[llvm] [StaticDataLayout][PGO] Add profile format for static data layout, and the classes to operate on the profiles. (PR #138170)

[Snehasish Kumar via llvm-commits]

================
@@ -0,0 +1,263 @@
+#include "llvm/ProfileData/DataAccessProf.h"
+#include "llvm/ADT/DenseMapInfoVariant.h"
+#include "llvm/ADT/STLExtras.h"
+#include "llvm/ProfileData/InstrProf.h"
+#include "llvm/Support/Compression.h"
+#include "llvm/Support/Endian.h"
+#include "llvm/Support/Errc.h"
+#include "llvm/Support/Error.h"
+#include "llvm/Support/StringSaver.h"
+#include "llvm/Support/raw_ostream.h"
+#include <sys/types.h>
+
+namespace llvm {
+namespace data_access_prof {
+
+// If `Map` has an entry keyed by `Str`, returns the entry iterator. Otherwise,
+// creates an owned copy of `Str`, adds a map entry for it and returns the
+// iterator.
+static MapVector<StringRef, uint64_t>::iterator
+saveStringToMap(MapVector<StringRef, uint64_t> &Map,
+                llvm::UniqueStringSaver &Saver, StringRef Str) {
+  auto [Iter, Inserted] = Map.try_emplace(Saver.save(Str), Map.size());
+  return Iter;
+}
+
+// Returns the canonical name or error.
+static Expected<StringRef> getCanonicalName(StringRef Name) {
+  if (Name.empty())
+    return make_error<StringError>("Empty symbol name",
+                                   llvm::errc::invalid_argument);
+  return InstrProfSymtab::getCanonicalName(Name);
+}
+
+const DataAccessProfRecord *
+DataAccessProfData::getProfileRecord(const SymbolHandle SymbolID) const {
+  auto Key = SymbolID;
+  if (std::holds_alternative<StringRef>(SymbolID)) {
+    auto NameOrErr = getCanonicalName(std::get<StringRef>(SymbolID));
+    // If name canonicalization fails, suppress the error inside.
+    if (!NameOrErr) {
+      assert(
+          std::get<StringRef>(SymbolID).empty() &&
+          "Name canonicalization only fails when stringified string is empty.");
+      return nullptr;
+    }
+    Key = *NameOrErr;
+  }
+
+  auto It = Records.find(Key);
+  if (It != Records.end())
+    return &It->second;
+
+  return nullptr;
+}
+
+bool DataAccessProfData::isKnownColdSymbol(const SymbolHandle SymID) const {
+  if (std::holds_alternative<uint64_t>(SymID))
+    return KnownColdHashes.contains(std::get<uint64_t>(SymID));
+  return KnownColdSymbols.contains(std::get<StringRef>(SymID));
+}
+
+Error DataAccessProfData::setDataAccessProfile(SymbolHandle Symbol,
+                                               uint64_t AccessCount) {
+  uint64_t RecordID = -1;
+  bool IsStringLiteral = false;
----------------
snehasish wrote:

Maybe we can hoist the condition below

```
const bool IsStringLiteral = std::holds_alternative<uint64_t>(Symbol);
if (IsStringLiteral) {
 ...
} else {
 ...
}
```

https://github.com/llvm/llvm-project/pull/138170