diff mbox series

c++: Make braced-init-list as template arg work with aggr init [PR95369]

Message ID 20200528232308.1206783-1-polacek@redhat.com
State New
Headers show
Series c++: Make braced-init-list as template arg work with aggr init [PR95369] | expand

Commit Message

Marek Polacek May 28, 2020, 11:23 p.m. UTC 
Barry pointed out to me that our braced-init-list as a template-argument
extension doesn't work as expected when we aggregate-initialize.  Thus
fixed by calling digest_init in convert_nontype_argument so that we can
actually convert the CONSTRUCTOR.

I don't think we can call digest_init any earlier, and it needs to
happen before the call to build_converted_constant_expr.

Barry also noticed that we allow designated initializers for
non-aggregate types in the template-argument argument context, i.e. this

  struct S {
    unsigned a;
    unsigned b;
    constexpr S(unsigned _a, unsigned _b) noexcept: a{_a}, b{_b} { }
  };

  template<S s> struct X { };

  void f()
  {
    X<{.a = 1, .b = 2}> x;
  }

probably should not compile.  But I'm not too sure about it, and don't
know how I would fix it anyway, so I'm not dealing with it in this
patch.

Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?

gcc/cp/ChangeLog:

	PR c++/95369
	* pt.c (convert_nontype_argument): In C++20, reshape and digest
	a braced-init-list if the type is an aggregate.

gcc/testsuite/ChangeLog:

	PR c++/95369
	* g++.dg/cpp2a/nontype-class38.C: New test.
---
 gcc/cp/pt.c                                  | 13 +++++++++
 gcc/testsuite/g++.dg/cpp2a/nontype-class38.C | 30 ++++++++++++++++++++
 2 files changed, 43 insertions(+)
 create mode 100644 gcc/testsuite/g++.dg/cpp2a/nontype-class38.C


base-commit: 3d8d5ddb539a5254c7ef83414377f4c74c7701d4

Comments

Jason Merrill May 29, 2020, 7:17 p.m. UTC | #1 
On 5/28/20 7:23 PM, Marek Polacek wrote:
> Barry pointed out to me that our braced-init-list as a template-argument
> extension doesn't work as expected when we aggregate-initialize.  Thus
> fixed by calling digest_init in convert_nontype_argument so that we can
> actually convert the CONSTRUCTOR.
> 
> I don't think we can call digest_init any earlier, and it needs to
> happen before the call to build_converted_constant_expr.

Or we could fix build_converted_constant_expr to allow it; aggregate 
list-initialization is a user-defined conversion sequence, so I tihnk it 
should be allowed as part of a converted constant expression.

