[v5] c++: reference tparm refers to temporary object [PR107124]
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On Wed, Jun 03, 2026 at 08:54:51AM -0400, Jason Merrill wrote:
> On 6/2/26 6:01 PM, Marek Polacek wrote:
> > On Fri, May 29, 2026 at 04:37:55PM -0400, Jason Merrill wrote:
> > > On 5/29/26 4:21 PM, Marek Polacek wrote:
> > > > On Thu, May 28, 2026 at 03:21:35PM -0400, Jason Merrill wrote:
> > > > > On 5/28/26 11:42 AM, Marek Polacek wrote:
> > > > > > On Wed, May 27, 2026 at 06:15:04PM -0400, Jason Merrill wrote:
> > > > > > > On 5/27/26 4:32 PM, Marek Polacek wrote:
> > > > > > > > Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
> > > > > > > >
> > > > > > > > -- >8 --
> > > > > > > > [temp.arg.nontype] tells us that a temporary object is not an acceptable
> > > > > > > > template-argument when the corresponding template parameter has reference
> > > > > > > > type. So
> > > > > > > >
> > > > > > > > template<const int &> struct B {};
> > > > > > > > B<1> b;
> > > > > > > >
> > > > > > > > is ill-formed. In the test below we have a tparm `const int &I` and we
> > > > > > > > are trying to deduce `I` from `A<0>`. Since a temporary would be required
> > > > > > > > for the template argument, this should be a deduction failure.
> > > > > > > >
> > > > > > > > PR c++/107124
> > > > > > > >
> > > > > > > > gcc/cp/ChangeLog:
> > > > > > > >
> > > > > > > > * pt.cc (unify) <case TEMPLATE_PARM_INDEX>: Return
> > > > > > > > unify_type_mismatch if a temporary would be required for the
> > > > > > > > template argument.
> > > > > > > >
> > > > > > > > gcc/testsuite/ChangeLog:
> > > > > > > >
> > > > > > > > * g++.dg/template/deduce11.C: New test.
> > > > > > > > * g++.dg/template/deduce12.C: New test.
> > > > > > > > ---
> > > > > > > > gcc/cp/pt.cc | 7 ++++++-
> > > > > > > > gcc/testsuite/g++.dg/template/deduce11.C | 15 +++++++++++++++
> > > > > > > > gcc/testsuite/g++.dg/template/deduce12.C | 11 +++++++++++
> > > > > > > > 3 files changed, 32 insertions(+), 1 deletion(-)
> > > > > > > > create mode 100644 gcc/testsuite/g++.dg/template/deduce11.C
> > > > > > > > create mode 100644 gcc/testsuite/g++.dg/template/deduce12.C
> > > > > > > >
> > > > > > > > diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
> > > > > > > > index ada5f53a9f1..41b86a4e4f7 100644
> > > > > > > > --- a/gcc/cp/pt.cc
> > > > > > > > +++ b/gcc/cp/pt.cc
> > > > > > > > @@ -26485,7 +26485,12 @@ unify (tree tparms, tree targs, tree parm, tree arg, int strict,
> > > > > > > > ;
> > > > > > > > else if (same_type_ignoring_top_level_qualifiers_p
> > > > > > > > (non_reference (TREE_TYPE (arg)),
> > > > > > > > - non_reference (tparm)))
> > > > > > > > + non_reference (tparm))
> > > > > > > > + /* A temporary object is not an acceptable template-argument
> > > > > > > > + when the corresponding template parm has reference type. */
> > > > > > > > + && !(TYPE_REF_P (tparm)
> > > > > > > > + && ref_conv_binds_to_temporary
> > > > > > > > + (tparm, convert_from_reference (arg)).is_true ()))
> > > > > > >
> > > > > > > This seems like an awkward place for this check since it isn't a type
> > > > > > > mismatch, which leads to the unhelpful diagnostic
> > > > > > >
> > > > > > > > • mismatched types ‘const int&’ and ‘int’
> > > > > > >
> > > > > > > I think better would be to after checking for pack mismatch, check
> > > > > > > invalid_tparm_referent_p, get the diagnostic from there, and return plain
> > > > > > > unify_invalid if it fails.
> > > > > >
> > > > > > I put it there because it seemed simple to fall back on unify_type_mismatch
> > > > > > (and it's what clang++ says too). But fair enough; I agree with your point.
> > > > > >
> > > > > > I can't use invalid_tparm_referent_p because it wouldn't detect the problem
> > > > > > (it's the first thing I tried). So I propose this version.
