Flang – A Fortran compiler targeting LLVM

I've heard a horror story of someone doing signal processing in node.js. It'd be nice to use a well tested Fortran FFT routine - there aren't many .js libs for doing numerics AFAIK (disclaimer: not a js programmer)

neurostimulant2• 9 years ago

There are many useful computational model written in fortran that would be absolutely useful if they can be run in a browser, simply because telling the user to compile them on their own is impossible unless they're familiar the toolkit themselves.

For example, it would be incredibly useful if you can run various US EPA's dispersion models right in your browser.

https://www3.epa.gov/scram001/dispersion_prefrec.htm

nonsince3• 9 years ago

This is the most Hacker News comment I have seen in years and I love it

genericpseudo2• 9 years ago

Me of fifteen years ago would love this for lab classes on, e.g., classical molecular dynamics.

The computational load of these simulations is, in modern terms, not large, so Emscripten-compiled simulations would be plenty fast enough, and deployment of web pages in a computer-lab environment (or for people working from their dorms!) is way easier than the alternatives.

So there are real, non-trivial applications. You wouldn't want to be running ABINIT or whatever in your web browser, but GROMACS on some small system? Not unreasonable.

waldir2• 9 years ago

Not just JavaScript: https://mohd-akram.github.io/languages/?source=LLVM%20IR

waldir2• 9 years ago

In fact, Flang has now been added: https://mohd-akram.github.io/languages/?source=Fortran

s-macke• 9 years ago

I asked the same question two years ago on another LLVM Fortran project.

https://news.ycombinator.com/item?id=10574243

jabl8• 9 years ago

This is the same LLVM Fortran project as discussed two years ago in the thread you linked. Two years ago was just an announcement, now they are publishing some open source code (which might or might not actually work, for some definition of "work", I haven't tried it).

So the backstory is that Nvidia bought PGI, a company which produced a C/C++/Fortran compiler suite which was moderately commonly used in HPC. Then they took the Fortran frontend from the PGI suite and bolted it to LLVM and open sourced it as flang.

hackcasual• 9 years ago

Probably. The biggest stumbling block will be inline assembly.

acomjean• 9 years ago

Funny.... but:

In a past job we had some ada code in our codebase that was just awful looking. It was machine translated from fortran to ada. From what I could tell, it was just a few files that were translated and then fixed up and checked in before they gave up on that conversion project.

we nicknamed such code "ada-tran"

Thus the I feel the new translated code should be called "Forscript"

kbenson• 9 years ago

To my understanding, Emscripten thankfully does not attempt to keep the JS sane for humamn consumption at all. It's basically a higher level assembly language that targets a browser. What Emscripten does is more compiling to JS, not translating to it.

we nicknamed such code "ada-tran"

If Fortran -> Ada is ada-tran, then wouldn't Fortran -> Javascript be Javascran? :)

nonsince3• 9 years ago

Ok, so the only reason anyone's using Fortran is for crazy speeds, what's the codegen like compared to gfortran?

atemerev3• 9 years ago

Actually, modern Fortran is a pretty decent numeric programming language, comparable (if not superior) to MATLAB, and much faster than it. The only problem is that finding documentation on modern programming idioms and styles is complicated among MEGATONS of legacy code lying around literally from Cold War times (still perfectly working, of course, so if you urgently need to write a Monte Carlo solver for neutron transport equations — you got it covered).

nonsince3• 9 years ago

I'm really interested in Fortran because I love super down-to-the-metal optimisation stuff, but I have no meaningful use-case for it. Where would you recommend someone start if they wanted to get into modern Fortran?

tachyonbeam• 9 years ago

Am I the only one who thinks that Forlang would have been a better name? ;)

Someone• 9 years ago

http://www.phoronix.com/scan.php?page=news_item&px=LLVM-NVID...: "Flang is to Fortran as Clang is to C/C++."

This is a NVIDIA project.

hawski• 9 years ago

Is it sensible to implement math heavy part of C application in Fortran and call it via FFI? Or is -Ofast enough in most cases without the costs (multiple, because performance may be one of them) of FFI?

jabl8• 9 years ago

Not for speed reasons alone. It's certainly possible to tune C code to have roughly equivalent performance to Fortran.

The real appeal for using Fortran is that for beginners it's a much easier language to pick up than C (much less footguns, for one), and that working with (dense) multidimensional arrays is very nice, roughly on par with high-level languages like numpy, R, or MATLAB.

m_mueller• 9 years ago

To expand on this, I think the footguns you're talking about are specifically performance related.

Just an example: How do you specify a fast readonly array in C? If I recall correctly it's

restrict const * const int my_array[n]

In Fortran?

integer(4), intent(in) :: my_array(n)

Not even starting with array ops, multidimensionals, array slicing etc., that's already a big win in readability. Having a pass-by-reference language by default is refreshing for HPC purposes.

That being said there are disadvantages compared to C. Biggest one IMO is the lack of inline declarations, which especially makes privatizing things in OpenMP and OpenACC code a bit more tricky, i.e. it needs to be explicit.

wombatpm• 9 years ago

Thats what I did in grad school. C front end for datafile reading, writing, and data munging. Fortran for the heavy lifting and solver libraries.

alephnil• 9 years ago

Actually one of the reasons that Fortran is fast is not that the code you write in it is inherently faster than C. It is more that the idiomatic way of programming it is fast. This is not necessarily the case in C, where it is quite natural to use pointer structures, while in Fortran you would in most cases use large arrays that consists of continuously allocated memory instead.

