[llvm-dev] RFC: metadata attachments for global variables

[David Blaikie via llvm-dev]

On Fri, May 6, 2016 at 1:55 PM, Peter Collingbourne via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

>
>
> On Fri, May 6, 2016 at 1:21 PM, Duncan P. N. Exon Smith <
> dexonsmith at apple.com> wrote:
>
>>
>> > On 2016-May-06, at 13:17, Peter Collingbourne <peter at pcc.me.uk> wrote:
>> >
>> > Hi all,
>> >
>> > I'd like to add support for metadata attachments for global variables
>> in the same way as we did for functions.
>> >
>> > Syntax would be pretty simple:
>> > @foo = global i32 0, !foo !0, !bar !1
>> > (the extra commas are required to disambiguate from a named metadata on
>> the next line)
>>
>> SGTM.
>>
>> > Benefits:
>> > 1) Lets us reverse the DIGlobalVariable -> GlobalVariable edge, which
>> should hopefully clear the way for removing the llvm.dbg.cu named
>> metadata node.
>>
>> A little harder than it sounds (need to somehow support a GlobalVariable
>> that is RAUW'ed with a ConstantInt), but I think this is important to do.
>>
>
> How can a GlobalVariable be replaced with a ConstantInt? Wouldn't that
> just be an absolute address?
>

If the global variable has a known constant value & the address is never
needed, then we might optimize away the storage and still want debug info
describing the constant.


>
> Thanks,
> --
> --
> Peter
>
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