Rollup merge of #106012 - JakobDegen:retag-raw, r=RalfJung

Clarify that raw retags are not permitted in Mir

Not sure when this changed, but documentation and the validator needed to be updated. This also removes raw retags from custom mir.

cc rust-lang/miri#2735

r? `@RalfJung`

7 files changed, 16 insertions, 19 deletions

diff --git a/compiler/rustc_const_eval/src/transform/validate.rs b/compiler/rustc_const_eval/src/transform/validate.rs
index bb897b95b2c..94e1b95a0eb 100644
--- a/compiler/rustc_const_eval/src/transform/validate.rs
+++ b/compiler/rustc_const_eval/src/transform/validate.rs
@@ -9,8 +9,8 @@ use rustc_middle::mir::visit::{PlaceContext, Visitor};
 use rustc_middle::mir::{
     traversal, AggregateKind, BasicBlock, BinOp, Body, BorrowKind, CastKind, CopyNonOverlapping,
     Local, Location, MirPass, MirPhase, NonDivergingIntrinsic, Operand, Place, PlaceElem, PlaceRef,
-    ProjectionElem, RuntimePhase, Rvalue, SourceScope, Statement, StatementKind, Terminator,
-    TerminatorKind, UnOp, START_BLOCK,
+    ProjectionElem, RetagKind, RuntimePhase, Rvalue, SourceScope, Statement, StatementKind,
+    Terminator, TerminatorKind, UnOp, START_BLOCK,
 };
 use rustc_middle::ty::{self, InstanceDef, ParamEnv, Ty, TyCtxt, TypeVisitable};
 use rustc_mir_dataflow::impls::MaybeStorageLive;
@@ -667,10 +667,13 @@ impl<'a, 'tcx> Visitor<'tcx> for TypeChecker<'a, 'tcx> {
                     self.fail(location, "`Deinit`is not allowed until deaggregation");
                 }
             }
-            StatementKind::Retag(_, _) => {
+            StatementKind::Retag(kind, _) => {
                 // FIXME(JakobDegen) The validator should check that `self.mir_phase <
                 // DropsLowered`. However, this causes ICEs with generation of drop shims, which
                 // seem to fail to set their `MirPhase` correctly.
+                if *kind == RetagKind::Raw || *kind == RetagKind::TwoPhase {
+                    self.fail(location, format!("explicit `{:?}` is forbidden", kind));
+                }
             }
             StatementKind::StorageLive(..)
             | StatementKind::StorageDead(..)
diff --git a/compiler/rustc_middle/src/mir/syntax.rs b/compiler/rustc_middle/src/mir/syntax.rs
index 99e59c770d7..bb03359b138 100644
--- a/compiler/rustc_middle/src/mir/syntax.rs
+++ b/compiler/rustc_middle/src/mir/syntax.rs
@@ -320,8 +320,10 @@ pub enum StatementKind<'tcx> {
     /// <https://internals.rust-lang.org/t/stacked-borrows-an-aliasing-model-for-rust/8153/> for
     /// more details.
     ///
-    /// For code that is not specific to stacked borrows, you should consider retags to read
-    /// and modify the place in an opaque way.
+    /// For code that is not specific to stacked borrows, you should consider retags to read and
+    /// modify the place in an opaque way.
+    ///
+    /// Only `RetagKind::Default` and `RetagKind::FnEntry` are permitted.
     Retag(RetagKind, Box<Place<'tcx>>),
 
