[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;
   uint64_t LeadingAddr;
+
+  if (Records.size() < (MultiProcessProfile ? 2 : 1)) {
+    WarnInvalidLBR(TraceIt);
+    TraceIt.advance();
+    return false;
+  }
+
+  if (MultiProcessProfile) {
+    // If we read the PID elsewhere, use that instead of trying to read it here
+    if (PIDIfKnown.has_value()) {
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apolloww wrote:

Would the just read PID be different from `PIDIfKnown`?

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