strict aliasing and memory alignment

Question

I have performance critical code and there is a huge function that allocates like 40 arrays of different size on the stack at the beginning of the function. Most of these arrays

Answer 1

First I'd like to say I'm definitely with you when you ask not to buzz about "standard violation", "implementation-dependent" and etc. Your question is absolutely legitimate IMHO.

Your approach to pack all the arrays within one struct also makes sense, that's what I'd do.

It's unclear from the question formulation which "artifacts" do you observe. Is there any unneeded code generated? Or data misalignment? If the latter is the case - you may (hopefully) use things like STATIC_ASSERT to ensure at compile-time that things are aligned properly. Or at least have some run-time ASSERT at debug build.

As Eric Postpischil proposed, you may consider declaring this structure as global (if this is applicable for the case, I mean multi-threading and recursion are not an option).

One more point that I'd like to notice is so-called stack probes. When you allocate a lot of memory from the stack in a single function (more than 1 page to be exact) - on some platforms (such as Win32) the compiler adds an extra initialization code, known as stack probes. This may also have some performance impact (though likely to be minor).

Also, if you don't need all the 40 arrays simultaneously you may arrange some of them in a union. That is, you'll have one big struct, inside which some sub-structs will be grouped into union.