Hello!
I am doing some pre-studies for my masters thesis, which (hopefully) will result in a compiler prototype for Ruby to LLVM, and I have a question:
1. When reading the reference manual, I do not understand how e.g. simple I/O operations as printf() can be implemented in LLVM. Are there any external functions available, or how do I proceed?
Kind regards
Anders
I am doing some pre-studies for my masters thesis, which (hopefully)
will result in a compiler prototype for Ruby to LLVM, and I have a
question:
Cool! 
1. When reading the reference manual, I do not understand how e.g.
simple I/O operations as printf() can be implemented in LLVM. Are there
any external functions available, or how do I proceed?
Basically, LLVM relies on the operating system for this. printf is part
of the "standard I/O" library provided by libc on most unix-like systems.
After adding a layer of buffering, libc ends up turning stdio calls into
low-level system calls like read() and write().
If you want _direct_ access to the OS, you could do similar things.
On the other hand, if you're working on a Ruby backend for LLVM, it might
make most sense to define a Ruby/LLVM runtime library that includes
more-or-less direct implementations of things like the ruby 'print'
message for various types. This runtime library could be written in C,
C++, Ruby, or for that matter, LLVM directly. When compiling a user
program, the Ruby front-end would emit calls to these runtime library
routines.
Let me know if this doesn't make any sense and I can supply an example.
-Chris
Anders,
It will be interesting to hear how your project goes. To generalize Chris's answer a bit, for any language, you have to implement the standard libraries and runtime system (if any) somehow. LLVM is just a compiler infrastructure, i.e. it is mainly intended to implement the compiler system (language-to-LLVM-to-target). The standard libraries and runtime system can either be compiled to the target language directly, or can be compiled to LLVM. In either case, they get linked into the code generated by the compiler, either by the system linker or by the LLVM linker.
--Vikram
http://www.cs.uiuc.edu/~vadve
http://llvm.cs.uiuc.edu/