Merge pull request #5578 from SlowDepend/master

For fix slow dependency issue(base on 1.0.0).

CHANGELOG.md

@@ -12,6 +12,10 @@ To install release candidates run `[sudo] gem install cocoapods --pre`
   [Danielle Tomlinson](https://github.com/dantoml)
   [#5635](https://github.com/CocoaPods/CocoaPods/pull/5635)  
   
+* Improve performance of dependency resolution.
+  [yanzhiwei147](https://github.com/yanzhiwei147)
+  [#5510](https://github.com/CocoaPods/CocoaPods/pull/5510)
+
 ##### Bug Fixes
 
 * Hash scope suffixes if they are over 50 characters to prevent file paths from being too long. 

lib/cocoapods/resolver.rb

@@ -73,9 +73,10 @@ module Pod
     def specs_by_target
       @specs_by_target ||= {}.tap do |specs_by_target|
         podfile.target_definition_list.each do |target|
+          dependencies = {}
           specs = target.dependencies.map(&:name).flat_map do |name|
             node = @activated.vertex_named(name)
-            valid_dependencies_for_target_from_node(target, node) << node
+            valid_dependencies_for_target_from_node(target, dependencies, node) << node
           end
 
           specs_by_target[target] = specs.
@@ -471,13 +472,19 @@ module Pod
     #         An array of target-appropriate nodes whose `payload`s are
     #         dependencies for `target`.
     #
-    def valid_dependencies_for_target_from_node(target, node)
+    def valid_dependencies_for_target_from_node(target, dependencies, node)
+      dependencies[node.name] ||= begin
         validate_platform(node.payload, target)
         dependency_nodes = node.outgoing_edges.select do |edge|
           edge_is_valid_for_target?(edge, target)
         end.map(&:destination)
 
-      dependency_nodes + dependency_nodes.flat_map { |n| valid_dependencies_for_target_from_node(target, n) }
+        dependency_nodes + dependency_nodes.flat_map do |item|
+          node_result = valid_dependencies_for_target_from_node(target, dependencies, item)
+
+          node_result
+        end
+      end
     end
 
     # Whether the given `edge` should be followed to find dependencies for the