On Fri, Mar 22, 2013 at 1:46 PM, John McCall <[email protected]> wrote:
> > On Mar 22, 2013, at 12:02 PM, Reid Kleckner <[email protected]> wrote: > > > Author: rnk > > Date: Fri Mar 22 14:02:54 2013 > > New Revision: 177753 > > > > URL: http://llvm.org/viewvc/llvm-project?rev=177753&view=rev > > Log: > > [ms-cxxabi] Implement member data pointers for non-dynamic classes > > > > Summary: > > For non-dynamic classes (no virtual bases), member data pointers are > > simple offsets from the base of the record. Dynamic classes use an > > aggregate for member data pointers and are therefore currently > > unsupported. > > > > Unlike Itanium, the ms ABI uses 0 to represent null for polymorphic > > classes. Non-polymorphic classes use -1 like Itanium, since 0 is a > > valid field offset. > > Oh, you should also implement isZeroInitializable. I looked into this, and MSVC seems to zero-initialize most things regardless of the null representation. For example: struct POD { int a; }; int POD::*pod_memptr; // should be -1, but goes into .bss and becomes 0 int POD::*null_memptr = 0; // gets -1 and goes into .data as expected But we probably don't have to be bug-for-bug compatible here. IMO the right thing is to use -1 and .data for this case.
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