diff --git a/src/librustc_middle/mir/mono.rs b/src/librustc_middle/mir/mono.rs
index c889dbc0a4498..03b29deb56fdd 100644
--- a/src/librustc_middle/mir/mono.rs
+++ b/src/librustc_middle/mir/mono.rs
@@ -1,7 +1,9 @@
 use crate::dep_graph::{DepConstructor, DepNode, WorkProduct, WorkProductId};
 use crate::ich::{NodeIdHashingMode, StableHashingContext};
 use crate::ty::print::obsolete::DefPathBasedNames;
-use crate::ty::{subst::InternalSubsts, Instance, InstanceDef, SymbolName, TyCtxt};
+use crate::ty::{
+    subst::GenericArgKind, subst::InternalSubsts, Instance, InstanceDef, SymbolName, TyCtxt,
+};
 use rustc_attr::InlineAttr;
 use rustc_data_structures::base_n;
 use rustc_data_structures::fingerprint::Fingerprint;
@@ -48,6 +50,13 @@ pub enum MonoItem<'tcx> {
 }
 
 impl<'tcx> MonoItem<'tcx> {
+    pub fn def_id(&self) -> Option<DefId> {
+        match self {
+            MonoItem::Fn(instance) => Some(instance.def_id()),
+            MonoItem::Static(def_id) => Some(*def_id),
+            MonoItem::GlobalAsm(..) => None,
+        }
+    }
     pub fn size_estimate(&self, tcx: TyCtxt<'tcx>) -> usize {
         match *self {
             MonoItem::Fn(instance) => {
@@ -68,6 +77,18 @@ impl<'tcx> MonoItem<'tcx> {
         }
     }
 
+    pub fn has_closure_generic_argument(&self) -> bool {
+        match *self {
+            MonoItem::Fn(instance) => {
+                instance.substs.non_erasable_generics().any(|arg| match arg {
+                    GenericArgKind::Type(ty) => ty.is_closure(),
+                    GenericArgKind::Lifetime(_) | GenericArgKind::Const(_) => false,
+                })
+            }
+            MonoItem::Static(..) | MonoItem::GlobalAsm(..) => false,
+        }
+    }
+
     pub fn symbol_name(&self, tcx: TyCtxt<'tcx>) -> SymbolName {
         match *self {
             MonoItem::Fn(instance) => tcx.symbol_name(instance),
@@ -207,6 +228,14 @@ impl<'tcx> MonoItem<'tcx> {
         }
         .map(|hir_id| tcx.hir().span(hir_id))
     }
+
+    pub fn is_local(&self) -> bool {
+        match *self {
+            MonoItem::Fn(Instance { def, .. }) => def.def_id().is_local(),
+            MonoItem::Static(def_id) => def_id.is_local(),
+            MonoItem::GlobalAsm(..) => true,
+        }
+    }
 }
 
 impl<'a, 'tcx> HashStable<StableHashingContext<'a>> for MonoItem<'tcx> {
diff --git a/src/librustc_mir/monomorphize/partitioning.rs b/src/librustc_mir/monomorphize/partitioning.rs
index db1ea72c0a531..cae94975896a2 100644
--- a/src/librustc_mir/monomorphize/partitioning.rs
+++ b/src/librustc_mir/monomorphize/partitioning.rs
@@ -106,6 +106,7 @@ use rustc_middle::mir::mono::{InstantiationMode, MonoItem};
 use rustc_middle::ty::print::characteristic_def_id_of_type;
 use rustc_middle::ty::query::Providers;
 use rustc_middle::ty::{self, DefIdTree, InstanceDef, TyCtxt};
+use rustc_session::config::OptLevel;
 use rustc_span::symbol::{Symbol, SymbolStr};
 
 use crate::monomorphize::collector::InliningMap;
@@ -137,6 +138,8 @@ where
 
     initial_partitioning.codegen_units.iter_mut().for_each(|cgu| cgu.estimate_size(tcx));
 
+    initial_partitioning.codegen_units.sort_by_key(|cgu| cgu.name().as_str());
+
     debug_dump(tcx, "INITIAL PARTITIONING:", initial_partitioning.codegen_units.iter());
 
     // Merge until we have at most `max_cgu_count` codegen units.
@@ -152,7 +155,9 @@ where
     // local functions the definition of which is marked with `#[inline]`.
     let mut post_inlining = {
         let _prof_timer = tcx.prof.generic_activity("cgu_partitioning_place_inline_items");
-        place_inlined_mono_items(initial_partitioning, inlining_map)
+        let is_debug_incremental =
+            tcx.sess.opts.optimize == OptLevel::No && tcx.sess.opts.incremental.is_some();
+        place_inlined_mono_items(initial_partitioning, inlining_map, is_debug_incremental)
     };
 
     post_inlining.codegen_units.iter_mut().for_each(|cgu| cgu.estimate_size(tcx));
@@ -206,6 +211,7 @@ where
     let mut roots = FxHashSet::default();
     let mut codegen_units = FxHashMap::default();
     let is_incremental_build = tcx.sess.opts.incremental.is_some();
+    let is_debug_incremental = is_incremental_build && tcx.sess.opts.optimize == OptLevel::No;
     let mut internalization_candidates = FxHashSet::default();
 
     // Determine if monomorphizations instantiated in this crate will be made
@@ -223,18 +229,30 @@ where
             InstantiationMode::LocalCopy => continue,
         }
 
