Move metadata encoding earlier.

This commit separates metadata encoding (`tcx.encode_metadata`) from the
creation of the metadata module (which is now handled by
`write_compressed_metadata`, formerly `write_metadata`).

The metadata encoding now occurs slightly earlier in the pipeline, at
the very start of code generation within `start_codegen`.

Metadata *writing* still occurs near the end of compilation; that will
be moved forward in subsequent commits.

2 files changed, 25 insertions, 30 deletions

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>,