[Dwarf-Discuss] DW_LNE_set_discriminator usage

[Cary Coutant]

> I've never seen DW_LNE_set_discriminator used. ?GCC doesn't generate it.

I submitted patches last June to add this to binutils and gcc:

  http://gcc.gnu.org/ml/gcc-patches/2009-04/msg01679.html (and follow-ups)

> The definition of the "discriminator register" in 6.2.2 is clear enough:
> "Discriminator values are assigned arbitrarily by the DWARF producer ..."
> But nothing anywhere mentions what this might be for.
> ...
> Enough of my speculations.  Someone just reveal it!  What is the plan?
> What does any extant or imagined DWARF consumer actually use the
> discriminator for?

There's a complete description on the DWARF wiki:

  http://wiki.dwarfstd.org/index.php?title=Path_Discriminators

> The DWARF specification document doesn't have big informative "rationale"
> appendices like some other standards do. ?It sure would be nice to have
> some quasi-official commentary about where all this stuff came from. ?In
> some parts of the specification, there are long italicized paragraphs that
> serve the same purpose as "rationale" sections do in other standards. ?But
> there are plenty more things like DW_LNE_set_discriminator where there is
> just nothing to be found in the document itself to help a person figure out
> what the intent of the feature was.

In many cases, the DWARF wiki is probably the place to look for that.

-cary