Auto merge of #3130 - RalfJung:rustup, r=RalfJung

Rustup

22 files changed, 98 insertions, 44 deletions

diff --git a/src/tools/cargo b/src/tools/cargo
-Subproject 6fa6fdc7606cfa664f9bee2fb33ee2ed904f4e8
+Subproject 8eb8acbb116e7923ea2ce33a50109933ed5ab37
diff --git a/src/tools/clippy/clippy_lints/src/dereference.rs b/src/tools/clippy/clippy_lints/src/dereference.rs
index 14877385646..5134cf66050 100644
--- a/src/tools/clippy/clippy_lints/src/dereference.rs
+++ b/src/tools/clippy/clippy_lints/src/dereference.rs
@@ -701,7 +701,7 @@ fn deref_method_same_type<'tcx>(result_ty: Ty<'tcx>, arg_ty: Ty<'tcx>) -> bool {
 
 fn in_postfix_position<'tcx>(cx: &LateContext<'tcx>, e: &'tcx Expr<'tcx>) -> bool {
     if let Some(parent) = get_parent_expr(cx, e)
-        && parent.span.ctxt() == e.span.ctxt()
+        && parent.span.eq_ctxt(e.span)
     {
         match parent.kind {
             ExprKind::Call(child, _) | ExprKind::MethodCall(_, child, _, _) | ExprKind::Index(child, _, _)
diff --git a/src/tools/clippy/clippy_lints/src/entry.rs b/src/tools/clippy/clippy_lints/src/entry.rs
index 6197b5b19eb..70a467dde61 100644
--- a/src/tools/clippy/clippy_lints/src/entry.rs
+++ b/src/tools/clippy/clippy_lints/src/entry.rs
@@ -241,7 +241,7 @@ fn try_parse_contains<'tcx>(cx: &LateContext<'_>, expr: &'tcx Expr<'_>) -> Optio
                 },
             ],
             _,
-        ) if key_span.ctxt() == expr.span.ctxt() => {
+        ) if key_span.eq_ctxt(expr.span) => {
             let id = cx.typeck_results().type_dependent_def_id(expr.hir_id)?;
             let expr = ContainsExpr {
                 negated,
diff --git a/src/tools/clippy/clippy_lints/src/formatting.rs b/src/tools/clippy/clippy_lints/src/formatting.rs
index d03480c2108..4ebf0e9667d 100644
--- a/src/tools/clippy/clippy_lints/src/formatting.rs
+++ b/src/tools/clippy/clippy_lints/src/formatting.rs
@@ -274,7 +274,7 @@ fn check_array(cx: &EarlyContext<'_>, expr: &Expr) {
         for element in array {
             if_chain! {
                 if let ExprKind::Binary(ref op, ref lhs, _) = element.kind;
-                if has_unary_equivalent(op.node) && lhs.span.ctxt() == op.span.ctxt();
+                if has_unary_equivalent(op.node) && lhs.span.eq_ctxt(op.span);
                 let space_span = lhs.span.between(op.span);
                 if let Some(space_snippet) = snippet_opt(cx, space_span);
                 let lint_span = lhs.span.with_lo(lhs.span.hi());
diff --git a/src/tools/clippy/clippy_lints/src/let_with_type_underscore.rs b/src/tools/clippy/clippy_lints/src/let_with_type_underscore.rs
index 4e9d77ea156..79d728a021c 100644
--- a/src/tools/clippy/clippy_lints/src/let_with_type_underscore.rs
+++ b/src/tools/clippy/clippy_lints/src/let_with_type_underscore.rs
@@ -31,7 +31,7 @@ impl LateLintPass<'_> for UnderscoreTyped {
             if !in_external_macro(cx.tcx.sess, local.span);
             if let Some(ty) = local.ty; // Ensure that it has a type defined
             if let TyKind::Infer = &ty.kind; // that type is '_'
-            if local.span.ctxt() == ty.span.ctxt();
+            if local.span.eq_ctxt(ty.span);
             then {
                 // NOTE: Using `is_from_proc_macro` on `init` will require that it's initialized,
                 // this doesn't. Alternatively, `WithSearchPat` can be implemented for `Ty`
diff --git a/src/tools/clippy/clippy_lints/src/manual_let_else.rs b/src/tools/clippy/clippy_lints/src/manual_let_else.rs
index 2117308cd40..86bbdb4ea19 100644
--- a/src/tools/clippy/clippy_lints/src/manual_let_else.rs
+++ b/src/tools/clippy/clippy_lints/src/manual_let_else.rs
@@ -59,7 +59,7 @@ impl<'tcx> QuestionMark {
             let Some(init) = local.init &&
             local.els.is_none() &&
             local.ty.is_none() &&
-            init.span.ctxt() == stmt.span.ctxt() &&
+            init.span.eq_ctxt(stmt.span) &&
             let Some(if_let_or_match) = IfLetOrMatch::parse(cx, init)
         {
             match if_let_or_match {
diff --git a/src/tools/clippy/clippy_lints/src/matches/collapsible_match.rs b/src/tools/clippy/clippy_lints/src/matches/collapsible_match.rs
index 33a052c41a3..29b935fb61a 100644
