Rollup merge of #143046 - RalfJung:zst-unsafe-cell, r=lcnr,oli-obk

const validation: properly ignore zero-sized UnsafeCell

Fixes rust-lang/rust#142948
r? `@oli-obk`

Author: matthiaskrgr

src/borrow_tracker/stacked_borrows/mod.rs

@@ -814,7 +814,7 @@ trait EvalContextPrivExt<'tcx, 'ecx>: crate::MiriInterpCxExt<'tcx> {
         info: RetagInfo, // diagnostics info about this retag
     ) -> InterpResult<'tcx, MPlaceTy<'tcx>> {
         let this = self.eval_context_mut();
-        let size = this.size_and_align_of_mplace(place)?.map(|(size, _)| size);
+        let size = this.size_and_align_of_val(place)?.map(|(size, _)| size);
         // FIXME: If we cannot determine the size (because the unsized tail is an `extern type`),
         // bail out -- we cannot reasonably figure out which memory range to reborrow.
         // See https://github.com/rust-lang/unsafe-code-guidelines/issues/276.

src/borrow_tracker/tree_borrows/mod.rs

@@ -469,7 +469,7 @@ trait EvalContextPrivExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
         // - if the pointer is not reborrowed (raw pointer) then we override the size
         //   to do a zero-length reborrow.
         let reborrow_size = this
-            .size_and_align_of_mplace(place)?
+            .size_and_align_of_val(place)?
             .map(|(size, _)| size)
             .unwrap_or(place.layout.size);
         trace!("Creating new permission: {:?} with size {:?}", new_perm, reborrow_size);

src/helpers.rs

@@ -489,7 +489,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
         trace!("visit_frozen(place={:?}, size={:?})", *place, size);
         debug_assert_eq!(
             size,
-            this.size_and_align_of_mplace(place)?
+            this.size_and_align_of_val(place)?
                 .map(|(size, _)| size)
                 .unwrap_or_else(|| place.layout.size)
         );
@@ -530,7 +530,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
                     trace!("unsafe_cell_action on {:?}", place.ptr());
                     // We need a size to go on.
                     let unsafe_cell_size = this
-                        .size_and_align_of_mplace(place)?
+                        .size_and_align_of_val(place)?
                         .map(|(size, _)| size)
                         // for extern types, just cover what we can
                         .unwrap_or_else(|| place.layout.size);