1 use cranelift_codegen::ir;
2 use cranelift_codegen::ir::InstBuilder;
3 
4 /// Returns the Cranelift type used to represent all of the following:
5 /// - wasm values of type `(ref null $ct)` and `(ref $ct)`
6 /// - equivalently: runtime values of type `Option<VMContObj>` and `VMContObj`
7 /// Note that a `VMContObj` is a fat pointer consisting of a pointer to
8 /// `VMContRef` and a pointer-sized revision counter. We represent this as 2 words
9 /// (pointer and usize).
10 pub fn fatpointer_type(env: &crate::func_environ::FuncEnvironment) -> ir::Type {
11     let ptr_bits = env.pointer_type().bits();
12     ir::Type::int((2 * ptr_bits).try_into().unwrap()).unwrap()
13 }
14 
15 /// Turns a (possibly null) reference to a continuation object into a tuple
16 /// (revision, contref_ptr). If `contobj` denotes a wasm null reference, the
17 /// contref_ptr part will be a null pointer.
18 pub(crate) fn deconstruct<'a>(
19     env: &mut crate::func_environ::FuncEnvironment<'a>,
20     pos: &mut cranelift_codegen::cursor::FuncCursor,
21     contobj: ir::Value,
22 ) -> (ir::Value, ir::Value) {
23     debug_assert_eq!(pos.func.dfg.value_type(contobj), fatpointer_type(env));
24     let ptr_ty = env.pointer_type();
25     let ptr_bits = ptr_ty.bits();
26 
27     let contref = pos.ins().ireduce(ptr_ty, contobj);
28     let shifted = pos.ins().ushr_imm(contobj, i64::from(ptr_bits));
29     let revision_counter = pos.ins().ireduce(ptr_ty, shifted);
30 
31     (revision_counter, contref)
32 }
33 
34 /// Constructs a continuation object from a given contref and revision pointer.
35 /// The contref_addr may be 0, to indicate that we want to build a wasm null reference.
36 pub(crate) fn construct<'a>(
37     env: &mut crate::func_environ::FuncEnvironment<'a>,
38     pos: &mut cranelift_codegen::cursor::FuncCursor,
39     revision_counter: ir::Value,
40     contref_addr: ir::Value,
41 ) -> ir::Value {
42     let ptr_ty = env.pointer_type();
43     let ptr_bits = ptr_ty.bits();
44     let fat_ptr_ty = fatpointer_type(env);
45 
46     debug_assert_eq!(pos.func.dfg.value_type(contref_addr), ptr_ty);
47     debug_assert_eq!(pos.func.dfg.value_type(revision_counter), ptr_ty);
48 
49     let contref_addr = pos.ins().uextend(fat_ptr_ty, contref_addr);
50     let revision_counter = pos.ins().uextend(fat_ptr_ty, revision_counter);
51     let shifted_counter = pos.ins().ishl_imm(revision_counter, i64::from(ptr_bits));
52     let contobj = pos.ins().bor(shifted_counter, contref_addr);
53 
54     contobj
55 }
56