Auto merge of #55549 - RalfJung:miri-visitor, r=oli-obk

Value visitors for miri

Generalize the traversal part of validation to a `ValueVisitor`.

~~This includes #55316, [click here](RalfJung/rust@retagging...RalfJung:miri-visitor) for just the new commits.~~

src/librustc/mir/interpret/error.rs

@@ -15,7 +15,7 @@ use ty::{Ty, layout};
 use ty::layout::{Size, Align, LayoutError};
 use rustc_target::spec::abi::Abi;
 
-use super::Pointer;
+use super::{Pointer, Scalar};
 
 use backtrace::Backtrace;
 
@@ -240,7 +240,7 @@ pub enum EvalErrorKind<'tcx, O> {
     InvalidMemoryAccess,
     InvalidFunctionPointer,
     InvalidBool,
-    InvalidDiscriminant(u128),
+    InvalidDiscriminant(Scalar),
     PointerOutOfBounds {
         ptr: Pointer,
         access: bool,

src/librustc/mir/interpret/mod.rs

@@ -91,42 +91,43 @@ pub trait PointerArithmetic: layout::HasDataLayout {
     }
 
     //// Trunace the given value to the pointer size; also return whether there was an overflow
+    #[inline]
     fn truncate_to_ptr(&self, val: u128) -> (u64, bool) {
         let max_ptr_plus_1 = 1u128 << self.pointer_size().bits();
         ((val % max_ptr_plus_1) as u64, val >= max_ptr_plus_1)
     }
 
-    // Overflow checking only works properly on the range from -u64 to +u64.
-    fn overflowing_signed_offset(&self, val: u64, i: i128) -> (u64, bool) {
-        // FIXME: is it possible to over/underflow here?
-        if i < 0 {
-            // trickery to ensure that i64::min_value() works fine
-            // this formula only works for true negative values, it panics for zero!
-            let n = u64::max_value() - (i as u64) + 1;
-            val.overflowing_sub(n)
-        } else {
-            self.overflowing_offset(val, i as u64)
-        }
+    #[inline]
+    fn offset<'tcx>(&self, val: u64, i: u64) -> EvalResult<'tcx, u64> {
+        let (res, over) = self.overflowing_offset(val, i);
+        if over { err!(Overflow(mir::BinOp::Add)) } else { Ok(res) }
     }
 
+    #[inline]
     fn overflowing_offset(&self, val: u64, i: u64) -> (u64, bool) {
         let (res, over1) = val.overflowing_add(i);
-        let (res, over2) = self.truncate_to_ptr(res as u128);
+        let (res, over2) = self.truncate_to_ptr(u128::from(res));
         (res, over1 || over2)
     }
 
+    #[inline]
     fn signed_offset<'tcx>(&self, val: u64, i: i64) -> EvalResult<'tcx, u64> {
-        let (res, over) = self.overflowing_signed_offset(val, i as i128);
+        let (res, over) = self.overflowing_signed_offset(val, i128::from(i));
         if over { err!(Overflow(mir::BinOp::Add)) } else { Ok(res) }
     }
 
-    fn offset<'tcx>(&self, val: u64, i: u64) -> EvalResult<'tcx, u64> {
-        let (res, over) = self.overflowing_offset(val, i);
-        if over { err!(Overflow(mir::BinOp::Add)) } else { Ok(res) }
-    }
-
-    fn wrapping_signed_offset(&self, val: u64, i: i64) -> u64 {
-        self.overflowing_signed_offset(val, i as i128).0
+    // Overflow checking only works properly on the range from -u64 to +u64.
+    #[inline]
+    fn overflowing_signed_offset(&self, val: u64, i: i128) -> (u64, bool) {
+        // FIXME: is it possible to over/underflow here?
+        if i < 0 {
+            // trickery to ensure that i64::min_value() works fine
+            // this formula only works for true negative values, it panics for zero!
+            let n = u64::max_value() - (i as u64) + 1;
+            val.overflowing_sub(n)
+        } else {
+            self.overflowing_offset(val, i as u64)
+        }
     }
 }
 
@@ -176,19 +177,27 @@ impl<'tcx, Tag> Pointer<Tag> {
         Pointer { alloc_id, offset, tag }
     }
 
-    pub fn wrapping_signed_offset(self, i: i64, cx: &impl HasDataLayout) -> Self {
-        Pointer::new_with_tag(
+    #[inline]
+    pub fn offset(self, i: Size, cx: &impl HasDataLayout) -> EvalResult<'tcx, Self> {
+        Ok(Pointer::new_with_tag(
             self.alloc_id,
-            Size::from_bytes(cx.data_layout().wrapping_signed_offset(self.offset.bytes(), i)),
-            self.tag,
-        )
+            Size::from_bytes(cx.data_layout().offset(self.offset.bytes(), i.bytes())?),
+            self.tag
+        ))
     }
 
