On 09/02/2014 06:00 PM, Stefan Monnier wrote:

> Have you made some preliminary measurements (on microbenchmarks) to try
> and see how much speed up we might gain?  Given the cost of strlen and
> parse_str_as_multibyte, I'd expect that the best-case benefit might turn
> out to be rather small.

For the moment, I don't have an idea how to benchmark parse_str_as_multibyte
in "near-to-real-use" conditions.  But I guess that we can have some gain
for "simple" (short, especially short unibyte) strings. That guess is based
on the following results (note ~3x speedup in strcpy/strcat workload):

$ gcc -Wall -O2 -o t-alloca t-alloca.c t-use.c
$
$ /usr/bin/time ./t-alloca 100 100
Use malloc for allocation and sprintf for workload
2.23user 0.00system 0:02.23elapsed 100%CPU (0avgtext+0avgdata 1440maxresident)k
0inputs+0outputs (0major+59minor)pagefaults 0swaps
$
$ /usr/bin/time ./t-alloca 100 100 x
Use alloca for allocation and sprintf for workload
1.85user 0.00system 0:01.85elapsed 99%CPU (0avgtext+0avgdata 1436maxresident)k
0inputs+0outputs (0major+59minor)pagefaults 0swaps
$
$ gcc -DFAST -Wall -O2 -o t-alloca t-alloca.c t-use.c
$
$ /usr/bin/time ./t-alloca 100 100
Use malloc for allocation and strcpy/strcat for workload
0.56user 0.00system 0:00.56elapsed 99%CPU (0avgtext+0avgdata 1440maxresident)k
0inputs+0outputs (0major+59minor)pagefaults 0swaps
$
$ /usr/bin/time ./t-alloca 100 100 x
Use alloca for allocation and strcpy/strcat for workload
0.20user 0.00system 0:00.20elapsed 100%CPU (0avgtext+0avgdata 1440maxresident)k
0inputs+0outputs (0major+60minor)pagefaults 0swaps

Dmitry