librustc: Only emit visitor glue if it's necessary.

src/librustc/middle/trans/base.rs

@@ -290,7 +290,7 @@ pub fn malloc_raw_dyn(bcx: block,
 
     // Get the tydesc for the body:
     let static_ti = get_tydesc(ccx, t);
-    glue::lazily_emit_all_tydesc_glue(ccx, static_ti);
+    glue::lazily_emit_most_tydesc_glue(ccx, static_ti);
 
     // Allocate space:
     let tydesc = PointerCast(bcx, static_ti.tydesc, T_ptr(T_i8()));
@@ -2329,9 +2329,7 @@ pub fn create_entry_wrapper(ccx: @CrateContext,
             llvm::LLVMPositionBuilderAtEnd(bld, llbb);
 
             let start_def_id = ccx.tcx.lang_items.start_fn();
-            if start_def_id.crate == ast::local_crate {
-                ccx.sess.bug("start lang item is never in the local crate")
-            } else {
+            if start_def_id.crate != ast::local_crate {
                 let start_fn_type = csearch::get_type(ccx.tcx,
                                                       start_def_id).ty;
                 trans_external_path(ccx, start_def_id, start_fn_type);
@@ -2348,8 +2346,7 @@ pub fn create_entry_wrapper(ccx: @CrateContext,
             let (start_fn, args) = if use_start_lang_item {
                 let start_def_id = ccx.tcx.lang_items.start_fn();
                 let start_fn = if start_def_id.crate == ast::local_crate {
-                    ccx.sess.bug("start lang item is never in the local \
-                                  crate")
+                    get_item_val(ccx, start_def_id.node)
                 } else {
                     let start_fn_type = csearch::get_type(ccx.tcx,
                             start_def_id).ty;

src/librustc/middle/trans/foreign.rs

@@ -724,6 +724,16 @@ pub fn trans_intrinsic(ccx: @CrateContext,
                   fcx.llretptr.get());
         }
         ~"get_tydesc" => {
+            let tp_ty = substs.tys[0];
+            let static_ti = get_tydesc(ccx, tp_ty);
+            glue::lazily_emit_most_tydesc_glue(ccx, static_ti);
+
+            // FIXME (#3727): change this to T_ptr(ccx.tydesc_ty) when the
+            // core::sys copy of the get_tydesc interface dies off.
+            let td = PointerCast(bcx, static_ti.tydesc, T_ptr(T_nil()));
+            Store(bcx, td, fcx.llretptr.get());
+        }
+        ~"get_tydesc_for_visiting" => {
             let tp_ty = substs.tys[0];
             let static_ti = get_tydesc(ccx, tp_ty);
             glue::lazily_emit_all_tydesc_glue(ccx, static_ti);

src/librustc/middle/trans/glue.rs

@@ -153,6 +153,15 @@ pub fn free_ty_immediate(bcx: block, v: ValueRef, t: ty::t) -> block {
     }
 }
 
+/// Emits all tydesc glue except for visitor glue.
+pub fn lazily_emit_most_tydesc_glue(ccx: @CrateContext,
+                                    static_ti: @mut tydesc_info) {
+    lazily_emit_tydesc_glue(ccx, abi::tydesc_field_take_glue, static_ti);
+    lazily_emit_tydesc_glue(ccx, abi::tydesc_field_drop_glue, static_ti);
+    lazily_emit_tydesc_glue(ccx, abi::tydesc_field_free_glue, static_ti);
+}
+
+/// Emits all tydesc glue, including visitor glue.
 pub fn lazily_emit_all_tydesc_glue(ccx: @CrateContext,
                                    static_ti: @mut tydesc_info) {
     lazily_emit_tydesc_glue(ccx, abi::tydesc_field_take_glue, static_ti);

src/librustc/middle/trans/meth.rs

@@ -864,7 +864,7 @@ pub fn make_impl_vtable(ccx: @CrateContext,
 
     // Generate a type descriptor for the vtable.
     let tydesc = get_tydesc(ccx, self_ty);
-    glue::lazily_emit_all_tydesc_glue(ccx, tydesc);
+    glue::lazily_emit_most_tydesc_glue(ccx, tydesc);
 
     make_vtable(ccx, tydesc, methods)
 }

src/librustc/middle/trans/type_use.rs

@@ -121,7 +121,8 @@ pub fn type_uses_for(ccx: @CrateContext, fn_id: def_id, n_tps: uint)
                 ~"uninit"   | ~"init" | ~"transmute" | ~"move_val" |
                 ~"move_val_init" => use_repr,
 
-                ~"get_tydesc" | ~"needs_drop" => use_tydesc,
+                ~"get_tydesc" | ~"get_tydesc_for_visiting" |
+                ~"needs_drop" => use_tydesc,
 
                 ~"atomic_cxchg"    | ~"atomic_cxchg_acq"|
                 ~"atomic_cxchg_rel"| ~"atomic_load"     |

src/librustc/middle/typeck/check/mod.rs

@@ -3508,6 +3508,10 @@ pub fn check_intrinsic_type(ccx: @mut CrateCtxt, it: @ast::foreign_item) {
           // FIXME (#3730): return *intrinsic::tydesc, not *()
           (1u, ~[], ty::mk_nil_ptr(ccx.tcx))
         }
+        ~"get_tydesc_for_visiting" => {
+          // FIXME (#3730): return *intrinsic::tydesc, not *()
+          (1u, ~[], ty::mk_nil_ptr(ccx.tcx))
+        }
         ~"visit_tydesc" => {
           let tydesc_name = special_idents::tydesc;
           assert!(tcx.intrinsic_defs.contains_key(&tydesc_name));

src/libstd/repr.rs

@@ -27,6 +27,7 @@ use reflect;
 use reflect::{MovePtr, align};
 use str::StrSlice;
 use to_str::ToStr;
+use unstable::intrinsics;
 use vec::raw::{VecRepr, SliceRepr};
 use vec;
 use vec::{OwnedVector, UnboxedVecRepr};
@@ -570,6 +571,7 @@ impl TyVisitor for ReprVisitor {
     fn visit_closure_ptr(&self, _ck: uint) -> bool { true }
 }
 
+#[cfg(stage0)]
 pub fn write_repr<T>(writer: @Writer, object: &T) {
     unsafe {
         let ptr = ptr::to_unsafe_ptr(object) as *c_void;
@@ -580,6 +582,18 @@ pub fn write_repr<T>(writer: @Writer, object: &T) {
     }
 }
 
+#[cfg(not(stage0))]
+pub fn write_repr<T>(writer: @Writer, object: &T) {
+    unsafe {
+        let ptr = ptr::to_unsafe_ptr(object) as *c_void;
+        let tydesc: *intrinsic::TyDesc =
+            transmute(intrinsics::get_tydesc_for_visiting::<T>());
+        let u = ReprVisitor(ptr, writer);
+        let v = reflect::MovePtrAdaptor(u);
+        visit_tydesc(tydesc, @v as @TyVisitor)
+    }
+}
+
 #[cfg(test)]
 struct P {a: int, b: float}
 

src/libstd/unstable/intrinsics.rs

@@ -122,6 +122,9 @@ pub extern "rust-intrinsic" {
     // and TyVisitor which are in librustc
     //fn visit_tydesc(++td: *TyDesc, &&tv: TyVisitor) -> ();
 
+    #[cfg(not(stage0))]
+    pub fn get_tydesc_for_visiting<T>() -> *();
+
     pub fn frame_address(f: &once fn(*u8));
 
     /// Get the address of the `__morestack` stack growth function.