Rollup merge of #60385 - nnethercote:earlier-metadata, r=alexcrichton

Emit metadata files earlier

This will make cargo pipelining much more effective.

10 files changed, 166 insertions, 156 deletions

diff --git a/Cargo.lock b/Cargo.lock
index f6713496f5b..fd6a7a5604e 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -2802,6 +2802,7 @@ dependencies = [
  "rustc-rayon 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "rustc_allocator 0.0.0",
  "rustc_borrowck 0.0.0",
+ "rustc_codegen_ssa 0.0.0",
  "rustc_codegen_utils 0.0.0",
  "rustc_data_structures 0.0.0",
  "rustc_errors 0.0.0",
@@ -2821,6 +2822,7 @@ dependencies = [
  "syntax 0.0.0",
  "syntax_ext 0.0.0",
  "syntax_pos 0.0.0",
+ "tempfile 3.0.5 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
diff --git a/src/librustc_codegen_llvm/base.rs b/src/librustc_codegen_llvm/base.rs
index 7ea5e912309..9077e89a402 100644
--- a/src/librustc_codegen_llvm/base.rs
+++ b/src/librustc_codegen_llvm/base.rs
@@ -28,7 +28,7 @@ use rustc::mir::mono::{Linkage, Visibility, Stats};
 use rustc::middle::cstore::{EncodedMetadata};
 use rustc::ty::TyCtxt;
 use rustc::middle::exported_symbols;
-use rustc::session::config::{self, DebugInfo};
+use rustc::session::config::DebugInfo;
 use rustc_codegen_ssa::mono_item::MonoItemExt;
 use rustc_data_structures::small_c_str::SmallCStr;
 
@@ -42,47 +42,16 @@ use rustc::hir::CodegenFnAttrs;
 
 use crate::value::Value;
 
-
-pub fn write_metadata<'a, 'gcx>(
+pub fn write_compressed_metadata<'a, 'gcx>(
     tcx: TyCtxt<'a, 'gcx, 'gcx>,
+    metadata: &EncodedMetadata,
     llvm_module: &mut ModuleLlvm
-) -> EncodedMetadata {
+) {
     use std::io::Write;
     use flate2::Compression;
     use flate2::write::DeflateEncoder;
 
     let (metadata_llcx, metadata_llmod) = (&*llvm_module.llcx, llvm_module.llmod());
-
-    #[derive(PartialEq, Eq, PartialOrd, Ord)]
-    enum MetadataKind {
-        None,
-        Uncompressed,
-        Compressed
-    }
-
-    let kind = tcx.sess.crate_types.borrow().iter().map(|ty| {
-        match *ty {
-            config::CrateType::Executable |
-            config::CrateType::Staticlib |
-            config::CrateType::Cdylib => MetadataKind::None,
-
-            config::CrateType::Rlib => MetadataKind::Uncompressed,
-
-            config::CrateType::Dylib |
-            config::CrateType::ProcMacro => MetadataKind::Compressed,
-        }
-    }).max().unwrap_or(MetadataKind::None);
-
-    if kind == MetadataKind::None {
-        return EncodedMetadata::new();
-    }
-
-    let metadata = tcx.encode_metadata();
-    if kind == MetadataKind::Uncompressed {
-        return metadata;
-    }
-
-    assert!(kind == MetadataKind::Compressed);
     let mut compressed = tcx.metadata_encoding_version();
     DeflateEncoder::new(&mut compressed, Compression::fast())
         .write_all(&metadata.raw_data).unwrap();
@@ -107,7 +76,6 @@ pub fn write_metadata<'a, 'gcx>(
         let directive = CString::new(directive).unwrap();
         llvm::LLVMSetModuleInlineAsm(metadata_llmod, directive.as_ptr())
     }
-    return metadata;
 }
 
 pub struct ValueIter<'ll> {
diff --git a/src/librustc_codegen_llvm/lib.rs b/src/librustc_codegen_llvm/lib.rs
index 08424e7c322..09b284052b3 100644
--- a/src/librustc_codegen_llvm/lib.rs
+++ b/src/librustc_codegen_llvm/lib.rs
@@ -110,12 +110,13 @@ impl ExtraBackendMethods for LlvmCodegenBackend {
         ModuleLlvm::new_metadata(tcx, mod_name)
     }
 