--- a/src/tools/clippy/clippy_lints/src/matches/collapsible_match.rs
+++ b/src/tools/clippy/clippy_lints/src/matches/collapsible_match.rs
@@ -57,7 +57,7 @@ fn check_arm<'tcx>(
                 }
             },
         };
-        if outer_pat.span.ctxt() == inner_scrutinee.span.ctxt();
+        if outer_pat.span.eq_ctxt(inner_scrutinee.span);
         // match expression must be a local binding
         // match <local> { .. }
         if let Some(binding_id) = path_to_local(peel_ref_operators(cx, inner_scrutinee));
diff --git a/src/tools/clippy/clippy_lints/src/matches/manual_utils.rs b/src/tools/clippy/clippy_lints/src/matches/manual_utils.rs
index 6b611f567ae..781ee138c76 100644
--- a/src/tools/clippy/clippy_lints/src/matches/manual_utils.rs
+++ b/src/tools/clippy/clippy_lints/src/matches/manual_utils.rs
@@ -119,7 +119,7 @@ where
     // it's being passed by value.
     let scrutinee = peel_hir_expr_refs(scrutinee).0;
     let (scrutinee_str, _) = snippet_with_context(cx, scrutinee.span, expr_ctxt, "..", &mut app);
-    let scrutinee_str = if scrutinee.span.ctxt() == expr.span.ctxt() && scrutinee.precedence().order() < PREC_POSTFIX {
+    let scrutinee_str = if scrutinee.span.eq_ctxt(expr.span) && scrutinee.precedence().order() < PREC_POSTFIX {
         format!("({scrutinee_str})")
     } else {
         scrutinee_str.into()
@@ -130,7 +130,7 @@ where
         if_chain! {
             if !some_expr.needs_unsafe_block;
             if let Some(func) = can_pass_as_func(cx, id, some_expr.expr);
-            if func.span.ctxt() == some_expr.expr.span.ctxt();
+            if func.span.eq_ctxt(some_expr.expr.span);
             then {
                 snippet_with_applicability(cx, func.span, "..", &mut app).into_owned()
             } else {
diff --git a/src/tools/clippy/clippy_lints/src/methods/map_unwrap_or.rs b/src/tools/clippy/clippy_lints/src/methods/map_unwrap_or.rs
index 5464e455dea..e70a1bc9879 100644
--- a/src/tools/clippy/clippy_lints/src/methods/map_unwrap_or.rs
+++ b/src/tools/clippy/clippy_lints/src/methods/map_unwrap_or.rs
@@ -56,7 +56,7 @@ pub(super) fn check<'tcx>(
         // lint, with note if neither arg is > 1 line and both map() and
         // unwrap_or_else() have the same span
         let multiline = map_snippet.lines().count() > 1 || unwrap_snippet.lines().count() > 1;
-        let same_span = map_arg.span.ctxt() == unwrap_arg.span.ctxt();
+        let same_span = map_arg.span.eq_ctxt(unwrap_arg.span);
         if same_span && !multiline {
             let var_snippet = snippet(cx, recv.span, "..");
             span_lint_and_sugg(
diff --git a/src/tools/clippy/clippy_lints/src/needless_question_mark.rs b/src/tools/clippy/clippy_lints/src/needless_question_mark.rs
index 7b0f7eaf1f0..0e834fb3ac7 100644
--- a/src/tools/clippy/clippy_lints/src/needless_question_mark.rs
+++ b/src/tools/clippy/clippy_lints/src/needless_question_mark.rs
@@ -125,7 +125,7 @@ fn check(cx: &LateContext<'_>, expr: &Expr<'_>) {
         if let ExprKind::Match(inner_expr_with_q, _, MatchSource::TryDesugar(_)) = &arg.kind;
         if let ExprKind::Call(called, [inner_expr]) = &inner_expr_with_q.kind;
         if let ExprKind::Path(QPath::LangItem(LangItem::TryTraitBranch, ..)) = &called.kind;
-        if expr.span.ctxt() == inner_expr.span.ctxt();
+        if expr.span.eq_ctxt(inner_expr.span);
         let expr_ty = cx.typeck_results().expr_ty(expr);
         let inner_ty = cx.typeck_results().expr_ty(inner_expr);
         if expr_ty == inner_ty;
diff --git a/src/tools/clippy/clippy_lints/src/non_octal_unix_permissions.rs b/src/tools/clippy/clippy_lints/src/non_octal_unix_permissions.rs
index d47728f190a..e94e4589966 100644
--- a/src/tools/clippy/clippy_lints/src/non_octal_unix_permissions.rs
+++ b/src/tools/clippy/clippy_lints/src/non_octal_unix_permissions.rs
@@ -51,7 +51,7 @@ impl<'tcx> LateLintPass<'tcx> for NonOctalUnixPermissions {
                         || (path.ident.name == sym!(set_mode)
                             && cx.tcx.is_diagnostic_item(sym::FsPermissions, adt.did()));
                     if let ExprKind::Lit(_) = param.kind;
-                    if param.span.ctxt() == expr.span.ctxt();
+                    if param.span.eq_ctxt(expr.span);
 
