Auto merge of #3972 - rust-lang:eager_dyn, r=RalfJung

Avoid some needless monomorphizations
All code paths always end up boxing the type, so let's do it eagerly in the `callback!` macro instead

Author: bors

src/tools/miri/src/concurrency/init_once.rs

@@ -2,6 +2,7 @@ use std::collections::VecDeque;
 
 use rustc_index::Idx;
 
+usesuper::thread::DynUnblockCallback;
 usesuper::vector_clock::VClock;
 usecrate::*;
 
@@ -34,11 +35,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
 
 /// Put the thread into the queue waiting for the initialization.
 #[inline]
-fninit_once_enqueue_and_block(
-&mutself,
-id:InitOnceId,
-callback:implUnblockCallback<'tcx> + 'tcx,
-){
+fninit_once_enqueue_and_block(&mutself,id:InitOnceId,callback:DynUnblockCallback<'tcx>){
 let this = self.eval_context_mut();
 let thread = this.active_thread();
 let init_once = &mut this.machine.sync.init_onces[id];

src/tools/miri/src/concurrency/thread.rs

@@ -50,7 +50,7 @@ pub trait UnblockCallback<'tcx>: VisitProvenance {
 fntimeout(self:Box<Self>,_ecx:&mutInterpCx<'tcx,MiriMachine<'tcx>>)
  -> InterpResult<'tcx>;
 }
-typeDynUnblockCallback<'tcx> = Box<dynUnblockCallback<'tcx> + 'tcx>;
+pubtypeDynUnblockCallback<'tcx> = Box<dynUnblockCallback<'tcx> + 'tcx>;
 
 #[macro_export]
 macro_rules! callback {
@@ -101,7 +101,7 @@ macro_rules! callback {
 }
 }
 
-Callback{ $($name,)* _phantom: std::marker::PhantomData}
+Box::new(Callback{ $($name,)* _phantom: std::marker::PhantomData})
 }}
 }
 
@@ -715,11 +715,11 @@ impl<'tcx> ThreadManager<'tcx> {
 &mutself,
 reason:BlockReason,
 timeout:Option<Timeout>,
-callback:implUnblockCallback<'tcx> + 'tcx,
+callback:DynUnblockCallback<'tcx>,
 ){
 let state = &mutself.threads[self.active_thread].state;
 assert!(state.is_enabled());
-*state = ThreadState::Blocked{ reason, timeout,callback:Box::new(callback)}
+*state = ThreadState::Blocked{ reason, timeout, callback }
 }
 
 /// Change the active thread to some enabled thread.
@@ -1032,7 +1032,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
 &mutself,
 reason:BlockReason,
 timeout:Option<(TimeoutClock,TimeoutAnchor,Duration)>,
-callback:implUnblockCallback<'tcx> + 'tcx,
+callback:DynUnblockCallback<'tcx>,
 ){
 let this = self.eval_context_mut();
 let timeout = timeout.map(|(clock, anchor, duration)| {