On 7/14/21 10:23 AM, Jason Merrill wrote:
> On 7/14/21 10:46 AM, Martin Sebor wrote:
>> On 7/13/21 9:39 PM, Jason Merrill wrote:
>>> On 7/13/21 4:02 PM, Martin Sebor wrote:
>>>> On 7/13/21 12:37 PM, Jason Merrill wrote:
>>>>> On 7/13/21 10:08 AM, Jonathan Wakely wrote:
>>>>>> On Mon, 12 Jul 2021 at 12:02, Richard Biener wrote:
>>>>>>> Somebody with more C++ knowledge than me needs to approve the
>>>>>>> vec.h changes - I don't feel competent to assess all effects of 
>>>>>>> the change.
>>>>>>
>>>>>> They look OK to me except for:
>>>>>>
>>>>>> -extern vnull vNULL;
>>>>>> +static constexpr vnull vNULL{ };
>>>>>>
>>>>>> Making vNULL have static linkage can make it an ODR violation to use
>>>>>> vNULL in templates and inline functions, because different
>>>>>> instantiations will refer to a different "vNULL" in each translation
>>>>>> unit.
>>>>>
>>>>> The ODR says this is OK because it's a literal constant with the 
>>>>> same value (6.2/12.2.1).
>>>>>
>>>>> But it would be better without the explicit 'static'; then in C++17 
>>>>> it's implicitly inline instead of static.
>>>>
>>>> I'll remove the static.
>>>>
>>>>>
>>>>> But then, do we really want to keep vNULL at all?  It's a weird 
>>>>> blurring of the object/pointer boundary that is also dependent on 
>>>>> vec being a thin wrapper around a pointer.  In almost all cases it 
>>>>> can be replaced with {}; one exception is == comparison, where it 
>>>>> seems to be testing that the embedded pointer is null, which is a 
>>>>> weird thing to want to test.
>>>>
>>>> The one use case I know of for vNULL where I can't think of
>>>> an equally good substitute is in passing a vec as an argument by
>>>> value.  The only way to do that that I can think of is to name
>>>> the full vec type (i.e., the specialization) which is more typing
>>>> and less generic than vNULL.  I don't use vNULL myself so I wouldn't
>>>> miss this trick if it were to be removed but others might feel
>>>> differently.
>>>
>>> In C++11, it can be replaced by {} in that context as well.
>>
>> Cool.  I thought I'd tried { } here but I guess not.
>>
>>>
>>>> If not, I'm all for getting rid of vNULL but with over 350 uses
>>>> of it left, unless there's some clever trick to make the removal
>>>> (mostly) effortless and seamless, I'd much rather do it independently
>>>> of this initial change. I also don't know if I can commit to making
>>>> all this cleanup.
>>>
>>> I already have a patch to replace all but one use of vNULL, but I'll 
>>> hold off with it until after your patch.
>>
>> So what's the next step?  The patch only removes a few uses of vNULL
>> but doesn't add any.  Is it good to go as is (without the static and
>> with the additional const changes Richard suggested)?  This patch is
>> attached to my reply to Richard:
>> https://gcc.gnu.org/pipermail/gcc-patches/2021-July/575199.html
> 
> As Richard wrote:
> 
>> The pieces where you change vec<> passing to const vec<>& and the few
>> where you change vec<> * to const vec<> * are OK - this should make the
>> rest a smaller piece to review.
> 
> Please go ahead and apply those changes and send a new patch with the 
> remainder of the changes.

I have just pushed r12-2418:
https://gcc.gnu.org/pipermail/gcc-cvs/2021-July/350886.html

> 
> A few other comments:
> 
>> -                       omp_declare_simd_clauses);
>> +                       *omp_declare_simd_clauses);
> 
> Instead of doing this indirection in all of the callers, let's change 
> c_finish_omp_declare_simd to take a pointer as well, and do the 
> indirection in initializing a reference variable at the top of the 
> function.

Okay.

> 
>> +    sched_init_luids (bbs.to_vec ());
>> +    haifa_init_h_i_d (bbs.to_vec ());
> 
> Why are these to_vec changes needed when you are also changing the 
> functions to take const&?

Calling to_vec() here isn't necessary so I've removed it.

> 
>> -  vec<tree> checks = LOOP_VINFO_CHECK_NONZERO (loop_vinfo);
>> +  vec<tree> checks = LOOP_VINFO_CHECK_NONZERO (loop_vinfo).to_vec ();
> 
> Why not use a reference here and in other similar spots?

Sure, that works too.

Attached is what's left of the original changes now that r12-2418
has been applied.

Martin