> > > > >
> > > > > Ah, because arg is still INTEGER_CST. This suggests that we want the full
> > > > > convert_nontype_argument, which gives
> > > > >
> > > > > > initializing ‘const int&’ with ‘int’ in converted constant expression does not bind directly
> > > > >
> > > > > then we should be able to drop the separate strip_typedefs_expr.
> > > >
> > > > So like this? I'm not certain about the forced argument. But the
> > > > dependent_implicit_conv_p is necessary to avoid crashing on dependent
> > > > trees.
> > >
> > > I think forced false is correct, we shouldn't be dealing with aliases or
> > > concepts here.
> > >
> > > > -- >8 --
> > > > [temp.arg.nontype] tells us that a temporary object is not an acceptable
> > > > template-argument when the corresponding template parameter has reference
> > > > type. So
> > > >
> > > > template<const int& CRI> struct B { };
> > > > B<1> b;
> > > >
> > > > is ill-formed. In the test below we have a tparm `const int &I` and we
> > > > are trying to deduce `I` from `A<0>`. Since a temporary would be required
> > > > for the template argument, this should be a deduction failure.
> > > >
> > > > PR c++/107124
> > > >
> > > > gcc/cp/ChangeLog:
> > > >
> > > > * pt.cc (unify) <case TEMPLATE_PARM_INDEX>: Call
> > > > convert_nontype_argument and return unify_invalid if it failed.
> > > > Don't call strip_typedefs_expr.
> > > >
> > > > gcc/testsuite/ChangeLog:
> > > >
> > > > * g++.dg/template/deduce11.C: New test.
> > > > * g++.dg/template/deduce12.C: New test.
> > > > ---
> > > > gcc/cp/pt.cc | 12 ++++++++----
> > > > gcc/testsuite/g++.dg/template/deduce11.C | 15 +++++++++++++++
> > > > gcc/testsuite/g++.dg/template/deduce12.C | 12 ++++++++++++
> > > > 3 files changed, 35 insertions(+), 4 deletions(-)
> > > > create mode 100644 gcc/testsuite/g++.dg/template/deduce11.C
> > > > create mode 100644 gcc/testsuite/g++.dg/template/deduce12.C
> > > >
> > > > diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
> > > > index ada5f53a9f1..a70a758c61f 100644
> > > > --- a/gcc/cp/pt.cc
> > > > +++ b/gcc/cp/pt.cc
> > > > @@ -26530,10 +26530,14 @@ unify (tree tparms, tree targs, tree parm, tree arg, int strict,
> > > > && !TEMPLATE_PARM_PARAMETER_PACK (parm))
> > > > return unify_parameter_pack_mismatch (explain_p, parm, arg);
> > > > - {
> > > > - bool removed_attr = false;
> > > > - arg = strip_typedefs_expr (arg, &removed_attr);
> > > > - }
> > > > + if (!dependent_implicit_conv_p (tparm, arg, /*forced=*/false))
> > > > + {
> > > > + arg = convert_from_reference (arg);
> > > > + arg = convert_nontype_argument (tparm, arg, complain);
> > > > + if (!arg || arg == error_mark_node)
> > > > + return unify_invalid (explain_p);
> > > > + }
> > >
> > > We probably want the else from convert_template_argument, too:
> > >
> > > > if (!dependent_implicit_conv_p (t, orig_arg, force_conv))
> > > > /* We used to call digest_init here. However, digest_init
> > > > will report errors, which we don't want when complain
> > > > is zero. More importantly, digest_init will try too
> > > > hard to convert things: for example, `0' should not be
> > > > converted to pointer type at this point according to
> > > > the standard. Accepting this is not merely an
> > > > extension, since deciding whether or not these
> > > > conversions can occur is part of determining which
> > > > function template to call, or whether a given explicit
> > > > argument specification is valid. */
> > > > val = convert_nontype_argument (t, orig_arg, complain);
> > > > else
> > > > {
> > > > val = canonicalize_expr_argument (orig_arg, complain);
> > > > val = maybe_convert_nontype_argument (t, val, force_conv);
> > > > }
> > >
> > > ...maybe factoring that out into another function.
> >
> > Sounds good, done here.
> >
> > Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
> >
> > -- >8 --
> > [temp.arg.nontype] tells us that a temporary object is not an acceptable
> > template-argument when the corresponding template parameter has reference
> > type. So
> >
> > template<const int& CRI> struct B { };
> > B<1> b;
> >
> > is ill-formed. In the test below we have a tparm `const int &I` and we
> > are trying to deduce `I` from `A<0>`. Since a temporary would be required
> > for the template argument, this should be a deduction failure.
