on 2021/7/20 下午5:49, Jonathan Wakely wrote:
> On Tue, 20 Jul 2021 at 09:58, Kewen.Lin <li...@linux.ibm.com> wrote:
>>
>> on 2021/7/19 下午11:59, Martin Sebor wrote:
>>> On 7/19/21 12:20 AM, Kewen.Lin wrote:
>>>> Hi,
>>>>
>>>> This patch follows Martin's suggestion here[1], to support
>>>> range-based for loops for traversing loops, analogously to
>>>> the patch for vec[2].
>>>>
>>>> Bootstrapped and regtested on powerpc64le-linux-gnu P9,
>>>> x86_64-redhat-linux and aarch64-linux-gnu, also
>>>> bootstrapped on ppc64le P9 with bootstrap-O3 config.
>>>>
>>>> Any comments are appreciated.
>>>
>>> Thanks for this nice cleanup! Just a few suggestions:
>>>
>>> I would recommend against introducing new macros unless they
>>> offer a significant advantage over alternatives (for the two
>>> macros the patch adds I don't think they do).
>>>
>>> If improving const-correctness is one of our a goals
>>> the loops_list iterator type would need to a corresponding
>>> const_iterator type, and const overloads of the begin()
>>> and end() member functions.
>>>
>>> Rather than introducing more instances of the loop_p typedef
>>> I'd suggest to use loop *. It has at least two advantages:
>>> it's clearer (it's obvious it refers to a pointer), and lends
>>> itself more readily to making code const-correct by declaring
>>> the control variable const: for (const class loop *loop: ...)
>>> while avoiding the mistake of using const loop_p loop to
>>> declare a pointer to a const loop.
>>>
>>
>> Thanks for the suggestions, Martin! Will update them in V2.
>>
>> With some experiments, I noticed that even provided const_iterator
>> like:
>>
>> iterator
>> begin ()
>> {
>> return iterator (*this, 0);
>> }
>>
>> + const_iterator
>> + begin () const
>> + {
>> + return const_iterator (*this, 0);
>> + }
>>
>> for (const class loop *loop: ...) will still use iterator instead
>> of const_iterator pair. We have to make the code look like:
>>
>> const auto& const_loops = loops_list (...);
>> for (const class loop *loop: const_loops)
>>
>> or
>> template<typename T> constexpr const T &as_const(T &t) noexcept { return
>> t; }
>> for (const class loop *loop: as_const(loops_list...))
>>
>> Does it look good to add below as_const along with loops_list in cfgloop.h?
>>
>> +/* Provide the functionality of std::as_const to support range-based for
>> + to use const iterator. (We can't use std::as_const itself because it's
>> + a C++17 feature.) */
>> +template <typename T>
>> +constexpr const T &
>> +as_const (T &t) noexcept
>
> The noexcept is not needed because GCC is built -fno-exceptions. For
> consistency with all the other code that doesn't use noexcept, it
> should probably not be there.
>
Thanks for pointing out! Fixed it in v2.
>> +{
>> + return t;
>> +}
>> +
>
> That's one option. Another option (which could coexist with as_const)
> is to add cbegin() and cend() members, which are not overloaded for
> const and non-const, and so always return a const_iterator:
>
> const_iterator cbegin () const { return const_iterator (*this, 0); }
> iterator begin () const { return cbegin(); }
>
> And similarly for `end () const` and `cend () const`.
>
Thanks for the suggestion. As you pointed out in the later reply, the
range-based for loop doesn't use cbegin and cend, so I didn't add them
in v2.
BR,
Kewen
