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

[Aaron Smith via llvm-commits]

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
> 
> 
>