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Auto merge of #54183 - qnighy:by-value-object-safety, r=oli-obk

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Implement by-value object safety

This PR implements **by-value object safety**, which is part of unsized rvalues #48055. That means, with `#![feature(unsized_locals)]`, you can call a method `fn foo(self, ...)` on trait objects. One aim of this is to enable `Box<FnOnce>`  in the near future.

The difficulty here is this: when constructing a vtable for a trait `Foo`, we can't just put the function `<T as Foo>::foo` into the table. If `T` is no larger than `usize`, `self` is usually passed directly. However, as the caller of the vtable doesn't know the concrete `Self` type, we want a variant of `<T as Foo>::foo` where `self` is always passed by reference.

Therefore, when the compiler encounters such a method to be generated as a vtable entry, it produces a newly introduced instance called `InstanceDef::VtableShim(def_id)` (that wraps the original instance). the shim just derefs the receiver and calls the original method. We give different symbol names for the shims by appending `::{{vtable-shim}}` to the symbol path (and also adding vtable-shimness as an ingredient to the symbol hash).

r? @eddyb
This commit is contained in:
bors 2018-10-27 19:29:35 +00:00
commit cae6efc37d
46 changed files with 870 additions and 171 deletions
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5
src/librustc_codegen_llvm/base.rs
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@ -56,7 +56,7 @@ use callee;
use common::{C_bool, C_bytes_in_context, C_i32, C_usize};
use rustc_mir::monomorphize::collector::{self, MonoItemCollectionMode};
use rustc_mir::monomorphize::item::DefPathBasedNames;
use common::{self, C_struct_in_context, C_array, val_ty};
use common::{C_struct_in_context, C_array, val_ty};
use consts;
use context::CodegenCx;
use debuginfo;
@ -491,8 +491,7 @@ pub fn codegen_instance<'a, 'tcx>(cx: &CodegenCx<'a, 'tcx>, instance: Instance<'
// release builds.
info!("codegen_instance({})", instance);
let fn_ty = instance.ty(cx.tcx);
let sig = common::ty_fn_sig(cx, fn_ty);
let sig = instance.fn_sig(cx.tcx);
let sig = cx.tcx.normalize_erasing_late_bound_regions(ty::ParamEnv::reveal_all(), &sig);
let lldecl = cx.instances.borrow().get(&instance).cloned().unwrap_or_else(||