From f729f289255bcc8d1bfad614ac74bc51d411826a Mon Sep 17 00:00:00 2001
From: Andy Wang <cbeuw.andy@gmail.com>
Date: Sat, 7 May 2022 17:34:18 +0100
Subject: [PATCH] Move cpp20_rwc_syncs into compile-fail

---
 .../weak_memory/cpp20_rwc_syncs.rs            | 85 +++++++++++++++++++
 tests/run-pass/concurrency/weak_memory.rs     | 58 +------------
 2 files changed, 86 insertions(+), 57 deletions(-)
 create mode 100644 tests/compile-fail/weak_memory/cpp20_rwc_syncs.rs

diff --git a/tests/compile-fail/weak_memory/cpp20_rwc_syncs.rs b/tests/compile-fail/weak_memory/cpp20_rwc_syncs.rs
new file mode 100644
index 00000000000..b9e395fd774
--- /dev/null
+++ b/tests/compile-fail/weak_memory/cpp20_rwc_syncs.rs
@@ -0,0 +1,85 @@
+// ignore-windows: Concurrency on Windows is not supported yet.
+// compile-flags: -Zmiri-ignore-leaks
+
+// https://plv.mpi-sws.org/scfix/paper.pdf
+// 2.2 Second Problem: SC Fences are Too Weak
+// This test should pass under the C++20 model Rust is using.
+// Unfortunately, Miri's weak memory emulation only follows C++11 model
+// as we don't know how to correctly emulate C++20's revised SC semantics,
+// so we have to stick to C++11 emulation from exiting research.
+
+use std::sync::atomic::Ordering::*;
+use std::thread::{spawn, yield_now};
+use std::sync::atomic::{fence, AtomicUsize};
+
+// Spins and yields until until it reads value
+fn reads_value(loc: &AtomicUsize, val: usize) -> usize {
+    while loc.load(Relaxed) != val {
+        yield_now();
+    }
+    val
+}
+
+// We can't create static items because we need to run each test
+// multiple tests
+fn static_atomic(val: usize) -> &'static AtomicUsize {
+    let ret = Box::leak(Box::new(AtomicUsize::new(val)));
+    // A workaround to put the initialisation value in the store buffer
+    ret.store(val, Relaxed);
+    ret
+}
+
+fn test_cpp20_rwc_syncs() {
+    /*
+    int main() {
+        atomic_int x = 0;
+        atomic_int y = 0;
+
+        {{{ x.store(1,mo_relaxed);
+        ||| { r1=x.load(mo_relaxed).readsvalue(1);
+              fence(mo_seq_cst);
+              r2=y.load(mo_relaxed); }
+        ||| { y.store(1,mo_relaxed);
+              fence(mo_seq_cst);
+              r3=x.load(mo_relaxed); }
+        }}}
+        return 0;
+    }
+    */
+    let x = static_atomic(0);
+    let y = static_atomic(0);
+
+    let j1 = spawn(move || {
+        x.store(1, Relaxed);
+    });
+
+    let j2 = spawn(move || {
+        reads_value(&x, 1);
+        fence(SeqCst);
+        y.load(Relaxed)
+    });
+
+    let j3 = spawn(move || {
+        y.store(1, Relaxed);
+        fence(SeqCst);
+        x.load(Relaxed)
+    });
+
+    j1.join().unwrap();
+    let b = j2.join().unwrap();
+    let c = j3.join().unwrap();
+
+    if (b, c) == (0, 0) {
+        // FIXME: the standalone compiletest-rs needs to support
+        // failure-status header to allow us to write assert_ne!((b, c), (0, 0))
+        // https://rustc-dev-guide.rust-lang.org/tests/headers.html#miscellaneous-headers
+        // because panic exits with 101 but compile-rs expects 1
+        let _ = unsafe { std::mem::MaybeUninit::<*const u32>::uninit().assume_init() }; //~ ERROR uninitialized
+    }
+}
+
+pub fn main() {
+    for _ in 0..500 {
+        test_cpp20_rwc_syncs();
+    }
+}
\ No newline at end of file
diff --git a/tests/run-pass/concurrency/weak_memory.rs b/tests/run-pass/concurrency/weak_memory.rs
index 90820d4348d..e85c2d1960c 100644
--- a/tests/run-pass/concurrency/weak_memory.rs
+++ b/tests/run-pass/concurrency/weak_memory.rs
@@ -31,7 +31,7 @@
 #![feature(atomic_from_mut)]
 
 use std::sync::atomic::Ordering::*;
-use std::sync::atomic::{fence, AtomicU16, AtomicU32, AtomicUsize};
+use std::sync::atomic::{AtomicU16, AtomicU32, AtomicUsize};
 use std::thread::{spawn, yield_now};
 
 #[derive(Copy, Clone)]
@@ -57,13 +57,6 @@ fn acquires_value(loc: &AtomicUsize, val: usize) -> usize {
     val
 }
 
-fn reads_value(loc: &AtomicUsize, val: usize) -> usize {
-    while loc.load(Relaxed) != val {
-        yield_now();
-    }
-    val
-}
-
 fn test_corr() {
     let x = static_atomic(0);
     let y = static_atomic(0);
@@ -242,54 +235,6 @@ fn test_sc_store_buffering() {
     assert_ne!((a, b), (0, 0));
 }
 
-// 2.2 Second Problem: SC Fences are Too Weak
-// This test should pass under the C++20 model Rust is using.
-// Unfortunately, Miri's weak memory emulation only follows C++11 model
-// as we don't know how to correctly emulate C++20's revised SC semantics
-#[allow(dead_code)]
-fn test_cpp20_rwc_syncs() {
-    /*
-    int main() {
-        atomic_int x = 0;
-        atomic_int y = 0;
-
-        {{{ x.store(1,mo_relaxed);
-        ||| { r1=x.load(mo_relaxed).readsvalue(1);
-              fence(mo_seq_cst);
-              r2=y.load(mo_relaxed); }
-        ||| { y.store(1,mo_relaxed);
-              fence(mo_seq_cst);
-              r3=x.load(mo_relaxed); }
-        }}}
-        return 0;
-    }
-    */
-    let x = static_atomic(0);
-    let y = static_atomic(0);
-
-    let j1 = spawn(move || {
-        x.store(1, Relaxed);
-    });
-
-    let j2 = spawn(move || {
-        reads_value(&x, 1);
-        fence(SeqCst);
-        y.load(Relaxed)
-    });
-
-    let j3 = spawn(move || {
-        y.store(1, Relaxed);
-        fence(SeqCst);
-        x.load(Relaxed)
-    });
-
-    j1.join().unwrap();
-    let b = j2.join().unwrap();
-    let c = j3.join().unwrap();
-
-    assert_ne!((b, c), (0, 0));
-}
-
 pub fn main() {
     test_imperfectly_overlapping_access();
     // TODO: does this make chances of spurious success
@@ -303,6 +248,5 @@ pub fn main() {
         test_wrc();
         test_corr();
         test_sc_store_buffering();
-        // test_cpp20_rwc_syncs();
     }
 }