Auto merge of #23376 - eddyb:die-tydesc-die, r=nikomatsakis

Final remnant of reflection is gone. Also, virtual `Trait` destructors are no longer tied to `Box`.
That means they can be used to drop any instance of the type (used in libarena to replace TyDesc).

This is [breaking-change] for direct users of intrinsics:
* use `intrinsics::type_name::<T>()` instead of `(*intrinsics::get_tydesc::<T>()).name`
* the only way to get the destructor is from a trait object's vtable (see libarena changes)

r? @pcwalton f? @dotdash

Author: bors

src/libarena/lib.rs

@@ -42,8 +42,9 @@ extern crate alloc;
 
 use std::cell::{Cell, RefCell};
 use std::cmp;
-use std::intrinsics::{TyDesc, get_tydesc};
 use std::intrinsics;
+#[cfg(stage0)] // SNAP 270a677
+use std::intrinsics::{get_tydesc, TyDesc};
 use std::marker;
 use std::mem;
 #[cfg(stage0)]
@@ -186,6 +187,27 @@ fn un_bitpack_tydesc_ptr(p: usize) -> (*const TyDesc, bool) {
     ((p & !1) as *const TyDesc, p & 1 == 1)
 }
 
+// HACK(eddyb) TyDesc replacement using a trait object vtable.
+// This could be replaced in the future with a custom DST layout,
+// or `&'static (drop_glue, size, align)` created by a `const fn`.
+#[cfg(not(stage0))] // SNAP 270a677
+struct TyDesc {
+    drop_glue: fn(*const i8),
+    size: usize,
+    align: usize
+}
+
+#[cfg(not(stage0))] // SNAP 270a677
+unsafe fn get_tydesc<T>() -> *const TyDesc {
+    use std::raw::TraitObject;
+
+    let ptr = &*(1 as *const T);
+
+    // Can use any trait that is implemented for all types.
+    let obj = mem::transmute::<&marker::MarkerTrait, TraitObject>(ptr);
+    obj.vtable as *const TyDesc
+}
+
 impl<'longer_than_self> Arena<'longer_than_self> {
     fn chunk_size(&self) -> usize {
         self.copy_head.borrow().capacity()

src/libcore/intrinsics.rs

@@ -44,10 +44,12 @@
 
 use marker::Sized;
 
+#[cfg(stage0)] // SNAP 270a677
 pub type GlueFn = extern "Rust" fn(*const i8);
 
 #[lang="ty_desc"]
 #[derive(Copy)]
+#[cfg(stage0)] // SNAP 270a677
 pub struct TyDesc {
     // sizeof(T)
     pub size: usize,
@@ -197,8 +199,13 @@ extern "rust-intrinsic" {
     pub fn pref_align_of<T>() -> usize;
 
     /// Get a static pointer to a type descriptor.
+    #[cfg(stage0)] // SNAP 270a677
     pub fn get_tydesc<T: ?Sized>() -> *const TyDesc;
 
+    /// Gets a static string slice containing the name of a type.
+    #[cfg(not(stage0))] // SNAP 270a677
+    pub fn type_name<T: ?Sized>() -> &'static str;
+
     /// Gets an identifier which is globally unique to the specified type. This
     /// function will return the same value for a type regardless of whichever
     /// crate it is invoked in.

src/librustc/middle/lang_items.rs

@@ -316,9 +316,6 @@ lets_do_this! {
 
     StartFnLangItem,                 "start",                   start_fn;
 
-    TyDescStructLangItem,            "ty_desc",                 ty_desc;
-    OpaqueStructLangItem,            "opaque",                  opaque;
-
     EhPersonalityLangItem,           "eh_personality",          eh_personality;
 
     ExchangeHeapLangItem,            "exchange_heap",           exchange_heap;

src/librustc/middle/ty.rs

@@ -47,8 +47,7 @@ use middle::check_const;
 use middle::const_eval;
 use middle::def::{self, DefMap, ExportMap};
 use middle::dependency_format;
-use middle::lang_items::{FnTraitLangItem, FnMutTraitLangItem};
-use middle::lang_items::{FnOnceTraitLangItem, TyDescStructLangItem};
+use middle::lang_items::{FnTraitLangItem, FnMutTraitLangItem, FnOnceTraitLangItem};
 use middle::mem_categorization as mc;
 use middle::region;
 use middle::resolve_lifetime;
@@ -723,7 +722,6 @@ pub struct ctxt<'tcx> {
     pub object_cast_map: ObjectCastMap<'tcx>,
 
