Enhanced Makefile System

[llvmbot]

Bugzilla Link	731
Resolution	WONTFIX
Resolved on	Feb 18, 2008 00:43
Version	trunk
OS	All
Blocks	#970
Reporter	LLVM Bugzilla Contributor
CC	@tlattner

Extended Description

Currently, all significant Makefile logic is located in the Makefile.rules file.
This organization is awkward as it does not isoloate or encapsulate separate
functionalities into separate files. It also means that on every invocation (of
which there are many), make must process the entire file, most of which isn't
used on any given directory. Consequently, a revision to the makefile system is
desireable.

The envisioned system remains mostly compatible with the existing system, with a
few notable exceptions:

1. All Makefile* crud is located in a new "make" directory at the top level.
2. The Makefile.rules logic is split into separate Makefile. files where
   indicates the kind of thing to build (lib,archive,module,tool,etc.)
3. Makefiles in the individual build directories no longer simply include
   Makefile.common but, rather, include one (or more) of the task makefiles
   found in the
4. Certain variables such as BUILD_ARCHIVE are no longer necessitated, as they
   are replaced by including the appropriate Makefile.

In conjunction with this change, variable names should (once again) be
regularized using an understandable pattern, especially one that corresponds to
the use of the task names (e.g. all vars in Makefile.lib should be prefixed by
"lib" or "Lib" or "LIB"). Furthermore, the documentation will need to be updated.

Such a makefile system will make future enhancements easier as LLVM grows as
well as making it easier to maintain without having to grok all 1700 lines of
Makefile.rules.

[llvmbot]

Another feature we need. Build mode in the current makefile system is confusing.
We should have a set of independent toggles each signified by a letter. Upper
case indicates the feature is enabled, lower case indicates the feature is
disabled. Build mode names are then just the set of letters in specific order.
The list below shows the toggles we need and their default state is indicated by
the case of the letter.

p = profiling (no) -- build with profiling enabled
o = optimize (no) -- non-optimized build (easier debugging)
D = debug (yes) -- compiled with debug flags
A = assert (yes) -- assertions are compiled in
s = small (no) -- favors speed over size

This forms an acronym, PODAS which defaults to poDAs. That is, by default debug
flags and assertions are included. Each of these toggles should be available via
both a configure options (e.g. --enable-profiling, --enable-optimized) as well
as Makefile variables that control the toggles as well.

[llvmbot]

It is clear that I don't have time to work on this. It is a major rewrite of the
makefile system and I've already done that once for LLVM. I might consider it if
was okay to change the build tool to scons, but we can't for pragmatic reasons.
So, if this is to get done, someone else will need to do it.

[lattner]

no problem

[llvmbot]

Didn't get done in 1.8, not sure it will ever get done.

[llvmbot]

I might take another crack at this.

[llvmbot]

Given that HLVM and LLVM are merging, it seems more useful to revise the HLVM
build system (scons based) to meet the configuration and build needs of LLVM.
scons is easily as fast as make, python is ubiquitous and the scons build system
affords us the ability to build across our major platforms (win32, Unix, MacOS)
from one build specification. It can generate the MSVC++ project files so the
win32 directory could disappear without any loss of functionality.

[llvmbot]

Too late for 2.0

[llvmbot]

I won't have time to do this any time in the foreseeable future.

[lattner]

This is certainly still interesting, but needs to be reevaluated in the context of llvm-top. When we get back to this we should also see if there are other options interesting.

[llvmbot]

I think using scons at this point is just too much of a change for llvm. What I would like to do is the original proposal of modularizing the makefiles so that each directory builds one kind of thing, etc. I've already started that work in the support module (currently unused). I'd like to see all the supportish type things moved there and all the other modules start using it. Of course, it needs significant upgrade since I last worked on it. I need a makefile system for HLVM and I'm abandoning scons there because I don't want HLVM looking any different from any of the other LLVM projects. So, I'll be working on this in the support module so that HLVM and sample projects can use it. When those are sufficiently working well, I'll retro-fit LLVM .. don't hold your breath :)

[lattner]

how is llvm-top going?

[tlattner]

This bug should probably still be closed or renamed since SCONS is no longer considered.