-O3 gcc libraries

[classilla]

Based on @NapalmSauce 's comments in #607, we need new libgcc, libatomic and libstdc++ for G3, 7400, 7450 and G5 built -O3 for 10.4.

[classilla]

(currently we use a single genericized libgcc etc anyway, so this could be an architecture-specific benefit)

[NapalmSauce]

(nevermind, just looked at an .app from sourceforge)

Also @kencu of course I'm not messing with the bootstrap flags; I keep it to bootstrap-debug, just for the final build flags. I used gcc-5's stock libraries, including the gmp, mpfr and mpc versions. I haven't encountered any issues with bootstrap and so far, but still, I'm interested to know if something really breaks that I'm overlooking.

[kencu]

Well -- Iain tells me that the optflags for the libgcc and gcc builds are intrinsic to the gcc build system, they are set to optimal settings, and they totally ignore how we set the optflags or build the the bootstrap compiler.

Are you modifying the deep-in-the-guts gcc Makefiles? If so, I can't sell that to MacPorts.

Perhaps you can show me what you are doing, so i understand better?

[kencu]

@iains -- can you weigh in here for a second? We're trying to make sure that gcc builds itself with optimal settings and there is some question whether it does.

Specifically the gcc is gcc48, but as you know, MacPorts uses parts of libgcc from libgcc 5,6, & 7 in the final mix.

[kencu]

(aside -- gcc8 / libgcc8 builds on 10.4 and 10.5 PPC too -- I just haven't rolled that out to macports yet. I haven't tried gcc9 in a while, but Iain may well have done).

[NapalmSauce]

No, really, I don't want to hack the build system, all I'm doing is setting custom CFLAGS and CXXFLAGS, which the build ignores during stage1, but uses for stage2 and 3. Even in stage2 and stage3 an -O3 flag seems to be discarded in various directories. The resulting libraries, though, get fatter with -O3, so CFLAGS/CXXFLAGS, at the very least, does something.

[kencu]

Well if that does change the compiler, and I take your word for it for now, that is news to me as I was under the impression that gcc totally ignored all that beyond the bootstrap compiler (unless you go to some lengths https://github.com/kencu/TigerPorts/commit/d26a0bfb366eeda7a1385c61239bdf8d421fbde1#diff-969dec99a801dec9918fbde6ddf5d442 to force gcc to do something you want it to). Live and learn, I guess.

I have to stick with macports builds, as I use that infrastructure to fix hundreds of other tickets and issues with ports, so can't veer too far off the farm.

[kencu]

One thing to know, btw, if you're comparing to the macports libgcc build -- the overall libgcc infrastructure on macports comes from (at least) three different versions of libgcc.

The approach is to use the libgcc dylibs from the last version supported on the OS, so the "libgcc" that gcc48 uses on 10.4 Tiger with macports is actually mostly libgcc 7.5.0, with parts of libgcc 6, and parts from libgcc48.

[kencu]

well, yes indeedy, you can -- this is for libc, but presumably the same for other libraries. https://www.gnu.org/software/libc/manual/html_node/Configuring-and-compiling.html. Look at that. I learn so much from you guys.

Now I will have to ponder how I can use that information...

[NapalmSauce]

I'm working on getting the gcc runtimes. I hoped I could lazily cross-compile everything from 10.5 for 10.4 but it fails to. :-( I'll just properly boot into tiger.

It says default to -O2 -g . GCC (the compiler portion) might default to no -O flag specified, with runtimes libraries defaulting to -O2 -g just like glibc does.. That would make sense from my tests.

[kencu]

I am still trying to understand how compiling a library with a different opt setting could speed up your compilation, though.

The gcc48 compiler, sure -- it does a lot of this and that -- but the library is just a bunch of precompiled routines.

[iains]

Hi folks, Ken <notifications@github.com> wrote:

I am still trying to understand how compiling a library with a different opt setting could speed up your compilation, though. The gcc48 compiler, sure -- it does a lot of this and that -- but the library is just a bunch of precompiled routines.

let’s try to separate concerns. ===== 1. How to build GCC with non-standard stage 2/3 bootstrap flags. - this is done by setting BOOT_CFLAGS= to whatever you want [ you can specify the stage flags specifically too STAGEN_???FLAGS= … but that’s tedious ] - it’s not necessary, useful, or wise to build the stage1 compiler with complex optimisation; one might be trying to build using c++ features that were very new when the bootstrap compiler was made…. - in the “old days” it was said by at least two major vendors that the optimum code on Darwin was -Os (smallest achieved fastest)… so for folks building on 10.4 / 10.5 that’s a consideration. Unfortunately, I am only repeating what I’ve been told by vendors and major users - no hard evidence to back this up. - If you are using sources (unpatched) <= 6.5 then I would recommend -Os or -fdeclone-ctor-dtor (CXXFLAGS) to work around a bug with cloneing functions [I’ve fixed this in all open branches and will back port to Darwin-specific 6.5 and 5.5.]. ====== 2. if one is building a cross compiler without bootstrapping then CFLAGS/CXXFLAGS take effect. ===== 3. I can bootstrap all open branches natively on Darwin8, with two constraints : A) the current sources need ld64-58.2.1 at least B) patches mentioned here: https://gcc.gnu.org/pipermail/gcc-testresults/2020-May/560310.html On my 500MHz G4 bootstrap & test takes almost a week …. ===== 4. Non-native Darwin8 bootstrap is possible on Darwin9: A) the current sources need ld64-58.2.1 B) patches mentioned here: https://gcc.gnu.org/pipermail/gcc-testresults/2020-May/560310.html C) You _must_ use —with-sysroot=/Developer/SDKs/MacOSX10.4u.sdk D) You must ‘export MACOSX_DEVELOPMENT_TARGET=10.4 E) It’s advisable to bootstrap GMP and friends with the compiler. ====== 5. The library mess .. - we need to find a usable technical solution to cleaning this up … The fundamental problem is that we have a bunch of work-arounds to try and allow “after market upgrades” to system libraries .. I’m not convinced that this is the right solution for these old platforms, it could be better to “make a backup and install an updated working library” — at least for libgcc_s and libstdc++. Anyway, sorry that I don’t have many cycles free for this right now - but hopefully once GCC 10.2 is out I’ll poke at some of these things. Could we try to make separate threads for each problem, if possible - to help us figure out what we decided :) cheers Iain

[iains]

iains <notifications@github.com> wrote:

Hi folks, Ken ***@***.***> wrote: > > I am still trying to understand how compiling a library with a different > opt setting could speed up your compilation, though. > > The gcc48 compiler, sure -- it does a lot of this and that -- but the > library is just a bunch of precompiled routines. let’s try to separate concerns. ===== 1. How to build GCC with non-standard stage 2/3 bootstrap flags. - this is done by setting BOOT_CFLAGS= to whatever you want

Iff you want to build the [eventual target] libraries with non-standard optimisation this is done with CFLAGS_FOR_TARGET= this will also apply to the target libraries that are bootstrapped with the compiler. fine tweaking is possible - there are settable flags for everything…. … but TBH, I’ve never found it necessary in ≈ 15 years of working with GCC (including many native crosses etc). I’d say “you should have a very clear idea of what you are intending to achieve and why” before moving off the path that is well-tested. Iain

[NapalmSauce]

-O3 10.4-native libgcc and friends, one set per subarch. Do you plan to ship them next beta, or something like upload them loose on sourceforge so beta-users can test outside of cycles?

gcc-runtimes.zip

[classilla]

Wow, that's great! Thank you, that saves me a lot of time. I think we can probably ship them in the beta.