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Matthias Krüger
2f6e85567a
update comment regarding TargetOptions.features The claim that `-Ctarget-features` cannot disable these features set in the target spec is definitely wrong -- I tried it for `x86_64-pc-windows-gnu`, which enables SSE3 that way. Building with `-Ctarget-feature=-sse3` works fine, and `cfg!(target_feature = "sse3")` is `false` in that build. There are also some indications that these are actually intended to be overwritten: https://github.com/rust-lang/rust/blob/3b14526cead4105f82c398d8d4c7954efa3bab6b/compiler/rustc_target/src/spec/targets/i686_unknown_uefi.rs#L22-L23 https://github.com/rust-lang/rust/blob/84ac80f1921afc243d71fd0caaa4f2838c294102/compiler/rustc_target/src/spec/targets/x86_64h_apple_darwin.rs#L18-L23 So... let's update the comment to match reality, I guess? The claim that they overwrite `-Ctarget-cpu` is based on - for `native`, the comment in the apple target spec quoted above - for other CPU strings, the assumption that `LLVMRustCreateTargetMachine` will apply these features after doing whatever the base CPU model does. I am not sure how to check that, I hope some LLVM backend people can chime in. :)
rustc_target contains some very low-level details that are
specific to different compilation targets and so forth.
For more information about how rustc works, see the rustc dev guide.