Add custom mir support for PtrMetadata

Author: scottmcm

compiler/rustc_mir_build/src/build/custom/parse/instruction.rs

@@ -212,6 +212,7 @@ impl<'tcx, 'body> ParseCtxt<'tcx, 'body> {
                 Ok(Rvalue::BinaryOp(BinOp::Offset, Box::new((ptr, offset))))
             },
             @call(mir_len, args) => Ok(Rvalue::Len(self.parse_place(args[0])?)),
+            @call(mir_ptr_metadata, args) => Ok(Rvalue::UnaryOp(UnOp::PtrMetadata, self.parse_operand(args[0])?)),
             @call(mir_copy_for_deref, args) => Ok(Rvalue::CopyForDeref(self.parse_place(args[0])?)),
             ExprKind::Borrow { borrow_kind, arg } => Ok(
                 Rvalue::Ref(self.tcx.lifetimes.re_erased, *borrow_kind, self.parse_place(*arg)?)

compiler/rustc_span/src/symbol.rs

@@ -1179,6 +1179,7 @@ symbols! {
         mir_make_place,
         mir_move,
         mir_offset,
+        mir_ptr_metadata,
         mir_retag,
         mir_return,
         mir_return_to,

library/core/src/intrinsics/mir.rs

@@ -360,6 +360,10 @@ define!("mir_assume", fn Assume(operand: bool));
 define!("mir_deinit", fn Deinit<T>(place: T));
 define!("mir_checked", fn Checked<T>(binop: T) -> (T, bool));
 define!("mir_len", fn Len<T>(place: T) -> usize);
+define!(
+    "mir_ptr_metadata",
+    fn PtrMetadata<P: ?Sized>(place: *const P) -> <P as ::core::ptr::Pointee>::Metadata
+);
 define!("mir_copy_for_deref", fn CopyForDeref<T>(place: T) -> T);
 define!("mir_retag", fn Retag<T>(place: T));
 define!("mir_move", fn Move<T>(place: T) -> T);

tests/mir-opt/building/custom/operators.g.runtime.after.mir

@@ -0,0 +1,13 @@
+// MIR for `g` after runtime
+
+fn g(_1: *const i32, _2: *const [i32]) -> () {
+    let mut _0: ();
+    let mut _3: ();
+    let mut _4: usize;
+
+    bb0: {
+        _3 = PtrMetadata(_1);
+        _4 = PtrMetadata(_2);
+        return;
+    }
+}

tests/mir-opt/building/custom/operators.rs

@@ -30,3 +30,13 @@ pub fn f(a: i32, b: bool) -> i32 {
         Return()
     })
 }
+
+// EMIT_MIR operators.g.runtime.after.mir
+#[custom_mir(dialect = "runtime")]
+pub fn g(p: *const i32, q: *const [i32]) {
+    mir!({
+        let a = PtrMetadata(p);
+        let b = PtrMetadata(q);
+        Return()
+    })
+}