linux-kernel - Re: [kbuild-all] mipsel-linux-gnu-gcc: error: unrecognized command line option '-mcompact-branches=optimal'

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Message-ID: <alpine.DEB.2.00.1604212159440.21846@tp.orcam.me.uk>
Date:	Thu, 21 Apr 2016 22:10:51 +0100
From:	"Maciej W. Rozycki" <macro@...tec.com>
To:	Ralf Baechle <ralf@...ux-mips.org>
CC:	Fengguang Wu <fengguang.wu@...el.com>, <kbuild-all@...org>,
	Paul Burton <paul.burton@...tec.com>,
	<linux-kernel@...r.kernel.org>, Philip Li <philip.li@...el.com>
Subject: Re: [kbuild-all] mipsel-linux-gnu-gcc: error: unrecognized command
 line option '-mcompact-branches=optimal'

On Thu, 21 Apr 2016, Ralf Baechle wrote:

> >  I don't think it makes sense as the compiler won't support MIPSr6 code 
> > anyway, so first it'll bail out on `-march=mips32r6', and if we go even 
> > further and disable that too, then GAS will probably break somewhere on 
> > inline asm and GCC will produce code which does not make sense otherwise.
> 
> GCC 5.2.0 claims to support mips32r6 and mips64r6.  It's just the option
> -mcompact-branches which seem to have been added later only.

 Ah, I see -- I didn't track the timeline of support for this compiler's 
option and I took it from an earlier response that the compiler does not 
support R6 at all.

 In that case however it looks to me like these `-mcompact-branches=' 
options (all the three we support) need to be wrapped into `$(call 
cc-option,...)'.  They do not affect any functionality and they are an 
optimisation choice only anyway (and therefore I wonder why they've been 
placed in arch/mips/Kconfig.debug rather than arch/mips/Kconfig).

  Maciej