Reduce loops from 8 to 2

This removes 6 duplicate loops from the refresh service.

app/services/merge_requests/refresh_service.rb

@@ -2,6 +2,7 @@
 
 module MergeRequests
   class RefreshService < MergeRequests::BaseService
+    include Gitlab::Utils::StrongMemoize
     attr_reader :push
 
     def execute(oldrev, newrev, ref)
@@ -23,25 +24,37 @@ module MergeRequests
       post_merge_manually_merged
       link_forks_lfs_objects
       reload_merge_requests
-      outdate_suggestions
-      refresh_pipelines_on_merge_requests
-      abort_auto_merges
+
+      merge_requests_for_source_branch.each do |mr|
+        outdate_suggestions(mr)
+        refresh_pipelines_on_merge_requests(mr)
+        abort_auto_merges(mr)
+        mark_pending_todos_done(mr)
+      end
+
       abort_ff_merge_requests_with_when_pipeline_succeeds
-      mark_pending_todos_done
       cache_merge_requests_closing_issues
 
+      merge_requests_for_source_branch.each do |mr|
         # Leave a system note if a branch was deleted/added
-      if @push.branch_added? || @push.branch_removed?
-        comment_mr_branch_presence_changed
+        if branch_added_or_removed?
+          comment_mr_branch_presence_changed(mr)
         end
 
-      notify_about_push
-      mark_mr_as_wip_from_commits
-      execute_mr_web_hooks
+        notify_about_push(mr)
+        mark_mr_as_wip_from_commits(mr)
+        execute_mr_web_hooks(mr)
+      end
 
       true
     end
 
+    def branch_added_or_removed?
+      strong_memoize(:branch_added_or_removed) do
+        @push.branch_added? || @push.branch_removed?
+      end
+    end
+
     def close_upon_missing_source_branch_ref
       # MergeRequest#reload_diff ignores not opened MRs. This means it won't
       # create an `empty` diff for `closed` MRs without a source branch, keeping
@@ -140,26 +153,23 @@ module MergeRequests
         merge_request.source_branch == @push.branch_name
     end
 
-    def outdate_suggestions
-      outdate_service = Suggestions::OutdateService.new
-
-      merge_requests_for_source_branch.each do |merge_request|
+    def outdate_suggestions(merge_request)
       outdate_service.execute(merge_request)
     end
+
+    def outdate_service
+      @outdate_service ||= Suggestions::OutdateService.new
     end
 
-    def refresh_pipelines_on_merge_requests
-      merge_requests_for_source_branch.each do |merge_request|
+    def refresh_pipelines_on_merge_requests(merge_request)
       create_pipeline_for(merge_request, current_user)
+
       UpdateHeadPipelineForMergeRequestWorker.perform_async(merge_request.id)
     end
-    end
 
-    def abort_auto_merges
-      merge_requests_for_source_branch.each do |merge_request|
+    def abort_auto_merges(merge_request)
       abort_auto_merge(merge_request, 'source branch was updated')
     end
-    end
 
     def abort_ff_merge_requests_with_when_pipeline_succeeds
       return unless @project.ff_merge_must_be_possible?
@@ -187,11 +197,9 @@ module MergeRequests
         .with_auto_merge_enabled
     end
 
-    def mark_pending_todos_done
-      merge_requests_for_source_branch.each do |merge_request|
+    def mark_pending_todos_done(merge_request)
       todo_service.merge_request_push(merge_request, @current_user)
     end
-    end
 
     def find_new_commits
       if @push.branch_added?
@@ -218,21 +226,18 @@ module MergeRequests
     end
 
     # Add comment about branches being deleted or added to merge requests
-    def comment_mr_branch_presence_changed
+    def comment_mr_branch_presence_changed(merge_request)
       presence = @push.branch_added? ? :add : :delete
 
-      merge_requests_for_source_branch.each do |merge_request|
       SystemNoteService.change_branch_presence(
         merge_request, merge_request.project, @current_user,
         :source, @push.branch_name, presence)
     end
-    end
 
     # Add comment about pushing new commits to merge requests and send nofitication emails
-    def notify_about_push
+    def notify_about_push(merge_request)
       return unless @commits.present?
 
-      merge_requests_for_source_branch.each do |merge_request|
       mr_commit_ids = Set.new(merge_request.commit_shas)
 
       new_commits, existing_commits = @commits.partition do |commit|
@@ -245,12 +250,10 @@ module MergeRequests
 
       notification_service.push_to_merge_request(merge_request, @current_user, new_commits: new_commits, existing_commits: existing_commits)
     end
-    end
 
-    def mark_mr_as_wip_from_commits
+    def mark_mr_as_wip_from_commits(merge_request)
       return unless @commits.present?
 
-      merge_requests_for_source_branch.each do |merge_request|
       commit_shas = merge_request.commit_shas
 
       wip_commit = @commits.detect do |commit|
@@ -267,14 +270,11 @@ module MergeRequests
         )
       end
     end
-    end
 
     # Call merge request webhook with update branches
-    def execute_mr_web_hooks
-      merge_requests_for_source_branch.each do |merge_request|
+    def execute_mr_web_hooks(merge_request)
       execute_hooks(merge_request, 'update', old_rev: @push.oldrev)
     end
-    end
 
     # If the merge requests closes any issues, save this information in the
     # `MergeRequestsClosingIssues` model (as a performance optimization).