BACKGROUND (optional) I've now reached the point of writing the GCC middle/back end interface for my Cobol compiler. See http://cobolforgcc.sourceforge.net/
Previously I wrote two front ends but that was a while ago. These were the original iteration of cobolforgcc 1998-2003, and the now defunct treelang of similar vintage. I also translated and updated the "how to write a front end document", now sadly out of date http://cobolforgcc.sourceforge.net/cobol_14.html But that was all a while ago and a lot has happened. I read the GCC Summit papers and the GCC Wiki but a few questions remain and there are some things I'm not quite sure about. QUESTIONS 1. Sample front-end: Given treelang no longer exists and "is not a good example anyway" what would be the best front end to use as a model and to plagiarize code? I have found that the Ada front end, while large, is quite easy to follow and I've been using that. C/C++ seem to have the back end interface very enmeshed in the hand coded parsers. The Java front end is reasonably small (only handles class files?) but the back end (BE) interface is spread among 30 files. The fortran Front End (FE) has 58 files with BE interfaces. Objective C/++ are mostly just add-ons to C. What I don't know is how up-to-date the various front ends are and how good an example they are. 2. Most-Gimplified front-end: Allied to Q1, which front ends have been most thoroughly converted to GIMPLE? 3. LANG_HOOKS: There has been some discussion about LANG_HOOKS being removed in the future. From memory this was in the context of the "optimization in the linker (LTI)" projects. Is there a replacement I should use now, or is there anything I should do to prepare for the replacement? 4. What does Gimple cover: What is the scope of GIMPLE? Most of the discussion is about procedural code. Does it also cover variable definition, function prototype definition etc. 5. What is deprecated: Is there any time-effective way to identify constructs, header files, macros, variable and functions that are "deprecated". 6. Tuples: I am a bit confused about tuples. Tuples seem to be really just structs by another name, unless I have missed the point. The idea is not a bad one - I went through the same process in the Lisp code in the front end where initially I stored everything in arrays and later switched to structs/tuples. In lisp this provided the advantages of run-time type-checking and the ability to use mnemonic names. The first email about tuples that I can find seems to assume a reasonable amount of background on the part of the reader: http://www.mailinglistarchive.com/gcc@gcc.gnu.org/msg01669.html Some clarification about what the tuples project is trying to do, and in particular how I should position for the advent of tuples would be very useful. I have read the material in the Wiki and from the GCC summit. 7. Should I target GENERIC, High Gimple or Low Gimple? Would I miss optimizations if I went straight to a Gimple representation? Is one interface more likely to change radically in the future? The assumption here is that the front end will be using an entirely different representation so there is no question of using one of these in the Front End. It is just a question of which format to convert into. Thank you all for any help you can provide, Tim Josling