                     then {
                         let Some(snip) = snippet_opt(cx, param.span) else {
@@ -70,7 +70,7 @@ impl<'tcx> LateLintPass<'tcx> for NonOctalUnixPermissions {
                     if let Some(def_id) = cx.qpath_res(path, func.hir_id).opt_def_id();
                     if match_def_path(cx, def_id, &paths::PERMISSIONS_FROM_MODE);
                     if let ExprKind::Lit(_) = param.kind;
-                    if param.span.ctxt() == expr.span.ctxt();
+                    if param.span.eq_ctxt(expr.span);
                     if let Some(snip) = snippet_opt(cx, param.span);
                     if !snip.starts_with("0o");
                     then {
diff --git a/src/tools/clippy/clippy_lints/src/redundant_async_block.rs b/src/tools/clippy/clippy_lints/src/redundant_async_block.rs
index 534b2762ba7..8193057a6eb 100644
--- a/src/tools/clippy/clippy_lints/src/redundant_async_block.rs
+++ b/src/tools/clippy/clippy_lints/src/redundant_async_block.rs
@@ -48,7 +48,7 @@ impl<'tcx> LateLintPass<'tcx> for RedundantAsyncBlock {
             let Some(body_expr) = desugar_async_block(cx, expr) &&
             let Some(expr) = desugar_await(peel_blocks(body_expr)) &&
             // The await prefix must not come from a macro as its content could change in the future.
-            expr.span.ctxt() == body_expr.span.ctxt() &&
+            expr.span.eq_ctxt(body_expr.span) &&
             // An async block does not have immediate side-effects from a `.await` point-of-view.
             (!expr.can_have_side_effects() || desugar_async_block(cx, expr).is_some()) &&
             let Some(shortened_span) = walk_span_to_context(expr.span, span.ctxt())
diff --git a/src/tools/clippy/clippy_lints/src/reference.rs b/src/tools/clippy/clippy_lints/src/reference.rs
index db870ec4c5b..12da29f1108 100644
--- a/src/tools/clippy/clippy_lints/src/reference.rs
+++ b/src/tools/clippy/clippy_lints/src/reference.rs
@@ -50,7 +50,7 @@ impl EarlyLintPass for DerefAddrOf {
         if_chain! {
             if let ExprKind::Unary(UnOp::Deref, ref deref_target) = e.kind;
             if let ExprKind::AddrOf(_, ref mutability, ref addrof_target) = without_parens(deref_target).kind;
-            if deref_target.span.ctxt() == e.span.ctxt();
+            if deref_target.span.eq_ctxt(e.span);
             if !addrof_target.span.from_expansion();
             then {
                 let mut applicability = Applicability::MachineApplicable;
diff --git a/src/tools/clippy/clippy_lints/src/suspicious_xor_used_as_pow.rs b/src/tools/clippy/clippy_lints/src/suspicious_xor_used_as_pow.rs
index 8e156b8829b..39cd289b67a 100644
--- a/src/tools/clippy/clippy_lints/src/suspicious_xor_used_as_pow.rs
+++ b/src/tools/clippy/clippy_lints/src/suspicious_xor_used_as_pow.rs
@@ -33,7 +33,7 @@ impl LateLintPass<'_> for ConfusingXorAndPow {
         if !in_external_macro(cx.sess(), expr.span)
             && let ExprKind::Binary(op, left, right) = &expr.kind
             && op.node == BinOpKind::BitXor
-            && left.span.ctxt() == right.span.ctxt()
+            && left.span.eq_ctxt(right.span)
             && let ExprKind::Lit(lit_left) = &left.kind
             && let ExprKind::Lit(lit_right) = &right.kind
             && matches!(lit_right.node, LitKind::Int(..) | LitKind::Float(..))
diff --git a/src/tools/clippy/clippy_utils/src/macros.rs b/src/tools/clippy/clippy_utils/src/macros.rs
index eaf590f6ad7..46ce4ffdce5 100644
--- a/src/tools/clippy/clippy_utils/src/macros.rs
+++ b/src/tools/clippy/clippy_utils/src/macros.rs
@@ -245,7 +245,7 @@ impl<'a> PanicExpn<'a> {
             return None;
         };
         let result = match name {
-            "panic" if arg.span.ctxt() == expr.span.ctxt() => Self::Empty,
+            "panic" if arg.span.eq_ctxt(expr.span) => Self::Empty,
             "panic" | "panic_str" => Self::Str(arg),
             "panic_display" | "panic_cold_display" => {
                 let ExprKind::AddrOf(_, _, e) = &arg.kind else {
diff --git a/src/tools/clippy/clippy_utils/src/ty.rs b/src/tools/clippy/clippy_utils/src/ty.rs
index 2d305a63eca..673b259523e 100644
--- a/src/tools/clippy/clippy_utils/src/ty.rs
+++ b/src/tools/clippy/clippy_utils/src/ty.rs
@@ -1133,7 +1133,7 @@ pub fn make_projection<'tcx>(
         #[cfg(debug_assertions)]
         assert_generic_args_match(tcx, assoc_item.def_id, args);
 
