[C++ PATCH v2] PR c++/93324 - ICE with -Wall on constexpr if.

[Jason Merrill]

On 1/19/20 4:18 PM, Marek Polacek wrote:
> On Sun, Jan 19, 2020 at 10:00:42PM +0100, Jakub Jelinek wrote:
>> On Sun, Jan 19, 2020 at 03:34:48PM -0500, Marek Polacek wrote:
>>> Bootstrapped/regtested on x86_64-linux, ok for trunk?
>>>
>>> 	* semantics.c (is_std_constant_evaluated_p): Check fndecl.
>>>
>>> 	* g++.dg/cpp1z/constexpr-if33.C: New test.
>>> ---
>>>   gcc/cp/semantics.c                          |  4 ++--
>>>   gcc/testsuite/g++.dg/cpp1z/constexpr-if33.C | 16 ++++++++++++++++
>>>   2 files changed, 18 insertions(+), 2 deletions(-)
>>>   create mode 100644 gcc/testsuite/g++.dg/cpp1z/constexpr-if33.C
>>>
>>> diff --git a/gcc/cp/semantics.c b/gcc/cp/semantics.c
>>> index 3669b247e34..9051a2863e0 100644
>>> --- a/gcc/cp/semantics.c
>>> +++ b/gcc/cp/semantics.c
>>> @@ -734,8 +734,8 @@ is_std_constant_evaluated_p (tree fn)
>>>       return false;
>>>   
>>>     tree fndecl = cp_get_callee_fndecl_nofold (fn);
>>> -  if (fndecl_built_in_p (fndecl, CP_BUILT_IN_IS_CONSTANT_EVALUATED,
>>> -			 BUILT_IN_FRONTEND))
>>> +  if (fndecl && fndecl_built_in_p (fndecl, CP_BUILT_IN_IS_CONSTANT_EVALUATED,
>>> +				   BUILT_IN_FRONTEND))
>>>       return true;
>>>   
>>>     if (!decl_in_std_namespace_p (fndecl))
>>
>> Shouldn't it instead do
>>    if (fndecl == NULL_TREE)
>>      return false;
>> before the fndecl_built_in_p check?
>>
>> While decl_in_std_namespace_p apparently will return false for NULL
>> argument, relying on that is werid.
> 
> Can do that, too.
> 
> -- >8 --
> This is a crash with constexpr if, when trying to see if the call in
> the if-statement is std::is_constant_evaluated.
> 
> cp_get_callee_fndecl_nofold can return NULL_TREE and fndecl_built_in_p
> doesn't expect to get a null tree, so check FNDECL first.
> 
> Bootstrapped/regtested on x86_64-linux, ok for trunk?

OK.

> 	* semantics.c (is_std_constant_evaluated_p): Check fndecl.
> 
> 	* g++.dg/cpp1z/constexpr-if33.C: New test.
> ---
>   gcc/cp/semantics.c                          |  3 +++
>   gcc/testsuite/g++.dg/cpp1z/constexpr-if33.C | 16 ++++++++++++++++
>   2 files changed, 19 insertions(+)
>   create mode 100644 gcc/testsuite/g++.dg/cpp1z/constexpr-if33.C
> 
> diff --git a/gcc/cp/semantics.c b/gcc/cp/semantics.c
> index 3669b247e34..3b88f1520bc 100644
> --- a/gcc/cp/semantics.c
> +++ b/gcc/cp/semantics.c
> @@ -734,6 +734,9 @@ is_std_constant_evaluated_p (tree fn)
>       return false;
>   
>     tree fndecl = cp_get_callee_fndecl_nofold (fn);
> +  if (fndecl == NULL_TREE)
> +    return false;
> +
>     if (fndecl_built_in_p (fndecl, CP_BUILT_IN_IS_CONSTANT_EVALUATED,
>   			 BUILT_IN_FRONTEND))
>       return true;
> diff --git a/gcc/testsuite/g++.dg/cpp1z/constexpr-if33.C b/gcc/testsuite/g++.dg/cpp1z/constexpr-if33.C
> new file mode 100644
> index 00000000000..e5ef659932b
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp1z/constexpr-if33.C
> @@ -0,0 +1,16 @@
> +// PR c++/93324 - ICE with -Wall on constexpr if.
> +// { dg-do compile { target c++17 } }
> +// { dg-options "-Wall" }
> +
> +struct {
> +  template <int>
> +  static constexpr bool a() { return 0; }
> +} e;
> +
> +template <typename>
> +void d()
> +{
> +  auto c(e);
> +  using b = decltype(c);
> +  if constexpr (b::a<2>());
> +}
> 
> base-commit: bcfc2227c556f2801a657ce3007374732baa8333
>