[BOLT][NFC] Avoid computing BF hash twice in YAML reader

We compute BF hashes in `YAMLProfileReader::readProfile` when first
matching profile functions with binary functions, and second time in
`YAMLProfileReader::parseFunctionProfile` during the profile assignment
(we need to do that to account for LTO private functions with
mismatching suffix).

Avoid recomputing the hash if it's been set.

Author: aaupov

bolt/lib/Core/BinaryFunction.cpp

@@ -3698,6 +3698,13 @@ BinaryFunction::BasicBlockListType BinaryFunction::dfs() const {
 
 size_t BinaryFunction::computeHash(bool UseDFS, HashFunction HashFunction,
                                    OperandHashFuncTy OperandHashFunc) const {
+  LLVM_DEBUG({
+    dbgs() << "BOLT-DEBUG: computeHash " << getPrintName() << ' '
+           << (UseDFS ? "dfs" : "bin") << " order "
+           << (HashFunction == HashFunction::StdHash ? "std::hash" : "xxh3")
+           << '\n';
+  });
+
   if (size() == 0)
     return 0;
 

bolt/lib/Profile/YAMLProfileReader.cpp

@@ -102,11 +102,14 @@ bool YAMLProfileReader::parseFunctionProfile(
   if (BF.empty())
     return true;
 
-  if (!opts::IgnoreHash &&
-      YamlBF.Hash != BF.computeHash(IsDFSOrder, HashFunction)) {
-    if (opts::Verbosity >= 1)
-      errs() << "BOLT-WARNING: function hash mismatch\n";
-    ProfileMatched = false;
+  if (!opts::IgnoreHash) {
+    if (!BF.getHash())
+      BF.computeHash(IsDFSOrder, HashFunction);
+    if (YamlBF.Hash != BF.getHash()) {
+      if (opts::Verbosity >= 1)
+        errs() << "BOLT-WARNING: function hash mismatch\n";
+      ProfileMatched = false;
+    }
   }
 
   if (YamlBF.NumBasicBlocks != BF.size()) {