[llvm] [ProfData] Improve efficiency of reader (PR #169730)

[Vitaly Buka via llvm-commits]

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@@ -399,15 +399,30 @@ LLVM_DUMP_METHOD void FunctionSamples::dump() const { print(dbgs(), 0); }
 std::error_code ProfileSymbolList::read(const uint8_t *Data,
                                         uint64_t ListSize) {
   const char *ListStart = reinterpret_cast<const char *>(Data);
-  uint64_t Size = 0;
+  uint64_t Offset = 0;
   uint64_t StrNum = 0;
-  while (Size < ListSize && StrNum < ProfileSymbolListCutOff) {
-    StringRef Str(ListStart + Size);
+  uint64_t ExpectedCount = 0;
+
+  Scan forward to see how many elements we expect.
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vitalybuka wrote:

// is missing?

https://github.com/llvm/llvm-project/pull/169730