On Wednesday, 17 November 2021 19:25:46 CET Jason Merrill wrote:
> On 11/17/21 04:04, Matthias Kretz wrote:
> > On Wednesday, 17 November 2021 07:09:18 CET Jason Merrill wrote:
> >>> - if (CHECKING_P)
> >>> - SET_NON_DEFAULT_TEMPLATE_ARGS_COUNT (a, TREE_VEC_LENGTH (a));
> >>> + SET_NON_DEFAULT_TEMPLATE_ARGS_COUNT (a, nondefault);
> >>
> >> should have been
> >>
> >> if (CHECKING_P || nondefault != TREE_VEC_LENGTH (a))
> >>
> >> SET_NON_DEFAULT_TEMPLATE_ARGS_COUNT (a, nondefault);
> >
> > TBH, I don't understand the purpose of CHECKING_P here, or rather it makes
> > me nervous because AFAIU I'm only testing with CHECKING_P enabled. Why
> > make behavior dependent on CHECKING_P? I expected CHECKING_P to basically
> > only add more assertions.
>
> The idea when NON_DEFAULT_TEMPLATE_ARGS_COUNT was added years back was
> to leave the TREE_CHAIN null when !CHECKING_P and treat that as
> equivalent to TREE_VEC_LENGTH (args). But perhaps you're right that
> it's not a savings worth the complexity.
Thanks, now I understand.
> >>> (copy_template_args): Jason?
> >>
> >> Only copy the non-default template args count on TREE_VECs that should
> >> have it.
> >
> > Why not simply set the count on all args? Is it a performance concern? The
> > INTEGER_CST the TREE_CHAIN has to point to exists anyway, so it's not
> > wasting any memory, right?
>
> In this case the TREE_VEC we're excluding is the one wrapping multiple
> levels of template args; it doesn't contain args directly, so setting
> NON_DEFAULT_ARGS_COUNT on it doesn't make sense.
Right, I had already added a `gcc_assert (!TMPL_ARGS_HAVE_MULTIPLE_LEVELS
(args))` to my new set_non_default_template_args_count function and found cp/
constraint.cc:2896 (get_mapped_args), which calls
SET_NON_DEFAULT_TEMPLATE_ARGS_COUNT on the outer TREE_VEC. Was this supposed
to apply to all inner TREE_VECs? Or is deleting the line the correct fix?
> >>> + /* Pretty print only template instantiations. Don't pretty print
> >>> explicit
> >>> + specializations like 'template <> void fun<int> (int)'.
> >>
> >> This seems like a significant change of behavior unrelated to printing
> >> default template arguments. What's the rationale for handling
> >> specializations differently from instantiations?
> >
> > Right, this is about "The general idea of this change is to print template
> > parms wherever they would appear in the source code as well".
> >
> > Initially, the change to print function template arguments/parameters only
> > if the args were explicitly specified lead to printing 'void fun (T)
> > [with T = ...]' or 'template <> void fun (int)'. Both are not telling the
> > full story, even if the former is how the function would be called.
>
> and the latter is how I expect the specialization to be declared, not
> with the deducible template argument made explicit.
You're right. From my tests:
template <class a>
[[deprecated]] void f4(a);
template <>
[[deprecated]] void f4<int>(int);
template <>
[[deprecated]] void f4(float);
f4(1.); // { dg-warning "'void f4\\(a\\) .with a = double.'" }
f4(1); // { dg-warning "'void f4<int>\\(int\\)'" }
f4(1.f); // { dg-warning "'void f4\\(float\\)'" }
So how it's printed depends on how the specialization is declared. It just
falls out that way and it didn't seem awfully wrong... ;)
> > But if the reader
> > should quickly recognize what code is getting called, it is helpful to see
> > right away that a function template specialization is called. (It might
> > also reveal an implementation detail of a library, so it's not 100%
> > obvious how to choose here.) Also, saying 'T = int' is kind of wrong.
