Testing GDC (GCC 7.1) on Runtime-less ARM Cortex-M

[Iain Buclaw via D.gnu]

On 28 June 2017 at 23:15, Mike via D.gnu <d.gnu at puremagic.com> wrote:
> -------------------------------------------------------------------------
> The vast majority of time is spent in "phase opt and generate".  A few
> observations:
>
> * Elapsed time isn't much different between -O3 and -O2 -finline-functions
> * -O2 -finline-functions gave me a smaller binary :)

I did say that -Os (optimize for size) is practically identical to
this. So I'm not surprised. ;-)

And yeah, one of the big differences between -O2 and -O3 is that when
it comes to inlining, -O3 mostly disregards size and cost heuristics.


> * -O0 reduced time significantly, but "phase opt and generate" still takes
> an awfully long time relative to everything else
>
> What exactly is "phase opt and generate"?  I'm assuming "opt" means
> optimizer, but why is it taking such a long time even with -O0?  Maybe it's
> the "generate" part of that that's the most significant.
>

Phase opt and generate is the topl-evel timer for the entire "backend"
compilation phase.  I was expecting to see more of a breakdown of
individual passes.


> With -O0 there's still quite a few things enabled, so maybe I'll start
> appending a "-fno" to each one and see if I can find a culprit.
>

A thought just occurred to me, you are compiling the entire program +
object.d right?  Nothing else will link/be linked to the binary?

If that is the case, you should definitely compile with
-fwhole-program.  I suspect that may cut down your compilation time by
half or even more.


Regards,
Iain.