnu, but didn't get the failure there either. > So I'd go with: > > 2020-10-20 Jakub Jelinek > > * env.c (parse_target_offload): Change new_offload var type to int, > preinitialize to -1, remove found var and test new_offload != -1 > instead of found. That worked just fine. Thanks. Rainer -- - Rainer Orth, Center for Biotechnology, Bielefeld University
Re: [PATCH] openmp: Implement support for OMP_TARGET_OFFLOAD
On 20/10/2020 1:57 pm, Jakub Jelinek wrote:
On Tue, Oct 20, 2020 at 02:17:26PM +0200, Tobias Burnus wrote:
On 10/20/20 2:11 PM, Tobias Burnus wrote:
Unfortunately, the committed patch
(r11-4121-g1bfc07d150790fae93184a79a7cce897655cb37b)
causes build errors.
The error seems to be provoked by function cloning – as the code
itself looks fine:
...
struct gomp_device_descr *devices_s
= malloc (num_devices * sizeof (struct gomp_device_descr));
...
for (i = 0; i < num_devices; i++)
if (!(devices[i].capabilities & GOMP_OFFLOAD_CAP_OPENMP_400))
devices_s[num_devices_after_openmp++] = devices[i];
gomp_target_init.part.0 ()
{
...
devices_s_1 = malloc (0);
...
num_devices.16_67 = num_devices;
...
if (num_devices.16_67 > 0)
goto ; [89.00%]
else
goto ; [11.00%]
Which seems to have an ordering problem.
This patch fixes the warning that breaks the bootstrap, but haven't
tested it with offloading to see if it doesn't break offloading somehow.
Thank you for the fix.
It appears that the issue only occurs when offloading is not enabled (I tested
with offloading to Nvidia and AMD GCN devices, but forgot to test no offloading).
Kwok
Re: [PATCH] openmp: Implement support for OMP_TARGET_OFFLOAD
On Tue, Oct 20, 2020 at 06:39:39PM +0200, Rainer Orth wrote:
> Hi Tobias,
>
> > On 10/19/20 8:21 PM, Jakub Jelinek via Gcc-patches wrote:
> >
> >> On Mon, Oct 19, 2020 at 06:57:49PM +0100, Kwok Cheung Yeung wrote:
> >>> --- a/libgomp/target.c
> >>> +++ b/libgomp/target.c
> > ...
> >> Otherwise LGTM.
> >
> > Unfortunately, the committed patch
> > (r11-4121-g1bfc07d150790fae93184a79a7cce897655cb37b)
> > causes build errors.
>
> the patch also breaks bootstrap on both i386-pc-solaris2.11 and
> sparc-sun-solaris2.11:
>
> /vol/gcc/src/hg/master/local/libgomp/env.c: In function 'initialize_env':
> /vol/gcc/src/hg/master/local/libgomp/env.c:414:16: error: 'new_offload' may
> be used uninitialized in this function [-Werror=maybe-uninitialized]
> 414 | *offload = new_offload;
> | ~^
> /vol/gcc/src/hg/master/local/libgomp/env.c:384:30: note: 'new_offload' was
> declared here
> 384 | enum gomp_target_offload_t new_offload;
> | ^~~
I can't reproduce that, but I fail to see why we need two separate
variables, one with actual value and one tracking if the value is valid.
So I'd go with:
2020-10-20 Jakub Jelinek
* env.c (parse_target_offload): Change new_offload var type to int,
preinitialize to -1, remove found var and test new_offload != -1
instead of found.
