Rollup merge of rust-lang#61164 - RalfJung:scalar, r=oli-obk

rename Scalar::Bits to Scalar::Raw and bits field to data

Also use this opportunity to seal some abstraction leaks (other modules constructing `Scalar::Bits` directly instead of using a constructor).

r? @oli-obk

src/librustc/mir/interpret/allocation.rs

@@ -2,7 +2,6 @@
 
 use super::{
     Pointer, EvalResult, AllocId, ScalarMaybeUndef, write_target_uint, read_target_uint, Scalar,
-    truncate,
 };
 
 use crate::ty::layout::{Size, Align};
@@ -407,18 +406,9 @@ impl<'tcx, Tag: Copy, Extra: AllocationExtra<Tag>> Allocation<Tag, Extra> {
             ScalarMaybeUndef::Undef => return self.mark_definedness(ptr, type_size, false),
         };
 
-        let bytes = match val {
-            Scalar::Ptr(val) => {
-                assert_eq!(type_size, cx.data_layout().pointer_size);
-                val.offset.bytes() as u128
-            }
-
-            Scalar::Bits { bits, size } => {
-                assert_eq!(size as u64, type_size.bytes());
-                debug_assert_eq!(truncate(bits, Size::from_bytes(size.into())), bits,
-                    "Unexpected value of size {} when writing to memory", size);
-                bits
-            },
+        let bytes = match val.to_bits_or_ptr(type_size, cx) {
+            Err(val) => val.offset.bytes() as u128,
+            Ok(data) => data,
         };
 
         let endian = cx.data_layout().endian;

src/librustc/mir/interpret/mod.rs

@@ -349,6 +349,7 @@ impl<'tcx> AllocMap<'tcx> {
     /// illegal and will likely ICE.
     /// This function exists to allow const eval to detect the difference between evaluation-
     /// local dangling pointers and allocations in constants/statics.
+    #[inline]
     pub fn get(&self, id: AllocId) -> Option<AllocKind<'tcx>> {
         self.id_to_kind.get(&id).cloned()
     }
@@ -397,6 +398,7 @@ impl<'tcx> AllocMap<'tcx> {
 // Methods to access integers in the target endianness
 ////////////////////////////////////////////////////////////////////////////////
 
+#[inline]
 pub fn write_target_uint(
     endianness: layout::Endian,
     mut target: &mut [u8],
@@ -409,6 +411,7 @@ pub fn write_target_uint(
     }
 }
 
+#[inline]
 pub fn read_target_uint(endianness: layout::Endian, mut source: &[u8]) -> Result<u128, io::Error> {
     match endianness {
         layout::Endian::Little => source.read_uint128::<LittleEndian>(source.len()),
@@ -420,17 +423,30 @@ pub fn read_target_uint(endianness: layout::Endian, mut source: &[u8]) -> Result
 // Methods to facilitate working with signed integers stored in a u128
 ////////////////////////////////////////////////////////////////////////////////
 
+/// Truncate `value` to `size` bits and then sign-extend it to 128 bits
+/// (i.e., if it is negative, fill with 1's on the left).
+#[inline]
 pub fn sign_extend(value: u128, size: Size) -> u128 {
     let size = size.bits();
+    if size == 0 {
+        // Truncated until nothing is left.
+        return 0;
+    }
     // sign extend
     let shift = 128 - size;
     // shift the unsigned value to the left
     // and back to the right as signed (essentially fills with FF on the left)
     (((value << shift) as i128) >> shift) as u128
 }
 
+/// Truncate `value` to `size` bits.
+#[inline]
 pub fn truncate(value: u128, size: Size) -> u128 {
     let size = size.bits();
+    if size == 0 {
+        // Truncated until nothing is left.
+        return 0;
+    }
     let shift = 128 - size;
     // truncate (shift left to drop out leftover values, shift right to fill with zeroes)
     (value << shift) >> shift

src/librustc/mir/interpret/pointer.rs

@@ -20,45 +20,48 @@ pub trait PointerArithmetic: layout::HasDataLayout {
         self.data_layout().pointer_size
     }
 
-    //// Trunace the given value to the pointer size; also return whether there was an overflow
+    /// Helper function: truncate given value-"overflowed flag" pair to pointer size and
+    /// update "overflowed flag" if there was an overflow.
+    /// This should be called by all the other methods before returning!
     #[inline]
-    fn truncate_to_ptr(&self, val: u128) -> (u64, bool) {
+    fn truncate_to_ptr(&self, (val, over): (u64, bool)) -> (u64, bool) {
+        let val = val as u128;
         let max_ptr_plus_1 = 1u128 << self.pointer_size().bits();
-        ((val % max_ptr_plus_1) as u64, val >= max_ptr_plus_1)
-    }
-
-    #[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) }
+        ((val % max_ptr_plus_1) as u64, over || val >= max_ptr_plus_1)
     }
 
     #[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(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, i128::from(i));
-        if over { err!(Overflow(mir::BinOp::Add)) } else { Ok(res) }
+        let res = val.overflowing_add(i);
+        self.truncate_to_ptr(res)
     }
 
     // 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!
+            // Trickery to ensure that i64::min_value() works fine: compute n = -i.
+            // This formula only works for true negative values, it overflows for zero!
             let n = u64::max_value() - (i as u64) + 1;
-            val.overflowing_sub(n)
+            let res = val.overflowing_sub(n);
+            self.truncate_to_ptr(res)
         } 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 signed_offset<'tcx>(&self, val: u64, i: i64) -> EvalResult<'tcx, u64> {
+        let (res, over) = self.overflowing_signed_offset(val, i128::from(i));
+        if over { err!(Overflow(mir::BinOp::Add)) } else { Ok(res) }
+    }
 }
 
 impl<T: layout::HasDataLayout> PointerArithmetic for T {}