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Rollup merge of #98738 - tmiasko:checked-binop, r=oli-obk

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Clarify MIR semantics of checked binary operations
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Matthias Krüger 2022-07-04 23:11:07 +02:00 committed by GitHub
commit 82660a2525
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1 changed files with 12 additions and 4 deletions
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16
compiler/rustc_middle/src/mir/syntax.rs
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@ -990,11 +990,19 @@ pub enum Rvalue<'tcx> {
/// matching types and return a value of that type.
BinaryOp(BinOp, Box<(Operand<'tcx>, Operand<'tcx>)>),
/// Same as `BinaryOp`, but yields `(T, bool)` instead of `T`. In addition to performing the
/// same computation as the matching `BinaryOp`, checks if the infinite precison result would be
/// unequal to the actual result and sets the `bool` if this is the case.
/// Same as `BinaryOp`, but yields `(T, bool)` with a `bool` indicating an error condition.
///
/// This only supports addition, subtraction, multiplication, and shift operations on integers.
/// When overflow checking is disabled, the error condition is false. Otherwise, the error
/// condition is determined as described below.
///
/// For addition, subtraction, and multiplication on integers the error condition is set when
/// the infinite precision result would be unequal to the actual result.
///
/// For shift operations on integers the error condition is set when the value of right-hand
/// side is greater than or equal to the number of bits in the type of the left-hand side, or
/// when the value of right-hand side is negative.
///
/// Other combinations of types and operators are unsupported.
CheckedBinaryOp(BinOp, Box<(Operand<'tcx>, Operand<'tcx>)>),
/// Computes a value as described by the operation.