-    fn write_metadata<'b, 'gcx>(
+    fn write_compressed_metadata<'b, 'gcx>(
         &self,
         tcx: TyCtxt<'b, 'gcx, 'gcx>,
-        metadata: &mut ModuleLlvm
-    ) -> EncodedMetadata {
-        base::write_metadata(tcx, metadata)
+        metadata: &EncodedMetadata,
+        llvm_module: &mut ModuleLlvm
+    ) {
+        base::write_compressed_metadata(tcx, metadata, llvm_module)
     }
     fn codegen_allocator<'b, 'gcx>(
         &self,
@@ -289,9 +290,12 @@ impl CodegenBackend for LlvmCodegenBackend {
     fn codegen_crate<'b, 'tcx>(
         &self,
         tcx: TyCtxt<'b, 'tcx, 'tcx>,
+        metadata: EncodedMetadata,
+        need_metadata_module: bool,
         rx: mpsc::Receiver<Box<dyn Any + Send>>
     ) -> Box<dyn Any> {
-        box rustc_codegen_ssa::base::codegen_crate(LlvmCodegenBackend(()), tcx, rx)
+        box rustc_codegen_ssa::base::codegen_crate(
+            LlvmCodegenBackend(()), tcx, metadata, need_metadata_module, rx)
     }
 
     fn join_codegen_and_link(
diff --git a/src/librustc_codegen_ssa/back/link.rs b/src/librustc_codegen_ssa/back/link.rs
index 4cae20b698a..f25891d77ce 100644
--- a/src/librustc_codegen_ssa/back/link.rs
+++ b/src/librustc_codegen_ssa/back/link.rs
@@ -7,7 +7,7 @@ use rustc::session::config::{
 };
 use rustc::session::search_paths::PathKind;
 use rustc::middle::dependency_format::Linkage;
-use rustc::middle::cstore::{LibSource, NativeLibrary, NativeLibraryKind};
+use rustc::middle::cstore::{EncodedMetadata, LibSource, NativeLibrary, NativeLibraryKind};
 use rustc::util::common::{time, time_ext};
 use rustc::hir::def_id::CrateNum;
 use rustc_data_structures::fx::FxHashSet;
@@ -50,9 +50,9 @@ pub fn link_binary<'a, B: ArchiveBuilder<'a>>(sess: &'a Session,
                                               outputs: &OutputFilenames,
                                               crate_name: &str,
                                               target_cpu: &str) {
+    let output_metadata = sess.opts.output_types.contains_key(&OutputType::Metadata);
     for &crate_type in sess.crate_types.borrow().iter() {
         // Ignore executable crates if we have -Z no-codegen, as they will error.
-        let output_metadata = sess.opts.output_types.contains_key(&OutputType::Metadata);
         if (sess.opts.debugging_opts.no_codegen || !sess.opts.output_types.should_codegen()) &&
            !output_metadata &&
            crate_type == config::CrateType::Executable {
@@ -63,12 +63,43 @@ pub fn link_binary<'a, B: ArchiveBuilder<'a>>(sess: &'a Session,
            bug!("invalid output type `{:?}` for target os `{}`",
                 crate_type, sess.opts.target_triple);
         }
-        link_binary_output::<B>(sess,
-                                codegen_results,
-                                crate_type,
-                                outputs,
-                                crate_name,
-                                target_cpu);
+
+        for obj in codegen_results.modules.iter().filter_map(|m| m.object.as_ref()) {
+            check_file_is_writeable(obj, sess);
+        }
+
+        let tmpdir = TempFileBuilder::new().prefix("rustc").tempdir().unwrap_or_else(|err|
+            sess.fatal(&format!("couldn't create a temp dir: {}", err)));
+
+        if outputs.outputs.should_codegen() {
+            let out_filename = out_filename(sess, crate_type, outputs, crate_name);
+            match crate_type {
+                config::CrateType::Rlib => {
+                    link_rlib::<B>(sess,
+                              codegen_results,
+                              RlibFlavor::Normal,
+                              &out_filename,
+                              &tmpdir).build();
+                }
+                config::CrateType::Staticlib => {
+                    link_staticlib::<B>(sess, codegen_results, &out_filename, &tmpdir);
+                }
+                _ => {
+                    link_natively::<B>(
+                        sess,
+                        crate_type,
+                        &out_filename,
+                        codegen_results,
+                        tmpdir.path(),
+                        target_cpu,
+                    );
+                }
+            }
+        }
+
+        if sess.opts.cg.save_temps {
+            let _ = tmpdir.into_path();
+        }
     }
 