-        Some(tcx.mk_alias_ty(assoc_item.def_id, args))
+        Some(ty::AliasTy::new(tcx, assoc_item.def_id, args))
     }
     helper(
         tcx,
diff --git a/src/tools/clippy/tests/ui/builtin_type_shadow.stderr b/src/tools/clippy/tests/ui/builtin_type_shadow.stderr
index cb8462182b8..e051c00eb8d 100644
--- a/src/tools/clippy/tests/ui/builtin_type_shadow.stderr
+++ b/src/tools/clippy/tests/ui/builtin_type_shadow.stderr
@@ -13,7 +13,7 @@ error[E0308]: mismatched types
 LL | fn foo<u32>(a: u32) -> u32 {
    |        ---             --- expected `u32` because of return type
    |        |
-   |        this type parameter
+   |        expected this type parameter
 LL |     42
    |     ^^ expected type parameter `u32`, found integer
    |
diff --git a/src/tools/compiletest/Cargo.toml b/src/tools/compiletest/Cargo.toml
index bb1fa6e9237..31c6353e675 100644
--- a/src/tools/compiletest/Cargo.toml
+++ b/src/tools/compiletest/Cargo.toml
@@ -11,6 +11,7 @@ colored = "2"
 diff = "0.1.10"
 unified-diff = "0.2.1"
 getopts = "0.2"
+indexmap = "2.0.0"
 miropt-test-tools = { path = "../miropt-test-tools" }
 build_helper = { path = "../build_helper" }
 tracing = "0.1"
diff --git a/src/tools/compiletest/src/runtest.rs b/src/tools/compiletest/src/runtest.rs
index 7b42d8e9b58..875671c64e0 100644
--- a/src/tools/compiletest/src/runtest.rs
+++ b/src/tools/compiletest/src/runtest.rs
@@ -4258,6 +4258,39 @@ impl<'test> TestCx<'test> {
                 V0_BACK_REF_RE.replace_all(&normalized, V0_BACK_REF_PLACEHOLDER).into_owned();
         }
 
