Re: [PATCH] c++/modules: Prevent treating suppressed debug info as extern template [PR112820]

[Nathaniel Shead <nathanieloshead@gmail.com>]

Ping for https://gcc.gnu.org/pipermail/gcc-patches/2023-December/639082.html.

On Sun, Dec 03, 2023 at 11:46:36PM +1100, Nathaniel Shead wrote:
> Bootstrapped and regtested on x86_64-pc-linux-gnu, OK for trunk?
> 
> -- >8 --
> 
> The TYPE_DECL_SUPPRESS_DEBUG and DECL_EXTERNAL flags use the same
> underlying bit. This is causing confusion when attempting to determine
> the interface for a streamed-in class type, since the modules code
> currently assumes that all DECL_EXTERNAL types are extern templates.
> However, when -g is specified then TYPE_DECL_SUPPRESS_DEBUG (and hence
> DECL_EXTERNAL) is marked on various other kinds of declarations, such as
> vtables, which causes them to never be emitted.
> 
> This patch constrains the checks for DECL_EXTERNAL for this to only
> consider template instantiations, thus avoiding the issue.
> 
> 	PR c++/102607
> 	PR c++/112820
> 
> gcc/cp/ChangeLog:
> 
> 	* module.cc (trees_in::read_class_def): Only set interface for
> 	template instantiations.
> 
> gcc/testsuite/ChangeLog:
> 
> 	* g++.dg/modules/debug-2_a.C: New test.
> 	* g++.dg/modules/debug-2_b.C: New test.
> 	* g++.dg/modules/debug-2_c.C: New test.
> 	* g++.dg/modules/debug-3_a.C: New test.
> 	* g++.dg/modules/debug-3_b.C: New test.
> 
> Signed-off-by: Nathaniel Shead <nathanieloshead@gmail.com>
> ---
>  gcc/cp/module.cc                         | 4 +++-
>  gcc/testsuite/g++.dg/modules/debug-2_a.C | 9 +++++++++
>  gcc/testsuite/g++.dg/modules/debug-2_b.C | 8 ++++++++
>  gcc/testsuite/g++.dg/modules/debug-2_c.C | 9 +++++++++
>  gcc/testsuite/g++.dg/modules/debug-3_a.C | 8 ++++++++
>  gcc/testsuite/g++.dg/modules/debug-3_b.C | 9 +++++++++
>  6 files changed, 46 insertions(+), 1 deletion(-)
>  create mode 100644 gcc/testsuite/g++.dg/modules/debug-2_a.C
>  create mode 100644 gcc/testsuite/g++.dg/modules/debug-2_b.C
>  create mode 100644 gcc/testsuite/g++.dg/modules/debug-2_c.C
>  create mode 100644 gcc/testsuite/g++.dg/modules/debug-3_a.C
>  create mode 100644 gcc/testsuite/g++.dg/modules/debug-3_b.C
> 
> diff --git a/gcc/cp/module.cc b/gcc/cp/module.cc
> index 33fcf396875..257f39421d0 100644
> --- a/gcc/cp/module.cc
> +++ b/gcc/cp/module.cc
> @@ -12041,7 +12041,9 @@ trees_in::read_class_def (tree defn, tree maybe_template)
>    bool installing = maybe_dup && !TYPE_SIZE (type);
>    if (installing)
>      {
> -      if (DECL_EXTERNAL (defn) && TYPE_LANG_SPECIFIC (type))
> +      if (DECL_EXTERNAL (defn)
> +	  && TYPE_LANG_SPECIFIC (type)
> +	  && CLASSTYPE_TEMPLATE_INSTANTIATION (type))
>  	{
>  	  /* We don't deal with not-really-extern, because, for a
>  	     module you want the import to be the interface, and for a
> diff --git a/gcc/testsuite/g++.dg/modules/debug-2_a.C b/gcc/testsuite/g++.dg/modules/debug-2_a.C
> new file mode 100644
> index 00000000000..eed0905542b
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/modules/debug-2_a.C
> @@ -0,0 +1,9 @@
> +// PR c++/112820
> +// { dg-additional-options "-fmodules-ts -g" }
> +// { dg-module-cmi io }
> +
> +export module io;
> +
> +export struct error {
> +  virtual const char* what() const noexcept;
> +};
> diff --git a/gcc/testsuite/g++.dg/modules/debug-2_b.C b/gcc/testsuite/g++.dg/modules/debug-2_b.C
> new file mode 100644
> index 00000000000..fc9afbc02e0
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/modules/debug-2_b.C
> @@ -0,0 +1,8 @@
> +// PR c++/112820
> +// { dg-additional-options "-fmodules-ts -g" }
> +
> +module io;
> +
> +const char* error::what() const noexcept {
> +  return "bla";
> +}
> diff --git a/gcc/testsuite/g++.dg/modules/debug-2_c.C b/gcc/testsuite/g++.dg/modules/debug-2_c.C
> new file mode 100644
> index 00000000000..37117f69dcd
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/modules/debug-2_c.C
> @@ -0,0 +1,9 @@
> +// PR c++/112820
> +// { dg-module-do link }
> +// { dg-additional-options "-fmodules-ts -g" }
> +
> +import io;
> +
> +int main() {
> +  error{};
> +}
> diff --git a/gcc/testsuite/g++.dg/modules/debug-3_a.C b/gcc/testsuite/g++.dg/modules/debug-3_a.C
> new file mode 100644
> index 00000000000..9e33d8260fd
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/modules/debug-3_a.C
> @@ -0,0 +1,8 @@
> +// PR c++/102607
> +// { dg-additional-options "-fmodules-ts -g" }
> +// { dg-module-cmi mod }
> +
> +export module mod;
> +export struct B {
> +  virtual ~B() = default;
> +};
> diff --git a/gcc/testsuite/g++.dg/modules/debug-3_b.C b/gcc/testsuite/g++.dg/modules/debug-3_b.C
> new file mode 100644
> index 00000000000..03c78b71b5d
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/modules/debug-3_b.C
> @@ -0,0 +1,9 @@
> +// PR c++/102607
> +// { dg-module-do link }
> +// { dg-additional-options "-fmodules-ts -g" }
> +
> +import mod;
> +int main() {
> +  struct D : B {};
> +  (void)D{};
> +}
> -- 
> 2.42.0
>