     // Remove the temporary object file and metadata if we aren't saving temps
@@ -85,7 +116,7 @@ pub fn link_binary<'a, B: ArchiveBuilder<'a>>(sess: &'a Session,
             if let Some(ref obj) = metadata_module.object {
                 remove(sess, obj);
             }
-         }
+        }
         if let Some(ref allocator_module) = codegen_results.allocator_module {
             if let Some(ref obj) = allocator_module.object {
                 remove(sess, obj);
@@ -97,73 +128,6 @@ pub fn link_binary<'a, B: ArchiveBuilder<'a>>(sess: &'a Session,
     }
 }
 
-fn link_binary_output<'a, B: ArchiveBuilder<'a>>(sess: &'a Session,
-                                                 codegen_results: &CodegenResults,
-                                                 crate_type: config::CrateType,
-                                                 outputs: &OutputFilenames,
-                                                 crate_name: &str,
-                                                 target_cpu: &str) {
-    for obj in codegen_results.modules.iter().filter_map(|m| m.object.as_ref()) {
-        check_file_is_writeable(obj, sess);
-    }
-
-    if outputs.outputs.contains_key(&OutputType::Metadata) {
-        let out_filename = filename_for_metadata(sess, crate_name, outputs);
-        // To avoid races with another rustc process scanning the output directory,
-        // we need to write the file somewhere else and atomically move it to its
-        // final destination, with a `fs::rename` call. In order for the rename to
-        // always succeed, the temporary file needs to be on the same filesystem,
-        // which is why we create it inside the output directory specifically.
-        let metadata_tmpdir = TempFileBuilder::new()
-            .prefix("rmeta")
-            .tempdir_in(out_filename.parent().unwrap())
-            .unwrap_or_else(|err| sess.fatal(&format!("couldn't create a temp dir: {}", err)));
-        let metadata = emit_metadata(sess, codegen_results, &metadata_tmpdir);
-        match fs::rename(&metadata, &out_filename) {
-            Ok(_) => {
-                if sess.opts.debugging_opts.emit_directives {
-                    sess.parse_sess.span_diagnostic.maybe_emit_json_directive(
-                        format!("metadata file written: {}", out_filename.display()));
-                }
-            }
-            Err(e) => sess.fatal(&format!("failed to write {}: {}", out_filename.display(), e)),
-        }
-    }
-
-    let tmpdir = TempFileBuilder::new().prefix("rustc").tempdir().unwrap_or_else(|err|
-        sess.fatal(&format!("couldn't create a temp dir: {}", err)));
-
-    if outputs.outputs.should_codegen() {
-        let out_filename = out_filename(sess, crate_type, outputs, crate_name);
-        match crate_type {
-            config::CrateType::Rlib => {
-                link_rlib::<B>(sess,
-                          codegen_results,
-                          RlibFlavor::Normal,
-                          &out_filename,
-                          &tmpdir).build();
-            }
-            config::CrateType::Staticlib => {
-                link_staticlib::<B>(sess, codegen_results, &out_filename, &tmpdir);
-            }
-            _ => {
-                link_natively::<B>(
-                    sess,
-                    crate_type,
-                    &out_filename,
-                    codegen_results,
-                    tmpdir.path(),
-                    target_cpu,
-                );
-            }
-        }
-    }
-
-    if sess.opts.cg.save_temps {
-        let _ = tmpdir.into_path();
-    }
-}
-
 // The third parameter is for env vars, used on windows to set up the
 // path for MSVC to find its DLLs, and gcc to find its bundled
 // toolchain
@@ -261,13 +225,13 @@ pub fn each_linked_rlib(sess: &Session,
 /// building an `.rlib` (stomping over one another), or writing an `.rmeta` into a
 /// directory being searched for `extern crate` (observing an incomplete file).
 /// The returned path is the temporary file containing the complete metadata.
-fn emit_metadata<'a>(
+pub fn emit_metadata<'a>(
     sess: &'a Session,
-    codegen_results: &CodegenResults,
+    metadata: &EncodedMetadata,
     tmpdir: &TempDir
 ) -> PathBuf {
     let out_filename = tmpdir.path().join(METADATA_FILENAME);
-    let result = fs::write(&out_filename, &codegen_results.metadata.raw_data);
+    let result = fs::write(&out_filename, &metadata.raw_data);
 
