[cfe-dev] Using other front end work as a basis?

Mon Aug 20 07:23:09 PDT 2007

On Aug 20, 2007, at 12:32 AM, Ar18 at comcast.net wrote:

> Is the plan to start completely from scratch

Our current C front-end (named clang) builds on LLVM (a well  
established back-end framework).

That said, the C++ front-end we envision would be built atop both  
clang/LLVM (which is far from starting from scratch, fortunately:-)

If you are interested in learning more about our goals, you might try  
starting with the email below.

Thanks for your interest,

snaroff

Begin forwarded message:
> From: Chris Lattner <clattner at apple.com>
> Date: July 11, 2007 1:57:35 PM PDT
> To: llvmdev at cs.uiuc.edu, cfe-dev at cs.uiuc.edu
> Subject: [cfe-dev] New LLVM C front-end: "clang"
>
> Hi Everyone,
>
> I'm happy to say that we just got approval to open source the new C
> front-end for LLVM we've been working on.
>
> The goal of this work is to provide a high quality front-end for LLVM
> that is built with the same principles as the rest of LLVM (it is
> built as a set of reusable libraries, integrates well with rest of
> the LLVM architecture, same license, etc).  Among other things, this
> means that LLVM can now be used for a variety source-level analysis
> and transformation tasks that it was not suitable for before.
>
> For more information about the motivation behind this work, please
> see Steve's talk at the LLVM '07 developer meeting:
>    http://llvm.org/devmtg/2007-05/09-Naroff-CFE.pdf
>    http://llvm.org/devmtg/2007-05/09-Naroff-CFE.mov
>
> Currently, there is not a lot of documentation for the project, but
> the code is well commented, and there is a README.txt file at the
> root of the tree with some notes, here: http://llvm.org/svn/llvm-
> project/cfe/trunk/README.txt
>
> While this work aims to provide a fully functional C/C++/ObjC front-
> end, it is *still very early work*.  In particular, there is no real
> ObjC or C++ support yet (these are obviously big projects), and C
> support is still missing some features.  Some of the more notable
> missing pieces of C support are:
>
> 1. The parser currently skip initializers in braces "int A[] =
> { 1,2,3,};" without trying to understand them.
> 2. The semantic analyzer does not produce all of the warnings and
> errors it should.
> 3. The LLVM code generator is still very early on.  It does not
> support many important things, like any support for structs and
> unions.  That said, it does handle scalar operations and vectors.
> 4. We don't consider the API to be stable yet, and reserve the right
> to change fundamental things :)
>
> We plan to continue chipping away at these issues until C works
> really well, but we'd love help from other interested contributors.
> I did create a new CFE component in bugzilla, but problems are
> probably better reported on cfe-dev for now.
>
>
> If you are interested in contributing, or just want to follow along
> with the project, I recommend signing for the cfe-dev and/or cfe-
> commits lists:
>    http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev
>    http://lists.cs.uiuc.edu/mailman/listinfo/cfe-commits
>
> Note that we primed the cfe-commits list will all the revision
> history of the project, it doesn't normally get this much traffic ;-).
>
>
> If you'd like to check out and build the project, the current scheme
> is (many thanks to Reid for his help converting our CVS repository to
> SVN):
>
> 1. Check out llvm and build it (the C front-end uses libsupport and
> libsystem).  You don't need llvm-gcc :)
> 2. cd llvm/tools
> 3. svn co http://llvm.org/svn/llvm-project/cfe/trunk clang
> 4. cd clang
> 5. make
>
> We will eventually integrate this better as a sub-project, but for
> now it builds a single tool named 'clang'.  If you're not on a Mac,
> you'll need to make one change: paths to system header files are
> currently hard coded into the tool.  To get this to work for you,
> you'll probably have to change clang/Driver/clang.cpp:606 to include
> the paths that 'touch empty.c; gcc -v empty.c -fsyntax-only' prints
> (it should list some lines after "#include <...> search starts  
> here:").
>
>
> Once this is built, you can compile C code (amazing, I know!).  The
> clang driver takes a lot of GCC compatible options, which you can see
> with 'clang --help'.  As a simple example:
>
> $ cat ~/t.c
>
> typedef float V __attribute__((vector_size(16)));
> V foo(V a, V b) { return a+b*a; }
>
>
> Preprocessing:
> $ clang ~/t.c -E
> # 1 "/Users/sabre/t.c" 1
>
> typedef float V __attribute__((vector_size(16)));
>
> V foo(V a, V b) { return a+b*a; }
>
>
> Type checking:
> $ clang -fsyntax-only ~/t.c
>
>
> GCC options:
> $ clang -fsyntax-only ~/t.c -pedantic
> /Users/sabre/t.c:2:17: warning: extension used
> typedef float V __attribute__((vector_size(16)));
>                  ^
> 1 diagnostic generated.
>
>
>
> Pretty printing from the AST:
> $ clang ~/t.c -parse-ast-print
> typedef float V __attribute__(( vector_size(16) ));
>
> V foo(V a, V b) {
>    return a + b * a;
> }
>
>
> LLVM code generation:
> $ clang ~/t.c -emit-llvm | llvm-as | opt -std-compile-opts | llvm-dis
> define <4 x float> @foo(<4 x float> %a, <4 x float> %b) {
> entry:
>          %mul = mul <4 x float> %b, %a           ; <<4 x float>>
> [#uses=1]
>          %add = add <4 x float> %mul, %a         ; <<4 x float>>
> [#uses=1]
>          ret <4 x float> %add
> }
> $ clang ~/t.c -emit-llvm | llvm-as | opt -std-compile-opts | llc -
> march=ppc32 -mcpu=g5
> ..
> _foo:
>          vmaddfp v2, v3, v2, v2
>          blr
> $ clang ~/t.c -emit-llvm | llvm-as | opt -std-compile-opts | llc -
> march=x86 -mcpu=yonah
> ..
> _foo:
>          mulps %xmm0, %xmm1
>          addps %xmm0, %xmm1
>          movaps %xmm1, %xmm0
>          ret
>
> etc.
>
>
>
> In any case, we welcome questions, comments, and especially
> patches :).  To avoid spamming llvmdev, please take all discussion to
> the cfe-dev mailing list, and patch submission/discussion to cfe-
> commits.
>
> Thanks!
>
> -Chris
>
> _______________________________________________
> cfe-dev mailing list
> cfe-dev at cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev
>
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