Add Offset binary op to custom mir

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

@@ -148,6 +148,11 @@ impl<'tcx, 'body> ParseCtxt<'tcx, 'body> {
                     )),
                 )
             },
+            @call("mir_offset", args) => {
+                let ptr = self.parse_operand(args[0])?;
+                let offset = self.parse_operand(args[1])?;
+                Ok(Rvalue::BinaryOp(BinOp::Offset, Box::new((ptr, offset))))
+            },
             @call("mir_len", args) => Ok(Rvalue::Len(self.parse_place(args[0])?)),
             ExprKind::Borrow { borrow_kind, arg } => Ok(
                 Rvalue::Ref(self.tcx.lifetimes.re_erased, *borrow_kind, self.parse_place(*arg)?)

library/core/src/intrinsics/mir.rs

@@ -232,6 +232,7 @@
 //!  - `&`, `&mut`, `addr_of!`, and `addr_of_mut!` all work to create their associated rvalue.
 //!  - [`Discriminant`] and [`Len`] 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`].
 //!  - Checked binary operations are represented by wrapping the associated binop in [`Checked`].
 //!  - Array repetition syntax (`[foo; 10]`) creates the associated rvalue.
 //!
@@ -289,6 +290,7 @@ define!(
     fn Discriminant<T>(place: T) -> <T as ::core::marker::DiscriminantKind>::Discriminant
 );
 define!("mir_set_discriminant", fn SetDiscriminant<T>(place: T, index: u32));
+define!("mir_offset", fn Offset<T, U>(ptr: T, count: U) -> T);
 define!(
     "mir_field",
     /// Access the field with the given index of some place.

tests/mir-opt/building/custom/references.raw_pointer_offset.built.after.mir

@@ -0,0 +1,10 @@
+// MIR for `raw_pointer_offset` after built
+
+fn raw_pointer_offset(_1: *const i32) -> *const i32 {
+    let mut _0: *const i32;              // return place in scope 0 at $DIR/references.rs:+0:45: +0:55
+
+    bb0: {
+        _0 = Offset(_1, const 1_isize);  // scope 0 at $DIR/references.rs:+2:9: +2:33
+        return;                          // scope 0 at $DIR/references.rs:+3:9: +3:17
+    }
+}

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

@@ -45,11 +45,22 @@ pub fn raw_pointer(x: *const i32) -> *const i32 {
     })
 }
 
+// EMIT_MIR references.raw_pointer_offset.built.after.mir
+#[custom_mir(dialect = "built")]
+pub fn raw_pointer_offset(x: *const i32) -> *const i32 {
+    mir!({
+        RET = Offset(x, 1_isize);
+        Return()
+    })
+}
+
 fn main() {
     let mut x = 5;
+    let arr = [1, 2];
     assert_eq!(*mut_ref(&mut x), 5);
     assert_eq!(*immut_ref(&x), 5);
     unsafe {
         assert_eq!(*raw_pointer(addr_of!(x)), 5);
+        assert_eq!(*raw_pointer_offset(addr_of!(arr[0])), 2);
     }
 }