From 9eacd3a8097d365bdb5815cb039578e946523da7 Mon Sep 17 00:00:00 2001
From: Dan Engelbrecht <dan.engelbrecht@epicgames.com>
Date: Mon, 30 Sep 2024 10:45:40 +0200
Subject: use alternate IoHash comparision function (#177)

* Use alternate IoHash comparision function - reduces KeepUnusedReferences execution time by ~20%
---
 src/zenstore/gc.cpp | 27 +++++++++++++++++++++++----
 1 file changed, 23 insertions(+), 4 deletions(-)

(limited to 'src/zenstore/gc.cpp')

diff --git a/src/zenstore/gc.cpp b/src/zenstore/gc.cpp
index 159b13af0..3e0dc5e04 100644
--- a/src/zenstore/gc.cpp
+++ b/src/zenstore/gc.cpp
@@ -593,6 +593,24 @@ Sum(GcResult& Stat, bool Cancelled = false)
 	return Stat;
 }
 
+// For GC the has order only needs to be predictable, it does not have to be "true" sort order
+static inline bool
+LessForGC(const IoHash& Lhs, const IoHash& Rhs)
+{
+	const uint32_t* LhsData = reinterpret_cast<const uint32_t*>(Lhs.Hash);
+	const uint32_t* RhsData = reinterpret_cast<const uint32_t*>(Rhs.Hash);
+
+	return LhsData[0] < RhsData[0]	  ? true
+		   : LhsData[0] != RhsData[0] ? false
+		   : LhsData[1] < RhsData[1]  ? true
+		   : LhsData[1] != RhsData[1] ? false
+		   : LhsData[2] < RhsData[2]  ? true
+		   : LhsData[2] != RhsData[2] ? false
+		   : LhsData[3] < RhsData[3]  ? true
+		   : LhsData[3] != RhsData[3] ? false
+									  : LhsData[4] < RhsData[4];
+}
+
 bool
 FilterReferences(GcCtx& Ctx, std::string_view Context, std::vector<IoHash>& InOutReferences)
 {
@@ -631,7 +649,7 @@ FilterReferences(GcCtx& Ctx, std::string_view Context, std::vector<IoHash>& InOu
 	{
 		return false;
 	}
-	std::sort(InOutReferences.begin(), InOutReferences.end());
+	std::sort(InOutReferences.begin(), InOutReferences.end(), LessForGC);
 	auto NewEnd = std::unique(InOutReferences.begin(), InOutReferences.end());
 	InOutReferences.erase(NewEnd, InOutReferences.end());
 	return true;
@@ -666,7 +684,7 @@ KeepUnusedReferences(std::span<const IoHash> SortedUsedReferences, std::span<IoH
 			ReferencesRead++;
 			UsedReferencesRead++;
 		}
-		else if (Reference < UsedReference)
+		else if (LessForGC(Reference, UsedReference))
 		{
 			// Keep it
 			if (ReferencesRead > ReferencesWrite)
@@ -3017,9 +3035,10 @@ TEST_CASE("scrub.basic")
 
 TEST_CASE("gc.keepunusedreferences")
 {
-	const IoHash Hashes[] = {IoHash::FromHexString("177030568fdd461bf4fe5ddbf4d463e514e8178e"),
+	// Order is important, this is the order the hashes would be sorted by FilterReferences
+	const IoHash Hashes[] = {IoHash::FromHexString("75ab3917854bfef7e72d795bb907a15cab1af2c3"),
+							 IoHash::FromHexString("177030568fdd461bf4fe5ddbf4d463e514e8178e"),
 							 IoHash::FromHexString("372d795bb907a15cab15ab3917854bfef7e7af2c"),
-							 IoHash::FromHexString("75ab3917854bfef7e72d795bb907a15cab1af2c3"),
 							 IoHash::FromHexString("ab3917854bfef7e7af2c372d795bb907a15cab15"),
 							 IoHash::FromHexString("d1df59fcab06793a5f2c372d795bb907a15cab15")};
 	{
-- 
cgit v1.2.3