[cfe-dev] motivations for approaches to macros in Index/IndexingAction.cpp ?

[James Widman via cfe-dev]

On Mon, May 20, 2019 at 6:32 PM Jan Korous <jkorous at apple.com> wrote:
>
> + Argyrios and Ben who might comment on current use of index-store.
> + clangd-dev in case anyone is interested.
>
> > On May 20, 2019, at 3:23 PM, James Widman <james.widman at gmail.com> wrote:
> >
> > On Mon, May 20, 2019 at 5:32 PM Jan Korous <jkorous at apple.com> wrote:
> >>
> >> Hi James,
> >>
> >> The current implementation of this hashing function ignores some cases. We're in the process of upstreaming the whole index-while-building feature to LLVM project and decided to fix this by temporarily using trivial implementation - just hashing the full bitcode representation of index record. Eventually we need a new implementation that is both correct and performant - so far the idea was to explore the possibility of using the existing ODR violation hasher for this purpose.
> >
> > Ok, so... I guess "correct and performant" means "yes, we do want to
> > incorporate macro definitions & expansions in the future", in which
> > case I'm looking forward to it! (:
> >
> > separate topic, under "performance": it seems like it would be good if
> > declarations & definitions of entities with external linkage were not
> > represented as "occurrences", because currently, if I want to get the
> > locations of all such decls, it seems like I need to visit all
> > "occurrences", which seems like a lot of extra work if the user ends
> > up visiting only two translation units. (And currently, doing this for
> > an index-store for the clang & llvm source code takes about 11.5
> > seconds on my macbook.)
> >
> > In other words, upon loading the index-store, I need to know the
> > locations of all external decls & defs for the whole program (because
> > the user should be able to jump to any of those from the outset, from
> > any TU), but it seems like loading for all *other* occurrences could
> > be done more lazily.

On second thought, I guess you want to be able to jump to any
namespace-scope decl from any file (or no file), i.e. you also want to
load all decls with internal linkage on startup. (That would still be
a significantly lighter load than "all occurrences" though.)


> > I don't know where this topic fits in the pipeline of design
> > discussions for upstreaming index-while-building tho.
> >
> > --James
>