5 files changed, 15 insertions, 8 deletions
diff --git a/compiler/rustc_mir_transform/src/cleanup_post_borrowck.rs b/compiler/rustc_mir_transform/src/cleanup_post_borrowck.rs
index 1164dcf29da..5b4bc4fa134 100644
--- a/compiler/rustc_mir_transform/src/cleanup_post_borrowck.rs
+++ b/compiler/rustc_mir_transform/src/cleanup_post_borrowck.rs
@@ -10,7 +10,7 @@
 //! [`Assign`]: rustc_middle::mir::StatementKind::Assign
 //! [`FakeRead`]: rustc_middle::mir::StatementKind::FakeRead
 //! [`Nop`]: rustc_middle::mir::StatementKind::Nop
-//! [`Shallow`]: rustc_middle::mir::BorrowKind::Shallow
+//! [`Fake`]: rustc_middle::mir::BorrowKind::Fake
 
 use crate::MirPass;
 use rustc_middle::mir::{Body, BorrowKind, Rvalue, StatementKind, TerminatorKind};
@@ -24,7 +24,7 @@ impl<'tcx> MirPass<'tcx> for CleanupPostBorrowck {
             for statement in basic_block.statements.iter_mut() {
                 match statement.kind {
                     StatementKind::AscribeUserType(..)
-                    | StatementKind::Assign(box (_, Rvalue::Ref(_, BorrowKind::Shallow, _)))
+                    | StatementKind::Assign(box (_, Rvalue::Ref(_, BorrowKind::Fake, _)))
                     | StatementKind::FakeRead(..) => statement.make_nop(),
                     _ => (),
                 }
diff --git a/compiler/rustc_mir_transform/src/const_prop.rs b/compiler/rustc_mir_transform/src/const_prop.rs
index 53c0d0dea29..0adbb078105 100644
--- a/compiler/rustc_mir_transform/src/const_prop.rs
+++ b/compiler/rustc_mir_transform/src/const_prop.rs
@@ -668,7 +668,7 @@ impl<'tcx> Visitor<'tcx> for CanConstProp {
             // These can't ever be propagated under any scheme, as we can't reason about indirect
             // mutation.
             | NonMutatingUse(NonMutatingUseContext::SharedBorrow)
-            | NonMutatingUse(NonMutatingUseContext::ShallowBorrow)
+            | NonMutatingUse(NonMutatingUseContext::FakeBorrow)
             | NonMutatingUse(NonMutatingUseContext::AddressOf)
             | MutatingUse(MutatingUseContext::Borrow)
             | MutatingUse(MutatingUseContext::AddressOf) => {
diff --git a/compiler/rustc_mir_transform/src/copy_prop.rs b/compiler/rustc_mir_transform/src/copy_prop.rs
index be4af3b76f1..f5db7ce97eb 100644
--- a/compiler/rustc_mir_transform/src/copy_prop.rs
+++ b/compiler/rustc_mir_transform/src/copy_prop.rs
@@ -131,7 +131,7 @@ impl<'tcx> MutVisitor<'tcx> for Replacer<'_, 'tcx> {
         let observes_address = match ctxt {
             PlaceContext::NonMutatingUse(
                 NonMutatingUseContext::SharedBorrow
-                | NonMutatingUseContext::ShallowBorrow
+                | NonMutatingUseContext::FakeBorrow
                 | NonMutatingUseContext::AddressOf,
             ) => true,
             // For debuginfo, merging locals is ok.
diff --git a/compiler/rustc_mir_transform/src/coroutine.rs b/compiler/rustc_mir_transform/src/coroutine.rs
index fc30a718cbb..dfafd859830 100644
--- a/compiler/rustc_mir_transform/src/coroutine.rs
+++ b/compiler/rustc_mir_transform/src/coroutine.rs
@@ -637,6 +637,14 @@ struct LivenessInfo {
     storage_liveness: IndexVec<BasicBlock, Option<BitSet<Local>>>,
 }
 
+/// Computes which locals have to be stored in the state-machine for the
+/// given coroutine.
+///
+/// The basic idea is as follows:
+/// - a local is live until we encounter a `StorageDead` statement. In
+///   case none exist, the local is considered to be always live.
+/// - a local has to be stored if it is either directly used after the
+///   the suspend point, or if it is live and has been previously borrowed.
 fn locals_live_across_suspend_points<'tcx>(
     tcx: TyCtxt<'tcx>,
     body: &Body<'tcx>,
@@ -1449,16 +1457,15 @@ pub(crate) fn mir_coroutine_witnesses<'tcx>(
     // The first argument is the coroutine type passed by value
     let coroutine_ty = body.local_decls[ty::CAPTURE_STRUCT_LOCAL].ty;
 
-    // Get the interior types and args which typeck computed
     let movable = match *coroutine_ty.kind() {
         ty::Coroutine(_, _, movability) => movability == hir::Movability::Movable,
         ty::Error(_) => return None,
         _ => span_bug!(body.span, "unexpected coroutine type {}", coroutine_ty),
     };
 
-    // When first entering the coroutine, move the resume argument into its new local.
-    let always_live_locals = always_storage_live_locals(&body);
+    // The witness simply contains all locals live across suspend points.
 
+    let always_live_locals = always_storage_live_locals(&body);
     let liveness_info = locals_live_across_suspend_points(tcx, body, &always_live_locals, movable);
 
     // Extract locals which are live across suspension point into `layout`
diff --git a/compiler/rustc_mir_transform/src/ssa.rs b/compiler/rustc_mir_transform/src/ssa.rs
index 8dc7b60c4e5..1f59c790b4e 100644
--- a/compiler/rustc_mir_transform/src/ssa.rs
+++ b/compiler/rustc_mir_transform/src/ssa.rs
@@ -234,7 +234,7 @@ impl<'tcx> Visitor<'tcx> for SsaVisitor<'_> {
             // so we have to remove them too.
             PlaceContext::NonMutatingUse(
                 NonMutatingUseContext::SharedBorrow
-                | NonMutatingUseContext::ShallowBorrow
+                | NonMutatingUseContext::FakeBorrow
                 | NonMutatingUseContext::AddressOf,
             )
             | PlaceContext::MutatingUse(_) => {