-    pub fn overflowing_signed_offset(self, i: i128, cx: &impl HasDataLayout) -> (Self, bool) {
-        let (res, over) = cx.data_layout().overflowing_signed_offset(self.offset.bytes(), i);
+    #[inline]
+    pub fn overflowing_offset(self, i: Size, cx: &impl HasDataLayout) -> (Self, bool) {
+        let (res, over) = cx.data_layout().overflowing_offset(self.offset.bytes(), i.bytes());
         (Pointer::new_with_tag(self.alloc_id, Size::from_bytes(res), self.tag), over)
     }
 
+    #[inline(always)]
+    pub fn wrapping_offset(self, i: Size, cx: &impl HasDataLayout) -> Self {
+        self.overflowing_offset(i, cx).0
+    }
+
+    #[inline]
     pub fn signed_offset(self, i: i64, cx: &impl HasDataLayout) -> EvalResult<'tcx, Self> {
         Ok(Pointer::new_with_tag(
             self.alloc_id,
@@ -197,20 +206,18 @@ impl<'tcx, Tag> Pointer<Tag> {
         ))
     }
 
-    pub fn overflowing_offset(self, i: Size, cx: &impl HasDataLayout) -> (Self, bool) {
-        let (res, over) = cx.data_layout().overflowing_offset(self.offset.bytes(), i.bytes());
+    #[inline]
+    pub fn overflowing_signed_offset(self, i: i128, cx: &impl HasDataLayout) -> (Self, bool) {
+        let (res, over) = cx.data_layout().overflowing_signed_offset(self.offset.bytes(), i);
         (Pointer::new_with_tag(self.alloc_id, Size::from_bytes(res), self.tag), over)
     }
 
-    pub fn offset(self, i: Size, cx: &impl HasDataLayout) -> EvalResult<'tcx, Self> {
-        Ok(Pointer::new_with_tag(
-            self.alloc_id,
-            Size::from_bytes(cx.data_layout().offset(self.offset.bytes(), i.bytes())?),
-            self.tag
-        ))
+    #[inline(always)]
+    pub fn wrapping_signed_offset(self, i: i64, cx: &impl HasDataLayout) -> Self {
+        self.overflowing_signed_offset(i128::from(i), cx).0
     }
 
-    #[inline]
+    #[inline(always)]
     pub fn erase_tag(self) -> Pointer {
         Pointer { alloc_id: self.alloc_id, offset: self.offset, tag: () }
     }

src/librustc/mir/interpret/value.rs

@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#![allow(unknown_lints)]
+use std::fmt;
 
 use ty::layout::{HasDataLayout, Size};
 use ty::subst::Substs;
@@ -99,6 +99,15 @@ pub enum Scalar<Tag=(), Id=AllocId> {
     Ptr(Pointer<Tag, Id>),
 }
 
+impl<Tag> fmt::Display for Scalar<Tag> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            Scalar::Ptr(_) => write!(f, "a pointer"),
+            Scalar::Bits { bits, .. } => write!(f, "{}", bits),
+        }
+    }
+}
+
 impl<'tcx> Scalar<()> {
     #[inline]
     pub fn with_default_tag<Tag>(self) -> Scalar<Tag>
@@ -134,32 +143,47 @@ impl<'tcx, Tag> Scalar<Tag> {
     }
 
     #[inline]
-    pub fn ptr_signed_offset(self, i: i64, cx: &impl HasDataLayout) -> EvalResult<'tcx, Self> {
+    pub fn ptr_offset(self, i: Size, cx: &impl HasDataLayout) -> EvalResult<'tcx, Self> {
         let dl = cx.data_layout();
         match self {
             Scalar::Bits { bits, size } => {
                 assert_eq!(size as u64, dl.pointer_size.bytes());
                 Ok(Scalar::Bits {
-                    bits: dl.signed_offset(bits as u64, i)? as u128,
+                    bits: dl.offset(bits as u64, i.bytes())? as u128,
                     size,
                 })
             }
-            Scalar::Ptr(ptr) => ptr.signed_offset(i, dl).map(Scalar::Ptr),
+            Scalar::Ptr(ptr) => ptr.offset(i, dl).map(Scalar::Ptr),
         }
     }
 
