Auto merge of rust-lang#124113 - RalfJung:interpret-scalar-ops, r=oli-obk

interpret: use ScalarInt for bin-ops; avoid PartialOrd for ScalarInt

Best reviewed commit-by-commit

r? `@oli-obk`

Author: bors

compiler/rustc_codegen_cranelift/src/constant.rs

@@ -110,7 +110,7 @@ pub(crate) fn codegen_const_value<'tcx>(
                 if fx.clif_type(layout.ty).is_some() {
                     return CValue::const_val(fx, layout, int);
                 } else {
-                    let raw_val = int.size().truncate(int.to_bits(int.size()).unwrap());
+                    let raw_val = int.size().truncate(int.assert_bits(int.size()));
                     let val = match int.size().bytes() {
                         1 => fx.bcx.ins().iconst(types::I8, raw_val as i64),
                         2 => fx.bcx.ins().iconst(types::I16, raw_val as i64),
@@ -491,27 +491,24 @@ pub(crate) fn mir_operand_get_const_val<'tcx>(
                                         return None;
                                     }
                                     let scalar_int = mir_operand_get_const_val(fx, operand)?;
-                                    let scalar_int = match fx
-                                        .layout_of(*ty)
-                                        .size
-                                        .cmp(&scalar_int.size())
-                                    {
-                                        Ordering::Equal => scalar_int,
-                                        Ordering::Less => match ty.kind() {
-                                            ty::Uint(_) => ScalarInt::try_from_uint(
-                                                scalar_int.try_to_uint(scalar_int.size()).unwrap(),
-                                                fx.layout_of(*ty).size,
-                                            )
-                                            .unwrap(),
-                                            ty::Int(_) => ScalarInt::try_from_int(
-                                                scalar_int.try_to_int(scalar_int.size()).unwrap(),
-                                                fx.layout_of(*ty).size,
-                                            )
-                                            .unwrap(),
-                                            _ => unreachable!(),
-                                        },
-                                        Ordering::Greater => return None,
-                                    };
+                                    let scalar_int =
+                                        match fx.layout_of(*ty).size.cmp(&scalar_int.size()) {
+                                            Ordering::Equal => scalar_int,
+                                            Ordering::Less => match ty.kind() {
+                                                ty::Uint(_) => ScalarInt::try_from_uint(
+                                                    scalar_int.assert_uint(scalar_int.size()),
+                                                    fx.layout_of(*ty).size,
+                                                )
+                                                .unwrap(),
+                                                ty::Int(_) => ScalarInt::try_from_int(
+                                                    scalar_int.assert_int(scalar_int.size()),
+                                                    fx.layout_of(*ty).size,
+                                                )
+                                                .unwrap(),
+                                                _ => unreachable!(),
+                                            },
+                                            Ordering::Greater => return None,
+                                        };
                                     computed_scalar_int = Some(scalar_int);
                                 }
                                 Rvalue::Use(operand) => {

compiler/rustc_codegen_cranelift/src/value_and_place.rs

@@ -326,7 +326,7 @@ impl<'tcx> CValue<'tcx> {
 
         let val = match layout.ty.kind() {
             ty::Uint(UintTy::U128) | ty::Int(IntTy::I128) => {
-                let const_val = const_val.to_bits(layout.size).unwrap();
+                let const_val = const_val.assert_bits(layout.size);
                 let lsb = fx.bcx.ins().iconst(types::I64, const_val as u64 as i64);
                 let msb = fx.bcx.ins().iconst(types::I64, (const_val >> 64) as u64 as i64);
                 fx.bcx.ins().iconcat(lsb, msb)
@@ -338,7 +338,7 @@ impl<'tcx> CValue<'tcx> {
             | ty::Ref(..)
             | ty::RawPtr(..)
             | ty::FnPtr(..) => {
-                let raw_val = const_val.size().truncate(const_val.to_bits(layout.size).unwrap());
+                let raw_val = const_val.size().truncate(const_val.assert_bits(layout.size));
                 fx.bcx.ins().iconst(clif_ty, raw_val as i64)
             }
             ty::Float(FloatTy::F32) => {

compiler/rustc_const_eval/src/interpret/discriminant.rs

@@ -295,8 +295,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                         &niche_start_val,
                     )?
                     .to_scalar()
-                    .try_to_int()
-                    .unwrap();
+                    .assert_int();
                 Ok(Some((tag, tag_field)))
             }
         }

compiler/rustc_const_eval/src/interpret/operand.rs

@@ -6,9 +6,10 @@ use std::assert_matches::assert_matches;
 use either::{Either, Left, Right};
 
 use rustc_hir::def::Namespace;
+use rustc_middle::mir::interpret::ScalarSizeMismatch;
 use rustc_middle::ty::layout::{LayoutOf, TyAndLayout};
 use rustc_middle::ty::print::{FmtPrinter, PrettyPrinter};
-use rustc_middle::ty::{ConstInt, Ty, TyCtxt};
+use rustc_middle::ty::{ConstInt, ScalarInt, Ty, TyCtxt};
 use rustc_middle::{mir, ty};
 use rustc_target::abi::{self, Abi, HasDataLayout, Size};
 
@@ -210,6 +211,12 @@ impl<'tcx, Prov: Provenance> ImmTy<'tcx, Prov> {
         ImmTy { imm: Immediate::Uninit, layout }
     }
 
