Re: [C++ Patch] [PR c++/88146] do not crash synthesizing inherited ctor(...)

[Jason Merrill <jason@redhat.com>]

On 12/6/18 7:23 PM, Alexandre Oliva wrote:
> This patch started out from the testcase in PR88146, that attempted to
> synthesize an inherited ctor without any args before a varargs
> ellipsis and crashed while at that, because of the unguarded
> dereferencing of the parm type list, that usually contains a
> terminator.  The terminator is not there for varargs functions,
> however, and without any other args, we ended up dereferencing a NULL
> pointer.  Oops.
> 
> Guarding the accesses there was easy, but I missed the sorry message
> we got in other testcases that passed arguments through the ellipsis
> in inherited ctors.  I put a check in, and noticed the inherited ctors
> were synthesized with the location assigned to the class name,
> although they were initially assigned the location of the using
> declaration.  I decided the latter was better, and arranged for the
> better location to be retained.
> 
> Further investigation revealed the lack of a sorry message had to do
> with the call being in a non-evaluated context, in this case, a
> noexcept expression.  The sorry would be correctly reported in other
> contexts, so I rolled back the check I'd added, but retained the
> source location improvement.
> 
> I was still concerned about issuing sorry messages while instantiating
> template ctors even in non-evaluated contexts, e.g., if a template
> ctor had a base initializer that used an inherited ctor with enough
> arguments that they'd go through an ellipsis.  I wanted to defer the
> instantiation of such template ctors, but that would have been wrong
> for constexpr template ctors, and already done for non-constexpr ones.
> So, I just consolidated multiple test variants into a single testcase
> that explores and explains various of the possibilities I thought of.
> 
> Regstrapped on x86_64- and i686-linux-gnu, mistakenly along with a patch
> with a known regression, and got only that known regression.  Retesting
> without it.  Ok to install?
> 
> 
> for  gcc/cp/ChangeLog
> 
> 	PR c++/88146
> 	* method.c (do_build_copy_constructor): Do not crash with
> 	ellipsis-only parm list.
> 	(synthesize_method): Retain location of inherited ctor.
> 
> for  gcc/testsuite/ChangeLog
> 
> 	PR c++/88146
> 	* g++.dg/cpp0x/inh-ctor32.C: New.
> ---
>   gcc/cp/method.c                         |    9 +
>   gcc/testsuite/g++.dg/cpp0x/inh-ctor32.C |  229 +++++++++++++++++++++++++++++++
>   2 files changed, 234 insertions(+), 4 deletions(-)
>   create mode 100644 gcc/testsuite/g++.dg/cpp0x/inh-ctor32.C
> 
> diff --git a/gcc/cp/method.c b/gcc/cp/method.c
> index fd023e200538..41d609fb1de6 100644
> --- a/gcc/cp/method.c
> +++ b/gcc/cp/method.c
> @@ -643,7 +643,7 @@ do_build_copy_constructor (tree fndecl)
>     bool trivial = trivial_fn_p (fndecl);
>     tree inh = DECL_INHERITED_CTOR (fndecl);
>   
> -  if (!inh)
> +  if (parm && !inh)
>       parm = convert_from_reference (parm);

If inh is false, we're a copy constructor, which always has a parm, so 
this hunk seems unnecessary.

>   
>     if (trivial)
> @@ -677,7 +677,7 @@ do_build_copy_constructor (tree fndecl)
>       {
>         tree fields = TYPE_FIELDS (current_class_type);
>         tree member_init_list = NULL_TREE;
> -      int cvquals = cp_type_quals (TREE_TYPE (parm));
> +      int cvquals = parm ? cp_type_quals (TREE_TYPE (parm)) : 0;

This could also check !inh.

Jason