title: What are the consequences of having almost duplicate target rules in a Makefile?
body: <p>I have inherited a problematic Makefile.am that has been causing build issues. In this makefile, there are a couple instances where there are almost duplicate target rules. They are almost duplicate because the second one has one or two extra prerequisites. Here is an example:</p>
  
  <pre><code>target1 target2: prereq1 prereq2 
          ACTION
  
  target1 target2: prereq1 prereq2 prereq3
          ACTION
  </code></pre>
  
  <p>The action is identical, and target1 and target2 are identical. What is the consequence of this? Will both rules be executed?</p>
  
  <p>To extend this question a bit, if prereq3 was auto generated during the make process, how would this play out? If make is run in parallel, could this cause big issues?</p>