Add a VirtualFrame class to the IA32 code generator. All frame...

Add a VirtualFrame class to the IA32 code generator.  All frame
accesses (eg, parameters, locals, and the expression stack elements)
and mutation (pushes and pops) go through the virtual frame.

The frame initially contains no state, and directly emits instructions
in the obvious way.  It is not currently used for deferred code.

Committed: http://code.google.com/p/v8/source/detail?r=489

[Kasper Lund, 2008-10-10 12:19:11]

LGTM.

[iposva, 2008-10-10 12:53:02]

I am sure there are more situations where a Pop() with no target would be
useful, I just found a couple that just jumped out at me.

http://codereview.chromium.org/7076/diff/1/3
File src/codegen-ia32.cc (right):

http://codereview.chromium.org/7076/diff/1/3#newcode304
Line 304: frame_->Pop(eax);  // Value is no longer needed.
If the value is really no longer needed the there should also be a Pop()
operation that takes no target register and just pops the value from the virtual
frame without causing memory traffic. In the current implementation this could
translate to add(sp, sp, 4).

I understand that Pop() is equivalent to Drop(1), but it is sort of more
readable in these situations.

http://codereview.chromium.org/7076/diff/1/3#newcode1394
Line 1394: frame_->Pop(eax);  // Pop(no_reg);
Another potential use of Pop()...

http://codereview.chromium.org/7076/diff/1/3#newcode1405
Line 1405: frame_->Pop(eax);  // remove the lingering expression result from the
top of stack
And another potential use of Pop()...