dash performance regression with [ in latest github code

[Jan Pechanec <Jan.Pechanec@oracle.com>]

Hi,

thank you for working on dash.  I was testing it recently and it worked
really well.

However, I noticed the dash code from github does filename pattern
matching even for code like "[ x = x ] && echo ok".  I believe the
unquoted space after '[' should not trigger pattern matching but rather
only to invoke the test/[ utility, as before.  It seems it works fine
though and only doing some extra unneeded work which may not be
immediatelly noticeable.

dash installed on my Oracle Linux 9:

janp:len49:~/_INST/dash$ strings /usr/bin/dash | grep dash
dash-0.5.11.5-4.el9.x86_64.debug
janp:len49:~/_INST/dash$ time dash -c 'i=0; while :; do : $((i=i+1)); [ $i -eq 500000 ] && break; done'

real    0m0.752s
user    0m0.748s
sys     0m0.002s

dash from github (commit b3e38adf6718801e7f06267b438c45caec9523bb) take
way more time to do the same thing:

janp:len49:~/_INST/dash$ time ./src/dash -c 'i=0; while :; do : $((i=i+1)); [ $i -eq 500000 ] && break; done'

real    0m4.202s
user    0m1.361s
sys     0m2.804s

For the latter, strace shows open, fstat, getdents*, and close system
calls for each iteration and it depends on number of files in the
current directory.  With more files, it takes more time:

janp:len49:/etc$ time ~/_INST/dash/src/dash -c 'i=0; while :; do : $((i=i+1)); [ $i -eq 500000 ] && break; done'
real    0m15.591s
user    0m5.704s
sys     0m9.828s

If I change [ to test, the dash github version behaves as before, and
possibly even faster:

janp:len49:~/_INST/dash$ time ~/_INST/dash/src/dash -c 'i=0; while :; do : $((i=i+1)); test $i -eq 500000 && break; done'

real    0m0.662s
user    0m0.659s
sys     0m0.002s

Even bash would be faster than the current github version of dash:

janp:len49:~/_INST/dash$ time bash -c 'i=0; while :; do : $((i=i+1)); [ $i -eq 500000 ] && break; done'
real    0m1.943s
user    0m1.939s
sys     0m0.002s

Unfortunately, I do not have time to work on a patch.

Best regards,
Jan

-- 
Jan Pechanec <jan.pechanec@oracle.com>