Blogged by Ujihisa. Standard methods of programming and thoughts including Clojure, Vim, LLVM, Haskell, Ruby and Mathematics written by a Japanese programmer. github/ujihisa

Thursday, February 25, 2010

LLVM Workshop at

I gave a lecture about LLVM.

The slides are available here:

I emphasized the following points. The optimizer of LLVM is awesome. I explained it with giving an example code.

First, I generated a very long helloworld code. To generate lavish code, I used a Brainf**k compiler. The helloworld written in Brainf**k doesn't have something like String literal, so it's natural that the code is longer than necessary, therefore the generated LLVM assembly language code would be lavish as well.

$ bfc.rb --llvm > helloworld.ll

The line number of the automatically generated LLVM assembly language code was 2714. Here let me optimize the code.

$ llvms helloworld.ll -o a.bc
$ opt -O3 a.bc -o a2.bc
$ opt -O3 a2.bc -o a3.bc
$ llvm-dis a3.bc -o > a.ll

The optimized code, a.ll, is semantically equivalent to the original helloworld.ll, though the lines of code is only 25.

All attendees were surprized about the result.

1 comment: