netdev - Re: [PATCH] of_mdio: merge branch tails in of_phy_register_fixed

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Date:   Sun, 13 Aug 2017 20:09:08 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     sergei.shtylyov@...entembedded.com
Cc:     andrew@...n.ch, f.fainelli@...il.com, robh+dt@...nel.org,
        frowand.list@...il.com, netdev@...r.kernel.org,
        devicetree@...r.kernel.org
Subject: Re: [PATCH] of_mdio: merge branch tails in
 of_phy_register_fixed_link()

From: Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
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 <sergei.shtylyov@...entembedded.com>

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.