--- libgomp/env.c.jj2020-10-20 14:37:36.593968443 +0200
+++ libgomp/env.c 2020-10-20 18:43:00.338389023 +0200
@@ -380,8 +380,7 @@ static void
parse_target_offload (const char *name, enum gomp_target_offload_t *offload)
{
const char *env;
- bool found = false;
- enum gomp_target_offload_t new_offload;
+ int new_offload = -1;
env = getenv (name);
if (env == NULL)
@@ -392,24 +391,21 @@ parse_target_offload (const char *name,
if (strncasecmp (env, "default", 7) == 0)
{
env += 7;
- found = true;
new_offload = GOMP_TARGET_OFFLOAD_DEFAULT;
}
else if (strncasecmp (env, "mandatory", 9) == 0)
{
env += 9;
- found = true;
new_offload = GOMP_TARGET_OFFLOAD_MANDATORY;
}
else if (strncasecmp (env, "disabled", 8) == 0)
{
env += 8;
- found = true;
new_offload = GOMP_TARGET_OFFLOAD_DISABLED;
}
while (isspace ((unsigned char) *env))
++env;
- if (found && *env == '\0')
+ if (new_offload != -1 && *env == '\0')
{
*offload = new_offload;
return;
Jakub
Re: [PATCH] openmp: Implement support for OMP_TARGET_OFFLOAD
Hi Tobias, > On 10/19/20 8:21 PM, Jakub Jelinek via Gcc-patches wrote: > >> On Mon, Oct 19, 2020 at 06:57:49PM +0100, Kwok Cheung Yeung wrote: >>> --- a/libgomp/target.c >>> +++ b/libgomp/target.c > ... >> Otherwise LGTM. > > Unfortunately, the committed patch > (r11-4121-g1bfc07d150790fae93184a79a7cce897655cb37b) > causes build errors. the patch also breaks bootstrap on both i386-pc-solaris2.11 and sparc-sun-solaris2.11: /vol/gcc/src/hg/master/local/libgomp/env.c: In function 'initialize_env': /vol/gcc/src/hg/master/local/libgomp/env.c:414:16: error: 'new_offload' may be used uninitialized in this function [-Werror=maybe-uninitialized] 414 | *offload = new_offload; | ~^ /vol/gcc/src/hg/master/local/libgomp/env.c:384:30: note: 'new_offload' was declared here 384 | enum gomp_target_offload_t new_offload; | ^~~ Rainer -- - Rainer Orth, Center for Biotechnology, Bielefeld University
Re: [PATCH] openmp: Implement support for OMP_TARGET_OFFLOAD
On Tue, Oct 20, 2020 at 02:17:26PM +0200, Tobias Burnus wrote:
> On 10/20/20 2:11 PM, Tobias Burnus wrote:
>
> > Unfortunately, the committed patch
> > (r11-4121-g1bfc07d150790fae93184a79a7cce897655cb37b)
> > causes build errors.
> >
> > The error seems to be provoked by function cloning – as the code
> > itself looks fine:
> > ...
> > struct gomp_device_descr *devices_s
> > = malloc (num_devices * sizeof (struct gomp_device_descr));
> > ...
> > for (i = 0; i < num_devices; i++)
> > if (!(devices[i].capabilities & GOMP_OFFLOAD_CAP_OPENMP_400))
> > devices_s[num_devices_after_openmp++] = devices[i];
>
> gomp_target_init.part.0 ()
> {
> ...
>
> devices_s_1 = malloc (0);
> ...
> num_devices.16_67 = num_devices;
> ...
> if (num_devices.16_67 > 0)
> goto ; [89.00%]
> else
> goto ; [11.00%]
>
> Which seems to have an ordering problem.
This patch fixes the warning that breaks the bootstrap, but haven't
tested it with offloading to see if it doesn't break offloading somehow.
2020-10-20 Jakub Jelinek
* target.c (gomp_target_init): Inside of the function, use automatic
variables corresponding to num_devices, num_devices_openmp and devices
global variables and update the globals only at the end of the
function.
