Auto merge of #38574 - Mark-Simulacrum:box-free-unspecialize, r=eddyb

Remove special case for Box<ZST> in trans

Remove extra lang item, `exchange_free`; use `box_free` instead.

Trans used to insert code equivalent to `box_free` in a wrapper around
`exchange_free`, and that code is now removed from trans.

Fixes #37710.

src/liballoc/heap.rs

@@ -144,6 +144,7 @@ unsafe fn exchange_malloc(size: usize, align: usize) -> *mut u8 {
 }
 
 #[cfg(not(test))]
+#[cfg(stage0)]
 #[lang = "exchange_free"]
 #[inline]
 unsafe fn exchange_free(ptr: *mut u8, old_size: usize, align: usize) {

src/librustc/middle/lang_items.rs

@@ -328,7 +328,6 @@ language_item_table! {
     PanicFmtLangItem,                "panic_fmt",               panic_fmt;
 
     ExchangeMallocFnLangItem,        "exchange_malloc",         exchange_malloc_fn;
-    ExchangeFreeFnLangItem,          "exchange_free",           exchange_free_fn;
     BoxFreeFnLangItem,               "box_free",                box_free_fn;
     StrDupUniqFnLangItem,            "strdup_uniq",             strdup_uniq_fn;
 

src/librustc_trans/collector.rs

@@ -193,9 +193,9 @@ use rustc::hir::itemlikevisit::ItemLikeVisitor;
 
 use rustc::hir::map as hir_map;
 use rustc::hir::def_id::DefId;
-use rustc::middle::lang_items::{ExchangeFreeFnLangItem, ExchangeMallocFnLangItem};
+use rustc::middle::lang_items::{BoxFreeFnLangItem, ExchangeMallocFnLangItem};
 use rustc::traits;
-use rustc::ty::subst::{Substs, Subst};
+use rustc::ty::subst::{Kind, Substs, Subst};
 use rustc::ty::{self, TypeFoldable, TyCtxt};
 use rustc::ty::adjustment::CustomCoerceUnsized;
 use rustc::mir::{self, Location};
@@ -215,6 +215,8 @@ use util::nodemap::{FxHashSet, FxHashMap, DefIdMap};
 
 use trans_item::{TransItem, DefPathBasedNames};
 
+use std::iter;
+
 #[derive(PartialEq, Eq, Hash, Clone, Copy, Debug)]
 pub enum TransItemCollectionMode {
     Eager,
@@ -723,23 +725,17 @@ fn find_drop_glue_neighbors<'a, 'tcx>(scx: &SharedCrateContext<'a, 'tcx>,
 
     debug!("find_drop_glue_neighbors: {}", type_to_string(scx.tcx(), ty));
 
-    // Make sure the exchange_free_fn() lang-item gets translated if
-    // there is a boxed value.
-    if let ty::TyBox(_) = ty.sty {
-        let exchange_free_fn_def_id = scx.tcx()
-                                         .lang_items
-                                         .require(ExchangeFreeFnLangItem)
-                                         .unwrap_or_else(|e| scx.sess().fatal(&e));
-
-        assert!(can_have_local_instance(scx.tcx(), exchange_free_fn_def_id));
-        let fn_substs = scx.empty_substs_for_def_id(exchange_free_fn_def_id);
-        let exchange_free_fn_trans_item =
+    // Make sure the BoxFreeFn lang-item gets translated if there is a boxed value.
+    if let ty::TyBox(content_type) = ty.sty {
+        let def_id = scx.tcx().require_lang_item(BoxFreeFnLangItem);
+        assert!(can_have_local_instance(scx.tcx(), def_id));
+        let box_free_fn_trans_item =
             create_fn_trans_item(scx,
-                                 exchange_free_fn_def_id,
-                                 fn_substs,
+                                 def_id,
+                                 scx.tcx().mk_substs(iter::once(Kind::from(content_type))),
                                  scx.tcx().intern_substs(&[]));
 
-        output.push(exchange_free_fn_trans_item);
+        output.push(box_free_fn_trans_item);
     }
 
     // If the type implements Drop, also add a translation item for the

src/librustc_trans/glue.rs

@@ -13,13 +13,15 @@
 // Code relating to drop glue.
 
 use std;
+use std::iter;
 
 use llvm;
 use llvm::{ValueRef, get_param};
-use middle::lang_items::ExchangeFreeFnLangItem;
+use middle::lang_items::BoxFreeFnLangItem;
 use rustc::ty::subst::{Substs};
 use rustc::traits;
 use rustc::ty::{self, AdtKind, Ty, TypeFoldable};
+use rustc::ty::subst::Kind;
 use adt::{self, MaybeSizedValue};
 use base::*;
 use callee::Callee;
@@ -36,38 +38,22 @@ use cleanup::CleanupScope;
 
 use syntax_pos::DUMMY_SP;
 
