Auto merge of rust-lang#69550 - RalfJung:scalar, r=oli-obk

interpret engine: Scalar cleanup

* Remove `to_ptr`
* Make `to_bits` private

r? @oli-obk

Author: bors

src/librustc/mir/interpret/value.rs

@@ -170,6 +170,10 @@ impl<Tag> From<Double> for Scalar<Tag> {
 }
 
 impl Scalar<()> {
+    /// Make sure the `data` fits in `size`.
+    /// This is guaranteed by all constructors here, but since the enum variants are public,
+    /// it could still be violated (even though no code outside this file should
+    /// construct `Scalar`s).
     #[inline(always)]
     fn check_data(data: u128, size: u8) {
         debug_assert_eq!(
@@ -364,10 +368,10 @@ impl<'tcx, Tag> Scalar<Tag> {
         target_size: Size,
         cx: &impl HasDataLayout,
     ) -> Result<u128, Pointer<Tag>> {
+        assert_ne!(target_size.bytes(), 0, "you should never look at the bits of a ZST");
         match self {
             Scalar::Raw { data, size } => {
                 assert_eq!(target_size.bytes(), size as u64);
-                assert_ne!(size, 0, "you should never look at the bits of a ZST");
                 Scalar::check_data(data, size);
                 Ok(data)
             }
@@ -378,19 +382,15 @@ impl<'tcx, Tag> Scalar<Tag> {
         }
     }
 
-    #[inline(always)]
-    pub fn check_raw(data: u128, size: u8, target_size: Size) {
-        assert_eq!(target_size.bytes(), size as u64);
-        assert_ne!(size, 0, "you should never look at the bits of a ZST");
-        Scalar::check_data(data, size);
-    }
-
-    /// Do not call this method!  Use either `assert_bits` or `force_bits`.
+    /// This method is intentionally private!
+    /// It is just a helper for other methods in this file.
     #[inline]
-    pub fn to_bits(self, target_size: Size) -> InterpResult<'tcx, u128> {
+    fn to_bits(self, target_size: Size) -> InterpResult<'tcx, u128> {
+        assert_ne!(target_size.bytes(), 0, "you should never look at the bits of a ZST");
         match self {
             Scalar::Raw { data, size } => {
-                Self::check_raw(data, size, target_size);
+                assert_eq!(target_size.bytes(), size as u64);
+                Scalar::check_data(data, size);
                 Ok(data)
             }
             Scalar::Ptr(_) => throw_unsup!(ReadPointerAsBytes),
@@ -402,22 +402,14 @@ impl<'tcx, Tag> Scalar<Tag> {
         self.to_bits(target_size).expect("expected Raw bits but got a Pointer")
     }
 
-    /// Do not call this method!  Use either `assert_ptr` or `force_ptr`.
-    /// This method is intentionally private, do not make it public.
     #[inline]
-    fn to_ptr(self) -> InterpResult<'tcx, Pointer<Tag>> {
+    pub fn assert_ptr(self) -> Pointer<Tag> {
         match self {
-            Scalar::Raw { data: 0, .. } => throw_unsup!(InvalidNullPointerUsage),
-            Scalar::Raw { .. } => throw_unsup!(ReadBytesAsPointer),
-            Scalar::Ptr(p) => Ok(p),
+            Scalar::Ptr(p) => p,
+            Scalar::Raw { .. } => bug!("expected a Pointer but got Raw bits"),
         }
     }
 
-    #[inline(always)]
-    pub fn assert_ptr(self) -> Pointer<Tag> {
-        self.to_ptr().expect("expected a Pointer but got Raw bits")
-    }
-
     /// Do not call this method!  Dispatch based on the type instead.
     #[inline]
     pub fn is_bits(self) -> bool {
@@ -595,12 +587,6 @@ impl<'tcx, Tag> ScalarMaybeUndef<Tag> {
         }
     }
 