> >
> > PR c++/107124
> >
> > gcc/cp/ChangeLog:
> >
> > * pt.cc (coerce_nontype_argument): New, factored out of...
> > (convert_template_argument): ...here.
>
> Hmm, this name adds to the already-confusing group of similarly-named
> functions. How about convert_nontype_argument_maybe_dependent, and note in
Done.
> the convert_nontype_argument function comment that it expects non-dependent
> TYPE and non-type-dependent EXPR? And the existing
We already say that: "Both TYPE and EXPR must be non-dependent."
> maybe_convert_nontype_argument should probably be something more distinct
> like maybe_build_nontype_implicit_conv.
Done. Ran dg.exp. Ok for trunk?
-- >8 --
[temp.arg.nontype] tells us that a temporary object is not an acceptable
template-argument when the corresponding template parameter has reference
type. So
template<const int& CRI> struct B { };
B<1> b;
is ill-formed. In the test below we have a tparm `const int &I` and we
are trying to deduce `I` from `A<0>`. Since a temporary would be required
for the template argument, this should be a deduction failure.
PR c++/107124
gcc/cp/ChangeLog:
* cp-tree.h: Adjust comments to mention
maybe_build_nontype_implicit_conv instead of
maybe_convert_nontype_argument.
* pt.cc (maybe_convert_nontype_argument): Rename to...
(maybe_build_nontype_implicit_conv): ...this.
(convert_nontype_argument_maybe_dependent): New, factored
out of...
(convert_template_argument): ...here.
(unify) <case TEMPLATE_PARM_INDEX>: Call
convert_nontype_argument_maybe_dependent and return unify_invalid
if it failed. Don't call strip_typedefs_expr.
gcc/testsuite/ChangeLog:
* g++.dg/template/deduce11.C: New test.
* g++.dg/template/deduce12.C: New test.
---
gcc/cp/cp-tree.h | 4 +-
gcc/cp/pt.cc | 58 +++++++++++++++---------
gcc/testsuite/g++.dg/template/deduce11.C | 15 ++++++
gcc/testsuite/g++.dg/template/deduce12.C | 12 +++++
4 files changed, 65 insertions(+), 24 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/template/deduce11.C
create mode 100644 gcc/testsuite/g++.dg/template/deduce12.C
base-commit: 42989c22cfdbcd4207482bc6476ddb8d00a3424d
Comments
On 6/3/26 10:47 AM, Marek Polacek wrote:
> On Wed, Jun 03, 2026 at 08:54:51AM -0400, Jason Merrill wrote:
>> On 6/2/26 6:01 PM, Marek Polacek wrote:
>>> On Fri, May 29, 2026 at 04:37:55PM -0400, Jason Merrill wrote:
>>>> On 5/29/26 4:21 PM, Marek Polacek wrote:
>>>>> On Thu, May 28, 2026 at 03:21:35PM -0400, Jason Merrill wrote:
>>>>>> On 5/28/26 11:42 AM, Marek Polacek wrote:
>>>>>>> On Wed, May 27, 2026 at 06:15:04PM -0400, Jason Merrill wrote:
>>>>>>>> On 5/27/26 4:32 PM, Marek Polacek wrote:
>>>>>>>>> Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
>>>>>>>>>
>>>>>>>>> -- >8 --
>>>>>>>>> [temp.arg.nontype] tells us that a temporary object is not an acceptable
>>>>>>>>> template-argument when the corresponding template parameter has reference
>>>>>>>>> type. So
>>>>>>>>>
>>>>>>>>> template<const int &> struct B {};
>>>>>>>>> B<1> b;
>>>>>>>>>
>>>>>>>>> is ill-formed. In the test below we have a tparm `const int &I` and we
>>>>>>>>> are trying to deduce `I` from `A<0>`. Since a temporary would be required
>>>>>>>>> for the template argument, this should be a deduction failure.
>>>>>>>>>
>>>>>>>>> PR c++/107124
>>>>>>>>>
>>>>>>>>> gcc/cp/ChangeLog:
>>>>>>>>>
>>>>>>>>> * pt.cc (unify) <case TEMPLATE_PARM_INDEX>: Return
>>>>>>>>> unify_type_mismatch if a temporary would be required for the
>>>>>>>>> template argument.
>>>>>>>>>
>>>>>>>>> gcc/testsuite/ChangeLog:
>>>>>>>>>
>>>>>>>>> * g++.dg/template/deduce11.C: New test.
>>>>>>>>> * g++.dg/template/deduce12.C: New test.
