[LLVMdev] [Debug Info + LTO] Type Uniquing for C types?

[Eric Christopher]

On Mon, Oct 14, 2013 at 4:14 PM, Manman Ren <manman.ren at gmail.com> wrote:
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> On Mon, Oct 14, 2013 at 1:08 PM, Manman Ren <manman.ren at gmail.com> wrote:
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>> On Fri, Oct 11, 2013 at 12:40 PM, Eric Christopher <echristo at gmail.com>
>> wrote:
>>>
>>> >> It depends upon the goals. If the goal is to make debug information
>>> >> post-link smaller then just using the type hashing machinery for
>>> >> structs will be sufficient.
>>> >
>>> >
>>> > By "the type hashing machinery for structs", are you referring to the
>>> > type
>>> > hashing at the back end?
>>> >
>>>
>>> I am, yes, since there's no other place we do currently.
>>>
>>> >>
>>> >> However, if it's to save space during an
>>> >> LTO link then we'll want to do it in the front end.
>>> >
>>> >
>>> > Yes, my purpose here is to save memory space in number of MDNodes (also
>>> > # of
>>> > DIEs) generated in a LTO build.
>>> > Type hashing at the DIE level can reduce the dwarf size.
>>> >
>>>
>>> I agree with both of these statements.
>>>
>>> I also agree with the desire to help LTO memory consumption so we'll
>>> need something from the front end for this since we'd like to continue
>>> to use the folding set to do the uniquing.
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>>
>> Hi Eric,
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>> Assume that we need to do type hashing (i.e. assume Doug's rules for
>> merging C types do not apply),
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> Now the assumption is true, any opinion on where to do the hashing?
>

We should still do it in the front end for the types with a language
specific way. Nothing has greatly changed versus, say, C++ here - it's
just easier in C++ because of the language.

-eric