Richard Biener <rguent...@suse.de> writes:
> On Mon, 29 Aug 2022, Martin Jambor wrote:
>
>> Hi,
>>
>> On Mon, Aug 29 2022, Richard Biener wrote:
>> > On Mon, 29 Aug 2022, Martin Jambor wrote:
>> >
>> >> Hi again,
>> >>
>> >> On Mon, Aug 29 2022, Richard Biener wrote:
>> >> > On Fri, 26 Aug 2022, Martin Jambor wrote:
>> >> >
>> >> >> Hi,
>> >> >>
>> >> >> On Fri, Aug 26 2022, Richard Biener wrote:
>> >> >> >> Am 26.08.2022 um 18:39 schrieb Martin Jambor <mjam...@suse.cz>:
>> >> >> >>
>> >> >> >> Hi,
>> >> >> >>
>> >> >> >> This patch adds constructors of array_slice that are required to
>> >> >> >> create them from non-const (heap or auto) vectors or from GC
>> >> >> >> vectors.
>> >> >> >>
>> >> >> >> The use of non-const array_slices is somewhat limited, as creating
>> >> >> >> one
>> >> >> >> from const vec<some_type> still leads to array_slice<const
>> >> >> >> some_type>,
>> >> >> >> so I eventually also only resorted to having read-only array_slices.
>> >> >> >> But I do need the constructor from the gc vector.
>> >> >> >>
>> >> >> >> Bootstrapped and tested along code that actually uses it on
>> >> >> >> x86_64-linux. OK for trunk?
>> >> >> >>
>> >> >> >> Thanks,
>> >> >> >>
>> >> >> >> Martin
>> >> >> >>
>> >> >> >>
>> >> >> >> gcc/ChangeLog:
>> >> >> >>
>> >> >> >> 2022-08-08 Martin Jambor <mjam...@suse.cz>
>> >> >> >>
>> >> >> >> * vec.h (array_slice): Add constructors for non-const reference
>> >> >> >> to
>> >> >> >> heap vector and pointers to heap vectors.
>> >> >> >> ---
>> >> >> >> gcc/vec.h | 12 ++++++++++++
>> >> >> >> 1 file changed, 12 insertions(+)
>> >> >> >>
>> >> >> >> diff --git a/gcc/vec.h b/gcc/vec.h
>> >> >> >> index eed075addc9..b0477e1044c 100644
>> >> >> >> --- a/gcc/vec.h
>> >> >> >> +++ b/gcc/vec.h
>> >> >> >> @@ -2264,6 +2264,18 @@ public:
>> >> >> >> array_slice (const vec<OtherT> &v)
>> >> >> >> : m_base (v.address ()), m_size (v.length ()) {}
>> >> >> >>
>> >> >> >> + template<typename OtherT>
>> >> >> >> + array_slice (vec<OtherT> &v)
>> >> >> >> + : m_base (v.address ()), m_size (v.length ()) {}
>> >> >> >> +
>> >> >> >> + template<typename OtherT>
>> >> >> >> + array_slice (const vec<OtherT, va_gc> *v)
>> >> >> >> + : m_base (v ? v->address () : nullptr), m_size (v ? v->length
>> >> >> >> () : 0) {}
>> >> >> >> +
>> >> >> >> + template<typename OtherT>
>> >> >> >> + array_slice (vec<OtherT, va_gc> *v)
>> >> >> >> + : m_base (v ? v->address () : nullptr), m_size (v ? v->length
>> >> >> >> () : 0) {}
>> >> >> >> +
>> >> >> >
>> >> >> > I don?t quite understand why the generic ctor doesn?t cover the GC
>> >> >> > case. It looks more like reference vs pointer?
>> >> >> >
>> >> >>
>> >> >> If you think that this should work:
>> >> >>
>> >> >> vec<tree, va_gc> *heh = cfun->local_decls;
>> >> >> array_slice<tree> arr_slice (*heh);
>> >> >>
>> >> >> then it does not:
>> >> >>
>> >> >> /home/mjambor/gcc/mine/src/gcc/ipa-cp.cc:6693:36: error: no matching
>> >> >> function for call to
>> >> >> ?array_slice<tree_node*>::array_slice(vec<tree_node*, va_gc>&)?