>>>>>>>>> ---
>>>>>>>>> gcc/cp/pt.cc | 7 ++++++-
>>>>>>>>> gcc/testsuite/g++.dg/template/deduce11.C | 15 +++++++++++++++
>>>>>>>>> gcc/testsuite/g++.dg/template/deduce12.C | 11 +++++++++++
>>>>>>>>> 3 files changed, 32 insertions(+), 1 deletion(-)
>>>>>>>>> create mode 100644 gcc/testsuite/g++.dg/template/deduce11.C
>>>>>>>>> create mode 100644 gcc/testsuite/g++.dg/template/deduce12.C
>>>>>>>>>
>>>>>>>>> diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
>>>>>>>>> index ada5f53a9f1..41b86a4e4f7 100644
>>>>>>>>> --- a/gcc/cp/pt.cc
>>>>>>>>> +++ b/gcc/cp/pt.cc
>>>>>>>>> @@ -26485,7 +26485,12 @@ unify (tree tparms, tree targs, tree parm, tree arg, int strict,
>>>>>>>>> ;
>>>>>>>>> else if (same_type_ignoring_top_level_qualifiers_p
>>>>>>>>> (non_reference (TREE_TYPE (arg)),
>>>>>>>>> - non_reference (tparm)))
>>>>>>>>> + non_reference (tparm))
>>>>>>>>> + /* A temporary object is not an acceptable template-argument
>>>>>>>>> + when the corresponding template parm has reference type. */
>>>>>>>>> + && !(TYPE_REF_P (tparm)
>>>>>>>>> + && ref_conv_binds_to_temporary
>>>>>>>>> + (tparm, convert_from_reference (arg)).is_true ()))
>>>>>>>>
>>>>>>>> This seems like an awkward place for this check since it isn't a type
>>>>>>>> mismatch, which leads to the unhelpful diagnostic
>>>>>>>>
>>>>>>>>> • mismatched types ‘const int&’ and ‘int’
>>>>>>>>
>>>>>>>> I think better would be to after checking for pack mismatch, check
>>>>>>>> invalid_tparm_referent_p, get the diagnostic from there, and return plain
>>>>>>>> unify_invalid if it fails.
>>>>>>>
>>>>>>> I put it there because it seemed simple to fall back on unify_type_mismatch
>>>>>>> (and it's what clang++ says too). But fair enough; I agree with your point.
>>>>>>>
>>>>>>> I can't use invalid_tparm_referent_p because it wouldn't detect the problem
>>>>>>> (it's the first thing I tried). So I propose this version.
>>>>>>
>>>>>> Ah, because arg is still INTEGER_CST. This suggests that we want the full
>>>>>> convert_nontype_argument, which gives
>>>>>>
>>>>>>> initializing ‘const int&’ with ‘int’ in converted constant expression does not bind directly
>>>>>>
>>>>>> then we should be able to drop the separate strip_typedefs_expr.
>>>>>
>>>>> So like this? I'm not certain about the forced argument. But the
>>>>> dependent_implicit_conv_p is necessary to avoid crashing on dependent
>>>>> trees.
>>>>
>>>> I think forced false is correct, we shouldn't be dealing with aliases or
>>>> concepts here.
>>>>
>>>>> -- >8 --
>>>>> [temp.arg.nontype] tells us that a temporary object is not an acceptable
>>>>> template-argument when the corresponding template parameter has reference
>>>>> type. So
>>>>>
>>>>> template<const int& CRI> struct B { };
>>>>> B<1> b;
>>>>>
>>>>> is ill-formed. In the test below we have a tparm `const int &I` and we
>>>>> are trying to deduce `I` from `A<0>`. Since a temporary would be required
>>>>> for the template argument, this should be a deduction failure.
>>>>>
>>>>> PR c++/107124
>>>>>
>>>>> gcc/cp/ChangeLog:
>>>>>
>>>>> * pt.cc (unify) <case TEMPLATE_PARM_INDEX>: Call
>>>>> convert_nontype_argument and return unify_invalid if it failed.
>>>>> Don't call strip_typedefs_expr.
>>>>>
>>>>> gcc/testsuite/ChangeLog:
>>>>>
>>>>> * g++.dg/template/deduce11.C: New test.
>>>>> * g++.dg/template/deduce12.C: New test.
