[PATCH] D42995: [ThinLTO] Ignore object files with empty ThinLTO index

[Vitaly Buka via Phabricator via cfe-commits]

vitalybuka added a comment.

In https://reviews.llvm.org/D42995#1000155, @vitalybuka wrote:

> In https://reviews.llvm.org/D42995#1000025, @tejohnson wrote:
>
> > > Empty ThinLTOIndexFile signals that we don't need this module during
> > >  linking.
> >
> > Not the only case actually. We now also pass an empty index file when we want to compile the bitcode down to object without applying any LTO optimization (there are a few cases where we decide we want to turn off LTO optimizations for some links), and this is currently relying on being able to pass /dev/null for the index file that would be broken by this change.
>
>
> I'd expect this should be done by indexing and content is already in the merged object file.
>  Not sure how to reproduce this. I've build some large targets and I never seen this.


At least with gold I don't see how this possible. I see that thinlto.bc can be empty only
if getSymbolsAndView returns nullptr or if LTOInfo for input object was false.
Former means that we don't need this object and so I created this patch.
For latter we already going to do the same anyway: https://reviews.llvm.org/D42680


https://reviews.llvm.org/D42995