rustc_trans: don't do on-demand drop glue instantiation.

Author: eddyb

src/librustc_trans/glue.rs

@@ -216,30 +216,14 @@ fn get_drop_glue_core<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>,
                                 g: DropGlueKind<'tcx>) -> ValueRef {
     let g = g.map_ty(|t| get_drop_glue_type(ccx.tcx(), t));
     match ccx.drop_glues().borrow().get(&g) {
-        Some(&(glue, _)) => return glue,
+        Some(&(glue, _)) => glue,
         None => {
-            debug!("Could not find drop glue for {:?} -- {} -- {}. \
-                    Falling back to on-demand instantiation.",
+            bug!("Could not find drop glue for {:?} -- {} -- {}.",
                     g,
                     TransItem::DropGlue(g).to_raw_string(),
                     ccx.codegen_unit().name());
         }
     }
-
-    // FIXME: #34151
-    // Normally, getting here would indicate a bug in trans::collector,
-    // since it seems to have missed a translation item. When we are
-    // translating with non-MIR-based trans, however, the results of the
-    // collector are not entirely reliable since it bases its analysis
-    // on MIR. Thus, we'll instantiate the missing function on demand in
-    // this codegen unit, so that things keep working.
-
-    TransItem::DropGlue(g).predefine(ccx, llvm::InternalLinkage);
-    TransItem::DropGlue(g).define(ccx);
-
-    // Now that we made sure that the glue function is in ccx.drop_glues,
-    // give it another try
-    get_drop_glue_core(ccx, g)
 }
 
 pub fn implement_drop_glue<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>,

src/test/codegen-units/item-collection/instantiation-through-vtable.rs

@@ -31,6 +31,7 @@ impl<T> Trait for Struct<T> {
 fn main() {
     let s1 = Struct { _a: 0u32 };
 
+    //~ TRANS_ITEM drop-glue i8
     //~ TRANS_ITEM fn instantiation_through_vtable::{{impl}}[0]::foo[0]<u32>
     //~ TRANS_ITEM fn instantiation_through_vtable::{{impl}}[0]::bar[0]<u32>
     let _ = &s1 as &Trait;

src/test/codegen-units/item-collection/unsizing.rs

@@ -57,6 +57,7 @@ fn main()
 {
     // simple case
     let bool_sized = &true;
+    //~ TRANS_ITEM drop-glue i8
     //~ TRANS_ITEM fn unsizing::{{impl}}[0]::foo[0]
     let _bool_unsized = bool_sized as &Trait;
 

src/test/codegen-units/partitioning/vtable-through-const.rs

@@ -69,6 +69,7 @@ mod mod1 {
 
 //~ TRANS_ITEM fn vtable_through_const::main[0] @@ vtable_through_const[External]
 fn main() {
+    //~ TRANS_ITEM drop-glue i8 @@ vtable_through_const[Internal]
 
     // Since Trait1::do_something() is instantiated via its default implementation,
     // it is considered a generic and is instantiated here only because it is