     pub map: ast_map::Map<'tcx>,
-    pub intrinsic_defs: RefCell<DefIdMap<Ty<'tcx>>>,
     pub freevars: RefCell<FreevarMap>,
     pub tcache: RefCell<DefIdMap<TypeScheme<'tcx>>>,
     pub rcache: RefCell<FnvHashMap<creader_cache_key, Ty<'tcx>>>,
@@ -2575,7 +2573,6 @@ pub fn mk_ctxt<'tcx>(s: Session,
         super_predicates: RefCell::new(DefIdMap()),
         object_cast_map: RefCell::new(NodeMap()),
         map: map,
-        intrinsic_defs: RefCell::new(DefIdMap()),
         freevars: freevars,
         tcache: RefCell::new(DefIdMap()),
         rcache: RefCell::new(FnvHashMap()),
@@ -5951,13 +5948,6 @@ pub fn required_region_bounds<'tcx>(tcx: &ctxt<'tcx>,
         .collect()
 }
 
-pub fn get_tydesc_ty<'tcx>(tcx: &ctxt<'tcx>) -> Result<Ty<'tcx>, String> {
-    tcx.lang_items.require(TyDescStructLangItem).map(|tydesc_lang_item| {
-        tcx.intrinsic_defs.borrow().get(&tydesc_lang_item).cloned()
-            .expect("Failed to resolve TyDesc")
-    })
-}
-
 pub fn item_variances(tcx: &ctxt, item_id: ast::DefId) -> Rc<ItemVariances> {
     lookup_locally_or_in_crate_store(
         "item_variance_map", item_id, &mut *tcx.item_variance_map.borrow_mut(),

src/librustc_trans/trans/_match.rs

@@ -660,7 +660,7 @@ fn bind_subslice_pat(bcx: Block,
                      offset_right: uint) -> ValueRef {
     let _icx = push_ctxt("match::bind_subslice_pat");
     let vec_ty = node_id_type(bcx, pat_id);
-    let vt = tvec::vec_types(bcx, ty::sequence_element_type(bcx.tcx(), ty::type_content(vec_ty)));
+    let unit_ty = ty::sequence_element_type(bcx.tcx(), ty::type_content(vec_ty));
     let vec_datum = match_datum(val, vec_ty);
     let (base, len) = vec_datum.get_vec_base_and_len(bcx);
 
@@ -669,7 +669,7 @@ fn bind_subslice_pat(bcx: Block,
     let slice_len = Sub(bcx, len, slice_len_offset, DebugLoc::None);
     let slice_ty = ty::mk_slice(bcx.tcx(),
                                 bcx.tcx().mk_region(ty::ReStatic),
-                                ty::mt {ty: vt.unit_ty, mutbl: ast::MutImmutable});
+                                ty::mt {ty: unit_ty, mutbl: ast::MutImmutable});
     let scratch = rvalue_scratch_datum(bcx, slice_ty, "");
     Store(bcx, slice_begin,
           GEPi(bcx, scratch.val, &[0, abi::FAT_PTR_ADDR]));

src/librustc_trans/trans/base.rs

@@ -57,8 +57,7 @@ use trans::common::{C_null, C_struct_in_context, C_u64, C_u8, C_undef};
 use trans::common::{CrateContext, ExternMap, FunctionContext};
 use trans::common::{Result, NodeIdAndSpan};
 use trans::common::{node_id_type, return_type_is_void};
-use trans::common::{tydesc_info, type_is_immediate};
-use trans::common::{type_is_zero_size, val_ty};
+use trans::common::{type_is_immediate, type_is_zero_size, val_ty};
 use trans::common;
 use trans::consts;
 use trans::context::SharedCrateContext;
@@ -90,7 +89,6 @@ use std::ffi::{CStr, CString};
 use std::cell::{Cell, RefCell};
 use std::collections::HashSet;
 use std::mem;
-use std::rc::Rc;
 use std::str;
 use std::{i8, i16, i32, i64};
 use syntax::abi::{Rust, RustCall, RustIntrinsic, Abi};
@@ -392,22 +390,6 @@ pub fn malloc_raw_dyn<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
     Result::new(r.bcx, PointerCast(r.bcx, r.val, llty_ptr))
 }
 
