remove copyforderef from custom_mir

it did not create DerefTemp locals when used, so it was never actually correct.

Author: beepster4096

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

@@ -253,7 +253,6 @@ impl<'a, 'tcx> ParseCtxt<'a, 'tcx> {
                 Ok(Rvalue::BinaryOp(BinOp::Offset, Box::new((ptr, offset))))
             },
             @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

@@ -1423,7 +1423,6 @@ symbols! {
         mir_cast_transmute,
         mir_cast_unsize,
         mir_checked,
-        mir_copy_for_deref,
         mir_debuginfo,
         mir_deinit,
         mir_discriminant,

library/core/src/intrinsics/mir.rs

@@ -233,7 +233,7 @@
 //!
 //!  - Operands implicitly convert to `Use` rvalues.
 //!  - `&`, `&mut`, `addr_of!`, and `addr_of_mut!` all work to create their associated rvalue.
-//!  - [`CopyForDeref`], [`CastTransmute`], [`CastPtrToPtr`], [`CastUnsize`], and [`Discriminant`]
+//!  - [`CastTransmute`], [`CastPtrToPtr`], [`CastUnsize`], and [`Discriminant`]
 //!    have associated functions.
 //!  - Unary and binary operations use their normal Rust syntax - `a * b`, `!c`, etc.
 //!  - The binary operation `Offset` can be created via [`Offset`].
@@ -406,7 +406,6 @@ 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);
 define!("mir_static", fn Static<T>(s: T) -> &'static T);

tests/mir-opt/building/custom/projections.copy_for_deref.built.after.mir

@@ -79,19 +79,6 @@ fn simple_index(a: [i32; 10], b: &[i32]) -> i32 {
     }
 }
 
-// EMIT_MIR projections.copy_for_deref.built.after.mir
-#[custom_mir(dialect = "runtime", phase = "initial")]
-fn copy_for_deref(x: (&i32, i32)) -> i32 {
-    mir! {
-        let temp: &i32;
-        {
-            temp = CopyForDeref(x.0);
-            RET = *temp;
-            Return()
-        }
-    }
-}
-
 fn main() {
     assert_eq!(unions(U { a: 5 }), 5);
     assert_eq!(tuples((5, 6)), (5, 6));
@@ -103,7 +90,4 @@ fn main() {
     assert_eq!(o, Some(10));
 
     assert_eq!(simple_index([0; 10], &[0; 10]), 0);
-
-    let one = 1;
-    assert_eq!(copy_for_deref((&one, one)), 1);
 }