-        let characteristic_def_id = characteristic_def_id_of_mono_item(tcx, mono_item);
+        let characteristic_def_id =
+            characteristic_def_id_of_mono_item(tcx, mono_item, is_debug_incremental);
         let is_volatile = is_incremental_build && mono_item.is_generic_fn();
 
-        let codegen_unit_name = match characteristic_def_id {
-            Some(def_id) => compute_codegen_unit_name(
+        let codegen_unit_name = match (characteristic_def_id, mono_item.is_local()) {
+            (Some(def_id), false) if is_debug_incremental => {
+                let crate_name = tcx.crate_name(def_id.krate);
+                cgu_name_builder.build_cgu_name(
+                    LOCAL_CRATE,
+                    &[
+                        &*crate_name.as_str(),
+                        if mono_item.has_closure_generic_argument() { "has_closure" } else { "" },
+                    ],
+                    Some("cgu"),
+                )
+            }
+            (Some(def_id), _) => compute_codegen_unit_name(
                 tcx,
                 cgu_name_builder,
                 def_id,
                 is_volatile,
                 cgu_name_cache,
             ),
-            None => fallback_cgu_name(cgu_name_builder),
+            (None, _) => fallback_cgu_name(cgu_name_builder),
         };
 
         let codegen_unit = codegen_units
@@ -459,7 +477,9 @@ fn merge_codegen_units<'tcx>(
     assert!(target_cgu_count >= 1);
     let codegen_units = &mut initial_partitioning.codegen_units;
 
-    if tcx.is_compiler_builtins(LOCAL_CRATE) {
+    if tcx.is_compiler_builtins(LOCAL_CRATE)
+        || (tcx.dep_graph.is_fully_enabled() && tcx.sess.opts.optimize == OptLevel::No)
+    {
         // Compiler builtins require some degree of control over how mono items
         // are partitioned into compilation units. Provide it by keeping the
         // original partitioning when compiling the compiler builtins crate.
@@ -555,6 +575,7 @@ fn merge_codegen_units<'tcx>(
 fn place_inlined_mono_items<'tcx>(
     initial_partitioning: PreInliningPartitioning<'tcx>,
     inlining_map: &InliningMap<'tcx>,
+    is_debug_incremental: bool,
 ) -> PostInliningPartitioning<'tcx> {
     let mut new_partitioning = Vec::new();
     let mut mono_item_placements = FxHashMap::default();
@@ -587,10 +608,14 @@ fn place_inlined_mono_items<'tcx>(
                     );
                 }
 
-                // This is a CGU-private copy.
-                new_codegen_unit
-                    .items_mut()
-                    .insert(mono_item, (Linkage::Internal, Visibility::Default));
+                // In debug-incremental, do not create CGU-private copies unless it's for an external symbol
+                // FIXME: put external symbols in a separate codegen unit
+                if !is_debug_incremental || !mono_item.is_local() {
+                    // This is a CGU-private copy.
+                    new_codegen_unit
+                        .items_mut()
+                        .insert(mono_item, (Linkage::Internal, Visibility::Default));
+                }
             }
 
             if !single_codegen_unit {
@@ -707,7 +732,12 @@ fn internalize_symbols<'tcx>(
 fn characteristic_def_id_of_mono_item<'tcx>(
     tcx: TyCtxt<'tcx>,
     mono_item: MonoItem<'tcx>,
+    is_debug_incremental: bool,
 ) -> Option<DefId> {
+    if is_debug_incremental {
+        return mono_item.def_id();
+    }
+
     match mono_item {
         MonoItem::Fn(instance) => {
             let def_id = match instance.def {
diff --git a/src/librustc_ty/ty.rs b/src/librustc_ty/ty.rs
index 1aa11a761c821..e0861e15fd39d 100644
--- a/src/librustc_ty/ty.rs
+++ b/src/librustc_ty/ty.rs
@@ -2,6 +2,7 @@ use rustc_data_structures::svh::Svh;
 use rustc_hir as hir;
 use rustc_hir::def_id::{CrateNum, DefId, LocalDefId, LOCAL_CRATE};
 use rustc_middle::hir::map as hir_map;
+use rustc_middle::mir::StatementKind;
 use rustc_middle::ty::subst::Subst;
 use rustc_middle::ty::{self, ToPredicate, Ty, TyCtxt, WithConstness};
 use rustc_session::CrateDisambiguator;
@@ -299,7 +300,23 @@ fn instance_def_size_estimate<'tcx>(
     match instance_def {
         InstanceDef::Item(..) | InstanceDef::DropGlue(..) => {
             let mir = tcx.instance_mir(instance_def);
-            mir.basic_blocks().iter().map(|bb| bb.statements.len()).sum()
+            mir.basic_blocks()
+                .iter()
+                .map(|bb| {
+                    bb.statements
+                        .iter()
+                        .filter(|stmt| match stmt.kind {
+                            StatementKind::StorageLive(_)
+                            | StatementKind::StorageDead(_)
+                            | StatementKind::AscribeUserType(..)
+                            | StatementKind::FakeRead(..)
+                            | StatementKind::Retag(..)
+                            | StatementKind::Nop => false,
+                            _ => true,
+                        })
+                        .count()
+                })
+                .sum()
         }
         // Estimate the size of other compiler-generated shims to be 1.
         _ => 1,