[llvm] [memprof] Speed up caller-callee pair extraction (PR #116184)

[Snehasish Kumar via llvm-commits]

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@@ -771,15 +773,26 @@ static Error writeMemProfV3(ProfOStream &OS,
       writeMemProfFrameArray(OS, MemProfData.Frames, FrameHistogram);
 
   uint64_t CallStackPayloadOffset = OS.tell();
+  // The number of elements in the call stack array.
+  unsigned NumElements;
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snehasish wrote:

Initialize to zero?

https://github.com/llvm/llvm-project/pull/116184