-// Type descriptor and type glue stuff
-
-pub fn get_tydesc<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>,
-                            t: Ty<'tcx>) -> Rc<tydesc_info<'tcx>> {
-    match ccx.tydescs().borrow().get(&t) {
-        Some(inf) => return inf.clone(),
-        _ => { }
-    }
-
-    ccx.stats().n_static_tydescs.set(ccx.stats().n_static_tydescs.get() + 1);
-    let inf = Rc::new(glue::declare_tydesc(ccx, t));
-
-    ccx.tydescs().borrow_mut().insert(t, inf.clone());
-    inf
-}
-
 #[allow(dead_code)] // useful
 pub fn set_optimize_for_size(f: ValueRef) {
     llvm::SetFunctionAttribute(f, llvm::OptimizeForSizeAttribute)
@@ -702,6 +684,10 @@ pub fn iter_structural_ty<'blk, 'tcx, F>(cx: Block<'blk, 'tcx>,
         let unit_ty = ty::sequence_element_type(cx.tcx(), t);
         cx = tvec::iter_vec_raw(cx, base, unit_ty, len, f);
       }
+      ty::ty_vec(_, None) | ty::ty_str => {
+        let unit_ty = ty::sequence_element_type(cx.tcx(), t);
+        cx = tvec::iter_vec_raw(cx, data_ptr, unit_ty, info.unwrap(), f);
+      }
       ty::ty_tup(ref args) => {
           let repr = adt::represent_type(cx.ccx(), t);
           for (i, arg) in args.iter().enumerate() {
@@ -3133,7 +3119,6 @@ pub fn trans_crate<'tcx>(analysis: ty::CrateAnalysis<'tcx>)
     }
 
     for ccx in shared_ccx.iter() {
-        glue::emit_tydescs(&ccx);
         if ccx.sess().opts.debuginfo != NoDebugInfo {
             debuginfo::finalize(&ccx);
         }
@@ -3145,7 +3130,6 @@ pub fn trans_crate<'tcx>(analysis: ty::CrateAnalysis<'tcx>)
     if shared_ccx.sess().trans_stats() {
         let stats = shared_ccx.stats();
         println!("--- trans stats ---");
-        println!("n_static_tydescs: {}", stats.n_static_tydescs.get());
         println!("n_glues_created: {}", stats.n_glues_created.get());
         println!("n_null_glues: {}", stats.n_null_glues.get());
         println!("n_real_glues: {}", stats.n_real_glues.get());

src/librustc_trans/trans/common.rs

@@ -316,15 +316,6 @@ pub fn gensym_name(name: &str) -> PathElem {
     PathName(token::gensym(&format!("{}:{}", name, num)))
 }
 
-#[derive(Copy)]
-pub struct tydesc_info<'tcx> {
-    pub ty: Ty<'tcx>,
-    pub tydesc: ValueRef,
-    pub size: ValueRef,
-    pub align: ValueRef,
-    pub name: ValueRef,
-}
-
 /*
 * A note on nomenclature of linking: "extern", "foreign", and "upcall".
 *

src/librustc_trans/trans/consts.rs

@@ -314,7 +314,6 @@ pub fn const_expr<'a, 'tcx>(cx: &CrateContext<'a, 'tcx>,
                     let info =
                         expr::unsized_info(
                             cx, k, e.id, ty, param_substs,
-                            |t| ty::mk_imm_rptr(cx.tcx(), cx.tcx().mk_region(ty::ReStatic), t),
                             || const_get_elt(cx, llconst, &[abi::FAT_PTR_EXTRA as u32]));
 
                     let unsized_ty = ty::unsize_ty(cx.tcx(), ty, k, e.span);

src/librustc_trans/trans/context.rs

@@ -18,7 +18,7 @@ use middle::traits;
 use trans::adt;
 use trans::base;
 use trans::builder::Builder;
-use trans::common::{ExternMap,tydesc_info,BuilderRef_res};
+use trans::common::{ExternMap,BuilderRef_res};
 use trans::debuginfo;
 use trans::monomorphize::MonoId;
 use trans::type_::{Type, TypeNames};
@@ -38,7 +38,6 @@ use syntax::ast;
 use syntax::parse::token::InternedString;
 
