miri: Detect uninitialized integers and floats

compiler/rustc_const_eval/src/interpret/machine.rs

@@ -131,6 +131,10 @@ pub trait Machine<'mir, 'tcx>: Sized {
     /// Whether to enforce the validity invariant
     fn enforce_validity(ecx: &InterpCx<'mir, 'tcx, Self>) -> bool;
 
+    /// Whether to enforce validity (e.g., initialization and not having ptr provenance)
+    /// of integers and floats.
+    fn enforce_number_validity(ecx: &InterpCx<'mir, 'tcx, Self>) -> bool;
+
     /// Whether function calls should be [ABI](Abi)-checked.
     fn enforce_abi(_ecx: &InterpCx<'mir, 'tcx, Self>) -> bool {
         true
@@ -426,6 +430,11 @@ pub macro compile_time_machine(<$mir: lifetime, $tcx: lifetime>) {
         false // for now, we don't enforce validity
     }
 
+    #[inline(always)]
+    fn enforce_number_validity(_ecx: &InterpCx<$mir, $tcx, Self>) -> bool {
+        true
+    }
+
     #[inline(always)]
     fn call_extra_fn(
         _ecx: &mut InterpCx<$mir, $tcx, Self>,

compiler/rustc_const_eval/src/interpret/validity.rs

@@ -520,17 +520,14 @@ impl<'rt, 'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> ValidityVisitor<'rt, 'mir, '
                 let value = self.read_scalar(value)?;
                 // NOTE: Keep this in sync with the array optimization for int/float
                 // types below!
-                if self.ctfe_mode.is_some() {
+                if M::enforce_number_validity(self.ecx) {
                     // Integers/floats in CTFE: Must be scalar bits, pointers are dangerous
                     let is_bits = value.check_init().map_or(false, |v| v.try_to_int().is_ok());
                     if !is_bits {
                         throw_validation_failure!(self.path,
                             { "{}", value } expected { "initialized plain (non-pointer) bytes" }
                         )
                     }
-                } else {
-                    // At run-time, for now, we accept *anything* for these types, including
-                    // uninit. We should fix that, but let's start low.
                 }
                 Ok(true)
             }
@@ -855,9 +852,10 @@ impl<'rt, 'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> ValueVisitor<'mir, 'tcx, M>
                     }
                 };
 
+                let allow_uninit_and_ptr = !M::enforce_number_validity(self.ecx);
                 match alloc.check_bytes(
                     alloc_range(Size::ZERO, size),
-                    /*allow_uninit_and_ptr*/ self.ctfe_mode.is_none(),
+                    allow_uninit_and_ptr,
                 ) {
                     // In the happy case, we needn't check anything else.
                     Ok(()) => {}