+    #[inline]
+    pub fn from_scalar_int(s: ScalarInt, layout: TyAndLayout<'tcx>) -> Self {
+        assert_eq!(s.size(), layout.size);
+        Self::from_scalar(Scalar::from(s), layout)
+    }
+
     #[inline]
     pub fn try_from_uint(i: impl Into<u128>, layout: TyAndLayout<'tcx>) -> Option<Self> {
         Some(Self::from_scalar(Scalar::try_from_uint(i, layout.size)?, layout))
@@ -223,7 +230,6 @@ impl<'tcx, Prov: Provenance> ImmTy<'tcx, Prov> {
     pub fn try_from_int(i: impl Into<i128>, layout: TyAndLayout<'tcx>) -> Option<Self> {
         Some(Self::from_scalar(Scalar::try_from_int(i, layout.size)?, layout))
     }
-
     #[inline]
     pub fn from_int(i: impl Into<i128>, layout: TyAndLayout<'tcx>) -> Self {
         Self::from_scalar(Scalar::from_int(i, layout.size), layout)
@@ -242,6 +248,20 @@ impl<'tcx, Prov: Provenance> ImmTy<'tcx, Prov> {
         Self::from_scalar(Scalar::from_i8(c as i8), layout)
     }
 
+    /// Return the immediate as a `ScalarInt`. Ensures that it has the size that the layout of the
+    /// immediate indicates.
+    #[inline]
+    pub fn to_scalar_int(&self) -> InterpResult<'tcx, ScalarInt> {
+        let s = self.to_scalar().to_scalar_int()?;
+        if s.size() != self.layout.size {
+            throw_ub!(ScalarSizeMismatch(ScalarSizeMismatch {
+                target_size: self.layout.size.bytes(),
+                data_size: s.size().bytes(),
+            }));
+        }
+        Ok(s)
+    }
+
     #[inline]
     pub fn to_const_int(self) -> ConstInt {
         assert!(self.layout.ty.is_integral());

compiler/rustc_const_eval/src/interpret/operator.rs

@@ -2,7 +2,7 @@ use rustc_apfloat::{Float, FloatConvert};
 use rustc_middle::mir;
 use rustc_middle::mir::interpret::{InterpResult, Scalar};
 use rustc_middle::ty::layout::{LayoutOf, TyAndLayout};
-use rustc_middle::ty::{self, FloatTy, Ty};
+use rustc_middle::ty::{self, FloatTy, ScalarInt, Ty};
 use rustc_span::symbol::sym;
 use rustc_target::abi::Abi;
 
@@ -146,14 +146,20 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
     fn binary_int_op(
         &self,
         bin_op: mir::BinOp,
-        // passing in raw bits
-        l: u128,
-        left_layout: TyAndLayout<'tcx>,
-        r: u128,
-        right_layout: TyAndLayout<'tcx>,
+        left: &ImmTy<'tcx, M::Provenance>,
+        right: &ImmTy<'tcx, M::Provenance>,
     ) -> InterpResult<'tcx, (ImmTy<'tcx, M::Provenance>, bool)> {
         use rustc_middle::mir::BinOp::*;
 
+        // This checks the size, so that we can just assert it below.
+        let l = left.to_scalar_int()?;
+        let r = right.to_scalar_int()?;
+        // Prepare to convert the values to signed or unsigned form.
+        let l_signed = || l.assert_int(left.layout.size);
+        let l_unsigned = || l.assert_uint(left.layout.size);
+        let r_signed = || r.assert_int(right.layout.size);
+        let r_unsigned = || r.assert_uint(right.layout.size);
+
         let throw_ub_on_overflow = match bin_op {
             AddUnchecked => Some(sym::unchecked_add),
             SubUnchecked => Some(sym::unchecked_sub),
@@ -165,69 +171,72 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
 
         // Shift ops can have an RHS with a different numeric type.
         if matches!(bin_op, Shl | ShlUnchecked | Shr | ShrUnchecked) {
-            let size = left_layout.size.bits();
+            let size = left.layout.size.bits();
             // The shift offset is implicitly masked to the type size. (This is the one MIR operator
             // that does *not* directly map to a single LLVM operation.) Compute how much we
             // actually shift and whether there was an overflow due to shifting too much.
-            let (shift_amount, overflow) = if right_layout.abi.is_signed() {
-                let shift_amount = self.sign_extend(r, right_layout) as i128;
+            let (shift_amount, overflow) = if right.layout.abi.is_signed() {
+                let shift_amount = r_signed();
                 let overflow = shift_amount < 0 || shift_amount >= i128::from(size);
+                // Deliberately wrapping `as` casts: shift_amount *can* be negative, but the result
+                // of the `as` will be equal modulo `size` (since it is a power of two).
                 let masked_amount = (shift_amount as u128) % u128::from(size);
-                debug_assert_eq!(overflow, shift_amount != (masked_amount as i128));
+                assert_eq!(overflow, shift_amount != (masked_amount as i128));
                 (masked_amount, overflow)
             } else {
-                let shift_amount = r;
+                let shift_amount = r_unsigned();
                 let masked_amount = shift_amount % u128::from(size);
                 (masked_amount, shift_amount != masked_amount)
             };
             let shift_amount = u32::try_from(shift_amount).unwrap(); // we masked so this will always fit
             // Compute the shifted result.
-            let result = if left_layout.abi.is_signed() {
-                let l = self.sign_extend(l, left_layout) as i128;
+            let result = if left.layout.abi.is_signed() {
+                let l = l_signed();
                 let result = match bin_op {
                     Shl | ShlUnchecked => l.checked_shl(shift_amount).unwrap(),
                     Shr | ShrUnchecked => l.checked_shr(shift_amount).unwrap(),
                     _ => bug!(),
                 };
-                result as u128
+                ScalarInt::truncate_from_int(result, left.layout.size).0
             } else {
-                match bin_op {
+                let l = l_unsigned();
+                let result = match bin_op {
                     Shl | ShlUnchecked => l.checked_shl(shift_amount).unwrap(),
                     Shr | ShrUnchecked => l.checked_shr(shift_amount).unwrap(),
                     _ => bug!(),
-                }
+                };
+                ScalarInt::truncate_from_uint(result, left.layout.size).0
             };
-            let truncated = self.truncate(result, left_layout);
 
