Kazu Hirata d89914f30b [memprof] Add Version2 of IndexedMemProfRecord serialization (#87455) ...

I'm currently developing a new version of the indexed memprof format
where we deduplicate call stacks in IndexedAllocationInfo::CallStack
and IndexedMemProfRecord::CallSites.  We refer to call stacks with
integer IDs, namely CallStackId, just as we refer to Frame with
FrameId.  The deduplication will cut down the profile file size by 80%
in a large memprof file of mine.

As a step toward the goal, this patch teaches
IndexedMemProfRecord::{serialize,deserialize} to speak Version2.  A
subsequent patch will add Version2 support to llvm-profdata.

The essense of the patch is to replace the serialization of a call
stack, a vector of FrameIDs, with that of a CallStackId.  That is:

  const IndexedAllocationInfo &N = ...;
  ...
  LE.write<uint64_t>(N.CallStack.size());
  for (const FrameId &Id : N.CallStack)
    LE.write<FrameId>(Id);

becomes:

  LE.write<CallStackId>(N.CSId);

2024-04-03 21:48:38 -07:00

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