Auto merge of #83640 - bjorn3:shared_metadata_reader, r=nagisa

Use the object crate for metadata reading

This allows sharing the metadata reader between cg_llvm, cg_clif and other codegen backends.

This is not currently useful for rlib reading with cg_spirv ([rust-gpu](https://github.com/EmbarkStudios/rust-gpu/)) as it uses tar rather than ar as .rlib format, but it is useful for dylib reading required for loading proc macros. (cc `@eddyb)`

The object crate is already trusted as dependency of libstd through backtrace. As far as I know it supports reading all object file formats used by targets for which we support rust dylibs with crate metadata, but I am not certain. If this happens to not be the case, I could keep using LLVM for reading dylib metadata.

Marked as WIP for a perf run and as it is based on #83637.

1 files changed, 1 insertions, 2 deletions

diff --git a/compiler/rustc_codegen_llvm/src/lib.rs b/compiler/rustc_codegen_llvm/src/lib.rs
index 91062926788..329458773ff 100644
--- a/compiler/rustc_codegen_llvm/src/lib.rs
+++ b/compiler/rustc_codegen_llvm/src/lib.rs
@@ -69,7 +69,6 @@ pub mod llvm {
 }
 
 mod llvm_util;
-mod metadata;
 mod mono_item;
 mod type_;
 mod type_of;
@@ -251,7 +250,7 @@ impl CodegenBackend for LlvmCodegenBackend {
     }
 
     fn metadata_loader(&self) -> Box<MetadataLoaderDyn> {
-        Box::new(metadata::LlvmMetadataLoader)
+        Box::new(rustc_codegen_ssa::back::metadata::DefaultMetadataLoader)
     }
 
     fn provide(&self, _providers: &mut ty::query::Providers) {}