# Usage

`treereduce` needs a *testcase* and an *interestingness test*.  The test
case can be provided on stdin or via a file with `--source` (`-s`). The
interestingness test is an executable (or script) that exits with 0 if the test
is still interesting, or with any other code otherwise. The interestingness
test is provided on the `treereduce` command line after a `--`. It can either
receive the partially-reduced program on stdin, or via a file provided as
command-line argument. In the latter case, the special symbol `@@` in the
command line tells `treereduce` how to provide the file path. For example,
here's how to reduce a C program while making sure it still compiles with
`clang`:

```sh
treereduce-c -s program.c -- clang -o /dev/null @@.c
```

By default, the resulting file is saved to `treereduce.out`; this can be
changed with `--output`. See `--help` for more information.

## Getting results faster

Try `--fast`. If that's not fast enough, read on.

The following tips are in order of descending utility, the last few will
technically make things a bit faster but the gains will be very minor.

- Try `--passes 1`.
- Set `--jobs` to something close to your number of CPU cores.
<!-- TODO(#6): --interesting-stdout-regex -->
- Pass the input to your program on stdin instead of via a file. If your program
  must take a file, put it on a tmpfs.
- Avoid using a script to wrap your interestingness test if you can, using
  `--interesting-exit-code` instead.
- For really slow tests, use `--no-verify` once you've set up your
  interestingness test.
- If the input file is generated, pass it to `treereduce` on stdin.
- If you don't need the output to be a file, pass `--output -` to get output on
  stdout.

## Getting smaller tests

Try `--slow`. If that's not small enough, read on.

- Use `--stable`. If that's too slow, increase `--passes`.
- Set `--min-reduction 1`.
- Run [Halfempty][halfempty] or another test-case reducer on the output.

[halfempty]: https://github.com/googleprojectzero/halfempty