Hi, this patch is for adding a warning when a constexpr cannot be evaluated at
compile time.
This is a single case:
type var = fun(args...), with fun declared as a constexpr.
diff --git a/gcc/common.opt b/gcc/common.opt
index b49ac46..88374b1 100644
--- a/gcc/common.opt
+++ b/gcc/common.opt
@@ -581,6 +581,10 @@ Winline
Common Var(warn_inline) Warning
Warn when an inlined function cannot be inlined
+Wconstexpr
+Common Var(warn_constexpr) Warning
+Warn when a constexpr function is not evaluated at compile time
+
Winvalid-memory-model
Common Var(warn_invalid_memory_model) Init(1) Warning
Warn when an atomic memory model parameter is known to be outside the valid
range.
diff --git a/gcc/cp/typeck2.c b/gcc/cp/typeck2.c
index 80a6939..e25c240 100644
--- a/gcc/cp/typeck2.c
+++ b/gcc/cp/typeck2.c
@@ -842,6 +842,15 @@ store_init_value (tree decl, tree init, vec<tree, va_gc>**
cleanups, int flags)
DECL_INITIALIZED_BY_CONSTANT_EXPRESSION_P (decl) = const_init;
TREE_CONSTANT (decl) = const_init && decl_maybe_constant_var_p (decl);
}
+ else if (TREE_CODE(init) == CALL_EXPR)
+ {
+ tree fn = TREE_OPERAND(CALL_EXPR_FN(init), 0);
+ if (DECL_DECLARED_CONSTEXPR_P(fn) && warn_constexpr)
+ {
+ warning (OPT_Wconstexpr, "function %q+F cannot be evaluated at
compile time", fn);
+ warning (OPT_Wconstexpr, "called from here");
+ }
+ }
if (cxx_dialect >= cxx14)
/* Handle aggregate NSDMI in non-constant initializers, too. */