     if let Err(e) = result {
         sess.fatal(&format!("failed to write {}: {}", out_filename.display(), e));
@@ -351,7 +315,7 @@ fn link_rlib<'a, B: ArchiveBuilder<'a>>(sess: &'a Session,
         RlibFlavor::Normal => {
             // Instead of putting the metadata in an object file section, rlibs
             // contain the metadata in a separate file.
-            ab.add_file(&emit_metadata(sess, codegen_results, tmpdir));
+            ab.add_file(&emit_metadata(sess, &codegen_results.metadata, tmpdir));
 
             // For LTO purposes, the bytecode of this library is also inserted
             // into the archive.
diff --git a/src/librustc_codegen_ssa/base.rs b/src/librustc_codegen_ssa/base.rs
index 3046c069981..3cd47dfbb29 100644
--- a/src/librustc_codegen_ssa/base.rs
+++ b/src/librustc_codegen_ssa/base.rs
@@ -17,6 +17,7 @@ use crate::{ModuleCodegen, ModuleKind, CachedModuleCodegen};
 
 use rustc::dep_graph::cgu_reuse_tracker::CguReuse;
 use rustc::hir::def_id::{DefId, LOCAL_CRATE};
+use rustc::middle::cstore::EncodedMetadata;
 use rustc::middle::lang_items::StartFnLangItem;
 use rustc::middle::weak_lang_items;
 use rustc::mir::mono::{Stats, CodegenUnitNameBuilder};
@@ -25,7 +26,7 @@ use rustc::ty::layout::{self, Align, TyLayout, LayoutOf, VariantIdx, HasTyCtxt};
 use rustc::ty::query::Providers;
 use rustc::middle::cstore::{self, LinkagePreference};
 use rustc::util::common::{time, print_time_passes_entry};
-use rustc::session::config::{self, CrateType, EntryFnType, Lto};
+use rustc::session::config::{self, EntryFnType, Lto};
 use rustc::session::Session;
 use rustc_mir::monomorphize::item::DefPathBasedNames;
 use rustc_mir::monomorphize::Instance;
@@ -530,26 +531,13 @@ pub const CODEGEN_WORKER_ID: usize = ::std::usize::MAX;
 pub fn codegen_crate<B: ExtraBackendMethods>(
     backend: B,
     tcx: TyCtxt<'a, 'tcx, 'tcx>,
+    metadata: EncodedMetadata,
+    need_metadata_module: bool,
     rx: mpsc::Receiver<Box<dyn Any + Send>>
 ) -> OngoingCodegen<B> {
 
     check_for_rustc_errors_attr(tcx);
 
-    let cgu_name_builder = &mut CodegenUnitNameBuilder::new(tcx);
-
-    // Codegen the metadata.
-    tcx.sess.profiler(|p| p.start_activity("codegen crate metadata"));
-
-    let metadata_cgu_name = cgu_name_builder.build_cgu_name(LOCAL_CRATE,
-                                                            &["crate"],
-                                                            Some("metadata")).as_str()
-                                                                             .to_string();
-    let mut metadata_llvm_module = backend.new_metadata(tcx, &metadata_cgu_name);
-    let metadata = time(tcx.sess, "write metadata", || {
-        backend.write_metadata(tcx, &mut metadata_llvm_module)
-    });
-    tcx.sess.profiler(|p| p.end_activity("codegen crate metadata"));
-
     // Skip crate items and just output metadata in -Z no-codegen mode.
     if tcx.sess.opts.debugging_opts.no_codegen ||
        !tcx.sess.opts.output_types.should_codegen() {
@@ -569,6 +557,8 @@ pub fn codegen_crate<B: ExtraBackendMethods>(
         return ongoing_codegen;
     }
 
