[PATCH] D59348: [DebugInfo] Combine Trivial and NonTrivial flags

[Adrian Prantl via llvm-commits]

This is all assuming that both flags are only present when compiling with PDB debug info and zero when compiling for DWARF. Is that correct?

> On Apr 10, 2019, at 3:52 PM, Adrian Prantl <aprantl at apple.com> wrote:
> 
> If it wasn't in the last LLVM release and nobody in the community released an LLVM-based product to users that use PDB debug info and LTO in the mean time, it will not be a big deal.
> 
> -- adrian
> 
>> On Apr 10, 2019, at 3:50 PM, Aaron Smith <aaron.lee.smith at gmail.com> wrote:
>> 
>> I know very little about bitcode compatibility in llvm. Since both of these flags were added in the last two or three months this is probably not a big deal? The whole reason for the change is to reclaim the bit.
>> 
>>> On Apr 10, 2019, at 4:43 PM, Adrian Prantl via Phabricator <reviews at reviews.llvm.org> wrote:
>>> 
>>> aprantl added inline comments.
>>> 
>>> 
>>> ================
>>> Comment at: include/llvm/IR/DebugInfoFlags.def:57-60
>>> +HANDLE_DI_FLAG((1 << 26), NonTrivial)
>>> HANDLE_DI_FLAG((1 << 27), BigEndian)
>>> HANDLE_DI_FLAG((1 << 28), LittleEndian)
>>> HANDLE_DI_FLAG((1 << 29), AllCallsDescribed)
>>> ----------------
>>> dblaikie wrote:
>>>> @aprantl - could you review this for bitcode compatibility?
>>>> 
>>>> I  imagine reusing a bit for a different meaning (the exact opposite) would be problematic?
>>>> 
>>>> Would we have to settle for keeping the bitcode encoding as 1=trivial 0=nontrivial (only for structs/classes? Maybe enums too?) - or burn the 26th bit and keep the 30th bit as NonTrivial?
>>> Since this only affects PDB debug info I personally don't worry about breaking bitcode compatibility, however other people may do so.
>>> 
>>> The correct way to update this is to bump the version of the records (DICompositeType) and parse the old or the new format accordingly.
>>> 
>>> If this isn't done any LLVM module with bitcode that currently uses bit 30 (which is now > Largest) will cause a verifier error and the debug info from that module will be dropped with a warning. LTO users may or may not care about this.
>>> 
>>> 
>>> CHANGES SINCE LAST ACTION
>>> https://reviews.llvm.org/D59348/new/
>>> 
>>> https://reviews.llvm.org/D59348
>>> 
>>> 
>>> 
>