Remove return_ty from Mir

https://github.com/rust-lang/rust/issues/46001

src/librustc/mir/mod.rs

@@ -82,9 +82,6 @@ pub struct Mir<'tcx> {
     /// in scope, but a separate set of locals.
     pub promoted: IndexVec<Promoted, Mir<'tcx>>,
 
-    /// Return type of the function.
-    pub return_ty: Ty<'tcx>,
-
     /// Yield type of the function, if it is a generator.
     pub yield_ty: Option<Ty<'tcx>>,
 
@@ -135,7 +132,6 @@ impl<'tcx> Mir<'tcx> {
                visibility_scope_info: ClearOnDecode<IndexVec<VisibilityScope,
                                                              VisibilityScopeInfo>>,
                promoted: IndexVec<Promoted, Mir<'tcx>>,
-               return_ty: Ty<'tcx>,
                yield_ty: Option<Ty<'tcx>>,
                local_decls: IndexVec<Local, LocalDecl<'tcx>>,
                arg_count: usize,
@@ -145,14 +141,12 @@ impl<'tcx> Mir<'tcx> {
         // We need `arg_count` locals, and one for the return pointer
         assert!(local_decls.len() >= arg_count + 1,
             "expected at least {} locals, got {}", arg_count + 1, local_decls.len());
-        assert_eq!(local_decls[RETURN_POINTER].ty, return_ty);
 
         Mir {
             basic_blocks,
             visibility_scopes,
             visibility_scope_info,
             promoted,
-            return_ty,
             yield_ty,
             generator_drop: None,
             generator_layout: None,
@@ -273,6 +267,11 @@ impl<'tcx> Mir<'tcx> {
             &block.terminator().source_info
         }
     }
+
+    /// Return the return type, it always return first element from `local_decls` array
+    pub fn return_ty(&self) -> Ty<'tcx> {
+        self.local_decls[RETURN_POINTER].ty
+    }
 }
 
 #[derive(Clone, Debug)]
@@ -299,7 +298,6 @@ impl_stable_hash_for!(struct Mir<'tcx> {
     visibility_scopes,
     visibility_scope_info,
     promoted,
-    return_ty,
     yield_ty,
     generator_drop,
     generator_layout,
@@ -1744,7 +1742,6 @@ impl<'tcx> TypeFoldable<'tcx> for Mir<'tcx> {
             visibility_scopes: self.visibility_scopes.clone(),
             visibility_scope_info: self.visibility_scope_info.clone(),
             promoted: self.promoted.fold_with(folder),
-            return_ty: self.return_ty.fold_with(folder),
             yield_ty: self.yield_ty.fold_with(folder),
             generator_drop: self.generator_drop.fold_with(folder),
             generator_layout: self.generator_layout.fold_with(folder),
@@ -1763,7 +1760,6 @@ impl<'tcx> TypeFoldable<'tcx> for Mir<'tcx> {
         self.generator_layout.visit_with(visitor) ||
         self.yield_ty.visit_with(visitor) ||
         self.promoted.visit_with(visitor)     ||
-        self.return_ty.visit_with(visitor)    ||
         self.local_decls.visit_with(visitor)
     }
 }

src/librustc/mir/visit.rs

@@ -292,7 +292,7 @@ macro_rules! make_mir_visitor {
                     self.visit_visibility_scope_data(scope);
                 }
 
-                self.visit_ty(&$($mutability)* mir.return_ty, TyContext::ReturnTy(SourceInfo {
+                self.visit_ty(&$($mutability)* mir.return_ty(), TyContext::ReturnTy(SourceInfo {
                     span: mir.span,
                     scope: ARGUMENT_VISIBILITY_SCOPE,
                 }));

src/librustc_mir/build/mod.rs

@@ -444,7 +444,7 @@ fn construct_fn<'a, 'gcx, 'tcx, A>(hir: Cx<'a, 'gcx, 'tcx>,
         }).collect()
     });
 
-    let mut mir = builder.finish(upvar_decls, return_ty, yield_ty);
+    let mut mir = builder.finish(upvar_decls, yield_ty);
     mir.spread_arg = spread_arg;
     mir
 }
@@ -469,7 +469,7 @@ fn construct_const<'a, 'gcx, 'tcx>(hir: Cx<'a, 'gcx, 'tcx>,
     // Constants can't `return` so a return block should not be created.
     assert_eq!(builder.cached_return_block, None);
 
