[llvm-commits] [patch] Implement a pass to instrument function entry and exit

[Chris Lattner]

On Jun 5, 2010, at 6:38 PM, Nelson Elhage wrote:

> This patch adds a pass that adds calls to instrument function exit and
> entry, in a way compatible with GCC's -finstrument-functions flag.
> 
> Options are also provided to selectively exclude certain functions from
> instrumenting, analogous to those provided by GCC.
> 
> If this patch is not totally off-base, I'm planning to also implement
> and send along a function attribute to disable instrumenting on specific
> functions, and frontend support in clang.

Nice, adding -finstrument-functions support would be great.

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This makes it easier to apply.

> +//===----------------------------------------------------------------------===//
> +//
> +// This pass inserts instrumentation calls for entry and exit to
> +// functions. After function entry and before exit, calls are inserted
> +// to the following instrumentation functions:
> +//
> +//        void __cyg_profile_func_enter (void *this_fn,
> +//                                       void *call_site);
> +//        void __cyg_profile_func_exit  (void *this_fn,
> +//                                       void *call_site);
> +//
> +//===----------------------------------------------------------------------===//
> +
> +#define DEBUG_TYPE "instrument-functions"
> +#include "llvm/CodeGen/Passes.h"

This should be added to the scalar passes.

> +namespace {
> +  class CommaSeparatedStringParser :
> +    public cl::basic_parser<std::vector<std::string> > {
> +  public:
> +    // parse - Return true on error.
> +    bool parse(cl::Option &O, StringRef ArgName, StringRef ArgValue,
> +               std::vector<std::string> &Val);
> +  };

Instead of handling this with command line options, how about adding a function attribute?  That way the frontend can slap it on functions where it makes sense and manage the no_instrument_function attribute.

However, backing up a little bit, I'm not sure I understand this from the GCC man page:

"This instrumentation is also done for functions expanded inline in other functions."

Does that mean that *all* source-level function (that don't have the no_instrument_function attribute) get instrumented, even if they get inlined etc?

If so, then I think this entire thing can be handled in the Clang IR generation routines, not needing LLVM IR attributes and not needing an LLVM IR pass.

What do you think?

-Chris