--- libgomp/target.c.jj 2020-10-20 14:37:36.630967911 +0200
+++ libgomp/target.c2020-10-20 14:52:36.556023803 +0200
@@ -3279,10 +3279,9 @@ gomp_target_init (void)
const char *suffix = SONAME_SUFFIX (1);
const char *cur, *next;
char *plugin_name;
- int i, new_num_devices;
-
- num_devices = 0;
- devices = NULL;
+ int i, new_num_devs;
+ int num_devs = 0, num_devs_openmp;
+ struct gomp_device_descr *devs = NULL;
if (gomp_target_offload_var == GOMP_TARGET_OFFLOAD_DISABLED)
return;
@@ -3303,7 +3302,7 @@ gomp_target_init (void)
plugin_name = (char *) malloc (prefix_len + cur_len + suffix_len + 1);
if (!plugin_name)
{
- num_devices = 0;
+ num_devs = 0;
break;
}
@@ -3313,16 +3312,16 @@ gomp_target_init (void)
if (gomp_load_plugin_for_device (_device, plugin_name))
{
- new_num_devices = current_device.get_num_devices_func ();
- if (new_num_devices >= 1)
+ new_num_devs = current_device.get_num_devices_func ();
+ if (new_num_devs >= 1)
{
/* Augment DEVICES and NUM_DEVICES. */
- devices = realloc (devices, (num_devices + new_num_devices)
- * sizeof (struct gomp_device_descr));
- if (!devices)
+ devs = realloc (devs, (num_devs + new_num_devs)
+ * sizeof (struct gomp_device_descr));
+ if (!devs)
{
- num_devices = 0;
+ num_devs = 0;
free (plugin_name);
break;
}
@@ -3332,12 +3331,12 @@ gomp_target_init (void)
current_device.type = current_device.get_type_func ();
current_device.mem_map.root = NULL;
current_device.state = GOMP_DEVICE_UNINITIALIZED;
- for (i = 0; i < new_num_devices; i++)
+ for (i = 0; i < new_num_devs; i++)
{
current_device.target_id = i;
- devices[num_devices] = current_device;
- gomp_mutex_init ([num_devices].lock);
- num_devices++;
+ devs[num_devs] = current_device;
+ gomp_mutex_init ([num_devs].lock);
+ num_devs++;
}
}
}
@@ -3349,34 +3348,37 @@ gomp_target_init (void)
/* In DEVICES, sort the GOMP_OFFLOAD_CAP_OPENMP_400 ones first, and set
NUM_DEVICES_OPENMP. */
- struct gomp_device_descr *devices_s
-= malloc (num_devices * sizeof (struct gomp_device_descr));
- if (!devices_s)
+ struct gomp_device_descr *devs_s
+= malloc (num_devs * sizeof (struct gomp_device_descr));
+ if (!devs_s)
{
- num_devices = 0;
- free (devices);
- devices = NULL;
+ num_devs = 0;
+ free (devs);
+ devs = NULL;
}
- num_devices_openmp = 0;
- for (i = 0; i < num_devices; i++)
-if (devices[i].capabilities & GOMP_OFFLOAD_CAP_OPENMP_400)
- devices_s[num_devices_openmp++] = devices[i];
- int num_devices_after_openmp = num_devices_openmp;
- for (i = 0; i < num_devices; i++)
-if (!(devices[i].capabilities & GOMP_OFFLOAD_CAP_OPENMP_400))
- devices_s[num_devices_after_openmp++] = devices[i];
- free (devices);
- devices = devices_s;
+ num_devs_openmp = 0;
+ for (i = 0; i < num_devs; i++)
+if (devs[i].capabilities & GOMP_OFFLOAD_CAP_OPENMP_400)
+ devs_s[num_devs_openmp++] = devs[i];
+ int num_devs_after_openmp = num_devs_openmp;
+ for (i = 0; i < num_devs; i++)
+if (!(devs[i].capabilities
Re: [PATCH] openmp: Implement support for OMP_TARGET_OFFLOAD
On 10/20/20 2:11 PM, Tobias Burnus wrote:
Unfortunately, the committed patch
(r11-4121-g1bfc07d150790fae93184a79a7cce897655cb37b)
causes build errors.
The error seems to be provoked by function cloning – as the code
itself looks fine:
...
struct gomp_device_descr *devices_s
= malloc (num_devices * sizeof (struct gomp_device_descr));
...
for (i = 0; i < num_devices; i++)
if (!(devices[i].capabilities & GOMP_OFFLOAD_CAP_OPENMP_400))
devices_s[num_devices_after_openmp++] = devices[i];
gomp_target_init.part.0 ()
{
...
devices_s_1 = malloc (0);
...
num_devices.16_67 = num_devices;
...
if (num_devices.16_67 > 0)
goto ; [89.00%]
else
goto ; [11.00%]
Which seems to have an ordering problem.
Tobias
-
Mentor Graphics (Deutschland) GmbH, Arnulfstraße 201, 80634 München / Germany
Registergericht München HRB 106955, Geschäftsführer: Thomas Heurung, Alexander
Walter
Re: [PATCH] openmp: Implement support for OMP_TARGET_OFFLOAD
On 10/19/20 8:21 PM, Jakub Jelinek via Gcc-patches wrote:
On Mon, Oct 19, 2020 at 06:57:49PM +0100, Kwok Cheung Yeung wrote:
--- a/libgomp/target.c
+++ b/libgomp/target.c
...
Otherwise LGTM.
Unfortunately, the committed patch
(r11-4121-g1bfc07d150790fae93184a79a7cce897655cb37b)
causes build errors.
