Discussing The LLVM IR Shortcomings
Written by Michael Larabel in Compiler on 5 October 2011 at 07:36 AM EDT. Add A Comment
While GCC developers are currently discussing merging the D programming language front-end into their compiler, LLVM developers are currently discussing their IR and its sufficiency.

Dan Gohman, an Apple engineer, volleyed a long and technical e-mail to the LLVM development list about the LLVM IR. Dan argues that the intermediate representation for this Apple-sponsored compiler infrastructure is "a poor system for building a Platform." He and many felt that LLVM IR would work well for multiple architectures, but in the end it's not been so pretty. In his email he argues his case at length.

Dan ends up proposing a new platform IR for LLVM. "In conclusion, consider the task of writing an independent implementation of an LLVM IR Platform. The set of capabilities it provides depends on who you talk to. Semantic details are left to chance. There are features which require a bunch of complicated infrastructure to implement which are rarely used. And if you want light-weight execution, you'll probably need to translate it into something else better suited for it first. This all doesn't sound very appealing."

There's many responses already from his message that was sent yesterday. Most of the developers agree with his points. Chris Lattner, the primary developer behind LLVM/Clang and who's been heading Apple's Compiler Group, also agrees with most points raised by his colleague. However, he doesn't agree with the conclusion of creating a new IR. The email from Chris can be read here.

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Michael Larabel is the principal author of Phoronix.com and founded the site in 2004 with a focus on enriching the Linux hardware experience. Michael has written more than 10,000 articles covering the state of Linux hardware support, Linux performance, graphics drivers, and other topics. Michael is also the lead developer of the Phoronix Test Suite, Phoromatic, and OpenBenchmarking.org automated benchmarking software. He can be followed via Twitter or contacted via MichaelLarabel.com.

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