[PATCH 1/5] gas: streamline expr_build_dot()

[Maciej W. Rozycki]

On Tue, 26 Nov 2024, Jan Beulich wrote:

> >> There's no point involving symbol_clone_if_forward_ref(), just for it to
> >> replace dot_symbol by one obtained from symbol_temp_new_now(). For the
> >> abs-section case also produce a slightly more "complete" (as in: all
> >> potentially relevant fields filled) expression by going through
> >> expr_build_uconstant().
> > 
> >  As I recall this cloning is needed for equated symbols, so that the value 
> > of `.' used in an expression used for a symbol's calculation is obtained 
> > at the time of the symbol's reference and not the symbol's definition.
> 
> Yet then symbol_clone_if_forward_ref() would be wrong to use here, as that
> pins down . at the present location (the cloning is done to keep this
> "pinning down" from affecting the original symbol). Aiui it's quite the
> opposite: expr_build_dot() _wants_ to latch . at its current location. At
> least according to my interpretation of all the uses of it that we
> presently have.

 Correct indeed, I misremembered.

 I'm not convinced by your simplification though, as the key here is to
tie `expr_build_dot' to `dot_symbol', even if it adds extra layering and 
effectively boils down to the same calculation your proposed replacement 
does.  This layering is so that we have a single tracking symbol, as 
proposed by Richard Sandiford to represent ".".  See the discussion in: 
<https://inbox.sourceware.org/binutils/alpine.DEB.1.10.1010291442440.25860@tp.orcam.me.uk/> 
for the rationale.

 Any inconsistency between `dot_symbol' and `dot_frag'/`dot_value' can I 
think be sorted by setting the latter values to corresponding pieces of 
information retrieved from `dot_symbol', or maybe even discarding them as 
redundant.

 I can see there are three places where they are set, namely `md_assemble' 
in the POWER backend (which I suppose knows what it's doing, so should 
presumably just call `symbol_set_value_now (&dot_symbol)' instead), and 
then `expr' and `emit_expr_with_reloc'.  Perhaps the latter two can be 
discarded now that we have `dot_symbol' updated at every assembly line, 
but that would have to be verified.  I don't know offhand.

  Maciej