Re: GNAT's stack checking in Ubuntu 9.04 (and Shootout regex-dna)

[Ludovic Brenta <ludovic@ludovic-brenta.org>]

jonathan wrote on comp.lang.ada:
> Step 1.  Compile without the -a switch:
>
>   -O3 -gnatnp -funroll-all-loops -march=native regexdna.adb
>
>   Running time of ./regexdna: 63 seconds.
>
>   Comment: compilation near instanteous; I suppose it is
>   linking to precompiled  Gnat.Spitbol.Pattern  packages.
>
> Step 2.  Compile with the -a switch:
>
>   -O3 -a -gnatnp -funroll-all-loops -march=native regexdna.adb
>
>   Running time of ./regexdna: 51 seconds.
>
>   Comment: Compilation is slow. Looks like it is recompiling
>   the  Gnat.Spitbol.Pattern  packages.
>
>   So it looks like the performance problem I was complaining
>   about was due to the suboptimal precompiled Spitbol.Pattern.
>   In fact it was almost *entirely* due to the sub-optimal
>   Spitbol.Pattern, because running time is now close
>   to the running time I get from the GNAT GPL compilation.
>   (The GNAT GPL I downloaded was for 64-bit machines. I
>   would speculate that the precompiled Spitbol.Pattern
>   used by the Debian Lenny GNAT was for more general
>   architectures.)

If you use the amd64 port of Debian Lenny, your compiler is optimized
for 64-bit. However, I use the default options for the library. For
example, the i386 (actually i486) build daemon compiled g-spipat.adb
thus:

/build/buildd-gnat-4.3_4.3.2-1.1-i386-3dUv7K/gnat-4.3-4.3.2/build/./
gcc/xgcc -B/build/buildd-gnat-4.3_4.3.2-1.1-i386-3dUv7K/gnat-4.3-4.3.2/
build/./gcc/ -B/usr/i486-linux-gnu/bin/ -B/usr/i486-linux-gnu/lib/ -
isystem /usr/i486-linux-gnu/include -isystem /usr/i486-linux-gnu/sys-
include -c -g -O2      -W -Wall -gnatpg  g-spipat.adb -o g-spipat.o

If anyone is interested, I can try to compile with -O3 -funroll-all-
loops -gnatpg instead.

--
Ludovic Brenta (maintainer of gnat in Debian).