Rollup merge of #69880 - RalfJung:miri-assert-error-sanity, r=oli-obk

miri engine: turn error sanity checks into assertions

We had these as debug assertions so far to make sure our test suite is clean, but really these are conditions that should never arise and also @eddyb told me to turn non-performance-critical debug assertions into full assertions so here we go. ;)

I propose that we do a check-only crater run to make sure this does not actually happen in practice.

r? @oli-obk

src/librustc_mir/interpret/validity.rs

@@ -825,11 +825,10 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         // Run it.
         match visitor.visit_value(op) {
             Ok(()) => Ok(()),
+            // We should only get validation errors here. Avoid other errors as
+            // those do not show *where* in the value the issue lies.
             Err(err) if matches!(err.kind, err_ub!(ValidationFailure { .. })) => Err(err),
-            Err(err) if cfg!(debug_assertions) => {
-                bug!("Unexpected error during validation: {}", err)
-            }
-            Err(err) => Err(err),
+            Err(err) => bug!("Unexpected error during validation: {}", err),
         }
     }
 

src/librustc_mir/transform/const_prop.rs

@@ -404,8 +404,7 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
                 // Some errors shouldn't come up because creating them causes
                 // an allocation, which we should avoid. When that happens,
                 // dedicated error variants should be introduced instead.
-                // Only test this in debug builds though to avoid disruptions.
-                debug_assert!(
+                assert!(
                     !error.kind.allocates(),
                     "const-prop encountered allocating error: {}",
                     error