The error seems to be provoked by function cloning – as the code
itself looks fine:
static void
gomp_target_init (void)
{
...
num_devices = 0;
...
// NEW LINES:
if (gomp_target_offload_var == GOMP_TARGET_OFFLOAD_DISABLED)
return;
...
struct gomp_device_descr *devices_s
= malloc (num_devices * sizeof (struct gomp_device_descr));
...
for (i = 0; i < num_devices; i++)
if (!(devices[i].capabilities & GOMP_OFFLOAD_CAP_OPENMP_400))
devices_s[num_devices_after_openmp++] = devices[i];
I fail so see why this gives now the -Werror warning:
../../../repos/gcc/libgomp/target.c: In function ‘gomp_target_init.part.0’:
../../../repos/gcc/libgomp/target.c:3367:45: error: array subscript
[-27450512014448737, 27450512014448737] is outside array bounds of ‘struct
gomp_device_descr[0]’ [-Werror=array-bounds]
3367 | devices_s[num_devices_after_openmp++] = devices[i];
| ~~^~~~
../../../repos/gcc/libgomp/target.c:3353:7: note: referencing an object of size
0 allocated by ‘malloc’
3353 | = malloc (num_devices * sizeof (struct gomp_device_descr));
| ^~~~
../../../repos/gcc/libgomp/target.c:3363:39: error: array subscript
[-27450512014448737, 27450512014448737] is outside array bounds of ‘struct
gomp_device_descr[0]’ [-Werror=array-bounds]
3363 | devices_s[num_devices_openmp++] = devices[i];
| ^~~~
../../../repos/gcc/libgomp/target.c:3353:7: note: referencing an object of size
0 allocated by ‘malloc’
3353 | = malloc (num_devices * sizeof (struct gomp_device_descr));
| ^~~~
Tobias
-
Mentor Graphics (Deutschland) GmbH, Arnulfstraße 201, 80634 München / Germany
Registergericht München HRB 106955, Geschäftsführer: Thomas Heurung, Alexander
Walter
Re: [PATCH] openmp: Implement support for OMP_TARGET_OFFLOAD
On Mon, Oct 19, 2020 at 06:57:49PM +0100, Kwok Cheung Yeung wrote:
> --- a/libgomp/env.c
> +++ b/libgomp/env.c
> @@ -75,6 +75,7 @@ struct gomp_task_icv gomp_global_icv = {
>
> unsigned long gomp_max_active_levels_var = gomp_supported_active_levels;
> bool gomp_cancel_var = false;
> +enum gomp_target_offload_t gomp_target_offload_var =
> GOMP_TARGET_OFFLOAD_DEFAULT;
Too long line.
> --- a/libgomp/target.c
> +++ b/libgomp/target.c
> @@ -116,7 +116,13 @@ resolve_device (int device_id)
> }
>
>if (device_id < 0 || device_id >= gomp_get_num_devices ())
> -return NULL;
> +{
> + if (gomp_target_offload_var == GOMP_TARGET_OFFLOAD_MANDATORY
> + && device_id != GOMP_DEVICE_HOST_FALLBACK)
> + gomp_fatal ("OMP_TARGET_OFFLOAD is set to MANDATORY, but device not
> found.");
No full stop at the end of gomp_fatal messages (everywhere in your patch)
for consistency with other gomp_fatal calls. Also, too long line (similarly
other gomp_fatal calls). Just use
gomp_fatal (" . ... "
"..");
Otherwise LGTM.
Jakub
Re: [PATCH] openmp: Implement support for OMP_TARGET_OFFLOAD
On 15/10/2020 12:02 pm, Jakub Jelinek wrote:
On Thu, Oct 15, 2020 at 12:50:18PM +0200, Jakub Jelinek via Gcc-patches wrote:
Ok, the first response indicates that both if (false) and
omp_get_initial_device () are valid.
Therefore, I think until omp_get_initial_device () value is changed, we
want in resolve_device:
if (device_id < 0 || device_id >= gomp_get_num_devices ())
{
if (device_id != GOMP_DEVICE_HOST_FALLBACK)
gomp_fatal (...);
return NULL;
}
and do gomp_fatal also for further return NULLs in the function.
