Auto merge of #2484 - RalfJung:rustup, r=RalfJung

rustup; enable extra const UB checks

rust-version

@@ -1 +1 @@
-20ffea6938b5839c390252e07940b99e3b6a889a
+75b7e52e92c3b00fc891b47f5b2efdff0a2be55a

src/lib.rs

@@ -116,4 +116,5 @@
     "-Zmir-opt-level=0",
     "--cfg=miri",
     "-Cdebug-assertions=on",
+    "-Zextra-const-ub-checks",
 ];

tests/fail/const-ub-checks.rs

@@ -0,0 +1,11 @@
+#![feature(const_ptr_read)]
+
+const UNALIGNED_READ: () = unsafe {
+    let x = &[0u8; 4];
+    let ptr = x.as_ptr().cast::<u32>();
+    ptr.read(); //~ERROR: evaluation of constant value failed
+};
+
+fn main() {
+    let _x = UNALIGNED_READ;
+}

tests/fail/const-ub-checks.stderr

@@ -0,0 +1,9 @@
+error[E0080]: evaluation of constant value failed
+  --> $DIR/const-ub-checks.rs:LL:CC
+   |
+LL |     ptr.read();
+   |     ^^^^^^^^^^ accessing memory with alignment ALIGN, but alignment ALIGN is required
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0080`.

tests/pass/concurrency/data_race.rs

@@ -1,5 +1,5 @@
 //@ignore-target-windows: Concurrency on Windows is not supported yet.
-//@compile-flags: -Zmiri-disable-weak-memory-emulation
+//@compile-flags: -Zmiri-disable-weak-memory-emulation -Zmiri-preemption-rate=0
 
 use std::sync::atomic::{fence, AtomicUsize, Ordering};
 use std::thread::spawn;
@@ -10,9 +10,9 @@
 unsafe impl<T> Send for EvilSend<T> {}
 unsafe impl<T> Sync for EvilSend<T> {}
 
-static SYNC: AtomicUsize = AtomicUsize::new(0);
-
 fn test_fence_sync() {
+    static SYNC: AtomicUsize = AtomicUsize::new(0);
+
     let mut var = 0u32;
     let ptr = &mut var as *mut u32;
     let evil_ptr = EvilSend(ptr);
@@ -28,7 +28,7 @@ fn test_fence_sync() {
             fence(Ordering::Acquire);
             unsafe { *evil_ptr.0 }
         } else {
-            0
+            panic!(); // relies on thread 2 going last
         }
     });
 
@@ -56,6 +56,8 @@ fn test_multiple_reads() {
 }
 
 pub fn test_rmw_no_block() {
+    static SYNC: AtomicUsize = AtomicUsize::new(0);
+
     let mut a = 0u32;
     let b = &mut a as *mut u32;
     let c = EvilSend(b);
@@ -77,11 +79,13 @@ pub fn test_rmw_no_block() {
         j1.join().unwrap();
         j2.join().unwrap();
         let v = j3.join().unwrap();
-        assert!(v == 1 || v == 2);
+        assert!(v == 1 || v == 2); // relies on thread 3 going last
     }
 }
 
 pub fn test_simple_release() {
+    static SYNC: AtomicUsize = AtomicUsize::new(0);
+
     let mut a = 0u32;
     let b = &mut a as *mut u32;
     let c = EvilSend(b);
@@ -95,7 +99,7 @@ pub fn test_simple_release() {
         let j2 = spawn(move || if SYNC.load(Ordering::Acquire) == 1 { *c.0 } else { 0 });
 
         j1.join().unwrap();
-        assert_eq!(j2.join().unwrap(), 1);
+        assert_eq!(j2.join().unwrap(), 1); // relies on thread 2 going last
     }
 }