     #[inline]
-    pub fn ptr_offset(self, i: Size, cx: &impl HasDataLayout) -> EvalResult<'tcx, Self> {
+    pub fn ptr_wrapping_offset(self, i: Size, cx: &impl HasDataLayout) -> Self {
         let dl = cx.data_layout();
         match self {
             Scalar::Bits { bits, size } => {
                 assert_eq!(size as u64, dl.pointer_size.bytes());
+                Scalar::Bits {
+                    bits: dl.overflowing_offset(bits as u64, i.bytes()).0 as u128,
+                    size,
+                }
+            }
+            Scalar::Ptr(ptr) => Scalar::Ptr(ptr.wrapping_offset(i, dl)),
+        }
+    }
+
+    #[inline]
+    pub fn ptr_signed_offset(self, i: i64, cx: &impl HasDataLayout) -> EvalResult<'tcx, Self> {
+        let dl = cx.data_layout();
+        match self {
+            Scalar::Bits { bits, size } => {
+                assert_eq!(size as u64, dl.pointer_size().bytes());
                 Ok(Scalar::Bits {
-                    bits: dl.offset(bits as u64, i.bytes())? as u128,
+                    bits: dl.signed_offset(bits as u64, i)? as u128,
                     size,
                 })
             }
-            Scalar::Ptr(ptr) => ptr.offset(i, dl).map(Scalar::Ptr),
+            Scalar::Ptr(ptr) => ptr.signed_offset(i, dl).map(Scalar::Ptr),
         }
     }
 
@@ -170,14 +194,27 @@ impl<'tcx, Tag> Scalar<Tag> {
             Scalar::Bits { bits, size } => {
                 assert_eq!(size as u64, dl.pointer_size.bytes());
                 Scalar::Bits {
-                    bits: dl.wrapping_signed_offset(bits as u64, i) as u128,
+                    bits: dl.overflowing_signed_offset(bits as u64, i128::from(i)).0 as u128,
                     size,
                 }
             }
             Scalar::Ptr(ptr) => Scalar::Ptr(ptr.wrapping_signed_offset(i, dl)),
         }
     }
 
+    /// Returns this pointers offset from the allocation base, or from NULL (for
+    /// integer pointers).
+    #[inline]
+    pub fn get_ptr_offset(self, cx: &impl HasDataLayout) -> Size {
+        match self {
+            Scalar::Bits { bits, size } => {
+                assert_eq!(size as u64, cx.pointer_size().bytes());
+                Size::from_bytes(bits as u64)
+            }
+            Scalar::Ptr(ptr) => ptr.offset,
+        }
+    }
+
     #[inline]
     pub fn is_null_ptr(self, cx: &impl HasDataLayout) -> bool {
         match self {

src/librustc_mir/const_eval.rs

@@ -539,10 +539,10 @@ fn validate_const<'a, 'tcx>(
     let val = (|| {
         let op = ecx.const_to_op(constant)?;
         let mut ref_tracking = RefTracking::new(op);
-        while let Some((op, mut path)) = ref_tracking.todo.pop() {
+        while let Some((op, path)) = ref_tracking.todo.pop() {
             ecx.validate_operand(
                 op,
-                &mut path,
+                path,
                 Some(&mut ref_tracking),
                 /* const_mode */ true,
             )?;

src/librustc_mir/interpret/eval_context.rs

@@ -521,7 +521,7 @@ impl<'a, 'mir, 'tcx: 'mir, M: Machine<'a, 'mir, 'tcx>> EvalContext<'a, 'mir, 'tc
                 // return place is always a local and then this cannot happen.
                 self.validate_operand(
                     self.place_to_op(return_place)?,
-                    &mut vec![],
+                    vec![],
                     None,
                     /*const_mode*/false,
                 )?;

src/librustc_mir/interpret/machine.rs

@@ -17,11 +17,11 @@ use std::hash::Hash;
 
 use rustc::hir::{self, def_id::DefId};
 use rustc::mir;
-use rustc::ty::{self, Ty, layout::{Size, TyLayout}, query::TyCtxtAt};
+use rustc::ty::{self, layout::{Size, TyLayout}, query::TyCtxtAt};
 
 use super::{
     Allocation, AllocId, EvalResult, Scalar,
-    EvalContext, PlaceTy, OpTy, Pointer, MemPlace, MemoryKind,
+    EvalContext, PlaceTy, MPlaceTy, OpTy, Pointer, MemoryKind,
 };
 
 /// Whether this kind of memory is allowed to leak
@@ -217,26 +217,22 @@ pub trait Machine<'a, 'mir, 'tcx>: Sized {
     #[inline]
     fn tag_reference(
         _ecx: &mut EvalContext<'a, 'mir, 'tcx, Self>,
-        place: MemPlace<Self::PointerTag>,
-        _ty: Ty<'tcx>,
-        _size: Size,
+        place: MPlaceTy<'tcx, Self::PointerTag>,
         _mutability: Option<hir::Mutability>,
-    ) -> EvalResult<'tcx, MemPlace<Self::PointerTag>> {
-        Ok(place)
+    ) -> EvalResult<'tcx, Scalar<Self::PointerTag>> {
+        Ok(place.ptr)
     }
 
