Adding upstream version 115.7.0esr.upstream/115.7.0esrupstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 56 insertions, 0 deletions

diff --git a/js/src/jit/JitHints.h b/js/src/jit/JitHints.h
new file mode 100644
index 0000000000..34b8da36d6
--- /dev/null
+++ b/js/src/jit/JitHints.h
@@ -0,0 +1,56 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * vim: set ts=8 sts=2 et sw=2 tw=80:
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef jit_JitHints_h
+#define jit_JitHints_h
+
+#include "mozilla/BloomFilter.h"
+#include "vm/JSScript.h"
+
+namespace js::jit {
+
+/*
+ * The JitHintsMap implements a BitBloomFilter to track whether or not a script,
+ * identified by filename+sourceStart, has been baseline compiled before in the
+ * same process.  This can occur frequently during navigations.
+ *
+ * The bloom filter allows us to have very efficient storage and lookup costs,
+ * at the expense of occasional false positives.  The number of entries added
+ * to the bloom filter is monitored in order to try and keep the false
+ * positivity rate below 1%.  If the entry count exceeds MaxEntries_, which
+ * indicates the false positivity rate may exceed 1.5%, then the filter is
+ * completely cleared to reset the cache.
+ */
+
+class JitHintsMap {
+  // ScriptKey is a hash on the filename+sourceStart.
+  using ScriptKey = HashNumber;
+
+  static constexpr uint32_t CacheSize_ = 16;
+  mozilla::BitBloomFilter<CacheSize_, ScriptKey> map_;
+
+  /*
+   * MaxEntries_ is the approximate entry count for which the
+   * false positivity rate will exceed p=0.015 using k=2 and m=2**CacheSize.
+   * Formula is as follows:
+   * MaxEntries_ = floor(m / (-k / ln(1-exp(ln(p) / k))))
+   */
+  static constexpr uint32_t MaxEntries_ = 4281;
+  static_assert(CacheSize_ == 16 && MaxEntries_ == 4281,
+                "MaxEntries should be recalculated for given CacheSize.");
+
+  uint32_t entryCount_ = 0;
+
+  ScriptKey getScriptKey(JSScript* script) const;
+  void incrementEntryCount();
+
+ public:
+  void setEagerBaselineHint(JSScript* script);
+  bool mightHaveEagerBaselineHint(JSScript* script) const;
+};
+
+}  // namespace js::jit
+#endif /* jit_JitHints_h */