Auto merge of #95707 - RalfJung:initialized, r=oli-obk

interp/validity: enforce Scalar::Initialized

This is a follow-up to https://github.com/rust-lang/rust/pull/94527, to also account for the new kind of `Scalar` layout inside the validity checker.

r? `@oli-obk`

compiler/rustc_const_eval/src/interpret/validity.rs

@@ -629,11 +629,24 @@ impl<'rt, 'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> ValidityVisitor<'rt, 'mir, '
         op: &OpTy<'tcx, M::PointerTag>,
         scalar_layout: ScalarAbi,
     ) -> InterpResult<'tcx> {
-        if scalar_layout.valid_range(self.ecx).is_full_for(op.layout.size) {
+        // We check `is_full_range` in a slightly complicated way because *if* we are checking
+        // number validity, then we want to ensure that `Scalar::Initialized` is indeed initialized,
+        // i.e. that we go over the `check_init` below.
+        let is_full_range = match scalar_layout {
+            ScalarAbi::Initialized { valid_range, .. } => {
+                if M::enforce_number_validity(self.ecx) {
+                    false // not "full" since uninit is not accepted
+                } else {
+                    valid_range.is_full_for(op.layout.size)
+                }
+            }
+            ScalarAbi::Union { .. } => true,
+        };
+        if is_full_range {
             // Nothing to check
             return Ok(());
         }
-        // At least one value is excluded.
+        // We have something to check.
         let valid_range = scalar_layout.valid_range(self.ecx);
         let WrappingRange { start, end } = valid_range;
         let max_value = op.layout.size.unsigned_int_max();
@@ -647,9 +660,11 @@ impl<'rt, 'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> ValidityVisitor<'rt, 'mir, '
                 expected { "something {}", wrapping_range_format(valid_range, max_value) },
         );
         let bits = match value.try_to_int() {
+            Ok(int) => int.assert_bits(op.layout.size),
             Err(_) => {
                 // So this is a pointer then, and casting to an int failed.
                 // Can only happen during CTFE.
+                // We support 2 kinds of ranges here: full range, and excluding zero.
                 if start == 1 && end == max_value {
                     // Only null is the niche.  So make sure the ptr is NOT null.
                     if self.ecx.scalar_may_be_null(value) {
@@ -660,7 +675,11 @@ impl<'rt, 'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> ValidityVisitor<'rt, 'mir, '
                                 wrapping_range_format(valid_range, max_value)
                             }
                         )
+                    } else {
+                        return Ok(());
                     }
+                } else if scalar_layout.valid_range(self.ecx).is_full_for(op.layout.size) {
+                    // Easy. (This is reachable if `enforce_number_validity` is set.)
                     return Ok(());
                 } else {
                     // Conservatively, we reject, because the pointer *could* have a bad
@@ -674,9 +693,8 @@ impl<'rt, 'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> ValidityVisitor<'rt, 'mir, '
                     )
                 }
             }
-            Ok(int) => int.assert_bits(op.layout.size),
         };
-        // Now compare. This is slightly subtle because this is a special "wrap-around" range.
+        // Now compare.
         if valid_range.contains(bits) {
             Ok(())
         } else {