GCC 16 has been released

179

HHeliumHydride about 4 hours ago 32 commentsRead Article on gcc.gnu.org

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Discussion (32 Comments)Read Original on HackerNews

gavinray•about 2 hours ago

I want to point out an implemented feature that people SHOULD be adopting but that I doubt will be picked up:

  P2590R2, Explicit lifetime management (PR106658)

This is for "std::start_lifetime_as<T>". If you have not heard of this before, it's the non-UB way to type-pun a pointer into a structured type.

Nearly all zero-copy code that deals with external I/O buffers looks something like:

  std::unique_ptr<char[]> buffer = stream->read();
  if (buffer[0] == FOO)
    processFoo(reinterpret_cast<Foo*>(buffer.get())); // undefined behavior
  else
    processBar(reinterpret_cast<Bar*>(buffer.get())); // undefined behaviour

With this merged, swap the reinterpret_cast for start_lifetime_as and you're no longer being naughty.

https://en.cppreference.com/cpp/memory/start_lifetime_as

groundzeros2015•about 2 hours ago

You’re allowed to type pun char buffers.

jcranmer•about 2 hours ago

No, you're not.

You're allowed to access any type via a char buffer. But the converse is not true (quoting https://eel.is/c++draft/expr#basic.lval-11):

> An object of dynamic type Tobj is type-accessible through a glvalue of type Tref if Tref is similar ([conv.qual]) to: Tobj, a type that is the signed or unsigned type corresponding to Tobj, or a char, unsigned char, or std :: byte type. If a program attempts to access ([defns.access]) the stored value of an object through a glvalue through which it is not type-accessible, the behavior is undefined.

The dynamic type of a char buffer is, well, a char buffer, and can only be accessed via things that are the same type as a char buffer up to signedness and cv-qualification. The actual strict aliasing rules are not commutative!

groundzeros2015•about 1 hour ago

I’m not a language lawyer but i think the part you are missing is about “type establishment”. (Is this a C vs C++ thing?)

Malloc returns a buffer and then you cast it to the type you want. Similarly for all memory allocators.

Punning the same region of char buffer as two different types is a bit different.

ozgrakkurt•about 2 hours ago

And should always use -fno-strict-aliasing anyways. The default rules are insane

t-3•about 3 hours ago

Somehow I never realized that GCC has a very regular release schedule until looking it up just now: https://gcc.gnu.org/develop.html

bluGill•about 2 hours ago

Large projects have been going to regular scheduled releases for a long time. Until the 90's people thought they could waterfall a large release with all your desired features (and for tiny projects this is still a good idea), but as your projects grow (possibly just to small) you reach a point where someone is always working on a feature that isn't ready yet, so a regular release means you still can support your customers with releases. This forces developers who are unsure they will be ready to have some sort of "disabled this unstable feature" toggle, which is about the best you can do.

cogman10•about 2 hours ago

Yup. OpenJDK is one of the best success stories of this.

Up until Java 8, they would release once features were complete. But that meant there were years between the 7 and 8 release and even more years between the 8 and 9 release.

The industry had gotten into the habit of always running old versions of Java (my company was on 6 for an uncomfortable amount of time. But others have had it worse).

More frequent smaller releases has gotten companies more into the habit of updating frequently which also, very helpfully, gives devs new features frequently.

uyjulian•about 3 hours ago

It has been that way since people from Cygnus (now RedHat->IBM) reorganized the project

r2vcap•about 3 hours ago

Yeah, GCC’s recent major releases have been remarkably regular, much like Fedora’s spring releases, and their releases seem to fit into the same broader rhythm. Hint? Red Hat.

tosti•about 3 hours ago

IIRC, since GCC got covered by GPL3.

It used to be slower and I've spent way too much time working around C++ bugs in GCC 2.95

(The fact that I remember the problematic version is telling :)

gpderetta•about 3 hours ago

Everybody remembers that specific version :). And I wasn't even programming professionally at that time!

bluGill•about 2 hours ago

For many years that was the only version that could be used. What become gcc3 took years. In the end it was better, but for a while gcc 2.95 was the best we had despite the bugs.

physicsguy•about 2 hours ago

They changed their major release numbers too tbf. 4.x it was point release per year, now it's a major release per year.

xzstas•about 2 hours ago

I've already been using it for some time (debian sid has a trunk package). it has c++26 reflection, so I already do some magical things with reflection (much better for some cases e.g. for ser-des). I only wish they had a lsp server in their eco-system!

klaussilveira•about 2 hours ago

libstd has been giving me issues running gcc 16 binaries on Debian 12 and 13.

dapperdrake•about 2 hours ago

Does -Ofast still ignore -fno-fast-math ?

shevy-java•about 1 hour ago

I tried the unstable sources for a while, in the last ~3 months. I ran into some issues with some programs (could not compile them with recent GCC, but older GCC worked fine), so gcc 15.x works better for me in general (presently) - but from, say, +3000 programs to compile, the vast majority works well, and a few may need patches (which can often be found in LFS/BLFS by the way, they often use sed instructions to fix individual things and then it works usually).

Hopefully they fixed those issues. We all need stability and things-to-work.