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GCC 16 has been released

gcc.gnu.org

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Re: GCC 16 has been released

#11

Post by gavinray »

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". 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 buffer = stream->read();
  if (buffer[0] == FOO)
    processFoo(reinterpret_cast(buffer.get())); // undefined behavior
  else
    processBar(reinterpret_cast(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

Re: GCC 16 has been released

#12

Post by bluGill »

gpderetta wrote: post #4
tosti wrote: post #3

Earlier quoted context omitted.

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 :)

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

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.

Re: GCC 16 has been released

#13

Post by groundzeros2015 »

gavinray wrote: post #11

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 ". 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 buffer = stream->…

You’re allowed to type pun char buffers.

Re: GCC 16 has been released

#14

Post by cogman10 »

bluGill wrote: post #10
t-3 wrote: post #2

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

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 cus…

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.

Re: GCC 16 has been released

#16

Post by ozgrakkurt »

groundzeros2015 wrote: post #13
gavinray wrote: post #11

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 ". 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 buffer = stream->…

You’re allowed to type pun char buffers.

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

Re: GCC 16 has been released

#17

Post by jcranmer »

groundzeros2015 wrote: post #13
gavinray wrote: post #11

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 ". 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 buffer = stream->…

You’re allowed to type pun char buffers.

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!

Re: GCC 16 has been released

#18

Post by jabl »

cogman10 wrote: post #14
bluGill wrote: post #10

Earlier quoted context omitted.

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 cus…

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…

The Linux kernel is another example. The 2.5 development cycle (which led to the stable 2.6 series) was brutally long, and distros resorted to back-porting new features into their own kernels based on the stable 2.4 series that they provided to their users, creating all kinds of excitement. After 2.6.0 was released, Linus basically went nope, not gonna do that again.

Re: GCC 16 has been released

#19

Post by throw834948398 »

gavinray wrote: post #11

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 ". 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 buffer = stream->…

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

Re: GCC 16 has been released

#20

Post by gjvc »

klaussilveira wrote: post #9
xzstas wrote: post #7

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!

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

are you using

    -static-libstdc++ -static-libgcc

?
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