rust/src/test/mir-opt

This folder contains tests for MIR optimizations.

The test format is:

(arbitrary rust code)
// END RUST SOURCE
// START $file_name_of_some_mir_dump_0
//  $expected_line_0
// ...
// $expected_line_N
// END $file_name_of_some_mir_dump_0
// ...
// START $file_name_of_some_mir_dump_N
//  $expected_line_0
// ...
// $expected_line_N
// END $file_name_of_some_mir_dump_N

All the test information is in comments so the test is runnable.

For each $file_name, compiletest expects [$expected_line_0, ..., $expected_line_N] to appear in the dumped MIR in order. Currently it allows other non-matched lines before, after and in-between. Note that this includes lines that end basic blocks or begin new ones; it is good practice in your tests to include the terminator for each of your basic blocks as an internal sanity check guarding against a test like:

bb0: {
    StorageLive(_1);
    _1 = const true;
    StorageDead(_1);
}

that will inadvertantly pattern-matching against:

bb0: {
    StorageLive(_1);
    _1 = const true;
    goto -> bb1
}
bb1: {
    StorageDead(_1);
    return;
}

Lines match ignoring whitespace, and the prefix "//" is removed.

It also currently strips trailing comments -- partly because the full file path in "scope comments" is unpredictable and partly because tidy complains about the lines being too long.

compiletest handles dumping the MIR before and after every pass for you. The test writer only has to specify the file names of the dumped files (not the full path to the file) and what lines to expect. There is an option to rustc that tells it to dump the mir into some directly (rather then always dumping to the current directory).