Douglas B Rupp wrote:
The HP debugger on IA64 VMS defines a new Dwarf2 attribute that computes the
offset of the end of the prologue from the beginning of the function. To
implement this an end prologue label must be emitted and some related info
saved in dwarf2out.c.
However I've noted that calling debug_hooks->end_prologue as it is now
results in a label at the beginning of the prologue, not the end. I've
attached the obvious fix below, but I fear it might mess up sdbout.c. Should
I create a new hook or investigate the impact on sdbout and try to fix it?
Belatedly looking at this, you seem to be confused over the purpose of
the NOTE_INSN_FUNCTION_BEG note. It does not mark the beginning of the
function. That is the first RTL insn. Instead, it marks the beginning
of the function body.
If you compile without optimization, then this is the same as the
prologue end. If you compile with optimization, then the function body
and the prologue overlap. Now the question is, do you really want to
mark the beginning of the function body (which may be before the
prologue end), or the end of the prologue (which may be after the
function body beginning). Either way, it is likely that someone may not
be happy. However, in general, the former (function body beginning) is
more useful to end users, as otherwise they won't be able to debug all
of the code in the function body. So the current code in final.c looks
correct.
Othogonal to this, there is the problem of what to do with these notes
when instruction scheduling is enabled. It looks like the current code
just always moves notes to the beginning of the basic block containing
them. That means effectively that the function beginning is always
before the prologue. However, the prologue end note also ends up before
the prologue in the same place. So using that one doesn't help. The
only solution is a more general one. In the scheduler, before
scheduling, you need to mark all instructions that originally came from
the prologue. After scheduling, you go back through, find the first
non-prologue instruction, and insert the NOTE_INSN_FUNCTION_BEG note
before it. You find the last prologue instruction, and insert the
NOTE_INSN_PROLOGUE_END note after it. You would also have to do the
same (reversed) for the epilogue. It isn't clear if this extra work is
worthwhile.
--
Jim Wilson, GNU Tools Support, http://www.specifix.com
