GOMP: OMP 5.1: simd construct for non-pointer random access iterators

GOMP: OMP 5.1: simd construct for non-pointer random access iterators

[Grosse-Bley, Paul Leonard]

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Hi together,

I just ran into the issue that `#pragma omp simd` does not work on C++ iterator loops (godbolt).
From going through the specifications I understand that this restriction was part of 4.5 and 5.0, but was dropped with 5.1.
As I couldn't find this change in the table of 5.1 (or 5.2) features for libgomp, I wanted to ask if this is on the horizon.

Best,
Paul Große-Bley

Re: GOMP: OMP 5.1: simd construct for non-pointer random access iterators

[Jakub Jelinek]

On Thu, Dec 15, 2022 at 09:31:50PM +0100, Grosse-Bley, Paul Leonard wrote:
> 
> Hi together,
> 
> I just ran into the issue that `#pragma omp simd` does not work on C++ iterator loops (godbolt).
> >From going through the specifications I understand that this restriction was part of 4.5 and 5.0, but was dropped with 5.1.
> As I couldn't find this change in the table of 5.1 (or 5.2) features for libgomp, I wanted to ask if this is on the horizon.

That is not the case.
OpenMP 5.1 has the restriction on p. 137 l. 22:
"The only random access iterator types that are allowed for the associated loops are pointer
types."
OpenMP 5.2 has the same thing on p. 235 l. 31.
Even TR11 (first OpenMP 6.0 draft) has the same wording on p. 246 l. 2.

	Jakub

Re: GOMP: OMP 5.1: simd construct for non-pointer random access iterators

[Tobias Burnus]

Hi,

On 15.12.22 21:31, Grosse-Bley, Paul Leonard wrote:
> I just ran into the issue that `#pragma omp simd` does not work on C++ iterator loops (godbolt).
>  From going through the specifications I understand that this restriction was part of 4.5 and 5.0, but was dropped with 5.1.
I assume that it is about "non-pointer random access iterators" – as the
subject line states.

In OpenMP 5.0, there is:

"2.9.1 Canonical Loop Form":  "In the simd construct the only random
access iterator types that are allowed for var are pointer types."
[OpenMP 5.0, 100:15-16]

But I still see in OpenMP 5.1:

"2.11.5.1 simd Construct": "Restrictions to the simd construct are as
follows: ... [C++] The only random access iterator types that are
allowed for the associated loops are pointer types." [OpenMP 5.1, 137:2,
137:22].

Same words as in 5.1 are also in OpenMP 5.2 in "10.4 simd Construct"
[235:31].

Did I miss something? If so, can you provide the example?

Tobias

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