> > Yes, 'int' was deduced. But there's no T in fun<int>:
> >
> > template <class T> void fun (T);
> > template <> void fun<int> (int);
>
> There's a T in the template, and as you said above, that's how it's
> called (and mangled).
>
> > __FUNCTION__ was 'fun<int>' all the time, but __PRETTY_FUNCTION__ was
> > 'void
> > fun(T) [with T = int]'.
>
> Isn't that true for instantiations, as well?
No, instantiations don't have template args/parms in __FUNCTION__.
> > It's more consistent that __PRETTY_FUNCTION__ contains __FUNCTION__, IMHO
>
> I suppose, but I don't see that as a strong enough motivation to mix
> this up.
What about
template <class T> void f();
template <> void f<int>();
With -fpretty-templates shouldn't it print as 'void f<T>() [with T = float]'
and 'void f<int>()'? Yes, it's probably too subtle for most users to notice
the difference. But I find it's more consistent this way.
> > so it would have to be at least 'void fun<int>(T) [with T
> > = int]'. But that's strange: How it uses T and int for the same type. So I
> > settled on 'void fun<int>(int)'.
> >
> >> I also don't understand the purpose of TFF_AS_PRIMARY.
> >
> > dump_function_decl generalizes the TEMPLATE_DECL (if flag_pretty_templates
> > is true) and, before this change, passes the generalized TEMPLATE_DECL to
> > dump_type (... DECL_CONTEXT (t) ...) and dump_function_name (... t ...).
> > That's why the whole template is printed as primary template (i.e. with
> > template parms instead of template args, as is needed for
> > flag_pretty_templates). But this drops the count of non-default template
> > args.
> Ah, you're trying to omit defaulted parms from the <list>? I'm not sure
> that's necessary, leaving them out of the [with ...] list should be
> sufficient.
I was thinking about all the std::allocator defaults in the standard library.
I don't want to see them. E.g. vector<int>::clear() on const object:
error: passing 'const std::vector<int>' as 'this' argument discards qualifiers
[...]/stl_vector.h:1498:7: note: in call to 'void std::vector<_Tp,
_Alloc>::clear() [with _Tp = int; _Alloc = std::allocator<int>]'
With my patch the last line becomes
[...]/stl_vector.h:1498:7: note: in call to 'void std::vector<_Tp>::clear()
[with _Tp = int]'
Another case I didn't consider before:
template <class T, class U = int> struct A {
[[deprecated]] void f(U);
};
A<float> a; a.f(1);
With my patch it prints 'void A<T>::f(U) [with T = float]', with your
suggestion 'void A<T, U>::f(U) [with T = float]'. Both are missing important
information in the substitution list, IMHO. Would 'void A<T, U = int>::f(U)
[with T = float]' be an improvement? Or should find_typenames (in cp/error.c)
find defaulted template parms and add them to its list? IIUC find_typenames
would find all template parms and couldn't know whether they're defaulted.
> >>> + 4. either
> >>> + - flags requests to show no function arguments, in which case
> >>> deduced + types could be hidden, or
> >>> + - at least one function template argument was given explicitly,
> >>> or
> >>> + - we're printing a DWARF name,
> >>
> >> Though, why do we want
> >> different behavior here when printing a DWARF name?
> >
> > Sorry, I should have asked ... I also added the same issue as an open
> > question on the diagnose_as patch. When I ran the whole testsuite I had
> > failures in the DWARF tests. This change resolved them. I don't know
> > enough about how those strings are used and whether they may change
> > between GCC versions. Anyway, the DWARF strings in that test had only the
> > function name and template argument list (i.e. no function arguments).
>
> If they only have arguments, isn't TFF_NO_FUNCTION_ARGUMENTS set?
No, it isn't set. I could try to set it for DWARF names. It sounds like the
right solution here.
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Dr. Matthias Kretz https://mattkretz.github.io
GSI Helmholtz Centre for Heavy Ion Research https://gsi.de
stdₓ::simd
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