[PATCH] c++: Don't add built-in operator for ++ on bool.

[Jason Merrill]

On 5/16/20 6:33 PM, Marek Polacek wrote:
> This feels extremely obscure but at least it's an opportunity to fix the
> comments.  P0002R1 removed deprecated operator++(bool) in C++17 so let's
> avoid adding a builtin overload candidate for ++ when the type is bool.
> 
> Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?

OK.

> 	* call.c (add_builtin_candidate): Don't create a builtin overload
> 	candidate for ++ when type is bool in C++17.
> 
> 	* g++.dg/overload/builtin5.C: New test.
> ---
>   gcc/cp/call.c                            | 18 +++++++++++-------
>   gcc/testsuite/g++.dg/overload/builtin5.C | 21 +++++++++++++++++++++
>   2 files changed, 32 insertions(+), 7 deletions(-)
>   create mode 100644 gcc/testsuite/g++.dg/overload/builtin5.C
> 
> diff --git a/gcc/cp/call.c b/gcc/cp/call.c
> index c5871974eb1..b96bc06a364 100644
> --- a/gcc/cp/call.c
> +++ b/gcc/cp/call.c
> @@ -2672,19 +2672,19 @@ add_builtin_candidate (struct z_candidate **candidates, enum tree_code code,
>     switch (code)
>       {
>   
> -/* 4 For every pair T, VQ), where T is an arithmetic or  enumeration  type,
> +/* 4 For every pair (T, VQ), where T is an arithmetic type other than bool,
>        and  VQ  is  either  volatile or empty, there exist candidate operator
>        functions of the form
>   	     VQ T&   operator++(VQ T&);
>   	     T       operator++(VQ T&, int);
> -   5 For every pair T, VQ), where T is an enumeration type or an arithmetic
> -     type  other than bool, and VQ is either volatile or empty, there exist
> -     candidate operator functions of the form
> +   5 For every pair (T, VQ), where T is an arithmetic type other than bool,
> +     and VQ is either volatile or empty, there exist candidate operator
> +     functions of the form
>   	     VQ T&   operator--(VQ T&);
>   	     T       operator--(VQ T&, int);
> -   6 For every pair T, VQ), where T is  a  cv-qualified  or  cv-unqualified
> -     complete  object type, and VQ is either volatile or empty, there exist
> -     candidate operator functions of the form
> +   6 For every pair (T, VQ), where T is a cv-qualified or cv-unqualified object
> +     type, and VQ is either volatile or empty, there exist candidate operator
> +     functions of the form
>   	     T*VQ&   operator++(T*VQ&);
>   	     T*VQ&   operator--(T*VQ&);
>   	     T*      operator++(T*VQ&, int);
> @@ -2697,6 +2697,10 @@ add_builtin_candidate (struct z_candidate **candidates, enum tree_code code,
>         /* FALLTHRU */
>       case POSTINCREMENT_EXPR:
>       case PREINCREMENT_EXPR:
> +      /* P0002R1, Remove deprecated operator++(bool) added "other than bool"
> +	 to p4.  */
> +      if (TREE_CODE (type1) == BOOLEAN_TYPE && cxx_dialect >= cxx17)
> +	return;
>         if (ARITHMETIC_TYPE_P (type1) || TYPE_PTROB_P (type1))
>   	{
>   	  type1 = build_reference_type (type1);
> diff --git a/gcc/testsuite/g++.dg/overload/builtin5.C b/gcc/testsuite/g++.dg/overload/builtin5.C
> new file mode 100644
> index 00000000000..a30251dc79d
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/overload/builtin5.C
> @@ -0,0 +1,21 @@
> +// { dg-do compile { target c++17 } }
> +// Don't add built-in operator for ++ on bool.
> +
> +template<typename T>
> +struct S { operator T&(); };
> +
> +template<int> void
> +foo (S<bool>& s)
> +{
> +  --s; // { dg-error "no match for" }
> +  ++s; // { dg-error "no match for" }
> +  s++; // { dg-error "declared for postfix" }
> +  s--; // { dg-error "declared for postfix" }
> +}
> +
> +void
> +bar ()
> +{
> +  S<bool> s;
> +  foo<0> (s);
> +}
> 
> base-commit: f5b461d453043c6b6dda50db0439e4c78b241f03
>