diff options
author | Jakub Jelinek <jakub@redhat.com> | 2024-04-09 09:31:42 +0200 |
---|---|---|
committer | Jakub Jelinek <jakub@redhat.com> | 2024-04-21 06:08:05 +0200 |
commit | ae3b6dea0445f9650cf1a684527efac06497f1b4 (patch) | |
tree | 710be539e87f36ff962a6011c915784eaa581d0e | |
parent | 38af0d59043da4cc07cd62c17da599e43668e3be (diff) |
c++: Fix up maybe_warn_for_constant_evaluated calls [PR114580]
When looking at maybe_warn_for_constant_evaluated for the trivial
infinite loops patch, I've noticed that it can emit weird diagnostics
for if constexpr in templates, first warn that std::is_constant_evaluted()
always evaluates to false (because the function template is not constexpr)
and then during instantiation warn that std::is_constant_evaluted()
always evaluates to true (because it is used in if constexpr condition).
Now, only the latter is actually true, even when the if constexpr
is in a non-constexpr function, it will still always evaluate to true.
So, the following patch fixes it to call maybe_warn_for_constant_evaluated
always with IF_STMT_CONSTEXPR_P (if_stmt) as the second argument rather than
true if it is if constexpr with non-dependent condition etc.
2024-04-09 Jakub Jelinek <jakub@redhat.com>
PR c++/114580
* semantics.cc (finish_if_stmt_cond): Call
maybe_warn_for_constant_evaluated with IF_STMT_CONSTEXPR_P (if_stmt)
as the second argument, rather than true/false depending on if
it is if constexpr with non-dependent constant expression with
bool type.
* g++.dg/cpp2a/is-constant-evaluated15.C: New test.
(cherry picked from commit cfed80b9e4f562c99679739548df9369117dd791)
-rw-r--r-- | gcc/cp/semantics.cc | 10 | ||||
-rw-r--r-- | gcc/testsuite/g++.dg/cpp2a/is-constant-evaluated15.C | 28 |
2 files changed, 31 insertions, 7 deletions
diff --git a/gcc/cp/semantics.cc b/gcc/cp/semantics.cc index ff5252905fe..a9fabf92a2a 100644 --- a/gcc/cp/semantics.cc +++ b/gcc/cp/semantics.cc @@ -1046,6 +1046,7 @@ tree finish_if_stmt_cond (tree orig_cond, tree if_stmt) { tree cond = maybe_convert_cond (orig_cond); + maybe_warn_for_constant_evaluated (cond, IF_STMT_CONSTEXPR_P (if_stmt)); if (IF_STMT_CONSTEXPR_P (if_stmt) && !type_dependent_expression_p (cond) && require_constant_expression (cond) @@ -1054,16 +1055,11 @@ finish_if_stmt_cond (tree orig_cond, tree if_stmt) converted to bool. */ && TYPE_MAIN_VARIANT (TREE_TYPE (cond)) == boolean_type_node) { - maybe_warn_for_constant_evaluated (cond, /*constexpr_if=*/true); cond = instantiate_non_dependent_expr (cond); cond = cxx_constant_value (cond); } - else - { - maybe_warn_for_constant_evaluated (cond, /*constexpr_if=*/false); - if (processing_template_decl) - cond = orig_cond; - } + else if (processing_template_decl) + cond = orig_cond; finish_cond (&IF_COND (if_stmt), cond); add_stmt (if_stmt); THEN_CLAUSE (if_stmt) = push_stmt_list (); diff --git a/gcc/testsuite/g++.dg/cpp2a/is-constant-evaluated15.C b/gcc/testsuite/g++.dg/cpp2a/is-constant-evaluated15.C new file mode 100644 index 00000000000..50a3cac6e07 --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp2a/is-constant-evaluated15.C @@ -0,0 +1,28 @@ +// PR c++/114580 +// { dg-do compile { target c++17 } } +// { dg-options "-Wtautological-compare" } + +namespace std { + constexpr inline bool + is_constant_evaluated () noexcept + { +#if __cpp_if_consteval >= 202106L + if consteval { return true; } else { return false; } +#else + return __builtin_is_constant_evaluated (); +#endif + } +} + +template <typename T> +void foo () +{ + if constexpr ((T) std::is_constant_evaluated ()) // { dg-warning "'std::is_constant_evaluated' always evaluates to true in 'if constexpr'" } + ; // { dg-bogus "'std::is_constant_evaluated' always evaluates to false in a non-'constexpr' function" } +} + +void +bar () +{ + foo <bool> (); +} |