diff options
Diffstat (limited to 'compiler/rustc_const_eval/src/interpret/operator.rs')
| -rw-r--r-- | compiler/rustc_const_eval/src/interpret/operator.rs | 61 |
1 files changed, 29 insertions, 32 deletions
diff --git a/compiler/rustc_const_eval/src/interpret/operator.rs b/compiler/rustc_const_eval/src/interpret/operator.rs index a3ba9530f..eef154257 100644 --- a/compiler/rustc_const_eval/src/interpret/operator.rs +++ b/compiler/rustc_const_eval/src/interpret/operator.rs @@ -20,7 +20,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> { right: &ImmTy<'tcx, M::Provenance>, dest: &PlaceTy<'tcx, M::Provenance>, ) -> InterpResult<'tcx> { - let (val, overflowed) = self.overflowing_binary_op(op, &left, &right)?; + let (val, overflowed) = self.overflowing_binary_op(op, left, right)?; debug_assert_eq!( Ty::new_tup(self.tcx.tcx, &[val.layout.ty, self.tcx.types.bool]), dest.layout.ty, @@ -114,9 +114,8 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> { use rustc_middle::mir::BinOp::*; // Performs appropriate non-deterministic adjustments of NaN results. - let adjust_nan = |f: F| -> F { - if f.is_nan() { M::generate_nan(self, &[l, r]) } else { f } - }; + let adjust_nan = + |f: F| -> F { if f.is_nan() { M::generate_nan(self, &[l, r]) } else { f } }; let val = match bin_op { Eq => ImmTy::from_bool(l == r, *self.tcx), @@ -157,41 +156,35 @@ 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 = u128::from(left_layout.size.bits()); - // Even if `r` is signed, we treat it as if it was unsigned (i.e., we use its - // zero-extended form). This matches the codegen backend: - // <https://github.com/rust-lang/rust/blob/c274e4969f058b1c644243181ece9f829efa7594/compiler/rustc_codegen_ssa/src/base.rs#L315-L317>. - // The overflow check is also ignorant to the sign: - // <https://github.com/rust-lang/rust/blob/c274e4969f058b1c644243181ece9f829efa7594/compiler/rustc_codegen_ssa/src/mir/rvalue.rs#L728>. - // This would behave rather strangely if we had integer types of size 256: a shift by - // -1i8 would actually shift by 255, but that would *not* be considered overflowing. A - // shift by -1i16 though would be considered overflowing. If we had integers of size - // 512, then a shift by -1i8 would even produce a different result than one by -1i16: - // the first shifts by 255, the latter by u16::MAX % 512 = 511. Lucky enough, our - // integers are maximally 128bits wide, so negative shifts *always* overflow and we have - // consistent results for the same value represented at different bit widths. - assert!(size <= 128); - let original_r = r; - let overflow = r >= size; - // The shift offset is implicitly masked to the type size, to make sure this operation - // is always defined. This is the one MIR operator that does *not* directly map to a - // single LLVM operation. See - // <https://github.com/rust-lang/rust/blob/c274e4969f058b1c644243181ece9f829efa7594/compiler/rustc_codegen_ssa/src/common.rs#L131-L158> - // for the corresponding truncation in our codegen backends. - let r = r % size; - let r = u32::try_from(r).unwrap(); // we masked so this will always fit + 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 overflow = shift_amount < 0 || shift_amount >= i128::from(size); + let masked_amount = (shift_amount as u128) % u128::from(size); + debug_assert_eq!(overflow, shift_amount != (masked_amount as i128)); + (masked_amount, overflow) + } else { + let shift_amount = r; + 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 = match bin_op { - Shl | ShlUnchecked => l.checked_shl(r).unwrap(), - Shr | ShrUnchecked => l.checked_shr(r).unwrap(), + Shl | ShlUnchecked => l.checked_shl(shift_amount).unwrap(), + Shr | ShrUnchecked => l.checked_shr(shift_amount).unwrap(), _ => bug!(), }; result as u128 } else { match bin_op { - Shl | ShlUnchecked => l.checked_shl(r).unwrap(), - Shr | ShrUnchecked => l.checked_shr(r).unwrap(), + Shl | ShlUnchecked => l.checked_shl(shift_amount).unwrap(), + Shr | ShrUnchecked => l.checked_shr(shift_amount).unwrap(), _ => bug!(), } }; @@ -200,7 +193,11 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> { if overflow && let Some(intrinsic_name) = throw_ub_on_overflow { throw_ub_custom!( fluent::const_eval_overflow_shift, - val = original_r, + val = if right_layout.abi.is_signed() { + (self.sign_extend(r, right_layout) as i128).to_string() + } else { + r.to_string() + }, name = intrinsic_name ); } |