             if overflow && let Some(intrinsic_name) = throw_ub_on_overflow {
                 throw_ub_custom!(
                     fluent::const_eval_overflow_shift,
-                    val = if right_layout.abi.is_signed() {
-                        (self.sign_extend(r, right_layout) as i128).to_string()
+                    val = if right.layout.abi.is_signed() {
+                        r_signed().to_string()
                     } else {
-                        r.to_string()
+                        r_unsigned().to_string()
                     },
                     name = intrinsic_name
                 );
             }
 
-            return Ok((ImmTy::from_uint(truncated, left_layout), overflow));
+            return Ok((ImmTy::from_scalar_int(result, left.layout), overflow));
         }
 
         // For the remaining ops, the types must be the same on both sides
-        if left_layout.ty != right_layout.ty {
+        if left.layout.ty != right.layout.ty {
             span_bug!(
                 self.cur_span(),
                 "invalid asymmetric binary op {bin_op:?}: {l:?} ({l_ty}), {r:?} ({r_ty})",
-                l_ty = left_layout.ty,
-                r_ty = right_layout.ty,
+                l_ty = left.layout.ty,
+                r_ty = right.layout.ty,
             )
         }
 
-        let size = left_layout.size;
+        let size = left.layout.size;
 
         // Operations that need special treatment for signed integers
-        if left_layout.abi.is_signed() {
+        if left.layout.abi.is_signed() {
             let op: Option<fn(&i128, &i128) -> bool> = match bin_op {
                 Lt => Some(i128::lt),
                 Le => Some(i128::le),
@@ -236,18 +245,14 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                 _ => None,
             };
             if let Some(op) = op {
-                let l = self.sign_extend(l, left_layout) as i128;
-                let r = self.sign_extend(r, right_layout) as i128;
-                return Ok((ImmTy::from_bool(op(&l, &r), *self.tcx), false));
+                return Ok((ImmTy::from_bool(op(&l_signed(), &r_signed()), *self.tcx), false));
             }
             if bin_op == Cmp {
-                let l = self.sign_extend(l, left_layout) as i128;
-                let r = self.sign_extend(r, right_layout) as i128;
-                return Ok(self.three_way_compare(l, r));
+                return Ok(self.three_way_compare(l_signed(), r_signed()));
             }
             let op: Option<fn(i128, i128) -> (i128, bool)> = match bin_op {
-                Div if r == 0 => throw_ub!(DivisionByZero),
-                Rem if r == 0 => throw_ub!(RemainderByZero),
+                Div if r.is_null() => throw_ub!(DivisionByZero),
+                Rem if r.is_null() => throw_ub!(RemainderByZero),
                 Div => Some(i128::overflowing_div),
                 Rem => Some(i128::overflowing_rem),
                 Add | AddUnchecked => Some(i128::overflowing_add),
@@ -256,8 +261,8 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                 _ => None,
             };
             if let Some(op) = op {
-                let l = self.sign_extend(l, left_layout) as i128;
-                let r = self.sign_extend(r, right_layout) as i128;
+                let l = l_signed();
+                let r = r_signed();
 
                 // We need a special check for overflowing Rem and Div since they are *UB*
                 // on overflow, which can happen with "int_min $OP -1".
@@ -272,17 +277,19 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                 }
 
                 let (result, oflo) = op(l, r);
-                // This may be out-of-bounds for the result type, so we have to truncate ourselves.
+                // This may be out-of-bounds for the result type, so we have to truncate.
                 // If that truncation loses any information, we have an overflow.
-                let result = result as u128;
-                let truncated = self.truncate(result, left_layout);
-                let overflow = oflo || self.sign_extend(truncated, left_layout) != result;
+                let (result, lossy) = ScalarInt::truncate_from_int(result, left.layout.size);
+                let overflow = oflo || lossy;
                 if overflow && let Some(intrinsic_name) = throw_ub_on_overflow {
                     throw_ub_custom!(fluent::const_eval_overflow, name = intrinsic_name);
                 }
-                return Ok((ImmTy::from_uint(truncated, left_layout), overflow));
+                return Ok((ImmTy::from_scalar_int(result, left.layout), overflow));
             }
         }
+        // From here on it's okay to treat everything as unsigned.
+        let l = l_unsigned();
+        let r = r_unsigned();
 
         if bin_op == Cmp {
             return Ok(self.three_way_compare(l, r));
@@ -297,12 +304,12 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
             Gt => ImmTy::from_bool(l > r, *self.tcx),
             Ge => ImmTy::from_bool(l >= r, *self.tcx),
 
