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Rollup merge of #132774 - bjorn3:cranelift_lld, r=lqd

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Use lld with non-LLVM backends

On arm64, Cranelift used to produce object files that don't work with lld. This has since been fixed. The GCC backend should always produce object files that work with lld unless lld for whatever reason drops GCC support. Most of the other more niche backends don't use cg_ssa's linker code at all. If they do and don't work with lld, they can always disable lld usage using a cli argument.

 Without this commit using cg_clif is by default in a non-trivial amount of cases a perf regression on Linux due to ld.bfd being a fair bit slower than lld. It is possible to explicitly enable it without this commit, but most users are unlikely to do this.
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Matthias Krüger 2024-11-09 19:16:45 +01:00 committed by GitHub
commit 9b47807b13
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17
compiler/rustc_codegen_ssa/src/back/link.rs
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@ -3305,23 +3305,6 @@ fn add_lld_args(
let self_contained_cli = sess.opts.cg.link_self_contained.is_linker_enabled();
let self_contained_target = self_contained_components.is_linker_enabled();
// FIXME: in the future, codegen backends may need to have more control over this process: they
// don't always support all the features the linker expects here, and vice versa. For example,
// at the time of writing this, lld expects a newer style of aarch64 TLS relocations that
// cranelift doesn't implement yet. That in turn can impact whether linking would succeed on
// such a target when using the `cg_clif` backend and lld.
//
// Until interactions between backends and linker features are expressible, we limit target
// specs to opt-in to lld only when we're on the llvm backend, where it's expected to work and
// tested on CI. As usual, the CLI still has precedence over this, so that users and developers
// can still override this default when needed (e.g. for tests).
let uses_llvm_backend =
matches!(sess.opts.unstable_opts.codegen_backend.as_deref(), None | Some("llvm"));
if !uses_llvm_backend && !self_contained_cli && sess.opts.cg.linker_flavor.is_none() {
// We bail if we're not using llvm and lld was not explicitly requested on the CLI.
return;
}
let self_contained_linker = self_contained_cli || self_contained_target;
if self_contained_linker && !sess.opts.cg.link_self_contained.is_linker_disabled() {
let mut linker_path_exists = false;