ScalarInt: add methods to assert being a (u)int of given size

13 files changed, 78 insertions, 72 deletions

diff --git a/compiler/rustc_codegen_cranelift/src/constant.rs b/compiler/rustc_codegen_cranelift/src/constant.rs
index 635ed6c8e88..cb05c17ec2a 100644
--- a/compiler/rustc_codegen_cranelift/src/constant.rs
+++ b/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) => {
diff --git a/compiler/rustc_codegen_cranelift/src/value_and_place.rs b/compiler/rustc_codegen_cranelift/src/value_and_place.rs
index fc5b88a54fe..ad863903cee 100644
--- a/compiler/rustc_codegen_cranelift/src/value_and_place.rs
+++ b/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) => {
diff --git a/compiler/rustc_const_eval/src/interpret/discriminant.rs b/compiler/rustc_const_eval/src/interpret/discriminant.rs
index 704f597cfdb..caacc6f57d3 100644
--- a/compiler/rustc_const_eval/src/interpret/discriminant.rs
+++ b/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)))
             }
         }
diff --git a/compiler/rustc_const_eval/src/interpret/operand.rs b/compiler/rustc_const_eval/src/interpret/operand.rs
index 8283c29207f..604b78358b3 100644
--- a/compiler/rustc_const_eval/src/interpret/operand.rs
+++ b/compiler/rustc_const_eval/src/interpret/operand.rs
@@ -249,7 +249,7 @@ impl<'tcx, Prov: Provenance> ImmTy<'tcx, Prov> {
     }
 
     /// Return the immediate as a `ScalarInt`. Ensures that it has the size that the layout of the
-    /// immediate indcates.
+    /// immediate indicates.
     #[inline]
     pub fn to_scalar_int(&self) -> InterpResult<'tcx, ScalarInt> {
         let s = self.to_scalar().to_scalar_int()?;
diff --git a/compiler/rustc_const_eval/src/interpret/operator.rs b/compiler/rustc_const_eval/src/interpret/operator.rs
index 1a126d1fbb0..9af755e40de 100644
--- a/compiler/rustc_const_eval/src/interpret/operator.rs
+++ b/compiler/rustc_const_eval/src/interpret/operator.rs
@@ -155,10 +155,10 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         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.try_to_int(left.layout.size).unwrap();
-        let l_unsigned = || l.try_to_uint(left.layout.size).unwrap();
-        let r_signed = || r.try_to_int(right.layout.size).unwrap();
-        let r_unsigned = || r.try_to_uint(right.layout.size).unwrap();
+        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),
diff --git a/compiler/rustc_middle/src/mir/consts.rs b/compiler/rustc_middle/src/mir/consts.rs
index 155af062012..0af012e90cb 100644
--- a/compiler/rustc_middle/src/mir/consts.rs
+++ b/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> {
@@ -260,7 +260,7 @@ impl<'tcx> Const<'tcx> {
 
     #[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 +334,7 @@ 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.
diff --git a/compiler/rustc_middle/src/mir/interpret/value.rs b/compiler/rustc_middle/src/mir/interpret/value.rs
index 38ddd34777a..22779b38830 100644
--- a/compiler/rustc_middle/src/mir/interpret/value.rs
+++ b/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) => {
@@ -316,7 +316,7 @@ 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.to_scalar_int()?.to_bits(target_size).map_err(|size| {
+        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(),
diff --git a/compiler/rustc_middle/src/ty/consts.rs b/compiler/rustc_middle/src/ty/consts.rs
index 49b806b8369..6d2d91dc9ab 100644
--- a/compiler/rustc_middle/src/ty/consts.rs
+++ b/compiler/rustc_middle/src/ty/consts.rs
@@ -406,7 +406,7 @@ 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]
diff --git a/compiler/rustc_middle/src/ty/consts/int.rs b/compiler/rustc_middle/src/ty/consts/int.rs
index 046ced36b64..2bf2341cbc4 100644
--- a/compiler/rustc_middle/src/ty/consts/int.rs
+++ b/compiler/rustc_middle/src/ty/consts/int.rs
@@ -247,14 +247,7 @@ impl ScalarInt {
     }
 
     #[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())
-        })
-    }
-
-    #[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();
@@ -264,16 +257,28 @@ 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> {
@@ -281,7 +286,7 @@ impl ScalarInt {
     }
 
     /// 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> {
@@ -289,7 +294,7 @@ impl ScalarInt {
     }
 
     /// 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> {
@@ -297,7 +302,7 @@ impl ScalarInt {
     }
 
     /// 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> {
@@ -305,7 +310,7 @@ impl ScalarInt {
     }
 
     /// 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> {
@@ -318,7 +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> {
@@ -334,40 +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))
@@ -381,7 +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]
@@ -430,7 +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())
                 }
             }
@@ -465,7 +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()) {
@@ -487,7 +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)
     }
 }
 
@@ -503,7 +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)
     }
 }
 
@@ -519,7 +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)
     }
 }
 
@@ -535,7 +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)
     }
 }
 
diff --git a/compiler/rustc_mir_transform/src/known_panics_lint.rs b/compiler/rustc_mir_transform/src/known_panics_lint.rs
index 2218154ea5e..2744026a7c9 100644
--- a/compiler/rustc_mir_transform/src/known_panics_lint.rs
+++ b/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.
diff --git a/compiler/rustc_mir_transform/src/match_branches.rs b/compiler/rustc_mir_transform/src/match_branches.rs
index 4d9a198eeb2..a8a576e4efe 100644
--- a/compiler/rustc_mir_transform/src/match_branches.rs
+++ b/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.
diff --git a/compiler/rustc_mir_transform/src/promote_consts.rs b/compiler/rustc_mir_transform/src/promote_consts.rs
index a9d4b860b7a..1f4af0ec63d 100644
--- a/compiler/rustc_mir_transform/src/promote_consts.rs
+++ b/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
                                         }
diff --git a/compiler/rustc_transmute/src/layout/tree.rs b/compiler/rustc_transmute/src/layout/tree.rs
index 12c984f1603..edd3227210b 100644
--- a/compiler/rustc_transmute/src/layout/tree.rs
+++ b/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 => {