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| -rw-r--r-- | compiler/rustc_abi/src/lib.rs | 8 |
1 files changed, 8 insertions, 0 deletions
diff --git a/compiler/rustc_abi/src/lib.rs b/compiler/rustc_abi/src/lib.rs index be42bc84932..4e27ad0c366 100644 --- a/compiler/rustc_abi/src/lib.rs +++ b/compiler/rustc_abi/src/lib.rs @@ -781,6 +781,14 @@ impl Align { } /// A pair of alignments, ABI-mandated and preferred. +/// +/// The "preferred" alignment is an LLVM concept that is virtually meaningless to Rust code: +/// it is not exposed semantically to programmers nor can they meaningfully affect it. +/// The only concern for us is that preferred alignment must not be less than the mandated alignment +/// and thus in practice the two values are almost always identical. +/// +/// An example of a rare thing actually affected by preferred alignment is aligning of statics. +/// It is of effectively no consequence for layout in structs and on the stack. #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)] #[cfg_attr(feature = "nightly", derive(HashStable_Generic))] pub struct AbiAndPrefAlign { |