Add size_of annotation to help CBMC's allocator

[tautschnig]

Description of changes:

CBMC's heap allocator will produce objects that aren't just a byte array when a prior call to size_of was involved in computing the number of bytes to be allocated via malloc/calloc/realloc. This, in turn, permits type-safe member accesses to heap-allocated objects. This should speed up copying as well as all other operations on the resulting object (which will then not have to go through byte extract/byte update operations).

It also seems that there no longer is a "size_of" intrinsic.

Resolved issues:

Fixes: #1286

Related RFC:

n/a

Call-outs:

n/a

Testing:

• How is this change tested? Locally reviewed CBMC's --program-only output on some Vector examples.

• Is this a refactor change? No.

Checklist

• Each commit message has a non-empty body, explaining why the change was made
• n/a Methods or procedures are documented
• Regression or unit tests are included, or existing tests cover the modified code
• My PR is restricted to a single feature or bugfix

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 and MIT licenses.

[adpaco-aws]

Thanks for this detailed explanation, @tautschnig ! A few questions.

[tautschnig]

With thanks to @karkhaz for making this happen, and with the hope that this isn't just about some GitHub runner anomaly (but at least the numbers stack up with my local experiment):

  s2n-quic/quic/s2n-quic-core/slice::tests::vectored_copy_fuzz_test:
    variants:
      kani_new:
        metrics:
          solver_runtime: 74.86000000000001
          success: true
          symex_runtime: 7.85538
          verification_time: 93.35263
      kani_old:
        metrics:
          solver_runtime: 178.3941
          success: true
          symex_runtime: 7.67614
          verification_time: 196.657

[adpaco-aws]

It's looking great, @tautschnig ! Just wondering if you think we should add any more tests to the performance regression or not. Is vectored_copy_fuzz_test already in there?

[zhassan-aws]

Thanks @tautschnig!

One small point. The OP says:

Fixes: #1781

But #1781 seems unrelated?

[tautschnig]

Thanks @tautschnig!

One small point. The OP says:

Fixes: #1781

But #1781 seems unrelated?

My apologies, looks like I wrongly inferred this from #1286 (comment). I just confirmed that (as expected) #1781 is not fixed.

[tautschnig]

It's looking great, @tautschnig ! Just wondering if you think we should add any more tests to the performance regression or not. Is vectored_copy_fuzz_test already in there?

That test is already there.