+        // AllocId are numbered globally in a compilation session. This can lead to changes
+        // depending on the exact compilation flags and host architecture. Meanwhile, we want
+        // to keep them numbered, to see if the same id appears multiple times.
+        // So we remap to deterministic numbers that only depend on the subset of allocations
+        // that actually appear in the output.
+        // We use uppercase ALLOC to distinguish from the non-normalized version.
+        {
+            let mut seen_allocs = indexmap::IndexSet::new();
+
+            // The alloc-id appears in pretty-printed allocations.
+            let re = Regex::new(r"╾─*a(lloc)?([0-9]+)(\+0x[0-9]+)?─*╼").unwrap();
+            normalized = re
+                .replace_all(&normalized, |caps: &Captures<'_>| {
+                    // Renumber the captured index.
+                    let index = caps.get(2).unwrap().as_str().to_string();
+                    let (index, _) = seen_allocs.insert_full(index);
+                    let offset = caps.get(3).map_or("", |c| c.as_str());
+                    // Do not bother keeping it pretty, just make it deterministic.
+                    format!("╾ALLOC{index}{offset}╼")
+                })
+                .into_owned();
+
+            // The alloc-id appears in a sentence.
+            let re = Regex::new(r"\balloc([0-9]+)\b").unwrap();
+            normalized = re
+                .replace_all(&normalized, |caps: &Captures<'_>| {
+                    let index = caps.get(1).unwrap().as_str().to_string();
+                    let (index, _) = seen_allocs.insert_full(index);
+                    format!("ALLOC{index}")
+                })
+                .into_owned();
+        }
+
         // Custom normalization rules
         for rule in custom_rules {
             let re = Regex::new(&rule.0).expect("bad regex in custom normalization rule");
diff --git a/src/tools/miri/rust-version b/src/tools/miri/rust-version
index a7c9d720c0c..4664cc39820 100644
--- a/src/tools/miri/rust-version
+++ b/src/tools/miri/rust-version
@@ -1 +1 @@
-c07693c1608258f3577eb15057fc0744fa924ae9
+c104861b7b51d2c28e7023e7e53db16cc6677e29
diff --git a/src/tools/miri/src/intptrcast.rs b/src/tools/miri/src/intptrcast.rs
index 4fd0af35304..0bdea157633 100644
--- a/src/tools/miri/src/intptrcast.rs
+++ b/src/tools/miri/src/intptrcast.rs
@@ -119,24 +119,14 @@ impl<'mir, 'tcx> GlobalStateInner {
         Ok(())
     }
 
-    pub fn ptr_from_addr_transmute(
-        _ecx: &MiriInterpCx<'mir, 'tcx>,
-        addr: u64,
-    ) -> Pointer<Option<Provenance>> {
-        trace!("Transmuting {:#x} to a pointer", addr);
-
-        // We consider transmuted pointers to be "invalid" (`None` provenance).
-        Pointer::new(None, Size::from_bytes(addr))
-    }
-
     pub fn ptr_from_addr_cast(
         ecx: &MiriInterpCx<'mir, 'tcx>,
         addr: u64,
     ) -> InterpResult<'tcx, Pointer<Option<Provenance>>> {
         trace!("Casting {:#x} to a pointer", addr);
 
