[cfe-dev] [LLVMdev] Help me do Hacking Clang source code

[Cesar Mello]

Thanks a lot.

Best regards
Mello

On Thu, Jul 19, 2012 at 7:05 PM, Sean Silva <silvas at purdue.edu> wrote:

> You should look at <http://clang.llvm.org/docs/DriverInternals.html>,
> which illustrates how the driver works. The driver is the program
> responsible for deciding things like compile vs. assemble vs. link.
>
> For the actual step of parsing and compiling C/C++, this diagram maybe
> helpful <http://web.ics.purdue.edu/~silvas/deps.svg>. The diagram was
> made just by looking at the constructor arguments of each class. The
> arrows represent arguments to constructors, so you can see, for
> example, that Parser depends on Sema and Preprocessor. The purple
> nodes represent interfaces/abstract classes: these usually represent
> points of customizability. The diagram by no means contains all the
> classes involved, but it should give you a better idea of the "big
> picture".
>
> The main actors in the compilation step are Sema, Parser, and
> Preprocessor. Effectively, Parser calls methods on Preprocessor to get
> tokens; depending on the tokens themselves (i.e., which syntactic
> constructs are found), Parser then takes information taken from those
> tokens and calls into Sema, which acts on that information and builds
> AST nodes. In effect, Sema is a giant class with a bunch of callbacks
> ("semantic actions") corresponding to different aspects of
> semantically analyzing C/C++ and building up the C/C++ AST.
>
> For example, if you look at Parser::ParseWhileStatement in
> lib/Parse/ParseStmt.cpp, you can see this flow: it first consumes a
> `tok::kw_while` from the Preprocessor (it knows (and asserts) that the
> next token is a "while" token because otherwise it would not be called
> to parse a while (by
> Parser::ParseStatementOrDeclarationAfterAttributes)). It then does
> some diagnostics checking that it is followed by the "(" of the while
> condition. It then enters a scope (which through an RAII object calls
> Parser::EnterScope) by setting Actions.CurScope (`Actions` is a Sema
> object) to a new scope (and chaining the current one as the parent of
> this new scope). It then recursively calls ParseParenExprOrCondition
> and returns an error if that fails. If you then skip down a little
> bit, you'll see that it recursively calls ParseStatement to parse the
> body of the while loop. It then exits the scopes it has made and does
> some error checking. Finally, it calls Sema::ActOnWhileStmt
> (`Actions.ActOnWhileStmt([...])`) which builds the AST nodes
> corresponding to the "while", along with any semantic analysis it
> needs to do.
>
> Hope that helps.
>
> btw, there's a cfe-dev mailing list that would be more appropriate for
> this question (CFE=="C FrontEnd", but it should really be called
> "clang-dev"). I've CC'd them and un-CC'd llvmdev.
>
> --Sean Silva
>
> On Thu, Jul 19, 2012 at 5:59 AM, Journeyer J. Joh
> <oosaprogrammer at gmail.com> wrote:
> > Hi list,
> >
> > I am now started to read Clang source code.
> > And I found any conversion from input file(.c, .i, .s) to the output
> > file(.i, .s, .o) is done the process below.
> >
> > - FrontAction::BeginSourceFile()
> > - FrontAction::Execute
> > - FrontAction::EndSourceFile()
> >
> > And I drew some activity diagram below.
> >
> > http://www.opencpp.kr/behavior_of_clang.html
> >
> > >From the diagram I can guess that these are main actors in the movie,
> Clang.
> > - Diagnostic client
> > - Action
> > - Preprocessor
> > - Consumer of AST and AST
> > - File and Source Manager
> >
> >
> > Because Clang is well-structured C++ code, I believe there would be a
> > big picture for it's design.
> > If someone provide hints about this I would read Clang much more
> smoothly.
> > I'd like to know the architecture used in the back of those below.
> > - FrontAction::BeginSourceFile()
> > - FrontAction::Execute
> > - FrontAction::EndSourceFile()
> >
> > I even don't know where to find the starting point of compile, assemble.
> >
> > The pattern used, I also want to know.
> >
> > Thank you very much in advance.
> >
> >
> > Journeyer J. Joh
> > --
> > ----------------------------------------
> > Journeyer J. Joh
> > o o s a p r o g r a m m e r
> > a t
> > g m a i l  d o t  c o m
> > ----------------------------------------
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