-    builder.finish(vec![], ty, None)
+    builder.finish(vec![], None)
 }
 
 fn construct_error<'a, 'gcx, 'tcx>(hir: Cx<'a, 'gcx, 'tcx>,
@@ -481,7 +481,7 @@ fn construct_error<'a, 'gcx, 'tcx>(hir: Cx<'a, 'gcx, 'tcx>,
     let mut builder = Builder::new(hir, span, 0, Safety::Safe, ty);
     let source_info = builder.source_info(span);
     builder.cfg.terminate(START_BLOCK, source_info, TerminatorKind::Unreachable);
-    builder.finish(vec![], ty, None)
+    builder.finish(vec![], None)
 }
 
 impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
@@ -524,7 +524,6 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
 
     fn finish(self,
               upvar_decls: Vec<UpvarDecl>,
-              return_ty: Ty<'tcx>,
               yield_ty: Option<Ty<'tcx>>)
               -> Mir<'tcx> {
         for (index, block) in self.cfg.basic_blocks.iter().enumerate() {
@@ -537,7 +536,6 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
                  self.visibility_scopes,
                  ClearOnDecode::Set(self.visibility_scope_info),
                  IndexVec::new(),
-                 return_ty,
                  yield_ty,
                  self.local_decls,
                  self.arg_count,

src/librustc_mir/shim.rs

@@ -197,7 +197,6 @@ fn build_drop_shim<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
         ),
         ClearOnDecode::Clear,
         IndexVec::new(),
-        sig.output(),
         None,
         local_decls_for_sig(&sig, span),
         sig.inputs().len(),
@@ -345,7 +344,6 @@ impl<'a, 'tcx> CloneShimBuilder<'a, 'tcx> {
             ),
             ClearOnDecode::Clear,
             IndexVec::new(),
-            self.sig.output(),
             None,
             self.local_decls,
             self.sig.inputs().len(),
@@ -808,7 +806,6 @@ fn build_call_shim<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
         ),
         ClearOnDecode::Clear,
         IndexVec::new(),
-        sig.output(),
         None,
         local_decls,
         sig.inputs().len(),
@@ -881,7 +878,6 @@ pub fn build_adt_ctor<'a, 'gcx, 'tcx>(infcx: &infer::InferCtxt<'a, 'gcx, 'tcx>,
         ),
         ClearOnDecode::Clear,
         IndexVec::new(),
-        sig.output(),
         None,
         local_decls,
         sig.inputs().len(),

src/librustc_mir/transform/generator.rs

@@ -557,7 +557,6 @@ fn create_generator_drop_shim<'a, 'tcx>(
     }
 
     // Replace the return variable
-    mir.return_ty = tcx.mk_nil();
     mir.local_decls[RETURN_POINTER] = LocalDecl {
         mutability: Mutability::Mut,
         ty: tcx.mk_nil(),
@@ -777,7 +776,7 @@ impl MirPass for StateTransform {
         let state_did = tcx.lang_items().gen_state().unwrap();
         let state_adt_ref = tcx.adt_def(state_did);
         let state_substs = tcx.mk_substs([Kind::from(yield_ty),
-            Kind::from(mir.return_ty)].iter());
+            Kind::from(mir.return_ty())].iter());
         let ret_ty = tcx.mk_adt(state_adt_ref, state_substs);
 
         // We rename RETURN_POINTER which has type mir.return_ty to new_ret_local
@@ -808,7 +807,6 @@ impl MirPass for StateTransform {
         transform.visit_mir(mir);
 
