[PATCH] c++: Fix ICE from op_unqualified_lookup [PR97582]

[Jason Merrill]

On 2/2/21 12:19 AM, Patrick Palka wrote:
> In this testcase, we're crashing because the lookup of operator+ from
> within the generic lambda via lookup_name finds multiple bindings
> (namely C1::operator+ and C2::operator+) and returns a TREE_LIST
> thereof, something which maybe_save_operator_binding isn't prepared to
> handle.
> 
> Since we already discard the result of lookup_name when it returns a
> class-scope binding here, it seems cleaner (and equivalent) to instead
> communicate to lookup_name that we don't want such bindings in the first
> place.  While this change seems like an improvement on its own, it also
> fixes the mentioned PR, because the call to lookup_name now returns
> NULL_TREE rather than a TREE_LIST of (unwanted) class-scope bindings.
> 
> Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
> trunk/9/10?
> 
> gcc/cp/ChangeLog:
> 
> 	PR c++/97582
> 	* name-lookup.c (op_unqualified_lookup): Pass BLOCK_NAMESPACE to
> 	lookup_name in order to ignore class-scope bindings, rather
> 	than discarding them after the fact.
> 
> gcc/testsuite/ChangeLog:
> 
> 	PR c++/97582
> 	* g++.dg/cpp0x/lambda/lambda-template17.C: New test.
> ---
>   gcc/cp/name-lookup.c                                  | 11 +++--------
>   gcc/testsuite/g++.dg/cpp0x/lambda/lambda-template17.C |  8 ++++++++
>   2 files changed, 11 insertions(+), 8 deletions(-)
>   create mode 100644 gcc/testsuite/g++.dg/cpp0x/lambda/lambda-template17.C
> 
> diff --git a/gcc/cp/name-lookup.c b/gcc/cp/name-lookup.c
> index 52e4a630e25..46d6cc0dfa4 100644
> --- a/gcc/cp/name-lookup.c
> +++ b/gcc/cp/name-lookup.c
> @@ -9213,17 +9213,12 @@ op_unqualified_lookup (tree fnname)
>   	return NULL_TREE;
>       }
>   
> -  tree fns = lookup_name (fnname);
> +  /* We don't need to remember class-scope functions or declarations,
> +     normal unqualified lookup will find them again.  */
> +  tree fns = lookup_name (fnname, LOOK_where::BLOCK_NAMESPACE);

Hmm, I'd expect this to look past class-scope declarations to find 
namespace-scope declarations, but we want class decls to hide decls in 
an outer scope.

>     if (!fns)
>       /* Remember we found nothing!  */
>       return error_mark_node;
> -
> -  tree d = is_overloaded_fn (fns) ? get_first_fn (fns) : fns;
> -  if (DECL_CLASS_SCOPE_P (d))
> -    /* We don't need to remember class-scope functions or declarations,
> -       normal unqualified lookup will find them again.  */
> -    fns = NULL_TREE;
> -
>     return fns;
>   }
>   
> diff --git a/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-template17.C b/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-template17.C
> new file mode 100644
> index 00000000000..6cafbab8cb0
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-template17.C
> @@ -0,0 +1,8 @@
> +// PR c++/97582
> +// { dg-do compile { target c++11 } }
> +
> +struct C1 { void operator+(); };
> +struct C2 { void operator+(); };
> +struct C3 : C1, C2 {
> +  template <class T> void get() { [] (T x) { +x; }; }
> +};
>