[PATCH] D15393: [X86] Order the local stack symbols to improve code size and locality.

[Zia Ansari via llvm-commits]

zansari added a comment.

In http://reviews.llvm.org/D15393#306468, @hans wrote:

> This looks very interesting.
>
> Maybe update the commit message and/or add to the comments in the file why this is beneficial for code size, since it wasn't obvious for me at least. Do I understand correctly that the idea is that addressing objects closer to %esp generally requires  less code because it can use a tighter addressing mode?


Hi Hans.. Thanks for the review.

Yes, sorry I didn't make that clear in the description. The saving are from allocating more frequently (statically) accessed addresses closer to sp/fp and saving 3-4 bytes of address encoding by doing so.. For example, if a large array is allocated early on the stack and only accessed once, that would cause all other symbols on the stack to cost an extra 3-4 bytes to access, which is a fair bit of bloat if they're accessed frequently.

Hope that helps.


http://reviews.llvm.org/D15393