FYI: what it takes for RAM+swap to build devel/llvm40 with 4 processors or cores and WITH__DEBUG= (powerpc64 example)

[Dimitry Andric]

On 27 Mar 2017, at 23:11, Mark Millard <markmi at dsl-only.net> wrote:
> 
> On 2017-Mar-27, at 5:53 AM, Dimitry Andric <dim at FreeBSD.org> wrote:
>> On 27 Mar 2017, at 12:25, Mark Millard <markmi at dsl-only.net> wrote:
>>> 
>>> On 2017-Mar-27, at 2:41 AM, Dimitry Andric <dim at FreeBSD.org> wrote:
>>>> On 26 Mar 2017, at 23:36, Mark Millard <markmi at dsl-only.net> wrote:
>> ...
>>>>> Installed packages to be REMOVED:
>>>>> 	llvm40-4.0.0.r4
>>>>> 
>>>>> Number of packages to be removed: 1
>>>>> 
>>>>> The operation will free 49 GiB.
>>>> 
>>>> Yes, this is big.  But there is no real need to build the llvm ports
>>>> with debug information, unless you want to hack on llvm itself.  And
>>>> in that case, you are better served by a Subversion checkout or Git
>>>> clone from upstream instead.
>> ...
>>> Historically unless something extreme like this ends up
>>> involved I build everything using WITH_DEBUG=  or explicit
>>> -g's in order to have better information on any failure.
>> 
>> The problem with the ports implementation of WITH_DEBUG is that it
>> always disables all optimizations, without a possibility to override.
>> Which bloats the resulting object files, libraries and executables, and
>> especially so for large C++ projects such as LLVM.
>> 
>> I can recommend the following workaround.  If you want to build a port
>> with optimizations disabled, you can always pass -O0 in CFLAGS.
>> 
>> -Dimitry
>> 
>> Index: Mk/bsd.port.mk
>> ===================================================================
>> --- Mk/bsd.port.mk	(revision 436685)
>> +++ Mk/bsd.port.mk	(working copy)
>> @@ -1646,7 +1646,7 @@ MAKE_ENV+=	DONTSTRIP=yes
>> STRIP_CMD=	${TRUE}
>> .endif
>> DEBUG_FLAGS?=	-g
>> -CFLAGS:=		${CFLAGS:N-O*:N-fno-strict*} ${DEBUG_FLAGS}
>> +CFLAGS:=		${CFLAGS} ${DEBUG_FLAGS}
>> .if defined(INSTALL_TARGET)
>> INSTALL_TARGET:=	${INSTALL_TARGET:S/^install-strip$/install/g}
>> .endif
> 
> Interesting. WITH_DEBUG's description in the file does not
> mention that stripping of optimization flags:
> 
> # WITH_DEBUG            - If set, debugging flags are added to CFLAGS and the
> #                         binaries don't get stripped by INSTALL_PROGRAM or
> #                         INSTALL_LIB. Besides, individual ports might
> #                         add their specific to produce binaries for debugging
> #                         purposes. You can override the debug flags that are
> #                         passed to the compiler by setting DEBUG_FLAGS. It is
> #                         set to "-g" at default.
> 
> I'll probably give myself an override that I can specify in
> /etc/make.conf , such as:
> 
> # svnlite diff /usr/ports/Mk/bsd.port.mk
> Index: /usr/ports/Mk/bsd.port.mk
> ===================================================================
> --- /usr/ports/Mk/bsd.port.mk	(revision 436747)
> +++ /usr/ports/Mk/bsd.port.mk	(working copy)
> @@ -1646,7 +1646,11 @@
> STRIP_CMD=	${TRUE}
> .endif
> DEBUG_FLAGS?=	-g
> +.if defined(ALLOW_OPTIMIZATIONS_FOR_WITH_DEBUG)
> +CFLAGS:=		${CFLAGS} ${DEBUG_FLAGS}
> +.else
> CFLAGS:=		${CFLAGS:N-O*:N-fno-strict*} ${DEBUG_FLAGS}
> +.endif
> .if defined(INSTALL_TARGET)
> INSTALL_TARGET:=	${INSTALL_TARGET:S/^install-strip$/install/g}
> .endif

Effectively, this gives some sort of support for three of CMake's build
types, e.g:
* Debug, which disables optimization, and obviously adds debuginfo
* Release, which optimizes for speed, and does not add debuginfo
* RelWithDebInfo, similar to Release but does add debuginfo

It would be nice if there was some way of directly utilizing these.  The
RelWithDebInfo target is very useful with the LLVM projects.

-Dimitry

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