Complete C++20 Modules Support with GCC

by Boris Kolpackov

build2 now provides conforming and scalable support for all the major C++20 Modules features when used with GCC. This includes named modules, module partitions (both interface and implementation), header unit importation, and include translation. All of these features are also supported in libraries, including consumption of installed libraries with information about modules and importable headers conveyed in pkg-config files. As part of this effort we have also created a collection of examples that demonstrate C++20 Modules features that impact the build process...

PVS-Studio 6.26 Released

by Andrey Karpov

A developer believes that this is a bug in the compiler. Nevertheless, it is the author of the code who is wrong. The function does not work correctly due to the fact that undefined behavior occurs in it. The compiler follows that in the r variable a certain sum is calculated. Overflow of the r variable must not happen. Otherwise, it is undefined behavior, which doesn't have to be considered or taken into account by a compiler. So, the compiler thinks that since the value of r variable after ending the loop cannot be negative, then r & 0x7fffffff operation is not needed to reset the sigh bit and the compiler just returns the value of r variable from the function.

Bugs found in GCC with the help of PVS-Studio

by Andrey Karpov

This part could also be called "Example number one thousand, why macros are bad". I really don't like macros and always urge people to avoid using them if possible. Macros make it difficult to read the code, provoke errors, and make the work of static analyzers harder. As best I can tell, from a brief interaction with the GCC code, the authors are big fans of macros. I was really tired looking at what the macros are expanded to, and perhaps missed quite a number of interesting errors. I should confess that I was lazy at times. But still, I will demonstrate a couple of errors, connected with macros.

The C++ highlights of GCC 5.1 and more

by Jens Weller

Just recently, GCC 5.0 has been released as GCC5.1, the not only the newest version of GCC, but also bumping up the version number from 4 to 5. This release is a major milestone for GCC, but also for C++, as it brings full C++14 support, but yet not C++11(std=c++11) as the new default...

Address and Thread Sanitizers in GCC

by Dodji Seketeli on Red Hat Developer Blog

Since their 4.8 version, the C and C++ compilers of the GNU Compiler Collection are equipped with built-in memory and data race errors detectors named Address Sanitizer and Thread Sanitizer.

This article intends to quickly walk you through the highlights of these two interesting tools.

New optimizations for X86 in upcoming GCC 5.0

by Evgeny Stupachenko

Part 1. Vectorization of loads/stores group.

GCC 5.0 significantly improves vector code quality for load groups and store groups. By loads/stores group I mean iterated consecutive sequence of loads/stores. For example:

x = a[i], y = a[i + 1], z = a[i + 2] iterated by “i” is loads group of size 3

...

1. Image conversion (RGB structure to some other) ...
2. N-dimentional coordinates. (Normalize array of XYZ points) ...
3. Multiplication of vectors by constant matrix: ...

... GCC 5.0:

1. Introduces vectorization of load/store groups of size 3
2. Improves load groups vectorization for all supported sizes
3. Maximizes load/store groups performance by generating code that is more optimal for particular x86 CPU...