1. Computers
  2. Display Drivers
  3. Graphics Cards
  4. Memory
  5. Motherboards
  6. Processors
  7. Software
  8. Storage
  9. Operating Systems


Facebook RSS Twitter Twitter Google Plus


Phoronix Test Suite

OpenBenchmarking.org

LLVM Gets An Automatic Loop Vectorizer

Compiler

Published on 26 October 2012 08:21 AM EDT
Written by Michael Larabel in Compiler
4 Comments

A loop vectorizer has been committed to LLVM 3.2 that's capable of automatically vectorizing small loops.

After a few weeks of discussions about a new loop vectorizer for LLVM, Apple's Nadav Rotem shared this week that a new implementation has been committed.

While it's been committed, the feature is currently disabled by default and when using the Clang C/C++ front-end the -mllvm -vectorize switches must be set for turning on this automatic loop vectorizer.

Nadav mentions, "The loop vectorizer is far from being 'ready', and this feature should be considered as 'highly experimental'. The work on the loop vectorizer had just began, and there is lots of work ahead...We currently know of a number of areas where we can improve. At the moment the vectorizer will vectorize anything it can, because we do not have a 'cost-model' to estimate the profitability of vectorization. Implementing a cost model is a high-priority for us, and until this is ready you should expect to see slowdowns on many loops. Another area which we need to improve is the memory dependence check. At the moment we have a very basic memory legality check which can be improved. Additionally, there are a number of cases where we generate poor vector code or suffer from a phase-rdering problem. Once we solve these problems we can continue to implement additional features."

The recent LLVM loop vectorizer discussions began in this thread at the beginning of October. "We are starting to work on an LLVM loop vectorizer. There's number of different projects that already vectorize LLVM IR. For example Hal's BB-Vectorizer, Intel's OpenCL Vectorizer, Polly, ISPC, AnySL, just to name a few. I think that it would be great if we could collaborate on the areas that are shared between the different projects. I think that refactoring LLVM in away that would expose target information to IR-level transformations would be a good way to start. Vectorizers, as well as other IR-level transformations, require target-specific information, such as the cost of different instruction or the availability of certain features. Currently, llvm-based vectorizers do not make use of this information, or just hard-code target information. A loop vectorizer would need target information. After we have some basic target information infrastructure in place we can start discussing the vectorizer itself."

LLVM 3.2 is planned for release in mid-December.

About The Author
Michael Larabel is the principal author of Phoronix.com and founded the web-site in 2004 with a focus on enriching the Linux hardware experience and being the largest web-site devoted to Linux hardware reviews, particularly for products relevant to Linux gamers and enthusiasts but also commonly reviewing servers/workstations and embedded Linux devices. Michael has written more than 10,000 articles covering the state of Linux hardware support, Linux performance, graphics hardware drivers, and other topics. Michael is also the lead developer of the Phoronix Test Suite, Phoromatic, and OpenBenchmarking.org automated testing software. He can be followed via and or contacted via .
Latest Linux Hardware Reviews
  1. Preview: AMD's FX-9590 Eight-Core At Up To 5.0GHz On Linux
  2. Intel Launches The Core i7 5960X, Mighty Powerful Haswell-E CPUs
  3. AMD Radeon R9 290: Gallium3D vs. Catalyst Drivers
  4. AMD Radeon R9 290 Open-Source Driver Works, But Has A Ways To Go
Latest Linux Articles
  1. How Intel Graphics On Linux Compare To Open-Source AMD/NVIDIA Drivers
  2. The Fastest NVIDIA GPUs For Open-Source Nouveau With Steam Linux Gaming
  3. Testing For The Latest Linux Kernel Power Regression
  4. The Most Energy Efficient Radeon GPU For AMD Linux Gaming
Latest Linux News
  1. Nouveau X.Org Driver Released With DRI3+Present, Maxwell, GLAMOR
  2. Microsoft & AMD Release C++ AMP Compiler With Linux Support
  3. AMD, Wine & Valve Dominated August For Linux Users
  4. Linux 3.17-rc3 Kernel Released Back On Schedule
  5. Lennart Poettering Talks Up His New Linux Vision That Involves Btrfs
  6. Mesa 10.3 RC2 Arrives Via Its New Release Manager
  7. Ubuntu 14.10's Lack Of X.Org Server 1.16 Gets Blamed On AMD
  8. MSI Motherboard BIOS Updating Remains A Pain For Linux Users
  9. See How Your Linux System Performs Against The Latest Intel/AMD CPUs
  10. AMD Steppe Eagle Flys To Coreboot
Latest Forum Discussions
  1. Lennart Poettering Talks Up His New Linux Vision That Involves Btrfs
  2. The dangers of Linux kernel development
  3. Updated and Optimized Ubuntu Free Graphics Drivers
  4. AMD Releases UVD Video Decode Support For R600 GPUs
  5. SSD seems slow
  6. Is laptop with Intel CPU and AMD dGPU worth buying considering especially AMD Enduro?
  7. Radeon HD5670 and Ubuntu 14.04
  8. Btrfs Gets Talked Up, Googler Encourages You To Try Btrfs