[LLVMdev] Automake Notes (Long)

[Reid Spencer]

Folks,

I have completed the addition of automake makefiles to LLVM. All
libraries, tools, and runtime libs build now with automake. Note that
there are still many missing things in the automake support. Right now
it just builds the basic software. 

However, before I invest more time in it, I thought some comparison
would help us make some decisions about whether or not to proceed with
automake for the LLVM standard. There are costs and benefits on both
sides.

BUILD/CONFIGURE TIMES
=================================================================
Item                                        Elapsed          User        System
-----------------------------   ----------  ----------   ----------
Configure With Automake            0m48.835s    0m22.700s    0m21.890s
Configure With Current System    0m37.939s    0m18.230s    0m16.980s
Build With Automake                20m29.057s   18m30.230s    1m28.080s
Build With Current System        30m56.017s   25m56.750s    3m15.790s

This was recorded on a 2x2.4GHz Xeon RH9 Linux machine (same one used
for the optimized nightly test). The build was run with "gmake -j 1" in
both cases. The time includes the total time taken to build utils, lib,
tools, and runtime.

Note that while the automake configure takes longer, automake builds the
software in about 1/3 less time than our existing system. A "gmake -j 3"
builds from scratch on my machine in under 10 minutes. Since building is
done much more frequently than configuring, this is a development win.

EXECUTABLE SIZES
================

Below is a list of the sizes of some of the larger/important executables
that LLVM builds. The bytesize of the Automake built version and the
Existing version are shown as well as a percentage. In every case the
automake executable is smaller, by an order of magnitude.

AutoMake Existing   Pct Program 
-------- --------  ---- -------
 2084426 46046545    5% analyze
 6118914 77679274    8% bugpoint*
 2038252 19137945   11% extract*
 3817030 47578060    8% gccas*
 3244568 34163210    9% gccld*
 5713818 60263187    9% llc*
 6446641 52162647   12% lli*
 1892254 16435732   12% llvm-as*
 6630877 54185542   12% llvm-db*
 1811843 15667554   12% llvm-dis*
 5752934 73995210    8% opt
  556978   5153127   11% tblgen

I tried to explain this with two things: -On options. The existing
makefiles build without using -O. I've configure automake to use -O1 on
its compilations. That could still be the difference but I don't see how
it explains an order of magnitude.  Another possibility was that I just
wasn't linking in all the static (pre-linked) object libraries in some
of the executables. But that doesn't explain llvm-as or llvm-db and I
have very meticulously made sure that what gets linked is the same as
the existing system (if I deviated, usually it didn't link). All the
programs run and produces the same --help out.  That's significant
because if certain libraries were not being linked in, their command
line options wouldn't appear in the --help output. 

The only thing I can think of is that the existing makefiles are doing
something weird that causes the bloat (probably in the debug info).

automake PROS/CONS
==================
+ builds faster
+ builds smaller executables
+ we don't have to maintain it 
+ new features/platforms are an upgrade away
+ standard makefile system known by lots of developers
+ GNU Makefile Standards compliance
+ rules are tried and tested and work well on lots of platforms
+ supports automatically creating a distribution (dist target)
+ supports automatically testing a distribution (distcheck target)
+ fast/standard  install/uninstall targets
+ handles install/uninstall of scripts, headers, data, etc.
+ handles installcheck (checking programs after installation)
+ supports automated testing via dejagnu 
+ completely groks libtool for building shared libs on lots of platforms
+ autoconf flags can determine nature of the build
+ supports C, C++, Fortran, Java, Obj-C, Lex, Yacc, Python
+ knows how to build texinfo & man page documentation
+ perfect dependency tracking (each compile updates the info)
+ automatically handles .exe (or other) extensions for executables 
  wherever its needed
+ automatically handles C/C++ tags/etags
+ supports building different targets with different compile options
+ can still be extended in any way GNU make can be
- have to specify each source input file (currently searching 
  for a workaround)
- completely dependent on gmake
- requires Perl (automake written in Perl)

existing PROS/CONS
==================
+ its done and working
+ we have full control over anything
+ somewhat similar to the BSD makefile system
- completely dependent on gmake
- we must maintain it ourselves
- doesn't handle automatic distribution generation
- installs slowly
- testing support is adhoc/inconsistent

CURRENT THINGS TO FIX/FINISH IN AUTOMAKE RULES
==============================================

1. The default/only mode of output is VERBOSE. 
2. Don't use more Makefile.am files than is necessary (e.g. SparcV9
    should just have one, not 5) 
3. Find a way to make it handle bytecode output better
4. Find a way to not maintain list of sources if the library
    developer so chooses (i.e. assume all sources found)
5. Add support in test, examples, projects directories

Reid

-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 189 bytes
Desc: This is a digitally signed message part
URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20041016/1e09efac/attachment.sig>