Added interop_iolist_fold

[fadushin]

This PR adds a function that supports traversal of values (integers and binaries) in an IO list.

These changes are made under both the "Apache 2.0" and the "GNU Lesser General
Public License 2.1 or later" license terms (dual license).

SPDX-License-Identifier: Apache-2.0 OR LGPL-2.1-or-later

[bettio]

I would like to play a little bit with inline and some other attributes to make sure performance are not reduced by function calls.

[pguyot]

I would like to play a little bit with inline and some other attributes to make sure performance are not reduced by function calls.

#define would work as well

[bettio]

I did a first investigation:

static inline InteropFunctionResult size_fold_fun(term t, void *accum)

and

inline InteropFunctionResult interop_iolist_fold(term t, interop_iolist_fold_fun fold_fun, void *accum)

on x86_64 allow gcc to perform a fair level of optimization, on xtensa doesn't look yet nearly the same, anyway I would love to do some additional investigation, but definitely using inline would be a good first step.

[bettio]

I would slightly defer merging this PR after some investigation, minor changes and tricks to allow compiler optimizing it back to something comparable to previous version.
Right now without some changes it would have a significant penalty due to function calls / branching.

[fadushin]

Can you quantify the difference in performance with a test? And for the majority of cases, is it even measurable? Or are these a priori analyses based on generated code? It might be hard to make assessments about performance without actual measurements, e.g., due to processor pipelining and other tricks.

[fadushin]

The problem with in-lining is code bloat. We are already pushing the boundaries on some platforms, especially smaller microcontrollers.

[bettio]

The problem with in-lining is code bloat. We are already pushing the boundaries on some platforms, especially smaller microcontrollers.

If we do inline it doesn't get worse than now since those functions are already duplicated, however by using inline I think the compiler is allowed to keep them not inlined when using -Os.

[pguyot]

For what is worth, emscripten builds require -O3 -sINLINING_LIMIT to run in the browser.

[fadushin]

If we do inline it doesn't get worse than now since those functions are already duplicated, however by using inline I think the compiler is allowed to keep them not inlined when using -Os.

True, but bear in mind that in the crypto branch, on ESP32 (due to the mbedtls API) we need to call this function for each crypto algorithm (for hashing, but maybe later for encryption as well). There are currently 6 hashing algorithms supported in that branch (md5, sha1, sha224, sha256, sha384, and sha512)

[bettio]

I used this version for testing purposes.

2-inlines-fold.txt