C++

What’s new in OpenMP 5.0

What’s new in OpenMP 5.0

A new version of the OpenMP standard, 5.0, was released in November 2018 and brings several new constructs to the users. OpenMP is an API consisting of compiler directives and library routines for high-level parallelism in C, C++, and Fortran programs. The upcoming version of GCC adds support for some parts of this newest version of the standard.

This article highlights some of the latest features, changes, and “gotchas” to look for in the OpenMP standard.

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A gentle introduction to jump threading optimizations

A gentle introduction to jump threading optimizations

As part of the GCC developers‘ on-demand range work for GCC 10, I’ve been playing with improving the backward jump threader so it can thread paths that are range-dependent. This, in turn, had me looking at the jump threader, which is a part of the compiler I’ve been carefully avoiding for years. If, like me, you’re curious about compiler optimizations, but are jump-threading-agnostic, perhaps you’ll be interested in this short introduction.

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Understanding GCC warnings, Part 2

Understanding GCC warnings, Part 2

In part 1, I shed light on trade-offs involved in the GCC implementation choices for various types of front-end warnings, such as preprocessor warnings, lexical warnings, type-safety warnings, and other warnings.

As useful as front-end warnings are, those based on the flow of control or data through the program have rather inconvenient limitations. To overcome them, flow-based warnings have increasingly been implemented in what GCC calls the “middle end.” Middle-end warnings are the focus of this article.

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Understanding GCC warnings

Understanding GCC warnings

Most of us appreciate when our compiler lets us know we made a mistake. Finding coding errors early lets us correct them before they embarrass us in a code review or, worse, turn into bugs that impact our customers. Besides the compulsory errors, many projects enable additional diagnostics by using the -Wall and -Wextra command-line options. For this reason, some projects even turn them into errors via -Werror as their first line of defense. But not every instance of a warning necessarily means the code is buggy. Conversely, the absence of warnings for a piece of code is no guarantee that there are no bugs lurking in it.

In this article, I would like to shed more light on trade-offs involved in the GCC implementation choices. Besides illuminating underlying issues for GCC contributors interested in implementing new warnings or improving existing ones, I hope it will help calibrate expectations for GCC users about what kinds of problems can be expected to be detected and with what efficacy. Having a better understanding of the challenges should also reduce the frustration the limitations of the available solutions can sometimes cause. (See part 2 to learn more about middle-end warnings.)

The article isn’t specific to any GCC version, but some command-line options it refers to are more recent than others. Most are in GCC 4 that ships with Red Hat Enterprise Linux (RHEL), but some are as recent as GCC 7. The output of the compiler shown in the examples may vary between GCC versions. See How to install GCC 8 on RHEL if you’d like to use the latest GCC.

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Changes made to the Libabigail ABI change analysis framework in 2018

Changes made to the Libabigail ABI change analysis framework in 2018

This article is for people interested in the long-term maintenance of software systems that expose application binary interfaces (a.k.a. ABIs) to other systems. That long-term maintenance involves detecting and analyzing inevitable changes in the ABIs and assessing whether these changes allow the maintained systems to stay compatible with the components with which they interact.

In this article, I describe what happened to the ABI change analysis framework that I worked on during 2018: the Abigail library (Libabigail) and its associated set of tools. The goal is not to list the myriad changes that happened throughout releases 1.2, 1.3, 1.4, and 1.5 that occurred during that year, but I will walk you through the main changes that happened and put them in perspective.

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How to install GCC 8 and Clang/LLVM 6 on Red Hat Enterprise Linux 7

How to install GCC 8 and Clang/LLVM 6 on Red Hat Enterprise Linux 7

There has been a lot of work to improve C/C++ compilers in recent years. A number of articles have been posted by Red Hat engineers working on the compilers themselves covering usability improvements, features to detect possible bugs, and security issues in your code.

Red Hat Enterprise Linux 8 Beta ships with GCC 8 as the default compiler. This article shows you how to install GCC 8 as well as Clang/LLVM 6 on Red Hat Enterprise Linux 7. You’ll be able to use the same updated (and supported) compilers from Red Hat on both RHEL 7 and 8.

If you want your default gcc to always be GCC 8, or you want clang to always be in your path, this article shows how to permanently enable a software collection by adding it to the profile (dot files) for your user account. A number of common questions about software collections are also answered.

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November 2018 ISO C++ meeting trip report (Core Language)

November 2018 ISO C++ meeting trip report (Core Language)

The ISO C++ standards meeting in November 2018 was held in San Diego, CA. As usual, Red Hat sent three of us to the meeting: me (for the Core Language Working Group), Jonathan Wakely (for the Library Working Group [LEWG]), and Thomas Rodgers (for the Concurrency and Parallelism Study Group [SG1]). I felt the meeting was productive, though some features that had been expected to make it into C++20 are now in question.

Here are new C++ features accepted at the meeting:

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Fall 2018 ISO WG21 C++ Standards Committee meeting trip report

Fall 2018 ISO WG21 C++ Standards Committee meeting trip report

The fall C++ meeting was held in San Diego, CA. As usual, Red Hat sent three of us to the meeting: myself from the Concurrency and Parallelism Study Group (SG1), Jason Merrill from the Core Language Working Group, and Jonathan Wakely from the Library Working Group (LEWG).

SG1 had a fairly full plate but finished the week with a bit of breathing room to spare. This article describes the major topics discussed this week in SG1.

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Support Lifecycle for Clang/LLVM, Go, and Rust

Support Lifecycle for Clang/LLVM, Go, and Rust

On the heels of our recently announcement, General Availability of Clang/LLVM 6.0, Go 1.10, and Rust 1.29, I want to share how we’ll be supporting them going forward. Previously, these packages had been in “Technology Preview” status, which means that they were provided for “you to test functionality and provide feedback during the development process”, and were “not fully supported under Red Hat Subscription Level Agreements, may not be functionally complete, and are not intended for production use”.

So now that we’ve promoted them to fully supported status, what does that mean? In the simplest terms, General Availability (GA) means that these packages have officially entered the “Full Support Phase” of their lifecycle:

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