fix #[loop_match] on diverging loop

this generated invalid MIR before

Author: folkertdev

compiler/rustc_mir_build/src/builder/expr/into.rs

@@ -345,7 +345,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                                         expr_span,
                                         |this| {
                                             this.lower_match_arms(
-                                                destination,
+                                                state_place,
                                                 scrutinee_place_builder,
                                                 scrutinee_span,
                                                 arms,

tests/ui/loop-match/diverges.rs

@@ -0,0 +1,44 @@
+//@ build-pass
+//@ compile-flags: -Zvalidate-mir
+#![allow(incomplete_features)]
+#![feature(loop_match)]
+#![crate_type = "lib"]
+
+// Test that a #[loop_match] without an explicit break from the loop generates valid MIR.
+
+fn break_to_block_unit() -> u8 {
+    let mut state = 0;
+    #[loop_match]
+    loop {
+        state = 'blk: {
+            match state {
+                _ => 'b: {
+                    break 'b 2;
+                }
+            }
+        }
+    }
+}
+
+fn break_to_block_value() -> u8 {
+    let mut state = 0u8;
+    #[loop_match]
+    'a: loop {
+        state = 'blk: {
+            match state {
+                _ => break 'blk state,
+            }
+        }
+    }
+}
+
+fn infinite_a(mut state: u8) {
+    #[loop_match]
+    loop {
+        state = 'blk: {
+            match state {
+                a => a,
+            }
+        }
+    }
+}