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Rollup merge of #125148 - RalfJung:codegen-sh, r=scottmcm

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codegen: tweak/extend shift comments

r? `@scottmcm`
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Guillaume Gomez 2024-05-27 13:10:34 +02:00 • committed by GitHub
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2 changed files with 13 additions and 4 deletions
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9
compiler/rustc_codegen_ssa/src/base.rs
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@ -294,12 +294,13 @@ 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`.
/// Returns `rhs` sufficiently masked, truncated, and/or extended so that it can be used to shift
/// `lhs`: it has the same size as `lhs`, and the value, when interpreted unsigned (no matter its
/// type), will not exceed the size of `lhs`.
///
/// Shifts in MIR are all allowed to have mismatched LHS & RHS types.
/// Shifts in MIR are all allowed to have mismatched LHS & RHS types, and signed RHS.
/// The shift methods in `BuilderMethods`, however, are fully homogeneous
/// (both parameters and the return type are all the same type).
/// (both parameters and the return type are all the same size) and assume an unsigned RHS.
///
/// 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.