Revert "Auto merge of #134330 - scottmcm:no-more-rvalue-len, r=matthewjasper"

This reverts commit e108481f74ff123ad98a63bd107a18d13035b275, reversing
changes made to 303e8bd768526a5812bb1776e798e829ddb7d3ca.

(cherry picked from commit ca1c17c88d1f625763859396ba7a50f36ac45cc0)

4 files changed, 13 insertions, 3 deletions

diff --git a/compiler/rustc_const_eval/src/check_consts/check.rs b/compiler/rustc_const_eval/src/check_consts/check.rs
index e895c44199b..f4257ad9671 100644
--- a/compiler/rustc_const_eval/src/check_consts/check.rs
+++ b/compiler/rustc_const_eval/src/check_consts/check.rs
@@ -488,7 +488,8 @@ impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> {
             Rvalue::Use(_)
             | Rvalue::CopyForDeref(..)
             | Rvalue::Repeat(..)
-            | Rvalue::Discriminant(..) => {}
+            | Rvalue::Discriminant(..)
+            | Rvalue::Len(_) => {}
 
             Rvalue::Aggregate(kind, ..) => {
                 if let AggregateKind::Coroutine(def_id, ..) = kind.as_ref()
diff --git a/compiler/rustc_const_eval/src/check_consts/qualifs.rs b/compiler/rustc_const_eval/src/check_consts/qualifs.rs
index b1b7fb406b1..e244b50a4b5 100644
--- a/compiler/rustc_const_eval/src/check_consts/qualifs.rs
+++ b/compiler/rustc_const_eval/src/check_consts/qualifs.rs
@@ -230,7 +230,9 @@ where
             Q::in_any_value_of_ty(cx, rvalue.ty(cx.body, cx.tcx))
         }
 
-        Rvalue::Discriminant(place) => in_place::<Q, _>(cx, in_local, place.as_ref()),
+        Rvalue::Discriminant(place) | Rvalue::Len(place) => {
+            in_place::<Q, _>(cx, in_local, place.as_ref())
+        }
 
         Rvalue::CopyForDeref(place) => in_place::<Q, _>(cx, in_local, place.as_ref()),
 
diff --git a/compiler/rustc_const_eval/src/check_consts/resolver.rs b/compiler/rustc_const_eval/src/check_consts/resolver.rs
index 5a6e7ab2bee..79df63a9e84 100644
--- a/compiler/rustc_const_eval/src/check_consts/resolver.rs
+++ b/compiler/rustc_const_eval/src/check_consts/resolver.rs
@@ -197,6 +197,7 @@ where
             | mir::Rvalue::CopyForDeref(..)
             | mir::Rvalue::ThreadLocalRef(..)
             | mir::Rvalue::Repeat(..)
+            | mir::Rvalue::Len(..)
             | mir::Rvalue::BinaryOp(..)
             | mir::Rvalue::NullaryOp(..)
             | mir::Rvalue::UnaryOp(..)
diff --git a/compiler/rustc_const_eval/src/interpret/step.rs b/compiler/rustc_const_eval/src/interpret/step.rs
index 32e77fe1024..a26c2eca107 100644
--- a/compiler/rustc_const_eval/src/interpret/step.rs
+++ b/compiler/rustc_const_eval/src/interpret/step.rs
@@ -15,7 +15,7 @@ use tracing::{info, instrument, trace};
 
 use super::{
     FnArg, FnVal, ImmTy, Immediate, InterpCx, InterpResult, Machine, MemPlaceMeta, PlaceTy,
-    Projectable, interp_ok, throw_ub,
+    Projectable, Scalar, interp_ok, throw_ub,
 };
 use crate::util;
 
@@ -218,6 +218,12 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
                 self.write_repeat(operand, &dest)?;
             }
 
+            Len(place) => {
+                let src = self.eval_place(place)?;
+                let len = src.len(self)?;
+                self.write_scalar(Scalar::from_target_usize(len, self), &dest)?;
+            }
+
             Ref(_, borrow_kind, place) => {
                 let src = self.eval_place(place)?;
                 let place = self.force_allocation(&src)?;