compiler/rustc_codegen_ssa/src/meth.rs

   1 use crate::traits::*;
   2
   3 use rustc_middle::ty::{self, Instance, Ty};
   4 use rustc_target::abi::call::FnAbi;
   5
   6 #[derive(Copy, Clone, Debug)]
   7 pub struct VirtualIndex(u64);
   8
   9 pub const DESTRUCTOR: VirtualIndex = VirtualIndex(0);
  10 pub const SIZE: VirtualIndex = VirtualIndex(1);
  11 pub const ALIGN: VirtualIndex = VirtualIndex(2);
  12
  13 impl<'a, 'tcx> VirtualIndex {
  14     pub fn from_index(index: usize) -> Self {
  15         VirtualIndex(index as u64 + 3)
  16     }
  17
  18     pub fn get_fn<Bx: BuilderMethods<'a, 'tcx>>(
  19         self,
  20         bx: &mut Bx,
  21         llvtable: Bx::Value,
  22         fn_abi: &FnAbi<'tcx, Ty<'tcx>>,
  23     ) -> Bx::Value {
  24         // Load the data pointer from the object.
  25         debug!("get_fn({:?}, {:?})", llvtable, self);
  26
  27         let llvtable = bx.pointercast(llvtable, bx.type_ptr_to(bx.fn_ptr_backend_type(fn_abi)));
  28         let ptr_align = bx.tcx().data_layout.pointer_align.abi;
  29         let gep = bx.inbounds_gep(llvtable, &[bx.const_usize(self.0)]);
  30         let ptr = bx.load(gep, ptr_align);
  31         bx.nonnull_metadata(ptr);
  32         // Vtable loads are invariant.
  33         bx.set_invariant_load(ptr);
  34         ptr
  35     }
  36
  37     pub fn get_usize<Bx: BuilderMethods<'a, 'tcx>>(
  38         self,
  39         bx: &mut Bx,
  40         llvtable: Bx::Value,
  41     ) -> Bx::Value {
  42         // Load the data pointer from the object.
  43         debug!("get_int({:?}, {:?})", llvtable, self);
  44
  45         let llvtable = bx.pointercast(llvtable, bx.type_ptr_to(bx.type_isize()));
  46         let usize_align = bx.tcx().data_layout.pointer_align.abi;
  47         let gep = bx.inbounds_gep(llvtable, &[bx.const_usize(self.0)]);
  48         let ptr = bx.load(gep, usize_align);
  49         // Vtable loads are invariant.
  50         bx.set_invariant_load(ptr);
  51         ptr
  52     }
  53 }
  54
  55 /// Creates a dynamic vtable for the given type and vtable origin.
  56 /// This is used only for objects.
  57 ///
  58 /// The vtables are cached instead of created on every call.
  59 ///
  60 /// The `trait_ref` encodes the erased self type. Hence if we are
  61 /// making an object `Foo<dyn Trait>` from a value of type `Foo<T>`, then
  62 /// `trait_ref` would map `T: Trait`.
  63 pub fn get_vtable<'tcx, Cx: CodegenMethods<'tcx>>(
  64     cx: &Cx,
  65     ty: Ty<'tcx>,
  66     trait_ref: Option<ty::PolyExistentialTraitRef<'tcx>>,
  67 ) -> Cx::Value {
  68     let tcx = cx.tcx();
  69
  70     debug!("get_vtable(ty={:?}, trait_ref={:?})", ty, trait_ref);
  71
  72     // Check the cache.
  73     if let Some(&val) = cx.vtables().borrow().get(&(ty, trait_ref)) {
  74         return val;
  75     }
  76
  77     // Not in the cache; build it.
  78     let nullptr = cx.const_null(cx.type_i8p_ext(cx.data_layout().instruction_address_space));
  79
  80     let methods_root;
  81     let methods = if let Some(trait_ref) = trait_ref {
  82         methods_root = tcx.vtable_methods(trait_ref.with_self_ty(tcx, ty));
  83         methods_root.iter()
  84     } else {
  85         (&[]).iter()
  86     };
  87
  88     let methods = methods.cloned().map(|opt_mth| {
  89         opt_mth.map_or(nullptr, |(def_id, substs)| {
  90             cx.get_fn_addr(
  91                 ty::Instance::resolve_for_vtable(
  92                     cx.tcx(),
  93                     ty::ParamEnv::reveal_all(),
  94                     def_id,
  95                     substs,
  96                 )
  97                 .unwrap()
  98                 .polymorphize(cx.tcx()),
  99             )
 100         })
 101     });
 102
 103     let layout = cx.layout_of(ty);
 104     // /////////////////////////////////////////////////////////////////////////////////////////////
 105     // If you touch this code, be sure to also make the corresponding changes to
 106     // `get_vtable` in `rust_mir/interpret/traits.rs`.
 107     // /////////////////////////////////////////////////////////////////////////////////////////////
 108     let components: Vec<_> = [
 109         cx.get_fn_addr(Instance::resolve_drop_in_place(cx.tcx(), ty)),
 110         cx.const_usize(layout.size.bytes()),
 111         cx.const_usize(layout.align.abi.bytes()),
 112     ]
 113     .iter()
 114     .cloned()
 115     .chain(methods)
 116     .collect();
 117
 118     let vtable_const = cx.const_struct(&components, false);
 119     let align = cx.data_layout().pointer_align.abi;
 120     let vtable = cx.static_addr_of(vtable_const, align, Some("vtable"));
 121
 122     cx.create_vtable_metadata(ty, vtable);
 123
 124     cx.vtables().borrow_mut().insert((ty, trait_ref), vtable);
 125     vtable
 126 }