libc++ and C++1Y
I am proud to announce that as of September 21, libc++ has a full implementation of the C++1Y standard library. In April of 2013, the C++ standards committee approved a draft version of the next revision of the C++ language, called "C++1Y". (C++11 was called "C++0x" while in development). We hope that this draft standard will be approved next year, and become C++14. The draft standard includes cha
LLVM 3.3 Vectorization Improvements
I would like to give a brief update regarding vectorization in LLVM. When LLVM 3.2 was released, it featured a new experimental loop vectorizer that was disabled by default. Since LLVM 3.2 was released, we have continued to work hard on improving vectorization, and we have some news to share. First, the loop vectorizer has new features and is now enabled by default on -O3. Second, we have a new SL
Status of the C++11 Migrator
Since the design document for cpp11-migrate, the C++11 migrator tool, was first proposed in early December 2012 development has been making steady progress. In this article I'll talk about what's been implemented in cpp11-migrate so far, what's coming up, and how you can get involved. The purpose of the C++11 Migrator is to do source-to-source translation to migrate existing C++ code to use C++11
LLVM 3.0 Type System Rewrite
One of the most pervasive IR (and thus compiler API) changes in LLVM 3.0 was a complete reimplementation of the LLVM IR type system. This change was long overdue (the original type system lasted from LLVM 1.0!) and made the compiler faster, greatly simplified a critical subsystem of VMCore, and eliminated some design points of IR that were frequently confusing and inconvenient. This post explains
Greedy Register Allocation in LLVM 3.0
LLVM has two new register allocators: Basic and Greedy. When LLVM 3.0 is released, the default optimizing register allocator will no longer be linear scan, but the new greedy register allocator. With its global live range splitting, the greedy algorithm generates code that is 1-2% smaller, and up to 10% faster than code produced by linear scan. Lessons learned from linear scanLinear scan has been
C++ at Google: Here Be Dragons
Google has one of the largest monolithic C++ codebases in the world. We have thousands of engineers working on millions of lines of C++ code every day. To help keep the entire thing running and all these engineers fast and productive we have had to build some unique C++ tools, centering around the Clang C++ compiler. These help engineers understand their code and prevent bugs before they get to ou
What Every C Programmer Should Know About Undefined Behavior #3/3
What Every C Programmer Should Know About Undefined Behavior #3/3 In Part 1 of the series, we took a look at undefined behavior in C and showed some cases where it allows C to be more performant than "safe" languages. In Part 2, we looked at the surprising bugs this causes and some widely held misconceptions that many programmers have about C. In this article, we look at the challenges that compil
What Every C Programmer Should Know About Undefined Behavior #2/3
What Every C Programmer Should Know About Undefined Behavior #2/3 In Part 1 of our series, we discussed what undefined behavior is, and how it allows C and C++ compilers to produce higher performance applications than "safe" languages. This post talks about how "unsafe" C really is, explaining some of the highly surprising effects that undefined behavior can cause. In Part #3, we talk about what f
What Every C Programmer Should Know About Undefined Behavior #1/3
What Every C Programmer Should Know About Undefined Behavior #1/3 People occasionally ask why LLVM-compiled code sometimes generates SIGTRAP signals when the optimizer is turned on. After digging in, they find that Clang generated a "ud2" instruction (assuming X86 code) - the same as is generated by __builtin_trap(). There are several issues at work here, all centering around undefined behavior in
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LLVM Project Blog: New libunwind implementation in libc++abi
Object Caching with the Kaleidoscope Example Program
Kaleidoscope Performance with MCJIT
LLVM 3.3 Released!
Static analysis tools: using Clang in CppDepend
LLVM Debian/Ubuntu nightly packages
New Loop Vectorizer
LLVM 3.1 vector changes
LLVM 3.0 Exception Handling Redesign