[llvm] [CGData] Stable Function Map (PR #112662)

[Vincent Lee via llvm-commits]

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+//===- StableFunctionMap.h -------------------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===---------------------------------------------------------------------===//
+//
+// This defines the StableFunctionMap class, to track similar functions.
+// It provides a mechanism to map stable hashes of functions to their
+// corresponding metadata. It includes structures for storing function details
+// and methods for managing and querying these mappings.
+//
+//===---------------------------------------------------------------------===//
+
+#ifndef LLVM_CGDATA_STABLEFUNCTIONMAP_H
+#define LLVM_CGDATA_STABLEFUNCTIONMAP_H
+
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/StringMap.h"
+#include "llvm/IR/StructuralHash.h"
+
+namespace llvm {
+
+using IndexPairHash = std::pair<IndexPair, stable_hash>;
+using IndexOperandHashVecType = SmallVector<IndexPairHash>;
+
+/// A stable function is a function with a stable hash while tracking the
+/// locations of ignored operands and their hashes.
+struct StableFunction {
+  /// The combined stable hash of the function.
+  stable_hash Hash;
+  /// The name of the function.
+  std::string FunctionName;
+  /// The name of the module the function is in.
+  std::string ModuleName;
+  /// The number of instructions.
+  unsigned InstCount;
+  /// A vector of pairs of IndexPair and operand hash which was skipped.
+  IndexOperandHashVecType IndexOperandHashes;
+
+  StableFunction(stable_hash Hash, const std::string FunctionName,
+                 const std::string ModuleName, unsigned InstCount,
+                 IndexOperandHashVecType &&IndexOperandHashes)
+      : Hash(Hash), FunctionName(FunctionName), ModuleName(ModuleName),
+        InstCount(InstCount),
+        IndexOperandHashes(std::move(IndexOperandHashes)) {}
+  StableFunction() = default;
+};
+
+/// An efficient form of StableFunction for fast look-up
+struct StableFunctionEntry {
+  /// The combined stable hash of the function.
+  stable_hash Hash;
+  /// Id of the function name.
+  unsigned FunctionNameId;
+  /// Id of the module name.
+  unsigned ModuleNameId;
+  /// The number of instructions.
+  unsigned InstCount;
+  /// A map from an IndexPair to a stable_hash which was skipped.
+  std::unique_ptr<IndexOperandHashMapType> IndexOperandHashMap;
+
+  StableFunctionEntry(
+      stable_hash Hash, unsigned FunctionNameId, unsigned ModuleNameId,
+      unsigned InstCount,
+      std::unique_ptr<IndexOperandHashMapType> IndexOperandHashMap)
+      : Hash(Hash), FunctionNameId(FunctionNameId), ModuleNameId(ModuleNameId),
+        InstCount(InstCount),
+        IndexOperandHashMap(std::move(IndexOperandHashMap)) {}
+};
+
+using HashFuncsMapType =
+    DenseMap<stable_hash, SmallVector<std::unique_ptr<StableFunctionEntry>>>;
+
+class StableFunctionMap {
+  /// A map from a stable_hash to a vector of functions with that hash.
+  HashFuncsMapType HashToFuncs;
+  /// A vector of strings to hold names.
+  SmallVector<std::string> IdToName;
+  /// A map from StringRef (name) to an ID.
+  StringMap<unsigned> NameToId;
+  /// True if the function map is finalized with minimal content.
+  bool Finalized = false;
+
+public:
+  /// Get the HashToFuncs map for serialization.
+  const HashFuncsMapType &getFunctionMap() const { return HashToFuncs; }
+
+  /// Get the NameToId vector for serialization.
+  const SmallVector<std::string> getNames() const { return IdToName; }
+
+  /// Get an existing ID associated with the given name or create a new ID if it
+  /// doesn't exist.
+  unsigned getIdOrCreateForName(StringRef Name);
+
+  /// Get the name associated with a given ID
+  std::optional<std::string> getNameForId(unsigned Id) const;
+
+  /// Insert a `StableFunction` object into the function map. This method
+  /// handles the uniquing of string names and create a `StableFunctionEntry`
+  /// for insertion.
+  void insert(const StableFunction &Func);
+
+  /// Insert a `StableFunctionEntry` into the function map directly. This
+  /// method assumes that string names have already been uniqued and the
+  /// `StableFunctionEntry` is ready for insertion.
+  void insert(std::unique_ptr<StableFunctionEntry> FuncEntry) {
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thevinster wrote:

If `StableFunctionEntry` is private, then this method can be private too. 

https://github.com/llvm/llvm-project/pull/112662