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Represent invalid UUIDs as UUIDs with length zero

Description

Represent invalid UUIDs as UUIDs with length zero

Summary:
During the previous attempt to generalize the UUID class, it was
suggested that we represent invalid UUIDs as length zero (previously, we
used an all-zero UUID for that). This meant that some valid build-ids
could not be represented (it's possible however unlikely that a checksum of
some file would be zero) and complicated adding support for variable
length build-ids (should a 16-byte empty UUID compare equal to a 20-byte
empty UUID?).

This patch resolves these issues by introducing a canonical
representation for an invalid UUID. The slight complication here is that
some clients (MachO) actually use the all-zero notation to mean "no UUID
has been set". To keep this use case working (while making it very
explicit about which construction semantices are wanted), replaced the
UUID constructors and the SetBytes functions with named factory methods.

  • "fromData" creates a UUID from the given data, and it treats all bytes equally.
  • "fromOptionalData" first checks the data contents - if all bytes are zero, it treats this as an invalid/empty UUID.

Reviewers: clayborg, sas, lemo, davide, espindola

Subscribers: emaste, lldb-commits, arichardson

Differential Revision: https://reviews.llvm.org/D48479

Details

Committed
labathJun 26 2018, 8:12 AM
Differential Revision
D48479: Represent invalid UUIDs as UUIDs with length zero
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