Build transactions at runtime

Drop _xbegin family intrinsics due to bad codegen
Implemented `notifier` class, replacing vm::notify
Minor optimization: detach transactions from global mutex on TSX path
Minor optimization: don't acquire vm::passive_lock on PPU on TSX path

Utilities/cond.h

@@ -9,6 +9,8 @@ class cond_variable
 	// Internal waiter counter
 	atomic_t<u32> m_value{0};
 
+	friend class notifier;
+
 protected:
 	// Internal waiting function
 	bool imp_wait(u32 _old, u64 _timeout) noexcept;
@@ -50,3 +52,94 @@ public:
 
 	static constexpr u64 max_timeout = u64{UINT32_MAX} / 1000 * 1000000;
 };
+
+// Pair of a fake shared mutex (only limited shared locking) and a condition variable
+class notifier
+{
+	atomic_t<u32> m_counter{0};
+	cond_variable m_cond;
+
+public:
+	constexpr notifier() = default;
+
+	void lock_shared()
+	{
+		m_counter++;
+	}
+
+	void unlock_shared()
+	{
+		const u32 counter = --m_counter;
+
+		if (counter & 0x7f)
+		{
+			return;
+		}
+
+		if (counter >= 0x80)
+		{
+			const u32 _old = m_counter.atomic_op([](u32& value) -> u32
+			{
+				if (value & 0x7f)
+				{
+					return 0;
+				}
+
+				return std::exchange(value, 0) >> 7;
+			});
+
+			if (_old && m_cond.m_value)
+			{
+				m_cond.imp_wake(_old);
+			}
+		}
+	}
+
+	explicit_bool_t wait(u64 usec_timeout = -1)
+	{
+		const u32 _old = m_cond.m_value.fetch_add(1);
+
+		if (0x80 <= m_counter.fetch_op([](u32& value)
+		{
+			value--;
+
+			if (value >= 0x80)
+			{
+				value -= 0x80;
+			}
+		}))
+		{
+			// Return without waiting
+			m_cond.imp_wait(_old, 0);
+			m_counter++;
+			return true;
+		}
+
+		const bool res = m_cond.imp_wait(_old, usec_timeout);
+		m_counter++;
+		return res;
+	}
+
+	void notify_all()
+	{
+		if (m_counter)
+		{
+			m_counter.atomic_op([](u32& value)
+			{
+				if (const u32 add = value & 0x7f)
+				{
+					// Mutex is locked in shared mode
+					value += add << 7;
+				}
+				else
+				{
+					// Mutex is unlocked
+					value = 0;
+				}
+			});
+		}
+
+		// Notify after imaginary "exclusive" lock+unlock
+		m_cond.notify_all();
+	}
+};