Fix Miri error with -Zmiri-tag-raw-pointers

[jturner314]

Before this PR, running MIRIFLAGS="-Zmiri-tag-raw-pointers" cargo miri test caused Miri to report undefined behavior in the test_dgemm test. This PR fixes the underlying issue – Miri doesn't like us using a reference to an element to access other elements.

There may be other Miri errors. Miri takes forever to run, and I haven't waited for it to finish yet.

[bluss]

I need to run this through the benchmark. I guess it's fine of course. Thanks a lot.

[ghost]

Miri takes forever to run, and I haven't waited for it to finish yet.

You could adjust the FAST_TEST in sgemm.rs to be

const FAST_TEST: bool = option_env!("MMTEST_FAST_TEST").is_some() || cfg!(miri);

which makes a full run take a minute on my machine

[bluss]

miri ci already sets MMTEST_FAST_TEST FWIW, that's why it's there.

[jturner314]

Oh, that's much better. MMTEST_FAST_TEST=1 MIRIFLAGS="-Zmiri-tag-raw-pointers -Zmiri-check-number-validity" RUSTFLAGS="-Zrandomize-layout" cargo +nightly miri test runs in less than 20 seconds and has no errors (with this PR).

@bluss Would you like me to add MIRIFLAGS="-Zmiri-tag-raw-pointers -Zmiri-check-number-validity" RUSTFLAGS="-Zrandomize-layout" to ci/miri.sh?

[bluss]

yes why not

[bluss]

Thanks!