Auto merge of #100043 - RalfJung:scalar-always-init, r=RalfJung

interpret: remove support for uninitialized scalars

With Miri no longer supporting `-Zmiri-allow-uninit-numbers`, we no longer need to support storing uninit data in a `Scalar`. We anyway already only use this representation for types with *initialized* `Scalar` layout (and we have to, due to partial initialization), so let's get rid of the `ScalarMaybeUninit` type entirely.

I tried to stage this into meaningful commits, but the one that changes `read_immediate` to always trigger UB on uninit is the largest chunk of the PR and I don't see how it could be subdivided.

Fixes rust-lang/miri#2187
r? `@oli-obk`

compiler/rustc_const_eval/src/const_eval/eval_queries.rs

@@ -3,7 +3,7 @@ use crate::interpret::eval_nullary_intrinsic;
 use crate::interpret::{
     intern_const_alloc_recursive, Allocation, ConstAlloc, ConstValue, CtfeValidationMode, GlobalId,
     Immediate, InternKind, InterpCx, InterpResult, MPlaceTy, MemoryKind, OpTy, RefTracking,
-    ScalarMaybeUninit, StackPopCleanup,
+    StackPopCleanup,
 };
 
 use rustc_hir::def::DefKind;
@@ -170,10 +170,7 @@ pub(super) fn op_to_const<'tcx>(
         // see comment on `let try_as_immediate` above
         Err(imm) => match *imm {
             _ if imm.layout.is_zst() => ConstValue::ZeroSized,
-            Immediate::Scalar(x) => match x {
-                ScalarMaybeUninit::Scalar(s) => ConstValue::Scalar(s),
-                ScalarMaybeUninit::Uninit => to_const_value(&op.assert_mem_place()),
-            },
+            Immediate::Scalar(x) => ConstValue::Scalar(x),
             Immediate::ScalarPair(a, b) => {
                 debug!("ScalarPair(a: {:?}, b: {:?})", a, b);
                 // We know `offset` is relative to the allocation, so we can use `into_parts`.

compiler/rustc_const_eval/src/const_eval/machine.rs

@@ -347,8 +347,8 @@ impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for CompileTimeInterpreter<'mir,
         };
         match intrinsic_name {
             sym::ptr_guaranteed_eq | sym::ptr_guaranteed_ne => {
-                let a = ecx.read_immediate(&args[0])?.to_scalar()?;
-                let b = ecx.read_immediate(&args[1])?.to_scalar()?;
+                let a = ecx.read_scalar(&args[0])?;
+                let b = ecx.read_scalar(&args[1])?;
                 let cmp = if intrinsic_name == sym::ptr_guaranteed_eq {
                     ecx.guaranteed_eq(a, b)?
                 } else {

compiler/rustc_const_eval/src/const_eval/valtrees.rs

@@ -3,7 +3,7 @@ use super::machine::CompileTimeEvalContext;
 use super::{ValTreeCreationError, ValTreeCreationResult, VALTREE_MAX_NODES};
 use crate::interpret::{
     intern_const_alloc_recursive, ConstValue, ImmTy, Immediate, InternKind, MemPlaceMeta,
-    MemoryKind, PlaceTy, Scalar, ScalarMaybeUninit,
+    MemoryKind, PlaceTy, Scalar,
 };
 use crate::interpret::{MPlaceTy, Value};
 use rustc_middle::ty::{self, ScalarInt, Ty, TyCtxt};
@@ -90,7 +90,7 @@ pub(crate) fn const_to_valtree_inner<'tcx>(
             let Ok(val) = ecx.read_immediate(&place.into()) else {
                 return Err(ValTreeCreationError::Other);
             };
-            let val = val.to_scalar().unwrap();
+            let val = val.to_scalar();
             *num_nodes += 1;
 
