[PATCH] c++: canonicity of fn types w/ instantiated eh specs [PR115223]

[PATCH] c++: canonicity of fn types w/ instantiated eh specs [PR115223]

[Patrick Palka]

Bootstrap and regtest on x86_64-pc-linux-gnu in progress,
does this look OK for trunk if successful?

-- >8 --

When propagating structural equality in build_cp_fntype_variant, we
should consider structural equality of the exception-less variant, not
of the given type which might use structural equality only because of
the (complex) noexcept-spec we're intending to replace, as in
maybe_instantiate_noexcept which calls build_exception_variant using
the function type with a deferred noexcept-spec.  Otherwise we might
pessimisticly use structural equality for a function type with a simple
instantiated noexcept-spec, leading to a failed LTO-specific sanity
check if we later use that (structural-equality) type as the canonical
version of some other variant.

	PR c++/115223

gcc/cp/ChangeLog:

	* tree.cc (build_cp_fntype_variant): Propagate structural
	equality of the exception-less variant.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp0x/noexcept87.C: New test.
---
 gcc/cp/tree.cc                          |  4 ++++
 gcc/testsuite/g++.dg/cpp0x/noexcept87.C | 11 +++++++++++
 2 files changed, 15 insertions(+)
 create mode 100644 gcc/testsuite/g++.dg/cpp0x/noexcept87.C

diff --git a/gcc/cp/tree.cc b/gcc/cp/tree.cc
index 4d87661b4ad..f810b8cd777 100644
--- a/gcc/cp/tree.cc
+++ b/gcc/cp/tree.cc
@@ -2796,6 +2796,10 @@ build_cp_fntype_variant (tree type, cp_ref_qualifier rqual,
   bool complex_eh_spec_p = (cr && cr != noexcept_true_spec
 			    && !UNPARSED_NOEXCEPT_SPEC_P (cr));
 
+  if (!complex_eh_spec_p && TYPE_RAISES_EXCEPTIONS (type))
+    /* We want to consider structural equality of the exception-less
+       variant since we'll be replacing the exception specification.  */
+    type = build_cp_fntype_variant (type, rqual, /*raises=*/NULL_TREE, late);
   if (TYPE_STRUCTURAL_EQUALITY_P (type) || complex_eh_spec_p)
     /* Propagate structural equality.  And always use structural equality
        for function types with a complex noexcept-spec since their identity
diff --git a/gcc/testsuite/g++.dg/cpp0x/noexcept87.C b/gcc/testsuite/g++.dg/cpp0x/noexcept87.C
new file mode 100644
index 00000000000..60b1497472b
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/noexcept87.C
@@ -0,0 +1,11 @@
+// PR c++/115223
+// { dg-do compile { target c++11 } }
+// { dg-additional-options -flto }
+
+template<class T>
+void f() noexcept(bool(T() || true));
+
+void g(int n) { f<int>(); }
+
+using type = void;
+type callDestructorIfNecessary() noexcept {}
-- 
2.45.1.246.gb9cfe4845c

Re: [PATCH] c++: canonicity of fn types w/ instantiated eh specs [PR115223]

[Jason Merrill]

On 5/25/24 19:18, Patrick Palka wrote:
> Bootstrap and regtest on x86_64-pc-linux-gnu in progress,
> does this look OK for trunk if successful?

OK.

> -- >8 --
> 
> When propagating structural equality in build_cp_fntype_variant, we
> should consider structural equality of the exception-less variant, not
> of the given type which might use structural equality only because of
> the (complex) noexcept-spec we're intending to replace, as in
> maybe_instantiate_noexcept which calls build_exception_variant using
> the function type with a deferred noexcept-spec.  Otherwise we might
> pessimisticly use structural equality for a function type with a simple
> instantiated noexcept-spec, leading to a failed LTO-specific sanity
> check if we later use that (structural-equality) type as the canonical
> version of some other variant.
> 
> 	PR c++/115223
> 
> gcc/cp/ChangeLog:
> 
> 	* tree.cc (build_cp_fntype_variant): Propagate structural
> 	equality of the exception-less variant.
> 
> gcc/testsuite/ChangeLog:
> 
> 	* g++.dg/cpp0x/noexcept87.C: New test.
> ---
>   gcc/cp/tree.cc                          |  4 ++++
>   gcc/testsuite/g++.dg/cpp0x/noexcept87.C | 11 +++++++++++
>   2 files changed, 15 insertions(+)
>   create mode 100644 gcc/testsuite/g++.dg/cpp0x/noexcept87.C
> 
> diff --git a/gcc/cp/tree.cc b/gcc/cp/tree.cc
> index 4d87661b4ad..f810b8cd777 100644
> --- a/gcc/cp/tree.cc
> +++ b/gcc/cp/tree.cc
> @@ -2796,6 +2796,10 @@ build_cp_fntype_variant (tree type, cp_ref_qualifier rqual,
>     bool complex_eh_spec_p = (cr && cr != noexcept_true_spec
>   			    && !UNPARSED_NOEXCEPT_SPEC_P (cr));
>   
> +  if (!complex_eh_spec_p && TYPE_RAISES_EXCEPTIONS (type))
> +    /* We want to consider structural equality of the exception-less
> +       variant since we'll be replacing the exception specification.  */
> +    type = build_cp_fntype_variant (type, rqual, /*raises=*/NULL_TREE, late);
>     if (TYPE_STRUCTURAL_EQUALITY_P (type) || complex_eh_spec_p)
>       /* Propagate structural equality.  And always use structural equality
>          for function types with a complex noexcept-spec since their identity
> diff --git a/gcc/testsuite/g++.dg/cpp0x/noexcept87.C b/gcc/testsuite/g++.dg/cpp0x/noexcept87.C
> new file mode 100644
> index 00000000000..60b1497472b
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp0x/noexcept87.C
> @@ -0,0 +1,11 @@
> +// PR c++/115223
> +// { dg-do compile { target c++11 } }
> +// { dg-additional-options -flto }
> +
> +template<class T>
> +void f() noexcept(bool(T() || true));
> +
> +void g(int n) { f<int>(); }
> +
> +using type = void;
> +type callDestructorIfNecessary() noexcept {}