Re: Studying and Maintaining GNAT, Is There Any Interest in a New Group?

[Lucretia <laguest9000@googlemail.com>]

On Monday, 27 August 2018 03:38:32 UTC+1, Dan'l Miller  wrote:

> > There is no quibbling, I was pointing out his error in what he thought was what.
> 
> No, I was the one at the risk of quibbling by pointing out that GNAT has this weird not-truly-front-end, not-truly-back-end 3rd layer called GIGI tree transducer to convert between the two (i.e., Ada versus C/C++) semantic trees, where the Ada semantic tree is in the Ada-language-source-code front-end and the C/C++ semantic tree is in the C-language-source-code back-end of GNAT.
> 
> My main point is:  I suspect that (except for brand new revisions of the Ada _LRM_) most bugs are not in the GNAT true-•front•-end in Ada-language source-code nor in the GNAT true-•back•-end in C-language source-code shared with the rest of GCC.  I suspect that the vast majority of lingering compiler bugs in GNAT have their root cause in less-than-perfect tree-transduction from Ada semantic tree to C/C++-GENERIC/GIMPLE semantic tree, due in turn to having blinders on or tunnel vision, not looking at enough context in the large.

You don't seem to understand how compilers or GCC is structured. There is no weird 3rd layer.

Compilers use multiple intermediate representations starting with an asbstract syntax tree, the passes take in the AST and modify it or create a new tree/IR until it gets to the point where code generation can take place. That's essentially it

Source Language -> Front-end -> AST -> IR -> IR -> .. -> IR -> Codegen -> Assembly code -> Assembler -> Machine code -> Linker -> Executable

 
> > > semantically-adorned AST (in Ada-language source code) into GENERIC/GIMPLE C/C++ semantic tree
> > > (in C-language 
> > 
> > What are you going on about?
> 
> My sentences are precisely worded to say what needs to be said without further rebuttal by me, stating the same thing again.  If something specific is unclear, please narrow your request for information.

Why use 1 word when 50 will do, right?
 
> > That's exactly the point, it would be a completely different design, a completely different compiler,
> > hence nothing from GCC/GNAT.
> 
> Yes, eliminating GNAT's need for a tree transducer between 2 semantic trees (one for Ada, the other for C/C++) is the “radical new design” of a next-gen Ada compiler.  We agree there.

No, see above, you always need that, because that's what compilers do. All compilers have language neutral IR's, your front end has to convert from source language to that IR, whether it's GCC's GENERIC/GIMPLE or LLVM or Firm.
 
> I seem to recall an unrelenting general pox on all historical-Ada houses as the overall gist from you.

Nope, I said that there is literally no point in trying to reimplement the same software which people didn't like at the time, repeating history, i.e. the source stored as an IR in a database. People didn't want it then, they ain't gonna want it now because getting source in and out of a DB is a pain, yes I know that's what happens with source control, but that's the way it is.

> Unlike all other replies along all branches of all threads deriving from the OP, I actually started doing what the OP sought technologically:  start discussing the actual internal design of GNAT for the purpose of how to understand it for the purpose of how to maintain it.  (I am not sure that we need a new group/forum; what is wrong with discussing the design/internals of GNAT here on c.l.a?)

https://gcc.gnu.org/onlinedocs/gccint/index.html <<- the book you need to read to understand the internals of GCC, it's not an easy or nice read.