GCC 16 has been released

https://gcc.gnu.org/gcc-16/changes.html

by HeliumHydride • 3 months ago

307 52 3 months ago

gcc.gnu.org

t-3• 3 months 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

tosti• 3 months 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 :)

gpderetta2• 3 months ago

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

physicsguy• 3 months 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.

r2vcap• 3 months 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.

uyjulian• 3 months ago

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

not2b• 3 months ago

That is why egcs was launched, to get around the inability of the old team to do gcc releases. The issues had little to do with ideology and were about fixing a broken process and replacing it with something that had a hope of working.

bluGill3• 3 months 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.

cogman102• 3 months ago

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

Up until Java 9, 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.

xzstas• 3 months 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• 3 months ago

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

gjvc• 3 months ago

are you using

    -static-libstdc++ -static-libgcc

?

gavinray• 3 months 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

groundzeros20153• 3 months ago

You’re allowed to type pun char buffers.

ozgrakkurt• 3 months ago

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

jcranmer2• 3 months 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!

throw834948398• 3 months ago

Your code is not only naughty, it’s also incorrect due to alignment issues.

jandrewrogers3• 3 months ago

There was already a legal way to achieve this that everyone should already have been using (laundering a pointer through a no-op memmove). Using reinterpret_cast here is a bug.

The "start_lifetime_as" facility does one additional thing beyond providing a tidy standard name for the memory laundering incantation. Semantically it doesn't touch the memory whereas the no-op memmove intrinsically does. In practice, this makes little difference, since the compiler could see that the memmove was a no-op and optimized accordingly.

kevin_thibedeau• 3 months ago

This still has unresolved alignment issues that blow up outside the amd64 ecosystem.

szmarczak• 3 months ago

No because the object does not exist after std::launder. It only exists after std::start_lifetime_as. The bytes being there says nothing about the object, per the C++ standard.

amluto2• 3 months ago

The cppreference description seems questionable to me:

Implicitly creates a complete object of type T (whose address is p) and objects nested within it. The value of each created object obj of TriviallyCopyable type U is determined in the same manner as for a call to std::bit_cast<U>(E) except that the storage is not actually accessed, where E is the lvalue of type U denoting obj. Otherwise, the values of such created objects are unspecified.

So T is the complete new object. It contains subobjects, and one of those subobjects has type U. U is initialized as if by bit_cast, and I presume they meant to say that bit_cast casted from the bits already present at the address in question. Since “obj” is mentioned without any definition of any sort, I’ll assume it means something at the correct address.

But what’s E? The page says “E is the lvalue of type U denoting obj,” but obj probably has type char or a similar type, and if it already had type U, there would be no need for bit_cast.

gpderetta2• 3 months ago

Well, ignoring alignment restrictions, it depends on the implementation of read. If it is truly opaque, as far as the compiler is concerned, the kernel (or the network card or whatever) is truly constructing a Foo in that buffer, making the cast perfectly legitimate.

start_lifetime_as is useful when the buffer lifetime is transparent to the compiler and it can mess up aliasing assumptions.

dapperdrake• 3 months ago

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

shevy-java• 3 months 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.

sintax2• 3 months ago

Did you file any bug reports for them?

wg0• 3 months ago

Noob question - Does gcc use LLVM anywhere under the hood or it has its own code generation and optimization pipeline? How does it stack in comparison to LLVM?

mshockwave• 3 months ago

Does gcc use LLVM anywhere under the hood

kouosi• 3 months ago

Does gcc use LLVM anywhere under the hood or it has its own code generation and optimization pipeline? No it doesn't use LLVM How does it stack in comparison to LLVM? Well it support more targets then LLVM and in most cases it generates similar if not better executable.

kelnos• 3 months ago

GCC far far far predates LLVM. They do not share code.

fweimer• 3 months ago

The libsanitizer library is imported from the LLVM sources into the GCC source tree. There are probably more examples of code sharing. Both projects are quite large.

sintax2• 3 months ago

Let me wikipedia that for you :-) Like people mentioned already, gcc predates LLVM by quite some years, ie. Wikipedia mentions March 22, 1987 for gcc, while LLVM's initial release was 2003.

A big difference between the 2 is also the license. GCC uses the GPL while LLVM uses Apache License, hence the projects don't share code.

ksherlock• 3 months ago

The other answers (NO!) are correct, but... there was a gcc plug-in to use the llvm backend with gcc. Apple used llvm-gcc (circa 2012; gcc front end, llvm back end) while transitioning from gcc to llvm.

https://dragonegg.llvm.org

kmoser• 3 months ago

The so-called "json" format for -fdiagnostics-format= has been removed in this release. Users seeking machine-readable diagnostics from GCC should use SARIF.

But:

GCC can now output diagnostics in HTML form via -fdiagnostics-add-output=experimental-html

I wonder what drove the decision to remove JSON output and add HTML output?

rcfox• 3 months ago

It looks like SARIF is JSON, with a formal schema. I'm guessing the JSON they used to output used their own, non-standard schema.

GCC 16 has been released

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