Add a standard for control-flow unreachable assertions in functions that return

values, so as to avoid warnings on some platforms.

llvm-svn: 51831

docs/CodingStandards.html

@@ -623,6 +623,29 @@ assert(isa<PHINode>(Succ->front()) && "Only works on PHId BBs!"
 
 <p>You get the idea...</p>
 
+<p>Please be aware when adding assert statements that not all compilers are aware of
+the semantics of the assert.  In some places, asserts are used to indicate a piece of
+code that should not be reached.  These are typically of the form:</p>
+
+<div class="doc_code">
+<pre>
+assert(0 && "Some helpful error message");
+</pre>
+</div>
+
+<p>When used in a function that returns a value, they should be followed with a return
+statement and a comment indicating that this line is never reached.  This will prevent
+a compiler which is unable to deduce that the assert statement never returns from
+generating a warning.</p>
+
+<div class="doc_code">
+<pre>
+assert(0 && "Some helpful error message");
+// Not reached
+return 0;
+</pre>
+</div>
+
 </div>
 
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