             Ok(ty::ValTree::Leaf(val.assert_int()))
@@ -349,11 +349,7 @@ fn valtree_into_mplace<'tcx>(
         ty::Bool | ty::Int(_) | ty::Uint(_) | ty::Float(_) | ty::Char => {
             let scalar_int = valtree.unwrap_leaf();
             debug!("writing trivial valtree {:?} to place {:?}", scalar_int, place);
-            ecx.write_immediate(
-                Immediate::Scalar(ScalarMaybeUninit::Scalar(scalar_int.into())),
-                &place.into(),
-            )
-            .unwrap();
+            ecx.write_immediate(Immediate::Scalar(scalar_int.into()), &place.into()).unwrap();
         }
         ty::Ref(_, inner_ty, _) => {
             let mut pointee_place = create_pointee_place(ecx, *inner_ty, valtree);
@@ -366,11 +362,10 @@ fn valtree_into_mplace<'tcx>(
             let imm = match inner_ty.kind() {
                 ty::Slice(_) | ty::Str => {
                     let len = valtree.unwrap_branch().len();
-                    let len_scalar =
-                        ScalarMaybeUninit::Scalar(Scalar::from_machine_usize(len as u64, &tcx));
+                    let len_scalar = Scalar::from_machine_usize(len as u64, &tcx);
 
                     Immediate::ScalarPair(
-                        ScalarMaybeUninit::from_maybe_pointer((*pointee_place).ptr, &tcx),
+                        Scalar::from_maybe_pointer((*pointee_place).ptr, &tcx),
                         len_scalar,
                     )
                 }

compiler/rustc_const_eval/src/interpret/cast.rs

@@ -123,10 +123,10 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         match src.layout.ty.kind() {
             // Floating point
             Float(FloatTy::F32) => {
-                return Ok(self.cast_from_float(src.to_scalar()?.to_f32()?, cast_ty).into());
+                return Ok(self.cast_from_float(src.to_scalar().to_f32()?, cast_ty).into());
             }
             Float(FloatTy::F64) => {
-                return Ok(self.cast_from_float(src.to_scalar()?.to_f64()?, cast_ty).into());
+                return Ok(self.cast_from_float(src.to_scalar().to_f64()?, cast_ty).into());
             }
             // The rest is integer/pointer-"like", including fn ptr casts
             _ => assert!(
@@ -153,7 +153,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                 assert_eq!(dest_layout.size, self.pointer_size());
                 assert!(src.layout.ty.is_unsafe_ptr());
                 return match **src {
-                    Immediate::ScalarPair(data, _) => Ok(data.check_init()?.into()),
+                    Immediate::ScalarPair(data, _) => Ok(data.into()),
                     Immediate::Scalar(..) => span_bug!(
                         self.cur_span(),
                         "{:?} input to a fat-to-thin cast ({:?} -> {:?})",
@@ -167,7 +167,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         }
 
         // # The remaining source values are scalar and "int-like".
-        let scalar = src.to_scalar()?;
+        let scalar = src.to_scalar();
         Ok(self.cast_from_int_like(scalar, src.layout, cast_ty)?.into())
     }
 
@@ -179,7 +179,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         assert_matches!(src.layout.ty.kind(), ty::RawPtr(_) | ty::FnPtr(_));
         assert!(cast_ty.is_integral());
 
-        let scalar = src.to_scalar()?;
+        let scalar = src.to_scalar();
         let ptr = scalar.to_pointer(self)?;
         match ptr.into_pointer_or_addr() {
             Ok(ptr) => M::expose_ptr(self, ptr)?,
@@ -197,7 +197,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         assert_matches!(cast_ty.kind(), ty::RawPtr(_));
 
         // First cast to usize.
-        let scalar = src.to_scalar()?;
+        let scalar = src.to_scalar();
         let addr = self.cast_from_int_like(scalar, src.layout, self.tcx.types.usize)?;
         let addr = addr.to_machine_usize(self)?;
 
