Reduce allocations in ProjectItemInstance.CommonConstructor by settin… (#12978)

nareshjo · Naresh Joshi · web-flow · commit 15593e93e6d9 · 2026-01-27T11:32:44.000Z
Co-authored-by: Naresh Joshi &lt;Naresh.Joshi@microsoft.com&gt;
diff --git a/src/Build/Instance/ProjectItemInstance.cs b/src/Build/Instance/ProjectItemInstance.cs
@@ -743,7 +743,8 @@ private void CommonConstructor(
             if (itemDefinitions == null || !useItemDefinitionsWithoutModification)
             {
                 // TaskItems don't have an item type. So for their benefit, we have to lookup and add the regular item definition.
-                inheritedItemDefinitions = (itemDefinitions == null) ? null : new List<ProjectItemDefinitionInstance>(itemDefinitions);
+                inheritedItemDefinitions = (itemDefinitions == null) ? null : new List<ProjectItemDefinitionInstance>(itemDefinitions.Count + 1);
+                ((List<ProjectItemDefinitionInstance>)inheritedItemDefinitions)?.AddRange(itemDefinitions);
 
                 ProjectItemDefinitionInstance itemDefinition;
                 if (projectToUse.ItemDefinitions.TryGetValue(itemTypeToUse, out itemDefinition))

Original file line number	Diff line number	Diff line change
`@@ -743,7 +743,8 @@ private void CommonConstructor(`
`743`	`743`	`if (itemDefinitions == null \|\| !useItemDefinitionsWithoutModification)`
`744`	`744`	`{`
`745`	`745`	`// TaskItems don't have an item type. So for their benefit, we have to lookup and add the regular item definition.`
`746`		`- inheritedItemDefinitions = (itemDefinitions == null) ? null : new List<ProjectItemDefinitionInstance>(itemDefinitions);`
	`746`	`+ inheritedItemDefinitions = (itemDefinitions == null) ? null : new List<ProjectItemDefinitionInstance>(itemDefinitions.Count + 1);`
	`747`	`+ ((List<ProjectItemDefinitionInstance>)inheritedItemDefinitions)?.AddRange(itemDefinitions);`
`747`	`748`
`748`	`749`	`ProjectItemDefinitionInstance itemDefinition;`
`749`	`750`	`if (projectToUse.ItemDefinitions.TryGetValue(itemTypeToUse, out itemDefinition))`