Improve performance of simple reflist merges

When merging reflists with ignoreConflicting set to true and
overrideMatching set to false, the individual ref components are never
examined, but the refs are still split anyway. Avoiding the split when
we never use the components brings a massive speedup: on my system, the
included benchmark goes from ~1500 us/it to ~180 us/it.

Signed-off-by: Ryan Gonzalez <ryan.gonzalez@collabora.com>

deb/reflist.go

@@ -310,38 +310,41 @@ func (l *PackageRefList) Merge(r *PackageRefList, overrideMatching, ignoreConfli
 			overridenName = nil
 			overriddenArch = nil
 		} else {
-			partsL := bytes.Split(rl, []byte(" "))
+			if !ignoreConflicting || overrideMatching {
-			archL, nameL, versionL := partsL[0][1:], partsL[1], partsL[2]
+				partsL := bytes.Split(rl, []byte(" "))
+				archL, nameL, versionL := partsL[0][1:], partsL[1], partsL[2]
 
-			partsR := bytes.Split(rr, []byte(" "))
+				partsR := bytes.Split(rr, []byte(" "))
-			archR, nameR, versionR := partsR[0][1:], partsR[1], partsR[2]
+				archR, nameR, versionR := partsR[0][1:], partsR[1], partsR[2]
 
-			if !ignoreConflicting && bytes.Equal(archL, archR) && bytes.Equal(nameL, nameR) && bytes.Equal(versionL, versionR) {
+				if !ignoreConflicting && bytes.Equal(archL, archR) &&
-				// conflicting duplicates with same arch, name, version, but different file hash
+					bytes.Equal(nameL, nameR) && bytes.Equal(versionL, versionR) {
-				result.Refs = append(result.Refs, r.Refs[ir])
+					// conflicting duplicates with same arch, name, version, but different file hash
-				il++
-				ir++
-				overridenName = nil
-				overriddenArch = nil
-				continue
-			}
-
-			if overrideMatching {
-				if bytes.Equal(archL, overriddenArch) && bytes.Equal(nameL, overridenName) {
-					// this package has already been overridden on the right
-					il++
-					continue
-				}
-
-				if bytes.Equal(archL, archR) && bytes.Equal(nameL, nameR) {
-					// override with package from the right
 					result.Refs = append(result.Refs, r.Refs[ir])
 					il++
 					ir++
-					overriddenArch = archL
+					overridenName = nil
-					overridenName = nameL
+					overriddenArch = nil
 					continue
 				}
+
+				if overrideMatching {
+					if bytes.Equal(archL, overriddenArch) && bytes.Equal(nameL, overridenName) {
+						// this package has already been overridden on the right
+						il++
+						continue
+					}
+
+					if bytes.Equal(archL, archR) && bytes.Equal(nameL, nameR) {
+						// override with package from the right
+						result.Refs = append(result.Refs, r.Refs[ir])
+						il++
+						ir++
+						overriddenArch = archL
+						overridenName = nameL
+						continue
+					}
+				}
 			}
 
 			// otherwise append smallest of two

deb/reflist_bench_test.go

@@ -0,0 +1,30 @@
+package deb
+
+import (
+	"fmt"
+	"sort"
+	"testing"
+)
+
+func BenchmarkReflistSimpleMerge(b *testing.B) {
+	const count = 4096
+
+	l := NewPackageRefList()
+	r := NewPackageRefList()
+
+	for i := 0; i < count; i++ {
+		if i%2 == 0 {
+			l.Refs = append(l.Refs, []byte(fmt.Sprintf("Pamd64 pkg%d %d", i, i)))
+		} else {
+			r.Refs = append(r.Refs, []byte(fmt.Sprintf("Pamd64 pkg%d %d", i, i)))
+		}
+	}
+
+	sort.Sort(l)
+	sort.Sort(r)
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		l.Merge(r, false, true)
+	}
+}