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

Message ID 20200528232308.1206783-1-polacek@redhat.com
State New
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  • c++: Make braced-init-list as template arg work with aggr init [PR95369]
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Kees Cook via Gcc-patches May 28, 2020, 11:23 p.m.
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
-- 
Marek Polacek • Red Hat, Inc. • 300 A St, Boston, MA

Comments

Kees Cook via Gcc-patches May 29, 2020, 7:17 p.m. | #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

>
diff --git a/gcc/cp/call.c b/gcc/cp/call.c
index a51ebb5d9e3..d38e23a7e9a 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.  */
Kees Cook via Gcc-patches June 5, 2020, 7:13 p.m. | #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
-- 
Marek Polacek • Red Hat, Inc. • 300 A St, Boston, MA
Kees Cook via Gcc-patches June 5, 2020, 7:48 p.m. | #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

>

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;
+}