+        // Potentially emit a warning.
         let global_state = ecx.machine.intptrcast.borrow();
-
         match global_state.provenance_mode {
             ProvenanceMode::Default => {
                 // The first time this happens at a particular location, print a warning.
@@ -158,7 +148,12 @@ impl<'mir, 'tcx> GlobalStateInner {
             ProvenanceMode::Permissive => {}
         }
 
-        // This is how wildcard pointers are born.
+        // We do *not* look up the `AllocId` here! This is a `ptr as usize` cast, and it is
+        // completely legal to do a cast and then `wrapping_offset` to another allocation and only
+        // *then* do a memory access. So the allocation that the pointer happens to point to on a
+        // cast is fairly irrelevant. Instead we generate this as a "wildcard" pointer, such that
+        // *every time the pointer is used*, we do an `AllocId` lookup to find the (exposed)
+        // allocation it might be referencing.
         Ok(Pointer::new(Some(Provenance::Wildcard), Size::from_bytes(addr)))
     }
 
@@ -219,22 +214,24 @@ impl<'mir, 'tcx> GlobalStateInner {
         })
     }
 
-    /// Convert a relative (tcx) pointer to an absolute address.
-    pub fn rel_ptr_to_addr(
+    /// Convert a relative (tcx) pointer to a Miri pointer.
+    pub fn ptr_from_rel_ptr(
         ecx: &MiriInterpCx<'mir, 'tcx>,
         ptr: Pointer<AllocId>,
-    ) -> InterpResult<'tcx, u64> {
+        tag: BorTag,
+    ) -> InterpResult<'tcx, Pointer<Provenance>> {
         let (alloc_id, offset) = ptr.into_parts(); // offset is relative (AllocId provenance)
         let base_addr = GlobalStateInner::alloc_base_addr(ecx, alloc_id)?;
 
         // Add offset with the right kind of pointer-overflowing arithmetic.
         let dl = ecx.data_layout();
-        Ok(dl.overflowing_offset(base_addr, offset.bytes()).0)
+        let absolute_addr = dl.overflowing_offset(base_addr, offset.bytes()).0;
+        Ok(Pointer::new(Provenance::Concrete { alloc_id, tag }, Size::from_bytes(absolute_addr)))
     }
 
     /// When a pointer is used for a memory access, this computes where in which allocation the
     /// access is going.
-    pub fn abs_ptr_to_rel(
+    pub fn ptr_get_alloc(
         ecx: &MiriInterpCx<'mir, 'tcx>,
         ptr: Pointer<Provenance>,
     ) -> Option<(AllocId, Size)> {
@@ -252,12 +249,11 @@ impl<'mir, 'tcx> GlobalStateInner {
         let base_addr = GlobalStateInner::alloc_base_addr(ecx, alloc_id).unwrap();
 
         // Wrapping "addr - base_addr"
-        let dl = ecx.data_layout();
         #[allow(clippy::cast_possible_wrap)] // we want to wrap here
         let neg_base_addr = (base_addr as i64).wrapping_neg();
         Some((
             alloc_id,
-            Size::from_bytes(dl.overflowing_signed_offset(addr.bytes(), neg_base_addr).0),
+            Size::from_bytes(ecx.overflowing_signed_offset(addr.bytes(), neg_base_addr).0),
         ))
     }
 