-            BitOr => ImmTy::from_uint(l | r, left_layout),
-            BitAnd => ImmTy::from_uint(l & r, left_layout),
-            BitXor => ImmTy::from_uint(l ^ r, left_layout),
+            BitOr => ImmTy::from_uint(l | r, left.layout),
+            BitAnd => ImmTy::from_uint(l & r, left.layout),
+            BitXor => ImmTy::from_uint(l ^ r, left.layout),
 
             Add | AddUnchecked | Sub | SubUnchecked | Mul | MulUnchecked | Rem | Div => {
-                assert!(!left_layout.abi.is_signed());
+                assert!(!left.layout.abi.is_signed());
                 let op: fn(u128, u128) -> (u128, bool) = match bin_op {
                     Add | AddUnchecked => u128::overflowing_add,
                     Sub | SubUnchecked => u128::overflowing_sub,
@@ -316,21 +323,21 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                 let (result, oflo) = op(l, r);
                 // Truncate to target type.
                 // If that truncation loses any information, we have an overflow.
-                let truncated = self.truncate(result, left_layout);
-                let overflow = oflo || truncated != result;
+                let (result, lossy) = ScalarInt::truncate_from_uint(result, left.layout.size);
+                let overflow = oflo || lossy;
                 if overflow && let Some(intrinsic_name) = throw_ub_on_overflow {
                     throw_ub_custom!(fluent::const_eval_overflow, name = intrinsic_name);
                 }
-                return Ok((ImmTy::from_uint(truncated, left_layout), overflow));
+                return Ok((ImmTy::from_scalar_int(result, left.layout), overflow));
             }
 
             _ => span_bug!(
                 self.cur_span(),
                 "invalid binary op {:?}: {:?}, {:?} (both {})",
                 bin_op,
-                l,
-                r,
-                right_layout.ty,
+                left,
+                right,
+                right.layout.ty,
             ),
         };
 
@@ -427,9 +434,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                     right.layout.ty
                 );
 
-                let l = left.to_scalar().to_bits(left.layout.size)?;
-                let r = right.to_scalar().to_bits(right.layout.size)?;
-                self.binary_int_op(bin_op, l, left.layout, r, right.layout)
+                self.binary_int_op(bin_op, left, right)
             }
             _ if left.layout.ty.is_any_ptr() => {
                 // The RHS type must be a `pointer` *or an integer type* (for `Offset`).

compiler/rustc_middle/src/mir/consts.rs

@@ -87,7 +87,7 @@ impl<'tcx> ConstValue<'tcx> {
     }
 
     pub fn try_to_bits(&self, size: Size) -> Option<u128> {
-        self.try_to_scalar_int()?.to_bits(size).ok()
+        self.try_to_scalar_int()?.try_to_bits(size).ok()
     }
 
     pub fn try_to_bool(&self) -> Option<bool> {
@@ -244,6 +244,8 @@ impl<'tcx> Const<'tcx> {
             Const::Ty(c) => match c.kind() {
                 ty::ConstKind::Value(valtree) if c.ty().is_primitive() => {
                     // A valtree of a type where leaves directly represent the scalar const value.
+                    // Just checking whether it is a leaf is insufficient as e.g. references are leafs
+                    // but the leaf value is the value they point to, not the reference itself!
                     Some(valtree.unwrap_leaf().into())
                 }
                 _ => None,
@@ -255,12 +257,22 @@ impl<'tcx> Const<'tcx> {
 
     #[inline]
     pub fn try_to_scalar_int(self) -> Option<ScalarInt> {
-        self.try_to_scalar()?.try_to_int().ok()
+        // This is equivalent to `self.try_to_scalar()?.try_to_int().ok()`, but measurably faster.
+        match self {
+            Const::Val(ConstValue::Scalar(Scalar::Int(x)), _) => Some(x),
+            Const::Ty(c) => match c.kind() {
+                ty::ConstKind::Value(valtree) if c.ty().is_primitive() => {
+                    Some(valtree.unwrap_leaf())
+                }
+                _ => None,
+            },
+            _ => None,
+        }
     }
 
     #[inline]
     pub fn try_to_bits(self, size: Size) -> Option<u128> {
-        self.try_to_scalar_int()?.to_bits(size).ok()
+        self.try_to_scalar_int()?.try_to_bits(size).ok()
     }
 
     #[inline]
@@ -334,7 +346,7 @@ impl<'tcx> Const<'tcx> {
         let int = self.try_eval_scalar_int(tcx, param_env)?;
         let size =
             tcx.layout_of(param_env.with_reveal_all_normalized(tcx).and(self.ty())).ok()?.size;
-        int.to_bits(size).ok()
+        int.try_to_bits(size).ok()
     }
 
     /// Panics if the value cannot be evaluated or doesn't contain a valid integer of the given type.

compiler/rustc_middle/src/mir/interpret/value.rs

@@ -236,7 +236,7 @@ impl<Prov> Scalar<Prov> {
     ) -> Result<Either<u128, Pointer<Prov>>, ScalarSizeMismatch> {
         assert_ne!(target_size.bytes(), 0, "you should never look at the bits of a ZST");
         Ok(match self {
-            Scalar::Int(int) => Left(int.to_bits(target_size).map_err(|size| {
+            Scalar::Int(int) => Left(int.try_to_bits(target_size).map_err(|size| {
                 ScalarSizeMismatch { target_size: target_size.bytes(), data_size: size.bytes() }
             })?),
             Scalar::Ptr(ptr, sz) => {
@@ -300,6 +300,11 @@ impl<'tcx, Prov: Provenance> Scalar<Prov> {
         }
     }
 
