diff --git a/app/controllers/projects/merge_requests_controller.rb b/app/controllers/projects/merge_requests_controller.rb
index d25adbe952dd4f33c187dae08705a9bcf973b74c..b70533ef7be225433b6cdc6edc074e8b38072bc4 100644
--- a/app/controllers/projects/merge_requests_controller.rb
+++ b/app/controllers/projects/merge_requests_controller.rb
@@ -104,7 +104,7 @@ class Projects::MergeRequestsController < Projects::ApplicationController
     @commit = @merge_request.last_commit
     @first_commit = @merge_request.first_commit
     @diffs = @merge_request.compare_diffs
-    @diff_refs = [@merge_request.target_sha, @merge_request.source_branch]
+    @diff_refs = [@merge_request.target_sha, @merge_request.source_sha]
 
     @ci_commit = @merge_request.ci_commit
     @statuses = @ci_commit.statuses if @ci_commit
diff --git a/app/helpers/blob_helper.rb b/app/helpers/blob_helper.rb
index 1230002e69c51acf63d877d14385bc63136023c5..a80162a3e33c8619f01c8f00c6dfd6560874c6c3 100644
--- a/app/helpers/blob_helper.rb
+++ b/app/helpers/blob_helper.rb
@@ -11,14 +11,14 @@ module BlobHelper
   end
 
   def highlight(blob_name, blob_content, nowrap: false, continue: false)
-    @formatter ||= rouge_formatter(nowrap: nowrap)
+    formatter = rouge_formatter(nowrap: nowrap)
 
     begin
       @lexer ||= Rouge::Lexer.guess(filename: blob_name, source: blob_content).new
-      result = @formatter.format(@lexer.lex(blob_content, continue: continue)).html_safe
+      result = formatter.format(@lexer.lex(blob_content, continue: continue)).html_safe
     rescue
       @lexer = Rouge::Lexers::PlainText
-      result = @formatter.format(@lexer.lex(blob_content)).html_safe
+      result = formatter.format(@lexer.lex(blob_content)).html_safe
     end
 
     result
diff --git a/lib/gitlab/diff/highlight.rb b/lib/gitlab/diff/highlight.rb
index 3c44abff3fbe772dd3e99103f66ffa09cb95e540..d0137ab5f08be0687f223d2101de28a8c8e01417 100644
--- a/lib/gitlab/diff/highlight.rb
+++ b/lib/gitlab/diff/highlight.rb
@@ -125,10 +125,6 @@ module Gitlab
           lines.map! { |line| " #{line}" }
         end
       end
-
-      def submodules
-        @submodules ||= diff_repository.raw_repository.submodules(diff_new_ref).keys
-      end
     end
   end
 end