[build2] Installation Error on Manjaro

[Matthew Krupcale]

On Tue, Apr 7, 2020 at 4:50 AM Boris Kolpackov <boris at codesynthesis.com> wrote:

> Yes, that would be an alternative and we already do something like this
> to detect the C/C++ stdlib (see libbuild2/cc/guess.cxx). However, I see
> a number of issues:
> ...
> 3. This would require a preprocessor run which is probably quite a bit
>    slower than --version.

Yeah, given that you have to run those other commands anyways, it's
probably best to avoid running the preprocessor if you can. For
reference:

$ time for i in $(seq 0 1000); do gcc -E -P -xc - <<<"__GNUC__"
&>/dev/null; done
real    0m8.694s
user    0m3.177s
sys    0m5.354s

$ time for i in $(seq 0 1000); do gcc -v -E < /dev/null &>/dev/null; done
real    0m2.192s
user    0m0.610s
sys    0m1.608s

So it's somewhere around 4 times more time-consuming to run the
preprocessor than just e.g. `-v`, `--version`, `-print-search-dirs` on
my system.

Matthew