diff mbox series

c++/modules: Fix propagating noexcept for templates [PR124785]

Message ID adJ4AoQdUp8Znpyj@Thaum.localdomain
State New
Headers
Series c++/modules: Fix propagating noexcept for templates [PR124785] |

Checks

Context Check Description
linaro-tcwg-bot/tcwg_gcc_build--master-arm success Build passed
linaro-tcwg-bot/tcwg_gcc_check--master-arm success Test passed
linaro-tcwg-bot/tcwg_gcc_build--master-aarch64 success Build passed
linaro-tcwg-bot/tcwg_gcc_check--master-aarch64 success Test passed

Commit Message

Nathaniel Shead April 5, 2026, 2:56 p.m. UTC 
  Bootstrapped and regtested on x86_64-pc-linux-gnu, OK for trunk/15?

-- >8 --

We triggered a checking assertion because when propagating deduced
noexcept, we were updating the type of the existing TEMPLATE_DECL but
not the type of its DECL_TEMPLATE_RESULT, violating assumptions made
later on during modules streaming.

But actually there was nothing to propagate here anyway, these
declarations are identical, so this patch also fixes the condition for
checking whether we need to propagate anything.  And so now I don't
think there is ever a case we should have a noexcept-spec to propagate
for a TEMPLATE_DECL, so add an assertion to validate this.

	PR c++/124785

gcc/cp/ChangeLog:

	* module.cc (trees_in::is_matching_decl): Narrow condition for
	when noexcept propagation occurs; assert that we don't propagate
	noexcept-specs for TEMPLATE_DECLs.

gcc/testsuite/ChangeLog:

	* g++.dg/modules/noexcept-5.h: New test.
	* g++.dg/modules/noexcept-5_a.C: New test.
	* g++.dg/modules/noexcept-5_b.C: New test.
	* g++.dg/modules/noexcept-5_c.C: New test.

Signed-off-by: Nathaniel Shead <nathanieloshead@gmail.com>
---
 gcc/cp/module.cc                            |  4 +++-
 gcc/testsuite/g++.dg/modules/noexcept-5.h   |  4 ++++
 gcc/testsuite/g++.dg/modules/noexcept-5_a.C |  7 +++++++
 gcc/testsuite/g++.dg/modules/noexcept-5_b.C |  7 +++++++
 gcc/testsuite/g++.dg/modules/noexcept-5_c.C | 11 +++++++++++
 5 files changed, 32 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/g++.dg/modules/noexcept-5.h
 create mode 100644 gcc/testsuite/g++.dg/modules/noexcept-5_a.C
 create mode 100644 gcc/testsuite/g++.dg/modules/noexcept-5_b.C
 create mode 100644 gcc/testsuite/g++.dg/modules/noexcept-5_c.C

Comments

Jason Merrill April 6, 2026, 4:41 p.m. UTC | #1 
On 4/5/26 10:56 AM, Nathaniel Shead wrote:
> Bootstrapped and regtested on x86_64-pc-linux-gnu, OK for trunk/15?

OK.

