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R600 Gallium3D Disables LLVM Back-End By Default

AMD

Published on 16 April 2014 09:51 PM EDT
Written by Michael Larabel in AMD
33 Comments

AMD has decided to disable the LLVM compiler back-end by default within the R600 era Gallium3D graphics driver.

The AMD GPU LLVM back-end was never a hard requirement to the R600 Gallium3D driver that supports the Radeon HD 2000 through 6000 series graphics cards, but had become an optional feature on the graphics shader compiler side and then only a requirement for those wishing to take advantage of OpenCL/GPGPU support for this pre-GCN hardware. The AMD GPU LLVM back-end meanwhile is a hard requirement for the RadeonSI Gallium3D driver with AMD's HD 7000 series hardware and newer -- for both graphics and compute support.

Mesa has supported using the --enable-r600-llvm-compiler compile-time switch for months for building R600g with the LLVM back-end on supported versions of the compiler infrastructure, but now not even that will disable the compiler back-end by default for this driver.

AMD's Michel Dänzer wrote in a Git commit a short time ago today, "For graphics, the LLVM compiler backend currently has many shortcomings compared to the non-LLVM one. E.g. it can't handle geometry shaders yet, but that's just the tip of the iceberg."

The R600g LLVM support is now disabled at run-time by default and will require setting the R600_DEBUG=llvm environment variable for enabling the LLVM back-end for graphics on this pre-RadeonSI driver.

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 .
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