Re: libtool 2.4 args parsing incredibly slow

[Peter O'Gorman]

Hi,

Dan reported a libtool performance regression in libtool-2.4 when 
running his binaries with a large number of arguments.

Libtool creates a shell script which usually sets some env vars and runs 
the binary, new in recent libtool, the script also takes arguments, so 
these have to be removed when execing the binary.

Because forking is usually quite expensive, this shell function avoids 
forks:

func_exec_program ()
{
  for lt_wr_arg
  do
    case \$lt_wr_arg in
    --lt-*) ;;
    *) set x "$@" "$lt_wr_arg"; shift;;
    esac
    shift
  done

  func_exec_program_core ${1+"$@"}
}

Turns out that bash is relatively slow here, even with a simpler loop:

for arg
do
echo "$@" >/dev/null
done

$ time bash ./s.sh `seq 1 1000`
real    0m9.866s
user    0m8.104s
sys     0m0.088s

$ time dash ./s.sh `seq 1 1000`
real    0m0.571s
user    0m0.355s
sys     0m0.097s

$ time zsh ./s.sh `seq 1 1000`
real    0m0.770s
user    0m0.541s
sys     0m0.079s

I have not investigated what the other shells are not doing that bash is 
doing here, it's entirely possible that they're buggy in some way that 
bash isn't.

We'll try to fix libtool to not cause this problem too, of course.

Thanks,
Peter