Eliminate a numLayers variable

The compiler is smart enough that referencing a local variable is not any faster than len(srcInfos). If anything, keeping the extra variable might add to register pressure because the compiler might not understand that the srcInfos change due to LayerInfosForCopy does not change the number of layers. Should not change behavior. Signed-off-by: Miloslav Trmač <mitr@redhat.com>
containers · Jul 9, 2024 · 1c586a8 · 1c586a8
1 parent a857d09
commit 1c586a8
Showing 1 changed file with 3 additions and 4 deletions.
diff --git a/copy/single.go b/copy/single.go
@@ -409,7 +409,6 @@ func (ic *imageCopier) compareImageDestinationManifestEqual(ctx context.Context,
 // copyLayers copies layers from ic.src/ic.c.rawSource to dest, using and updating ic.manifestUpdates if necessary and ic.cannotModifyManifestReason == "".
 func (ic *imageCopier) copyLayers(ctx context.Context) ([]compressiontypes.Algorithm, error) {
 	srcInfos := ic.src.LayerInfos()
-	numLayers := len(srcInfos)
 	updatedSrcInfos, err := ic.src.LayerInfosForCopy(ctx)
 	if err != nil {
 		return nil, err
@@ -440,7 +439,7 @@ func (ic *imageCopier) copyLayers(ctx context.Context) ([]compressiontypes.Algor
 	// copyGroup is used to determine if all layers are copied
 	copyGroup := sync.WaitGroup{}
 
-	data := make([]copyLayerData, numLayers)
+	data := make([]copyLayerData, len(srcInfos))
 	copyLayerHelper := func(index int, srcLayer types.BlobInfo, toEncrypt bool, pool *mpb.Progress, srcRef reference.Named) {
 		defer ic.c.concurrentBlobCopiesSemaphore.Release(1)
 		defer copyGroup.Done()
@@ -509,8 +508,8 @@ func (ic *imageCopier) copyLayers(ctx context.Context) ([]compressiontypes.Algor
 	}
 
 	compressionAlgos := set.New[string]()
-	destInfos := make([]types.BlobInfo, numLayers)
-	diffIDs := make([]digest.Digest, numLayers)
+	destInfos := make([]types.BlobInfo, len(srcInfos))
+	diffIDs := make([]digest.Digest, len(srcInfos))
 	for i, cld := range data {
 		if cld.err != nil {
 			return nil, cld.err