+    #[inline(always)]
+    pub fn to_scalar_int(self) -> InterpResult<'tcx, ScalarInt> {
+        self.try_to_int().map_err(|_| err_unsup!(ReadPointerAsInt(None)).into())
+    }
+
     #[inline(always)]
     #[cfg_attr(debug_assertions, track_caller)] // only in debug builds due to perf (see #98980)
     pub fn assert_int(self) -> ScalarInt {
@@ -311,16 +316,13 @@ impl<'tcx, Prov: Provenance> Scalar<Prov> {
     #[inline]
     pub 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");
-        self.try_to_int()
-            .map_err(|_| err_unsup!(ReadPointerAsInt(None)))?
-            .to_bits(target_size)
-            .map_err(|size| {
-                err_ub!(ScalarSizeMismatch(ScalarSizeMismatch {
-                    target_size: target_size.bytes(),
-                    data_size: size.bytes(),
-                }))
-                .into()
-            })
+        self.to_scalar_int()?.try_to_bits(target_size).map_err(|size| {
+            err_ub!(ScalarSizeMismatch(ScalarSizeMismatch {
+                target_size: target_size.bytes(),
+                data_size: size.bytes(),
+            }))
+            .into()
+        })
     }
 
     #[inline(always)]

compiler/rustc_middle/src/thir.rs

@@ -16,7 +16,7 @@ use rustc_hir::{BindingMode, ByRef, HirId, MatchSource, RangeEnd};
 use rustc_index::newtype_index;
 use rustc_index::IndexVec;
 use rustc_middle::middle::region;
-use rustc_middle::mir::interpret::{AllocId, Scalar};
+use rustc_middle::mir::interpret::AllocId;
 use rustc_middle::mir::{self, BinOp, BorrowKind, FakeReadCause, UnOp};
 use rustc_middle::ty::adjustment::PointerCoercion;
 use rustc_middle::ty::layout::IntegerExt;
@@ -1006,18 +1006,17 @@ impl<'tcx> PatRangeBoundary<'tcx> {
 
             // This code is hot when compiling matches with many ranges. So we
             // special-case extraction of evaluated scalars for speed, for types where
-            // raw data comparisons are appropriate. E.g. `unicode-normalization` has
+            // unsigned int comparisons are appropriate. E.g. `unicode-normalization` has
             // many ranges such as '\u{037A}'..='\u{037F}', and chars can be compared
             // in this way.
-            (Finite(mir::Const::Ty(a)), Finite(mir::Const::Ty(b)))
-                if matches!(ty.kind(), ty::Uint(_) | ty::Char) =>
-            {
-                return Some(a.to_valtree().cmp(&b.to_valtree()));
+            (Finite(a), Finite(b)) if matches!(ty.kind(), ty::Uint(_) | ty::Char) => {
+                if let (Some(a), Some(b)) = (a.try_to_scalar_int(), b.try_to_scalar_int()) {
+                    let sz = ty.primitive_size(tcx);
+                    let a = a.assert_uint(sz);
+                    let b = b.assert_uint(sz);
+                    return Some(a.cmp(&b));
+                }
             }
-            (
-                Finite(mir::Const::Val(mir::ConstValue::Scalar(Scalar::Int(a)), _)),
-                Finite(mir::Const::Val(mir::ConstValue::Scalar(Scalar::Int(b)), _)),
-            ) if matches!(ty.kind(), ty::Uint(_) | ty::Char) => return Some(a.cmp(&b)),
             _ => {}
         }
 

compiler/rustc_middle/src/ty/consts.rs

@@ -409,7 +409,7 @@ impl<'tcx> Const<'tcx> {
         let size =
             tcx.layout_of(param_env.with_reveal_all_normalized(tcx).and(self.ty())).ok()?.size;
         // if `ty` does not depend on generic parameters, use an empty param_env
-        int.to_bits(size).ok()
+        int.try_to_bits(size).ok()
     }
 
     #[inline]

compiler/rustc_middle/src/ty/consts/int.rs

@@ -126,7 +126,7 @@ impl IntoDiagArg for ConstInt {
 ///
 /// This is a packed struct in order to allow this type to be optimally embedded in enums
 /// (like Scalar).
-#[derive(Clone, Copy, Eq, PartialEq, Ord, PartialOrd, Hash)]
+#[derive(Clone, Copy, Eq, PartialEq, Hash)]
 #[repr(packed)]
 pub struct ScalarInt {
     /// The first `size` bytes of `data` are the value.
@@ -167,9 +167,12 @@ impl<D: Decoder> Decodable<D> for ScalarInt {
 
 impl ScalarInt {
     pub const TRUE: ScalarInt = ScalarInt { data: 1_u128, size: NonZero::new(1).unwrap() };
-
     pub const FALSE: ScalarInt = ScalarInt { data: 0_u128, size: NonZero::new(1).unwrap() };
 
+    fn raw(data: u128, size: Size) -> Self {
+        Self { data, size: NonZero::new(size.bytes() as u8).unwrap() }
+    }
+
     #[inline]
     pub fn size(self) -> Size {
         Size::from_bytes(self.size.get())
@@ -196,7 +199,7 @@ impl ScalarInt {
 
     #[inline]
     pub fn null(size: Size) -> Self {
-        Self { data: 0, size: NonZero::new(size.bytes() as u8).unwrap() }
+        Self::raw(0, size)
     }
 