> -- >8 --
> 
> We triggered a checking assertion because when propagating deduced
> noexcept, we were updating the type of the existing TEMPLATE_DECL but
> not the type of its DECL_TEMPLATE_RESULT, violating assumptions made
> later on during modules streaming.
> 
> But actually there was nothing to propagate here anyway, these
> declarations are identical, so this patch also fixes the condition for
> checking whether we need to propagate anything.  And so now I don't
> think there is ever a case we should have a noexcept-spec to propagate
> for a TEMPLATE_DECL, so add an assertion to validate this.
> 
> 	PR c++/124785
> 
> gcc/cp/ChangeLog:
> 
> 	* module.cc (trees_in::is_matching_decl): Narrow condition for
> 	when noexcept propagation occurs; assert that we don't propagate
> 	noexcept-specs for TEMPLATE_DECLs.
> 
> gcc/testsuite/ChangeLog:
> 
> 	* g++.dg/modules/noexcept-5.h: New test.
> 	* g++.dg/modules/noexcept-5_a.C: New test.
> 	* g++.dg/modules/noexcept-5_b.C: New test.
> 	* g++.dg/modules/noexcept-5_c.C: New test.
> 
> Signed-off-by: Nathaniel Shead <nathanieloshead@gmail.com>
> ---
>   gcc/cp/module.cc                            |  4 +++-
>   gcc/testsuite/g++.dg/modules/noexcept-5.h   |  4 ++++
>   gcc/testsuite/g++.dg/modules/noexcept-5_a.C |  7 +++++++
>   gcc/testsuite/g++.dg/modules/noexcept-5_b.C |  7 +++++++
>   gcc/testsuite/g++.dg/modules/noexcept-5_c.C | 11 +++++++++++
>   5 files changed, 32 insertions(+), 1 deletion(-)
>   create mode 100644 gcc/testsuite/g++.dg/modules/noexcept-5.h
>   create mode 100644 gcc/testsuite/g++.dg/modules/noexcept-5_a.C
>   create mode 100644 gcc/testsuite/g++.dg/modules/noexcept-5_b.C
>   create mode 100644 gcc/testsuite/g++.dg/modules/noexcept-5_c.C
> 
> diff --git a/gcc/cp/module.cc b/gcc/cp/module.cc
> index a8517569a1b..8b820f97fee 100644
> --- a/gcc/cp/module.cc
> +++ b/gcc/cp/module.cc
> @@ -12619,12 +12619,14 @@ trees_in::is_matching_decl (tree existing, tree decl, bool is_typedef)
>         tree d_spec = TYPE_RAISES_EXCEPTIONS (d_type);
>         if (DECL_MAYBE_DELETED (e_inner) || DEFERRED_NOEXCEPT_SPEC_P (e_spec))
>   	{
> -	  if (!DEFERRED_NOEXCEPT_SPEC_P (d_spec)
> +	  if (!(DECL_MAYBE_DELETED (d_inner)
> +		|| DEFERRED_NOEXCEPT_SPEC_P (d_spec))
>   	      || (UNEVALUATED_NOEXCEPT_SPEC_P (e_spec)
>   		  && !UNEVALUATED_NOEXCEPT_SPEC_P (d_spec)))
>   	    {
>   	      dump (dumper::MERGE)
>   		&& dump ("Propagating instantiated noexcept to %N", existing);
> +	      gcc_checking_assert (existing == e_inner);
>   	      TREE_TYPE (existing) = d_type;
>   
>   	      /* Propagate to existing clones.  */
> diff --git a/gcc/testsuite/g++.dg/modules/noexcept-5.h b/gcc/testsuite/g++.dg/modules/noexcept-5.h
> new file mode 100644
> index 00000000000..78d91322a1a
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/modules/noexcept-5.h
> @@ -0,0 +1,4 @@
> +// PR c++/124785
> +template <typename T> struct Iterator {
> +  constexpr friend auto operator<=>(const Iterator&, const Iterator&) = default;
> +};
> diff --git a/gcc/testsuite/g++.dg/modules/noexcept-5_a.C b/gcc/testsuite/g++.dg/modules/noexcept-5_a.C
> new file mode 100644
> index 00000000000..72085717e60
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/modules/noexcept-5_a.C
> @@ -0,0 +1,7 @@
> +// PR c++/124785
> +// { dg-do compile { target c++20 } }
> +// { dg-additional-options "-fmodules" }
> +// { dg-module-cmi M:A }
> +
> +export module M:A;
> +#include "noexcept-5.h"
> diff --git a/gcc/testsuite/g++.dg/modules/noexcept-5_b.C b/gcc/testsuite/g++.dg/modules/noexcept-5_b.C
> new file mode 100644
> index 00000000000..928980b6c1d
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/modules/noexcept-5_b.C
> @@ -0,0 +1,7 @@
> +// PR c++/124785
> +// { dg-do compile { target c++20 } }
> +// { dg-additional-options "-fmodules" }
> +// { dg-module-cmi M:B }
> +
> +export module M:B;
> +#include "noexcept-5.h"
> diff --git a/gcc/testsuite/g++.dg/modules/noexcept-5_c.C b/gcc/testsuite/g++.dg/modules/noexcept-5_c.C
> new file mode 100644
> index 00000000000..d9349147766
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/modules/noexcept-5_c.C
> @@ -0,0 +1,11 @@
> +// PR c++/124785
> +// { dg-do compile { target c++20 } }
> +// { dg-additional-options "-fmodules -fdump-lang-module-alias" }
> +// { dg-module-cmi M }
> +
> +export module M;
> +export import :A;
> +export import :B;
> +
> +// The noexcept-specifiers are equivalent, no need to merge.
> +// { dg-final { scan-lang-dump-not {Propagating instantiated noexcept} module } }
diff mbox series