>>>>> ---
>>>>> gcc/cp/pt.cc | 12 ++++++++----
>>>>> gcc/testsuite/g++.dg/template/deduce11.C | 15 +++++++++++++++
>>>>> gcc/testsuite/g++.dg/template/deduce12.C | 12 ++++++++++++
>>>>> 3 files changed, 35 insertions(+), 4 deletions(-)
>>>>> create mode 100644 gcc/testsuite/g++.dg/template/deduce11.C
>>>>> create mode 100644 gcc/testsuite/g++.dg/template/deduce12.C
>>>>>
>>>>> diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
>>>>> index ada5f53a9f1..a70a758c61f 100644
>>>>> --- a/gcc/cp/pt.cc
>>>>> +++ b/gcc/cp/pt.cc
>>>>> @@ -26530,10 +26530,14 @@ unify (tree tparms, tree targs, tree parm, tree arg, int strict,
>>>>> && !TEMPLATE_PARM_PARAMETER_PACK (parm))
>>>>> return unify_parameter_pack_mismatch (explain_p, parm, arg);
>>>>> - {
>>>>> - bool removed_attr = false;
>>>>> - arg = strip_typedefs_expr (arg, &removed_attr);
>>>>> - }
>>>>> + if (!dependent_implicit_conv_p (tparm, arg, /*forced=*/false))
>>>>> + {
>>>>> + arg = convert_from_reference (arg);
>>>>> + arg = convert_nontype_argument (tparm, arg, complain);
>>>>> + if (!arg || arg == error_mark_node)
>>>>> + return unify_invalid (explain_p);
>>>>> + }
>>>>
>>>> We probably want the else from convert_template_argument, too:
>>>>
>>>>> if (!dependent_implicit_conv_p (t, orig_arg, force_conv))
>>>>> /* We used to call digest_init here. However, digest_init
>>>>> will report errors, which we don't want when complain
>>>>> is zero. More importantly, digest_init will try too
>>>>> hard to convert things: for example, `0' should not be
>>>>> converted to pointer type at this point according to
>>>>> the standard. Accepting this is not merely an
>>>>> extension, since deciding whether or not these
>>>>> conversions can occur is part of determining which
>>>>> function template to call, or whether a given explicit
>>>>> argument specification is valid. */
>>>>> val = convert_nontype_argument (t, orig_arg, complain);
>>>>> else
>>>>> {
>>>>> val = canonicalize_expr_argument (orig_arg, complain);
>>>>> val = maybe_convert_nontype_argument (t, val, force_conv);
>>>>> }
>>>>
>>>> ...maybe factoring that out into another function.
>>>
>>> Sounds good, done here.
>>>
>>> Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
>>>
>>> -- >8 --
>>> [temp.arg.nontype] tells us that a temporary object is not an acceptable
>>> template-argument when the corresponding template parameter has reference
>>> type. So
>>>
>>> template<const int& CRI> struct B { };
>>> B<1> b;
>>>
>>> is ill-formed. In the test below we have a tparm `const int &I` and we
>>> are trying to deduce `I` from `A<0>`. Since a temporary would be required
>>> for the template argument, this should be a deduction failure.
>>>
>>> PR c++/107124
>>>
>>> gcc/cp/ChangeLog:
>>>
>>> * pt.cc (coerce_nontype_argument): New, factored out of...
>>> (convert_template_argument): ...here.
>>
>> Hmm, this name adds to the already-confusing group of similarly-named
>> functions. How about convert_nontype_argument_maybe_dependent, and note in
>
> Done.
>
>> the convert_nontype_argument function comment that it expects non-dependent
>> TYPE and non-type-dependent EXPR? And the existing
>
> We already say that: "Both TYPE and EXPR must be non-dependent."
>
>> maybe_convert_nontype_argument should probably be something more distinct
>> like maybe_build_nontype_implicit_conv.
>
> Done. Ran dg.exp. Ok for trunk?
OK, thanks.
> -- >8 --
> [temp.arg.nontype] tells us that a temporary object is not an acceptable
> template-argument when the corresponding template parameter has reference
> type. So
>
> template<const int& CRI> struct B { };
> B<1> b;
>
> is ill-formed. In the test below we have a tparm `const int &I` and we
> are trying to deduce `I` from `A<0>`. Since a temporary would be required
> for the template argument, this should be a deduction failure.
>
> PR c++/107124
>
> gcc/cp/ChangeLog:
>
> * cp-tree.h: Adjust comments to mention
> maybe_build_nontype_implicit_conv instead of
> maybe_convert_nontype_argument.
> * pt.cc (maybe_convert_nontype_argument): Rename to...
> (maybe_build_nontype_implicit_conv): ...this.
> (convert_nontype_argument_maybe_dependent): New, factored
> out of...
