3 files changed, 19 insertions, 4 deletions
diff --git a/compiler/rustc_target/src/spec/thumbv6m_none_eabi.rs b/compiler/rustc_target/src/spec/thumbv6m_none_eabi.rs
index 2546ab9b7e6..dffa19ae55c 100644
--- a/compiler/rustc_target/src/spec/thumbv6m_none_eabi.rs
+++ b/compiler/rustc_target/src/spec/thumbv6m_none_eabi.rs
@@ -14,8 +14,9 @@ pub fn target() -> Target {
             // The ARMv6-M architecture doesn't support unaligned loads/stores so we disable them
             // with +strict-align.
             features: "+strict-align".into(),
-            // There are no atomic CAS instructions available in the instruction set of the ARMv6-M
+            // There are no atomic instructions available in the instruction set of the ARMv6-M
             // architecture
+            max_atomic_width: Some(0),
             atomic_cas: false,
             ..super::thumb_base::opts()
         },
diff --git a/compiler/rustc_trait_selection/src/traits/const_evaluatable.rs b/compiler/rustc_trait_selection/src/traits/const_evaluatable.rs
index e6284b1c4ac..decbf013311 100644
--- a/compiler/rustc_trait_selection/src/traits/const_evaluatable.rs
+++ b/compiler/rustc_trait_selection/src/traits/const_evaluatable.rs
@@ -185,14 +185,20 @@ pub fn is_const_evaluatable<'cx, 'tcx>(
         }
         let concrete = infcx.const_eval_resolve(param_env, uv.expand(), Some(span));
         match concrete {
-            Err(ErrorHandled::TooGeneric) => Err(if !uv.has_infer_types_or_consts() {
+            Err(ErrorHandled::TooGeneric) => Err(if uv.has_infer_types_or_consts() {
+                NotConstEvaluatable::MentionsInfer
+            } else if uv.has_param_types_or_consts() {
                 infcx
                     .tcx
                     .sess
                     .delay_span_bug(span, &format!("unexpected `TooGeneric` for {:?}", uv));
                 NotConstEvaluatable::MentionsParam
             } else {
-                NotConstEvaluatable::MentionsInfer
+                let guar = infcx.tcx.sess.delay_span_bug(
+                    span,
+                    format!("Missing value for constant, but no error reported?"),
+                );
+                NotConstEvaluatable::Error(guar)
             }),
             Err(ErrorHandled::Linted) => {
                 let reported = infcx
@@ -240,8 +246,11 @@ pub fn is_const_evaluatable<'cx, 'tcx>(
 
             Err(ErrorHandled::TooGeneric) => Err(if uv.has_infer_types_or_consts() {
                 NotConstEvaluatable::MentionsInfer
-                } else {
+                } else if uv.has_param_types_or_consts() {
                 NotConstEvaluatable::MentionsParam
+            } else {
+                let guar = infcx.tcx.sess.delay_span_bug(span, format!("Missing value for constant, but no error reported?"));
+                NotConstEvaluatable::Error(guar)
             }),
             Err(ErrorHandled::Linted) => {
                 let reported =
diff --git a/compiler/rustc_ty_utils/src/instance.rs b/compiler/rustc_ty_utils/src/instance.rs
index 5e58f237982..979e997f244 100644
--- a/compiler/rustc_ty_utils/src/instance.rs
+++ b/compiler/rustc_ty_utils/src/instance.rs
@@ -280,6 +280,11 @@ fn resolve_associated_item<'tcx>(
                 return Ok(None);
             }
 
+            // If the item does not have a value, then we cannot return an instance.
+            if !leaf_def.item.defaultness.has_value() {
+                return Ok(None);
+            }
+
             let substs = tcx.erase_regions(substs);
 
             // Check if we just resolved an associated `const` declaration from