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 May Expand Its Use Of The Loop Vectorizer

Compiler

Published on 06 June 2013 01:05 AM EDT
Written by Michael Larabel in Compiler
8 Comments

LLVM's Loop Vectorizer, which is able to automatically vectorize code loops for performance benefits in many scenarios, may find its use expanded for other optimization levels in future LLVM releases.

LLVM's automatic loop vectorizer was merged for the LLVM 3.2 release and benchmarking the loop vectorizer showed it to provide performance benefits for many scenarios. In the LLVM 3.2 release it wasn't enabled by default, but for LLVM 3.3 it's now enabled when using the -O3 optimization level.

Besides enabling it default for this greatest optimization level, LLVM 3.3 also provided improvements to the loop vectorizer. The LLVM loop vectorizer is now in good standing and so it might be enabled too by default for -O2 and -Os.

There's still some differing views on why the vectorizer should be turned on for -O2, which is the mid optimization level before -O3, but for at least -Os it should be turned on. The -Os level is when optimizing generated binaries for size. The loop vectorizer has the potential of increasing the binary size for some loops, but LLVM is able to weight that information and decide when to vectorize or not.

Apple LLVM developers have now been discussing on the LLVM mailing list about expanding the loop vectorizer's usage by default. The performance wins provided by this vectorizer seem to be worth it to many people even at the potential cost of a slightly longer compile time or the chance that the resulting binary size is slightly larger. This is a change that won't come for LLVM 3.3 but will be for LLVM 3.4 or later; we'll see what happens and post the decision on Phoronix.

LLVM 3.3 also has the interesting SLP vectorizer to optimize straight-line code, but this current discussion is only talking about the loop vectorizer.

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. Scythe Mugen MAX
  2. Intel Core i7 5960X Haswell-E On Linux
  3. Intel 80GB 530 Series M.2 SSD On Linux
  4. With A New Motherboard, The Core i7 5960X Haswell-E Lights Up
Latest Linux Articles
  1. A Tour Of The New Phoronix Office
  2. 7-Way Linux Desktop Gaming Comparison On Ubuntu 14.10
  3. Intel P-State vs. CPUFreq Benchmarks On The i7-5960X
  4. RadeonSI GLAMOR Benchmarks With X.Org Server 1.16
Latest Linux News
  1. Linux 3.17-rc6 Released; Linux 3.17 Final Might Come In One Week
  2. X.Org Server 1.16.1 Released
  3. Mesa Gets Closer To Having OpenGL 4.0 Tessellation Support
  4. Uselessd: A Stripped Down Version Of Systemd
  5. F2FS Tools Gain FSCK Support
  6. FreeBSD 10.1 Has The New VT Driver, Hardware Improvements
  7. AntiMicro 2.6 Yields Greater Compatibility For Gamepads On Linux
  8. OpenGL 3.3 / GLSL 3.30 Lands For Intel Sandy Bridge On Mesa
  9. AMD's RadeonSI Gallium3D Driver Sees Some Improvements
  10. Mesa 10.3 Released With The Latest Open-Source GPU Driver Improvements
Latest Forum Discussions
  1. NVIDIA GTX 770/780 -works ?
  2. Wasteland 2 Officially Launched Today, Including For Linux Gamers
  3. Trolling on the Phoronix forums
  4. X.Org Women Outreach Program Only Turns Up Two Applicants So Far
  5. New stress testing utility for GPU's
  6. ASRock AM1H-ITX: One Of The Best AM1 Mini-ITX Motherboards
  7. Can Linux kill a motherboard?
  8. Stop grabbing my keyboard :(