+    let cgu_name_builder = &mut CodegenUnitNameBuilder::new(tcx);
+
     // Run the monomorphization collector and partition the collected items into
     // codegen units.
     let codegen_units = tcx.collect_and_partition_mono_items(LOCAL_CRATE).1;
@@ -632,17 +622,21 @@ pub fn codegen_crate<B: ExtraBackendMethods>(
         ongoing_codegen.submit_pre_codegened_module_to_llvm(tcx, allocator_module);
     }
 
-    let needs_metadata_module = tcx.sess.crate_types.borrow().iter().any(|ct| {
-        match *ct {
-            CrateType::Dylib |
-            CrateType::ProcMacro => true,
-            CrateType::Executable |
-            CrateType::Rlib |
-            CrateType::Staticlib |
-            CrateType::Cdylib => false,
-        }
-    });
-    if needs_metadata_module {
+    if need_metadata_module {
+        // Codegen the encoded metadata.
+        tcx.sess.profiler(|p| p.start_activity("codegen crate metadata"));
+
+        let metadata_cgu_name = cgu_name_builder.build_cgu_name(LOCAL_CRATE,
+                                                                &["crate"],
+                                                                Some("metadata")).as_str()
+                                                                                 .to_string();
+        let mut metadata_llvm_module = backend.new_metadata(tcx, &metadata_cgu_name);
+        time(tcx.sess, "write compressed metadata", || {
+            backend.write_compressed_metadata(tcx, &ongoing_codegen.metadata,
+                                              &mut metadata_llvm_module);
+        });
+        tcx.sess.profiler(|p| p.end_activity("codegen crate metadata"));
+
         let metadata_module = ModuleCodegen {
             name: metadata_cgu_name,
             module_llvm: metadata_llvm_module,
diff --git a/src/librustc_codegen_ssa/traits/backend.rs b/src/librustc_codegen_ssa/traits/backend.rs
index a9e0eadb198..530eba516a6 100644
--- a/src/librustc_codegen_ssa/traits/backend.rs
+++ b/src/librustc_codegen_ssa/traits/backend.rs
@@ -33,11 +33,12 @@ impl<'tcx, T> Backend<'tcx> for T where
 
 pub trait ExtraBackendMethods: CodegenBackend + WriteBackendMethods + Sized + Send {
     fn new_metadata(&self, sess: TyCtxt<'_, '_, '_>, mod_name: &str) -> Self::Module;
-    fn write_metadata<'b, 'gcx>(
+    fn write_compressed_metadata<'b, 'gcx>(
         &self,
         tcx: TyCtxt<'b, 'gcx, 'gcx>,
-        metadata: &mut Self::Module,
-    ) -> EncodedMetadata;
+        metadata: &EncodedMetadata,
+        llvm_module: &mut Self::Module,
+    );
     fn codegen_allocator<'b, 'gcx>(
         &self,
         tcx: TyCtxt<'b, 'gcx, 'gcx>,
diff --git a/src/librustc_codegen_utils/codegen_backend.rs b/src/librustc_codegen_utils/codegen_backend.rs
index 56eaffb1ca3..191c6605b43 100644
--- a/src/librustc_codegen_utils/codegen_backend.rs
+++ b/src/librustc_codegen_utils/codegen_backend.rs
@@ -18,7 +18,7 @@ use rustc::util::common::ErrorReported;
 use rustc::session::config::{OutputFilenames, PrintRequest};
 use rustc::ty::TyCtxt;
 use rustc::ty::query::Providers;
-use rustc::middle::cstore::MetadataLoader;
+use rustc::middle::cstore::{EncodedMetadata, MetadataLoader};
 use rustc::dep_graph::DepGraph;
 