     /// Executed when evaluating the `*` operator: Following a reference.
-    /// This has the change to adjust the tag.  It should not change anything else!
+    /// This has the chance to adjust the tag.  It should not change anything else!
     /// `mutability` can be `None` in case a raw ptr is being dereferenced.
     #[inline]
     fn tag_dereference(
         _ecx: &EvalContext<'a, 'mir, 'tcx, Self>,
-        place: MemPlace<Self::PointerTag>,
-        _ty: Ty<'tcx>,
-        _size: Size,
+        place: MPlaceTy<'tcx, Self::PointerTag>,
         _mutability: Option<hir::Mutability>,
-    ) -> EvalResult<'tcx, MemPlace<Self::PointerTag>> {
-        Ok(place)
+    ) -> EvalResult<'tcx, Scalar<Self::PointerTag>> {
+        Ok(place.ptr)
     }
 
     /// Execute a validation operation

src/librustc_mir/interpret/mod.rs

@@ -23,6 +23,7 @@ mod terminator;
 mod traits;
 mod validity;
 mod intrinsics;
+mod visitor;
 
 pub use rustc::mir::interpret::*; // have all the `interpret` symbols in one place: here
 
@@ -38,4 +39,6 @@ pub use self::machine::{Machine, AllocMap, MayLeak};
 
 pub use self::operand::{ScalarMaybeUndef, Immediate, ImmTy, Operand, OpTy};
 
+pub use self::visitor::ValueVisitor;
+
 pub use self::validity::RefTracking;

src/librustc_mir/interpret/operand.rs

@@ -12,6 +12,7 @@
 //! All high-level functions to read from memory work on operands as sources.
 
 use std::convert::TryInto;
+use std::fmt;
 
 use rustc::{mir, ty};
 use rustc::ty::layout::{self, Size, LayoutOf, TyLayout, HasDataLayout, IntegerExt};
@@ -36,6 +37,15 @@ impl<Tag> From<Scalar<Tag>> for ScalarMaybeUndef<Tag> {
     }
 }
 
+impl<Tag> fmt::Display for ScalarMaybeUndef<Tag> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            ScalarMaybeUndef::Undef => write!(f, "uninitialized bytes"),
+            ScalarMaybeUndef::Scalar(s) => write!(f, "{}", s),
+        }
+    }
+}
+
 impl<'tcx> ScalarMaybeUndef<()> {
     #[inline]
     pub fn with_default_tag<Tag>(self) -> ScalarMaybeUndef<Tag>
@@ -732,8 +742,12 @@ impl<'a, 'mir, 'tcx, M: Machine<'a, 'mir, 'tcx>> EvalContext<'a, 'mir, 'tcx, M>
         Ok(match rval.layout.variants {
             layout::Variants::Single { .. } => bug!(),
             layout::Variants::Tagged { .. } => {
+                let bits_discr = match raw_discr.to_bits(discr_val.layout.size) {
+                    Ok(raw_discr) => raw_discr,
+                    Err(_) => return err!(InvalidDiscriminant(raw_discr.erase_tag())),
+                };
                 let real_discr = if discr_val.layout.ty.is_signed() {
-                    let i = raw_discr.to_bits(discr_val.layout.size)? as i128;
+                    let i = bits_discr as i128;
                     // going from layout tag type to typeck discriminant type
                     // requires first sign extending with the layout discriminant
                     let shift = 128 - discr_val.layout.size.bits();
@@ -748,15 +762,15 @@ impl<'a, 'mir, 'tcx, M: Machine<'a, 'mir, 'tcx>> EvalContext<'a, 'mir, 'tcx, M>
                     let truncatee = sexted as u128;
                     (truncatee << shift) >> shift
                 } else {
-                    raw_discr.to_bits(discr_val.layout.size)?
+                    bits_discr
                 };
                 // Make sure we catch invalid discriminants
                 let index = rval.layout.ty
                     .ty_adt_def()
                     .expect("tagged layout for non adt")
                     .discriminants(self.tcx.tcx)
                     .position(|var| var.val == real_discr)
-                    .ok_or_else(|| EvalErrorKind::InvalidDiscriminant(real_discr))?;
+                    .ok_or_else(|| EvalErrorKind::InvalidDiscriminant(raw_discr.erase_tag()))?;
                 (real_discr, index)
             },
             layout::Variants::NicheFilling {