https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107087
--- Comment #10 from Jonathan Wakely <redi at gcc dot gnu.org> ---
I wonder if some other hints about properties of the empty rep would help
codegen:
--- a/libstdc++-v3/include/bits/cow_string.h
+++ b/libstdc++-v3/include/bits/cow_string.h
@@ -204,6 +204,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
bool
_M_is_leaked() const _GLIBCXX_NOEXCEPT
{
+#if _GLIBCXX_FULLY_DYNAMIC_STRING == 0 && __OPTIMIZE__
+ if (_S_empty_rep()._M_refcount != 0)
+ __builtin_unreachable();
+#endif
+
#if defined(__GTHREADS)
// _M_refcount is mutated concurrently by _M_refcopy/_M_dispose,
// so we need to use an atomic load. However, _M_is_leaked
@@ -218,6 +223,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
bool
_M_is_shared() const _GLIBCXX_NOEXCEPT
{
+#if _GLIBCXX_FULLY_DYNAMIC_STRING == 0 && __OPTIMIZE__
+ if (_S_empty_rep()._M_refcount != 0)
+ __builtin_unreachable();
+#endif
+
#if defined(__GTHREADS)
// _M_refcount is mutated concurrently by _M_refcopy/_M_dispose,
// so we need to use an atomic load. Another thread can drop last
@@ -907,17 +917,24 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
public:
// Capacity:
+
/// Returns the number of characters in the string, not including any
/// null-termination.
size_type
size() const _GLIBCXX_NOEXCEPT
- { return _M_rep()->_M_length; }
+ {
+#if _GLIBCXX_FULLY_DYNAMIC_STRING == 0 && __OPTIMIZE__
+ if (_S_empty_rep()._M_length != 0)
+ __builtin_unreachable();
+#endif
+ return _M_rep()->_M_length;
+ }
/// Returns the number of characters in the string, not including any
/// null-termination.
size_type
length() const _GLIBCXX_NOEXCEPT
- { return _M_rep()->_M_length; }
+ { return size(); }
/// Returns the size() of the largest possible %string.
size_type
