On Wed, 2009-09-23 at 10:29 +0200, Richard Guenther wrote: > On Wed, Sep 23, 2009 at 2:38 AM, Janis Johnson <janis...@us.ibm.com> wrote: > > I've been implementing ISO/IEC TR 24733, "an extension for the > > programming language C++ to support decimal floating-point arithmetic", > > in GCC. It might be ready as an experimental feature for 4.5, but I > > would particularly like to get in the compiler changes that are needed > > for it. > > > > Most of the support for the TR is in new header files in libstdc++ that > > depend on compiler support for decimal float scalar types. Most of that > > compiler functionality was already available in G++ via mode attributes. > > I've made a couple of small fixes and have a couple more to submit, and > > when those are in I'll starting running dfp tests for C++ as well as C. > > The suitable tests have already been moved from gcc.dg to c-c++-common. > > > > In order to provide interoperability with C, people on the C++ ABI > > mailing list suggested that a C++ compiler should recognize the new > > decimal classes defined in the TR and pass arguments of those types the > > same as scalar decimal float types for a particular target. I had this > > working in an ugly way using a langhook, but that broke with LTO. I'm > > looking for the right places to record that an argument or return value > > should be passed as if it were a different type, but could use some > > advice about that. > > How do we (do we?) handle std::complex<> there? My first shot would > be to make sure the aggregate type has the proper mode, but I guess > most target ABIs would already pass them in registers, no?
std::complex<> is not interoperable with GCC's complex extension, which is generally viewed as "unfortunate". The class types for std::decimal::decimal32 and friends do have the proper modes. I suppose I could special-case aggregates of those modes but the plan was to pass these particular classes (and typedefs of them) the same as scalars, rather than _any_ class with those modes. I'll bring this up again on the C++ ABI mailing list. Perhaps most target ABIs pass single-member aggregates using the mode of the aggregate, but not all. In particular, not the 32-bit ELF ABI for Power. Janis
