webassembly - 如何理解 WebAssembly 中的 "align"属性？

Question

为什么那些“加载”和“存储”操作符需要一个“对齐”属性，它是如何与内存对齐一起工作的？

顺便说一句，为什么我们需要这个操作符，因为底层系统会自动为我们做内存对齐？

Answer 1

对齐的使用在规范中有详细说明:

The alignment memarg.𝖺𝗅𝗂𝗀𝗇 in load and store instructions does not affect the semantics. It is an indication that the offset ea at which the memory is accessed is intended to satisfy the property ea mod 2^memarg.𝖺𝗅𝗂𝗀𝗇=0. A WebAssembly implementation can use this hint to optimize for the intended use. Unaligned access violating that property is still allowed and must succeed regardless of the annotation. However, it may be substantially slower on some hardware.

没有其他与对齐相关的语义影响；未对齐和未对齐的加载和存储仍然正常运行，这只是性能优化。