[const-prop] Fix ICE when trying to eval polymorphic promoted MIR

src/librustc_mir/interpret/place.rs

@@ -594,6 +594,13 @@ where
             StaticKind::Promoted(promoted, promoted_substs) => {
                 let substs = self.subst_from_frame_and_normalize_erasing_regions(promoted_substs);
                 let instance = ty::Instance::new(place_static.def_id, substs);
+
+                // Even after getting `substs` from the frame, this instance may still be
+                // polymorphic because `ConstProp` will try to promote polymorphic MIR.
+                if instance.needs_subst() {
+                    throw_inval!(TooGeneric);
+                }
+
                 self.const_eval_raw(GlobalId {
                     instance,
                     promoted: Some(promoted),

src/test/ui/consts/const-eval/issue-50814.rs

@@ -11,7 +11,6 @@ struct Sum<A,B>(A,B);
 
 impl<A: Unsigned, B: Unsigned> Unsigned for Sum<A,B> {
     const MAX: u8 = A::MAX + B::MAX; //~ ERROR any use of this value will cause an error
-    //~| ERROR any use of this value will cause an error
 }
 
 fn foo<T>(_: T) -> &'static u8 {

src/test/ui/consts/const-eval/issue-50814.stderr

@@ -9,21 +9,13 @@ LL |     const MAX: u8 = A::MAX + B::MAX;
    = note: `#[deny(const_err)]` on by default
 
 error[E0080]: evaluation of constant expression failed
-  --> $DIR/issue-50814.rs:18:5
+  --> $DIR/issue-50814.rs:17:5
    |
 LL |     &Sum::<U8,U8>::MAX
    |     ^-----------------
    |      |
    |      referenced constant has errors
 
-error: any use of this value will cause an error
-  --> $DIR/issue-50814.rs:13:21
-   |
-LL |     const MAX: u8 = A::MAX + B::MAX;
-   |     ----------------^^^^^^^^^^^^^^^-
-   |                     |
-   |                     attempt to add with overflow
-
-error: aborting due to 3 previous errors
+error: aborting due to 2 previous errors
 
 For more information about this error, try `rustc --explain E0080`.

src/test/ui/consts/const-eval/issue-64908.rs

@@ -0,0 +1,20 @@
+// run-pass
+
+// This test verifies that the `ConstProp` pass doesn't cause an ICE when evaluating polymorphic
+// promoted MIR.
+
+pub trait ArrowPrimitiveType {
+    type Native;
+}
+
+pub fn new<T: ArrowPrimitiveType>() {
+    assert_eq!(0, std::mem::size_of::<T::Native>());
+}
+
+impl ArrowPrimitiveType for () {
+    type Native = ();
+}
+
+fn main() {
+    new::<()>();
+}