From: David Miller
> Sent: 14 August 2017 04:09
> From: Sergei Shtylyov <[email protected]>
> Date: Sun, 13 Aug 2017 00:03:06 +0300
>
> > Looks like gcc isn't always able to figure out that 3 *if* branches in
> > of_phy_register_fixed_link() calling fixed_phy_register() at their ends
> > are similar enough and thus can be merged. The "manual" merge saves 40
> > bytes of the object code (AArch64 gcc 4.8.5), and still saves 12 bytes
> > even if gcc was able to merge the branch tails (ARM gcc 4.8.5)...
> >
> > Signed-off-by: Sergei Shtylyov <[email protected]>
>
> Applied, but if two instances of the "same" compiler just with
> different targets changes the optimization, it could be because of a
> tradeoff which is specific to parameters expressed in that target's
> backend.
>
> So in the future we should probably back away from trying to "help"
> the compiler in this way.
Probably a trade off between code size and execution speed.
I've had 'fun' trying to stop gcc merging tail code paths
in order to avoid the cost of the branch instruction.
David
