On Fri, Feb 08, 2019 at 08:58:18AM +0100, Alexander Graf wrote: > > > > Am 08.02.2019 um 05:11 schrieb Simon Glass <s...@chromium.org>: > > > > Hi Alex, > > > >> On Sat, 2 Feb 2019 at 09:07, Alexander Graf <ag...@suse.de> wrote: > >> > >> > >> > >>> Am 02.02.2019 um 15:13 schrieb Simon Glass <s...@chromium.org>: > >>> > >>> Hi Alex, > >>> > >>>> On Thu, 31 Jan 2019 at 08:06, Alexander Graf <ag...@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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