> (convert_template_argument): ...here.
> (unify) <case TEMPLATE_PARM_INDEX>: Call
> convert_nontype_argument_maybe_dependent and return unify_invalid
> if it failed. Don't call strip_typedefs_expr.
>
> gcc/testsuite/ChangeLog:
>
> * g++.dg/template/deduce11.C: New test.
> * g++.dg/template/deduce12.C: New test.
> ---
> gcc/cp/cp-tree.h | 4 +-
> gcc/cp/pt.cc | 58 +++++++++++++++---------
> gcc/testsuite/g++.dg/template/deduce11.C | 15 ++++++
> gcc/testsuite/g++.dg/template/deduce12.C | 12 +++++
> 4 files changed, 65 insertions(+), 24 deletions(-)
> create mode 100644 gcc/testsuite/g++.dg/template/deduce11.C
> create mode 100644 gcc/testsuite/g++.dg/template/deduce12.C
>
> diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
> index 65f112714d1..bf477a67a34 100644
> --- a/gcc/cp/cp-tree.h
> +++ b/gcc/cp/cp-tree.h
> @@ -5138,7 +5138,7 @@ get_vec_init_expr (tree t)
> (TREE_LANG_FLAG_0 (IMPLICIT_CONV_EXPR_CHECK (NODE)))
>
> /* True if NODE represents a dependent conversion of a non-type template
> - argument. Set by maybe_convert_nontype_argument. */
> + argument. Set by maybe_build_nontype_implicit_conv. */
> #define IMPLICIT_CONV_EXPR_NONTYPE_ARG(NODE) \
> (TREE_LANG_FLAG_1 (IMPLICIT_CONV_EXPR_CHECK (NODE)))
>
> @@ -5148,7 +5148,7 @@ get_vec_init_expr (tree t)
> (TREE_LANG_FLAG_2 (IMPLICIT_CONV_EXPR_CHECK (NODE)))
>
> /* True if NODE represents a conversion forced to be represented in
> - maybe_convert_nontype_argument, i.e. for an alias template. */
> + maybe_build_nontype_implicit_conv, i.e. for an alias template. */
> #define IMPLICIT_CONV_EXPR_FORCED(NODE) \
> (TREE_LANG_FLAG_3 (IMPLICIT_CONV_EXPR_CHECK (NODE)))
>
> diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
> index b334882de81..4683b57f34b 100644
> --- a/gcc/cp/pt.cc
> +++ b/gcc/cp/pt.cc
> @@ -8740,7 +8740,7 @@ is_compatible_template_arg (tree parm, tree arg, tree args)
> conversion for the benefit of cp_tree_equal. */
>
> static tree
> -maybe_convert_nontype_argument (tree type, tree arg, bool force)
> +maybe_build_nontype_implicit_conv (tree type, tree arg, bool force)
> {
> /* Auto parms get no conversion. */
> if (type_uses_auto (type))
> @@ -8780,6 +8780,33 @@ dependent_implicit_conv_p (tree type, tree expr, bool forced)
> && value_dependent_expression_p (expr)));
> }
>
> +/* Convert the non-type template parameter ARG to the indicated TYPE.
> + If one of them is dependent, create an appropriate conversion.