Jason

> Barry also noticed that we allow designated initializers for
> non-aggregate types in the template-argument argument context, i.e. this
> 
>    struct S {
>      unsigned a;
>      unsigned b;
>      constexpr S(unsigned _a, unsigned _b) noexcept: a{_a}, b{_b} { }
>    };
> 
>    template<S s> struct X { };
> 
>    void f()
>    {
>      X<{.a = 1, .b = 2}> x;
>    }
> 
> probably should not compile.  But I'm not too sure about it, and don't
> know how I would fix it anyway, so I'm not dealing with it in this
> patch.
> 
> Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
> 
> gcc/cp/ChangeLog:
> 
> 	PR c++/95369
> 	* pt.c (convert_nontype_argument): In C++20, reshape and digest
> 	a braced-init-list if the type is an aggregate.
> 
> gcc/testsuite/ChangeLog:
> 
> 	PR c++/95369
> 	* g++.dg/cpp2a/nontype-class38.C: New test.
> ---
>   gcc/cp/pt.c                                  | 13 +++++++++
>   gcc/testsuite/g++.dg/cpp2a/nontype-class38.C | 30 ++++++++++++++++++++
>   2 files changed, 43 insertions(+)
>   create mode 100644 gcc/testsuite/g++.dg/cpp2a/nontype-class38.C
> 
> diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
> index 90dafff3aa7..adb7593f77d 100644
> --- a/gcc/cp/pt.c
> +++ b/gcc/cp/pt.c
> @@ -7133,6 +7133,19 @@ convert_nontype_argument (tree type, tree expr, tsubst_flags_t complain)
>   	return error_mark_node;
>       }
>   
> +  /* For a { } template argument, like in X<{ 1, 2 }>, we need to digest
> +     here so that build_converted_constant_expr below is able to convert
> +     it to TYPE.  */
> +  if (cxx_dialect >= cxx20
> +      && BRACE_ENCLOSED_INITIALIZER_P (expr)
> +      && CP_AGGREGATE_TYPE_P (type))
> +    {
> +      expr = reshape_init (type, expr, complain);
> +      expr = digest_init (type, expr, complain);
> +      if (expr == error_mark_node)
> +	return error_mark_node;
> +    }
> +
>     /* If we are in a template, EXPR may be non-dependent, but still
>        have a syntactic, rather than semantic, form.  For example, EXPR
>        might be a SCOPE_REF, rather than the VAR_DECL to which the
> diff --git a/gcc/testsuite/g++.dg/cpp2a/nontype-class38.C b/gcc/testsuite/g++.dg/cpp2a/nontype-class38.C
> new file mode 100644
> index 00000000000..5b440fd1c9e
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp2a/nontype-class38.C
> @@ -0,0 +1,30 @@
> +// PR c++/95369
> +// { dg-do compile { target c++20 } }
> +
> +struct S {
> +  int a;
> +  int b;
> +};
> +
> +struct W {
> +  int i;
> +  S s;
> +};
> +
> +template <S p>
> +void fnc()
> +{
> +}
> +
> +template<S s> struct X { };
> +template<W w> struct Y { };
> +
> +void f()
> +{
> +  fnc<{ .a = 10, .b = 20 }>();
> +  fnc<{ 10, 20 }>();
> +  X<{ .a = 1, .b = 2 }> x;
> +  X<{ 1, 2 }> x2;
> +  // Brace elision is likely to be allowed.
> +  Y<{ 1, 2, 3 }> x3;
> +}
> 
> base-commit: 3d8d5ddb539a5254c7ef83414377f4c74c7701d4
>
Marek Polacek June 5, 2020, 7:13 p.m. UTC | #2 
On Fri, May 29, 2020 at 03:17:51PM -0400, Jason Merrill via Gcc-patches wrote:
> On 5/28/20 7:23 PM, Marek Polacek wrote:
> > Barry pointed out to me that our braced-init-list as a template-argument
> > extension doesn't work as expected when we aggregate-initialize.  Thus
> > fixed by calling digest_init in convert_nontype_argument so that we can
> > actually convert the CONSTRUCTOR.
> > 
> > I don't think we can call digest_init any earlier, and it needs to
> > happen before the call to build_converted_constant_expr.
> 
> Or we could fix build_converted_constant_expr to allow it; aggregate
> list-initialization is a user-defined conversion sequence, so I tihnk it
> should be allowed as part of a converted constant expression.

Ah, nice.  It works just fine.  Here's the complete patch:

Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?

-- >8 --
Barry pointed out to me that our braced-init-list as a template-argument
extension doesn't work as expected when we aggregate-initialize.  Since
aggregate list-initialization is a user-defined conversion sequence, we
allow it as part of a converted constant expression.

Co-authored-by: Jason Merrill <jason@redhat.com>

gcc/cp/ChangeLog:

	PR c++/95369
	* call.c (build_converted_constant_expr_internal): Allow
	list-initialization.

gcc/testsuite/ChangeLog:

	PR c++/95369
	* g++.dg/cpp2a/nontype-class38.C: New test.
---
 gcc/cp/call.c                                |  4 ++-
 gcc/testsuite/g++.dg/cpp2a/nontype-class38.C | 30 ++++++++++++++++++++
 2 files changed, 33 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/g++.dg/cpp2a/nontype-class38.C

diff --git a/gcc/cp/call.c b/gcc/cp/call.c
index 2b393f96e5b..3c97b9846e2 100644
--- a/gcc/cp/call.c
+++ b/gcc/cp/call.c
@@ -4348,7 +4348,7 @@ build_converted_constant_expr_internal (tree type, tree expr,
      and where the reference binding (if any) binds directly.  */
 
   for (conversion *c = conv;
-       conv && c->kind != ck_identity;
+       c && c->kind != ck_identity;
        c = next_conversion (c))
     {
       switch (c->kind)
@@ -4356,6 +4356,8 @@ build_converted_constant_expr_internal (tree type, tree expr,
 	  /* A conversion function is OK.  If it isn't constexpr, we'll
 	     complain later that the argument isn't constant.  */
 	case ck_user:
+	  /* List-initialization is OK.  */
+	case ck_aggr:
 	  /* The lvalue-to-rvalue conversion is OK.  */
 	case ck_rvalue:
 	  /* Array-to-pointer and function-to-pointer.  */
diff --git a/gcc/testsuite/g++.dg/cpp2a/nontype-class38.C b/gcc/testsuite/g++.dg/cpp2a/nontype-class38.C
new file mode 100644
index 00000000000..5b440fd1c9e
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/nontype-class38.C
@@ -0,0 +1,30 @@
+// PR c++/95369
+// { dg-do compile { target c++20 } }
+
+struct S {
+  int a;
+  int b;
+};
+
+struct W {
+  int i;
+  S s;
+};
+
+template <S p>
+void fnc()
+{
+}
+
+template<S s> struct X { };
+template<W w> struct Y { };
+
+void f()
+{
+  fnc<{ .a = 10, .b = 20 }>();
+  fnc<{ 10, 20 }>();
+  X<{ .a = 1, .b = 2 }> x;
+  X<{ 1, 2 }> x2;
+  // Brace elision is likely to be allowed.
+  Y<{ 1, 2, 3 }> x3;
+}

base-commit: 640e05e02b567fa5ccf4c207e6fc6c3e9a93b17c
Jason Merrill June 5, 2020, 7:48 p.m. UTC | #3 
On 6/5/20 3:13 PM, Marek Polacek wrote:
> On Fri, May 29, 2020 at 03:17:51PM -0400, Jason Merrill via Gcc-patches wrote:
>> On 5/28/20 7:23 PM, Marek Polacek wrote:
>>> Barry pointed out to me that our braced-init-list as a template-argument
>>> extension doesn't work as expected when we aggregate-initialize.  Thus
>>> fixed by calling digest_init in convert_nontype_argument so that we can
>>> actually convert the CONSTRUCTOR.
>>>
>>> I don't think we can call digest_init any earlier, and it needs to
>>> happen before the call to build_converted_constant_expr.
>>
>> Or we could fix build_converted_constant_expr to allow it; aggregate
>> list-initialization is a user-defined conversion sequence, so I tihnk it
>> should be allowed as part of a converted constant expression.
> 
> Ah, nice.  It works just fine.  Here's the complete patch:
> 
> Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?

OK.