     #[inline]
@@ -207,11 +210,15 @@ impl ScalarInt {
     #[inline]
     pub fn try_from_uint(i: impl Into<u128>, size: Size) -> Option<Self> {
         let data = i.into();
-        if size.truncate(data) == data {
-            Some(Self { data, size: NonZero::new(size.bytes() as u8).unwrap() })
-        } else {
-            None
-        }
+        if size.truncate(data) == data { Some(Self::raw(data, size)) } else { None }
+    }
+
+    /// Returns the truncated result, and whether truncation changed the value.
+    #[inline]
+    pub fn truncate_from_uint(i: impl Into<u128>, size: Size) -> (Self, bool) {
+        let data = i.into();
+        let r = Self::raw(size.truncate(data), size);
+        (r, r.data != data)
     }
 
     #[inline]
@@ -220,26 +227,27 @@ impl ScalarInt {
         // `into` performed sign extension, we have to truncate
         let truncated = size.truncate(i as u128);
         if size.sign_extend(truncated) as i128 == i {
-            Some(Self { data: truncated, size: NonZero::new(size.bytes() as u8).unwrap() })
+            Some(Self::raw(truncated, size))
         } else {
             None
         }
     }
 
+    /// Returns the truncated result, and whether truncation changed the value.
     #[inline]
-    pub fn try_from_target_usize(i: impl Into<u128>, tcx: TyCtxt<'_>) -> Option<Self> {
-        Self::try_from_uint(i, tcx.data_layout.pointer_size)
+    pub fn truncate_from_int(i: impl Into<i128>, size: Size) -> (Self, bool) {
+        let data = i.into();
+        let r = Self::raw(size.truncate(data as u128), size);
+        (r, size.sign_extend(r.data) as i128 != data)
     }
 
     #[inline]
-    pub fn assert_bits(self, target_size: Size) -> u128 {
-        self.to_bits(target_size).unwrap_or_else(|size| {
-            bug!("expected int of size {}, but got size {}", target_size.bytes(), size.bytes())
-        })
+    pub fn try_from_target_usize(i: impl Into<u128>, tcx: TyCtxt<'_>) -> Option<Self> {
+        Self::try_from_uint(i, tcx.data_layout.pointer_size)
     }
 
     #[inline]
-    pub fn to_bits(self, target_size: Size) -> Result<u128, Size> {
+    pub fn try_to_bits(self, target_size: Size) -> Result<u128, Size> {
         assert_ne!(target_size.bytes(), 0, "you should never look at the bits of a ZST");
         if target_size.bytes() == u64::from(self.size.get()) {
             self.check_data();
@@ -249,48 +257,60 @@ impl ScalarInt {
         }
     }
 
+    #[inline]
+    pub fn assert_bits(self, target_size: Size) -> u128 {
+        self.try_to_bits(target_size).unwrap_or_else(|size| {
+            bug!("expected int of size {}, but got size {}", target_size.bytes(), size.bytes())
+        })
+    }
+
     /// Tries to convert the `ScalarInt` to an unsigned integer of the given size.
     /// Fails if the size of the `ScalarInt` is not equal to `size` and returns the
     /// `ScalarInt`s size in that case.
     #[inline]
     pub fn try_to_uint(self, size: Size) -> Result<u128, Size> {
-        self.to_bits(size)
+        self.try_to_bits(size)
+    }
+
+    #[inline]
+    pub fn assert_uint(self, size: Size) -> u128 {
+        self.assert_bits(size)
     }
 
     // Tries to convert the `ScalarInt` to `u8`. Fails if the `size` of the `ScalarInt`
-    // in not equal to `Size { raw: 1 }` and returns the `size` value of the `ScalarInt` in
+    // in not equal to 1 byte and returns the `size` value of the `ScalarInt` in
     // that case.
     #[inline]
     pub fn try_to_u8(self) -> Result<u8, Size> {
         self.try_to_uint(Size::from_bits(8)).map(|v| u8::try_from(v).unwrap())
     }
 
     /// Tries to convert the `ScalarInt` to `u16`. Fails if the size of the `ScalarInt`
-    /// in not equal to `Size { raw: 2 }` and returns the `size` value of the `ScalarInt` in
+    /// in not equal to 2 bytes and returns the `size` value of the `ScalarInt` in
     /// that case.
     #[inline]
     pub fn try_to_u16(self) -> Result<u16, Size> {
         self.try_to_uint(Size::from_bits(16)).map(|v| u16::try_from(v).unwrap())
     }
 
     /// Tries to convert the `ScalarInt` to `u32`. Fails if the `size` of the `ScalarInt`
-    /// in not equal to `Size { raw: 4 }` and returns the `size` value of the `ScalarInt` in
+    /// in not equal to 4 bytes and returns the `size` value of the `ScalarInt` in
     /// that case.
     #[inline]
     pub fn try_to_u32(self) -> Result<u32, Size> {
         self.try_to_uint(Size::from_bits(32)).map(|v| u32::try_from(v).unwrap())
     }
 
     /// Tries to convert the `ScalarInt` to `u64`. Fails if the `size` of the `ScalarInt`
-    /// in not equal to `Size { raw: 8 }` and returns the `size` value of the `ScalarInt` in
+    /// in not equal to 8 bytes and returns the `size` value of the `ScalarInt` in
     /// that case.
     #[inline]
     pub fn try_to_u64(self) -> Result<u64, Size> {
         self.try_to_uint(Size::from_bits(64)).map(|v| u64::try_from(v).unwrap())
     }
 
