Rollup merge of #74411 - jonas-schievink:unbreak-mir, r=matthewjasper

Don't assign `()` to `!` MIR locals

Implements the fix described in #73860 (comment).

Fixes #73860

r? @matthewjasper

Author: Manishearth

src/librustc_mir_build/build/expr/into.rs

@@ -188,10 +188,9 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                     let ptr_ty = ptr.ty;
                     // Create an *internal* temp for the pointer, so that unsafety
                     // checking won't complain about the raw pointer assignment.
-                    let ptr_temp = this.local_decls.push(LocalDecl::with_source_info(
-                        ptr_ty,
-                        source_info,
-                    ).internal());
+                    let ptr_temp = this
+                        .local_decls
+                        .push(LocalDecl::with_source_info(ptr_ty, source_info).internal());
                     let ptr_temp = Place::from(ptr_temp);
                     let block = unpack!(this.into(ptr_temp, block, ptr));
                     this.into(this.hir.tcx().mk_place_deref(ptr_temp), block, val)
@@ -224,7 +223,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                                 Some((destination, success))
                             },
                             from_hir_call,
-                            fn_span
+                            fn_span,
                         },
                     );
                     success.unit()
@@ -387,15 +386,18 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
             // These cases don't actually need a destination
             ExprKind::Assign { .. }
             | ExprKind::AssignOp { .. }
-            | ExprKind::Continue { .. }
-            | ExprKind::Break { .. }
-            | ExprKind::LlvmInlineAsm { .. }
-            | ExprKind::Return { .. } => {
+            | ExprKind::LlvmInlineAsm { .. } => {
                 unpack!(block = this.stmt_expr(block, expr, None));
                 this.cfg.push_assign_unit(block, source_info, destination, this.hir.tcx());
                 block.unit()
             }
 
+            ExprKind::Continue { .. } | ExprKind::Break { .. } | ExprKind::Return { .. } => {
+                unpack!(block = this.stmt_expr(block, expr, None));
+                // No assign, as these have type `!`.
+                block.unit()
+            }
+
             // Avoid creating a temporary
             ExprKind::VarRef { .. }
             | ExprKind::SelfRef

src/test/mir-opt/issue-49232/rustc.main.mir_map.0.mir

@@ -79,13 +79,6 @@ fn main() -> () {
     }
 
     bb10: {
-        _4 = const ();                   // scope 0 at $DIR/issue-49232.rs:10:25: 10:30
-                                         // ty::Const
-                                         // + ty: ()
-                                         // + val: Value(Scalar(<ZST>))
-                                         // mir::Constant
-                                         // + span: $DIR/issue-49232.rs:10:25: 10:30
-                                         // + literal: Const { ty: (), val: Value(Scalar(<ZST>)) }
         unreachable;                     // scope 0 at $DIR/issue-49232.rs:10:25: 10:30
     }