[LLVMdev] [ARM] [PIC] optimizing the loading of hidden global variable

[Tim Northover]

>> Any thoughs?
>
> I'm now struggling to see how GCC justifies it. What if a different
> translation-unit declared those variables in a different order? I also
> can't get the same behaviour here, do you have a more complete
> command-line?

Ah, I see; the translation-unit that does the optimisation needs to
have them as a definition (i.e. "= {0}") rather than a declaration for
the optimisation to kick in, giving it precedence over other
declarations. And the hidden-visibility means they won't be
R_ARM_COPYed out of their initial location.

After a very brief thought, I'd still go for GlobalMerge now, in
conjunction with an enhanced "alias" so that you could emit something
like:

    @g1 = hidden alias [100 x i32]* bitcast(i32* getelementptr([300 x
i32]* @Merged, i32 0, i32 0) to [100 x i32]*)

We certainly don't seem to handle this alias properly now though, and
it may violate the intended uses. Rafael's doing some thinking about
"alias" at the moment, so I've CCed him.

Would that be a horrific abuse of the poor alias system?

Cheers.

Tim.