Auto merge of #68170 - wesleywiser:stop_const_prop_ref_taking, r=oli-obk

Turn off const propagation of ref taking

Fixes #67529
Fixes #67640
Fixes #67641
Fixes #67862

r? @oli-obk

Author: bors

src/librustc_mir/transform/const_prop.rs

@@ -636,28 +636,11 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
                 self.check_binary_op(*op, left, right, source_info, place_layout, overflow_check)?;
             }
 
-            // Work around: avoid ICE in miri. FIXME(wesleywiser)
-            // The Miri engine ICEs when taking a reference to an uninitialized unsized
-            // local. There's nothing it can do here: taking a reference needs an allocation
-            // which needs to know the size. Normally that's okay as during execution
-            // (e.g. for CTFE) it can never happen. But here in const_prop
-            // unknown data is uninitialized, so if e.g. a function argument is unsized
-            // and has a reference taken, we get an ICE.
+            // Do not try creating references (#67862)
             Rvalue::Ref(_, _, place_ref) => {
-                trace!("checking Ref({:?})", place_ref);
+                trace!("skipping Ref({:?})", place_ref);
 
-                if let Some(local) = place_ref.as_local() {
-                    let alive = if let LocalValue::Live(_) = self.ecx.frame().locals[local].value {
-                        true
-                    } else {
-                        false
-                    };
-
-                    if !alive {
-                        trace!("skipping Ref({:?}) to uninitialized local", place);
-                        return None;
-                    }
-                }
+                return None;
             }
 
             _ => {}

src/test/mir-opt/const_prop/ref_deref_project.rs

@@ -1,5 +1,5 @@
 fn main() {
-    *(&(4, 5).1);
+    *(&(4, 5).1); // This does not currently propagate (#67862)
 }
 
 // END RUST SOURCE
@@ -35,7 +35,7 @@ fn main() {
 //     ...
 //     _4 = const main::promoted[0];
 //     _2 = &((*_4).1: i32);
-//     _1 = const 5i32;
+//     _1 = (*_2);
 //     ...
 // }
 // END rustc.main.ConstProp.after.mir

src/test/ui/consts/issue-67529.rs

@@ -0,0 +1,11 @@
+// compile-flags: -Z mir-opt-level=2
+// run-pass
+
+struct Baz<T: ?Sized> {
+    a: T
+}
+
+fn main() {
+    let d : Baz<[i32; 4]> = Baz { a: [1,2,3,4] };
+    assert_eq!([1, 2, 3, 4], d.a);
+}

src/test/ui/consts/issue-67640.rs

@@ -0,0 +1,24 @@
+// compile-flags: -Z mir-opt-level=3
+// run-pass
+
+struct X {
+    x: isize
+}
+
+fn f1(a: &mut X, b: &mut isize, c: isize) -> isize {
+    let r = a.x + *b + c;
+    a.x = 0;
+    *b = 10;
+    return r;
+}
+
+fn f2<F>(a: isize, f: F) -> isize where F: FnOnce(isize) { f(1); return a; }
+
+pub fn main() {
+    let mut a = X {x: 1};
+    let mut b = 2;
+    let c = 3;
+    assert_eq!(f1(&mut a, &mut b, c), 6);
+    assert_eq!(a.x, 0);
+    assert_eq!(f2(a.x, |_| a.x = 50), 0);
+}

src/test/ui/consts/issue-67641.rs

@@ -0,0 +1,24 @@
+// compile-flags: -Z mir-opt-level=2
+// run-pass
+
+use std::cell::Cell;
+
+#[derive(Debug)]
+struct B<'a> {
+    a: [Cell<Option<&'a B<'a>>>; 2]
+}
+
+impl<'a> B<'a> {
+    fn new() -> B<'a> {
+        B { a: [Cell::new(None), Cell::new(None)] }
+    }
+}
+
+fn f() {
+    let b2 = B::new();
+    b2.a[0].set(Some(&b2));
+}
+
+fn main() {
+    f();
+}

src/test/ui/consts/issue-67862.rs

@@ -0,0 +1,18 @@
+// compile-flags: -Z mir-opt-level=2
+// run-pass
+
+fn e220() -> (i64, i64) {
+    #[inline(never)]
+    fn get_displacement() -> [i64; 2] {
+        [139776, 963904]
+    }
+
+    let res = get_displacement();
+    match (&res[0], &res[1]) {
+        (arg0, arg1) => (*arg0, *arg1),
+    }
+}
+
+fn main() {
+    assert_eq!(e220(), (139776, 963904));
+}