diff options
Diffstat (limited to 'gcc/cp/semantics.c')
| -rw-r--r-- | gcc/cp/semantics.c | 36 |
1 files changed, 36 insertions, 0 deletions
diff --git a/gcc/cp/semantics.c b/gcc/cp/semantics.c index 1f774593..8603e57 100644 --- a/gcc/cp/semantics.c +++ b/gcc/cp/semantics.c @@ -723,6 +723,28 @@ begin_if_stmt (void) return r; } +/* Returns true if FN, a CALL_EXPR, is a call to + std::is_constant_evaluated or __builtin_is_constant_evaluated. */ + +static bool +is_std_constant_evaluated_p (tree fn) +{ + /* std::is_constant_evaluated takes no arguments. */ + if (call_expr_nargs (fn) != 0) + 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)) + return true; + + if (!decl_in_std_namespace_p (fndecl)) + return false; + + tree name = DECL_NAME (fndecl); + return name && id_equal (name, "is_constant_evaluated"); +} + /* Process the COND of an if-statement, which may be given by IF_STMT. */ @@ -738,6 +760,20 @@ finish_if_stmt_cond (tree cond, tree if_stmt) converted to bool. */ && TYPE_MAIN_VARIANT (TREE_TYPE (cond)) == boolean_type_node) { + /* if constexpr (std::is_constant_evaluated()) is always true, + so give the user a clue. */ + if (warn_tautological_compare) + { + tree t = cond; + if (TREE_CODE (t) == CLEANUP_POINT_EXPR) + t = TREE_OPERAND (t, 0); + if (TREE_CODE (t) == CALL_EXPR + && is_std_constant_evaluated_p (t)) + warning_at (EXPR_LOCATION (cond), OPT_Wtautological_compare, + "%qs always evaluates to true in %<if constexpr%>", + "std::is_constant_evaluated"); + } + cond = instantiate_non_dependent_expr (cond); cond = cxx_constant_value (cond, NULL_TREE); } |