> + FORCE_CONV is true in a forced context (i.e. alias or concept). */
> +
> +static tree
> +convert_nontype_argument_maybe_dependent (tree type, tree arg,
> + bool force_conv,
> + tsubst_flags_t complain)
> +{
> + if (dependent_implicit_conv_p (type, arg, force_conv))
> + {
> + tree val = canonicalize_expr_argument (arg, complain);
> + return maybe_build_nontype_implicit_conv (type, val, force_conv);
> + }
> +
> + /* We used to call digest_init here. However, digest_init will report
> + errors, which we don't want when complain is zero. More importantly,
> + digest_init will try too hard to convert things: for example,
> + `0' should not be converted to pointer type at this point according to
> + the standard. Accepting this is not merely an extension, since
> + deciding whether or not these conversions can occur is part of
> + determining which function template to call, or whether a given
> + explicit argument specification is valid. */
> + return convert_nontype_argument (type, convert_from_reference (arg),
> + complain);
> +}
> +
> /* Convert the indicated template ARG as necessary to match the
> indicated template PARM. Returns the converted ARG, or
> error_mark_node if the conversion was unsuccessful. Error and
> @@ -9060,23 +9087,8 @@ convert_template_argument (tree parm,
> && same_type_p (TREE_TYPE (orig_arg), t))
> orig_arg = TREE_OPERAND (orig_arg, 0);
>
> - if (!dependent_implicit_conv_p (t, orig_arg, force_conv))
> - /* We used to call digest_init here. However, digest_init
> - will report errors, which we don't want when complain
> - is zero. More importantly, digest_init will try too
> - hard to convert things: for example, `0' should not be
> - converted to pointer type at this point according to
> - the standard. Accepting this is not merely an
> - extension, since deciding whether or not these
> - conversions can occur is part of determining which
> - function template to call, or whether a given explicit
> - argument specification is valid. */
> - val = convert_nontype_argument (t, orig_arg, complain);
> - else
> - {
> - val = canonicalize_expr_argument (orig_arg, complain);
> - val = maybe_convert_nontype_argument (t, val, force_conv);
> - }
> + val = convert_nontype_argument_maybe_dependent (t, orig_arg, force_conv,
> + complain);
>
> if (val == NULL_TREE)
> val = error_mark_node;
> @@ -26567,10 +26579,12 @@ unify (tree tparms, tree targs, tree parm, tree arg, int strict,
> && !TEMPLATE_PARM_PARAMETER_PACK (parm))
> return unify_parameter_pack_mismatch (explain_p, parm, arg);
>
> - {
> - bool removed_attr = false;
> - arg = strip_typedefs_expr (arg, &removed_attr);
> - }
> + arg = convert_nontype_argument_maybe_dependent (tparm, arg,
> + /*forced=*/false,
> + complain);
> + if (!arg || arg == error_mark_node)
> + return unify_invalid (explain_p);
> +
> TREE_VEC_ELT (INNERMOST_TEMPLATE_ARGS (targs), idx) = arg;
> return unify_success (explain_p);
>
> diff --git a/gcc/testsuite/g++.dg/template/deduce11.C b/gcc/testsuite/g++.dg/template/deduce11.C
> new file mode 100644
> index 00000000000..c7671c04397
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/template/deduce11.C
> @@ -0,0 +1,15 @@
> +// PR c++/107124
> +// { dg-do compile { target c++11 } }
> +
> +template<int>
> +struct A {};
> +
> +template<const int &I>
> +constexpr int f (A<I>) { return 0; }
> +
> +template<typename T>
> +constexpr int f (T) { return 1; }
> +
> +const int a = 42;
> +static_assert (f (A<0>{}) == 1, "");
> +static_assert (f (A<a>{}) == 1, "");
> diff --git a/gcc/testsuite/g++.dg/template/deduce12.C b/gcc/testsuite/g++.dg/template/deduce12.C
> new file mode 100644
> index 00000000000..0bd2762edd4
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/template/deduce12.C
> @@ -0,0 +1,12 @@
> +// PR c++/107124
> +// { dg-do compile { target c++11 } }
> +
> +template<int>
> +struct A {};
> +
> +template<const int &I>
> +constexpr int f (A<I>) { return 0; }
> +
> +constexpr int i = f (A<0>{}); // { dg-error "no matching function for call" }
> +// { dg-message "(candidate|does not bind directly|could not convert)" "candidate note" { target c++17 } .-1 }
> +// { dg-message "(candidate|not a valid template argument)" "candidate note" { target c++14_down } .-2 }
>
> base-commit: 42989c22cfdbcd4207482bc6476ddb8d00a3424d
@@ -5138,7 +5138,7 @@ get_vec_init_expr (tree t)
(TREE_LANG_FLAG_0 (IMPLICIT_CONV_EXPR_CHECK (NODE)))
/* True if NODE represents a dependent conversion of a non-type template
- argument. Set by maybe_convert_nontype_argument. */
+ argument. Set by maybe_build_nontype_implicit_conv. */
#define IMPLICIT_CONV_EXPR_NONTYPE_ARG(NODE) \
(TREE_LANG_FLAG_1 (IMPLICIT_CONV_EXPR_CHECK (NODE)))
@@ -5148,7 +5148,7 @@ get_vec_init_expr (tree t)
(TREE_LANG_FLAG_2 (IMPLICIT_CONV_EXPR_CHECK (NODE)))
/* True if NODE represents a conversion forced to be represented in
- maybe_convert_nontype_argument, i.e. for an alias template. */
+ maybe_build_nontype_implicit_conv, i.e. for an alias template. */
#define IMPLICIT_CONV_EXPR_FORCED(NODE) \
(TREE_LANG_FLAG_3 (IMPLICIT_CONV_EXPR_CHECK (NODE)))
@@ -8740,7 +8740,7 @@ is_compatible_template_arg (tree parm, tree arg, tree args)
conversion for the benefit of cp_tree_equal. */
static tree
-maybe_convert_nontype_argument (tree type, tree arg, bool force)
+maybe_build_nontype_implicit_conv (tree type, tree arg, bool force)
{
/* Auto parms get no conversion. */
if (type_uses_auto (type))
@@ -8780,6 +8780,33 @@ dependent_implicit_conv_p (tree type, tree expr, bool forced)
&& value_dependent_expression_p (expr)));
}
+/* Convert the non-type template parameter ARG to the indicated TYPE.
