diff options
| -rw-r--r-- | compiler/rustc_codegen_ssa/src/base.rs | 11 |
1 files changed, 7 insertions, 4 deletions
diff --git a/compiler/rustc_codegen_ssa/src/base.rs b/compiler/rustc_codegen_ssa/src/base.rs index ec21a7cee47..410b5d27c57 100644 --- a/compiler/rustc_codegen_ssa/src/base.rs +++ b/compiler/rustc_codegen_ssa/src/base.rs @@ -300,12 +300,15 @@ pub fn coerce_unsized_into<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>( } } -/// Shifts in MIR are all allowed to have mismatched LHS & RHS types. +/// Returns `rhs` sufficiently masked, truncated, and/or extended so that +/// it can be used to shift `lhs`. /// -/// This does all the appropriate conversions needed to pass it to the builder's -/// shift methods, which are UB for out-of-range shifts. +/// 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). /// -/// 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.) /// |