rsmith added a comment. In D154658#4479170 <https://reviews.llvm.org/D154658#4479170>, @rjmccall wrote:
> I don't think it's an intended guarantee of the Itanium ABI that the v-table > will be unique, and v-tables are frequently not unique in the presence of > shared libraries. https://itanium-cxx-abi.github.io/cxx-abi/abi.html#vtable-general explicitly guarantees this: "[...] However, the virtual table pointers within all the objects (instances) of a particular most-derived class point to the same set of virtual tables." > They should be unique for classes with internal linkage, but of course that's > a vastly reduced domain for the optimization. I think (hope?) we should be able to apply this to a much larger set of cases. Would it be correct to do this optimization unless the vtable might be emitted with vague linkage and non-default visibility (that is, unless we're in the odd case where people expect non-default visibility classes to be the same type across DSOs)? Or are there cases where we might be using a vtable that (eg) doesn't even have the right symbol? > If there are multiple subobjects of the source type in the destination type, > consider just casting to `void*` first instead of doing multiple comparisons. Ha, that seems obvious in retrospect :) Will do. Repository: rG LLVM Github Monorepo CHANGES SINCE LAST ACTION https://reviews.llvm.org/D154658/new/ https://reviews.llvm.org/D154658 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
