[llvm] [llvm-profgen][SPGO] Support profiles with multiple concurrent processes (PR #169353)

[Wei Wang via llvm-commits]

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@@ -670,14 +703,37 @@ bool PerfScriptReader::extractLBRStack(TraceStream &TraceIt,
 
   // Skip the leading instruction pointer.
   size_t Index = 0;
+  // Default to PID 0 if not provided
+  int32_t PID = 0;
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apolloww wrote:

There are multiple places uses 0 as the default PID, maybe we can use a const for this?

https://github.com/llvm/llvm-project/pull/169353