[llvm] [AMDGPU] Restore SP correctly in functions with dynamic allocas (PR #122743)

[Jay Foad via llvm-commits]

jayfoad wrote:

> `tmp = sp + (alignment - 1)`
> `fp &= -alignment`
> `sp += frameSize + alignment`

Can you edit the description so these sequences make sense? `tmp` is not used for anything here.

Also for formatting multiple lines of code it is better to use triple-backticks around the block, instead of single-backticks on each line. Or just indent the block by 4 spaces, then you don't need any backticks at all.

https://github.com/llvm/llvm-project/pull/122743