Avoid unnecessary duplicate metadata encoding

Author: bjorn3

src/driver/aot.rs

@@ -277,7 +277,7 @@ pub(crate) fn run_aot(
             let tmp_file =
                 tcx.output_filenames(()).temp_path(OutputType::Metadata, Some(&metadata_cgu_name));
 
-            let obj = crate::metadata::new_metadata_object(tcx, &metadata_cgu_name);
+            let obj = crate::metadata::new_metadata_object(tcx, &metadata_cgu_name, &metadata);
 
             if let Err(err) = std::fs::write(&tmp_file, obj) {
                 tcx.sess.fatal(&format!("error writing metadata object file: {}", err));

src/metadata.rs

@@ -3,14 +3,14 @@
 use object::write::{Object, StandardSegment, Symbol, SymbolSection};
 use object::{SectionKind, SymbolFlags, SymbolKind, SymbolScope};
 
+use rustc_middle::middle::cstore::EncodedMetadata;
 use rustc_middle::ty::TyCtxt;
 
 // Adapted from https://github.com/rust-lang/rust/blob/da573206f87b5510de4b0ee1a9c044127e409bd3/src/librustc_codegen_llvm/base.rs#L47-L112
-pub(crate) fn new_metadata_object(tcx: TyCtxt<'_>, cgu_name: &str) -> Vec<u8> {
+pub(crate) fn new_metadata_object(tcx: TyCtxt<'_>, cgu_name: &str, metadata: &EncodedMetadata) -> Vec<u8> {
     use snap::write::FrameEncoder;
     use std::io::Write;
 
-    let metadata = tcx.encode_metadata();
     let mut compressed = rustc_metadata::METADATA_HEADER.to_vec();
     FrameEncoder::new(&mut compressed).write_all(&metadata.raw_data).unwrap();