@@ -291,7 +291,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
 
         match (&src_pointee_ty.kind(), &dest_pointee_ty.kind()) {
             (&ty::Array(_, length), &ty::Slice(_)) => {
-                let ptr = self.read_immediate(src)?.to_scalar()?;
+                let ptr = self.read_scalar(src)?;
                 // u64 cast is from usize to u64, which is always good
                 let val =
                     Immediate::new_slice(ptr, length.eval_usize(*self.tcx, self.param_env), self);
@@ -303,7 +303,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                     // A NOP cast that doesn't actually change anything, should be allowed even with mismatching vtables.
                     return self.write_immediate(*val, dest);
                 }
-                let (old_data, old_vptr) = val.to_scalar_pair()?;
+                let (old_data, old_vptr) = val.to_scalar_pair();
                 let old_vptr = old_vptr.to_pointer(self)?;
                 let (ty, old_trait) = self.get_ptr_vtable(old_vptr)?;
                 if old_trait != data_a.principal() {
@@ -315,7 +315,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
             (_, &ty::Dynamic(ref data, _)) => {
                 // Initial cast from sized to dyn trait
                 let vtable = self.get_vtable_ptr(src_pointee_ty, data.principal())?;
-                let ptr = self.read_immediate(src)?.to_scalar()?;
+                let ptr = self.read_scalar(src)?;
                 let val = Immediate::new_dyn_trait(ptr, vtable, &*self.tcx);
                 self.write_immediate(val, dest)
             }

compiler/rustc_const_eval/src/interpret/eval_context.rs

@@ -21,7 +21,7 @@ use rustc_target::abi::{call::FnAbi, Align, HasDataLayout, Size, TargetDataLayou
 use super::{
     AllocId, GlobalId, Immediate, InterpErrorInfo, InterpResult, MPlaceTy, Machine, MemPlace,
     MemPlaceMeta, Memory, MemoryKind, Operand, Place, PlaceTy, PointerArithmetic, Provenance,
-    Scalar, ScalarMaybeUninit, StackPopJump,
+    Scalar, StackPopJump,
 };
 use crate::transform::validate::equal_up_to_regions;
 
@@ -991,16 +991,16 @@ impl<'a, 'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> std::fmt::Debug
                     }
                     LocalValue::Live(Operand::Immediate(Immediate::Scalar(val))) => {
                         write!(fmt, " {:?}", val)?;
-                        if let ScalarMaybeUninit::Scalar(Scalar::Ptr(ptr, _size)) = val {
+                        if let Scalar::Ptr(ptr, _size) = val {
                             allocs.push(ptr.provenance.get_alloc_id());
                         }
                     }
                     LocalValue::Live(Operand::Immediate(Immediate::ScalarPair(val1, val2))) => {
                         write!(fmt, " ({:?}, {:?})", val1, val2)?;
-                        if let ScalarMaybeUninit::Scalar(Scalar::Ptr(ptr, _size)) = val1 {
+                        if let Scalar::Ptr(ptr, _size) = val1 {
                             allocs.push(ptr.provenance.get_alloc_id());
                         }
-                        if let ScalarMaybeUninit::Scalar(Scalar::Ptr(ptr, _size)) = val2 {
+                        if let Scalar::Ptr(ptr, _size) = val2 {
                             allocs.push(ptr.provenance.get_alloc_id());
                         }
                     }

compiler/rustc_const_eval/src/interpret/intrinsics.rs

@@ -184,7 +184,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
             | sym::bitreverse => {
                 let ty = substs.type_at(0);
                 let layout_of = self.layout_of(ty)?;
-                let val = self.read_scalar(&args[0])?.check_init()?;
+                let val = self.read_scalar(&args[0])?;
                 let bits = val.to_bits(layout_of.size)?;
                 let kind = match layout_of.abi {
                     Abi::Scalar(scalar) => scalar.primitive(),
@@ -256,7 +256,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                 let (val, overflowed, _ty) = self.overflowing_binary_op(bin_op, &l, &r)?;
                 if overflowed {
                     let layout = self.layout_of(substs.type_at(0))?;
-                    let r_val = r.to_scalar()?.to_bits(layout.size)?;
+                    let r_val = r.to_scalar().to_bits(layout.size)?;
                     if let sym::unchecked_shl | sym::unchecked_shr = intrinsic_name {
                         throw_ub_format!("overflowing shift by {} in `{}`", r_val, intrinsic_name);
                     } else {
@@ -269,9 +269,9 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                 // rotate_left: (X << (S % BW)) | (X >> ((BW - S) % BW))
                 // rotate_right: (X << ((BW - S) % BW)) | (X >> (S % BW))
                 let layout = self.layout_of(substs.type_at(0))?;
-                let val = self.read_scalar(&args[0])?.check_init()?;
+                let val = self.read_scalar(&args[0])?;
                 let val_bits = val.to_bits(layout.size)?;
-                let raw_shift = self.read_scalar(&args[1])?.check_init()?;
+                let raw_shift = self.read_scalar(&args[1])?;
                 let raw_shift_bits = raw_shift.to_bits(layout.size)?;
                 let width_bits = u128::from(layout.size.bits());
                 let shift_bits = raw_shift_bits % width_bits;
@@ -507,7 +507,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                 self.copy_op(&args[0], dest, /*allow_transmute*/ false)?;
             }
             sym::assume => {
-                let cond = self.read_scalar(&args[0])?.check_init()?.to_bool()?;
+                let cond = self.read_scalar(&args[0])?.to_bool()?;
                 if !cond {
                     throw_ub_format!("`assume` intrinsic called with `false`");
                 }
@@ -570,7 +570,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                 // term since the sign of the second term can be inferred from this and
                 // the fact that the operation has overflowed (if either is 0 no
                 // overflow can occur)
-                let first_term: u128 = l.to_scalar()?.to_bits(l.layout.size)?;
+                let first_term: u128 = l.to_scalar().to_bits(l.layout.size)?;
                 let first_term_positive = first_term & (1 << (num_bits - 1)) == 0;
                 if first_term_positive {
                     // Negative overflow not possible since the positive first term

