FennelBuildVariations

From Eigenpedia

The main control over the way Fennel code gets generated is the --with[out]-optimization initBuild.sh flag. The setting for this flag implies defaults for two other flags (--with[out]-debug and --with[out]-assertions), although those two flags can always be specified explicitly.

initBuild.sh flag	implied default for debug symbols	implied default for assertions	compiler optimizations	STL bounds-checking	cache buffer paranoia	OpaqueInteger impl
--with-optimization	--without-debug	--without-assertions	-O3	disabled	disabled	weakly typed (primitive int)
--without-optimization (default)	--with-debug	--with-assertions	none	enabled	enabled	strongly typed (class)

• The --with[out]-assert flag controls whether the standard assert macro generates assertion-checking code (--with) or is treated as a NOP (--without). Note that Fennel supports a non-standard permAssert macro which always generates assertion-checking code regardless of this build variation.
• The --with[out]-debug flag only controls whether debug symbols are included in compiled binaries; it does not have any effect on the efficiency of the code generated.
• The --with-assertions option is currently only proposed and has not yet been implemented.
• There are no prohibited combinations, although some combinations aren't very useful.

Shortcuts

Various options exist to reduce the amount of time a Fennel "initial" build takes.

The --with[out]-tests flag controls whether or not unit tests are executed. They are skipped by default, but should be executed before checking in code.

The --without-thirdparty-build flag (also known as --without-fennel-thirdparty-build, --skip-thirdparty-build and --skip-fennel-thirdparty-build) skips building the Boost and STLport libraries. This is safe to do as long as you're certain that neither library has been upgraded since you last built it. The initBuild.sh script builds both the release and debug versions of the libraries, so switching Fennel's optimization and debug symbols is also okay.

In addition, Fennel's makefiles have enough dependency information in them to allow parallel execution in make. Running make -j2 can improve build times significantly. When running initBuild.sh you can specify the environment variable MAKEFLAGS to automatically enable a parallel build:

MAKEFLAGS=-j2 ./initBuild.sh 

Note, however, it is unwise to place MAKEFLAGS=-j2 in your shell startup scripts since build errors can occur if you execute a makefile from another project that doesn't have sufficient dependencies between targets.

Parallel Build Time Comparisons

Architecture / Build Config	Parallelism	Time (nearest 15s)
Intel Core 2 Duo, 2GHz, 2GB, Laptop / Unoptimized	none	11m
	-j2	7m
	-j3	6m 30s
	-j4	6m 30s
4 x dual core AMD Opteron 2210, 1.8 GHz, 8GB, Server / Unoptimized	none	17m 15s
	-j2	10m
	-j4	7m
	-j8	6m 45s
4 x dual core AMD Opteron 2210, 1.8 GHz, 8 GB, Server / Optimized	none	22m 30s
	-j2	12m 30s
	-j4	7m 45s
	-j8	7m 30s

These times include only the time it takes to execute Fennel's Makefile after executing make clean.