+ If one of them is dependent, create an appropriate conversion.
+ FORCE_CONV is true in a forced context (i.e. alias or concept). */
+
+static tree
+convert_nontype_argument_maybe_dependent (tree type, tree arg,
+ bool force_conv,
+ tsubst_flags_t complain)
+{
+ if (dependent_implicit_conv_p (type, arg, force_conv))
+ {
+ tree val = canonicalize_expr_argument (arg, complain);
+ return maybe_build_nontype_implicit_conv (type, val, force_conv);
+ }
+
+ /* We used to call digest_init here. However, digest_init will report
+ errors, which we don't want when complain is zero. More importantly,
+ digest_init will try too hard to convert things: for example,
+ `0' should not be converted to pointer type at this point according to
+ the standard. Accepting this is not merely an extension, since
+ deciding whether or not these conversions can occur is part of
+ determining which function template to call, or whether a given
+ explicit argument specification is valid. */
+ return convert_nontype_argument (type, convert_from_reference (arg),
+ complain);
+}
+
/* Convert the indicated template ARG as necessary to match the
indicated template PARM. Returns the converted ARG, or
error_mark_node if the conversion was unsuccessful. Error and
@@ -9060,23 +9087,8 @@ convert_template_argument (tree parm,
&& same_type_p (TREE_TYPE (orig_arg), t))
orig_arg = TREE_OPERAND (orig_arg, 0);
- if (!dependent_implicit_conv_p (t, orig_arg, force_conv))
- /* We used to call digest_init here. However, digest_init
- will report errors, which we don't want when complain
- is zero. More importantly, digest_init will try too
- hard to convert things: for example, `0' should not be
- converted to pointer type at this point according to
- the standard. Accepting this is not merely an
- extension, since deciding whether or not these
- conversions can occur is part of determining which
- function template to call, or whether a given explicit
- argument specification is valid. */
- val = convert_nontype_argument (t, orig_arg, complain);
- else
- {
- val = canonicalize_expr_argument (orig_arg, complain);
- val = maybe_convert_nontype_argument (t, val, force_conv);
- }
+ val = convert_nontype_argument_maybe_dependent (t, orig_arg, force_conv,
+ complain);
if (val == NULL_TREE)
val = error_mark_node;
@@ -26567,10 +26579,12 @@ unify (tree tparms, tree targs, tree parm, tree arg, int strict,
&& !TEMPLATE_PARM_PARAMETER_PACK (parm))
return unify_parameter_pack_mismatch (explain_p, parm, arg);
- {
- bool removed_attr = false;
- arg = strip_typedefs_expr (arg, &removed_attr);
- }
+ arg = convert_nontype_argument_maybe_dependent (tparm, arg,
+ /*forced=*/false,
+ complain);
+ if (!arg || arg == error_mark_node)
+ return unify_invalid (explain_p);
+
TREE_VEC_ELT (INNERMOST_TEMPLATE_ARGS (targs), idx) = arg;
return unify_success (explain_p);
new file mode 100644
@@ -0,0 +1,15 @@
+// PR c++/107124
+// { dg-do compile { target c++11 } }
+
+template<int>
+struct A {};
+
+template<const int &I>
+constexpr int f (A<I>) { return 0; }
+
+template<typename T>
+constexpr int f (T) { return 1; }
+
+const int a = 42;
+static_assert (f (A<0>{}) == 1, "");
+static_assert (f (A<a>{}) == 1, "");
new file mode 100644
@@ -0,0 +1,12 @@
+// PR c++/107124
+// { dg-do compile { target c++11 } }
+
+template<int>
+struct A {};
+
+template<const int &I>
+constexpr int f (A<I>) { return 0; }
+
+constexpr int i = f (A<0>{}); // { dg-error "no matching function for call" }
+// { dg-message "(candidate|does not bind directly|could not convert)" "candidate note" { target c++17 } .-1 }
+// { dg-message "(candidate|not a valid template argument)" "candidate note" { target c++14_down } .-2 }