[PATCH] D142733: Add _Optional as fast qualifier

[Richard Smith - zygoloid via Phabricator via cfe-commits]

rsmith added a comment.

Including a link to the RFC (https://discourse.llvm.org/t/rfc-optional-a-type-qualifier-to-indicate-pointer-nullability/68004/2) in each of the patches in this series would be helpful.

Assuming that we want to go in this direction, it seems quite expensive to model this as a fast qualifier rather than an extended qualifier. Are these annotations expected to be so common that it's better to increase the alignment of all types than perform extra allocations and indirections for `_Optional` qualifiers? Have you measured the memory impact of increasing the alignment of `Type`? I think that should be a prerequisite to adding any new kind of fast qualifier, and if we do add such a qualifier, we should select carefully which qualifier gets this precious bit in `QualType`.


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  https://reviews.llvm.org/D142733/new/

https://reviews.llvm.org/D142733