Re: [PATCH] c++ modules: ICE with dynamic_cast [PR106304]

[Nathan Sidwell <nathan@acm.org>]

On 10/13/22 15:04, Patrick Palka wrote:
> The FUNCTION_DECL we build for __dynamic_cast has an empty DECL_CONTEXT,
> but trees_out::tree_node expects all FUNCTION_DECLs to have non-empty
> DECL_CONTEXT thus we crash when streaming out the dynamic_cast in the
> below testcase.
> 
> This patch naively fixes this by setting DECL_CONTEXT for __dynamic_cast
> appropriately.  Like for __cxa_atexit which is similarly lazily declared,
> I suppose we should push it into the namespace too.
> 
> Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
> trunk?

This is correct, there were a bunch of similar issues, surprising these 
never triggered.

> 
> 	PR c++/106304
> 
> gcc/cp/ChangeLog:
> 
> 	* constexpr.cc (cxx_dynamic_cast_fn_p): Check for abi_node
> 	instead of global_namespace.
> 	* rtti.cc (build_dynamic_cast_1): Set DECL_CONTEXT and
> 	DECL_SOURCE_LOCATION on dynamic_cast_node, and push it
> 	into the namespace.
> 
> gcc/testsuite/ChangeLog:
> 
> 	* g++.dg/modules/pr106304_a.C: New test.
> 	* g++.dg/modules/pr106304_b.C: New test.
> ---
>   gcc/cp/constexpr.cc                       |  2 +-
>   gcc/cp/rtti.cc                            |  4 ++++
>   gcc/testsuite/g++.dg/modules/pr106304_a.C | 12 ++++++++++++
>   gcc/testsuite/g++.dg/modules/pr106304_b.C |  8 ++++++++
>   4 files changed, 25 insertions(+), 1 deletion(-)
>   create mode 100644 gcc/testsuite/g++.dg/modules/pr106304_a.C
>   create mode 100644 gcc/testsuite/g++.dg/modules/pr106304_b.C
> 
> diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc
> index 06dcd71c926..5939d2882f8 100644
> --- a/gcc/cp/constexpr.cc
> +++ b/gcc/cp/constexpr.cc
> @@ -2108,7 +2108,7 @@ cxx_dynamic_cast_fn_p (tree fndecl)
>   {
>     return (cxx_dialect >= cxx20
>   	  && id_equal (DECL_NAME (fndecl), "__dynamic_cast")
> -	  && CP_DECL_CONTEXT (fndecl) == global_namespace);
> +	  && CP_DECL_CONTEXT (fndecl) == abi_node);
>   }
>   
>   /* Often, we have an expression in the form of address + offset, e.g.
> diff --git a/gcc/cp/rtti.cc b/gcc/cp/rtti.cc
> index f5b43ec0fb2..a85c7b56409 100644
> --- a/gcc/cp/rtti.cc
> +++ b/gcc/cp/rtti.cc
> @@ -787,6 +787,10 @@ build_dynamic_cast_1 (location_t loc, tree type, tree expr,
>   			       NULL_TREE));
>   	      dcast_fn = (build_library_fn_ptr
>   			  (fn_name, fn_type, ECF_LEAF | ECF_PURE | ECF_NOTHROW));
> +	      /* As with __cxa_atexit in get_atexit_node.  */
> +	      DECL_CONTEXT (dcast_fn) = FROB_CONTEXT (current_namespace);
> +	      DECL_SOURCE_LOCATION (dcast_fn) = BUILTINS_LOCATION;
> +	      dcast_fn = pushdecl (dcast_fn, /*hiding=*/true);
>   	      pop_abi_namespace (flags);
>   	      dynamic_cast_node = dcast_fn;
>   	    }
> diff --git a/gcc/testsuite/g++.dg/modules/pr106304_a.C b/gcc/testsuite/g++.dg/modules/pr106304_a.C
> new file mode 100644
> index 00000000000..b999eeccf4a
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/modules/pr106304_a.C
> @@ -0,0 +1,12 @@
> +// PR c++/106304
> +// { dg-additional-options -fmodules-ts }
> +// { dg-module-cmi pr106304 }
> +
> +export module pr106304;
> +
> +struct A { virtual ~A() = default; };
> +struct B : A { };
> +
> +inline const B* as_b(const A& a) {
> +  return dynamic_cast<const B*>(&a);
> +}
> diff --git a/gcc/testsuite/g++.dg/modules/pr106304_b.C b/gcc/testsuite/g++.dg/modules/pr106304_b.C
> new file mode 100644
> index 00000000000..e8333909c8d
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/modules/pr106304_b.C
> @@ -0,0 +1,8 @@
> +// PR c++/106304
> +// { dg-additional-options -fmodules-ts }
> +
> +module pr106304;
> +
> +void f(A& a) {
> +  as_b(a);
> +}

-- 
Nathan Sidwell