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Make -Clinker-plugin-lto compatible with ld64 #118377

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Make -Clinker-plugin-lto compatible with ld64 #118377

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7ebb683
Make -Clinker-plugin-lto compatible with ld64
cormacrelf Nov 24, 2023
5ad9dfb
Remove -mcpu for Apple linker-plugin-lto.
cormacrelf Dec 11, 2023
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39 changes: 29 additions & 10 deletions compiler/rustc_codegen_ssa/src/back/linker.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -295,9 +295,15 @@ impl<'a> GccLinker<'a> {

fn push_linker_plugin_lto_args(&mut self, plugin_path: Option<&OsStr>) {
if let Some(plugin_path) = plugin_path {
let mut arg = OsString::from("-plugin=");
arg.push(plugin_path);
self.linker_arg(&arg);
// Note that LLD silently ignores these flags.
// It will always use the LLVM it was built with to perform LTO.
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Is this documented somewhere? If so, it would be good to add a link.

I'm not sure if we should emit a warning. It could be super helpful -- but it could also be annoying if you know it's fine but for some reason cannot get rid of the commandline argument.

if self.sess.target.is_like_osx {
self.linker_args(&[OsStr::new("-lto_library"), plugin_path]);
} else {
let mut arg = OsString::from("-plugin=");
arg.push(plugin_path);
self.linker_arg(&arg);
}
}

let opt_level = match self.sess.opts.optimize {
Expand All @@ -307,13 +313,26 @@ impl<'a> GccLinker<'a> {
config::OptLevel::Aggressive => "O3",
};

if let Some(path) = &self.sess.opts.unstable_opts.profile_sample_use {
self.linker_arg(&format!("-plugin-opt=sample-profile={}", path.display()));
};
self.linker_args(&[
&format!("-plugin-opt={opt_level}"),
&format!("-plugin-opt=mcpu={}", self.target_cpu),
]);
if self.sess.target.is_like_osx {
// Apple clang 15 passes -O3 through to ld64. We will do the same.
self.linker_arg(&format!("-{opt_level}"));

// Apple clang 15 does not seem to tell the linker about -mcpu. Unlike -O3 etc,
// ld64 does not accept -mcpu or GNU-style -plugin-opt=mcpu=.
//
// It's possible this has something to do with platform minimum versions AKA
// deployment targets; Apple drops support for CPU subfamilies at defined iOS
// versions, for example. Either that or ld64 is meant to infer a target CPU
// from the object files.
} else {
if let Some(path) = &self.sess.opts.unstable_opts.profile_sample_use {
self.linker_arg(&format!("-plugin-opt=sample-profile={}", path.display()));
}
self.linker_args(&[
&format!("-plugin-opt={opt_level}"),
&format!("-plugin-opt=mcpu={}", self.target_cpu),
]);
}
}

fn build_dylib(&mut self, out_filename: &Path) {
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