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Improve the `build_shift_expr_rhs` comment

This commit is contained in:
Scott McMurray 2024-04-02 10:17:21 -07:00
parent 0601f0c66d
commit 327aa199dd
1 changed files with 7 additions and 4 deletions
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11
compiler/rustc_codegen_ssa/src/base.rs
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@ -300,12 +300,15 @@ pub fn coerce_unsized_into<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
}
}
/// Returns `rhs` sufficiently masked, truncated, and/or extended so that
/// it can be used to shift `lhs`.
///
/// Shifts in MIR are all allowed to have mismatched LHS & RHS types.
/// The shift methods in `BuilderMethods`, however, are fully homogeneous
/// (both parameters and the return type are all the same type).
///
/// This does all the appropriate conversions needed to pass it to the builder's
/// shift methods, which are UB for out-of-range shifts.
///
/// If `is_unchecked` is false, this masks the RHS to ensure it stays in-bounds.
/// If `is_unchecked` is false, this masks the RHS to ensure it stays in-bounds,
/// as the `BuilderMethods` shifts are UB for out-of-bounds shift amounts.
/// For 32- and 64-bit types, this matches the semantics
/// of Java. (See related discussion on #1877 and #10183.)
///