diff options
| -rwxr-xr-x | src/ci/run.sh | 2 | ||||
| -rw-r--r-- | src/librustc_codegen_llvm/back/lto.rs | 32 |
2 files changed, 23 insertions, 11 deletions
diff --git a/src/ci/run.sh b/src/ci/run.sh index 29c11cceb15..67f51d0e866 100755 --- a/src/ci/run.sh +++ b/src/ci/run.sh @@ -43,7 +43,7 @@ fi # # FIXME: need a scheme for changing this `nightly` value to `beta` and `stable` # either automatically or manually. -export RUST_RELEASE_CHANNEL=beta +export RUST_RELEASE_CHANNEL=stable # Always set the release channel for bootstrap; this is normally not important (i.e., only dist # builds would seem to matter) but in practice bootstrap wants to know whether we're targeting diff --git a/src/librustc_codegen_llvm/back/lto.rs b/src/librustc_codegen_llvm/back/lto.rs index 447ba8c8a8a..ee56d0e26c3 100644 --- a/src/librustc_codegen_llvm/back/lto.rs +++ b/src/librustc_codegen_llvm/back/lto.rs @@ -500,15 +500,32 @@ fn thin_lto( let module_name = module_name_to_str(module_name); // If (1.) the module hasn't changed, and (2.) none of the modules - // it imports from nor exports to have changed, *and* (3.) the - // import and export sets themselves have not changed from the - // previous compile when it was last ThinLTO'ed, then we can re-use - // the post-ThinLTO version of the module. Otherwise, freshly - // perform LTO optimization. + // it imports from have changed, *and* (3.) the import and export + // sets themselves have not changed from the previous compile when + // it was last ThinLTO'ed, then we can re-use the post-ThinLTO + // version of the module. Otherwise, freshly perform LTO + // optimization. // // (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 @@ -531,13 +548,8 @@ fn thin_lto( let imports_all_green = curr_imports .iter() .all(|imported_module| green_modules.contains_key(imported_module)); - let exports_all_green = curr_exports - .iter() - .all(|exported_module| green_modules.contains_key(exported_module)); - if imports_all_green && equivalent_as_sets(prev_imports, curr_imports) - && exports_all_green && equivalent_as_sets(prev_exports, curr_exports) { let work_product = green_modules[module_name].clone(); |