Visual Studio參數對齊限制和Windows x64 ABI

Question

使用WIN32上的Visual C++，有4個或更多SSE參數的函數存在長期存在的問題，例如，

__m128i foo4(__m128i m0, __m128i m1, __m128i m2, __m128i m3) {} 

生成錯誤：

align.c(8) : error C2719: 'm3': formal parameter with __declspec(align('16')) won't be aligned 

使問題更加複雜時，Visual C++仍然不必要強加限制ABI即使功能是__inline。

我想知道這是否仍然是64位Windows上的問題？ ABI限制是否仍然適用於x64？

（我沒有訪問64位Windows系統，否則我想嘗試它自己，以及廣泛的谷歌搜索還沒有止跌回升什麼明確的。）

Answer 1

您可以通過儘可能多的128位在x64下你喜歡SSE內在參數。 x64 ABI的設計考慮了這些類型。

從MSDN documentation：

__m128 types, arrays and strings are never passed by immediate value but rather a pointer is passed to memory allocated by the caller. Structs/unions of size 8, 16, 32, or 64 bits and __m64 are passed as if they were integers of the same size. Structs/unions other than these sizes are passed as a pointer to memory allocated by the caller. For these aggregate types passed as a pointer (including __m128), the caller-allocated temporary memory will be 16-byte aligned.