src/objects/compilation-cache-table.h

// Copyright 2017 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef V8_OBJECTS_COMPILATION_CACHE_TABLE_H_
#define V8_OBJECTS_COMPILATION_CACHE_TABLE_H_

#include "src/objects/feedback-cell.h"
#include "src/objects/hash-table.h"
#include "src/objects/js-regexp.h"
#include "src/objects/shared-function-info.h"
#include "src/roots/roots.h"

// Has to be the last include (doesn't have include guards):
#include "src/objects/object-macros.h"

namespace v8 {
namespace internal {

struct ScriptDetails;

class CompilationCacheShape : public BaseShape<HashTableKey*> {
 public:
  static inline bool IsMatch(HashTableKey* key, Tagged<Object> value) {
    return key->IsMatch(value);
  }

  static inline uint32_t Hash(ReadOnlyRoots roots, HashTableKey* key) {
    return key->Hash();
  }

  static inline uint32_t RegExpHash(Tagged<String> string, Tagged<Smi> flags);

  static inline uint32_t EvalHash(Tagged<String> source,
                                  Tagged<SharedFunctionInfo> shared,
                                  LanguageMode language_mode, int position);

  static inline uint32_t HashForObject(ReadOnlyRoots roots,
                                       Tagged<Object> object);

  static const int kPrefixSize = 0;
  // An 'entry' is essentially a grouped collection of slots. Entries are used
  // in various ways by the different caches; most store the actual key in the
  // first entry slot, but it may also be used differently.
  // Why 3 slots? Because of the eval cache.
  static const int kEntrySize = 3;
  static const bool kMatchNeedsHoleCheck = true;
};

class InfoCellPair {
 public:
  InfoCellPair() = default;
  inline InfoCellPair(Isolate* isolate, Tagged<SharedFunctionInfo> shared,
                      Tagged<FeedbackCell> feedback_cell);

  Tagged<FeedbackCell> feedback_cell() const {
    DCHECK(is_compiled_scope_.is_compiled());
    return feedback_cell_;
  }
  Tagged<SharedFunctionInfo> shared() const {
    DCHECK(is_compiled_scope_.is_compiled());
    return shared_;
  }

  bool has_feedback_cell() const {
    return !feedback_cell_.is_null() && is_compiled_scope_.is_compiled();
  }
  bool has_shared() const {
    // Only return true if SFI is compiled - the bytecode could have been
    // flushed while it's in the compilation cache, and not yet have been
    // removed form the compilation cache.
    return !shared_.is_null() && is_compiled_scope_.is_compiled();
  }

 private:
  IsCompiledScope is_compiled_scope_;
  Tagged<SharedFunctionInfo> shared_;
  Tagged<FeedbackCell> feedback_cell_;
};

// A lookup result from the compilation cache for scripts. There are three
// possible states:
//
// 1. Cache miss: script and toplevel_sfi are both null.
// 2. Cache hit: script and toplevel_sfi are both non-null. toplevel_sfi is
//    guaranteed to be compiled, and to stay compiled while this lookup result
//    instance is alive.
// 3. Partial cache hit: script is non-null, but toplevel_sfi is null. The
//    script may contain an uncompiled toplevel SharedFunctionInfo.
class CompilationCacheScriptLookupResult {
 public:
  MaybeHandle<Script> script() const { return script_; }
  MaybeHandle<SharedFunctionInfo> toplevel_sfi() const { return toplevel_sfi_; }
  IsCompiledScope is_compiled_scope() const { return is_compiled_scope_; }

  using RawObjects = std::pair<Tagged<Script>, Tagged<SharedFunctionInfo>>;

  RawObjects GetRawObjects() const;

  static CompilationCacheScriptLookupResult FromRawObjects(RawObjects raw,
                                                           Isolate* isolate);

 private:
  MaybeHandle<Script> script_;
  MaybeHandle<SharedFunctionInfo> toplevel_sfi_;
  IsCompiledScope is_compiled_scope_;
};

EXTERN_DECLARE_HASH_TABLE(CompilationCacheTable, CompilationCacheShape)

class CompilationCacheTable
    : public HashTable<CompilationCacheTable, CompilationCacheShape> {
 public:
  NEVER_READ_ONLY_SPACE

  // The 'script' cache contains SharedFunctionInfos. Once a root
  // SharedFunctionInfo has become old enough that its bytecode is flushed, the
  // entry is still present and can be used to get the Script.
  static CompilationCacheScriptLookupResult LookupScript(
      Handle<CompilationCacheTable> table, Handle<String> src,
      const ScriptDetails& script_details, Isolate* isolate);
  static Handle<CompilationCacheTable> PutScript(
      Handle<CompilationCacheTable> cache, Handle<String> src,
      MaybeHandle<FixedArray> maybe_wrapped_arguments,
      Handle<SharedFunctionInfo> value, Isolate* isolate);

  // Eval code only gets cached after a second probe for the
  // code object. To do so, on first "put" only a hash identifying the
  // source is entered into the cache, mapping it to a lifetime count of
  // the hash. On each call to Age all such lifetimes get reduced, and
  // removed once they reach zero. If a second put is called while such
  // a hash is live in the cache, the hash gets replaced by an actual
  // cache entry. Age also removes stale live entries from the cache.
  // Such entries are identified by SharedFunctionInfos pointing to
  // either the recompilation stub, or to "old" code. This avoids memory
  // leaks due to premature caching of eval strings that are
  // never needed later.
  static InfoCellPair LookupEval(Handle<CompilationCacheTable> table,
                                 Handle<String> src,
                                 Handle<SharedFunctionInfo> shared,
                                 Handle<Context> native_context,
                                 LanguageMode language_mode, int position);
  static Handle<CompilationCacheTable> PutEval(
      Handle<CompilationCacheTable> cache, Handle<String> src,
      Handle<SharedFunctionInfo> outer_info, Handle<SharedFunctionInfo> value,
      Handle<Context> native_context, Handle<FeedbackCell> feedback_cell,
      int position);

  // The RegExp cache contains JSRegExp::data fixed arrays.
  Handle<Object> LookupRegExp(Handle<String> source, JSRegExp::Flags flags);
  static Handle<CompilationCacheTable> PutRegExp(
      Isolate* isolate, Handle<CompilationCacheTable> cache, Handle<String> src,
      JSRegExp::Flags flags, Handle<FixedArray> value);

  void Remove(Tagged<Object> value);
  void RemoveEntry(InternalIndex entry);

  inline Tagged<Object> PrimaryValueAt(InternalIndex entry);
  inline void SetPrimaryValueAt(InternalIndex entry, Tagged<Object> value,
                                WriteBarrierMode mode = UPDATE_WRITE_BARRIER);
  inline Tagged<Object> EvalFeedbackValueAt(InternalIndex entry);
  inline void SetEvalFeedbackValueAt(
      InternalIndex entry, Tagged<Object> value,
      WriteBarrierMode mode = UPDATE_WRITE_BARRIER);

  // The initial placeholder insertion of the eval cache survives this many GCs.
  static constexpr int kHashGenerations = 10;

  DECL_CAST(CompilationCacheTable)

 private:
  static Handle<CompilationCacheTable> EnsureScriptTableCapacity(
      Isolate* isolate, Handle<CompilationCacheTable> cache);

  OBJECT_CONSTRUCTORS(CompilationCacheTable,
                      HashTable<CompilationCacheTable, CompilationCacheShape>);
};

}  // namespace internal
}  // namespace v8

#include "src/objects/object-macros-undef.h"

#endif  // V8_OBJECTS_COMPILATION_CACHE_TABLE_H_