Auto merge of #66650 - matthewjasper:nonuniform-array-move, r=pnkfelix

Remove uniform array move MIR passes

This PR fixes a number of bugs caused by limitations of this pass

* Projections from constant indexes weren't being canonicalized
* Constant indexes from the start weren't being canonicalized (they could have different min_lengths)
* It didn't apply to non-moves

This PR makes the following changes to support removing this pass:

* ConstantIndex of arrays are now generated in a canonical form (from the start, min_length is the actual length).
* Subslices are now split when generating move paths and when checking subslices have been moved.

Additionally

* The parent move path of a projection from an array element is now calculated correctly

closes #66502

src/librustc/mir/mod.rs

@@ -1714,18 +1714,25 @@ pub enum ProjectionElem<V, T> {
     ConstantIndex {
         /// index or -index (in Python terms), depending on from_end
         offset: u32,
-        /// thing being indexed must be at least this long
+        /// The thing being indexed must be at least this long. For arrays this
+        /// is always the exact length.
         min_length: u32,
-        /// counting backwards from end?
+        /// Counting backwards from end? This is always false when indexing an
+        /// array.
         from_end: bool,
     },
 
     /// These indices are generated by slice patterns.
     ///
-    /// slice[from:-to] in Python terms.
+    /// If `from_end` is true `slice[from..slice.len() - to]`.
+    /// Otherwise `array[from..to]`.
     Subslice {
         from: u32,
         to: u32,
+        /// Whether `to` counts from the start or end of the array/slice.
+        /// For `PlaceElem`s this is `true` if and only if the base is a slice.
+        /// For `ProjectionKind`, this can also be `true` for arrays.
+        from_end: bool,
     },
 
     /// "Downcast" to a variant of an ADT. Currently, we only introduce
@@ -1914,15 +1921,18 @@ impl Debug for Place<'_> {
                 ProjectionElem::ConstantIndex { offset, min_length, from_end: true } => {
                     write!(fmt, "[-{:?} of {:?}]", offset, min_length)?;
                 }
-                ProjectionElem::Subslice { from, to } if *to == 0 => {
+                ProjectionElem::Subslice { from, to, from_end: true } if *to == 0 => {
                     write!(fmt, "[{:?}:]", from)?;
                 }
-                ProjectionElem::Subslice { from, to } if *from == 0 => {
+                ProjectionElem::Subslice { from, to, from_end: true } if *from == 0 => {
                     write!(fmt, "[:-{:?}]", to)?;
                 }
-                ProjectionElem::Subslice { from, to } => {
+                ProjectionElem::Subslice { from, to, from_end: true } => {
                     write!(fmt, "[{:?}:-{:?}]", from, to)?;
                 }
+                ProjectionElem::Subslice { from, to, from_end: false } => {
+                    write!(fmt, "[{:?}..{:?}]", from, to)?;
+                }
             }
         }
 
@@ -2456,7 +2466,7 @@ impl UserTypeProjection {
     }
 
     pub(crate) fn subslice(mut self, from: u32, to: u32) -> Self {
-        self.projs.push(ProjectionElem::Subslice { from, to });
+        self.projs.push(ProjectionElem::Subslice { from, to, from_end: true });
         self
     }
 

src/librustc/mir/tcx.rs

@@ -88,14 +88,17 @@ impl<'tcx> PlaceTy<'tcx> {
             }
             ProjectionElem::Index(_) | ProjectionElem::ConstantIndex { .. } =>
                 PlaceTy::from_ty(self.ty.builtin_index().unwrap()),
-            ProjectionElem::Subslice { from, to } => {
+            ProjectionElem::Subslice { from, to, from_end } => {
                 PlaceTy::from_ty(match self.ty.kind {
-                    ty::Array(inner, size) => {
+                    ty::Slice(..) => self.ty,
+                    ty::Array(inner, _) if !from_end => {
+                        tcx.mk_array(inner, (to - from) as u64)
+                    }
+                    ty::Array(inner, size) if from_end => {
                         let size = size.eval_usize(tcx, param_env);
                         let len = size - (from as u64) - (to as u64);
                         tcx.mk_array(inner, len)
                     }
-                    ty::Slice(..) => self.ty,
                     _ => {
                         bug!("cannot subslice non-array type: `{:?}`", self)
                     }

src/librustc/mir/visit.rs

@@ -954,7 +954,7 @@ macro_rules! visit_place_fns {
                     );
                 }
                 ProjectionElem::Deref |
-                ProjectionElem::Subslice { from: _, to: _ } |
+                ProjectionElem::Subslice { from: _, to: _, from_end: _ } |
                 ProjectionElem::ConstantIndex { offset: _,
                                                 min_length: _,
                                                 from_end: _ } |