[llvm] [PGO] Add support for writing previous indexed format (PR #84505)

[Snehasish Kumar via llvm-commits]

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@@ -433,6 +435,8 @@ Error InstrProfWriter::writeImpl(ProfOStream &OS) {
   IndexedInstrProf::Header Header;
   Header.Magic = IndexedInstrProf::Magic;
   Header.Version = IndexedInstrProf::ProfVersion::CurrentVersion;
+  if (WritePrevVersion)
+    Header.Version--;
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snehasish wrote:

Since the changes down below are VTableName change specific would it make more sense to explicitly set this to the version we want?

https://github.com/llvm/llvm-project/pull/84505