*&X allows referring to the static X by value as if X were a const

[oli-obk]

Found by @eddyb at #25570 (comment).

fn main() {
    static A: i32 = 0;
    static B: i32 = *&A;
    println!("{:?}", B);
}

aborts the compiler:

Illegal instruction (core dumped)
playpen: application terminated with error code 132

static A: i32 = 0;
static B: i32 = *&A;

fn main() {
    println!("{:?}", B);
}

prints 0 on the terminal without any warnings or errors

It doesn't really cause any weird behavior if it's a global static, it just acts as if the referred to static were a const: PlayPen

[oli-obk]

compiling the following:

static A: i32 = 42;
static B: i32 = *&A;

will (in my modified rustc to show CheckCrateVisitor::{consume, borrow}) yield the following relevant debug messages:

###snip###
DEBUG:rustc::middle::expr_use_visitor: consume_expr(expr=expr(6: 42))
DEBUG:rustc::middle::mem_categorization: cat_expr: id=6 expr=expr(6: 42)
DEBUG:rustc::middle::mem_categorization: cat_rvalue ret {cat_rvalue(ReStatic) id:6 m:McDeclared ty:i32}
DEBUG:rustc::middle::mem_categorization: cat_rvalue_node ret {cat_rvalue(ReStatic) id:6 m:McDeclared ty:i32}
DEBUG:rustc::middle::expr_use_visitor: delegate_consume(consume_id=6, cmt={cat_rvalue(ReStatic) id:6 m:McDeclared ty:i32})
DEBUG:rustc::middle::check_const: CheckCrateVisitor::consume: cur.cat=cat_rvalue(ReStatic), mode=Static
DEBUG:rustc::middle::expr_use_visitor: walk_expr(expr=expr(6: 42))
DEBUG:rustc::middle::check_const: visit_item(item=item(static B::B (id=7)))
###snip###
DEBUG:rustc::middle::expr_use_visitor: consume_expr(expr=expr(9: *&A))
DEBUG:rustc::middle::mem_categorization: cat_expr: id=9 expr=expr(9: *&A)
DEBUG:rustc::middle::mem_categorization: cat_expr: id=10 expr=expr(10: &A)
DEBUG:rustc::middle::region: temporary_scope(10) = None
DEBUG:rustc::middle::mem_categorization: cat_rvalue ret {cat_rvalue(ReStatic) id:10 m:McDeclared ty:&i32}
DEBUG:rustc::middle::mem_categorization: cat_rvalue_node ret {cat_rvalue(ReStatic) id:10 m:McDeclared ty:&i32}
DEBUG:rustc::middle::mem_categorization: cat_deref: method_call=MethodCall { expr_id: 9, autoderef: 0 } method_ty=None
DEBUG:rustc::middle::mem_categorization: MutabilityCategory::from_borrow_kind(ImmBorrow) => McImmutable
DEBUG:rustc::middle::mem_categorization: MutabilityCategory::from_pointer_kind(McDeclared, BorrowedPtr(ImmBorrow, ReScope(Misc(9)))) => McImmutable
DEBUG:rustc::middle::mem_categorization: cat_deref_common ret {cat_rvalue(ReStatic)-&ReScope(Misc(9))0-> id:9 m:McImmutable ty:i32}
DEBUG:rustc::middle::mem_categorization: cat_deref ret {cat_rvalue(ReStatic)-&ReScope(Misc(9))0-> id:9 m:McImmutable ty:i32}
DEBUG:rustc::middle::expr_use_visitor: delegate_consume(consume_id=9, cmt={cat_rvalue(ReStatic)-&ReScope(Misc(9))0-> id:9 m:McImmutable ty:i32})
DEBUG:rustc::middle::check_const: CheckCrateVisitor::consume: cur.cat=cat_deref(cmt_ { id: 10, span: Span { lo: BytePos(515), hi: BytePos(517), expn_id: ExpnId(4294967295) }, cat: cat_rvalue(ReStatic), mutbl: McDeclared, ty: TyS { sty: ty_rptr(ReScope(Misc(9)), mt { ty: TyS { sty: ty_int(i32), flags: Cell { value: 262144 }, region_depth: 0 }, mutbl: MutImmutable }), flags: Cell { value: 32 }, region_depth: 0 }, note: NoteNone }, 0, BorrowedPtr(ImmBorrow, ReScope(Misc(9)))), mode=Static
DEBUG:rustc::middle::check_const: CheckCrateVisitor::consume: cur.cat=cat_rvalue(ReStatic), mode=Static
DEBUG:rustc::middle::expr_use_visitor: walk_expr(expr=expr(9: *&A))
DEBUG:rustc::middle::expr_use_visitor: walk_expr(expr=expr(10: &A))
DEBUG:rustc::middle::expr_use_visitor: borrow_expr(expr=expr(11: A), r=ReScope(Misc(9)), bk=ImmBorrow)
DEBUG:rustc::middle::mem_categorization: cat_expr: id=11 expr=expr(11: A)
DEBUG:rustc::middle::mem_categorization: cat_def: id=11 expr=i32 def=DefStatic(DefId { krate: 0, node: 4 }, false)
DEBUG:rustc::middle::check_const: CheckCrateVisitor::borrow: cur.cat=cat_static_item, is_interior=false, mode=Static
DEBUG:rustc::middle::expr_use_visitor: walk_expr(expr=expr(11: A))
DEBUG:rustc::middle::check_const: visit_item(item=item(fn main::main (id=12)))
###snip###

[oli-obk]

produces cannot refer to other statics by value, use the address-of operator or a constant instead on all of the above examples on stable rust