RFC: implement DW_OP_bit_piece

[Tom Tromey]

>>>>> "Stan" == Stan Shebs <stan@codesourcery.com> writes:

Stan> In theory, evaluation of the expression while examining a trace frame
Stan> will just work, because the DWARF condition will evaluate to the same
Stan> value as it would have when looking at the live state.

My understanding is that tracepoint collection happens without GDB's
intervention.  I think this implies that either the conditions must be
uploaded, or the AX code must over-collect data along all branches of
the DWARF expression.

Stan> But yeah, this is the kind of thing that gets us to start muttering
Stan> again about the common compilation / evaluation pathway idea.

Yeah.  ISTR some other justifications for a big expression evaluator
rewrite -- async function calls or something like that.

But it seems like this can probably be done without that.  Though, I
haven't looked enough at ax.h to know whether it can represent all of
DWARF... which reminds me, how much trouble is it to add to AX?  Is it
versioned so we can detect old remotes?

Tom