         // Update our MIR struct to reflect the changed we've made
-        mir.return_ty = ret_ty;
         mir.yield_ty = None;
         mir.arg_count = 1;
         mir.spread_arg = None;

src/librustc_mir/transform/promote_consts.rs

@@ -287,7 +287,7 @@ impl<'a, 'tcx> Promoter<'a, 'tcx> {
         let span = self.promoted.span;
         let new_operand = Operand::Constant(box Constant {
             span,
-            ty: self.promoted.return_ty,
+            ty: self.promoted.return_ty(),
             literal: Literal::Promoted {
                 index: Promoted::new(self.source.promoted.len())
             }
@@ -385,7 +385,6 @@ pub fn promote_candidates<'a, 'tcx>(mir: &mut Mir<'tcx>,
                 mir.visibility_scopes.clone(),
                 mir.visibility_scope_info.clone(),
                 IndexVec::new(),
-                ty,
                 None,
                 initial_locals,
                 0,

src/librustc_mir/transform/qualify_consts.rs

@@ -380,7 +380,7 @@ impl<'a, 'tcx> Qualifier<'a, 'tcx, 'tcx> {
         // conservative type qualification instead.
         if self.qualif.intersects(Qualif::CONST_ERROR) {
             self.qualif = Qualif::empty();
-            let return_ty = mir.return_ty;
+            let return_ty = mir.return_ty();
             self.add_type(return_ty);
         }
 
@@ -938,7 +938,7 @@ fn mir_const_qualif<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
     // performing the steal.
     let mir = &tcx.mir_const(def_id).borrow();
 
-    if mir.return_ty.references_error() {
+    if mir.return_ty().references_error() {
         tcx.sess.delay_span_bug(mir.span, "mir_const_qualif: Mir had errors");
         return (Qualif::NOT_CONST.bits(), Rc::new(IdxSetBuf::new_empty(0)));
     }
@@ -956,7 +956,7 @@ impl MirPass for QualifyAndPromoteConstants {
                           src: MirSource,
                           mir: &mut Mir<'tcx>) {
         // There's not really any point in promoting errorful MIR.
-        if mir.return_ty.references_error() {
+        if mir.return_ty().references_error() {
             tcx.sess.delay_span_bug(mir.span, "QualifyAndPromoteConstants: Mir had errors");
             return;
         }
@@ -1045,7 +1045,7 @@ impl MirPass for QualifyAndPromoteConstants {
                     return;
                 }
             }
-            let ty = mir.return_ty;
+            let ty = mir.return_ty();
             tcx.infer_ctxt().enter(|infcx| {
                 let param_env = ty::ParamEnv::empty(Reveal::UserFacing);
                 let cause = traits::ObligationCause::new(mir.span, id, traits::SharedStatic);

src/librustc_mir/transform/type_check.rs

@@ -130,7 +130,7 @@ impl<'a, 'b, 'gcx, 'tcx> Visitor<'tcx> for TypeVerifier<'a, 'b, 'gcx, 'tcx> {
     }
 
     fn visit_mir(&mut self, mir: &Mir<'tcx>) {
-        self.sanitize_type(&"return type", mir.return_ty);
+        self.sanitize_type(&"return type", mir.return_ty());
         for local_decl in &mir.local_decls {
             self.sanitize_type(local_decl, local_decl.ty);
         }

src/librustc_mir/util/graphviz.rs

@@ -150,7 +150,7 @@ fn write_graph_label<'a, 'gcx, 'tcx, W: Write>(tcx: TyCtxt<'a, 'gcx, 'tcx>,
         write!(w, "{:?}: {}", Lvalue::Local(arg), escape(&mir.local_decls[arg].ty))?;
     }
 
-    write!(w, ") -&gt; {}", escape(mir.return_ty))?;
+    write!(w, ") -&gt; {}", escape(mir.return_ty()))?;
     write!(w, r#"<br align="left"/>"#)?;
 
     for local in mir.vars_and_temps_iter() {

src/librustc_mir/util/pretty.rs

@@ -392,13 +392,13 @@ fn write_mir_sig(tcx: TyCtxt, src: MirSource, mir: &Mir, w: &mut Write)
                 write!(w, "{:?}: {}", Lvalue::Local(arg), mir.local_decls[arg].ty)?;
             }
 
-            write!(w, ") -> {}", mir.return_ty)
+            write!(w, ") -> {}", mir.return_ty())
         }
         (hir::BodyOwnerKind::Const, _) |
         (hir::BodyOwnerKind::Static(_), _) |
         (_, Some(_)) => {
             assert_eq!(mir.arg_count, 0);
-            write!(w, ": {} =", mir.return_ty)
+            write!(w, ": {} =", mir.return_ty())
         }
     }
 }