> -- >8 --
> Barry pointed out to me that our braced-init-list as a template-argument
> extension doesn't work as expected when we aggregate-initialize.  Since
> aggregate list-initialization is a user-defined conversion sequence, we
> allow it as part of a converted constant expression.
> 
> Co-authored-by: Jason Merrill <jason@redhat.com>
> 
> gcc/cp/ChangeLog:
> 
> 	PR c++/95369
> 	* call.c (build_converted_constant_expr_internal): Allow
> 	list-initialization.
> 
> gcc/testsuite/ChangeLog:
> 
> 	PR c++/95369
> 	* g++.dg/cpp2a/nontype-class38.C: New test.
> ---
>   gcc/cp/call.c                                |  4 ++-
>   gcc/testsuite/g++.dg/cpp2a/nontype-class38.C | 30 ++++++++++++++++++++
>   2 files changed, 33 insertions(+), 1 deletion(-)
>   create mode 100644 gcc/testsuite/g++.dg/cpp2a/nontype-class38.C
> 
> diff --git a/gcc/cp/call.c b/gcc/cp/call.c
> index 2b393f96e5b..3c97b9846e2 100644
> --- a/gcc/cp/call.c
> +++ b/gcc/cp/call.c
> @@ -4348,7 +4348,7 @@ build_converted_constant_expr_internal (tree type, tree expr,
>        and where the reference binding (if any) binds directly.  */
>   
>     for (conversion *c = conv;
> -       conv && c->kind != ck_identity;
> +       c && c->kind != ck_identity;
>          c = next_conversion (c))
>       {
>         switch (c->kind)
> @@ -4356,6 +4356,8 @@ build_converted_constant_expr_internal (tree type, tree expr,
>   	  /* A conversion function is OK.  If it isn't constexpr, we'll
>   	     complain later that the argument isn't constant.  */
>   	case ck_user:
> +	  /* List-initialization is OK.  */
> +	case ck_aggr:
>   	  /* The lvalue-to-rvalue conversion is OK.  */
>   	case ck_rvalue:
>   	  /* Array-to-pointer and function-to-pointer.  */
> diff --git a/gcc/testsuite/g++.dg/cpp2a/nontype-class38.C b/gcc/testsuite/g++.dg/cpp2a/nontype-class38.C
> new file mode 100644
> index 00000000000..5b440fd1c9e
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp2a/nontype-class38.C
> @@ -0,0 +1,30 @@
> +// PR c++/95369
> +// { dg-do compile { target c++20 } }
> +
> +struct S {
> +  int a;
> +  int b;
> +};
> +
> +struct W {
> +  int i;
> +  S s;
> +};
> +
> +template <S p>
> +void fnc()
> +{
> +}
> +
> +template<S s> struct X { };
> +template<W w> struct Y { };
> +
> +void f()
> +{
> +  fnc<{ .a = 10, .b = 20 }>();
> +  fnc<{ 10, 20 }>();
> +  X<{ .a = 1, .b = 2 }> x;
> +  X<{ 1, 2 }> x2;
> +  // Brace elision is likely to be allowed.
> +  Y<{ 1, 2, 3 }> x3;
> +}
> 
> base-commit: 640e05e02b567fa5ccf4c207e6fc6c3e9a93b17c
>
diff mbox series

Patch

diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index 90dafff3aa7..adb7593f77d 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -7133,6 +7133,19 @@  convert_nontype_argument (tree type, tree expr, tsubst_flags_t complain)
 	return error_mark_node;
     }
 
+  /* For a { } template argument, like in X<{ 1, 2 }>, we need to digest
+     here so that build_converted_constant_expr below is able to convert
+     it to TYPE.  */
+  if (cxx_dialect >= cxx20
+      && BRACE_ENCLOSED_INITIALIZER_P (expr)
+      && CP_AGGREGATE_TYPE_P (type))
+    {
+      expr = reshape_init (type, expr, complain);
+      expr = digest_init (type, expr, complain);
+      if (expr == error_mark_node)
+	return error_mark_node;
+    }
+
   /* If we are in a template, EXPR may be non-dependent, but still
      have a syntactic, rather than semantic, form.  For example, EXPR
      might be a SCOPE_REF, rather than the VAR_DECL to which the
diff --git a/gcc/testsuite/g++.dg/cpp2a/nontype-class38.C b/gcc/testsuite/g++.dg/cpp2a/nontype-class38.C
new file mode 100644
index 00000000000..5b440fd1c9e
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/nontype-class38.C
@@ -0,0 +1,30 @@ 
+// PR c++/95369
+// { dg-do compile { target c++20 } }
+
+struct S {
+  int a;
+  int b;
+};
+
+struct W {
+  int i;
+  S s;
+};
+
+template <S p>
+void fnc()
+{
+}
+
+template<S s> struct X { };
+template<W w> struct Y { };
+
+void f()
+{
+  fnc<{ .a = 10, .b = 20 }>();
+  fnc<{ 10, 20 }>();
+  X<{ .a = 1, .b = 2 }> x;
+  X<{ 1, 2 }> x2;
+  // Brace elision is likely to be allowed.
+  Y<{ 1, 2, 3 }> x3;
+}