Hi,
in this test case, c-reduce had created various forms of undefined
behaviour, which did only show up on m68k and arm-none-eabi.
Most notably the original problem did only happen when
512/sizeof(basic_string) = 7, but with a non-zero remainder.
In the way that c-reduce used to reduce that structure
there is an array of enum as a place holder.
But that depends on sizeof(enum) to be 4, which is
not the case on arm-none-eabi.
Other problems come from a not-initialized _M_string_length
which ends up in a memcmp crash.
And the _Alloc_hider constructor, which is linked to
libstdc++, but that works only as long as the signature
of that function is not changed, so it turned out
the test case would not link with gcc-6 for instance.
I found no way how to write that template specialization
without breaking the purpose of reproducing the
original PR, because __attribute((noinline, noclone))
seems to be completely ignored in this case.
I made sure that PR 77550 can still be reproduced
with this test case both on gcc-6 and trunk.
Bootstrapped and reg-tested on x86_64-pc-linux-gnu.
Is it OK for trunk?
Thanks
Bernd.
2016-09-28 Bernd Edlinger <bernd.edlin...@hotmail.de>
PR c++/77748
* g++.dg/pr77550.C: Avoid undefined behavior.
ndex: pr77550.C
===================================================================
--- pr77550.C (revision 240540)
+++ pr77550.C (working copy)
@@ -1,6 +1,7 @@
// { dg-do run }
// { dg-options "-std=c++14 -O3" }
+#define enum enum __attribute((mode(SI)))
namespace std {
typedef int size_t;
inline namespace __cxx11 {}
@@ -229,15 +230,17 @@
struct _Alloc_hider {
_Alloc_hider(pointer, allocator<char> && = allocator<char>());
} _M_dataplus;
- size_type _M_string_length;
+ size_type _M_string_length = 0;
enum { _S_local_capacity = 15 } _M_local_buf[_S_local_capacity];
- pointer _M_local_data();
- void _M_set_length(size_type);
- basic_string() : _M_dataplus(_M_local_data()) { _M_set_length(0); }
+ basic_string() : _M_dataplus(0) {}
basic_string(const basic_string &) : _M_dataplus(0) {}
size_type size() { return _M_string_length; }
char *data() const {}
};
+//template<> basic_string<char, std::char_traits<char>, std::allocator<char>>::
+//_Alloc_hider::_Alloc_hider(char*, std::allocator<char>&&) {}
+extern "C" void
+_ZNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEE12_Alloc_hiderC1EPcOS3_ (...) {}
}
template <typename _CharT>
int operator==(basic_string<_CharT> &p1, const basic_string<_CharT> &p2) {
