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Miri/CTFE: properly treat overflow in (signed) division/rem as UB

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This commit is contained in:
Ralf Jung 2022-03-01 20:02:59 -05:00
parent f0c4da4998
commit 6739299d18
10 changed files with 93 additions and 76 deletions
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12
compiler/rustc_const_eval/src/interpret/intrinsics.rs
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@ -500,15 +500,9 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
// `x % y != 0` or `y == 0` or `x == T::MIN && 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.assert_bits(a.layout.size) != 0 {
// Then, check if `b` is -1, which is the "MIN / -1" case.
let minus1 = Scalar::from_int(-1, dest.layout.size);
let b_scalar = b.to_scalar().unwrap();
if b_scalar == minus1 {
throw_ub_format!("exact_div: result of dividing MIN by -1 cannot be represented")
} else {
throw_ub_format!("exact_div: {} cannot be divided by {} without remainder", a, b,)
}
assert!(!overflow); // All overflow is UB, so this should never return on overflow.
if res.assert_bits(a.layout.size) != 0 {
throw_ub_format!("exact_div: {} cannot be divided by {} without remainder", a, b)
}
// `Rem` says this is all right, so we can let `Div` do its job.
self.binop_ignore_overflow(BinOp::Div, &a, &b, dest)