rjmccall added a comment. In https://reviews.llvm.org/D31885#755456, @kparzysz wrote:
> In https://reviews.llvm.org/D31885#751164, @rjmccall wrote: > > > The right fix is probably just to make sure that EmitLValueForField doesn't > > add TBAA information when the base LValue doesn't have it. That will also > > fix problems with recursive member access where the base is may_alias. > > > That won't work for arrays that are member of unions. We'd need to change > EmitArraySubscriptExpr, which at some point calls MakeAddrLValue for the type > being loaded/stored. MakeAddrLValue adds TBAAInfo for that type (unsigned > short in case of the C testcase) and it does so regardless of any struct > paths. This TBAA info must be removed for the testcase to be fixed. At that > point we would have to examine the base expression to see if it refers to a > union member, which is not different from the approach in this review. The > LValue construction is done in a piecewise manner where some elements of the > previously (recursively) created LValues may or may not be preserved. This > makes me concerned that any more detailed attempt at fixing this may > accidentally omit some case. That is a reasonable concern. Hmm. It seems to me that we do already propagate an important semantic property from the base l-value in every important case: the alignment source. That audit has already been done, and all you really need to do do is generalize it: look at all the places that generically propagate an AlignmentSource, e.g. EmitPointerWithAlignment and almost everywhere that calls LValue::getAlignmentSource(), and make them propagate an LValueBaseInfo (or whatever) instead. You can then make sure that may_alias-ness is stored in an LValueBaseInfo along with the alignment source, and then suppress TBAA when a base info is known to be may_alias, and then your temporary fix is just to make all union accesses unconditionally set may_alias to true. Repository: rL LLVM https://reviews.llvm.org/D31885 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
