I've seen, that there is an considerable performance increase using llvm. Is there a way to compile a fortran code using llvm (or clang)?
Related
I am currently working on compiling a model with PGI, originally designed for Intel compilers. One of the scripts uses use ifcore which is an Intel-specific command that links in miscellaneous run-time libraries. I am having trouble finding the PGI equivalent (for a linux machine)...any ideas?
I was looking at dflib but that appears to be windows-specific.
I am using mpif90 to compile the model currently.
Context
Linux 64 bits / osx 64 bits. C++ (gcc 5.1, llvm 3.6.1)
Up to now, I always used gcc for my projects.
The problem for the next thing I am creating is the licence. Hence, I decided to give clang/llvm a go.
My needs : runtime self modifying code (and a very relaxed licence for compiler plugins for static analysis and other things.).
I played a lot with libgccjit and it works fine.
As for llvm, I read the Kaleidoscope project and some doc but it is unclear.
Question
I saw that llvm has some jit possibilities but I am not sure if it enables to self modify the code (more precisely, extend the code) at runtime as libgccjit does for c++ language.
I just need a starter here, llvm is huge and new to me, so anyone expert enough is very welcome to guide me a bit.
I'm currently working in a pet programming language (for learning purposes), and have gone through a lot of research over the past year, and I think its time to finally start modelling the concepts of such a languague. First of all I want it to compile to some intermediate form, such as JVM or .NET bytecode, the goal being multiplatform/architecture compatibily. Second, I want it to be fast (I also have many other things in mind, but its not the purpose of this topic to discuss those).
The best options that came to my mind were:
Compile to JVM bytecode and use OpenJDK as runtime environment,
Compile to .NET bytecode and use Mono as runtime environment,
Compile to LLVM IR and use LLVM as runtime environment.
As you may have imagined, I've chosen LLVM. Why? because its blazing fast. I did a little benchmark using the C++ N-Body code, and achieved 7s in my machine with lli jitted IR, in contrast with 27s with clang native compiled code (I know clang first make IR then machine code).
So, here is my question: Is there any redistributable version of the LLVM basic toolset (I just need lli) that I can use? Or I must compile my own? If the latter, can you provide me with any hints on how to do it? If I really must do it, I'm thinking is cross-compiling them from my machine (Intel Mac), and generating some installers (say, an .msi for windows, .rpm and .deb for popular linux distros and .pkg for Macs). Remember, I only need a minimal subset of LLVM, such that this subset is capable of acting like a VM, by using "lli ". The real question here is how to use LLVM as a typical virtual machine.
First, I think all 3 options - LLVM IR + LLVM, Java Bytecode + OpenJDK, and .NET CIL + Mono - are excellent options, and I agree deciding between them is not easy.
If you go for LLVM and you just want to use lli, you can compile LLVM to your target platform and pack the resulting lli executable with your distribution, it should work.
Another way to write a JIT compiler via LLVM is to use an execution engine - see the handy examples in the Kaleidoscope tutorial. That means that you write your own program which will JIT-compile your own language, compile it to whatever platform you want while statically linking it with LLVM, and then distribute it.
In any case, since a JIT compiler requires copying an LLVM binary to the client side, make sure to attach a copyright notice with your distribution (you don't have to open-source your distribution, though).
I have a question concerning llvm, clang, and gcc on OS X.
What is the difference between the llvm-gcc 4.2, llvm 2.0 and clang? I know that they all build on llvm but how are they different?
Besides faster compiling, what is the advantage of llvm over gcc?
LLVM originally stood for "low-level virtual machine", though it now just stands for itself as it has grown to be something other than a traditional virtual machine. It is a set of libraries and tools, as well as a standardized intermediate representation, that can be used to help build compilers and just-in-time compilers. It cannot compile anything other than its own intermediate representation on its own; it needs a language-specific frontend in order to do so. If people just refer to LLVM, they probably mean just the low-level library and tools. Some people might refer to Clang or llvm-gcc incorrectly as "LLVM", which may cause some confusion.
llvm-gcc is a modified version of GCC, which uses LLVM as its backend instead of GCC's own. It is now deprecated, in favor of DragonEgg, which uses GCC's new plugin system to do the same thing without forking GCC.
Clang is a whole new C/C++/Objective-C compiler, which uses its own frontend, and LLVM as the backend. The advantages it provides are better error messages, faster compile time, and an easier way for other tools to hook into the compilation process (like the LLDB debugger and Clang static analyzer). It's also reasonably modular, and so can be used as a library for other software that needs to analyze C, C++, or Objective-C code.
Each of these approaches (plain GCC, GCC + LLVM, and Clang) have their advantages and disadvantages. The last few sets of benchmarks I've seen showed GCC to produce slightly faster code in most test cases (though LLVM had a slight edge in a few), while LLVM and Clang gave significantly better compile times. GCC and the GCC/LLVM combos have the advantage that a lot more code has been tested and works on the GCC flavor of C; there are some compiler specific extensions that only GCC has, and some places where the standard allows the implementation to vary but code depends on one particular implementation. It is a lot more likely if you get a large amount of legacy C code that it will work in GCC than that it will work in Clang, though this is improving over time.
There are 2 different things here.
LLVM is a backend compiler meant to build compilers on top of it. It deals with optimizations and production of code adapted to the target architecture.
CLang is a front end which parses C, C++ and Objective C code and translates it into a representation suitable for LLVM.
llvm gcc was an initial version of a llvm based C++ compiler based on gcc 4.2, which is now deprecated since CLang can parse everything it could parse, and more.
Finally, the main difference between CLang and gcc does not lie in the produced code but in the approach. While gcc is monolithic, CLang has been built as a suite of libraries. This modular design allow great reuse opportunities for IDE or completion tools for example.
At the moment, the code produced by gcc 4.6 is generally a bit faster, but CLang is closing the gap.
llvm-gcc-4.2 uses the GCC front-end to parse your code, then generates the compiled output using LLVM.
The "llvm compiler 2.0" uses the clang front-end to parse your code, and generates the compiled output using LLVM. "clang" is actually just the name for this front-end, but it is often used casually as a name for the compiler as a whole.
I have a question concerning the LLVM compiler:
I would like to use it to compile my Objective-C source code for Mac and iOS and from their release notes it seems that LLVM is stable enough for using this.
Having made good experiences with the LLVM I would also like to use it to compile C++ or Objective-C++. However it is not clear to me if I should still use the hybrid LLVM-GCC compiler (the GCC parser and the LLVM code generator) or the pure LLVM compiler.
I am also unsure about the new C++ standard library and if I should use it and how I would make the transition from GNU's libstdc++.
The Questions
Which compiler would one use today to generate fast production quality code from C++: the LLVM-GCC hybrid compiler or pure LLVM?
Should one migrate the C++ standard library from GNU's libstdc++ to the new libc++ library created by the LLVM project?
Any comments and hints are appreciated.
Several questions asked here, I'll try to answer all of them.
There is no "pure LLVM compiler". LLVM is a set of libraries which do code optimization and code generation . There are several C/C++ frontends which can be hooked to LLVM. Among them are clang and llvm-gcc. See http://llvm.org/ for more information about various components of LLVM Compiler Infrastructure. As written at http://llvm.org/docs/ReleaseNotes.html, llvm-gcc is EOL since LLVM 2.9 release, so you'd better use clang, because it will certainly be developed and maintained in the future.
libc++ is still in development, so for production you should use vendor-provided C++ (libstdc++ in your case).
Remember, all this stuff is changing, so benchmarks gets easily outdated.
I've found following report interesting, not only as a kind of benchmark, but it seems showing some LLVM vs GCC compiler differences :
Clang/LLVM Maturity Evaluation Report by Dominic Fandrey