>> >> >> 6693 | array_slice<tree> arr_slice (*heh);
>> >> >> | ^
>> >> >> In file included from
>> >> >> /home/mjambor/gcc/mine/src/gcc/hash-table.h:248,
>> >> >> from /home/mjambor/gcc/mine/src/gcc/coretypes.h:486,
>> >> >> from /home/mjambor/gcc/mine/src/gcc/ipa-cp.cc:105:
>> >> >> /home/mjambor/gcc/mine/src/gcc/vec.h:2264:3: note: candidate:
>> >> >> ?template<class OtherT> array_slice<T>::array_slice(const
>> >> >> vec<OtherT>&) [with T = tree_node*]?
>> >> >> 2264 | array_slice (const vec<OtherT> &v)
>> >> >> | ^~~~~~~~~~~
>> >> >> /home/mjambor/gcc/mine/src/gcc/vec.h:2264:3: note: template
>> >> >> argument deduction/substitution failed:
>> >> >> /home/mjambor/gcc/mine/src/gcc/ipa-cp.cc:6693:36: note: mismatched
>> >> >> types ?va_heap? and ?va_gc?
>> >> >> 6693 | array_slice<tree> arr_slice (*heh);
>> >> >> | ^
>> >> >>
>> >> >> [... I trimmed notes about all other candidates...]
>> >> >>
>> >> >> Or did you mean something else?
>> >> >
>> >> > Hmm, so what if you change
>> >> >
>> >> > template<typename OtherT>
>> >> > array_slice (const vec<OtherT> &v)
>> >> > : m_base (v.address ()), m_size (v.length ()) {}
>> >> >
>> >> > to
>> >> >
>> >> > template<typename OtherT, typename l, typename a>
>> >> > array_slice (const vec<OtherT, l, a> &v)
>> >> > : m_base (v.address ()), m_size (v.length ()) {}
>> >> >
>> >> > instead? Thus allow any allocation / placement template arg?
>> >> >
>> >>
>> >> So being fully awake helps, the issue was of course in how I tested the
>> >> code, the above works fine and I can adapt my code to use that.
>> >>
>> >> However, is it really preferable?
>> >>
>> >> We often use NULL as to mean zero-length vector, which my code handled
>> >> gracefully:
>> >>
>> >> + template<typename OtherT>
>> >> + array_slice (const vec<OtherT, va_gc> *v)
>> >> + : m_base (v ? v->address () : nullptr), m_size (v ? v->length () :
>> >> 0) {}
>> >>
>> >> whereas using the generic method will mean that users constructing the
>> >> vector will have to special case it - and I bet most will end up using
>> >> the above sequence and the constructor from explicit pointer and size in
>> >> all constructors from gc vectors.
>> >>
>> >> So, should I really change the patch and my code?
>> >
>> > Well, it's also inconsistent with a supposed use like
>> >
>> > vec<tree> *v = NULL;
>> > auto slice = array_slice (v);
>> >
>> > no? So, if we want to provide a "safe" (as in, handle NULL pointer)
>> > CTOR, don't we want to handle non-GC allocated vectors the same way?
>> >
>>
>> Our safe_* functions usually do no work with normal non-GC vectors
>> (which are not vl_embed), they do not accept them. I guess that is
>> because that is not how we use normal vectors, we usually pass around
>> vNULL to mean empty vector of that type. So I'd at least be consistent
>> with our inconsistencies.
>>
>> But whatever, I can have both reference and pointer template
>> constructors, I can resort to constructing them from v->address() and
>> v->length() too. I do not care much, I guess I trust your sense of code
>> esthetics more than mine, just please let me know what you prefer and
>> I'll go with that.
>>
>> > Btw, we have
>> >
>> > template<size_t N>
>> > array_slice (T (&array)[N]) : m_base (array), m_size (N) {}
>> >
>> > which would suggest handling NULL isn't desired(?)
>> >
>>
>> That is not how I read for example:
>>
>> // True if the array is valid, false if it is an array like INVALID.
>> bool is_valid () const { return m_base || m_size == 0; }
>>
>> And IMHO it would be a very very strange limitation too.
>
> I see. That said, the high number of CTORs does look a bit odd,
> but I'm fine with them if Richard is.
Yeah, the patch LGTM FWWIW. I agree it feels a bit weird to convert
"pointer to vector of T" into "array-like of T" without a dereference,
but avoiding it might be more convoluted than going with the flow.
It doesn't look like it should introduce genuine ambiguity, since the
T template parameter would always need to be specified explicitly.
(But I don't think we should have a make_array_slice for vector pointers.)
Thanks,
Richard