compiler/rustc_const_eval/src/interpret/machine.rs

@@ -123,18 +123,15 @@ pub trait Machine<'mir, 'tcx>: Sized {
     /// Whether memory accesses should be alignment-checked.
     fn enforce_alignment(ecx: &InterpCx<'mir, 'tcx, Self>) -> bool;
 
-    /// Whether, when checking alignment, we should `force_int` and thus support
+    /// Whether, when checking alignment, we should look at the actual address and thus support
     /// custom alignment logic based on whatever the integer address happens to be.
     ///
-    /// Requires Provenance::OFFSET_IS_ADDR to be true.
-    fn force_int_for_alignment_check(ecx: &InterpCx<'mir, 'tcx, Self>) -> bool;
+    /// If this returns true, Provenance::OFFSET_IS_ADDR must be true.
+    fn use_addr_for_alignment_check(ecx: &InterpCx<'mir, 'tcx, Self>) -> bool;
 
     /// Whether to enforce the validity invariant
     fn enforce_validity(ecx: &InterpCx<'mir, 'tcx, Self>) -> bool;
 
-    /// Whether to enforce integers and floats being initialized.
-    fn enforce_number_init(ecx: &InterpCx<'mir, 'tcx, Self>) -> bool;
-
     /// Whether function calls should be [ABI](CallAbi)-checked.
     fn enforce_abi(_ecx: &InterpCx<'mir, 'tcx, Self>) -> bool {
         true
@@ -437,16 +434,11 @@ pub macro compile_time_machine(<$mir: lifetime, $tcx: lifetime>) {
     type FrameExtra = ();
 
     #[inline(always)]
-    fn force_int_for_alignment_check(_ecx: &InterpCx<$mir, $tcx, Self>) -> bool {
-        // We do not support `force_int`.
+    fn use_addr_for_alignment_check(_ecx: &InterpCx<$mir, $tcx, Self>) -> bool {
+        // We do not support `use_addr`.
         false
     }
 
-    #[inline(always)]
-    fn enforce_number_init(_ecx: &InterpCx<$mir, $tcx, Self>) -> bool {
-        true
-    }
-
     #[inline(always)]
     fn checked_binop_checks_overflow(_ecx: &InterpCx<$mir, $tcx, Self>) -> bool {
         true

compiler/rustc_const_eval/src/interpret/memory.rs

@@ -21,7 +21,6 @@ use rustc_target::abi::{Align, HasDataLayout, Size};
 use super::{
     alloc_range, AllocId, AllocMap, AllocRange, Allocation, CheckInAllocMsg, GlobalAlloc, InterpCx,
     InterpResult, Machine, MayLeak, Pointer, PointerArithmetic, Provenance, Scalar,
-    ScalarMaybeUninit,
 };
 
