From bc9e590727211d803cce7be84c1cbc026179b841 Mon Sep 17 00:00:00 2001
From: Dan Engelbrecht <dan.engelbrecht@epicgames.com>
Date: Mon, 23 Sep 2024 19:19:40 +0200
Subject: gc unused refactor (#165)

* optimize IoHash and OId comparisions
* refactor filtering of unused references
* add attachment filtering to gc
---
 src/zencore/include/zencore/iohash.h |  8 ++++----
 src/zencore/include/zencore/memory.h | 35 +++++++++++++++++++++++++++++++++++
 src/zencore/include/zencore/uid.h    |  4 +++-
 src/zencore/iohash.cpp               |  6 +++++-
 4 files changed, 47 insertions(+), 6 deletions(-)

(limited to 'src/zencore')

diff --git a/src/zencore/include/zencore/iohash.h b/src/zencore/include/zencore/iohash.h
index ff902399e..a8fc9e6c1 100644
--- a/src/zencore/include/zencore/iohash.h
+++ b/src/zencore/include/zencore/iohash.h
@@ -1,5 +1,4 @@
 // Copyright Epic Games, Inc. All Rights Reserved.
-// Copyright Epic Games, Inc. All Rights Reserved.
 
 #pragma once
 
@@ -55,10 +54,11 @@ struct IoHash
 	StringBuilderBase& ToHexString(StringBuilderBase& outBuilder) const;
 	std::string		   ToHexString() const;
 
-	static const int StringLength = 40;
-	typedef char	 String_t[StringLength + 1];
+	static constexpr int StringLength = 40;
+	typedef char		 String_t[StringLength + 1];
 
 	static const IoHash Zero;  // Initialized to all zeros
+	static const IoHash Max;   // Initialized to all ones
 
 	inline auto operator<=>(const IoHash& rhs) const = default;
 	inline bool operator==(const IoHash& rhs) const
@@ -75,7 +75,7 @@ struct IoHash
 		return LhsHash[0] != RhsHash[0] || LhsHash[1] != RhsHash[1] || LhsHash[2] != RhsHash[2] || LhsHash[3] != RhsHash[3] ||
 			   LhsHash[4] != RhsHash[4];
 	}
-	inline bool operator<(const IoHash& rhs) const { return memcmp(Hash, rhs.Hash, sizeof Hash) < 0; }
+	inline bool operator<(const IoHash& rhs) const { return MemCmpFixed<sizeof Hash, std::uint32_t>(Hash, rhs.Hash) < 0; }
 
 	struct Hasher
 	{
diff --git a/src/zencore/include/zencore/memory.h b/src/zencore/include/zencore/memory.h
index 6419252ff..7a893d3ab 100644
--- a/src/zencore/include/zencore/memory.h
+++ b/src/zencore/include/zencore/memory.h
@@ -402,6 +402,41 @@ MakeMutableMemoryView(void* Data, void* DataEnd)
 	return MutableMemoryView(Data, DataEnd);
 }
 
+template<std::size_t SIZE>
+inline int
+MemCmpFixed(const void* a1, const void* a2)
+{
+	auto const s1	= reinterpret_cast<const unsigned char*>(a1);
+	auto const s2	= reinterpret_cast<const unsigned char*>(a2);
+	auto const diff = *s1 - *s2;
+	return diff ? diff : MemCmpFixed<SIZE - 1>(s1 + 1, s2 + 1);
+}
+
+template<>
+inline int
+MemCmpFixed<0>(const void*, const void*)
+{
+	return 0;
+}
+
+template<std::size_t SIZE, typename EQTYPE>
+inline int
+MemCmpFixed(const void* a1, const void* a2)
+{
+	ZEN_ASSERT_SLOW((uintptr_t(a1) & (sizeof(EQTYPE) - 1)) == 0);
+	ZEN_ASSERT_SLOW((uintptr_t(a2) & (sizeof(EQTYPE) - 1)) == 0);
+	auto const s1 = reinterpret_cast<const EQTYPE*>(a1);
+	auto const s2 = reinterpret_cast<const EQTYPE*>(a2);
+	return (*s1 != *s2) ? MemCmpFixed<sizeof(EQTYPE)>(s1, s2) : MemCmpFixed<SIZE - sizeof(EQTYPE), EQTYPE>(s1 + 1, s2 + 1);
+}
+
+template<>
+inline int
+MemCmpFixed<0, uint32_t>(const void*, const void*)
+{
+	return 0;
+}
+
 void memory_forcelink();  // internal
 
 }  // namespace zen
diff --git a/src/zencore/include/zencore/uid.h b/src/zencore/include/zencore/uid.h
index f8b1ccf98..08a335392 100644
--- a/src/zencore/include/zencore/uid.h
+++ b/src/zencore/include/zencore/uid.h
@@ -2,6 +2,7 @@
 
 #pragma once
 
+#include <zencore/memory.h>
 #include <zencore/zencore.h>
 
 #include <compare>
@@ -67,7 +68,8 @@ struct Oid
 	std::string				 ToString() const;
 	[[nodiscard]] static Oid FromMemory(const void* Ptr);
 
-	auto						  operator<=>(const Oid& rhs) const = default;
+	auto		operator<=>(const Oid& rhs) const = default;
+	inline bool operator<(const Oid& rhs) const { return MemCmpFixed<sizeof OidBits, std::uint32_t>(OidBits, rhs.OidBits) < 0; }
 	[[nodiscard]] inline explicit operator bool() const { return *this != Zero; }
 
 	static const Oid Zero;	// Min (can be used to signify a "null" value, or for open range queries)
diff --git a/src/zencore/iohash.cpp b/src/zencore/iohash.cpp
index 1bf2c033d..8f3f8da26 100644
--- a/src/zencore/iohash.cpp
+++ b/src/zencore/iohash.cpp
@@ -12,7 +12,11 @@
 
 namespace zen {
 
-const IoHash IoHash::Zero{};  // Initialized to all zeros
+static const uint8_t MaxData[20] = {0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+									0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff};
+
+const IoHash IoHash::Max = IoHash::MakeFrom(MaxData);  // Initialized to all 0xff
+const IoHash IoHash::Zero{};						   // Initialized to all zeros
 
 IoHash
 IoHash::HashBuffer(const void* data, size_t byteCount)
-- 
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