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