https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63322
Bug ID: 63322
Summary: std::atomic<T> where T is not trivially copyable
should be disabled.
Product: gcc
Version: 5.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: roman at binarylife dot net
[atomic.types.generic]: There is a generic class template atomic<T>. The type
of the template argument T shall be trivially copyable (3.9).
It would be helpful if std::atomic<T> disallowed wrong T because the generated
code is obviously makes no sense (at least for x86_64): bar() returns a
hard-coded NaN.
$ cat test.cc
#include <atomic>
long double foo(const long double& f) noexcept;
struct X {
X() = default;
X(X const& o) noexcept : f(foo(o.f)) {}
X& operator=(X const& o) noexcept { f = foo(o.f); return *this; }
long double f = foo(0);
};
extern std::atomic<X> a;
long double bar() { a.load().f; }
$ g++ -c -O2 --save-temps -std=c++11 test.cc && echo ok
ok
$ cat test.s
.file "test.cc"
.section .text.unlikely,"ax",@progbits
.LCOLDB2:
.text
.LHOTB2:
.p2align 4,,15
.globl _Z3barv
.type _Z3barv, @function
_Z3barv:
.LFB330:
.cfi_startproc
fldz
subq $24, %rsp
.cfi_def_cfa_offset 32
movq %rsp, %rdi
fstpt (%rsp)
call _Z3fooRKe
fstp %st(0)
movl $5, %esi
movl $a, %edi
call __atomic_load_16
flds .LC1(%rip)
addq $24, %rsp
.cfi_def_cfa_offset 8
ret
.cfi_endproc
.LFE330:
.size _Z3barv, .-_Z3barv
.section .text.unlikely
.LCOLDE2:
.text
.LHOTE2:
.section .rodata.cst4,"aM",@progbits,4
.align 4
.LC1:
.long 2143289344
.ident "GCC: (GNU) 5.0.0 20140920 (experimental)"
.section .note.GNU-stack,"",@progbits