 #[derive(Debug, PartialEq, Copy, Clone)]
@@ -445,8 +444,8 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                 // Test align. Check this last; if both bounds and alignment are violated
                 // we want the error to be about the bounds.
                 if let Some(align) = align {
-                    if M::force_int_for_alignment_check(self) {
-                        // `force_int_for_alignment_check` can only be true if `OFFSET_IS_ADDR` is true.
+                    if M::use_addr_for_alignment_check(self) {
+                        // `use_addr_for_alignment_check` can only be true if `OFFSET_IS_ADDR` is true.
                         check_offset_align(ptr.addr().bytes(), align)?;
                     } else {
                         // Check allocation alignment and offset alignment.
@@ -901,11 +900,7 @@ impl<'a, 'mir, 'tcx, M: Machine<'mir, 'tcx>> std::fmt::Debug for DumpAllocs<'a,
 /// Reading and writing.
 impl<'tcx, 'a, Prov: Provenance, Extra> AllocRefMut<'a, 'tcx, Prov, Extra> {
     /// `range` is relative to this allocation reference, not the base of the allocation.
-    pub fn write_scalar(
-        &mut self,
-        range: AllocRange,
-        val: ScalarMaybeUninit<Prov>,
-    ) -> InterpResult<'tcx> {
+    pub fn write_scalar(&mut self, range: AllocRange, val: Scalar<Prov>) -> InterpResult<'tcx> {
         let range = self.range.subrange(range);
         debug!("write_scalar at {:?}{range:?}: {val:?}", self.alloc_id);
         Ok(self
@@ -915,11 +910,7 @@ impl<'tcx, 'a, Prov: Provenance, Extra> AllocRefMut<'a, 'tcx, Prov, Extra> {
     }
 
     /// `offset` is relative to this allocation reference, not the base of the allocation.
-    pub fn write_ptr_sized(
-        &mut self,
-        offset: Size,
-        val: ScalarMaybeUninit<Prov>,
-    ) -> InterpResult<'tcx> {
+    pub fn write_ptr_sized(&mut self, offset: Size, val: Scalar<Prov>) -> InterpResult<'tcx> {
         self.write_scalar(alloc_range(offset, self.tcx.data_layout().pointer_size), val)
     }
 
@@ -938,7 +929,7 @@ impl<'tcx, 'a, Prov: Provenance, Extra> AllocRef<'a, 'tcx, Prov, Extra> {
         &self,
         range: AllocRange,
         read_provenance: bool,
-    ) -> InterpResult<'tcx, ScalarMaybeUninit<Prov>> {
+    ) -> InterpResult<'tcx, Scalar<Prov>> {
         let range = self.range.subrange(range);
         let res = self
             .alloc
@@ -949,28 +940,23 @@ impl<'tcx, 'a, Prov: Provenance, Extra> AllocRef<'a, 'tcx, Prov, Extra> {
     }
 
     /// `range` is relative to this allocation reference, not the base of the allocation.
-    pub fn read_integer(&self, range: AllocRange) -> InterpResult<'tcx, ScalarMaybeUninit<Prov>> {
+    pub fn read_integer(&self, range: AllocRange) -> InterpResult<'tcx, Scalar<Prov>> {
         self.read_scalar(range, /*read_provenance*/ false)
     }
 
     /// `offset` is relative to this allocation reference, not the base of the allocation.
-    pub fn read_pointer(&self, offset: Size) -> InterpResult<'tcx, ScalarMaybeUninit<Prov>> {
+    pub fn read_pointer(&self, offset: Size) -> InterpResult<'tcx, Scalar<Prov>> {
         self.read_scalar(
             alloc_range(offset, self.tcx.data_layout().pointer_size),
             /*read_provenance*/ true,
         )
     }
 
     /// `range` is relative to this allocation reference, not the base of the allocation.
-    pub fn check_bytes(
-        &self,
-        range: AllocRange,
-        allow_uninit: bool,
-        allow_ptr: bool,
-    ) -> InterpResult<'tcx> {
+    pub fn check_bytes(&self, range: AllocRange) -> InterpResult<'tcx> {
         Ok(self
             .alloc
-            .check_bytes(&self.tcx, self.range.subrange(range), allow_uninit, allow_ptr)
+            .check_bytes(&self.tcx, self.range.subrange(range))
             .map_err(|e| e.to_interp_error(self.alloc_id))?)
     }