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Home » Developing U++ » U++ Developers corner » Using LLVM to compile U++
| Using LLVM to compile U++ [message #21355] |
Thu, 14 May 2009 20:27  |
phirox
Messages: 49
Registered: December 2007
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I was intrigued by the move of freebsd to switch from GNU GCC to LLVM. So I installed llvm 2.5 with the clang frontend(llvm-gcc and llvm-g++).
I added a new Build Method named LLVM(under Setup->Build methods). Then set all the flags exactly like with GCC and edit the field Compiler name and put in llvm-g++.
Everything compiled ok, except one little part. In Lang.cpp it gave a segfault. I fixed this error by adding a nonsense variable above the ONCELOCK { line: e.g. "bool llvm_fix;".
Ok the main advantages seem to be compiler speed, better error/warning descriptions, runtime optimilizations which lead to faster execution speeds. The compiler speed is noticeable, I would guess about 30% faster in my case. The messages do seem more verbose. But onto the fun stuff, I tested the speed using the Timing package in reference.
The results for the GCC Speed build(-pipe -O2 -ffunction-section -fomit-frame-pointers):
The restm.Elapsed() = 8242
TIMING Index::FindAdd : 721.85 ms - 721.85 ns ( 2.01 s / 1000000 )
TIMING AsString : 160.85 ms - 160.85 ns ( 1.45 s / 1000000 )
TIMING rand : 0.00 ns - 0.00 ns ( 1.16 s / 1000000 )
The results for the LLVM Speed build(identical flags):
tm.Elapsed() = 8334
TIMING Index::FindAdd : 726.35 ms - 726.35 ns ( 2.12 s / 1000000 )
TIMING AsString : 112.35 ms - 112.35 ns ( 1.50 s / 1000000 )
TIMING rand : 0.00 ns - 0.00 ns ( 1.14 s / 1000000 )
Interesting results as you can see, I will definitely keep using it for now. If not only to keep testing upp's compatibility.
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| Re: Using LLVM to compile U++ [message #21470 is a reply to message #21440] |
Thu, 21 May 2009 23:38  |
phirox
Messages: 49
Registered: December 2007
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With the gcc like frontend(llvm-gcc or llvm-g++), it automatically makes compatible/linkable object binaries like any other compiler. So basically there is no difference in input, arguments or ouput. To create llvm bytecode you have to compile with some extra flags, but you (currently) cannot make a cross-platform binary.
This is the link to the freebsd news about the move.
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