It is of cause possible to do that in C as well, but it is not as natural. You can use pointer structures in modern Fortrans as well (as in F90 and later). Again, the difference is that idiomatic Fortran often lead to faster code.

One real difference is that Fortran do not allow aliased memory in arrays unless that is specifically declared using the "equivalence" statement, while in C and C++ that is the default assumption. This allows for some optimizations that can't be done safely in C. In C99 and later, you can use the "restrict" keyword to state the opposite, namely that an array is not aliased, but usually you won't do that outside of tight loops if at all.

kxyvr• 9 years ago

One other nice benefit to this project is determining name mangling schemes when linking to other Fortran projects using a pure LLVM toolchain.

Say we want to use BLAS and LAPACK in a C/C++ project that uses clang as the compiler. All we have to do is write the appropriate prototype for the LAPACK function in C and then link to BLAS/LAPACK. That said, there are four different name mangling schemes that the BLAS/LAPACK could use, which are combinations of upper case or with trailing underscores, e.g. gemm, GEMM, gemm_, and GEMM_. Both Autotools and CMake will determine the mangling scheme for us, but they need a Fortran compiler to determine that. Right now, that's almost always GFortran. With this project, it could ostensibly be Flang, which would eliminate the need for GCC to determine the mangling if a pure LLVM toolchain is desired.

jabl8• 9 years ago

Modern LAPACK already comes with an official C binding, LAPACKE: http://www.netlib.org/lapack/lapacke.html

The C ABI is pretty stable, so if you're using LAPACKE you shouldn't need to worry about which Fortran compiler was used to compile LAPACK.

Other than that, AFAIK the most common name mangling these days is lowercasing + trailing underscore. That being said, for "modern Fortran" with modules, OOP etc. the issues are vastly more complex and AFAICS there is no commonly agreed upon ABI.

bonzini• 9 years ago

Do you mean a proprietary toolchain?

walshemj8• 9 years ago

what advantages over gfortran does this have and if its performance why not just pony up for the intel fortran

krallja• 9 years ago

It's Apache-licensed instead of GPL; for some people, that's an advantage.

jcranmer• 9 years ago

The ability to compile to LLVM IR, for one. Yeah, you could use dragonegg (and I have), but dragonegg is unmaintained and the last working versions are pretty old (LLVM 3.3 and gcc 4.8).

unit912• 9 years ago

why not just pony up for the intel fortran

I used to work in a government research lab. We mostly used GFortran instead of Intel for political stability reasons. Your budget can change drastically from year-to-year (even if there's no change at the congressional level) because every dollar has to go through the entire bureaucracy before it makes it to your cubicle. The budget wars are constant at every level in the org pyramid.

GFortran is free, and always will be. Whether we can pony up for Intel is completely unknown 5 or 50 years from now. And a lot of people in the Fortran world are ultimately funded by Uncle Sam.

walshemj8• 9 years ago

so your counting your power bill / cost per gflop when you do your budgeting and exactly how many licences would you need? you'd be building on a server not on everyone's desktop pc right?

ch_1232• 9 years ago

Based on the front-end of a mature, commercial Fortran compiler, see - https://developer.arm.com/-/media/developer/developers/hpc/f...

I know quite a few Fortran programmers, most of whom will avoid Gfortran because it lacks the features and performance of the commercial alternatives. When you consider that a lot of these people write code for large scale computer clusters and/or supercomputers, the cost of something like Intel Fortran pales in comparison to the cost of the hardware. I suspect this is a big part of why Gfortran is not of the same caliber as GCC

walshemj8• 9 years ago

That's the impression I got that the benefits of intel pays for its self in terms of more efficient use of compute budget

valarauca1• 9 years ago

This is actually an Nvidia Project so theoretically it'll be used to target GPU's

https://www.phoronix.com/scan.php?page=news_item&px=LLVM-NVI...

ch_1232• 9 years ago

Judging by the copyright notices in the files, this is probably the PGI-Fortran-on-LLVM compiler that was announced a year or two ago - https://www.llnl.gov/news/nnsa-national-labs-team-nvidia-dev...

EDIT: Confirmed - https://developer.arm.com/-/media/developer/developers/hpc/f...

santaclaus• 9 years ago

How easy is it to do OpenMP from LLVM front-ends, at the moment? Fortran without OpenMP would be a bit limiting.

Edit: It looks like Clang 3.8.0 supports OpenMP, so this should be doable.

rhabarba• 9 years ago

Now how about a COBOL version? :-)

atemerev3• 9 years ago

I would love to see a modernized COBOL in the same way they have modernized Fortran. It'd be an instant hit in enterprise IT environments.

0x09• 9 years ago

Apparently unrelated to Flang the 2013 LLVM GSOC project to implement a Fortran frontend.

https://github.com/hyp/flang

The name re-use was a bit confusing.

Flang – A Fortran compiler targeting LLVM

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