-    /// Do not call this method!  Use either `assert_bits` or `force_bits`.
-    #[inline(always)]
-    pub fn to_bits(self, target_size: Size) -> InterpResult<'tcx, u128> {
-        self.not_undef()?.to_bits(target_size)
-    }
-
     #[inline(always)]
     pub fn to_bool(self) -> InterpResult<'tcx, bool> {
         self.not_undef()?.to_bool()

src/librustc/ty/sty.rs

@@ -2571,7 +2571,7 @@ impl<'tcx> ConstKind<'tcx> {
 
     #[inline]
     pub fn try_to_bits(&self, size: ty::layout::Size) -> Option<u128> {
-        self.try_to_scalar()?.to_bits(size).ok()
+        if let ConstKind::Value(val) = self { val.try_to_bits(size) } else { None }
     }
 }
 

src/librustc_mir/interpret/intrinsics.rs

@@ -384,7 +384,7 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         // `x % y != 0` or `y == 0` or `x == T::min_value() && y == -1`.
         // First, check x % y != 0 (or if that computation overflows).
         let (res, overflow, _ty) = self.overflowing_binary_op(BinOp::Rem, a, b)?;
-        if overflow || res.to_bits(a.layout.size)? != 0 {
+        if overflow || res.assert_bits(a.layout.size) != 0 {
             // Then, check if `b` is -1, which is the "min_value / -1" case.
             let minus1 = Scalar::from_int(-1, dest.layout.size);
             let b_scalar = b.to_scalar().unwrap();

src/librustc_mir/interpret/operand.rs

@@ -96,40 +96,40 @@ pub struct ImmTy<'tcx, Tag = ()> {
 impl<Tag: Copy> std::fmt::Display for ImmTy<'tcx, Tag> {
     fn fmt(&self, fmt: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         match &self.imm {
-            Immediate::Scalar(ScalarMaybeUndef::Scalar(s)) => match s.to_bits(self.layout.size) {
-                Ok(s) => {
-                    match self.layout.ty.kind {
-                        ty::Int(_) => {
-                            return write!(
-                                fmt,
-                                "{}",
-                                super::sign_extend(s, self.layout.size) as i128,
-                            );
-                        }
-                        ty::Uint(_) => return write!(fmt, "{}", s),
-                        ty::Bool if s == 0 => return fmt.write_str("false"),
-                        ty::Bool if s == 1 => return fmt.write_str("true"),
-                        ty::Char => {
-                            if let Some(c) = u32::try_from(s).ok().and_then(std::char::from_u32) {
-                                return write!(fmt, "{}", c);
-                            }
+            // We cannot use `to_bits_or_ptr` as we do not have a `tcx`.
+            // So we use `is_bits` and circumvent a bunch of sanity checking -- but
+            // this is anyway only for printing.
+            Immediate::Scalar(ScalarMaybeUndef::Scalar(s)) if s.is_ptr() => {
+                fmt.write_str("{pointer}")
+            }
+            Immediate::Scalar(ScalarMaybeUndef::Scalar(s)) => {
+                let s = s.assert_bits(self.layout.size);
+                match self.layout.ty.kind {
+                    ty::Int(_) => {
+                        return write!(fmt, "{}", super::sign_extend(s, self.layout.size) as i128,);
+                    }
+                    ty::Uint(_) => return write!(fmt, "{}", s),
+                    ty::Bool if s == 0 => return fmt.write_str("false"),
+                    ty::Bool if s == 1 => return fmt.write_str("true"),
+                    ty::Char => {
+                        if let Some(c) = u32::try_from(s).ok().and_then(std::char::from_u32) {
+                            return write!(fmt, "{}", c);
                         }
-                        ty::Float(ast::FloatTy::F32) => {
-                            if let Ok(u) = u32::try_from(s) {
-                                return write!(fmt, "{}", f32::from_bits(u));
-                            }
+                    }
+                    ty::Float(ast::FloatTy::F32) => {
+                        if let Ok(u) = u32::try_from(s) {
+                            return write!(fmt, "{}", f32::from_bits(u));
                         }
-                        ty::Float(ast::FloatTy::F64) => {
-                            if let Ok(u) = u64::try_from(s) {
-                                return write!(fmt, "{}", f64::from_bits(u));
-                            }
+                    }
+                    ty::Float(ast::FloatTy::F64) => {
+                        if let Ok(u) = u64::try_from(s) {
+                            return write!(fmt, "{}", f64::from_bits(u));
                         }
-                        _ => {}
                     }
-                    write!(fmt, "{:x}", s)
+                    _ => {}
                 }
-                Err(_) => fmt.write_str("{pointer}"),
-            },
+                write!(fmt, "{:x}", s)
+            }
             Immediate::Scalar(ScalarMaybeUndef::Undef) => fmt.write_str("{undef}"),
             Immediate::ScalarPair(..) => fmt.write_str("{wide pointer or tuple}"),
         }
@@ -205,11 +205,6 @@ impl<'tcx, Tag: Copy> ImmTy<'tcx, Tag> {
     pub fn from_int(i: impl Into<i128>, layout: TyLayout<'tcx>) -> Self {
         Self::from_scalar(Scalar::from_int(i, layout.size), layout)
     }
-
-    #[inline]
-    pub fn to_bits(self) -> InterpResult<'tcx, u128> {
-        self.to_scalar()?.to_bits(self.layout.size)
-    }
 }
 
