Auto merge of #52266 - michaelwoerister:incr-thinlto-preliminaries, r=alexcrichton

Preliminary work for incremental ThinLTO.

Since implementing incremental ThinLTO is a bit more involved than I initially thought, I'm splitting out some of the things that already work. This PR (1) adds a way accessing some ThinLTO information in `rustc` and (2) does some cleanup around CGU/object file naming (which makes things quite a bit nicer).

This is probably best reviewed one commit at a time.

3 files changed, 47 insertions, 8 deletions

diff --git a/src/librustc_incremental/assert_module_sources.rs b/src/librustc_incremental/assert_module_sources.rs
index df8e0f056af..f6e9ee7b225 100644
--- a/src/librustc_incremental/assert_module_sources.rs
+++ b/src/librustc_incremental/assert_module_sources.rs
@@ -27,11 +27,11 @@
 //! the HIR doesn't change as a result of the annotations, which might
 //! perturb the reuse results.
 
+use rustc::hir::def_id::LOCAL_CRATE;
 use rustc::dep_graph::{DepNode, DepConstructor};
 use rustc::mir::mono::CodegenUnit;
 use rustc::ty::TyCtxt;
 use syntax::ast;
-use syntax_pos::symbol::Symbol;
 use rustc::ich::{ATTR_PARTITION_REUSED, ATTR_PARTITION_CODEGENED};
 
 const MODULE: &'static str = "module";
@@ -72,12 +72,37 @@ impl<'a, 'tcx> AssertModuleSource<'a, 'tcx> {
             return;
         }
 
-        let mname = self.field(attr, MODULE);
-        let mangled_cgu_name = CodegenUnit::mangle_name(&mname.as_str());
-        let mangled_cgu_name = Symbol::intern(&mangled_cgu_name).as_interned_str();
+        let user_path = self.field(attr, MODULE).as_str().to_string();
+        let crate_name = self.tcx.crate_name(LOCAL_CRATE).as_str().to_string();
+
+        if !user_path.starts_with(&crate_name) {
+            let msg = format!("Found malformed codegen unit name `{}`. \
+                Codegen units names must always start with the name of the \
+                crate (`{}` in this case).", user_path, crate_name);
+            self.tcx.sess.span_fatal(attr.span, &msg);
+        }
+
+        // Split of the "special suffix" if there is one.
+        let (user_path, cgu_special_suffix) = if let Some(index) = user_path.rfind(".") {
+            (&user_path[..index], Some(&user_path[index + 1 ..]))
+        } else {
+            (&user_path[..], None)
+        };
+
+        let mut cgu_path_components = user_path.split("-").collect::<Vec<_>>();
+
+        // Remove the crate name
+        assert_eq!(cgu_path_components.remove(0), crate_name);
+
+        let cgu_name = CodegenUnit::build_cgu_name(self.tcx,
+                                                   LOCAL_CRATE,
+                                                   cgu_path_components,
+                                                   cgu_special_suffix);
+
+        debug!("mapping '{}' to cgu name '{}'", self.field(attr, MODULE), cgu_name);
 
         let dep_node = DepNode::new(self.tcx,
-                                    DepConstructor::CompileCodegenUnit(mangled_cgu_name));
+                                    DepConstructor::CompileCodegenUnit(cgu_name));
 
         if let Some(loaded_from_cache) = self.tcx.dep_graph.was_loaded_from_cache(&dep_node) {
             match (disposition, loaded_from_cache) {
@@ -85,13 +110,13 @@ impl<'a, 'tcx> AssertModuleSource<'a, 'tcx> {
                     self.tcx.sess.span_err(
                         attr.span,
                         &format!("expected module named `{}` to be Reused but is Codegened",
-                                 mname));
+                                 user_path));
                 }
                 (Disposition::Codegened, true) => {
                     self.tcx.sess.span_err(
                         attr.span,
                         &format!("expected module named `{}` to be Codegened but is Reused",
-                                 mname));
+                                 user_path));
                 }
                 (Disposition::Reused, true) |
                 (Disposition::Codegened, false) => {
@@ -99,7 +124,19 @@ impl<'a, 'tcx> AssertModuleSource<'a, 'tcx> {
                 }
             }
         } else {
-            self.tcx.sess.span_err(attr.span, &format!("no module named `{}`", mname));
+            let available_cgus = self.tcx
+                .collect_and_partition_mono_items(LOCAL_CRATE)
+                .1
+                .iter()
+                .map(|cgu| format!("{}", cgu.name()))
+                .collect::<Vec<String>>()
+                .join(", ");
+
+            self.tcx.sess.span_err(attr.span,
+                &format!("no module named `{}` (mangled: {}).\nAvailable modules: {}",
+                    user_path,
+                    cgu_name,
+                    available_cgus));
         }
     }
 
diff --git a/src/librustc_incremental/lib.rs b/src/librustc_incremental/lib.rs
index 2ef88041d33..10efa1a2870 100644
--- a/src/librustc_incremental/lib.rs
+++ b/src/librustc_incremental/lib.rs
@@ -44,6 +44,7 @@ pub use persist::copy_cgu_workproducts_to_incr_comp_cache_dir;
 pub use persist::save_dep_graph;
 pub use persist::save_work_product_index;
 pub use persist::in_incr_comp_dir;
+pub use persist::in_incr_comp_dir_sess;
 pub use persist::prepare_session_directory;
 pub use persist::finalize_session_directory;
 pub use persist::delete_workproduct_files;
diff --git a/src/librustc_incremental/persist/mod.rs b/src/librustc_incremental/persist/mod.rs
index e1f00db56d5..17d36ba3fa7 100644
--- a/src/librustc_incremental/persist/mod.rs
+++ b/src/librustc_incremental/persist/mod.rs
@@ -23,6 +23,7 @@ mod file_format;
 pub use self::fs::finalize_session_directory;
 pub use self::fs::garbage_collect_session_directories;
 pub use self::fs::in_incr_comp_dir;
+pub use self::fs::in_incr_comp_dir_sess;
 pub use self::fs::prepare_session_directory;
 pub use self::load::dep_graph_tcx_init;
 pub use self::load::load_dep_graph;