From 5f4e4baddb104ee3e63d1db24a4c2a73e1a703cf Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Tomasz=20Mi=C4=85sko?= <tomasz.miasko@gmail.com>
Date: Thu, 15 Feb 2024 00:00:00 +0000
Subject: [PATCH] Skip coroutines in jump threading to avoid query cycles

---
 compiler/rustc_mir_transform/src/jump_threading.rs |  6 ++++++
 tests/ui/mir/mir_query_cycle.rs                    | 14 ++++++++++++++
 2 files changed, 20 insertions(+)
 create mode 100644 tests/ui/mir/mir_query_cycle.rs

diff --git a/compiler/rustc_mir_transform/src/jump_threading.rs b/compiler/rustc_mir_transform/src/jump_threading.rs
index 78ba166ba43..ad8f21ffbda 100644
--- a/compiler/rustc_mir_transform/src/jump_threading.rs
+++ b/compiler/rustc_mir_transform/src/jump_threading.rs
@@ -68,6 +68,12 @@ impl<'tcx> MirPass<'tcx> for JumpThreading {
         let def_id = body.source.def_id();
         debug!(?def_id);
 
+        // Optimizing coroutines creates query cycles.
+        if tcx.is_coroutine(def_id) {
+            trace!("Skipped for coroutine {:?}", def_id);
+            return;
+        }
+
         let param_env = tcx.param_env_reveal_all_normalized(def_id);
         let map = Map::new(tcx, body, Some(MAX_PLACES));
         let loop_headers = loop_headers(body);
diff --git a/tests/ui/mir/mir_query_cycle.rs b/tests/ui/mir/mir_query_cycle.rs
new file mode 100644
index 00000000000..22d1ccb6c6e
--- /dev/null
+++ b/tests/ui/mir/mir_query_cycle.rs
@@ -0,0 +1,14 @@
+// Regression test for #121094.
+// build-pass
+// compile-flags: -O --crate-type=lib
+// edition: 2021
+use std::{future::Future, pin::Pin};
+
+pub async fn foo(count: u32) {
+    if count == 0 {
+        return
+    } else {
+        let fut: Pin<Box<dyn Future<Output = ()>>> = Box::pin(foo(count - 1));
+        fut.await;
+    }
+}