Re: Bizarrely Poor Code from Bizarre Machine-Generated C Sources

["Barak A. Pearlmutter" <barak@cs.nuim.ie>]

Success!

Some working magic seems to be this:

    gcc -s -o particle1 \
	-O3 \
	-march=k8 \
	-mfpmath=sse \
	-finline-limit=100000 \
	--param large-function-insns=1000000 \
	--param inline-unit-growth=1000000 \
	--param sra-field-structure-ratio=0 \
	particle1.c -lm

although it looks like -Os gives an additional improvement.

This (with GCC 4.1) reduces code volume to about 16k from a previous
near 1M, and reduces runtime by a factor of about 2700, as compared to
just -O3.

Further improvements welcome.

I'd also suggest adding a section to the GCC documentation on "how to
use GCC as a back-end to another compiler" which gives some typical
magic options like the above that would be useful in circumstances
like these.
--
Barak A. Pearlmutter <barak@cs.nuim.ie>
 Hamilton Institute & Dept Comp Sci, NUI Maynooth, Co. Kildare, Ireland
 http://www.bcl.hamilton.ie/~barak/