Rollup merge of #57573 - Xanewok:querify-entry-fn, r=Zoxc

Querify `entry_fn`

Analogous to https://github.com/rust-lang/rust/pull/57570 but this will also require few fixups in Miri so I decided to separate that (and it seems [CI doesn't let us break tools anymore](https://github.com/rust-lang/rust/pull/57392#issuecomment-453801540)? Or was that because it was a rollup PR?)

r? @nikomatsakis

2 files changed, 4 insertions, 6 deletions

diff --git a/src/librustc_codegen_ssa/back/symbol_export.rs b/src/librustc_codegen_ssa/back/symbol_export.rs
index bf69089a254..c372892c521 100644
--- a/src/librustc_codegen_ssa/back/symbol_export.rs
+++ b/src/librustc_codegen_ssa/back/symbol_export.rs
@@ -194,7 +194,7 @@ fn exported_symbols_provider_local<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                                  })
                                  .collect();
 
-    if tcx.sess.entry_fn.borrow().is_some() {
+    if tcx.entry_fn(LOCAL_CRATE).is_some() {
         let exported_symbol = ExportedSymbol::NoDefId(SymbolName::new("main"));
 
         symbols.push((exported_symbol, SymbolExportLevel::C));
diff --git a/src/librustc_codegen_ssa/base.rs b/src/librustc_codegen_ssa/base.rs
index b88ec075653..38caacba4d0 100644
--- a/src/librustc_codegen_ssa/base.rs
+++ b/src/librustc_codegen_ssa/base.rs
@@ -441,10 +441,8 @@ pub fn codegen_instance<'a, 'tcx: 'a, Bx: BuilderMethods<'a, 'tcx>>(
 pub fn maybe_create_entry_wrapper<'a, 'tcx: 'a, Bx: BuilderMethods<'a, 'tcx>>(
     cx: &'a Bx::CodegenCx
 ) {
-    let (main_def_id, span) = match *cx.sess().entry_fn.borrow() {
-        Some((id, span, _)) => {
-            (cx.tcx().hir().local_def_id(id), span)
-        }
+    let (main_def_id, span) = match cx.tcx().entry_fn(LOCAL_CRATE) {
+        Some((def_id, _)) => { (def_id, cx.tcx().def_span(def_id)) },
         None => return,
     };
 
@@ -458,7 +456,7 @@ pub fn maybe_create_entry_wrapper<'a, 'tcx: 'a, Bx: BuilderMethods<'a, 'tcx>>(
 
     let main_llfn = cx.get_fn(instance);
 
-    let et = cx.sess().entry_fn.get().map(|e| e.2);
+    let et = cx.tcx().entry_fn(LOCAL_CRATE).map(|e| e.1);
     match et {
         Some(EntryFnType::Main) => create_entry_fn::<Bx>(cx, span, main_llfn, main_def_id, true),
         Some(EntryFnType::Start) => create_entry_fn::<Bx>(cx, span, main_llfn, main_def_id, false),