I found classtype_has_nothrow_assign_or_copy_p confusing, trying to
figure out when it should return false and when true.
AFAICT what it's trying to tell you is if *all* the copy/move ctors or
copy assignment ops are nothrow. Not, as its comment suggests that it
has *at least one* nothrow variant.
If there are no assignment ops it returns false, but if there's at least
one, but there is no copy-assignment op it'll return true. That seems
wrong. (but perhaps that never happens, because the copy-op will be
implicitly defined). It's certainly confusing.
Also the differing check on copy_fn_p's result is a difference that
means nothing -- the -ve result means 'this is a broken copy/move
ctor/assop', which IMHO puts it in the 'don't care' category.
This patch cleans it up to:
a) just consider well-formed fns (copy_fn_p returns > 0, but could just
as easily become != 0)
b) only return true if it finds at least one function of interest -- and
no functions of interest throw.
This caused no regressions, I'll commit in a few days unless someone
notices a mistake in the above logic.
nathan
--
Nathan Sidwell
2017-07-03 Nathan Sidwell <nat...@acm.org>
* semantics.c (classtype_has_nothrow_assign_or_copy_p): Clarify
semantics, simplify implementation.
Index: semantics.c
===================================================================
--- semantics.c (revision 249925)
+++ semantics.c (working copy)
@@ -9072,19 +9072,16 @@ finish_decltype_type (tree expr, bool id
}
/* Called from trait_expr_value to evaluate either __has_nothrow_assign or
- __has_nothrow_copy, depending on assign_p. */
+ __has_nothrow_copy, depending on assign_p. Returns true iff all
+ the copy {ctor,assign} fns are nothrow. */
static bool
classtype_has_nothrow_assign_or_copy_p (tree type, bool assign_p)
{
- tree fns;
+ tree fns = NULL_TREE;
if (assign_p)
- {
- fns = lookup_fnfields_slot (type, cp_assignment_operator_id (NOP_EXPR));
- if (!fns)
- return false;
- }
+ fns = lookup_fnfields_slot (type, cp_assignment_operator_id (NOP_EXPR));
else if (TYPE_HAS_COPY_CTOR (type))
{
/* If construction of the copy constructor was postponed, create
@@ -9095,27 +9092,22 @@ classtype_has_nothrow_assign_or_copy_p (
lazily_declare_fn (sfk_move_constructor, type);
fns = CLASSTYPE_CONSTRUCTORS (type);
}
- else
- return false;
+ bool saw_copy = false;
for (ovl_iterator iter (fns); iter; ++iter)
{
tree fn = *iter;
-
- if (assign_p)
+
+ if (copy_fn_p (fn) > 0)
{
- if (copy_fn_p (fn) == 0)
- continue;
+ saw_copy = true;
+ maybe_instantiate_noexcept (fn);
+ if (!TYPE_NOTHROW_P (TREE_TYPE (fn)))
+ return false;
}
- else if (copy_fn_p (fn) <= 0)
- continue;
-
- maybe_instantiate_noexcept (fn);
- if (!TYPE_NOTHROW_P (TREE_TYPE (fn)))
- return false;
}
- return true;
+ return saw_copy;
}
/* Actually evaluates the trait. */