 pub use rustc_data_structures::sync::MetadataRef;
@@ -37,6 +37,8 @@ pub trait CodegenBackend {
     fn codegen_crate<'a, 'tcx>(
         &self,
         tcx: TyCtxt<'a, 'tcx, 'tcx>,
+        metadata: EncodedMetadata,
+        need_metadata_module: bool,
         rx: mpsc::Receiver<Box<dyn Any + Send>>
     ) -> Box<dyn Any>;
 
diff --git a/src/librustc_interface/Cargo.toml b/src/librustc_interface/Cargo.toml
index fa2a5d2fc89..bcaa4216109 100644
--- a/src/librustc_interface/Cargo.toml
+++ b/src/librustc_interface/Cargo.toml
@@ -24,6 +24,7 @@ rustc_borrowck = { path = "../librustc_borrowck" }
 rustc_incremental = { path = "../librustc_incremental" }
 rustc_traits = { path = "../librustc_traits" }
 rustc_data_structures = { path = "../librustc_data_structures" }
+rustc_codegen_ssa = { path = "../librustc_codegen_ssa" }
 rustc_codegen_utils = { path = "../librustc_codegen_utils" }
 rustc_metadata = { path = "../librustc_metadata" }
 rustc_mir = { path = "../librustc_mir" }
@@ -34,3 +35,4 @@ rustc_errors = { path = "../librustc_errors" }
 rustc_plugin = { path = "../librustc_plugin" }
 rustc_privacy = { path = "../librustc_privacy" }
 rustc_resolve = { path = "../librustc_resolve" }
+tempfile = "3.0.5"
diff --git a/src/librustc_interface/passes.rs b/src/librustc_interface/passes.rs
index f8b1271b8b5..6d3115c6213 100644
--- a/src/librustc_interface/passes.rs
+++ b/src/librustc_interface/passes.rs
@@ -16,11 +16,13 @@ use rustc::traits;
 use rustc::util::common::{time, ErrorReported};
 use rustc::util::profiling::ProfileCategory;
 use rustc::session::{CompileResult, CrateDisambiguator, Session};
-use rustc::session::config::{self, Input, OutputFilenames, OutputType};
+use rustc::session::config::{self, CrateType, Input, OutputFilenames, OutputType};
 use rustc::session::search_paths::PathKind;
 use rustc_allocator as allocator;
 use rustc_borrowck as borrowck;
+use rustc_codegen_ssa::back::link::emit_metadata;
 use rustc_codegen_utils::codegen_backend::CodegenBackend;
+use rustc_codegen_utils::link::filename_for_metadata;
 use rustc_data_structures::{box_region_allow_access, declare_box_region_type, parallel};
 use rustc_data_structures::fingerprint::Fingerprint;
 use rustc_data_structures::stable_hasher::StableHasher;
@@ -50,6 +52,7 @@ use syntax_pos::{FileName, hygiene};
 use syntax_ext;
 
 use serialize::json;
+use tempfile::Builder as TempFileBuilder;
 
 use std::any::Any;
 use std::env;
@@ -999,6 +1002,68 @@ fn analysis<'tcx>(
     Ok(())
 }
 
