From 94070473307b4ded676b97b1a673b496c074cda0 Mon Sep 17 00:00:00 2001
From: JosJuice <josjuice@gmail.com>
Date: Sun, 9 Aug 2026 17:37:15 +0200
Subject: Jit: Use LazyMemoryRegion-backed bit sets

JitCache has been using a class called ValidBlockBitSet. This commit
replaces it with a new class called LazyMemoryRegionBitSet, which works
similarly but is backed by a LazyMemoryRegion, letting us skip
allocating memory for parts of the bit set that correspond to emulated
memory regions where the game isn't storing any code. I have also added
optimized functions for setting or clearing long runs of bits.

Additionally, this commit replaces JitBase's three std::unordered_sets
that are keeping track of instructions with LazyMemoryRegionBitSets.
Here the benefit is more speed than memory usage. This improves NBA Live
2005's menu performance by 1% or so in SuperSamus's testing.
---
 Source/Core/Common/LazyMemoryRegionBitSet.cpp | 96 +++++++++++++++++++++++++++
 1 file changed, 96 insertions(+)
 create mode 100644 Source/Core/Common/LazyMemoryRegionBitSet.cpp

(limited to 'Source/Core/Common/LazyMemoryRegionBitSet.cpp')

diff --git a/Source/Core/Common/LazyMemoryRegionBitSet.cpp b/Source/Core/Common/LazyMemoryRegionBitSet.cpp
new file mode 100644
index 0000000000..af9d79c8df
--- /dev/null
+++ b/Source/Core/Common/LazyMemoryRegionBitSet.cpp
@@ -0,0 +1,96 @@
+// Copyright 2026 Dolphin Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#include "Common/LazyMemoryRegionBitSet.h"
+
+#include <cstring>
+
+#include "Common/Align.h"
+#include "Common/MsgHandler.h"
+
+namespace Common
+{
+LazyMemoryRegionBitSet::LazyMemoryRegionBitSet(size_t bits) : m_bits(bits), m_valid(Create(bits))
+{
+}
+
+bool LazyMemoryRegionBitSet::Create(size_t bits)
+{
+  m_pointer = reinterpret_cast<u32*>(m_region.Create(Common::AlignUp(bits, 32) / 8));
+  if (!m_pointer)
+  {
+    PanicAlertFmt("LazyMemoryRegionBitSet failed to create backing region");
+    return false;
+  }
+
+  return true;
+}
+
+void LazyMemoryRegionBitSet::Clear()
+{
+  m_region.Clear();
+}
+
+void LazyMemoryRegionBitSet::CheckBitIndicesWriteable(size_t bits_start, size_t bits_end)
+{
+  CheckBitIndexReadable(bits_end - 1);
+  const size_t start_byte = Common::AlignDown(bits_start, 32) / 8;
+  const size_t end_byte = Common::AlignUp(bits_end, 32) / 8;
+  m_region.EnsureMemoryPagesWritable(start_byte, end_byte - start_byte);
+}
+
+void LazyMemoryRegionBitSet::SetBits(size_t bits_start, size_t bits_end)
+{
+  if (bits_start >= bits_end)
+    return;
+
+  CheckBitIndicesWriteable(bits_start, bits_end);
+
+  const u32 extra_first_word = 0xFFFFFFFF << bits_start % 32;
+  const u32 extra_last_word = ~(0xFFFFFFFF << bits_end % 32);
+
+  if (bits_start / 32 == bits_end / 32)
+  {
+    m_pointer[bits_start / 32] |= extra_first_word & extra_last_word;
+    return;
+  }
+
+  if (bits_start % 32 != 0)
+    m_pointer[bits_start / 32] |= extra_first_word;
+
+  const size_t start_index = Common::AlignUp(bits_start, 32) / 32;
+  const size_t end_index = bits_end / 32;
+  std::memset(m_pointer + start_index, 0xFF, (end_index - start_index) * 4);
+
+  if (bits_end % 32 != 0)
+    m_pointer[bits_end / 32] |= extra_last_word;
+}
+
+void LazyMemoryRegionBitSet::ClearBits(size_t bits_start, size_t bits_end)
+{
+  if (bits_start >= bits_end)
+    return;
+
+  CheckBitIndicesWriteable(bits_start, bits_end);
+
+  const u32 extra_first_word = ~(0xFFFFFFFF << bits_start % 32);
+  const u32 extra_last_word = 0xFFFFFFFF << bits_end % 32;
+
+  if (bits_start / 32 == bits_end / 32)
+  {
+    m_pointer[bits_start / 32] &= extra_first_word | extra_last_word;
+    return;
+  }
+
+  if (bits_start % 32 != 0)
+    m_pointer[bits_start / 32] &= extra_first_word;
+
+  const size_t start_index = Common::AlignUp(bits_start, 32) / 32;
+  const size_t end_index = bits_end / 32;
+  std::memset(m_pointer + start_index, 0x00, (end_index - start_index) * sizeof(u32));
+
+  if (bits_end % 32 != 0)
+    m_pointer[bits_end / 32] &= extra_last_word;
+}
+
+}  // namespace Common
-- 
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