Prazek marked 3 inline comments as done. ================ Comment at: lib/CodeGen/CGClass.cpp:1832 @@ +1831,3 @@ + // Generate vtable assumptions if we are calling dynamic class ctor + // and we are not in another ctor. + if (CGM.getCodeGenOpts().OptimizationLevel > 0 && ---------------- rsmith wrote: > Prazek wrote: > > rsmith wrote: > > > Prazek wrote: > > > > hfinkel wrote: > > > > > I think this comment should be a little more verbose. How about this: > > > > > > > > > > // Generate vtable assumptions if we are calling dynamic-class's > > > > > ctor, except when doing so as part of a derived class's ctor's > > > > > base-class initialization. Doing so in this latter case would be > > > > > useless, because the vtable is about to be overwritten by the derived > > > > > class's vtable. > > > > > > > > > The main point of not calling this function, is because it is useless > > > > to have assumption loads inside constructor, when they are generated > > > > also outside of ctor. I guess You could have case when You are not > > > > overriding base vptr, and You are calling base ctor from dynamic class > > > It might also be worth including in the comment that it is not correct to > > > call `EmitVTableAssumptionLoads` here, because it assumes the object's > > > vptr points to the complete object vtable; during a constructor call it > > > will probably have a construction vtable instead. > > Well, it would be correct, but it would be useless. Just after calling > > base constructor, assume loads would appear, and after there would be new > > store to vptr. > `EmitVTableAssumptionLoads` assumes that the `This` pointer points to an > object whose most-derived type is `ClassDecl`, and it assumes that the object > is not under construction. Both of those assumptions can be violated for a > base class constructor call, and can result in it emitting incorrect > assumptions (because virtual bases may be at different offsets and because > the vptr of an object under construction may be different from the > corresponding vptr of a fully-constructed object). ok, now I get it
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