Re: [PATCH v2 1/2] c++: implement __is_const built-in trait

[Ken Matsui <kmatsui@cs.washington.edu>]

Here is the benchmark result for is_const.

https://github.com/ken-matsui/gcc-benches/blob/main/is_const.md#sat-jun-24-044815-am-pdt-2023

Time: -2.86467%
Peak Memory Usage: -1.0654%
Total Memory Usage: -1.62369%

On Sat, Jun 24, 2023 at 6:41 AM Ken Matsui <kmatsui@cs.washington.edu> wrote:
>
> This patch implements built-in trait for std::is_const.
>
> gcc/cp/ChangeLog:
>
>         * cp-trait.def: Define __is_const.
>         * constraint.cc (diagnose_trait_expr): Handle CPTK_IS_CONST.
>         * semantics.cc (trait_expr_value): Likewise.
>         (finish_trait_expr): Likewise.
>
> gcc/testsuite/ChangeLog:
>
>         * g++.dg/ext/has-builtin-1.C: Test existence of __is_const.
>         * g++.dg/ext/is_const.C: New test.
>
> Signed-off-by: Ken Matsui <kmatsui@cs.washington.edu>
> ---
>  gcc/cp/constraint.cc                     |  3 +++
>  gcc/cp/cp-trait.def                      |  1 +
>  gcc/cp/semantics.cc                      |  4 ++++
>  gcc/testsuite/g++.dg/ext/has-builtin-1.C |  3 +++
>  gcc/testsuite/g++.dg/ext/is_const.C      | 19 +++++++++++++++++++
>  5 files changed, 30 insertions(+)
>  create mode 100644 gcc/testsuite/g++.dg/ext/is_const.C
>
> diff --git a/gcc/cp/constraint.cc b/gcc/cp/constraint.cc
> index 8cf0f2d0974..ff4ae831def 100644
> --- a/gcc/cp/constraint.cc
> +++ b/gcc/cp/constraint.cc
> @@ -3751,6 +3751,9 @@ diagnose_trait_expr (tree expr, tree args)
>      case CPTK_IS_UNION:
>        inform (loc, "  %qT is not a union", t1);
>        break;
> +    case CPTK_IS_CONST:
> +      inform (loc, "  %qT is not a const type", t1);
> +      break;
>      case CPTK_IS_AGGREGATE:
>        inform (loc, "  %qT is not an aggregate", t1);
>        break;
> diff --git a/gcc/cp/cp-trait.def b/gcc/cp/cp-trait.def
> index 8b7fece0cc8..b40b475b86d 100644
> --- a/gcc/cp/cp-trait.def
> +++ b/gcc/cp/cp-trait.def
> @@ -82,6 +82,7 @@ DEFTRAIT_EXPR (IS_TRIVIALLY_ASSIGNABLE, "__is_trivially_assignable", 2)
>  DEFTRAIT_EXPR (IS_TRIVIALLY_CONSTRUCTIBLE, "__is_trivially_constructible", -1)
>  DEFTRAIT_EXPR (IS_TRIVIALLY_COPYABLE, "__is_trivially_copyable", 1)
>  DEFTRAIT_EXPR (IS_UNION, "__is_union", 1)
> +DEFTRAIT_EXPR (IS_CONST, "__is_const", 1)
>  DEFTRAIT_EXPR (REF_CONSTRUCTS_FROM_TEMPORARY, "__reference_constructs_from_temporary", 2)
>  DEFTRAIT_EXPR (REF_CONVERTS_FROM_TEMPORARY, "__reference_converts_from_temporary", 2)
>  /* FIXME Added space to avoid direct usage in GCC 13.  */
> diff --git a/gcc/cp/semantics.cc b/gcc/cp/semantics.cc
> index 8fb47fd179e..011ba8e46e1 100644
> --- a/gcc/cp/semantics.cc
> +++ b/gcc/cp/semantics.cc
> @@ -12079,6 +12079,9 @@ trait_expr_value (cp_trait_kind kind, tree type1, tree type2)
>      case CPTK_IS_ENUM:
>        return type_code1 == ENUMERAL_TYPE;
>
> +    case CPTK_IS_CONST:
> +      return CP_TYPE_CONST_P (type1);
> +
>      case CPTK_IS_FINAL:
>        return CLASS_TYPE_P (type1) && CLASSTYPE_FINAL (type1);
>
> @@ -12296,6 +12299,7 @@ finish_trait_expr (location_t loc, cp_trait_kind kind, tree type1, tree type2)
>      case CPTK_IS_ENUM:
>      case CPTK_IS_UNION:
>      case CPTK_IS_SAME:
> +    case CPTK_IS_CONST:
>        break;
>
>      case CPTK_IS_LAYOUT_COMPATIBLE:
> diff --git a/gcc/testsuite/g++.dg/ext/has-builtin-1.C b/gcc/testsuite/g++.dg/ext/has-builtin-1.C
> index f343e153e56..965309a333a 100644
> --- a/gcc/testsuite/g++.dg/ext/has-builtin-1.C
> +++ b/gcc/testsuite/g++.dg/ext/has-builtin-1.C
> @@ -146,3 +146,6 @@
>  #if !__has_builtin (__remove_cvref)
>  # error "__has_builtin (__remove_cvref) failed"
>  #endif
> +#if !__has_builtin (__is_const)
> +# error "__has_builtin (__is_const) failed"
> +#endif
> diff --git a/gcc/testsuite/g++.dg/ext/is_const.C b/gcc/testsuite/g++.dg/ext/is_const.C
> new file mode 100644
> index 00000000000..8f2d7c2fce9
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/ext/is_const.C
> @@ -0,0 +1,19 @@
> +// { dg-do compile { target c++11 } }
> +
> +#include <testsuite_tr1.h>
> +
> +using namespace __gnu_test;
> +
> +#define SA(X) static_assert((X),#X)
> +
> +// Positive tests.
> +SA(__is_const(const int));
> +SA(__is_const(const volatile int));
> +SA(__is_const(cClassType));
> +SA(__is_const(cvClassType));
> +
> +// Negative tests.
> +SA(!__is_const(int));
> +SA(!__is_const(volatile int));
> +SA(!__is_const(ClassType));
> +SA(!__is_const(vClassType));
> --
> 2.41.0
>