 // Use the existing layout if given (but sanity check in debug mode),

src/librustc_mir/interpret/validity.rs

@@ -322,16 +322,17 @@ impl<'rt, 'mir, 'tcx, M: Machine<'mir, 'tcx>> ValidityVisitor<'rt, 'mir, 'tcx, M
             ty::Float(_) | ty::Int(_) | ty::Uint(_) => {
                 // NOTE: Keep this in sync with the array optimization for int/float
                 // types below!
-                let size = value.layout.size;
                 let value = value.to_scalar_or_undef();
                 if self.ref_tracking_for_consts.is_some() {
                     // Integers/floats in CTFE: Must be scalar bits, pointers are dangerous
-                    try_validation!(
-                        value.to_bits(size),
-                        value,
-                        self.path,
-                        "initialized plain (non-pointer) bytes"
-                    );
+                    let is_bits = value.not_undef().map_or(false, |v| v.is_bits());
+                    if !is_bits {
+                        throw_validation_failure!(
+                            value,
+                            self.path,
+                            "initialized plain (non-pointer) bytes"
+                        )
+                    }
                 } else {
                     // At run-time, for now, we accept *anything* for these types, including
                     // undef. We should fix that, but let's start low.

src/librustc_mir/transform/const_prop.rs

@@ -545,7 +545,9 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
             let left_ty = left.ty(&self.local_decls, self.tcx);
             let left_size_bits = self.ecx.layout_of(left_ty).ok()?.size.bits();
             let right_size = r.layout.size;
-            let r_bits = r.to_scalar().and_then(|r| r.to_bits(right_size));
+            let r_bits = r.to_scalar().ok();
+            // This is basically `force_bits`.
+            let r_bits = r_bits.and_then(|r| r.to_bits_or_ptr(right_size, &self.tcx).ok());
             if r_bits.map_or(false, |b| b >= left_size_bits as u128) {
                 self.report_assert_as_lint(
                     lint::builtin::ARITHMETIC_OVERFLOW,

src/librustc_mir_build/hair/pattern/_match.rs

@@ -1396,21 +1396,19 @@ impl<'tcx> IntRange<'tcx> {
     ) -> Option<IntRange<'tcx>> {
         if let Some((target_size, bias)) = Self::integral_size_and_signed_bias(tcx, value.ty) {
             let ty = value.ty;
-            let val = if let ty::ConstKind::Value(ConstValue::Scalar(Scalar::Raw { data, size })) =
-                value.val
-            {
-                // For this specific pattern we can skip a lot of effort and go
-                // straight to the result, after doing a bit of checking. (We
-                // could remove this branch and just use the next branch, which
-                // is more general but much slower.)
-                Scalar::<()>::check_raw(data, size, target_size);
-                data
-            } else if let Some(val) = value.try_eval_bits(tcx, param_env, ty) {
-                // This is a more general form of the previous branch.
-                val
-            } else {
-                return None;
-            };
+            let val = (|| {
+                if let ty::ConstKind::Value(ConstValue::Scalar(scalar)) = value.val {
+                    // For this specific pattern we can skip a lot of effort and go
+                    // straight to the result, after doing a bit of checking. (We
+                    // could remove this branch and just fall through, which
+                    // is more general but much slower.)
+                    if let Ok(bits) = scalar.to_bits_or_ptr(target_size, &tcx) {
+                        return Some(bits);
+                    }
+                }
+                // This is a more general form of the previous case.
+                value.try_eval_bits(tcx, param_env, ty)
+            })()?;
             let val = val ^ bias;
             Some(IntRange { range: val..=val, ty, span })
         } else {