 pub struct Stats {
-    pub n_static_tydescs: Cell<uint>,
     pub n_glues_created: Cell<uint>,
     pub n_null_glues: Cell<uint>,
     pub n_real_glues: Cell<uint>,
@@ -89,10 +88,6 @@ pub struct LocalCrateContext<'tcx> {
     needs_unwind_cleanup_cache: RefCell<FnvHashMap<Ty<'tcx>, bool>>,
     fn_pointer_shims: RefCell<FnvHashMap<Ty<'tcx>, ValueRef>>,
     drop_glues: RefCell<FnvHashMap<Ty<'tcx>, ValueRef>>,
-    tydescs: RefCell<FnvHashMap<Ty<'tcx>, Rc<tydesc_info<'tcx>>>>,
-    /// Set when running emit_tydescs to enforce that no more tydescs are
-    /// created.
-    finished_tydescs: Cell<bool>,
     /// Track mapping of external ids to local items imported for inlining
     external: RefCell<DefIdMap<Option<ast::NodeId>>>,
     /// Backwards version of the `external` map (inlined items to where they
@@ -102,7 +97,7 @@ pub struct LocalCrateContext<'tcx> {
     monomorphized: RefCell<FnvHashMap<MonoId<'tcx>, ValueRef>>,
     monomorphizing: RefCell<DefIdMap<uint>>,
     /// Cache generated vtables
-    vtables: RefCell<FnvHashMap<(Ty<'tcx>, ty::PolyTraitRef<'tcx>), ValueRef>>,
+    vtables: RefCell<FnvHashMap<ty::PolyTraitRef<'tcx>, ValueRef>>,
     /// Cache of constant strings,
     const_cstr_cache: RefCell<FnvHashMap<InternedString, ValueRef>>,
 
@@ -264,7 +259,6 @@ impl<'tcx> SharedCrateContext<'tcx> {
             symbol_hasher: RefCell::new(symbol_hasher),
             tcx: tcx,
             stats: Stats {
-                n_static_tydescs: Cell::new(0),
                 n_glues_created: Cell::new(0),
                 n_null_glues: Cell::new(0),
                 n_real_glues: Cell::new(0),
@@ -399,8 +393,6 @@ impl<'tcx> LocalCrateContext<'tcx> {
                 needs_unwind_cleanup_cache: RefCell::new(FnvHashMap()),
                 fn_pointer_shims: RefCell::new(FnvHashMap()),
                 drop_glues: RefCell::new(FnvHashMap()),
-                tydescs: RefCell::new(FnvHashMap()),
-                finished_tydescs: Cell::new(false),
                 external: RefCell::new(DefIdMap()),
                 external_srcs: RefCell::new(NodeMap()),
                 monomorphized: RefCell::new(FnvHashMap()),
@@ -442,8 +434,6 @@ impl<'tcx> LocalCrateContext<'tcx> {
                 str_slice_ty.set_struct_body(&[Type::i8p(&ccx), ccx.int_type()], false);
                 ccx.tn().associate_type("str_slice", &str_slice_ty);
 
-                ccx.tn().associate_type("tydesc", &Type::tydesc(&ccx, str_slice_ty));
-
                 if ccx.sess().count_llvm_insns() {
                     base::init_insn_ctxt()
                 }
@@ -519,10 +509,6 @@ impl<'b, 'tcx> CrateContext<'b, 'tcx> {
         self.local.builder.b
     }
 
-    pub fn tydesc_type(&self) -> Type {
-        self.local.tn.find_type("tydesc").unwrap()
-    }
-
     pub fn get_intrinsic(&self, key: & &'static str) -> ValueRef {
         if let Some(v) = self.intrinsics().borrow().get(key).cloned() {
             return v;
@@ -590,14 +576,6 @@ impl<'b, 'tcx> CrateContext<'b, 'tcx> {
         &self.local.drop_glues
     }
 
-    pub fn tydescs<'a>(&'a self) -> &'a RefCell<FnvHashMap<Ty<'tcx>, Rc<tydesc_info<'tcx>>>> {
-        &self.local.tydescs
-    }
-
-    pub fn finished_tydescs<'a>(&'a self) -> &'a Cell<bool> {
-        &self.local.finished_tydescs
-    }
-
     pub fn external<'a>(&'a self) -> &'a RefCell<DefIdMap<Option<ast::NodeId>>> {
         &self.local.external
     }
@@ -614,8 +592,7 @@ impl<'b, 'tcx> CrateContext<'b, 'tcx> {
         &self.local.monomorphizing
     }
 
-    pub fn vtables<'a>(&'a self) -> &'a RefCell<FnvHashMap<(Ty<'tcx>, ty::PolyTraitRef<'tcx>),
-                                                            ValueRef>> {
+    pub fn vtables<'a>(&'a self) -> &'a RefCell<FnvHashMap<ty::PolyTraitRef<'tcx>, ValueRef>> {
         &self.local.vtables
     }