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authorMatthias Krüger <matthias.krueger@famsik.de>2024-09-03 19:13:25 +0200
committerGitHub <noreply@github.com>2024-09-03 19:13:25 +0200
commit2f6e85567af202e5fd9f4e20c194396806fe949f (patch)
treec910ab7653022b43dbe4d7689d41e5e7f1ffcfac /compiler/rustc_codegen_llvm/src
parent1453cce5e9b1704e9e7a78fad513d233b752d94b (diff)
parent5c0dfc61822c5844aaa153c9c772633a583ca2a7 (diff)
downloadrust-2f6e85567af202e5fd9f4e20c194396806fe949f.tar.gz
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Rollup merge of #129863 - RalfJung:target-spec-features, r=wesleywiser
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. :)
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