On Wed, 30 Oct 2024 at 21:26, Jonathan Wakely <jwak...@redhat.com> wrote: > > The aligned versions of operator new should use the align_alloc > attribute to help the compiler. > > PR c++/86878 requests that the compiler would use the attribute to warn > about invalid attributes, so an XFAILed test is added for that. > > libstdc++-v3/ChangeLog: > > * libsupc++/new (operator new): Add attribute align_alloc(2) to > overloads taking a std::align_val_t argument. > * testsuite/18_support/new_aligned_warn.cc: New test. > --- > I think this makes sense, but maybe there's some property of the > attribute that means this isn't a good idea? I think the compiler can > use the value of align_val_t even though it's a scoped enumeration type. > > Tested x86_64-linux.
I forgot to say that this is also available for review at: https://forge.sourceware.org/gcc/gcc-TEST/pulls/12 > > libstdc++-v3/libsupc++/new | 6 +++--- > .../testsuite/18_support/new_aligned_warn.cc | 13 +++++++++++++ > 2 files changed, 16 insertions(+), 3 deletions(-) > create mode 100644 libstdc++-v3/testsuite/18_support/new_aligned_warn.cc > > diff --git a/libstdc++-v3/libsupc++/new b/libstdc++-v3/libsupc++/new > index e9a3d9b49a3..4345030071b 100644 > --- a/libstdc++-v3/libsupc++/new > +++ b/libstdc++-v3/libsupc++/new > @@ -167,7 +167,7 @@ void operator delete[](void*, const std::nothrow_t&) > #if __cpp_aligned_new > _GLIBCXX_NODISCARD void* operator new(std::size_t, std::align_val_t) > _GLIBCXX_TXN_SAFE > - __attribute__((__externally_visible__, __alloc_size__ (1), __malloc__)); > + __attribute__((__externally_visible__, __alloc_size__ (1), __alloc_align__ > (2), __malloc__)); > _GLIBCXX_NODISCARD void* operator new(std::size_t, std::align_val_t, const > std::nothrow_t&) > _GLIBCXX_TXN_SAFE > _GLIBCXX_USE_NOEXCEPT __attribute__((__externally_visible__, > __alloc_size__ (1), __malloc__)); > @@ -178,10 +178,10 @@ void operator delete(void*, std::align_val_t, const > std::nothrow_t&) > _GLIBCXX_USE_NOEXCEPT __attribute__((__externally_visible__)); > _GLIBCXX_NODISCARD void* operator new[](std::size_t, std::align_val_t) > _GLIBCXX_TXN_SAFE > - __attribute__((__externally_visible__, __alloc_size__ (1), __malloc__)); > + __attribute__((__externally_visible__, __alloc_size__ (1), __alloc_align__ > (2), __malloc__)); > _GLIBCXX_NODISCARD void* operator new[](std::size_t, std::align_val_t, const > std::nothrow_t&) > _GLIBCXX_TXN_SAFE > - _GLIBCXX_USE_NOEXCEPT __attribute__((__externally_visible__, > __alloc_size__ (1), __malloc__)); > + _GLIBCXX_USE_NOEXCEPT __attribute__((__externally_visible__, > __alloc_size__ (1), __alloc_align__ (2), __malloc__)); > void operator delete[](void*, std::align_val_t) _GLIBCXX_TXN_SAFE > _GLIBCXX_USE_NOEXCEPT __attribute__((__externally_visible__)); > void operator delete[](void*, std::align_val_t, const std::nothrow_t&) > diff --git a/libstdc++-v3/testsuite/18_support/new_aligned_warn.cc > b/libstdc++-v3/testsuite/18_support/new_aligned_warn.cc > new file mode 100644 > index 00000000000..e9d374abe31 > --- /dev/null > +++ b/libstdc++-v3/testsuite/18_support/new_aligned_warn.cc > @@ -0,0 +1,13 @@ > +// { dg-options "-Wattributes" } > +// { dg-do compile { target c++17 } } > + > +#include <new> > + > +int main() > +{ > + // PR c++/86878 has a patch to make these warn. > + (void) operator new(1, std::align_val_t(3)); // { dg-warning "power of > two" "" { xfail *-*-* } } > + (void) operator new[](1, std::align_val_t(10)); // { dg-warning "power of > two" "" { xfail *-*-* } } > + (void) operator new(1, std::align_val_t(0), std::nothrow_t()); // { > dg-warning "power of two" "" { xfail *-*-* } } > + (void) operator new[](1, std::align_val_t(-1), std::nothrow_t()); // { > dg-warning "power of two" "" { xfail *-*-* } } > +} > -- > 2.47.0 >
