[PATCH] c++: Fix ICE in check_local_shadow with enum [PR95560]

[Jason Merrill]

On 6/10/20 5:11 PM, Marek Polacek wrote:
> Another indication that perhaps this warning is emitted too early.  We
> crash because same_type_p gets a null type: we have an enumerator
> without a fixed underlying type and finish_enum_value_list hasn't yet
> run.  So check if the type is null before calling same_type_p.

Hmm, I wonder why we use NULL_TREE for the type of uninitialized 
enumerators in a template; why not give them integer_type_node temporarily?

> (This is a regression and this fix is suitable for backporting.  Delaying
> the warning would not be suitable to backport.)
> 
> Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk/10/9?
> 
> gcc/cp/ChangeLog:
> 
> 	PR c++/95560
> 	* name-lookup.c (check_local_shadow): Check if types are
> 	non-null before calling same_type_p.
> 
> gcc/testsuite/ChangeLog:
> 
> 	PR c++/95560
> 	* g++.dg/warn/Wshadow-local-3.C: New test.
> ---
>   gcc/cp/name-lookup.c                        | 4 +++-
>   gcc/testsuite/g++.dg/warn/Wshadow-local-3.C | 7 +++++++
>   2 files changed, 10 insertions(+), 1 deletion(-)
>   create mode 100644 gcc/testsuite/g++.dg/warn/Wshadow-local-3.C
> 
> diff --git a/gcc/cp/name-lookup.c b/gcc/cp/name-lookup.c
> index 2ff85f1cf5e..159c98a67cd 100644
> --- a/gcc/cp/name-lookup.c
> +++ b/gcc/cp/name-lookup.c
> @@ -2762,7 +2762,9 @@ check_local_shadow (tree decl)
>         enum opt_code warning_code;
>         if (warn_shadow)
>   	warning_code = OPT_Wshadow;
> -      else if (same_type_p (TREE_TYPE (old), TREE_TYPE (decl))
> +      else if ((TREE_TYPE (old)
> +		&& TREE_TYPE (decl)
> +		&& same_type_p (TREE_TYPE (old), TREE_TYPE (decl)))
>   	       || TREE_CODE (decl) == TYPE_DECL
>   	       || TREE_CODE (old) == TYPE_DECL
>   	       || (!dependent_type_p (TREE_TYPE (decl))
> diff --git a/gcc/testsuite/g++.dg/warn/Wshadow-local-3.C b/gcc/testsuite/g++.dg/warn/Wshadow-local-3.C
> new file mode 100644
> index 00000000000..fd743eca347
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/warn/Wshadow-local-3.C
> @@ -0,0 +1,7 @@
> +// PR c++/95560
> +// { dg-do compile { target c++11 } }
> +
> +template <typename> void fn1() {
> +  bool ready;
> +  enum class State { ready };
> +}
> 
> base-commit: 3a391adf7a38780f8d01dbac08a2a143fc80b469
>