[PATCH] D87966: [ThinLTO] Re-order modules for optimal multi-threaded processing

Teresa Johnson via Phabricator via llvm-commits llvm-commits at lists.llvm.org
Fri Oct 9 15:57:17 PDT 2020


tejohnson added a comment.

We had to revert due to unexpected side effects on distributed ThinLTO. See the comments on the revert commit about the type of failures. Essentially, for distributed ThinLTO, the backends is of type WriteIndexesThinBackend. It runs serially, not in parallel via threads, and writes all the files needed by the distributed backend processes. One of the files it writes is a list of files to include in the final native link, which is provided to the final link process. The order modules are written into this file is the order they will be linked. With this patch, the order is changed and no longer matches the original link order, and that can produce unexpected failures. Probably the best fix is to simply skip the reordering when BackendProc is a WriteIndexesThinBackend. It won't help anyway given that it is a serial backend.


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https://reviews.llvm.org/D87966



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