[LLVMdev] merging globals

[Eli Friedman]

On Mon, Oct 20, 2008 at 12:38 AM, Matthijs Kooijman <matthijs at stdin.nl> wrote:
> Hi Chris,
>
>> > Wouldn't it be slightly cleaner to mark the distinct objects in the
>> > LLVM intermediate representation?
>> That is what I'm suggesting.  Each llvm IR global variable would have
>> its own flag.
>
> I think the suggestion is to have a "notmergable" flag instead of a
> "mergeable" flag. In practice, it doesn't really matter, but I guess you'll
> see the difference in the IR. I agree here that it would be more logical to
> have a notmergable (or "distinct" ?) flag, instead of a mergeable flag, though
> it's not quite critical.

I'm pretty sure we want mergeable to be opt-in.  If it defaults to
being allowed, unaware frontends (like the current llvm-gcc and clang)
will introduce logical contradictions by assuming that globals aren't
mergeable, and optimization passes that mark globals const will have
to make sure to mark them unmergeable.

-Eli