1 files changed, 116 insertions, 0 deletions
diff --git a/compiler/rustc_codegen_ssa/src/meth.rs b/compiler/rustc_codegen_ssa/src/meth.rs
new file mode 100644
index 000000000..27d791d90
--- /dev/null
+++ b/compiler/rustc_codegen_ssa/src/meth.rs
@@ -0,0 +1,116 @@
+use crate::traits::*;
+
+use rustc_middle::ty::{self, subst::GenericArgKind, ExistentialPredicate, Ty, TyCtxt};
+use rustc_session::config::Lto;
+use rustc_symbol_mangling::typeid_for_trait_ref;
+use rustc_target::abi::call::FnAbi;
+
+#[derive(Copy, Clone, Debug)]
+pub struct VirtualIndex(u64);
+
+impl<'a, 'tcx> VirtualIndex {
+    pub fn from_index(index: usize) -> Self {
+        VirtualIndex(index as u64)
+    }
+
+    pub fn get_fn<Bx: BuilderMethods<'a, 'tcx>>(
+        self,
+        bx: &mut Bx,
+        llvtable: Bx::Value,
+        ty: Ty<'tcx>,
+        fn_abi: &FnAbi<'tcx, Ty<'tcx>>,
+    ) -> Bx::Value {
+        // Load the data pointer from the object.
+        debug!("get_fn({llvtable:?}, {ty:?}, {self:?})");
+        let llty = bx.fn_ptr_backend_type(fn_abi);
+        let llvtable = bx.pointercast(llvtable, bx.type_ptr_to(llty));
+
+        if bx.cx().sess().opts.unstable_opts.virtual_function_elimination
+            && bx.cx().sess().lto() == Lto::Fat
+        {
+            let typeid =
+                bx.typeid_metadata(typeid_for_trait_ref(bx.tcx(), get_trait_ref(bx.tcx(), ty)));
+            let vtable_byte_offset = self.0 * bx.data_layout().pointer_size.bytes();
+            let type_checked_load = bx.type_checked_load(llvtable, vtable_byte_offset, typeid);
+            let func = bx.extract_value(type_checked_load, 0);
+            bx.pointercast(func, llty)
+        } else {
+            let ptr_align = bx.tcx().data_layout.pointer_align.abi;
+            let gep = bx.inbounds_gep(llty, llvtable, &[bx.const_usize(self.0)]);
+            let ptr = bx.load(llty, gep, ptr_align);
+            bx.nonnull_metadata(ptr);
+            // VTable loads are invariant.
+            bx.set_invariant_load(ptr);
+            ptr
+        }
+    }
+
+    pub fn get_usize<Bx: BuilderMethods<'a, 'tcx>>(
+        self,
+        bx: &mut Bx,
+        llvtable: Bx::Value,
+    ) -> Bx::Value {
+        // Load the data pointer from the object.
+        debug!("get_int({:?}, {:?})", llvtable, self);
+
+        let llty = bx.type_isize();
+        let llvtable = bx.pointercast(llvtable, bx.type_ptr_to(llty));
+        let usize_align = bx.tcx().data_layout.pointer_align.abi;
+        let gep = bx.inbounds_gep(llty, llvtable, &[bx.const_usize(self.0)]);
+        let ptr = bx.load(llty, gep, usize_align);
+        // VTable loads are invariant.
+        bx.set_invariant_load(ptr);
+        ptr
+    }
+}
+
+fn get_trait_ref<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> ty::PolyExistentialTraitRef<'tcx> {
+    for arg in ty.peel_refs().walk() {
+        if let GenericArgKind::Type(ty) = arg.unpack() {
+            if let ty::Dynamic(trait_refs, _) = ty.kind() {
+                return trait_refs[0].map_bound(|trait_ref| match trait_ref {
+                    ExistentialPredicate::Trait(tr) => tr,
+                    ExistentialPredicate::Projection(proj) => proj.trait_ref(tcx),
+                    ExistentialPredicate::AutoTrait(_) => {
+                        bug!("auto traits don't have functions")
+                    }
+                });
+            }
+        }
+    }
+
+    bug!("expected a `dyn Trait` ty, found {ty:?}")
+}
+
+/// Creates a dynamic vtable for the given type and vtable origin.
+/// This is used only for objects.
+///
+/// The vtables are cached instead of created on every call.
+///
+/// The `trait_ref` encodes the erased self type. Hence if we are
+/// making an object `Foo<dyn Trait>` from a value of type `Foo<T>`, then
+/// `trait_ref` would map `T: Trait`.
+pub fn get_vtable<'tcx, Cx: CodegenMethods<'tcx>>(
+    cx: &Cx,
+    ty: Ty<'tcx>,
+    trait_ref: Option<ty::PolyExistentialTraitRef<'tcx>>,
+) -> Cx::Value {
+    let tcx = cx.tcx();
+
+    debug!("get_vtable(ty={:?}, trait_ref={:?})", ty, trait_ref);
+
+    // Check the cache.
+    if let Some(&val) = cx.vtables().borrow().get(&(ty, trait_ref)) {
+        return val;
+    }
+
+    let vtable_alloc_id = tcx.vtable_allocation((ty, trait_ref));
+    let vtable_allocation = tcx.global_alloc(vtable_alloc_id).unwrap_memory();
+    let vtable_const = cx.const_data_from_alloc(vtable_allocation);
+    let align = cx.data_layout().pointer_align.abi;
+    let vtable = cx.static_addr_of(vtable_const, align, Some("vtable"));
+
+    cx.create_vtable_debuginfo(ty, trait_ref, vtable);
+    cx.vtables().borrow_mut().insert((ty, trait_ref), vtable);
+    vtable
+}