+fn encode_and_write_metadata<'tcx>(
+    tcx: TyCtxt<'_, 'tcx, 'tcx>,
+    outputs: &OutputFilenames,
+) -> (middle::cstore::EncodedMetadata, bool) {
+    #[derive(PartialEq, Eq, PartialOrd, Ord)]
+    enum MetadataKind {
+        None,
+        Uncompressed,
+        Compressed
+    }
+
+    let metadata_kind = tcx.sess.crate_types.borrow().iter().map(|ty| {
+        match *ty {
+            CrateType::Executable |
+            CrateType::Staticlib |
+            CrateType::Cdylib => MetadataKind::None,
+
+            CrateType::Rlib => MetadataKind::Uncompressed,
+
+            CrateType::Dylib |
+            CrateType::ProcMacro => MetadataKind::Compressed,
+        }
+    }).max().unwrap_or(MetadataKind::None);
+
+    let metadata = match metadata_kind {
+        MetadataKind::None => middle::cstore::EncodedMetadata::new(),
+        MetadataKind::Uncompressed |
+        MetadataKind::Compressed => tcx.encode_metadata(),
+    };
+
+    let need_metadata_file = tcx.sess.opts.output_types.contains_key(&OutputType::Metadata);
+    if need_metadata_file {
+        let crate_name = &tcx.crate_name(LOCAL_CRATE).as_str();
+        let out_filename = filename_for_metadata(tcx.sess, crate_name, outputs);
+        // To avoid races with another rustc process scanning the output directory,
+        // we need to write the file somewhere else and atomically move it to its
+        // final destination, with an `fs::rename` call. In order for the rename to
+        // always succeed, the temporary file needs to be on the same filesystem,
+        // which is why we create it inside the output directory specifically.
+        let metadata_tmpdir = TempFileBuilder::new()
+            .prefix("rmeta")
+            .tempdir_in(out_filename.parent().unwrap())
+            .unwrap_or_else(|err| {
+                tcx.sess.fatal(&format!("couldn't create a temp dir: {}", err))
+            });
+        let metadata_filename = emit_metadata(tcx.sess, &metadata, &metadata_tmpdir);
+        match std::fs::rename(&metadata_filename, &out_filename) {
+            Ok(_) => {
+                if tcx.sess.opts.debugging_opts.emit_directives {
+                    tcx.sess.parse_sess.span_diagnostic.maybe_emit_json_directive(
+                        format!("metadata file written: {}", out_filename.display()));
+                }
+            }
+            Err(e) => tcx.sess.fatal(&format!("failed to write {}: {}", out_filename.display(), e)),
+        }
+    }
+
+    let need_metadata_module = metadata_kind == MetadataKind::Compressed;
+
+    (metadata, need_metadata_module)
+}
+
 /// Runs the codegen backend, after which the AST and analysis can
 /// be discarded.
 pub fn start_codegen<'tcx>(
@@ -1013,11 +1078,17 @@ pub fn start_codegen<'tcx>(
     }
 
     time(tcx.sess, "resolving dependency formats", || {
-        ::rustc::middle::dependency_format::calculate(tcx)
+        middle::dependency_format::calculate(tcx)
+    });
+
+    let (metadata, need_metadata_module) = time(tcx.sess, "metadata encoding and writing", || {
+        encode_and_write_metadata(tcx, outputs)
     });
 
     tcx.sess.profiler(|p| p.start_activity("codegen crate"));
-    let codegen = time(tcx.sess, "codegen", move || codegen_backend.codegen_crate(tcx, rx));
+    let codegen = time(tcx.sess, "codegen", move || {
+        codegen_backend.codegen_crate(tcx, metadata, need_metadata_module, rx)
+    });
     tcx.sess.profiler(|p| p.end_activity("codegen crate"));
 
     if log_enabled!(::log::Level::Info) {
diff --git a/src/test/run-make-fulldeps/hotplug_codegen_backend/the_backend.rs b/src/test/run-make-fulldeps/hotplug_codegen_backend/the_backend.rs
index 5330470da16..4e43aa96e1d 100644
--- a/src/test/run-make-fulldeps/hotplug_codegen_backend/the_backend.rs
+++ b/src/test/run-make-fulldeps/hotplug_codegen_backend/the_backend.rs
@@ -15,7 +15,7 @@ use rustc::session::Session;
 use rustc::session::config::OutputFilenames;
 use rustc::ty::TyCtxt;
 use rustc::ty::query::Providers;
-use rustc::middle::cstore::MetadataLoader;
+use rustc::middle::cstore::{EncodedMetadata, MetadataLoader};
 use rustc::dep_graph::DepGraph;
 use rustc::util::common::ErrorReported;
 use rustc_codegen_utils::codegen_backend::CodegenBackend;
@@ -61,6 +61,8 @@ impl CodegenBackend for TheBackend {
     fn codegen_crate<'a, 'tcx>(
         &self,
         tcx: TyCtxt<'a, 'tcx, 'tcx>,
+        _metadata: EncodedMetadata,
+        _need_metadata_module: bool,
         _rx: mpsc::Receiver<Box<Any + Send>>
     ) -> Box<Any> {
         use rustc::hir::def_id::LOCAL_CRATE;