Use more CGUs in incremental compilation

Author: saethlin

compiler/rustc_middle/src/mir/mono.rs

@@ -127,16 +127,7 @@ impl<'tcx> MonoItem<'tcx> {
                     return InstantiationMode::LocalCopy;
                 }
 
-                // Finally, if this is `#[inline(always)]` we're sure to respect
-                // that with an inline copy per CGU, but otherwise we'll be
-                // creating one copy of this `#[inline]` function which may
-                // conflict with upstream crates as it could be an exported
-                // symbol.
-                if tcx.codegen_fn_attrs(instance.def_id()).inline.always() {
-                    InstantiationMode::LocalCopy
-                } else {
-                    InstantiationMode::GloballyShared { may_conflict: true }
-                }
+                InstantiationMode::GloballyShared { may_conflict: true }
             }
             MonoItem::Static(..) | MonoItem::GlobalAsm(..) => {
                 InstantiationMode::GloballyShared { may_conflict: false }

compiler/rustc_monomorphize/src/partitioning.rs

@@ -690,6 +690,14 @@ fn compute_codegen_unit_name(
     let mut cgu_def_id = None;
     // Walk backwards from the item we want to find the module for.
     loop {
+        if tcx.sess.opts.incremental.is_some()
+            && tcx.sess.opts.optimize == rustc_session::config::OptLevel::No
+            && def_id.is_local()
+        {
+            cgu_def_id = Some(current_def_id);
+            break;
+        }
+
         if current_def_id.is_crate_root() {
             if cgu_def_id.is_none() {
                 // If we have not found a module yet, take the crate root.
@@ -716,8 +724,7 @@ fn compute_codegen_unit_name(
         let def_path = tcx.def_path(cgu_def_id);
 
         let components = def_path.data.iter().map(|part| match part.data.name() {
-            DefPathDataName::Named(name) => name,
-            DefPathDataName::Anon { .. } => unreachable!(),
+            DefPathDataName::Named(name) | DefPathDataName::Anon { namespace: name } => name,
         });
 
         let volatile_suffix = volatile.then_some("volatile");

compiler/rustc_session/src/session.rs

@@ -788,7 +788,7 @@ impl Session {
         // codegen units in order to reduce the "collateral damage" small
         // changes cause.
         if self.opts.incremental.is_some() {
-            return CodegenUnits::Default(256);
+            return CodegenUnits::Default(4096);
         }
 
         // Why is 16 codegen units the default all the time?