Custom pragmas handling

Hi,

I would like to have a C compiler which can handle some custom
pragmas. For instance consider the following C file:

#pragma starpu interface
void foo();

#pragma starpu implements(foo)
void foo_v1() {...}

#pragma starpu implements(foo)
void foo_v2() {...}

I would like the compiler to transform it into:

void foo() {
   //do something with foo_v1() and/or foo_v2()
}
void foo_v1() {...}
void foo_v2() {...}

And finally compile it.

I have copied clang-cc and modified it to detect "starpu" pragmas by
adding a PragmaHandler to the preprocessor. However I have a few
questions:
1) Is there a non intrusive way (ie without modifying clang-cc or
clang) to add this kind a custom pragma handling in Clang? That would
be helpful to implement OpenMP too. Maybe a plan for some sort of
plugin system?
2) How can I determine in the PragmaHandler which function the pragma
applies to? Then, how can I modify the function's body to add some
statements? I think I could create a custom Action class, which would
perform AST modification in the appropriate ActOn* callbacks, and
replace the ParseAST call in clang-cc by a call to an other Parser
using my Action, but then how do I compile/ast-dump/... the modified
AST?

Any help appreciated.
Thanks
-- Sylvain

Hi,

I've attached two files here which I use in my project. I didn't have to modify clang for this purpose.

Best
Olaf

AttachedPragmas.h (2.6 KB)

AttachedPragmas.cpp (7.76 KB)

Hi again

and sorry because I misinterpreted your question - at least the first part. For that I don't know a solution.
The second part (attaching a pragma to a function) I've solved using line numbers (as you can hopefully see in my previous reply).

Hth anyway
Olaf

Hi,

I would like to have a C compiler which can handle some custom
pragmas. For instance consider the following C file:

#pragma starpu interface
void foo();

#pragma starpu implements(foo)
void foo_v1() {...}

#pragma starpu implements(foo)
void foo_v2() {...}

I would like the compiler to transform it into:

void foo() {
  //do something with foo_v1() and/or foo_v2()
}
void foo_v1() {...}
void foo_v2() {...}

And finally compile it.

I have copied clang-cc and modified it to detect "starpu" pragmas by
adding a PragmaHandler to the preprocessor. However I have a few
questions:
1) Is there a non intrusive way (ie without modifying clang-cc or
clang) to add this kind a custom pragma handling in Clang? That would
be helpful to implement OpenMP too. Maybe a plan for some sort of
plugin system?

We don't have a non-intrusive way to add such pragmas, but I think that some kind of plugin system that allows one to add pragmas and then query them (say, as part of the ASTConsumer interface) would be very useful.

2) How can I determine in the PragmaHandler which function the pragma
applies to? Then, how can I modify the function's body to add some
statements? I think I could create a custom Action class, which would
perform AST modification in the appropriate ActOn* callbacks, and
replace the ParseAST call in clang-cc by a call to an other Parser
using my Action, but then how do I compile/ast-dump/... the modified
AST?

I think this would best be accomplished by extending the ASTConsumer interface. Sema could be taught to associate pragmas with declarations, notifying the AST consumer when an otherwise-unknown pragma is associated with a declaration that it has type-checked.

As for producing a modified AST, that's a little harder. The AST printing routines aren't good enough for source-to-source transformation, and I wouldn't recommend that route anyway: you'll lose all of the formatting. Instead, check out the Rewriter, which allows textual rewriting of a source file based on source location information.

  - Doug