Patch

diff --git a/gcc/cp/module.cc b/gcc/cp/module.cc
index a8517569a1b..8b820f97fee 100644
--- a/gcc/cp/module.cc
+++ b/gcc/cp/module.cc
@@ -12619,12 +12619,14 @@  trees_in::is_matching_decl (tree existing, tree decl, bool is_typedef)
       tree d_spec = TYPE_RAISES_EXCEPTIONS (d_type);
       if (DECL_MAYBE_DELETED (e_inner) || DEFERRED_NOEXCEPT_SPEC_P (e_spec))
 	{
-	  if (!DEFERRED_NOEXCEPT_SPEC_P (d_spec)
+	  if (!(DECL_MAYBE_DELETED (d_inner)
+		|| DEFERRED_NOEXCEPT_SPEC_P (d_spec))
 	      || (UNEVALUATED_NOEXCEPT_SPEC_P (e_spec)
 		  && !UNEVALUATED_NOEXCEPT_SPEC_P (d_spec)))
 	    {
 	      dump (dumper::MERGE)
 		&& dump ("Propagating instantiated noexcept to %N", existing);
+	      gcc_checking_assert (existing == e_inner);
 	      TREE_TYPE (existing) = d_type;
 
 	      /* Propagate to existing clones.  */
diff --git a/gcc/testsuite/g++.dg/modules/noexcept-5.h b/gcc/testsuite/g++.dg/modules/noexcept-5.h
new file mode 100644
index 00000000000..78d91322a1a
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/noexcept-5.h
@@ -0,0 +1,4 @@ 
+// PR c++/124785
+template <typename T> struct Iterator {
+  constexpr friend auto operator<=>(const Iterator&, const Iterator&) = default;
+};
diff --git a/gcc/testsuite/g++.dg/modules/noexcept-5_a.C b/gcc/testsuite/g++.dg/modules/noexcept-5_a.C
new file mode 100644
index 00000000000..72085717e60
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/noexcept-5_a.C
@@ -0,0 +1,7 @@ 
+// PR c++/124785
+// { dg-do compile { target c++20 } }
+// { dg-additional-options "-fmodules" }
+// { dg-module-cmi M:A }
+
+export module M:A;
+#include "noexcept-5.h"
diff --git a/gcc/testsuite/g++.dg/modules/noexcept-5_b.C b/gcc/testsuite/g++.dg/modules/noexcept-5_b.C
new file mode 100644
index 00000000000..928980b6c1d
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/noexcept-5_b.C
@@ -0,0 +1,7 @@ 
+// PR c++/124785
+// { dg-do compile { target c++20 } }
+// { dg-additional-options "-fmodules" }
+// { dg-module-cmi M:B }
+
+export module M:B;
+#include "noexcept-5.h"
diff --git a/gcc/testsuite/g++.dg/modules/noexcept-5_c.C b/gcc/testsuite/g++.dg/modules/noexcept-5_c.C
new file mode 100644
index 00000000000..d9349147766
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/noexcept-5_c.C
@@ -0,0 +1,11 @@ 
+// PR c++/124785
+// { dg-do compile { target c++20 } }
+// { dg-additional-options "-fmodules -fdump-lang-module-alias" }
+// { dg-module-cmi M }
+
+export module M;
+export import :A;
+export import :B;
+
+// The noexcept-specifiers are equivalent, no need to merge.
+// { dg-final { scan-lang-dump-not {Propagating instantiated noexcept} module } }