Add dump_stats() to _llvm

This produces reports like this:

>>> import _llvm
>>> _llvm.dump_stats()
LLVM functions: 1833
LLVM basic blocks: 229867
LLVM instructions: 1321540
>>>

[Collin Winter, 2009-07-24 22:40:20]

PTAL

[Jeffrey Yasskin, 2009-07-25 03:55:13]

http://codereview.appspot.com/97120/diff/1002/8
File Modules/_llvm.cc (right):

http://codereview.appspot.com/97120/diff/1002/8#newcode56
Line 56: void WalkModule(llvm::Module *mod) {
I would do this with an overloaded Area() function. You'd call Area() on each
sub-object, and add up the sizes. Then you have a simple organization for the
concrete types, rather than having to do complex things in some of the functions
to reduce the number of functions.

http://codereview.appspot.com/97120/diff/1002/8#newcode67
Line 67: this->byte_count_ += sizeof(f.getArgumentList());
Do you want me to nitpick where you're missing bytes? The ArgumentList is just
the head node; each element also occupies space.

http://codereview.appspot.com/97120/diff/1002/8#newcode72
Line 72: this->byte_count_ += sizeof(*it);
The ValueSymbolTable's entries also hold it->getKeyLength() bytes for the
value's name.

http://codereview.appspot.com/97120/diff/1002/8#newcode84
Line 84: this->byte_count_ += sizeof(inst);
This only gets the size of the Instruction. Subclasses occupy extra space, and
there are usually Use instances hung off the beginning of the Instruction.

[Collin Winter, 2009-08-04 00:10:38]

I've dropped adding the bytes together; I'm wary of treating whatever number I
come up with with too much weight just yet.

[Jeffrey Yasskin, 2009-08-04 22:59:12]

Otherwise, lgtm

http://codereview.appspot.com/97120/diff/1005/2001
File Modules/_llvm.cc (right):

http://codereview.appspot.com/97120/diff/1005/2001#newcode85
Line 85: fprintf(stderr, "LLVM functions: %ld\n", aggregator.FuncCount());
I think James was right that this should return a string or dict rather than
printing to stderr directly.