And then in
if (devicep == NULL
|| !(devicep->capabilities & GOMP_OFFLOAD_CAP_OPENMP_400)
/* All shared memory devices should use the GOMP_target_ext function. */
|| devicep->capabilities & GOMP_OFFLOAD_CAP_SHARED_MEM
|| !(fn_addr = gomp_get_target_fn_addr (devicep, fn)))
return gomp_target_fallback (fn, hostaddrs);
and similar do gomp_fatal before the gomp_target_fallback call
if target-offload-var ICV is mandatory and devicep != NULL.
Instead of doing a gomp_fatal before every call to
gomp_target_fallback/gomp_target_data_fallback, I think it would be tidier to
pass devicep into the fallback instead and keep the gomp_fatals in the fallback
functions? Although it is kind of odd to pass the device to the fallback
function to be used if the device in question does not work, but at least the
fallback functions are static to target.c.
Is this version okay for trunk?
Thanks
Kwok
commit 82555f50d2930f973ab20782ebcb836b719bce96
Author: Kwok Cheung Yeung
Date: Mon Oct 19 10:47:42 2020 -0700
openmp: Implement support for OMP_TARGET_OFFLOAD environment variable
This implements support for the OMP_TARGET_OFFLOAD environment variable
introduced in the OpenMP 5.0 standard, which controls how offloading
is handled. It may be set to MANDATORY (abort if offloading cannot be
performed), DISABLED (no offloading to devices) or DEFAULT (offload to
device if possible, fall back to host if not).
2020-10-19 Kwok Cheung Yeung
libgomp/
* env.c (gomp_target_offload_var): New.
(parse_target_offload): New.
(handle_omp_display_env): Print value of OMP_TARGET_OFFLOAD.
(initialize_env): Parse OMP_TARGET_OFFLOAD.
* libgomp.h (gomp_target_offload_t): New.
(gomp_target_offload_var): New.
* libgomp.texi (OMP_TARGET_OFFLOAD): New section.
* target.c (resolve_device): Generate error if device not found and
offloading is mandatory.
(gomp_target_fallback): Generate error if offloading is mandatory.
(GOMP_target): Add argument in call to gomp_target_fallback.
(GOMP_target_ext): Likewise.
(gomp_target_data_fallback): Generate error if offloading is mandatory.
(GOMP_target_data): Add argument in call to gomp_target_data_fallback.
(GOMP_target_data_ext): Likewise.
(gomp_target_task_fn): Add argument in call to gomp_target_fallback.
(gomp_target_init): Return early if offloading is disabled.
diff --git a/libgomp/env.c b/libgomp/env.c
index d730c48..d0eae8d 100644
--- a/libgomp/env.c
+++ b/libgomp/env.c
@@ -75,6 +75,7 @@ struct gomp_task_icv gomp_global_icv = {
unsigned long gomp_max_active_levels_var = gomp_supported_active_levels;
bool gomp_cancel_var = false;
+enum gomp_target_offload_t gomp_target_offload_var =
GOMP_TARGET_OFFLOAD_DEFAULT;
int gomp_max_task_priority_var = 0;
#ifndef HAVE_SYNC_BUILTINS
gomp_mutex_t gomp_managed_threads_lock;
@@ -374,6 +375,48 @@ parse_unsigned_long_list (const char *name, unsigned long
*p1stvalue,
return false;
}
+static void
+parse_target_offload (const char *name, enum gomp_target_offload_t *offload)
+{
+ const char *env;
+ bool found = false;
+ enum gomp_target_offload_t new_offload;
+
+ env = getenv (name);
+ if (env == NULL)
+return;
+
+ while (isspace ((unsigned char) *env))
+++env;
+ if (strncasecmp (env, "default", 7) == 0)
+{
+ env += 7;
+ found = true;
+ new_offload = GOMP_TARGET_OFFLOAD_DEFAULT;
+}
+ else if (strncasecmp (env, "mandatory", 9) == 0)
+{
+ env += 9;
+ found = true;
+ new_offload = GOMP_TARGET_OFFLOAD_MANDATORY;
+}
+ else if (strncasecmp (env, "disabled", 8) == 0)
+{
+ env += 8;
+ found = true;
+ new_offload = GOMP_TARGET_OFFLOAD_DISABLED;
+}
+ while (isspace ((unsigned char) *env))
+++env;
+ if (found && *env == '\0')
+{
+ *offload = new_offload;
+ return;
+}
+
+ gomp_error ("Invalid value for environment variable OMP_TARGET_OFFLOAD");
+}
+
/* Parse environment variable set to a boolean or list of omp_proc_bind_t
enum values. Return true if one was present and it was successfully
parsed. */
@@ -1334,6 +1377,21 @@ handle_omp_display_env (unsigned long stacksize, int
wait_policy)
}
fputs ("'\n", stderr);
+ fputs (" OMP_TARGET_OFFLOAD = '", stderr);
+ switch
Re: [PATCH] openmp: Implement support for OMP_TARGET_OFFLOAD
On Thu, Oct 15, 2020 at 12:50:18PM +0200, Jakub Jelinek via Gcc-patches wrote:
> If nothing of this is valid (i.e. mandatory forbids all the fallback), then
> your patch implements it, but if e.g. only if (false) is allowed and nothing
> else, then we are ATM in trouble (we pass -2 for if false as well as it is
> returned from omp_get_initial_device (); thankfully, OpenMP 5.0 changed it
> (something that should be implemented in libgomp too), so that
> omp_get_initial_device () is now required to be omp_get_num_devices (),
> i.e. the host device is always the last one; so, we would do fallback
> for -2 and not for anything else), if also omp_get_initial_device ()
> number is valid, then we should allow fallback for devices -2 and
> omp_get_initial_device () and punt on everything else.
