diff options
Diffstat (limited to 'src/librustc_codegen_llvm/back/lto.rs')
| -rw-r--r-- | src/librustc_codegen_llvm/back/lto.rs | 17 |
1 files changed, 17 insertions, 0 deletions
diff --git a/src/librustc_codegen_llvm/back/lto.rs b/src/librustc_codegen_llvm/back/lto.rs index 29912c56b38..7292492a0c0 100644 --- a/src/librustc_codegen_llvm/back/lto.rs +++ b/src/librustc_codegen_llvm/back/lto.rs @@ -509,6 +509,23 @@ fn thin_lto( // (Note that globally, the export set is just the inverse of the // import set.) // + // For further justification of why the above is necessary and sufficient, + // see the LLVM blog post on ThinLTO: + // + // http://blog.llvm.org/2016/06/thinlto-scalable-and-incremental-lto.html + // + // which states the following: + // + // ```quote + // any particular ThinLTO backend must be redone iff: + // + // 1. The corresponding (primary) module’s bitcode changed + // 2. The list of imports into or exports from the module changed + // 3. The bitcode for any module being imported from has changed + // 4. Any global analysis result affecting either the primary module + // or anything it imports has changed. + // ``` + // // This strategy means we can always save the computed imports as // canon: when we reuse the post-ThinLTO version, condition (3.) // ensures that the current import set is the same as the previous |