-pub fn trans_exchange_free_dyn<'a, 'tcx>(
+pub fn trans_exchange_free_ty<'a, 'tcx>(
     bcx: &BlockAndBuilder<'a, 'tcx>,
-    v: ValueRef,
-    size: ValueRef,
-    align: ValueRef
+    ptr: MaybeSizedValue,
+    content_ty: Ty<'tcx>
 ) {
-    let def_id = langcall(bcx.tcx(), None, "", ExchangeFreeFnLangItem);
-    let args = [bcx.pointercast(v, Type::i8p(bcx.ccx)), size, align];
-    let callee = Callee::def(bcx.ccx, def_id, bcx.tcx().intern_substs(&[]));
+    let def_id = langcall(bcx.tcx(), None, "", BoxFreeFnLangItem);
+    let substs = bcx.tcx().mk_substs(iter::once(Kind::from(content_ty)));
+    let callee = Callee::def(bcx.ccx, def_id, substs);
 
-    let ccx = bcx.ccx;
-    let fn_ty = callee.direct_fn_type(ccx, &[]);
+    let fn_ty = callee.direct_fn_type(bcx.ccx, &[]);
 
-    let llret = bcx.call(callee.reify(ccx), &args[..], None);
+    let llret = bcx.call(callee.reify(bcx.ccx),
+        &[ptr.value, ptr.meta][..1 + ptr.has_meta() as usize], None);
     fn_ty.apply_attrs_callsite(llret);
 }
 
-pub fn trans_exchange_free_ty<'a, 'tcx>(
-    bcx: &BlockAndBuilder<'a, 'tcx>, ptr: ValueRef, content_ty: Ty<'tcx>
-) {
-    assert!(bcx.ccx.shared().type_is_sized(content_ty));
-    let sizing_type = sizing_type_of(bcx.ccx, content_ty);
-    let content_size = llsize_of_alloc(bcx.ccx, sizing_type);
-
-    // `Box<ZeroSizeType>` does not allocate.
-    if content_size != 0 {
-        let content_align = align_of(bcx.ccx, content_ty);
-        let ccx = bcx.ccx;
-        trans_exchange_free_dyn(bcx, ptr, C_uint(ccx, content_size), C_uint(ccx, content_align));
-    }
-}
-
 pub fn get_drop_glue_type<'a, 'tcx>(scx: &SharedCrateContext<'a, 'tcx>, t: Ty<'tcx>) -> Ty<'tcx> {
     assert!(t.is_normalized_for_trans());
 
@@ -224,30 +210,16 @@ pub fn implement_drop_glue<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>, g: DropGlueKi
             // special. It may move to library and have Drop impl. As
             // a safe-guard, assert TyBox not used with TyContents.
             assert!(!skip_dtor);
-            if !bcx.ccx.shared().type_is_sized(content_ty) {
+            let ptr = if !bcx.ccx.shared().type_is_sized(content_ty) {
                 let llbox = bcx.load(get_dataptr(&bcx, ptr.value));
                 let info = bcx.load(get_meta(&bcx, ptr.value));
-                drop_ty(&bcx, MaybeSizedValue::unsized_(llbox, info), content_ty);
-                let (llsize, llalign) = size_and_align_of_dst(&bcx, content_ty, info);
-
-                // `Box<ZeroSizeType>` does not allocate.
-                let needs_free = bcx.icmp(llvm::IntNE, llsize, C_uint(bcx.ccx, 0u64));
-                if const_to_opt_uint(needs_free) == Some(0) {
-                    bcx
-                } else {
-                    let next_cx = bcx.fcx().build_new_block("next");
-                    let cond_cx = bcx.fcx().build_new_block("cond");
-                    bcx.cond_br(needs_free, cond_cx.llbb(), next_cx.llbb());
-                    trans_exchange_free_dyn(&cond_cx, llbox, llsize, llalign);
-                    cond_cx.br(next_cx.llbb());
-                    next_cx
-                }
+                MaybeSizedValue::unsized_(llbox, info)
             } else {
-                let llbox = bcx.load(ptr.value);
-                drop_ty(&bcx, MaybeSizedValue::sized(llbox), content_ty);
-                trans_exchange_free_ty(&bcx, llbox, content_ty);
-                bcx
-            }
+                MaybeSizedValue::sized(bcx.load(ptr.value))
+            };
+            drop_ty(&bcx, ptr, content_ty);
+            trans_exchange_free_ty(&bcx, ptr, content_ty);
+            bcx
         }
         ty::TyDynamic(..) => {
             // No support in vtable for distinguishing destroying with