     /// Tries to convert the `ScalarInt` to `u128`. Fails if the `size` of the `ScalarInt`
-    /// in not equal to `Size { raw: 16 }` and returns the `size` value of the `ScalarInt` in
+    /// in not equal to 16 bytes and returns the `size` value of the `ScalarInt` in
     /// that case.
     #[inline]
     pub fn try_to_u128(self) -> Result<u128, Size> {
@@ -303,7 +323,7 @@ impl ScalarInt {
     }
 
     // Tries to convert the `ScalarInt` to `bool`. Fails if the `size` of the `ScalarInt`
-    // in not equal to `Size { raw: 1 }` or if the value is not 0 or 1 and returns the `size`
+    // in not equal to 1 byte or if the value is not 0 or 1 and returns the `size`
     // value of the `ScalarInt` in that case.
     #[inline]
     pub fn try_to_bool(self) -> Result<bool, Size> {
@@ -319,40 +339,46 @@ impl ScalarInt {
     /// `ScalarInt`s size in that case.
     #[inline]
     pub fn try_to_int(self, size: Size) -> Result<i128, Size> {
-        let b = self.to_bits(size)?;
+        let b = self.try_to_bits(size)?;
         Ok(size.sign_extend(b) as i128)
     }
 
+    #[inline]
+    pub fn assert_int(self, size: Size) -> i128 {
+        let b = self.assert_bits(size);
+        size.sign_extend(b) as i128
+    }
+
     /// Tries to convert the `ScalarInt` to i8.
-    /// Fails if the size of the `ScalarInt` is not equal to `Size { raw: 1 }`
+    /// Fails if the size of the `ScalarInt` is not equal to 1 byte
     /// and returns the `ScalarInt`s size in that case.
     pub fn try_to_i8(self) -> Result<i8, Size> {
         self.try_to_int(Size::from_bits(8)).map(|v| i8::try_from(v).unwrap())
     }
 
     /// Tries to convert the `ScalarInt` to i16.
-    /// Fails if the size of the `ScalarInt` is not equal to `Size { raw: 2 }`
+    /// Fails if the size of the `ScalarInt` is not equal to 2 bytes
     /// and returns the `ScalarInt`s size in that case.
     pub fn try_to_i16(self) -> Result<i16, Size> {
         self.try_to_int(Size::from_bits(16)).map(|v| i16::try_from(v).unwrap())
     }
 
     /// Tries to convert the `ScalarInt` to i32.
-    /// Fails if the size of the `ScalarInt` is not equal to `Size { raw: 4 }`
+    /// Fails if the size of the `ScalarInt` is not equal to 4 bytes
     /// and returns the `ScalarInt`s size in that case.
     pub fn try_to_i32(self) -> Result<i32, Size> {
         self.try_to_int(Size::from_bits(32)).map(|v| i32::try_from(v).unwrap())
     }
 
     /// Tries to convert the `ScalarInt` to i64.
-    /// Fails if the size of the `ScalarInt` is not equal to `Size { raw: 8 }`
+    /// Fails if the size of the `ScalarInt` is not equal to 8 bytes
     /// and returns the `ScalarInt`s size in that case.
     pub fn try_to_i64(self) -> Result<i64, Size> {
         self.try_to_int(Size::from_bits(64)).map(|v| i64::try_from(v).unwrap())
     }
 
     /// Tries to convert the `ScalarInt` to i128.
-    /// Fails if the size of the `ScalarInt` is not equal to `Size { raw: 16 }`
+    /// Fails if the size of the `ScalarInt` is not equal to 16 bytes
     /// and returns the `ScalarInt`s size in that case.
     pub fn try_to_i128(self) -> Result<i128, Size> {
         self.try_to_int(Size::from_bits(128))
@@ -366,7 +392,7 @@ impl ScalarInt {
     #[inline]
     pub fn try_to_float<F: Float>(self) -> Result<F, Size> {
         // Going through `to_uint` to check size and truncation.
-        Ok(F::from_bits(self.to_bits(Size::from_bits(F::BITS))?))
+        Ok(F::from_bits(self.try_to_bits(Size::from_bits(F::BITS))?))
     }
 
     #[inline]
@@ -415,7 +441,7 @@ macro_rules! try_from {
                 fn try_from(int: ScalarInt) -> Result<Self, Size> {
                     // The `unwrap` cannot fail because to_bits (if it succeeds)
                     // is guaranteed to return a value that fits into the size.
-                    int.to_bits(Size::from_bytes(std::mem::size_of::<$ty>()))
+                    int.try_to_bits(Size::from_bytes(std::mem::size_of::<$ty>()))
                        .map(|u| u.try_into().unwrap())
                 }
             }
@@ -450,7 +476,7 @@ impl TryFrom<ScalarInt> for char {
 
     #[inline]
     fn try_from(int: ScalarInt) -> Result<Self, Self::Error> {
-        let Ok(bits) = int.to_bits(Size::from_bytes(std::mem::size_of::<char>())) else {
+        let Ok(bits) = int.try_to_bits(Size::from_bytes(std::mem::size_of::<char>())) else {
             return Err(CharTryFromScalarInt);
         };
         match char::from_u32(bits.try_into().unwrap()) {
@@ -472,7 +498,7 @@ impl TryFrom<ScalarInt> for Half {
     type Error = Size;
     #[inline]
     fn try_from(int: ScalarInt) -> Result<Self, Size> {
-        int.to_bits(Size::from_bytes(2)).map(Self::from_bits)
+        int.try_to_bits(Size::from_bytes(2)).map(Self::from_bits)
     }
 }
 
