[U-Boot] [PATCH] initcall: Move to inline function

[Tom Rini]

On Fri, Feb 08, 2019 at 08:58:18AM +0100, Alexander Graf wrote:
> 
> 
> > Am 08.02.2019 um 05:11 schrieb Simon Glass <sjg at chromium.org>:
> > 
> > Hi Alex,
> > 
> >> On Sat, 2 Feb 2019 at 09:07, Alexander Graf <agraf at suse.de> wrote:
> >> 
> >> 
> >> 
> >>> Am 02.02.2019 um 15:13 schrieb Simon Glass <sjg at chromium.org>:
> >>> 
> >>> Hi Alex,
> >>> 
> >>>> On Thu, 31 Jan 2019 at 08:06, Alexander Graf <agraf at suse.de> wrote:
> >>>> 
> >>>> The board_r init function was complaining that we are looping through
> >>>> an array, calling all our tiny init stubs sequentially via indirect
> >>>> function calls (which can't be speculated, so they are slow).
> >>> 
> >>> Is this a compiler warning? Could you let me know what this is?
> >> 
> >> It's the code comment I'm removing with this patch :).
> >> 
> >>> 
> >>>> 
> >>>> The solution to that is pretty easy though. All we need to do is inline
> >>>> the function that loops through the functions and the compiler will
> >>>> automatically convert almost all indirect calls into direct inlined code.
> >>> 
> >>> You mean it calls the functions one after the other without a
> >>> function-table array?
> >> 
> >> Exactly. Magical, eh? It even inlines them!
> > 
> > Yes it is surprising. I am also surprised that it reduces code size,
> > but I suppose that is why it does it. Presumably the inlining is what
> > does that.
> 
> Yes, of course. With separate object files, the compiler can not
> inline anything at all, because it does not know how the function
> pointers get used.
> 
> The alternative to this *might* be LTO, which we could think about as
> well. It should help reduce indirection and code size overall. But I
> don't know how well gold works with the linker scripts we have.

I don't object to LTO but there's a LOT of groundwork before it's an
option.  I think in addition to switching to gcc for ld, looking over an
old git stash from when I tried this last, we need to globally switch to
the "clang" method of keeping track of gd rather than how we do it
today.

-- 
Tom
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