     /// Encodes a user's type ascription. These need to be preserved
diff --git a/compiler/rustc_mir_build/src/build/custom/parse/instruction.rs b/compiler/rustc_mir_build/src/build/custom/parse/instruction.rs
index 7c39a93a8eb..dca4906c07d 100644
--- a/compiler/rustc_mir_build/src/build/custom/parse/instruction.rs
+++ b/compiler/rustc_mir_build/src/build/custom/parse/instruction.rs
@@ -15,9 +15,6 @@ impl<'tcx, 'body> ParseCtxt<'tcx, 'body> {
             @call("mir_retag", args) => {
                 Ok(StatementKind::Retag(RetagKind::Default, Box::new(self.parse_place(args[0])?)))
             },
-            @call("mir_retag_raw", args) => {
-                Ok(StatementKind::Retag(RetagKind::Raw, Box::new(self.parse_place(args[0])?)))
-            },
             @call("mir_set_discriminant", args) => {
                 let place = self.parse_place(args[0])?;
                 let var = self.parse_integer_literal(args[1])? as u32;
diff --git a/library/core/src/intrinsics/mir.rs b/library/core/src/intrinsics/mir.rs
index e08a15571fc..9e7099ddfd1 100644
--- a/library/core/src/intrinsics/mir.rs
+++ b/library/core/src/intrinsics/mir.rs
@@ -259,7 +259,6 @@ define!("mir_drop", fn Drop<T>(place: T, goto: BasicBlock));
 define!("mir_drop_and_replace", fn DropAndReplace<T>(place: T, value: T, goto: BasicBlock));
 define!("mir_call", fn Call<T>(place: T, goto: BasicBlock, call: T));
 define!("mir_retag", fn Retag<T>(place: T));
-define!("mir_retag_raw", fn RetagRaw<T>(place: T));
 define!("mir_move", fn Move<T>(place: T) -> T);
 define!("mir_static", fn Static<T>(s: T) -> &'static T);
 define!("mir_static_mut", fn StaticMut<T>(s: T) -> *mut T);
diff --git a/src/test/mir-opt/building/custom/references.immut_ref.built.after.mir b/src/test/mir-opt/building/custom/references.immut_ref.built.after.mir
index 4d38d45c0f4..f5ee1126235 100644
--- a/src/test/mir-opt/building/custom/references.immut_ref.built.after.mir
+++ b/src/test/mir-opt/building/custom/references.immut_ref.built.after.mir
@@ -6,9 +6,8 @@ fn immut_ref(_1: &i32) -> &i32 {
 
     bb0: {
         _2 = &raw const (*_1);           // scope 0 at $DIR/references.rs:+5:13: +5:29
-        Retag([raw] _2);                 // scope 0 at $DIR/references.rs:+6:13: +6:24
-        _0 = &(*_2);                     // scope 0 at $DIR/references.rs:+7:13: +7:23
-        Retag(_0);                       // scope 0 at $DIR/references.rs:+8:13: +8:23
-        return;                          // scope 0 at $DIR/references.rs:+9:13: +9:21
+        _0 = &(*_2);                     // scope 0 at $DIR/references.rs:+6:13: +6:23
+        Retag(_0);                       // scope 0 at $DIR/references.rs:+7:13: +7:23
+        return;                          // scope 0 at $DIR/references.rs:+8:13: +8:21
     }
 }
diff --git a/src/test/mir-opt/building/custom/references.mut_ref.built.after.mir b/src/test/mir-opt/building/custom/references.mut_ref.built.after.mir
index 01bc8a9cd35..8e2ffc33b1a 100644
--- a/src/test/mir-opt/building/custom/references.mut_ref.built.after.mir
+++ b/src/test/mir-opt/building/custom/references.mut_ref.built.after.mir
@@ -6,9 +6,8 @@ fn mut_ref(_1: &mut i32) -> &mut i32 {
 
     bb0: {
         _2 = &raw mut (*_1);             // scope 0 at $DIR/references.rs:+5:13: +5:33
-        Retag([raw] _2);                 // scope 0 at $DIR/references.rs:+6:13: +6:24
-        _0 = &mut (*_2);                 // scope 0 at $DIR/references.rs:+7:13: +7:26
-        Retag(_0);                       // scope 0 at $DIR/references.rs:+8:13: +8:23
-        return;                          // scope 0 at $DIR/references.rs:+9:13: +9:21
+        _0 = &mut (*_2);                 // scope 0 at $DIR/references.rs:+6:13: +6:26
+        Retag(_0);                       // scope 0 at $DIR/references.rs:+7:13: +7:23
+        return;                          // scope 0 at $DIR/references.rs:+8:13: +8:21
     }
 }
diff --git a/src/test/mir-opt/building/custom/references.rs b/src/test/mir-opt/building/custom/references.rs
index c93f6ec624b..a1c896de04c 100644
--- a/src/test/mir-opt/building/custom/references.rs
+++ b/src/test/mir-opt/building/custom/references.rs
@@ -12,7 +12,6 @@ pub fn mut_ref(x: &mut i32) -> &mut i32 {
 
         {
             t = addr_of_mut!(*x);
-            RetagRaw(t);
             RET = &mut *t;
             Retag(RET);
             Return()
@@ -28,7 +27,6 @@ pub fn immut_ref(x: &i32) -> &i32 {
 
         {
             t = addr_of!(*x);
-            RetagRaw(t);
             RET = & *t;
             Retag(RET);
             Return()