bors 0c341226ad Auto merge of #83084 - nagisa:nagisa/features-native, r=petrochenkov ... Adjust `-Ctarget-cpu=native` handling in cg_llvm When cg_llvm encounters the `-Ctarget-cpu=native` it computes an explciit set of features that applies to the target in order to correctly compile code for the host CPU (because e.g. `skylake` alone is not sufficient to tell if some of the instructions are available or not). However there were a couple of issues with how we did this. Firstly, the order in which features were overriden wasn't quite right – conceptually you'd expect `-Ctarget-cpu=native` option to override the features that are implicitly set by the target definition. However due to how other `-Ctarget-cpu` values are handled we must adopt the following order of priority: * Features from -Ctarget-cpu=*; are overriden by * Features implied by --target; are overriden by * Features from -Ctarget-feature; are overriden by * function specific features. Another problem was in that the function level `target-features` attribute would overwrite the entire set of the globally enabled features, rather than just the features the `#[target_feature(enable/disable)]` specified. With something like `-Ctarget-cpu=native` we'd end up in a situation wherein a function without `#[target_feature(enable)]` annotation would have a broader set of features compared to a function with one such attribute. This turned out to be a cause of heavy run-time regressions in some code using these function-level attributes in conjunction with `-Ctarget-cpu=native`, for example. With this PR rustc is more careful about specifying the entire set of features for functions that use `#[target_feature(enable/disable)]` or `#[instruction_set]` attributes. Sadly testing the original reproducer for this behaviour is quite impossible – we cannot rely on `-Ctarget-cpu=native` to be anything in particular on developer or CI machines. cc https://github.com/rust-lang/rust/issues/83027 `@BurntSushi`		2021-03-17 05:46:08 +00:00
..
archive.rs	Collapse all uses of target.options.foo into target.foo	2020-11-08 17:29:13 +03:00
lto.rs	rustc: Stabilize -Zrun-dsymutil as -Csplit-debuginfo	2021-01-28 08:51:11 -08:00
profiling.rs	mv compiler to compiler/	2020-08-30 18:45:07 +03:00
write.rs	Auto merge of #83084 - nagisa:nagisa/features-native, r=petrochenkov	2021-03-17 05:46:08 +00:00