[PATCH 0/6] Macrofying inline assembly for better compilation

David Laight
Fri, 18 May 2018 09:20:40 -0000

From: Nadav Amit
> Sent: 17 May 2018 17:14
> This patch-set deals with an interesting yet stupid problem: kernel code
> that does not get inlined despite its simplicity. There are several
> causes for this behavior: "cold" attribute on __init, different
function
> optimization levels; conditional constant computations based on
> __builtin_constant_p(); and finally large inline assembly blocks.
>
> This patch-set deals with the inline assembly problem. I separated these
> patches from the others (that were sent in the RFC) for easier
> inclusion.
>
> The problem with inline assembly is that inline assembly is often used
> by the kernel for things that are other than code - for example,
> assembly directives and data. GCC however is oblivious to the content of
> the blocks and assumes their cost in space and time is proportional to
> the number of the perceived assembly "instruction", according to
the
> number of newlines and semicolons. Alternatives, paravirt and other
> mechanisms are affected, causing code not to be inlined, and degrading
> compilation quality in general.
>
> The solution that this patch-set carries for this problem is to create
> an assembly macro, and then call it from the inline assembly block.  As
> a result, the compiler sees a single "instruction" and assigns
the more
> appropriate cost to the code. In addition, this patch-set removes
> unneeded new-lines from common x86 inline asm's, which
"confuse" GCC
> heuristics.

Can't you get the same effect by using always_inline ?

	David