@@ -488,7 +514,7 @@ impl TryFrom<ScalarInt> for Single {
     type Error = Size;
     #[inline]
     fn try_from(int: ScalarInt) -> Result<Self, Size> {
-        int.to_bits(Size::from_bytes(4)).map(Self::from_bits)
+        int.try_to_bits(Size::from_bytes(4)).map(Self::from_bits)
     }
 }
 
@@ -504,7 +530,7 @@ impl TryFrom<ScalarInt> for Double {
     type Error = Size;
     #[inline]
     fn try_from(int: ScalarInt) -> Result<Self, Size> {
-        int.to_bits(Size::from_bytes(8)).map(Self::from_bits)
+        int.try_to_bits(Size::from_bytes(8)).map(Self::from_bits)
     }
 }
 
@@ -520,7 +546,7 @@ impl TryFrom<ScalarInt> for Quad {
     type Error = Size;
     #[inline]
     fn try_from(int: ScalarInt) -> Result<Self, Size> {
-        int.to_bits(Size::from_bytes(16)).map(Self::from_bits)
+        int.try_to_bits(Size::from_bytes(16)).map(Self::from_bits)
     }
 }
 

compiler/rustc_middle/src/ty/consts/valtree.rs

@@ -3,7 +3,7 @@ use crate::mir::interpret::Scalar;
 use crate::ty::{self, Ty, TyCtxt};
 use rustc_macros::{HashStable, TyDecodable, TyEncodable};
 
-#[derive(Copy, Clone, Debug, Hash, TyEncodable, TyDecodable, Eq, PartialEq, Ord, PartialOrd)]
+#[derive(Copy, Clone, Debug, Hash, TyEncodable, TyDecodable, Eq, PartialEq)]
 #[derive(HashStable)]
 /// This datastructure is used to represent the value of constants used in the type system.
 ///

compiler/rustc_mir_transform/src/known_panics_lint.rs

@@ -796,7 +796,7 @@ impl<'tcx> Visitor<'tcx> for ConstPropagator<'_, 'tcx> {
                 if let Some(ref value) = self.eval_operand(discr)
                     && let Some(value_const) = self.use_ecx(|this| this.ecx.read_scalar(value))
                     && let Ok(constant) = value_const.try_to_int()
-                    && let Ok(constant) = constant.to_bits(constant.size())
+                    && let Ok(constant) = constant.try_to_bits(constant.size())
                 {
                     // We managed to evaluate the discriminant, so we know we only need to visit
                     // one target.

compiler/rustc_mir_transform/src/match_branches.rs

@@ -369,8 +369,7 @@ impl<'tcx> SimplifyMatch<'tcx> for SimplifyToExp {
         }
 
         fn int_equal(l: ScalarInt, r: impl Into<u128>, size: Size) -> bool {
-            l.try_to_int(l.size()).unwrap()
-                == ScalarInt::try_from_uint(r, size).unwrap().try_to_int(size).unwrap()
+            l.assert_int(l.size()) == ScalarInt::try_from_uint(r, size).unwrap().assert_int(size)
         }
 
         // We first compare the two branches, and then the other branches need to fulfill the same conditions.

compiler/rustc_mir_transform/src/promote_consts.rs

@@ -490,14 +490,14 @@ impl<'tcx> Validator<'_, 'tcx> {
                                 }
                                 _ => None,
                             };
-                            match rhs_val.map(|x| x.try_to_uint(sz).unwrap()) {
+                            match rhs_val.map(|x| x.assert_uint(sz)) {
                                 // for the zero test, int vs uint does not matter
                                 Some(x) if x != 0 => {}        // okay
                                 _ => return Err(Unpromotable), // value not known or 0 -- not okay
                             }
                             // Furthermore, for signed divison, we also have to exclude `int::MIN / -1`.
                             if lhs_ty.is_signed() {
-                                match rhs_val.map(|x| x.try_to_int(sz).unwrap()) {
+                                match rhs_val.map(|x| x.assert_int(sz)) {
                                     Some(-1) | None => {
                                         // The RHS is -1 or unknown, so we have to be careful.
                                         // But is the LHS int::MIN?
@@ -508,7 +508,7 @@ impl<'tcx> Validator<'_, 'tcx> {
                                             _ => None,
                                         };
                                         let lhs_min = sz.signed_int_min();
-                                        match lhs_val.map(|x| x.try_to_int(sz).unwrap()) {
+                                        match lhs_val.map(|x| x.assert_int(sz)) {
                                             Some(x) if x != lhs_min => {}  // okay
                                             _ => return Err(Unpromotable), // value not known or int::MIN -- not okay
                                         }

compiler/rustc_transmute/src/layout/tree.rs

@@ -420,7 +420,7 @@ pub(crate) mod rustc {
         fn from_tag(tag: ScalarInt, tcx: TyCtxt<'tcx>) -> Self {
             use rustc_target::abi::Endian;
             let size = tag.size();
-            let bits = tag.to_bits(size).unwrap();
+            let bits = tag.assert_bits(size);
             let bytes: [u8; 16];
             let bytes = match tcx.data_layout.endian {
                 Endian::Little => {