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Date:      Wed, 29 Mar 2017 19:25:43 +0200
From:      Dimitry Andric <dim@FreeBSD.org>
To:        Brooks Davis <brooks@freebsd.org>
Cc:        Mark Millard <markmi@dsl-only.net>, FreeBSD Ports <freebsd-ports@freebsd.org>, FreeBSD PowerPC ML <freebsd-ppc@freebsd.org>, FreeBSD Toolchain <freebsd-toolchain@freebsd.org>, FreeBSD Current <freebsd-current@freebsd.org>
Subject:   Re: FYI: what it takes for RAM+swap to build devel/llvm40 with 4 processors or cores and WITH__DEBUG= (powerpc64 example)
Message-ID:  <779FB7DC-C041-43CD-ADF2-1F5D791832A6@FreeBSD.org>
In-Reply-To: <20170329155316.GK59667@spindle.one-eyed-alien.net>
References:  <3EDEF0B7-59C5-4648-9737-6682E18645BC@dsl-only.net> <39C60316-F905-490D-B0AB-BC24D7F351A2@dsl-only.net> <7F94CE59-D2CC-4D6F-B1CD-FF3D1F8EDCE7@FreeBSD.org> <45E32F4F-A238-47AA-8E1E-7AD4D9E857D9@dsl-only.net> <20170329155316.GK59667@spindle.one-eyed-alien.net>

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On 29 Mar 2017, at 17:53, Brooks Davis <brooks@freebsd.org> wrote:
> 
> On Mon, Mar 27, 2017 at 03:25:04AM -0700, Mark Millard wrote:
...
>> This is extreme enough that next time I synchronize
>> /usr/ports and it has a devel/llvm40 update I'll
>> likely rebuild devel/llvm40 without using WITH_DEBUG= .
>> I'm more concerned with the time it takes than with
>> the file system space involved.
> 
> In the case of LLVM, enabling debug builds does a LOT more than adding
> symbols.  It's much more like enabling WITNESS and INVARIANTS in your
> kernel, except that the performance of the resulting binary is much
> worse than a WITNESS kernel (more like 10x slowdown).
> 
> As Dimitry points out, these builds are of questionable value in ports
> so garbage collecting the knob might be the sensable thing to do.

I suggest that for the LLVM ports, the DEBUG option should set the
RelWithDebInfo build type for CMake.  That will give you binaries which
can produce good backtraces, and a fair chance at debugging, in a pinch.

-Dimitry


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