diff --git a/src/tools/miri/src/machine.rs b/src/tools/miri/src/machine.rs
index 864374bfdf2..0ade43d4a8d 100644
--- a/src/tools/miri/src/machine.rs
+++ b/src/tools/miri/src/machine.rs
@@ -168,11 +168,29 @@ impl fmt::Display for MiriMemoryKind {
 /// Pointer provenance.
 #[derive(Clone, Copy)]
 pub enum Provenance {
+    /// For pointers with concrete provenance. we exactly know which allocation they are attached to
+    /// and what their borrow tag is.
     Concrete {
         alloc_id: AllocId,
         /// Borrow Tracker tag.
         tag: BorTag,
     },
+    /// Pointers with wildcard provenance are created on int-to-ptr casts. According to the
+    /// specification, we should at that point angelically "guess" a provenance that will make all
+    /// future uses of this pointer work, if at all possible. Of course such a semantics cannot be
+    /// actually implemented in Miri. So instead, we approximate this, erroring on the side of
+    /// accepting too much code rather than rejecting correct code: a pointer with wildcard
+    /// provenance "acts like" any previously exposed pointer. Each time it is used, we check
+    /// whether *some* exposed pointer could have done what we want to do, and if the answer is yes
+    /// then we allow the access. This allows too much code in two ways:
+    /// - The same wildcard pointer can "take the role" of multiple different exposed pointers on
+    ///   subsequenct memory accesses.
+    /// - In the aliasing model, we don't just have to know the borrow tag of the pointer used for
+    ///   the access, we also have to update the aliasing state -- and that update can be very
+    ///   different depending on which borrow tag we pick! Stacked Borrows has support for this by
+    ///   switching to a stack that is only approximately known, i.e. we overapproximate the effect
+    ///   of using *any* exposed pointer for this access, and only keep information about the borrow
+    ///   stack that would be true with all possible choices.
     Wildcard,
 }
 
@@ -1125,19 +1143,16 @@ impl<'mir, 'tcx> Machine<'mir, 'tcx> for MiriMachine<'mir, 'tcx> {
                 _ => {}
             }
         }
-        let absolute_addr = intptrcast::GlobalStateInner::rel_ptr_to_addr(ecx, ptr)?;
         let tag = if let Some(borrow_tracker) = &ecx.machine.borrow_tracker {
             borrow_tracker.borrow_mut().base_ptr_tag(ptr.provenance, &ecx.machine)
         } else {
             // Value does not matter, SB is disabled
             BorTag::default()
         };
-        Ok(Pointer::new(
-            Provenance::Concrete { alloc_id: ptr.provenance, tag },
-            Size::from_bytes(absolute_addr),
-        ))
+        intptrcast::GlobalStateInner::ptr_from_rel_ptr(ecx, ptr, tag)
     }
 
+    /// Called on `usize as ptr` casts.
     #[inline(always)]
     fn ptr_from_addr_cast(
         ecx: &MiriInterpCx<'mir, 'tcx>,
@@ -1146,6 +1161,9 @@ impl<'mir, 'tcx> Machine<'mir, 'tcx> for MiriMachine<'mir, 'tcx> {
         intptrcast::GlobalStateInner::ptr_from_addr_cast(ecx, addr)
     }
 
+    /// Called on `ptr as usize` casts.
+    /// (Actually computing the resulting `usize` doesn't need machine help,
+    /// that's just `Scalar::try_to_int`.)
     fn expose_ptr(
         ecx: &mut InterpCx<'mir, 'tcx, Self>,
         ptr: Pointer<Self::Provenance>,
@@ -1163,11 +1181,17 @@ impl<'mir, 'tcx> Machine<'mir, 'tcx> for MiriMachine<'mir, 'tcx> {
 
     /// Convert a pointer with provenance into an allocation-offset pair,
     /// or a `None` with an absolute address if that conversion is not possible.
+    ///
+    /// This is called when a pointer is about to be used for memory access,
+    /// an in-bounds check, or anything else that requires knowing which allocation it points to.
+    /// The resulting `AllocId` will just be used for that one step and the forgotten again
+    /// (i.e., we'll never turn the data returned here back into a `Pointer` that might be
+    /// stored in machine state).
     fn ptr_get_alloc(
         ecx: &MiriInterpCx<'mir, 'tcx>,
         ptr: Pointer<Self::Provenance>,
     ) -> Option<(AllocId, Size, Self::ProvenanceExtra)> {
-        let rel = intptrcast::GlobalStateInner::abs_ptr_to_rel(ecx, ptr);
+        let rel = intptrcast::GlobalStateInner::ptr_get_alloc(ecx, ptr);
 
         rel.map(|(alloc_id, size)| {
             let tag = match ptr.provenance {