[PATCH] D110365: [llvm][profile] Add padding after binary IDs

[Leonard Chan via Phabricator via llvm-commits]

leonardchan added inline comments.


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Comment at: llvm/lib/ProfileData/InstrProfReader.cpp:558
     // Increment by binary id data length.
     BI += BinaryIdLen;
     if (BI > (const uint8_t *)DataBuffer->getBufferEnd())
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leonardchan wrote:
> mcgrathr wrote:
> > What is the packing protocol?  It seems wise to pad after *each* ID to make the next size field naturally-aligned, rather than having the second size field be misaligned if the first build ID length is not a multiple of 8.
> > 
> Right now there's no alignment and the size just seems to be added after the previous build ID. I updated `__llvm_write_build_ids` to take this suggestion of adding padding after each ID. This should also prevent us from needing to add padding after all the build IDs if there's padding in between each.
> 
> I'm wondering though if maybe adding padding after each ID would lead to some bloat compared to just adding padding once.
> What is the packing protocol?

Oh, I may have misunderstood at first. In terms of packing, the only requirement seems to be that each header be 8-byte aligned (https://github.com/llvm/llvm-project/blob/dcadd64986b8a84dc244d4e7faa848fb4c18cea6/llvm/lib/ProfileData/InstrProfReader.cpp#L337). I believe all the other sections like counters, data, and names are aligned as a whole with padding coming after each section to make sure the next is aligned. So if we want to follow suite, we could stick to just padding after the binary IDs section unless padding in between IDs is more desireable.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D110365/new/

https://reviews.llvm.org/D110365