From b88479738ec8de29da27d9fd4bef5581c362e9b0 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Tomasz=20Mi=C4=85sko?= Date: Thu, 30 Jun 2022 00:00:00 +0000 Subject: [PATCH] Clarify MIR semantics of checked binary operations --- compiler/rustc_middle/src/mir/syntax.rs | 16 ++++++++++++---- 1 file changed, 12 insertions(+), 4 deletions(-) diff --git a/compiler/rustc_middle/src/mir/syntax.rs b/compiler/rustc_middle/src/mir/syntax.rs index f8ee59f306fbf..17824da2345a4 100644 --- a/compiler/rustc_middle/src/mir/syntax.rs +++ b/compiler/rustc_middle/src/mir/syntax.rs @@ -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.