Ok, the first response indicates that both if (false) and
omp_get_initial_device () are valid.
Therefore, I think until omp_get_initial_device () value is changed, we
want in resolve_device:
if (device_id < 0 || device_id >= gomp_get_num_devices ())
{
if (device_id != GOMP_DEVICE_HOST_FALLBACK)
gomp_fatal (...);
return NULL;
}
and do gomp_fatal also for further return NULLs in the function.
And then in
if (devicep == NULL
|| !(devicep->capabilities & GOMP_OFFLOAD_CAP_OPENMP_400)
/* All shared memory devices should use the GOMP_target_ext function. */
|| devicep->capabilities & GOMP_OFFLOAD_CAP_SHARED_MEM
|| !(fn_addr = gomp_get_target_fn_addr (devicep, fn)))
return gomp_target_fallback (fn, hostaddrs);
and similar do gomp_fatal before the gomp_target_fallback call
if target-offload-var ICV is mandatory and devicep != NULL.
And when we change omp_get_initial_device (), we'd use
device_id > gomp_get_num_devices () above instead, and
call gomp_fatal there only for
(device_id != GOMP_DEVICE_HOST_FALLBACK
&& device_id != gomp_get_num_devices ())
Jakub
Re: [PATCH] openmp: Implement support for OMP_TARGET_OFFLOAD
On Wed, Oct 14, 2020 at 09:32:42PM +0100, Kwok Cheung Yeung wrote:
> I'm not sure how this can be tested automatically, as the behaviour depends
> on whether the compiler has been built with offloading support, and whether
> any supported offloading hardware has been installed on the system. I have
> not included any testcases for now.
Not testing it is probably fine, unless we added some effective targets
that the test would be run only if the offloading is (or is not present) and
we would expect failures etc.
I'm really not sure what the behavior should be in various cases though,
so I've asked on omp-lang and will see what the committee members think.
The fuzzy things are e.g.:
void foo () {}
#pragma omp declare target to (foo)
int
main ()
{
#pragma omp target if(false)
foo (); // Is this ok?
omp_set_default_device (omp_get_initial_device ());
#pragma omp target
foo (); // What about this?
#pragma omp target device (omp_get_initial_device ())
foo (); // Or this?
#pragma omp target device (omp_get_num_devices () + 42)
foo (); // This one is clearly an error
if (omp_get_num_devices () == 3)
{
#pragma omp target device (1)
foo (); // This would be an error if we can't offload to device 1
}
}
Also, what about the case where there are no offloading devices at all,
so the default device defaults to the initial device number?
If nothing of this is valid (i.e. mandatory forbids all the fallback), then
your patch implements it, but if e.g. only if (false) is allowed and nothing
else, then we are ATM in trouble (we pass -2 for if false as well as it is
returned from omp_get_initial_device (); thankfully, OpenMP 5.0 changed it
(something that should be implemented in libgomp too), so that
omp_get_initial_device () is now required to be omp_get_num_devices (),
i.e. the host device is always the last one; so, we would do fallback
for -2 and not for anything else), if also omp_get_initial_device ()
number is valid, then we should allow fallback for devices -2 and
omp_get_initial_device () and punt on everything else.
Jakub
