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 Benchmarking Platform
Phoromatic Test Orchestration

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 Articles & Reviews
  1. Sub-$20 802.11n USB WiFi Adapter That's Linux Friendly
  2. The Lenovo T450s Is Working Beautifully With Linux
  3. Linux 4.0 SSD EXT4 / Btrfs / XFS / F2FS Benchmarks
  4. Linux 4.0 Hard Drive Comparison With Six File-Systems
  5. Lenovo ThinkPad T450s Broadwell Preview
  6. How Open-Source Allowed Valve To Implement VULKAN Much Faster On The Source 2 Engine
Latest Linux News
  1. SuperTuxKart 0.9 Released With Its New OpenGL 3 Engine
  2. 6-Disk ZFS On Linux RAID Server Benchmarks
  3. Daily Builds Of Wayland & Weston For Ubuntu Linux
  4. AMD Open-Sources "Addrlib" From Catalyst
  5. AMD Releases New "AMDGPU" Linux Kernel Driver & Mesa Support
  6. A Gigabyte Sandy/Ivy Bridge Motherboard Now Handled By Coreboot
  7. Linux 3.16 Through Linux 4.0 Performance Benchmarks
  8. Intel's Windows Driver Now Supports OpenGL 4.4, Linux Driver Still With OpenGL 3.3
  9. DRM Graphics Updates Sent In For The Linux 4.1 Kernel
  10. More eBPF Improvements Heading To Linux 4.1
Most Viewed News This Week
  1. Nouveau: NVIDIA's New Hardware Is "VERY Open-Source Unfriendly"
  2. LibreOffice 4.5 Bumped To Become LibreOffice 5.0
  3. Linux Audio Is Being Further Modernized With The 4.1 Kernel
  4. KDBUS Is Taking A Lot Of Heat, Might Be Delayed From Mainline Linux Kernel
  5. VirtualBox 5.0 Beta 2 Released
  6. Ubuntu 15.04 Now Under Final Freeze
  7. ZFS & Libdvdcss Should Soon Be In Debian
  8. EXT4 In Linux 4.1 Adds File-System Level Encryption